CA2037625C - Operating point trimming method for optical waveguide modulator and switch - Google Patents
Operating point trimming method for optical waveguide modulator and switchInfo
- Publication number
- CA2037625C CA2037625C CA002037625A CA2037625A CA2037625C CA 2037625 C CA2037625 C CA 2037625C CA 002037625 A CA002037625 A CA 002037625A CA 2037625 A CA2037625 A CA 2037625A CA 2037625 C CA2037625 C CA 2037625C
- Authority
- CA
- Canada
- Prior art keywords
- optical waveguide
- waveform
- operating point
- substrate
- buffer layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference
- G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference in an optical waveguide structure
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
- G02F1/31—Digital deflection, i.e. optical switching
- G02F1/313—Digital deflection, i.e. optical switching in an optical waveguide structure
- G02F1/3132—Digital deflection, i.e. optical switching in an optical waveguide structure of directional coupler type
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2203/00—Function characteristic
- G02F2203/20—Intrinsic phase difference, i.e. optical bias, of an optical modulator; Methods for the pre-set thereof
Abstract
Operating point trimming methods for an optical waveguide modulator and an optical waveguide switch are disclosed. One operating point trimming method for an optical waveguide modulator comprises, for example, the step of removing, while monitoring the waveform of an intensity modulated light beam, a portion of either one of a first and a second electrode such that the intensity modulated waveform takes on a desired waveform. One operating point trimming method for an optical waveguide switch comprises the step of removing a portion of either one of a first and a second electrode while monitoring output light beams.
Description
203762~
OPERATING POINT TRIMMING METIIOD FOR OPTICAL WAVEGUIDE
MODULATOR AND SWITCH
Back~round of the Invention The present invention relates to operating - point trimming methods e~ for an optical waveguide modulator and an optical waveguide switch.
In a general optical communication system, a light signal intensity modulated on the transmitter side is transmitted to the receiver side through an optical transmission line formed of an optical fiber or the like and the signal is directly detected and the transmitted information is reproduced on the receiver side. The intensity modulation may be performed on the transmitter side by having the drive curren-t of a light source, which is formed for example of a semiconductor laser, modulated with a modulating signal (direct modulation).
In the case of the direct modulation, however, there sometimes occurs a relatively large wavelength shift (chirping) when high speed modulation is performed.
Therefore, when an optical fiber whose dispersion characteristic is not good is used as the optical transmission line, the transmission is restricted in the transmission distance or the transmission speed. More -~ 20~762~
specifically, when a system is structured with a combination of a single mode op-tical fiber exhibiting zero dispersion at 1.3 y m band and a semiconductor laser oscillating at 1.55 y m band minimizing the transmission loss, the system has restriction of the transmission distance or the transmission speed due to the wavelength dispersion. As a means for removing such restriction on the transmission distance or transmission speed, there is an external modulation system using an optical modulator. The external modulation system is a system in which a light beam emitted from a light source at the level of constant intensity is modulated by, for example, an optical waveguide modulator provided independently of the light source and, with which, a system producing an extremely small quantity of wavelength chirping can be formed. In implementing such external modulation system, it is desired that a trimming method for controlling the operating point of the optical waveguide modulator is provided.
FIG. 1 is a plan view showing a structure of a conventional optical waveguide modulator 1.
Referring to FIG. 1, reference numeral 2 denotes a waveguide substrate in a parallelepiped form made from a ferroelectric material such as lithium nlobate (LlNbO3). At a predetermlned posltlon on the surface of the wavegulde substrate 2, there ls formed, by such a method as thermal dlffuslon of tltanlum (Tl), an optlcal wavegulde 3 havlng a flrst branch optlcal wavegulde 3a and a second branch optlcal wavegulde 3b of the same length and ln the form of a comblned two Y-branch waveguldes. On the surface of the wavegulde substrate 2, there ls further formed a buffer layer 4 of a slllcon dloxlde (SlO2) fllm for coverlng all of the optlcal waveguldes 3, 3a, and 3b.
Over the flrst branch optlcal wavegulde 3a, there ls formed, through the buffer layer 4, a flrst electrode 5a for applylng the drlvlng voltage, provlded by platlng of a conductlve materlal such as gold, and over the second branch optlcal wave-gulde 3b, there ls formed, through the buffer layer 4, a second electrode 5b. One end of each of the flrst and second electrodes 5a and 5b are connected wlth a drlve clrcult (not shown) for changlng the voltages applled to the electrodes 5a and 5b accord-lng to the modulatlng slgnal and the other ends thereof are con-nected wlth termlnatlng reslstors (not shown). One end portlon of the optlcal wavegulde 3 ls optlcally coupled on the wavegulde sub-strate 2 wlth an optlcal flber 6 on the lnput slde as lndlcated by the 203762~
arrow and the other end portion thereof is optically coupled with an optical fiber 7 on the output side. The buffer layer 4 is provided so that the li~ht beams propagating through the first and second branch optical waveguides 3a and 3b may not be absorbed by the first and second electrodes 5a and 5b.
With the described arrangement, the refractive indexes of the first and second branch optical waveguides 3a and 3b of the optical waveguide 3 are changed according to the electric fields applied thereto and, hence, the respective branch beams branched by the branch optical waveguides 3a and 3b in phase will suffer phase changes according to the refractive indexes of the respective branch optical waveguides 3a and 3b.
Since, except for the Y-branch portions, the optical waveguide 3 is arranged to be a single mode optical waveguide, which propagates only the light beam of the fundamental mode, the intensity of the interference light output from the optical waveguide 3 becomes a maximum when the phase difference between the branch light beams is zero, whereas the intensity of the interference light becomes a minimum when the phase difference between the branch light beams is ~ .
Further, when the phase difference is between 0 and ~ , 20~762~
the interference light takes on an intensity corresponding to the phase difference. In the described manner, the optical waveguide modulator 1 provides time-series changes to the output light intensity, by changing the voltages applied to the electrodes according to the modulating signal.
FIG. 2 shows the relationship between the applied voltage and the output light intensi-ty. In the diagram, the output light intensity is indicated along the axis of ordinate and the applied voltage is indicated along the axis of abscissa.
The relationship between the applied voltage V
to the Y-branch interferometric optical modulator and the output ligh-t intensity Po, under the conditions that either a TE mode wave or a TM mode wave is used, that the propagating light is equally divided and combined at the Y-branches suffering no loss, and that the wave guide has no loss, is expressed as Po = Pi cos2[(~ /2) (V/V~ ) + ~ ] , where Pi represents the input light intensity and V~ , called the half-wave length voltage, represents the minimum voltage difference providing the maximum output and the minimum output.
The angle ~ becomes 0 when the optical path 203762~
difference between the two waveguide paths 3a and 3b equals 0 or A (wavelength of the propagating light) / n (the refractive index of the medium for the propagating light) multiplied by 2k (k = i 1, i 2, ...). The so]id line 10 in FIG. 2 shows the case where the angle ~ = 0.
In such modulator, the intensity modulation can be achieved by changing the voltage between the applied voltage V1 (V3) providing a maximum of the light intensity and the applied voltage V2 (V4) providing a minimum of the light intensity. For example, when performing digital modulation, the applied voltage may be set to V1 at the mark period lOa corresponding to "1"
and the applied voltage may be set to V2 at the space period lOb corresponding to "0".
In the described optical waveguide modulator 1, the refractive indexes of the first and second branch optical waveguides 3a and 3b are changed by stress exerted -thereon from the buffer layer 4 and the electrodes 5a and 5b disposed on the waveguide substrate 2 and, as a result, the optical path lengths of these waveguides become different, leading to a shift of the operating point.
When the operating point is shifted as described above, the desired waveform 10 is shifted to -- 203762~
the position of the waveform 11 as indicted in FIG. 2 by the broken line. More specifically, the waveform is slipped by the shift amount ~ V corresponding to the operating point shifting. In order to compensate for this shift, it is required that a DC bias voltage is applied to the electrodes 5a and 5b to change the refractive indexes of the branch optical waveguides 3a and 3b and adjust the optical path difference therebetween.
The shift amount ~ V due to the operating point shifting differs from product to product because of lack of uniformity of the thickness of the evaporation film of the buffer layer etc. and of the size of various parts occurring in the course of fabrication. Such tendency is especially remarkable with optical waveguide modulators using, as the waveguide substrate, LiNbO3 having the photoelastic effect. Therefore, it becomes necessary to apply each optical modulator with the DC bias voltage corresponding to the operating point shift amount ~ V due to the operating point shifting resulted from the above described lack of uniformity to thereby adjust the DC
offset. Further, even if the shift amount ~ V is compensated for by taking the above measure, there 203762~
sometimes occurs, when such DC bias voltage is applied, a phenomenon called DC drift in which the operating point shifts with the lapse of time after the application of the DC bias voltage. This phenomenon for example is such, as shown in FIG. 3, that the waveform 10 adjusted to a desired output light intensity by application of a DC bias tends to shift to the waveform 12 indicated by the broken line.
When such a shift occurs, the applied voltage Vl providing the maximum light output is shifted to Vl', as shown in FIG. 3, while the applied voltage Vz providing the minimum light output is shifted to V2'.
Therefore, if the modulation is performed with the applied voltages V1 - Vz whereby the original waveform 10 was obtained, the output light intensity when the applied voltage is V1 decreases from lOa to lOb as shown in the same diagram, while the output light intensity 12a wherl the applied voltage is Vz increases from 12a to 12b. As a result, it becomes unable to obtain the maximum and minimum output light beams and the extinction ratio (the ratio of the output light intensity in the mark period to that in the space period given in decibels) is decreased, and a problem is presented that it becomes unable to have a suitable 203762~
optical signal output.
When i-t is attempted to obtain optical waveguide modulators having no operating point shifting such as the DC drift, since some nonuniformity of the operating point occurs in the fabrication process, it becomes necessary to select such products that have virtually equal operating point shiftings after fabrication thereof. This is indeed a difficult task in view of the fact that the nonuniformity of the operating point shifting is frequently produced in the fabrication process, and because of which, a problem is presented of a lowering of the yield rate.
Summary of the Invention Accordingly, an object of the present invention is to provide an operating point trimming method for an optical waveguide modulator, whereby the refractive index of one optical waveguide of a pair of branch optical waveguides is changed with respect to that of the other one so that the operating point is shifted to a voltage not causing the difficulty of the DC drift.
Another object of the present invention is to provide an operating point trimming method for an 203762~
optical waveguide switch, whereby the refractive index of one optical waveguide of a pair of independent optical waveguides is changed with respect to that of the other one so that the operating point is shifted to a voltage not causing the difficulty of the ~C drift.
A further object of the present invention is to provide a method of fabricating an optical waveguide modulator or an optical waveguide switch, in which the operating point is suitably shifted so that the yield rate is improved.
According to the present invention, the following operating point trimming methods (a) - (j) are provided for use in an optical waveguide modulator in which the voltage applied between a first electrode and a second electrode mounted on a first and a second branch optical waveguide is changed so that a phase difference is produced between the light beams guided thereby and the light beams thus caused to have the phase difference are combined so that an intensity modulated light beam is output from the optical waveguide modulator.
(a) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, a portion of either one of the 20~7~25 first and the second electrode is removed such tha-t the waveform of the intensity modulated light beam takes on a desired waveform.
(b) Whi]e the waveform of the described intensity modulated light beam is monitored with a waveform display device, a metallic material is deposited by evaporation on the buffer layer over a portion of either one of the first and the second optical waveguidel with the electrode not mounted thereon, such that the waveform of the intensity modulated light beam takes on a desired waveform.
(c) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, the buffer layer over a portion of either one of the first and the second optical waveguide, with the electrode not mounted thereon, is cut away such that the waveform of -the intensity modulated light beam takes on a desired waveform.
(d) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, a material increasing or decreasing the refractive index of the optical waveguide is deposited, from the top face of the buffer layer, into a portion of either one of the first and the second 2~3~2~
optical waveguide, with the electrode not mounted thereon, such that the waveform of the intensity modulated light beam takes on a desired waveform.
(e) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, a portion of either one of the first and the second optical waveguide, with the electrode not mounted thereon, is externally heated to be deformed, through the buffer layer, such that the waveform of the intensity modulated light beam takes on a desired waveform.
(f) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, a block for applying stress is attached to the side face of the waveguide substrate, mechanical stress is applied to the block, and the block is fixed up when the applied mechanical stress has reached a state where the waveform of the intensity modulated light beam takes on a desired waveform, such that the state is maintained.
(g) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, a por-tion at the side of the waveguide substrate is cut off such that the waveform of the intensity modulated light beam takes on a desired waveform.
(h) The buffer layer is removed at a plurality of portions thereof over either one of the first and the second optical waveguide, with the electrode not mounted thereon, and then, while the waveform of the described intensity modulated light beam is monitored wi-th a waveform display device, a material having a different refractive index from the refractive index of the optical waveguide is deposited on the plurality of portions of the buffer layer that have been removed such that the waveform of the intensity modulated light beam takes on a desired waveform.
(i) A metallic material is deposited by evaporation on the buffer layer over a plurality of portions of either one of the first and the second optical waveguide, with the electrode not mounted thereon, so that a plurality of independent metallic films are formed and, then, while the waveform of the described intensity modulated light beam is monitored with a waveform display device, the plurali-ty of the metallic films are removed one after another such that the waveform of the intensity modulated light beam takes on a desired waveform.
2037i~2~
(j) A gap is formed in a portion of either one of the first and the second optical waveguide, with the electrode not mounted thereon, and, then, while the waveform of the described intensity modulated light beam is monitored with a waveform display device, a material with different refractive index from the refractive index of the optical waveguide is filled into the gap such that the waveform of the intensity modulated light beam takes on a desired waveform.
It is preferred that optical fibers for inputting and outputting an optical signal are fixed to the optical waveguide modulator and this optical waveguide modulator is fixed to a member with a predetermined set of peripheral circuits attached thereto and, then, the operating point trimmi.ng is carried out according to any of the above described methods (a) - (j).
The operating point of an optical waveguide switch can also be trimmed by any of the methods (a) -(j).
The above and other objects, features andadvantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of 203762~
the following description and appended claims, with reference had to the attached drawings showing some preferred embodiments of the invention.
Brief Description of the Drawin~s FIG. 1 is a plan view showing struc-ture of a conventional optical waveguide modulator;
FIG. 2 is a diagram for explaining an operating point offset;
FIG. 3 is a diagram for explaining a DC drift;
FIG. 4 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a first embodiment of the present invention;
FIG. 5 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a second embodiment of the present invention;
FIG. 6 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a third embodiment of the present invention;
FIG. 7 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a fourth embodiment of the present invention;
FIG. 8 is a plan view of an optical waveguide modulator for explaining an operating point trimming - 2037t~2~
method as a fifth embodiment of the present invention;
FIG. 9 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a sixth embodiment of the present invention;
FIG. 10 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a seventh embodiment of the present invention;
FIG. ll is a plan view of an optical waveguide modulator for explaining an operating point trimming method as an eighth embodiment of the present invention;
FIG. 12 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a ninth embodiment of the present invention;
FIG. 13 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a tenth embodiment of the present invention;
and FIG. 14 is a plan view of an optical waveguide switch to which the operating point trimming method according to the present invention is suitably applicable.
Description of the Preferred Embodiments Embodiments of the present invention will now - 2~3762~
be described below with reference to the accompanying drawings. FIG. 4 is a plan view showing structure of an optical waveguide modulator lA according to -the first embodiment of the present invention, in WtliCtl parts corresponding to the parts in the prior art example shown in FIG. l are denoted by like reference numerals.
Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lA according to the firs-t embodiment differing from that l~ of the conventional optical waveguide modulator l shown in FIG. l is, as shown in FIG. 4, that a portion 5b1 of the second electrode 5b is removed so that the electrode is changed in its form and hence the stress exerted on the second branch optical waveguide 3b is changed, whereby the refractive index of the second branch optical waveguide 3b is changed and the optical path difference between the same and the first branch optical waveguide 3a is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lA to a desired operating point is achieved and the need for applying the DC bias voltage for compensating for the DC offset described as related to the prior art example is eliminated.
More specifically, in performing such ~03~762S
operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope, which is not shown. Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, a predetermined portion of the second electrode 5b of the optical waveguide modulator 1 is removed by a laser beam thereby having the portion heated and removed until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modula-tor lA as described above can be obtained.
Although a portion of the second electrode 5b was removed in the above described optical waveguide modulator lA, a portion of the first electrode 5a may be removed depending on the refractive indexes of the branch optical waveguides 3a and 3b.
With the described optical waveguide modulator lA, the need for applying the DC bias voltage as was necessary in the conventional optical waveguide modulator 1 can be eliminated. Further, since the DC
bias is not applied to the same, the DC drift usual with 2S3;7~2~
the prior art does not occur.
Now, referring to FIG. 5, a second embodiment of the present invention will be described. FIG. 5 is a plan view showing structure of an optical waveguide modula-tor lB according to the second embodiment of the present inven-tion, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lB according to the second embodiment dif-fering from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 5, that a metallic film 20 is formed on the buffer layer 4 over the first branch optical waveguide 3a, whereby the light beam propagating through the first branch optical waveguide 3a when traveling past the portion of the metallic film 20 senses the refractive index of the metallic film 20 and the refractive index of the first branch optical waveguide 3a is substantially changed and, accordingly, the optical path length of the first branch optical waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus -the trimming for bringing the ~ t7 3 ~
operating point of the optical waveguide modulator lB to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC
offset described as related to the prior art example is eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, a metallic material is deposited by evaporation on the buffer layer 4, to form the metallic film 20, over the first branch optical waveguide 3a until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lB as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA
can be obtained.
Although the metallic layer 20 was formed over the first branch optical waveguide 3a through the buffer layer 4 in the above described optical waveguide 2l~3~2~
modulator lB, the metallic layer 20 may be formed over the second branch optical waveguide 3b depending on the refractive indexes of the branch optical waveguides 3a and 3b. That is, the metallic film 20 may be formed at a portion over the branch optical waveguides 3a and 3b except for the portions where the electrodes 5a and 5b are formed.
Now, referring to FIG. 6, a third embodiment of the present invention will be described. FIG. 6 is a plan view showing structure of an optical waveguide modulator lC according to the third embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lC according to the third embodiment differing from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 6, that a portion 4a of the buffer layer 4 over the first branch optical waveguide 3a is removed, so that the first branch optical waveguide 3a a-t the position where the buffer layer 4 is removed changes its refractive index by contacting with air, whereby the optical path length of the first branch optical 2~3762~
waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lC ~o a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC
offset described as related to the prior art example is eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, the buffer layer 4 over a portion of the first branch optical waveguide 3a is removed by such a method as etching, grinding, or irradiation of an electron beam until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lC as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA can be obtained.
2~37~2~
Although a portion of the buffer layer 4 over the first branch optical waveguide 3a was removed in the above described optical waveguide modulator lC, it sometimes is better to remove a portion of the buffer layer 4 over the second branch optical waveguide 3b depending on the refractive indexes of the branch optical waveguides 3a and 3b. That iSJ the buffer layer 4 may be removed at a portion over the branch optical waveguides 3a and 3b except for the portions where the electrodes 5a ~ 5b are formed.
Now, referring to FIG. 7, a fourth embodiment of the present invention will be described. FIG. 7 is a plan view showing structure of an optical waveguide modulator lD according to the fourth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lD according to the fourth embodiment differing from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 7, that a material 21 increasing or decreasing the refractive index of the optical waveguide is attached to a portion on the first branch optical 203762~
waveguide 3a so that the refractive index of the first branch optical waveguide 3a is changed, whereby the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lD to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC offset described as related to the prior art example is eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, a material 21 increasing or decreasing the refractive index of the optical waveguide is injected by such a method as ion injection into a portion on the first branch optical waveguide 3a until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lD as described above can be obtained, and therefrom, the same effects as obtained ~03762~i from the above described optical waveguide modulator lA
can be obtained.
Although a material 21 increasing or decreasing the refractive index of the optical waveguide is attached to a portion on the first branch optical waveguide 3a in the optical waveguide lD, it may be attached to a portion on the second branch optical waveguide 3b instead.
Now, referring to FIG. 8, a fifth embodiment of the present invention will be described. FIG. 8 is a plan view showing structure of an optical waveguide modulator lE according to the fifth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lE according to the fifth embodiment differing from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 8, that a portion 3al of the first branch optical waveguide 3a is deformed so that the refractive index of the optical waveguide 3a is changed, whereby the optical path difference between the same and the second branch optical waveguide 3b is adjus-ted, and thus 2~7~
the trimming for bringing the operating point of the optical waveguide modulator lE to a desired operating point is achieved, and the need for applyirlg the DC bias voltage for compensating for the DC offset described as related to the prior art example is eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, a portion 3al or the portion surrounding it on the first branch optical waveguide 3a is heated by a heating means such as a laser beam so that the first branch optical waveguide 3a is deformed by diffusion until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lE as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA can be obtained.
Although a portion on the first branch optical waveguide 3a was deformed in the optical waveguide lE, a - 2~37~2~
portion on the seGond branch optical waveguide 3b may be deformed instead.
Now, referring to FIG. 9, a sixth embodiment of the present invention will be described. FIG. 9 is a plan view showing structure of an optical waveguide modulator lF according to the sixth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lF according to the sixth embodiment differing from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 9, that a block 22 for applying stress is fixed to a portion on the side face of the waveguide substrate 2, the refractive index of the optical waveguide 3a is changed by the stress applied thereon and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lF to a desired operating point is achieved, and the need for applying the DC bias vo]tage for compensating for the DC offset described as related to the prior art example is eliminated.
~037762~
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, the block 22 is attached to a portion on the side face of the waveguide substrate 2. Thereafter, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, mechanical stress is applied to the block 22, and when the waveform of the light signal takes on a desired waveform, the block 22 is fixed up such that the mechanical stress at that time is maintained. Thus, the optical waveguide modulator lF as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA
can be obtained.
Although the refractive index of the first branch optical waveguide 3a was changed by means of the block 22 for applying stress in the above described optical waveguide modulator lF, the block 22 may be fixed on the opposite side face of the waveguide substrate 2 so that the refractive index of the second - 20:3~62~
branch optical waveguide 3b is changed.
Now, referring -to FIG. lO, a seventh embodiment of the presen-t invention will be described.
FIG. lO is a plan view showing structure of an optical waveguide modulator lG according to the seventh embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. l are denoted by like reference numerals.
Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lG according to the seventh embodiment differing from that of the conventional optical waveguide modulator l is, as shown in FIG. 10, that a part at the side of the waveguide substrate 2 is cut off and an indented portion 2a is formed there so that the stress exerting on the first branch optical waveguide 3a is changed, whereby the refractive index of the first branch optical waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lG to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC
offset described as related to the prior art example is - 2037~i2~
eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, a portion at the side of the waveguide substrate 2 is cut off by grinding and the indented portion 2a is formed there until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lG as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA can be obtained.
The portion to be cut off may be anywhere at the side of the waveguide substrate 2 provided that the refractive index of either of the branch optical waveguides 3a and 3b is changed and an optical signa]
with a predetermined intensity modulated waveform is thereby obtained.
Now, referring to FIG. 11, an eighth embodiment of the present invention will be described.
20~2~
FIG. 11 is a plan view showing structure of an optical waveguide modulator lH according to the eighth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals.
Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lH according to the eighth embodiment differing from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 11, that a plurality of portions 4b, 4b, ... of the buffer layer 4 over the first branch optical waveguide 3a are removed and then a material 23 with a different refractive index from that of the optical waveguide 3 is mounted on the portions 4b, 4b, ... at which the buffer layer 4 is removed, whereby the refractive index of the first branch optical waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lH to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC
offset described as related to the prior art example is eliminated.
21337~5 More specifically, in performing such operating point trimming, the optical waveguide modula-tor 1 (refer to FIG. 1) is fabricated and, then, the buffer layer 4 is removed by etching or a similar method at a plurality of portions 4b, 4b, ... thereof over the first branch optical waveguide 3a. Then, the optical waveguide modulator 1 with the portions 4b, 4b, ... of the buffer layer 4 removed is connected to a waveform monitoring device such as an oscilloscope.
Thereafter, while the intensity modulated waveform of the light signal output from the optical waveguide modulator is monitored with the waveform monitoring device, a material 23 with a different refractive index from that of the optical waveguide 3 is mounted on the portions 4b, 4b, ... at which the buffer layer 4 is removed, one after another, until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lH as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA
can be obtained.
Although, in the described optical waveguide modulator lH, portions 4b, 4b, ... of the buffer layer 4 over the first branch optical waveguide 3a were removed 203762~
and the material 23 was mounted on these portions, it may also be well to have portions of the buffer layer 4 over the second branch optical waveguide 3b removed and have the material 23 mounted on these portions. That is, the portions to be removed may be over either of the branch optical waveguides 3a and 3b except the portions at which the electrodes 5a and 5b are formed. The same as in the previous embodiment, the portions to which the method according to the present embodiment is applied may be anywhere surrounding the branch optical waveguide 3a or 3b provided that the refractive index of either of the branch optical waveguides 3a and 3b is thereby changed.
Now, referring to FIG. 12, a ninth embodiment of the present invention will be described. FIG. 12 is a plan view showing structure of an optical waveguide modulator lI according to the ninth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lI according to the ninth embodiment differing from that of the conventional optical waveguide modulator 1 is, as 203762~
shown in FIG. 12, that a plurality of metallic films 24, 24, ... are formed on the buffer layer 4 over the first branch optical waveguide 3a and then the metallic films 24, 24, ... are removed one after another as indicated by the frame 24a drawn by the broken line, whereby the refractive index of the first branch optical waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lI -to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC
offset described as related to the prior art example is eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, a metallic material is deposited by evaporation on the buffer layer 4 over a plurality of positions of the first branch optical waveguide 3a and the plurality of metallic films 24, 24, ... are thereby formed. Then, the optical waveguide modulator with the plurality of metallic films 24, 24, ... formed thereon is connec-ted to a waveform monitoring device such as an oscilloscope.
2~37~
Thereafter, while the intensity modulated waveform of the light signal output from the optical waveguide modulator is monitored with the waveform monitoring device, the plurality of metallic films 24, 24, ... are removed one after another by such a method as -throwing a laser beam thereon until the waveform of the li~ht signal takes on a desired waveform. Thus, the optical waveguide modulator lI as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA
can be obtained.
A]though, in the described optical waveguide modula-tor lI, the metallic films 24, 24, ... were formed over the first branch optical waveguide 3a and then 1~ removed one after another, they may be formed over the second branch optical waveguide 3b instead.
Now, referring to FIG. 13, a tenth embodiment of the present invention will be described. FIG. 13 is a plan view showing structure of an optical waveguide modulator lJ according to the tenth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
203762~
The point of the optical waveguide modulator lJ according to the tenth embodiment differing from that of the conventional optical waveguide modulator l is, as shown in FIG. 13, that a. material 25 with a different refractive index from the refractive index of the first branch optical waveguide 3a is filled into a gap portion 3az formed in a portion of the first branch optical waveguide 3a, whereby the refractive index of the first branch optical waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lJ to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC offse-t described as related to the prior art example is eliminated.
More specifically, to perform such operating point trimming, first, before Ti is thermally diffused for forming -the optical waveguide 3 of the optical waveguide modulator l (refer to FIG. l), a predetermined pattern is formed with a resist or the like, so that the desired gap portion 3az may be formed, in a portion of the path along which the first branch optical waveguide 3a is to be formed, and then, Ti is thermally diffused `- 2037625 and the optical waveguide 3 is thereby formed. Then, the buffer layer 4 and the e]ectrodes 5a, 5b are formed in succession and, finally, the resist is removed. The portion at which the resist is removed becomes the gap portion 3a2. Thus, an optical waveguide modulator having the first branch optical waveguide 3a wi-th the gap portion 3a2 formed therein is fabricated. Then, the optical waveguide modulator is connected to a waveform monitoring device such as an oscilloscope. Thereafter, while the intensity modulated waveform of the light signal output from the optical waveguide modulator is monitored with the waveform monitoring device, the material 25 having a different refractive index from the refractive index of the first branch optical waveguide 3a is filled into the gap portion 3a2 until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lJ as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA can be obtained.
Although, in the described optical waveguide modulator lJ, the material 25 was filled into the first branch optical waveguide 3a, it may be filled into the second branch optical waveguide 3b instead.
- 2037G2~
As the method for forming the gap portion 3az, it may also be applicable to remove a portion of the first or second branch optical waveguide by etching or a similar method after the optical waveguide modulator 1 has been fabricated.
While, in all the above described first to tenth embodiments, the trimming was performed while the waveform of the output intensity modulated light signal is monitored by having the optical waveguide modulator connected to a waveform monitoring device, it is preferred that the optical waveguide modulator is arranged in a module by being fixed to a device such as a metallic box with a drive circuit and other peripheral circuits incorporated therein and the thus modularized optical waveguide modulator is connected to a waveform monitoring device and, thereupon, the trimming as described in the first to tenth embodiments is performed.
Although the operating point trimming methods described above as related to the first to tenth embodiments were all such that are performed to optical waveguide modulators whose branch optical waveguides are of the same length, it is possible, even if they are applied to an optical waveguide modulator whose branch - 203762~
optical waveguides are different in length, to achieve matching of the light beams joining together after propagating through -the waveguides.
Further, the operating point trimming methods described above as related to the first to tenth embodiments can also be applied to an optical waveguide switch 30 of a direction coupling type as shown in FIG.
14.
The optical waveguide switch 30 will be briefly described here. The optical waveguide switch 30 shown in FIG. 14 is arranged to have virtually equal form to the optical waveguide modulator 1, only differing therefrom is that first and second op-tical waveguides 31 and 32 independent of each other are formed on the waveguide substrate 2. The first and second optical waveguides 31 and 32 have a portion where they are arranged in parallel and provided with their respective electrodes 5a and 5b mounted thereon, and there, it is adapted such that a light beam is transferred from one optical waveguide to the other by an optical interaction. For example, as shown in the same figure, a light beam 33 introduced into the second optical waveguide 32 can be transferred to the first optical waveguide 31. Further, by applying 2~371~2~
predetermined voltages to the electrodes 5a and 5b, thereby changing the strengths of electric fields, and hence the refractive indexes of the optical waveguides 3l and 32, it is made possible to arrange such that a light beam 33 introduced into the second optical waveguide 32 is completely coupled with the first optical waveguide 31 and a light beam 34 is thereby output from the first optical waveguide 31, while no light beam is allowed to output from -the second optical waveguide 32, or, conversely, such that the light beam 35 is output from the second optical waveguide 32, while no light beam is allowed to output from the first optical waveguide 31. That is, the switch can perform switching such that each of the light beams 34 and 35 is turned on/off.
According to the present invention, as described above, since it is made possible to form optical wavegulde modulators and optical waveguide switches having a desired operating point, the operating point shift can be suppressed. Consequently, the need for applying the DC bias voltage for compensating for the DC offset can be eliminated. Since the DC bias voltage need not be applied, no DC drift is produced.
Because of such advantages gained from the present 2~62~
invention, a proper light signal can be obtained.
Further, since the operating point can be set as desired, it becomes possible to fabricate products with a steady operating point and to thereby greatly improve the yield rate of the products.
OPERATING POINT TRIMMING METIIOD FOR OPTICAL WAVEGUIDE
MODULATOR AND SWITCH
Back~round of the Invention The present invention relates to operating - point trimming methods e~ for an optical waveguide modulator and an optical waveguide switch.
In a general optical communication system, a light signal intensity modulated on the transmitter side is transmitted to the receiver side through an optical transmission line formed of an optical fiber or the like and the signal is directly detected and the transmitted information is reproduced on the receiver side. The intensity modulation may be performed on the transmitter side by having the drive curren-t of a light source, which is formed for example of a semiconductor laser, modulated with a modulating signal (direct modulation).
In the case of the direct modulation, however, there sometimes occurs a relatively large wavelength shift (chirping) when high speed modulation is performed.
Therefore, when an optical fiber whose dispersion characteristic is not good is used as the optical transmission line, the transmission is restricted in the transmission distance or the transmission speed. More -~ 20~762~
specifically, when a system is structured with a combination of a single mode op-tical fiber exhibiting zero dispersion at 1.3 y m band and a semiconductor laser oscillating at 1.55 y m band minimizing the transmission loss, the system has restriction of the transmission distance or the transmission speed due to the wavelength dispersion. As a means for removing such restriction on the transmission distance or transmission speed, there is an external modulation system using an optical modulator. The external modulation system is a system in which a light beam emitted from a light source at the level of constant intensity is modulated by, for example, an optical waveguide modulator provided independently of the light source and, with which, a system producing an extremely small quantity of wavelength chirping can be formed. In implementing such external modulation system, it is desired that a trimming method for controlling the operating point of the optical waveguide modulator is provided.
FIG. 1 is a plan view showing a structure of a conventional optical waveguide modulator 1.
Referring to FIG. 1, reference numeral 2 denotes a waveguide substrate in a parallelepiped form made from a ferroelectric material such as lithium nlobate (LlNbO3). At a predetermlned posltlon on the surface of the wavegulde substrate 2, there ls formed, by such a method as thermal dlffuslon of tltanlum (Tl), an optlcal wavegulde 3 havlng a flrst branch optlcal wavegulde 3a and a second branch optlcal wavegulde 3b of the same length and ln the form of a comblned two Y-branch waveguldes. On the surface of the wavegulde substrate 2, there ls further formed a buffer layer 4 of a slllcon dloxlde (SlO2) fllm for coverlng all of the optlcal waveguldes 3, 3a, and 3b.
Over the flrst branch optlcal wavegulde 3a, there ls formed, through the buffer layer 4, a flrst electrode 5a for applylng the drlvlng voltage, provlded by platlng of a conductlve materlal such as gold, and over the second branch optlcal wave-gulde 3b, there ls formed, through the buffer layer 4, a second electrode 5b. One end of each of the flrst and second electrodes 5a and 5b are connected wlth a drlve clrcult (not shown) for changlng the voltages applled to the electrodes 5a and 5b accord-lng to the modulatlng slgnal and the other ends thereof are con-nected wlth termlnatlng reslstors (not shown). One end portlon of the optlcal wavegulde 3 ls optlcally coupled on the wavegulde sub-strate 2 wlth an optlcal flber 6 on the lnput slde as lndlcated by the 203762~
arrow and the other end portion thereof is optically coupled with an optical fiber 7 on the output side. The buffer layer 4 is provided so that the li~ht beams propagating through the first and second branch optical waveguides 3a and 3b may not be absorbed by the first and second electrodes 5a and 5b.
With the described arrangement, the refractive indexes of the first and second branch optical waveguides 3a and 3b of the optical waveguide 3 are changed according to the electric fields applied thereto and, hence, the respective branch beams branched by the branch optical waveguides 3a and 3b in phase will suffer phase changes according to the refractive indexes of the respective branch optical waveguides 3a and 3b.
Since, except for the Y-branch portions, the optical waveguide 3 is arranged to be a single mode optical waveguide, which propagates only the light beam of the fundamental mode, the intensity of the interference light output from the optical waveguide 3 becomes a maximum when the phase difference between the branch light beams is zero, whereas the intensity of the interference light becomes a minimum when the phase difference between the branch light beams is ~ .
Further, when the phase difference is between 0 and ~ , 20~762~
the interference light takes on an intensity corresponding to the phase difference. In the described manner, the optical waveguide modulator 1 provides time-series changes to the output light intensity, by changing the voltages applied to the electrodes according to the modulating signal.
FIG. 2 shows the relationship between the applied voltage and the output light intensi-ty. In the diagram, the output light intensity is indicated along the axis of ordinate and the applied voltage is indicated along the axis of abscissa.
The relationship between the applied voltage V
to the Y-branch interferometric optical modulator and the output ligh-t intensity Po, under the conditions that either a TE mode wave or a TM mode wave is used, that the propagating light is equally divided and combined at the Y-branches suffering no loss, and that the wave guide has no loss, is expressed as Po = Pi cos2[(~ /2) (V/V~ ) + ~ ] , where Pi represents the input light intensity and V~ , called the half-wave length voltage, represents the minimum voltage difference providing the maximum output and the minimum output.
The angle ~ becomes 0 when the optical path 203762~
difference between the two waveguide paths 3a and 3b equals 0 or A (wavelength of the propagating light) / n (the refractive index of the medium for the propagating light) multiplied by 2k (k = i 1, i 2, ...). The so]id line 10 in FIG. 2 shows the case where the angle ~ = 0.
In such modulator, the intensity modulation can be achieved by changing the voltage between the applied voltage V1 (V3) providing a maximum of the light intensity and the applied voltage V2 (V4) providing a minimum of the light intensity. For example, when performing digital modulation, the applied voltage may be set to V1 at the mark period lOa corresponding to "1"
and the applied voltage may be set to V2 at the space period lOb corresponding to "0".
In the described optical waveguide modulator 1, the refractive indexes of the first and second branch optical waveguides 3a and 3b are changed by stress exerted -thereon from the buffer layer 4 and the electrodes 5a and 5b disposed on the waveguide substrate 2 and, as a result, the optical path lengths of these waveguides become different, leading to a shift of the operating point.
When the operating point is shifted as described above, the desired waveform 10 is shifted to -- 203762~
the position of the waveform 11 as indicted in FIG. 2 by the broken line. More specifically, the waveform is slipped by the shift amount ~ V corresponding to the operating point shifting. In order to compensate for this shift, it is required that a DC bias voltage is applied to the electrodes 5a and 5b to change the refractive indexes of the branch optical waveguides 3a and 3b and adjust the optical path difference therebetween.
The shift amount ~ V due to the operating point shifting differs from product to product because of lack of uniformity of the thickness of the evaporation film of the buffer layer etc. and of the size of various parts occurring in the course of fabrication. Such tendency is especially remarkable with optical waveguide modulators using, as the waveguide substrate, LiNbO3 having the photoelastic effect. Therefore, it becomes necessary to apply each optical modulator with the DC bias voltage corresponding to the operating point shift amount ~ V due to the operating point shifting resulted from the above described lack of uniformity to thereby adjust the DC
offset. Further, even if the shift amount ~ V is compensated for by taking the above measure, there 203762~
sometimes occurs, when such DC bias voltage is applied, a phenomenon called DC drift in which the operating point shifts with the lapse of time after the application of the DC bias voltage. This phenomenon for example is such, as shown in FIG. 3, that the waveform 10 adjusted to a desired output light intensity by application of a DC bias tends to shift to the waveform 12 indicated by the broken line.
When such a shift occurs, the applied voltage Vl providing the maximum light output is shifted to Vl', as shown in FIG. 3, while the applied voltage Vz providing the minimum light output is shifted to V2'.
Therefore, if the modulation is performed with the applied voltages V1 - Vz whereby the original waveform 10 was obtained, the output light intensity when the applied voltage is V1 decreases from lOa to lOb as shown in the same diagram, while the output light intensity 12a wherl the applied voltage is Vz increases from 12a to 12b. As a result, it becomes unable to obtain the maximum and minimum output light beams and the extinction ratio (the ratio of the output light intensity in the mark period to that in the space period given in decibels) is decreased, and a problem is presented that it becomes unable to have a suitable 203762~
optical signal output.
When i-t is attempted to obtain optical waveguide modulators having no operating point shifting such as the DC drift, since some nonuniformity of the operating point occurs in the fabrication process, it becomes necessary to select such products that have virtually equal operating point shiftings after fabrication thereof. This is indeed a difficult task in view of the fact that the nonuniformity of the operating point shifting is frequently produced in the fabrication process, and because of which, a problem is presented of a lowering of the yield rate.
Summary of the Invention Accordingly, an object of the present invention is to provide an operating point trimming method for an optical waveguide modulator, whereby the refractive index of one optical waveguide of a pair of branch optical waveguides is changed with respect to that of the other one so that the operating point is shifted to a voltage not causing the difficulty of the DC drift.
Another object of the present invention is to provide an operating point trimming method for an 203762~
optical waveguide switch, whereby the refractive index of one optical waveguide of a pair of independent optical waveguides is changed with respect to that of the other one so that the operating point is shifted to a voltage not causing the difficulty of the ~C drift.
A further object of the present invention is to provide a method of fabricating an optical waveguide modulator or an optical waveguide switch, in which the operating point is suitably shifted so that the yield rate is improved.
According to the present invention, the following operating point trimming methods (a) - (j) are provided for use in an optical waveguide modulator in which the voltage applied between a first electrode and a second electrode mounted on a first and a second branch optical waveguide is changed so that a phase difference is produced between the light beams guided thereby and the light beams thus caused to have the phase difference are combined so that an intensity modulated light beam is output from the optical waveguide modulator.
(a) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, a portion of either one of the 20~7~25 first and the second electrode is removed such tha-t the waveform of the intensity modulated light beam takes on a desired waveform.
(b) Whi]e the waveform of the described intensity modulated light beam is monitored with a waveform display device, a metallic material is deposited by evaporation on the buffer layer over a portion of either one of the first and the second optical waveguidel with the electrode not mounted thereon, such that the waveform of the intensity modulated light beam takes on a desired waveform.
(c) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, the buffer layer over a portion of either one of the first and the second optical waveguide, with the electrode not mounted thereon, is cut away such that the waveform of -the intensity modulated light beam takes on a desired waveform.
(d) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, a material increasing or decreasing the refractive index of the optical waveguide is deposited, from the top face of the buffer layer, into a portion of either one of the first and the second 2~3~2~
optical waveguide, with the electrode not mounted thereon, such that the waveform of the intensity modulated light beam takes on a desired waveform.
(e) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, a portion of either one of the first and the second optical waveguide, with the electrode not mounted thereon, is externally heated to be deformed, through the buffer layer, such that the waveform of the intensity modulated light beam takes on a desired waveform.
(f) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, a block for applying stress is attached to the side face of the waveguide substrate, mechanical stress is applied to the block, and the block is fixed up when the applied mechanical stress has reached a state where the waveform of the intensity modulated light beam takes on a desired waveform, such that the state is maintained.
(g) While the waveform of the described intensity modulated light beam is monitored with a waveform display device, a por-tion at the side of the waveguide substrate is cut off such that the waveform of the intensity modulated light beam takes on a desired waveform.
(h) The buffer layer is removed at a plurality of portions thereof over either one of the first and the second optical waveguide, with the electrode not mounted thereon, and then, while the waveform of the described intensity modulated light beam is monitored wi-th a waveform display device, a material having a different refractive index from the refractive index of the optical waveguide is deposited on the plurality of portions of the buffer layer that have been removed such that the waveform of the intensity modulated light beam takes on a desired waveform.
(i) A metallic material is deposited by evaporation on the buffer layer over a plurality of portions of either one of the first and the second optical waveguide, with the electrode not mounted thereon, so that a plurality of independent metallic films are formed and, then, while the waveform of the described intensity modulated light beam is monitored with a waveform display device, the plurali-ty of the metallic films are removed one after another such that the waveform of the intensity modulated light beam takes on a desired waveform.
2037i~2~
(j) A gap is formed in a portion of either one of the first and the second optical waveguide, with the electrode not mounted thereon, and, then, while the waveform of the described intensity modulated light beam is monitored with a waveform display device, a material with different refractive index from the refractive index of the optical waveguide is filled into the gap such that the waveform of the intensity modulated light beam takes on a desired waveform.
It is preferred that optical fibers for inputting and outputting an optical signal are fixed to the optical waveguide modulator and this optical waveguide modulator is fixed to a member with a predetermined set of peripheral circuits attached thereto and, then, the operating point trimmi.ng is carried out according to any of the above described methods (a) - (j).
The operating point of an optical waveguide switch can also be trimmed by any of the methods (a) -(j).
The above and other objects, features andadvantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of 203762~
the following description and appended claims, with reference had to the attached drawings showing some preferred embodiments of the invention.
Brief Description of the Drawin~s FIG. 1 is a plan view showing struc-ture of a conventional optical waveguide modulator;
FIG. 2 is a diagram for explaining an operating point offset;
FIG. 3 is a diagram for explaining a DC drift;
FIG. 4 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a first embodiment of the present invention;
FIG. 5 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a second embodiment of the present invention;
FIG. 6 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a third embodiment of the present invention;
FIG. 7 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a fourth embodiment of the present invention;
FIG. 8 is a plan view of an optical waveguide modulator for explaining an operating point trimming - 2037t~2~
method as a fifth embodiment of the present invention;
FIG. 9 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a sixth embodiment of the present invention;
FIG. 10 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a seventh embodiment of the present invention;
FIG. ll is a plan view of an optical waveguide modulator for explaining an operating point trimming method as an eighth embodiment of the present invention;
FIG. 12 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a ninth embodiment of the present invention;
FIG. 13 is a plan view of an optical waveguide modulator for explaining an operating point trimming method as a tenth embodiment of the present invention;
and FIG. 14 is a plan view of an optical waveguide switch to which the operating point trimming method according to the present invention is suitably applicable.
Description of the Preferred Embodiments Embodiments of the present invention will now - 2~3762~
be described below with reference to the accompanying drawings. FIG. 4 is a plan view showing structure of an optical waveguide modulator lA according to -the first embodiment of the present invention, in WtliCtl parts corresponding to the parts in the prior art example shown in FIG. l are denoted by like reference numerals.
Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lA according to the firs-t embodiment differing from that l~ of the conventional optical waveguide modulator l shown in FIG. l is, as shown in FIG. 4, that a portion 5b1 of the second electrode 5b is removed so that the electrode is changed in its form and hence the stress exerted on the second branch optical waveguide 3b is changed, whereby the refractive index of the second branch optical waveguide 3b is changed and the optical path difference between the same and the first branch optical waveguide 3a is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lA to a desired operating point is achieved and the need for applying the DC bias voltage for compensating for the DC offset described as related to the prior art example is eliminated.
More specifically, in performing such ~03~762S
operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope, which is not shown. Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, a predetermined portion of the second electrode 5b of the optical waveguide modulator 1 is removed by a laser beam thereby having the portion heated and removed until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modula-tor lA as described above can be obtained.
Although a portion of the second electrode 5b was removed in the above described optical waveguide modulator lA, a portion of the first electrode 5a may be removed depending on the refractive indexes of the branch optical waveguides 3a and 3b.
With the described optical waveguide modulator lA, the need for applying the DC bias voltage as was necessary in the conventional optical waveguide modulator 1 can be eliminated. Further, since the DC
bias is not applied to the same, the DC drift usual with 2S3;7~2~
the prior art does not occur.
Now, referring to FIG. 5, a second embodiment of the present invention will be described. FIG. 5 is a plan view showing structure of an optical waveguide modula-tor lB according to the second embodiment of the present inven-tion, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lB according to the second embodiment dif-fering from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 5, that a metallic film 20 is formed on the buffer layer 4 over the first branch optical waveguide 3a, whereby the light beam propagating through the first branch optical waveguide 3a when traveling past the portion of the metallic film 20 senses the refractive index of the metallic film 20 and the refractive index of the first branch optical waveguide 3a is substantially changed and, accordingly, the optical path length of the first branch optical waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus -the trimming for bringing the ~ t7 3 ~
operating point of the optical waveguide modulator lB to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC
offset described as related to the prior art example is eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, a metallic material is deposited by evaporation on the buffer layer 4, to form the metallic film 20, over the first branch optical waveguide 3a until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lB as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA
can be obtained.
Although the metallic layer 20 was formed over the first branch optical waveguide 3a through the buffer layer 4 in the above described optical waveguide 2l~3~2~
modulator lB, the metallic layer 20 may be formed over the second branch optical waveguide 3b depending on the refractive indexes of the branch optical waveguides 3a and 3b. That is, the metallic film 20 may be formed at a portion over the branch optical waveguides 3a and 3b except for the portions where the electrodes 5a and 5b are formed.
Now, referring to FIG. 6, a third embodiment of the present invention will be described. FIG. 6 is a plan view showing structure of an optical waveguide modulator lC according to the third embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lC according to the third embodiment differing from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 6, that a portion 4a of the buffer layer 4 over the first branch optical waveguide 3a is removed, so that the first branch optical waveguide 3a a-t the position where the buffer layer 4 is removed changes its refractive index by contacting with air, whereby the optical path length of the first branch optical 2~3762~
waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lC ~o a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC
offset described as related to the prior art example is eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, the buffer layer 4 over a portion of the first branch optical waveguide 3a is removed by such a method as etching, grinding, or irradiation of an electron beam until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lC as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA can be obtained.
2~37~2~
Although a portion of the buffer layer 4 over the first branch optical waveguide 3a was removed in the above described optical waveguide modulator lC, it sometimes is better to remove a portion of the buffer layer 4 over the second branch optical waveguide 3b depending on the refractive indexes of the branch optical waveguides 3a and 3b. That iSJ the buffer layer 4 may be removed at a portion over the branch optical waveguides 3a and 3b except for the portions where the electrodes 5a ~ 5b are formed.
Now, referring to FIG. 7, a fourth embodiment of the present invention will be described. FIG. 7 is a plan view showing structure of an optical waveguide modulator lD according to the fourth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lD according to the fourth embodiment differing from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 7, that a material 21 increasing or decreasing the refractive index of the optical waveguide is attached to a portion on the first branch optical 203762~
waveguide 3a so that the refractive index of the first branch optical waveguide 3a is changed, whereby the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lD to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC offset described as related to the prior art example is eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, a material 21 increasing or decreasing the refractive index of the optical waveguide is injected by such a method as ion injection into a portion on the first branch optical waveguide 3a until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lD as described above can be obtained, and therefrom, the same effects as obtained ~03762~i from the above described optical waveguide modulator lA
can be obtained.
Although a material 21 increasing or decreasing the refractive index of the optical waveguide is attached to a portion on the first branch optical waveguide 3a in the optical waveguide lD, it may be attached to a portion on the second branch optical waveguide 3b instead.
Now, referring to FIG. 8, a fifth embodiment of the present invention will be described. FIG. 8 is a plan view showing structure of an optical waveguide modulator lE according to the fifth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lE according to the fifth embodiment differing from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 8, that a portion 3al of the first branch optical waveguide 3a is deformed so that the refractive index of the optical waveguide 3a is changed, whereby the optical path difference between the same and the second branch optical waveguide 3b is adjus-ted, and thus 2~7~
the trimming for bringing the operating point of the optical waveguide modulator lE to a desired operating point is achieved, and the need for applyirlg the DC bias voltage for compensating for the DC offset described as related to the prior art example is eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, a portion 3al or the portion surrounding it on the first branch optical waveguide 3a is heated by a heating means such as a laser beam so that the first branch optical waveguide 3a is deformed by diffusion until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lE as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA can be obtained.
Although a portion on the first branch optical waveguide 3a was deformed in the optical waveguide lE, a - 2~37~2~
portion on the seGond branch optical waveguide 3b may be deformed instead.
Now, referring to FIG. 9, a sixth embodiment of the present invention will be described. FIG. 9 is a plan view showing structure of an optical waveguide modulator lF according to the sixth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lF according to the sixth embodiment differing from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 9, that a block 22 for applying stress is fixed to a portion on the side face of the waveguide substrate 2, the refractive index of the optical waveguide 3a is changed by the stress applied thereon and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lF to a desired operating point is achieved, and the need for applying the DC bias vo]tage for compensating for the DC offset described as related to the prior art example is eliminated.
~037762~
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, the block 22 is attached to a portion on the side face of the waveguide substrate 2. Thereafter, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, mechanical stress is applied to the block 22, and when the waveform of the light signal takes on a desired waveform, the block 22 is fixed up such that the mechanical stress at that time is maintained. Thus, the optical waveguide modulator lF as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA
can be obtained.
Although the refractive index of the first branch optical waveguide 3a was changed by means of the block 22 for applying stress in the above described optical waveguide modulator lF, the block 22 may be fixed on the opposite side face of the waveguide substrate 2 so that the refractive index of the second - 20:3~62~
branch optical waveguide 3b is changed.
Now, referring -to FIG. lO, a seventh embodiment of the presen-t invention will be described.
FIG. lO is a plan view showing structure of an optical waveguide modulator lG according to the seventh embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. l are denoted by like reference numerals.
Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lG according to the seventh embodiment differing from that of the conventional optical waveguide modulator l is, as shown in FIG. 10, that a part at the side of the waveguide substrate 2 is cut off and an indented portion 2a is formed there so that the stress exerting on the first branch optical waveguide 3a is changed, whereby the refractive index of the first branch optical waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lG to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC
offset described as related to the prior art example is - 2037~i2~
eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, the optical waveguide modulator 1 is connected to a waveform monitoring device such as an oscilloscope.
Then, while the intensity modulated waveform of the light signal output from the optical waveguide modulator 1 is monitored with the waveform monitoring device, a portion at the side of the waveguide substrate 2 is cut off by grinding and the indented portion 2a is formed there until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lG as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA can be obtained.
The portion to be cut off may be anywhere at the side of the waveguide substrate 2 provided that the refractive index of either of the branch optical waveguides 3a and 3b is changed and an optical signa]
with a predetermined intensity modulated waveform is thereby obtained.
Now, referring to FIG. 11, an eighth embodiment of the present invention will be described.
20~2~
FIG. 11 is a plan view showing structure of an optical waveguide modulator lH according to the eighth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals.
Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lH according to the eighth embodiment differing from that of the conventional optical waveguide modulator 1 is, as shown in FIG. 11, that a plurality of portions 4b, 4b, ... of the buffer layer 4 over the first branch optical waveguide 3a are removed and then a material 23 with a different refractive index from that of the optical waveguide 3 is mounted on the portions 4b, 4b, ... at which the buffer layer 4 is removed, whereby the refractive index of the first branch optical waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lH to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC
offset described as related to the prior art example is eliminated.
21337~5 More specifically, in performing such operating point trimming, the optical waveguide modula-tor 1 (refer to FIG. 1) is fabricated and, then, the buffer layer 4 is removed by etching or a similar method at a plurality of portions 4b, 4b, ... thereof over the first branch optical waveguide 3a. Then, the optical waveguide modulator 1 with the portions 4b, 4b, ... of the buffer layer 4 removed is connected to a waveform monitoring device such as an oscilloscope.
Thereafter, while the intensity modulated waveform of the light signal output from the optical waveguide modulator is monitored with the waveform monitoring device, a material 23 with a different refractive index from that of the optical waveguide 3 is mounted on the portions 4b, 4b, ... at which the buffer layer 4 is removed, one after another, until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lH as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA
can be obtained.
Although, in the described optical waveguide modulator lH, portions 4b, 4b, ... of the buffer layer 4 over the first branch optical waveguide 3a were removed 203762~
and the material 23 was mounted on these portions, it may also be well to have portions of the buffer layer 4 over the second branch optical waveguide 3b removed and have the material 23 mounted on these portions. That is, the portions to be removed may be over either of the branch optical waveguides 3a and 3b except the portions at which the electrodes 5a and 5b are formed. The same as in the previous embodiment, the portions to which the method according to the present embodiment is applied may be anywhere surrounding the branch optical waveguide 3a or 3b provided that the refractive index of either of the branch optical waveguides 3a and 3b is thereby changed.
Now, referring to FIG. 12, a ninth embodiment of the present invention will be described. FIG. 12 is a plan view showing structure of an optical waveguide modulator lI according to the ninth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
The point of the optical waveguide modulator lI according to the ninth embodiment differing from that of the conventional optical waveguide modulator 1 is, as 203762~
shown in FIG. 12, that a plurality of metallic films 24, 24, ... are formed on the buffer layer 4 over the first branch optical waveguide 3a and then the metallic films 24, 24, ... are removed one after another as indicated by the frame 24a drawn by the broken line, whereby the refractive index of the first branch optical waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lI -to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC
offset described as related to the prior art example is eliminated.
More specifically, in performing such operating point trimming, the optical waveguide modulator 1 (refer to FIG. 1) is fabricated and, then, a metallic material is deposited by evaporation on the buffer layer 4 over a plurality of positions of the first branch optical waveguide 3a and the plurality of metallic films 24, 24, ... are thereby formed. Then, the optical waveguide modulator with the plurality of metallic films 24, 24, ... formed thereon is connec-ted to a waveform monitoring device such as an oscilloscope.
2~37~
Thereafter, while the intensity modulated waveform of the light signal output from the optical waveguide modulator is monitored with the waveform monitoring device, the plurality of metallic films 24, 24, ... are removed one after another by such a method as -throwing a laser beam thereon until the waveform of the li~ht signal takes on a desired waveform. Thus, the optical waveguide modulator lI as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA
can be obtained.
A]though, in the described optical waveguide modula-tor lI, the metallic films 24, 24, ... were formed over the first branch optical waveguide 3a and then 1~ removed one after another, they may be formed over the second branch optical waveguide 3b instead.
Now, referring to FIG. 13, a tenth embodiment of the present invention will be described. FIG. 13 is a plan view showing structure of an optical waveguide modulator lJ according to the tenth embodiment of the present invention, in which parts corresponding to the parts in the prior art example shown in FIG. 1 are denoted by like reference numerals. Accordingly, explanation thereof will be omitted.
203762~
The point of the optical waveguide modulator lJ according to the tenth embodiment differing from that of the conventional optical waveguide modulator l is, as shown in FIG. 13, that a. material 25 with a different refractive index from the refractive index of the first branch optical waveguide 3a is filled into a gap portion 3az formed in a portion of the first branch optical waveguide 3a, whereby the refractive index of the first branch optical waveguide 3a is changed and the optical path difference between the same and the second branch optical waveguide 3b is adjusted, and thus the trimming for bringing the operating point of the optical waveguide modulator lJ to a desired operating point is achieved, and the need for applying the DC bias voltage for compensating for the DC offse-t described as related to the prior art example is eliminated.
More specifically, to perform such operating point trimming, first, before Ti is thermally diffused for forming -the optical waveguide 3 of the optical waveguide modulator l (refer to FIG. l), a predetermined pattern is formed with a resist or the like, so that the desired gap portion 3az may be formed, in a portion of the path along which the first branch optical waveguide 3a is to be formed, and then, Ti is thermally diffused `- 2037625 and the optical waveguide 3 is thereby formed. Then, the buffer layer 4 and the e]ectrodes 5a, 5b are formed in succession and, finally, the resist is removed. The portion at which the resist is removed becomes the gap portion 3a2. Thus, an optical waveguide modulator having the first branch optical waveguide 3a wi-th the gap portion 3a2 formed therein is fabricated. Then, the optical waveguide modulator is connected to a waveform monitoring device such as an oscilloscope. Thereafter, while the intensity modulated waveform of the light signal output from the optical waveguide modulator is monitored with the waveform monitoring device, the material 25 having a different refractive index from the refractive index of the first branch optical waveguide 3a is filled into the gap portion 3a2 until the waveform of the light signal takes on a desired waveform. Thus, the optical waveguide modulator lJ as described above can be obtained, and therefrom, the same effects as obtained from the above described optical waveguide modulator lA can be obtained.
Although, in the described optical waveguide modulator lJ, the material 25 was filled into the first branch optical waveguide 3a, it may be filled into the second branch optical waveguide 3b instead.
- 2037G2~
As the method for forming the gap portion 3az, it may also be applicable to remove a portion of the first or second branch optical waveguide by etching or a similar method after the optical waveguide modulator 1 has been fabricated.
While, in all the above described first to tenth embodiments, the trimming was performed while the waveform of the output intensity modulated light signal is monitored by having the optical waveguide modulator connected to a waveform monitoring device, it is preferred that the optical waveguide modulator is arranged in a module by being fixed to a device such as a metallic box with a drive circuit and other peripheral circuits incorporated therein and the thus modularized optical waveguide modulator is connected to a waveform monitoring device and, thereupon, the trimming as described in the first to tenth embodiments is performed.
Although the operating point trimming methods described above as related to the first to tenth embodiments were all such that are performed to optical waveguide modulators whose branch optical waveguides are of the same length, it is possible, even if they are applied to an optical waveguide modulator whose branch - 203762~
optical waveguides are different in length, to achieve matching of the light beams joining together after propagating through -the waveguides.
Further, the operating point trimming methods described above as related to the first to tenth embodiments can also be applied to an optical waveguide switch 30 of a direction coupling type as shown in FIG.
14.
The optical waveguide switch 30 will be briefly described here. The optical waveguide switch 30 shown in FIG. 14 is arranged to have virtually equal form to the optical waveguide modulator 1, only differing therefrom is that first and second op-tical waveguides 31 and 32 independent of each other are formed on the waveguide substrate 2. The first and second optical waveguides 31 and 32 have a portion where they are arranged in parallel and provided with their respective electrodes 5a and 5b mounted thereon, and there, it is adapted such that a light beam is transferred from one optical waveguide to the other by an optical interaction. For example, as shown in the same figure, a light beam 33 introduced into the second optical waveguide 32 can be transferred to the first optical waveguide 31. Further, by applying 2~371~2~
predetermined voltages to the electrodes 5a and 5b, thereby changing the strengths of electric fields, and hence the refractive indexes of the optical waveguides 3l and 32, it is made possible to arrange such that a light beam 33 introduced into the second optical waveguide 32 is completely coupled with the first optical waveguide 31 and a light beam 34 is thereby output from the first optical waveguide 31, while no light beam is allowed to output from -the second optical waveguide 32, or, conversely, such that the light beam 35 is output from the second optical waveguide 32, while no light beam is allowed to output from the first optical waveguide 31. That is, the switch can perform switching such that each of the light beams 34 and 35 is turned on/off.
According to the present invention, as described above, since it is made possible to form optical wavegulde modulators and optical waveguide switches having a desired operating point, the operating point shift can be suppressed. Consequently, the need for applying the DC bias voltage for compensating for the DC offset can be eliminated. Since the DC bias voltage need not be applied, no DC drift is produced.
Because of such advantages gained from the present 2~62~
invention, a proper light signal can be obtained.
Further, since the operating point can be set as desired, it becomes possible to fabricate products with a steady operating point and to thereby greatly improve the yield rate of the products.
Claims (11)
1. An operating point trimming method for an optical waveguide modulator, said optical waveguide modulator including a waveguide substrate, a first and a second branch optical waveguide formed on said substrate, a buffer layer covering said first and second branch optical waveguides, and a first and a second electrode respectively mounted on said first and second branch optical waveguides, and adapted such that a voltage from a voltage source applied between said first and second electrodes is varied so that a phase difference is produced between light beams propagating through said first and second branch optical waveguides and the light beams having the phase difference therebetween are combined to be output as an intensity modulated light beam, said operating point trimming method comprising the steps of:
monitoring the waveform of said intensity modulated light beam; and removing, while monitoring the waveform, said buffer layer over a portion of either one of said first and second branch optical waveguides, with one of said first and second electrodes not mounted thereon, such that the waveform of said intensity modulated light beam takes on a desired waveform.
monitoring the waveform of said intensity modulated light beam; and removing, while monitoring the waveform, said buffer layer over a portion of either one of said first and second branch optical waveguides, with one of said first and second electrodes not mounted thereon, such that the waveform of said intensity modulated light beam takes on a desired waveform.
2. An operating point trimming method for an optical waveguide modulator, said optical waveguide modulator including a waveguide substrate, a first and a second branch optical waveguide formed on said substrate, a buffer layer covering said first and second branch optical waveguides, and a first and a second electrode respectively mounted on said first and second branch optical waveguides, and adapted such that a voltage from a voltage source applied between said first and second electrodes is varied so that a phase difference is produced between light beams propagating through said first and second branch optical waveguides and the light beams having the phase difference therebetween are combined to be output as an intensity modulated light beam, said operating point trimming method comprising the steps of:
monitoring the waveform of said intensity modulated light beam; and heating while monitoring the waveform, a portion of either one of said first and second branch optical waveguides, with one of said first and second electrodes not mounted thereon, through said buffer layer, thereby deforming said portion such that the waveform of said intensity modulated light beam takes on a desired waveform.
monitoring the waveform of said intensity modulated light beam; and heating while monitoring the waveform, a portion of either one of said first and second branch optical waveguides, with one of said first and second electrodes not mounted thereon, through said buffer layer, thereby deforming said portion such that the waveform of said intensity modulated light beam takes on a desired waveform.
3. An operating point trimming method for an optical waveguide modulator, said optical waveguide modulator including a waveguide substrate, a first and a second branch optical waveguide formed on said substrate, a buffer layer covering said first and second branch optical waveguides, and a first and a second electrode respectively mounted on said first and second branch optical waveguides, and adapted such that a voltage from a voltage source applied between said first and second electrodes is varied so that a phase difference is produced between light beams propagating through said first and second branch optical waveguides and the light beams having the phase difference therebetween are combined to be output as an intensity modulated light beam, said operating point trimming method comprising the steps of:
attaching a stress applying block to a side face of said waveguide substrate;
applying, while monitoring the waveform of said intensity modulated light beam, a mechanical stress to said block such that the waveform of said intensity modulated light beam takes on a desired waveform; and fixing up said block in a state maintaining the stress.
attaching a stress applying block to a side face of said waveguide substrate;
applying, while monitoring the waveform of said intensity modulated light beam, a mechanical stress to said block such that the waveform of said intensity modulated light beam takes on a desired waveform; and fixing up said block in a state maintaining the stress.
4. An operating point trimming method for an optical waveguide modulator, said optical waveguide modulator including a waveguide substrate, a first and a second branch optical waveguide formed on said substrate, a buffer layer covering said first and second branch optical waveguides, and a first and a second electrode respectively mounted on said first and second branch optical waveguides, and adapted such that the voltage from a voltage source applied between said first and second electrodes is varied so that a phase difference is produced between light beams propagating through said first and second branch optical waveguides and the light beams having the phase difference therebetween are combined to be output as an intensity modulated light beam, said operating point trimming method comprising the steps of:
monitoring the waveform of said intensity modulated light beam; and cutting off, while monitoring the waveform, a portion at a side of said waveguide substrate such that the waveform of said intensity modulated light beam takes on a desired waveform.
monitoring the waveform of said intensity modulated light beam; and cutting off, while monitoring the waveform, a portion at a side of said waveguide substrate such that the waveform of said intensity modulated light beam takes on a desired waveform.
5. An optical waveguide modulator, comprising:
a waveguide substrate;
a first and a second branch optical waveguide formed on said substrate;
a buffer layer covering said first and second branch optical waveguides;
first and second electrode means respectively mounted on said first and second branch optical waveguides for receiving a voltage from a voltage source between said first and second electrode means, said voltage being varied so that a phase difference is produced between light beams propagating through said first and second branch optical waveguides and the light beams having the phase difference therebetween are combined to be output as an intensity modulated light beam; and said buffer layer having an exposure hole in which a portion of said buffer layer which is over a portion of either one of said first and second branch optical waveguides, with one of said first and second electrode means not mounted thereon, is removed, such that the waveform of said intensity modulated beam takes on a desired waveform.
a waveguide substrate;
a first and a second branch optical waveguide formed on said substrate;
a buffer layer covering said first and second branch optical waveguides;
first and second electrode means respectively mounted on said first and second branch optical waveguides for receiving a voltage from a voltage source between said first and second electrode means, said voltage being varied so that a phase difference is produced between light beams propagating through said first and second branch optical waveguides and the light beams having the phase difference therebetween are combined to be output as an intensity modulated light beam; and said buffer layer having an exposure hole in which a portion of said buffer layer which is over a portion of either one of said first and second branch optical waveguides, with one of said first and second electrode means not mounted thereon, is removed, such that the waveform of said intensity modulated beam takes on a desired waveform.
6. An optical waveguide switch, comprising:
a waveguide substrate;
a first and a second optical waveguide formed on said substrate;
a buffer layer covering said first and second optical waveguides;
a first and a second electrode respectively mounted on said first and second optical waveguides; and said buffer layer having an exposure hole in which a portion of said buffer layer which is over a portion of either one of said first and second optical waveguides, with one of said first and second electrode means not mounted thereon, is removed, so as to trim an operating point of the switch.
a waveguide substrate;
a first and a second optical waveguide formed on said substrate;
a buffer layer covering said first and second optical waveguides;
a first and a second electrode respectively mounted on said first and second optical waveguides; and said buffer layer having an exposure hole in which a portion of said buffer layer which is over a portion of either one of said first and second optical waveguides, with one of said first and second electrode means not mounted thereon, is removed, so as to trim an operating point of the switch.
7. An optical waveguide switch, comprising:
a waveguide substrate;
a first and a second optical waveguide formed on said substrate;
a buffer layer covering said first and second optical waveguides;
a first and a second electrode respectively mounted on said first and second optical waveguides; and said waveguide substrate having a removed portion in which a portion at one side of said waveguide substrate is cut off.
a waveguide substrate;
a first and a second optical waveguide formed on said substrate;
a buffer layer covering said first and second optical waveguides;
a first and a second electrode respectively mounted on said first and second optical waveguides; and said waveguide substrate having a removed portion in which a portion at one side of said waveguide substrate is cut off.
8. An operating point trimming method for an optical waveguide switch including a waveguide substrate, a first and a second optical waveguide formed on said substrate independently of each other, a buffer layer covering said first and second optical waveguides, and a first and a second electrode respectively mounted on said first and said second optical waveguide, said operating point trimming method comprising the step of:
removing, while monitoring the waveforms of output light beams of said first and said second optical waveguide, said buffer layer over a portion of either one of said first and said second optical waveguide, with said electrode not mounted thereon.
removing, while monitoring the waveforms of output light beams of said first and said second optical waveguide, said buffer layer over a portion of either one of said first and said second optical waveguide, with said electrode not mounted thereon.
9. An operating point trimming method for an optical waveguide switch including a waveguide substrate, a first and a second optical waveguide formed on said substrate independently of each other, a buffer layer covering said first and second optical waveguides, and a first and a second electrode respectively mounted on said first and said second optical waveguide, said operating point trimming method comprising the step of:
heating, while monitoring the waveforms of output light beams of said first and said second optical waveguide, a portion of either one of said first and said second optical waveguides, with said electrode not mounted thereon, through said buffer layer, thereby deforming said portion.
heating, while monitoring the waveforms of output light beams of said first and said second optical waveguide, a portion of either one of said first and said second optical waveguides, with said electrode not mounted thereon, through said buffer layer, thereby deforming said portion.
10. An operating point trimming method for an optical waveguide switch including a waveguide substrate, a first and a second optical waveguide formed on said substrate independently of each other, a buffer layer covering said first and second optical waveguides, and a first and a second electrode respectively mounted on said first and said second optical waveguide, said operating point trimming method comprising the steps of:
attaching a stress applying block to a side face of said waveguide substrate;
applying, while monitoring the waveforms of output light beams of said first and said second optical waveguide, a mechanical stress to said block; and fixing up said block in the state maintaining the stress.
attaching a stress applying block to a side face of said waveguide substrate;
applying, while monitoring the waveforms of output light beams of said first and said second optical waveguide, a mechanical stress to said block; and fixing up said block in the state maintaining the stress.
11. An operating point trimming method for an optical waveguide switch including a waveguide substrate, a first and a second optical waveguide formed on said substrate independently of each other, a buffer layer covering said first and second optical waveguides, and a first and a second electrode respectively mounted on said first and said second optical waveguide, said operating point trimming method comprising the step of:
cutting off, while monitoring the waveforms of output light beams of said first and said second optical waveguide, a portion at a side of said waveguide substrate.
cutting off, while monitoring the waveforms of output light beams of said first and said second optical waveguide, a portion at a side of said waveguide substrate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2054976A JPH03257423A (en) | 1990-03-08 | 1990-03-08 | Operation point trimming method of waveguide type optical modulator |
| JP02-054976 | 1990-03-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2037625C true CA2037625C (en) | 1994-11-15 |
Family
ID=12985682
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002037625A Expired - Fee Related CA2037625C (en) | 1990-03-08 | 1991-03-06 | Operating point trimming method for optical waveguide modulator and switch |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US5283842A (en) |
| EP (1) | EP0445763A3 (en) |
| JP (1) | JPH03257423A (en) |
| CA (1) | CA2037625C (en) |
Families Citing this family (21)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2270173B (en) * | 1992-08-28 | 1996-05-15 | Marconi Gec Ltd | Optical modulator |
| FR2706631B1 (en) * | 1993-06-17 | 1997-12-12 | Oki Electric Ind Co Ltd | Compact optical switching module. |
| KR100271188B1 (en) * | 1993-07-07 | 2000-11-01 | 도낀 가부시끼가이샤 | Optical modulator |
| JPH08146365A (en) * | 1994-11-16 | 1996-06-07 | Nec Corp | Semiconductor mach-zehnder modulation device and its production |
| US5515463A (en) * | 1995-03-10 | 1996-05-07 | Hewlett-Packard Company | Multi-branch microwave line for electro-optical devices |
| US5566263A (en) * | 1995-03-22 | 1996-10-15 | Minnesota Mining And Manufacturing Company | System for tuning an integrated optical switch element |
| JPH0961766A (en) * | 1995-08-19 | 1997-03-07 | Nec Corp | Semiconductor optical modulator |
| JP2792482B2 (en) * | 1995-09-28 | 1998-09-03 | 日本電気株式会社 | Semiconductor Mach-Zehnder modulator |
| FR2771517B1 (en) * | 1997-11-27 | 2001-12-14 | Dassault Electronique | ELECTRO-OPTICAL DEVICE, PARTICULARLY FOR OPTICAL DISTRIBUTION |
| AU7123600A (en) * | 1999-09-10 | 2001-04-10 | Nanovation Technologies, Inc. | Mach-zehnder interferometer with a ring resonator |
| US7068862B2 (en) | 2000-09-22 | 2006-06-27 | Massachusetts Institute Of Technology | Methods of altering the resonance of waveguide micro-resonators |
| GB2370372A (en) * | 2000-12-22 | 2002-06-26 | Bookham Technology Plc | Coupled optical waveguide system with grating and stress controlling layer |
| JP2005077987A (en) * | 2003-09-03 | 2005-03-24 | Sumitomo Osaka Cement Co Ltd | Optical modulator |
| JP2006126796A (en) * | 2004-09-28 | 2006-05-18 | Aisin Seiki Co Ltd | Method of driving mach-zehnder light modulator, and light modulating device |
| US20060078258A1 (en) * | 2004-10-07 | 2006-04-13 | University Of Toledo | Apparatus and method for trimming and tuning coupled photonic waveguides |
| JP4741258B2 (en) * | 2005-03-04 | 2011-08-03 | 住友大阪セメント株式会社 | Optical waveguide device and manufacturing method thereof |
| JP4694235B2 (en) * | 2005-03-30 | 2011-06-08 | 住友大阪セメント株式会社 | Optical waveguide device |
| JP2009162889A (en) * | 2007-12-28 | 2009-07-23 | Seikoh Giken Co Ltd | Light modulator |
| JP5443314B2 (en) * | 2010-09-28 | 2014-03-19 | 日本電信電話株式会社 | Light modulator |
| US8867874B2 (en) * | 2012-12-06 | 2014-10-21 | Finisar Sweden Ab | Method for modifying the combining or splitting ratio of a multimode interference coupler |
| JP7131565B2 (en) * | 2017-10-02 | 2022-09-06 | Tdk株式会社 | optical modulator |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2449291A1 (en) * | 1979-02-15 | 1980-09-12 | Carenco Alain | METHOD FOR BALANCING AN INTEGRATED OPTICAL DEVICE USING A THIN METAL LAYER AND DEVICE OBTAINED THEREBY |
| US4262992A (en) * | 1979-04-18 | 1981-04-21 | The United States Of America As Represented By The Director Of The National Security Agency | Variable integrated optical logic element |
| FR2562271B1 (en) * | 1984-03-29 | 1986-07-18 | Telecommunications Sa | CONNECTOR OF AN OPTICAL FIBER AND A PHOTO-ELEMENT, RECEIVER OR TRANSMITTER, AND POSITIONING METHOD THEREOF |
| US4677290A (en) * | 1985-04-12 | 1987-06-30 | Tektronix, Inc. | Method of aligning an optical fiber with a light emitter via directing light toward light emitter acting as a detector |
| CA1229904A (en) * | 1985-06-28 | 1987-12-01 | John C. Goodwin | Laser-fiber positioner |
| US4709978A (en) * | 1986-02-21 | 1987-12-01 | Bell Communications Research, Inc. | Mach-Zehnder integrated optical modulator |
| JPH0718964B2 (en) * | 1987-06-29 | 1995-03-06 | 日本電信電話株式会社 | Integrated optical device and manufacturing method thereof |
| US4899042A (en) * | 1987-11-17 | 1990-02-06 | The Boeing Company | Integrated optic field sensor consisting of an interferometer formed in substrate |
| JPH0816744B2 (en) * | 1988-12-01 | 1996-02-21 | 国際電信電話株式会社 | Light modulation element |
| US4955977A (en) * | 1989-10-11 | 1990-09-11 | Eastman Kodak Company | Nonlinear optical article with improved buffer layer |
-
1990
- 1990-03-08 JP JP2054976A patent/JPH03257423A/en active Pending
-
1991
- 1991-03-06 CA CA002037625A patent/CA2037625C/en not_active Expired - Fee Related
- 1991-03-06 EP EP19910103393 patent/EP0445763A3/en not_active Ceased
- 1991-03-07 US US07/666,051 patent/US5283842A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0445763A2 (en) | 1991-09-11 |
| JPH03257423A (en) | 1991-11-15 |
| US5283842A (en) | 1994-02-01 |
| EP0445763A3 (en) | 1992-06-03 |
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| EEER | Examination request | ||
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