CA2098343A1 - Laser bias and modulation circuit - Google Patents
Laser bias and modulation circuitInfo
- Publication number
- CA2098343A1 CA2098343A1 CA002098343A CA2098343A CA2098343A1 CA 2098343 A1 CA2098343 A1 CA 2098343A1 CA 002098343 A CA002098343 A CA 002098343A CA 2098343 A CA2098343 A CA 2098343A CA 2098343 A1 CA2098343 A1 CA 2098343A1
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- CA
- Canada
- Prior art keywords
- signal
- providing
- responsive
- sensed
- laser
- 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.)
- Abandoned
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/068—Stabilisation of laser output parameters
- H01S5/0683—Stabilisation of laser output parameters by monitoring the optical output parameters
- H01S5/06832—Stabilising during amplitude modulation
Abstract
ABSTRACT OF THE DISCLOSURE
Constant light output is provided by a laser diode over various temperatures or operating-points by adjusting the bias current in accordance with a midpoint of a detected peak and a detected valley of an output power level and adjusting the modulation current amplitude in accordance with the difference between the detected peak and the detected valley output power.
Constant light output is provided by a laser diode over various temperatures or operating-points by adjusting the bias current in accordance with a midpoint of a detected peak and a detected valley of an output power level and adjusting the modulation current amplitude in accordance with the difference between the detected peak and the detected valley output power.
Description
~0~S3~ 3 907-111 L~SER BIAS AND MODUL~TION CIRCUIT
_chnical Field This invention relates to the transmission of information on optical fibers and, more particularly, to a control circuit for controlling a laser for provlding optical signals to an optical fiber.
Background of the Invention Laser diodes are commonly used to provide optlcal signals to optical fibers for transmission thereon.
Typically, the laser diode will be biased at some selected bias current level, and the diode will then be intensity-modulated about that bias point at a ~odulation level necessary to achieve a desired light output level.
Unfortunately, laser characteristics ohange in two important ways when operated over a w~de te~perature rangQ. Fir~t, the lasing threshold tends to increase with increasing temperature. This implies that, to maintain a constant average optical output power with an increase in temperature, average drive current, often called bias current, must ~e incr~ased. Se~ond, the efficiency of the laser current-to-optical power conver~ion (known as slope efficiency) deoreases with increasing temperature.
One implication of the second e~*ect, i.e., tha ~lope efficiency decreasing with inareasing temper~ture, is the ~ame a~ the fir~t: to maintain at a constant averag~ optical output power with increasing temperature, bias current must be increased. Another implication of the second effect is that, to maintain a constant signal, or modulation, optical output power with increasing temperature, modulation current must be increased.
; : :
, In order to obtain reliable and repeatable results in many fiber optic transmission applications, both average and signal power out of the laser must be held relatively constant. Many times this problem i8 skirted through the use of thermo-electric cooling to maintain the laser at a relatively constant temperature. This solution is generally costly, power consumptive, and usually unacceptable for high-volume, low~cost applications. Another possible solution ha~ been to 10 8imply monitor the laser temperature and ad~ust the bias and 6ignal current levels according to expected performance curves. However, for low-cost lasers, the change in characteristics with temperature i8 usually not accurately predictable from device to device. This mandates that either each laser be individually characterized over temperature, or that a feedback loop be established to control the laser in operation.
Individual characterization, beside~ being expensive, has the addit1onal disadvantage of not a~counting Por any changes in laser characteristics that may occur as the laser ages.
A feedback loop can be ectabli~hed through the laser's own back facet monitor photodiode, or through the whole l~nk and the receiver at the oppo~ite end. The latter approach has the advantage of being able to acco~modate changes in tke cable plant, the receiver, and the laser-to-fiber coupling. It ha~ the di~advantage of requiring th~ addition of control cirouitry at the receiver and a link back to the tran~mitter. If the feedback link i9 already present link ca~acity may be used for feedback information. However, the possibility that feedback information ma~7 not arrive back to the ~ o 9 ~ 3 !1~ 3 907-111 laser in a timely fashion, causing instability in the laser performance, must also be considered.
Localized feedback through the back ~acet monitor is commonly used to regulate the bias current of the laser.
Slope efficiency variations, which are as high as 6 dB, are often ignored. In some cases, through the generation and addition of a fixed level 'pilot' carrier to the signal, modulation current is also regulated through the back facet monitor diode. Howevcr, circuitry must be added to generate the pilot carrier and a multiplexer with the 6ignal. Additionally, link bandwidth i~ taken up by the pilot.
Disclosure of Invention The ob~ect of the present invention is to regulate a laser.
According to the present invention, constant light output from a laser diode over various temperatures i8 achieved by adjusting the bias current in accordance with a first set of parameters and adjusting the modulation current amplitude in accordance with a second set of parameter~.
In further accord with ~he present invention, constant light output over various modulation coding 6chemes ~rom a laser dio~e ~B achieved by ad~usting the bias current in accordance with a first set of parameter~
and ~d~ustinq the modulation current amplitude in accordance with a second set of parameters.
In still further accord with the present invention, the first set of parameter~ may compriæe an aver~ge of detected peak and valley amplitudes of the light output from the laser diode.
In still further accord with the present invention, the second set of parameters may comprise a difference , . ' ' ~
~ , 3 '~ ~ 907-111 between the peak and valley of the light output from the la~er diode.
This invention was first conceived a~ a way to regulate a low~cost, uncooled laser, which was intended to be modulated with a frequency multiplexed hybrid signal consisting of a relatively low speed ~less than 50 megabaud) digital signal and a high-speed (up to 1 gigahertz) analog composite video signal. The application for the invention was in a fiber-to-the-curb 0 8y8tem, where wide temperature ranges must be handled by low-cost designs, and where the transmitted siqnal is a hybrid analog video/digital voice ~ignal.
Thus, the present invention provides a way to use the already-present digital signal in an all-digital or all-hybrid digital~analog application as a virtual pilot.
We al~o teach a technique for using the digital ~ignal such that ~ost non-balanced coding schemes and data-dependent DC-based line wander~ng in the digital signal will not incorrectly affect the laser b~as and modulation currents.
These and other objects, features and advantaqes of the present invention will become more apparent in light of the following detailed description o~ a best mode embodiment thereof, as i~lustrated in the accompanying drawings.
~rief Descri~tion of the Drawinqs:
Fig. 1 shows laser bias and ~odulation amplitude varied in order to achieve constant output power, according to the present invention.
Fig. 2 shows a block diagram of a circuit, according to the present invention, for automatic bias and 2 G ~! ~ 3 ;~ 3 907-111 modulation control for a hybrid digital/analog application according to the present invention.
Fig. 3 is an illustration of an embodiment of the laser driver of Fig. 2 for handling the digital data signal.
Fig. 4 is an illustration of an embodiment of the laser driver of Fig. 2 for handling the high-speed signal~.
Fig. 5 i3 a detailed illustration of one way to carry out the laser bias and automatic gain control circuitry of Fig. 2.
est Mode for Carryina Out the Invention Fig. 1 shows that a constant output power may be achieved for varying efficiencies or operating points of a laser diode modulated by a modulating 6ignal by controlling the bias point and the amplitude of the modulation. In the case of varying ~fficiencies as caused, for example, by varying temperatures, the present invention automatically co~pensates by varying the operating point and the amplitude of modulation. This is shown for three different temperatures, resulting in three different operat~ng points and amplitude~ of the modulating signal. In the case of varying operation points which could ke causQ~, for example, by a digital modulating signal without a 50 percent duty cycle, though the operating point would hav~ a tendency to deviate to some extent (as in the prior art) to the left or right of one of the operating po~nts (Il, I2, I3) as shown in Pig.
1, according to the present invention, the operating point is made to stay the same.
Fig. 2 shows an embodiment of the present invention which includes a feedback circuit 10 used to regulate a l~w-cost, uncooled laser 12, which is being modulated by ., ~ : ,. .
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2a~3'~3 907~
a frequency-division multiplexed signal 14 which is shown before being multiplexed within a driver 20 as two separate signals on a pair of lines 16, 18. The components 16, 18 of the signal 14 may comprise a S relatively low-speed digital data signal (for example, at less than 50 megabaud) and one or more high-speed RF
signals such as analog television channels (spaced along the frequency spectrum up to 1 gigahertz, for example).
The laser driver circuit 20 is responsive to the signals on the lines 16, 18, mult~plexes the signals 16, ~8 into the frequency-division multiplexed signal 14 and provides drive current for the laser 12, which in turn provides light output 22 to an optical fiber (not shown) for transmission thereon. The laser driver modulates the laser around a bias current level and transmits light 22 into the optical fiber through its front facet and also transmits light 24 into a monitor photodiode 26 through its back facet. The frequency response of ~he monitor diode ~s generally slow enough to block the analog video signals, but fast enough to pass the digital signal.
However, if the analog video signals are not 6ignificantly attenuated at the monitor diode, then a lowpa~s filter 28 may be inserted in the ~ignal path to filter them out. In any event, either the laser back facet monitor diode 26 or the lowpass filter, or both, will provide a filtered low,frequency signal on a line 30 to a current-to-voltage level converter 32, which ~ay be nothing more than a resistor network to a referenc~ to provide a voltage on the same line 30 to a voltaqe peak-to-peak detector 36a, 36b.
The peak and valley detection circuits 36a, 36b, respectively, where the highest and lowest absolute voltage levels found in the converted signals are held and provided on lines 38a, 38b, respectively. The response and hold times of the peak and valley detectors -2 ~ 3 ~ 907-111 are set depending upon the symbol rate of the digital data and the longest duration between tranRitions. It should be realized that true non-return-to-zero (NRZ) encoding, where the time between sy~bol transitions can be extremely long, cannot be used with the embodiment disclosed herein.
~ fter peak and valley detection, the control voltages on the lines 38a, 38b are provided to an averager 40 and a difference detector 42. In the averager, the peak and valley voltages 38a, 38b are averaged to find the midpoint, and a midpoint signal having a magnitude indicative thereof i8 provided on a line 44 to a laser bias control 46. Because peak and valley voltages are used to determine the midpoint, instead of perfor~ing average level detection immediately after the back facet monitor, data and coding scheme dependent wandering of the average level i8 avoided. If the coding 6cheme utilized does not have a true 50 percent effective duty cycle where one i8 guaranteed a transition in data and between bits, any variationa that would otherwi~e be caused in laser bias control due to variations away from 50 percent duty cycle are avoided.
The midpoint voltaqe on the line 44 i8 provided to the laser bias control block 46, where it i8 compared to a threshold signal on a line 48 which may be ad~ustable, as ind~cated by a thresh,old~ad~ust block 50. The thre6hold i8 chosen to place the la~er at a selected average optical output power level,~uch as the P0 level 6hown in Fig. 1. If the midpoint voltage i8 below the threshold, then the laser bia6 control block provides a signal on a line 52 to increase the bias current in the laser driver block 20 until the midpoint voltage equals the threshold. An opposite effect occurs if the midpoint voltage is above threshold.
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2a~ ~3il3 907-111 In the difference detector 42, the difference between the peak and valley voltages on the lines 38a, 38b, respectively, is determined. A difference voltage siynal is provided on a line 54 to a laser modulation control block 56, where it is compared to a threshold signal on a line 58 provided by a threshold ad~ust block 60 which may be capable of ad~usting the level of the threshold reference signal on the line 58. The threshold is set according to the desired modulation index or ratio of signal-power-to-average-power out of the laser of the digital signal. If the difference voltage is below threshold, then the laser modulation control block provides a signal on a line 62 to increase the qain of the signal in the laser driver 20. An opposite effect occurs if the difference voltage is above threshold. In the driver, both the digital and analog ~ignals are adjusted proportionately, so that the relative modulation indices set up for the two signal types is maintained.
Turning now to Fig. 3, a detailed illustration is shown of one way to construct a digital portion of the laser driver 20 of Fig. 2 for handling the relatively low-speed digital data input signal on the line 16. That signal is first terminated by a resistor 70 and capacitor 72 in parallel, which helps with proper switching of a transistor 74 to prevent pulsewidth distortion. The transi~tor 74 is sourced~by~a VCC voltage at a node 76 at +5V. The collector volt~ge is ~iltered by a capaoitor pair 78 in parallel, and a series of resistors 79 18 employed for the purpose of level conversion before be~ng buffered by a buffer stage 80, which also serves to convert the driving signal to a driving signal having negative excursions. This was do~e for the particular embodiment shown because of the particular laser selected, which needs to be driven negatively. This, of course, need not be the case~
2 ~ 3 An emitter follower section 82 follows the buffer stage 80 and further level converts the input to get closer to a negative 5V suited to the particular laser diode 12 we selected. A buffer section 84 buffers the output of the emitter follower section 82 and is itself followed by a lowpass filter section 86 which passes ~ignals, for example in the range of 0-20 MHz. Thi8 is not the same as the lowpass filter 28 shown in Fig. 2, but i8 merely provided to eliminate higher freguency components from the digital signal which would otherwise cause distortions in the analog video ~ignal, to be multiplexed with the digital at node 102.
The lowpass filter 86 is followed by a further conversion section 88 which places the most negative lS excursion of the filtered signal almost down to -5V ~o that a minimal DC current will be provided by this section.
For given signal excursion or swing at the base of transistor 90, the resistor 91 sets the modulation current for the digital signal in the laser 12.
The light output 24 from the laser diode 12 is detected by the bacX facet 26 thereof, and the detected signal i~ provided on the line 30, as described above in - connection with Fig. 2. Although a lowpass filter 28 is shown in Fig. 2, for the particular case illustrated, it wa~ found not necessary ,to include such a lowpass filter, since the capacitance oP the diode itsel~ plus the input resistance of the transistor 154 clrauit was ~u~ficient}y great to provide an effective lowpass filter, ln this particular case.
In connection with the de~cription of Fig. 4 below, it will be 6een that the output thereof is provided on a line 100 to a summing node 102 shown in Fig. 3, where the output of the video circuit of Fig. 4 is summed with the current contributed by the digital portion illustrated in - ~ .
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~ 3 ~1 3 907-111 Fig. 3. This effectively forms a frequency-division multiplexing node for multiplexing the low-frequency digital signals with the high-frequency video ~ignals.
The multiplexed signal thus modulates the diode 12.
Turning now to Fig. 4, an illustration i8 shown of video circuitry for a laser driver 20 embodiment, according to the present invention. The high-speed RF
signals 18 of Fig. 2 are shown at the upper left of Fig.
4 as an input signal to a voltage controlled attenuator 104 to keep the video level at a constant level as controlled by a signal on a line 106, which ~s in turn controlled by the feedback signal on the line 62 shown in both Fig. 2 and Fig. 4 (from the laser ~odulation control 56 to be disclosed in more detail below in connect~on with Fig. S).
An output signal on a line 106 from the voltage controlled attenuator 104 is filtered by a highpass filter 108 for getting rid of any low frequency components that might otherwise corrupt the digital signals to be ~oined with the video signals on the line 100, as shown summed at the junction 102 in Fig. 3.
The signal on the line 106 is also provided to a series of resistors 109, 110 and a capacitor 112, ~hich together serve the purpose of presenting an impedance 2S which prevents any influence of the aontrol circuitry on the video ~ignal path 106. In other words, resistors 109, 110 and the capa¢itor 112 have values selected su~h that the impedance presented to the main llne 106 i8 greater than ten times the characteristic impedance of the main line 106. A diode 114 (configured as a back diode to minimize temperature drift effects) and capacitor 116 serve the purpose of doing average power detection. The capacitor 116 also acts in concert with a resistor 118 as a pre-integrator to prevent instantaneous high peaks from being presented to an integrator 120 2 ~ 3 '. ~ 907~
which integrates a signal on a line 122, to provide an integrated output signal on a line 124. The integrator is with reference to a reference signal on a line 126, whereby the integrator 120 tries to zero the difference between the signal on the line 122 and the signal on the line 126. After the integrator 120, stages 128, 130 perform both gain and level shifting by moving the DC
swing of a signal on line 132 into a range that the voltage-controlled attenuator 104 needs as a control voltage, i.e., between 0 and -5V.
The dif~erential amplifier stage 130 drives the difference between the input signal on the line 132 and an input signal on a line 134 to zero. The signal on the line 134 is provided by a signal conditioninq stage 136 responsive to the feedback signal on the line 62 from Fig. 5.
Fig. 5 shows the laser bias and AGC control part of Fig. 2. A voltage regulator 150 i8 responsive to the -5V
on line 92 for providi~g a regulated -2.5V on a line 152.
At equilibrium, the voltag~ on the line 34 sits at -1.25V, and the amount of swing is determined by the way the ~odulation index is set up.
A transistor 154 is responsive at its collector to the ~5V on the line 76 and provides a current through a pair o~ resistors 156, 158, which have a connecting node 160 which, at equilibrium, 6it8 at -2.5V. The peak detector 36a and valley detector 36b o~ Fig. 2 are shown in one embodiment in Fig. 5. A buf~er operational amplifier 162 provides the captured peak signal on the line 38a, which is held by a circuit 164 having a resistor 166 and a capacitor 168 with values chosen ao as to have a time constant longer than the longest expected time between transitions of the digital input signal, which may be unbalanced in the sense of not having a 50 percent duty cycle. Thus, for a case where the longest ` :.
: :
~v ~J 3 1 ~) time between transitions is on the order of 180 nanoseconds, the resistive value may be chosen to be 162 Kohm, while the capacitor may be about 33 picofarad.
Similar values can be chosen for a resistor 170 and a capacitor 172 in a circuit 1~4 having a purpose of holding the peaX or valley of the Gignal on the line 160.
An operational amplifier 176 provides the valley signal on the line 38b to the averager 40, which is responsive to both the signal on the line 38b and to the signal on the line 38a for finding the midpoint. A differential amplifier 180 compares the reference signal on the line 48 to the average signal on the line 44, as previously discussed in connection with Fig. 2. The output of the differential amplifier lB0 is the signal on the line 52 shown in Fig. 2 as a feedback sig~al for the laser driver. This signal is used to drive a transistor 181.
For a given signal voltage at the base of transistor 181, a DC or bias current is set by resistor 181a and is then summed through line 182 at node 102 with the video and digital modulation currents passing through the laser diode 12.
The signal on the line 38a is a signal representing the latest peak value of the input signal. It is provided not only to the voltage follower 40 of the average detector, but also the difference detector 42 which i8 responsive also to ,the signal on the line 38b for providing the difference signal on the line 54 to a comparator 190, which compaxes the difference signal on the line 54 to the reference signal on the line 58 and provides the fee~back ~ignal on the line 62 to the video portion of the laser driver, as shown in Fig. 4. The signal on the line 62 is also used at the gate of an FET
192 used as a voltage-controlled resistor in the digital portion of the laser driver circuit of Pig. 3. The 3S signal changes the resistance of the FET in accordance 2 ~ ~ 3 ~3 `` ~ 907-111 with changes in the difference in the peak and valley, therefore changing the voltage division ration of the digital signal after transistor 80 in Fig. 3.
Although the invention has been 6hown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additional in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.
_chnical Field This invention relates to the transmission of information on optical fibers and, more particularly, to a control circuit for controlling a laser for provlding optical signals to an optical fiber.
Background of the Invention Laser diodes are commonly used to provide optlcal signals to optical fibers for transmission thereon.
Typically, the laser diode will be biased at some selected bias current level, and the diode will then be intensity-modulated about that bias point at a ~odulation level necessary to achieve a desired light output level.
Unfortunately, laser characteristics ohange in two important ways when operated over a w~de te~perature rangQ. Fir~t, the lasing threshold tends to increase with increasing temperature. This implies that, to maintain a constant average optical output power with an increase in temperature, average drive current, often called bias current, must ~e incr~ased. Se~ond, the efficiency of the laser current-to-optical power conver~ion (known as slope efficiency) deoreases with increasing temperature.
One implication of the second e~*ect, i.e., tha ~lope efficiency decreasing with inareasing temper~ture, is the ~ame a~ the fir~t: to maintain at a constant averag~ optical output power with increasing temperature, bias current must be increased. Another implication of the second effect is that, to maintain a constant signal, or modulation, optical output power with increasing temperature, modulation current must be increased.
; : :
, In order to obtain reliable and repeatable results in many fiber optic transmission applications, both average and signal power out of the laser must be held relatively constant. Many times this problem i8 skirted through the use of thermo-electric cooling to maintain the laser at a relatively constant temperature. This solution is generally costly, power consumptive, and usually unacceptable for high-volume, low~cost applications. Another possible solution ha~ been to 10 8imply monitor the laser temperature and ad~ust the bias and 6ignal current levels according to expected performance curves. However, for low-cost lasers, the change in characteristics with temperature i8 usually not accurately predictable from device to device. This mandates that either each laser be individually characterized over temperature, or that a feedback loop be established to control the laser in operation.
Individual characterization, beside~ being expensive, has the addit1onal disadvantage of not a~counting Por any changes in laser characteristics that may occur as the laser ages.
A feedback loop can be ectabli~hed through the laser's own back facet monitor photodiode, or through the whole l~nk and the receiver at the oppo~ite end. The latter approach has the advantage of being able to acco~modate changes in tke cable plant, the receiver, and the laser-to-fiber coupling. It ha~ the di~advantage of requiring th~ addition of control cirouitry at the receiver and a link back to the tran~mitter. If the feedback link i9 already present link ca~acity may be used for feedback information. However, the possibility that feedback information ma~7 not arrive back to the ~ o 9 ~ 3 !1~ 3 907-111 laser in a timely fashion, causing instability in the laser performance, must also be considered.
Localized feedback through the back ~acet monitor is commonly used to regulate the bias current of the laser.
Slope efficiency variations, which are as high as 6 dB, are often ignored. In some cases, through the generation and addition of a fixed level 'pilot' carrier to the signal, modulation current is also regulated through the back facet monitor diode. Howevcr, circuitry must be added to generate the pilot carrier and a multiplexer with the 6ignal. Additionally, link bandwidth i~ taken up by the pilot.
Disclosure of Invention The ob~ect of the present invention is to regulate a laser.
According to the present invention, constant light output from a laser diode over various temperatures i8 achieved by adjusting the bias current in accordance with a first set of parameters and adjusting the modulation current amplitude in accordance with a second set of parameter~.
In further accord with ~he present invention, constant light output over various modulation coding 6chemes ~rom a laser dio~e ~B achieved by ad~usting the bias current in accordance with a first set of parameter~
and ~d~ustinq the modulation current amplitude in accordance with a second set of parameters.
In still further accord with the present invention, the first set of parameter~ may compriæe an aver~ge of detected peak and valley amplitudes of the light output from the laser diode.
In still further accord with the present invention, the second set of parameters may comprise a difference , . ' ' ~
~ , 3 '~ ~ 907-111 between the peak and valley of the light output from the la~er diode.
This invention was first conceived a~ a way to regulate a low~cost, uncooled laser, which was intended to be modulated with a frequency multiplexed hybrid signal consisting of a relatively low speed ~less than 50 megabaud) digital signal and a high-speed (up to 1 gigahertz) analog composite video signal. The application for the invention was in a fiber-to-the-curb 0 8y8tem, where wide temperature ranges must be handled by low-cost designs, and where the transmitted siqnal is a hybrid analog video/digital voice ~ignal.
Thus, the present invention provides a way to use the already-present digital signal in an all-digital or all-hybrid digital~analog application as a virtual pilot.
We al~o teach a technique for using the digital ~ignal such that ~ost non-balanced coding schemes and data-dependent DC-based line wander~ng in the digital signal will not incorrectly affect the laser b~as and modulation currents.
These and other objects, features and advantaqes of the present invention will become more apparent in light of the following detailed description o~ a best mode embodiment thereof, as i~lustrated in the accompanying drawings.
~rief Descri~tion of the Drawinqs:
Fig. 1 shows laser bias and ~odulation amplitude varied in order to achieve constant output power, according to the present invention.
Fig. 2 shows a block diagram of a circuit, according to the present invention, for automatic bias and 2 G ~! ~ 3 ;~ 3 907-111 modulation control for a hybrid digital/analog application according to the present invention.
Fig. 3 is an illustration of an embodiment of the laser driver of Fig. 2 for handling the digital data signal.
Fig. 4 is an illustration of an embodiment of the laser driver of Fig. 2 for handling the high-speed signal~.
Fig. 5 i3 a detailed illustration of one way to carry out the laser bias and automatic gain control circuitry of Fig. 2.
est Mode for Carryina Out the Invention Fig. 1 shows that a constant output power may be achieved for varying efficiencies or operating points of a laser diode modulated by a modulating 6ignal by controlling the bias point and the amplitude of the modulation. In the case of varying ~fficiencies as caused, for example, by varying temperatures, the present invention automatically co~pensates by varying the operating point and the amplitude of modulation. This is shown for three different temperatures, resulting in three different operat~ng points and amplitude~ of the modulating signal. In the case of varying operation points which could ke causQ~, for example, by a digital modulating signal without a 50 percent duty cycle, though the operating point would hav~ a tendency to deviate to some extent (as in the prior art) to the left or right of one of the operating po~nts (Il, I2, I3) as shown in Pig.
1, according to the present invention, the operating point is made to stay the same.
Fig. 2 shows an embodiment of the present invention which includes a feedback circuit 10 used to regulate a l~w-cost, uncooled laser 12, which is being modulated by ., ~ : ,. .
' .
2a~3'~3 907~
a frequency-division multiplexed signal 14 which is shown before being multiplexed within a driver 20 as two separate signals on a pair of lines 16, 18. The components 16, 18 of the signal 14 may comprise a S relatively low-speed digital data signal (for example, at less than 50 megabaud) and one or more high-speed RF
signals such as analog television channels (spaced along the frequency spectrum up to 1 gigahertz, for example).
The laser driver circuit 20 is responsive to the signals on the lines 16, 18, mult~plexes the signals 16, ~8 into the frequency-division multiplexed signal 14 and provides drive current for the laser 12, which in turn provides light output 22 to an optical fiber (not shown) for transmission thereon. The laser driver modulates the laser around a bias current level and transmits light 22 into the optical fiber through its front facet and also transmits light 24 into a monitor photodiode 26 through its back facet. The frequency response of ~he monitor diode ~s generally slow enough to block the analog video signals, but fast enough to pass the digital signal.
However, if the analog video signals are not 6ignificantly attenuated at the monitor diode, then a lowpa~s filter 28 may be inserted in the ~ignal path to filter them out. In any event, either the laser back facet monitor diode 26 or the lowpass filter, or both, will provide a filtered low,frequency signal on a line 30 to a current-to-voltage level converter 32, which ~ay be nothing more than a resistor network to a referenc~ to provide a voltage on the same line 30 to a voltaqe peak-to-peak detector 36a, 36b.
The peak and valley detection circuits 36a, 36b, respectively, where the highest and lowest absolute voltage levels found in the converted signals are held and provided on lines 38a, 38b, respectively. The response and hold times of the peak and valley detectors -2 ~ 3 ~ 907-111 are set depending upon the symbol rate of the digital data and the longest duration between tranRitions. It should be realized that true non-return-to-zero (NRZ) encoding, where the time between sy~bol transitions can be extremely long, cannot be used with the embodiment disclosed herein.
~ fter peak and valley detection, the control voltages on the lines 38a, 38b are provided to an averager 40 and a difference detector 42. In the averager, the peak and valley voltages 38a, 38b are averaged to find the midpoint, and a midpoint signal having a magnitude indicative thereof i8 provided on a line 44 to a laser bias control 46. Because peak and valley voltages are used to determine the midpoint, instead of perfor~ing average level detection immediately after the back facet monitor, data and coding scheme dependent wandering of the average level i8 avoided. If the coding 6cheme utilized does not have a true 50 percent effective duty cycle where one i8 guaranteed a transition in data and between bits, any variationa that would otherwi~e be caused in laser bias control due to variations away from 50 percent duty cycle are avoided.
The midpoint voltaqe on the line 44 i8 provided to the laser bias control block 46, where it i8 compared to a threshold signal on a line 48 which may be ad~ustable, as ind~cated by a thresh,old~ad~ust block 50. The thre6hold i8 chosen to place the la~er at a selected average optical output power level,~uch as the P0 level 6hown in Fig. 1. If the midpoint voltage i8 below the threshold, then the laser bia6 control block provides a signal on a line 52 to increase the bias current in the laser driver block 20 until the midpoint voltage equals the threshold. An opposite effect occurs if the midpoint voltage is above threshold.
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' ...
. ~
2a~ ~3il3 907-111 In the difference detector 42, the difference between the peak and valley voltages on the lines 38a, 38b, respectively, is determined. A difference voltage siynal is provided on a line 54 to a laser modulation control block 56, where it is compared to a threshold signal on a line 58 provided by a threshold ad~ust block 60 which may be capable of ad~usting the level of the threshold reference signal on the line 58. The threshold is set according to the desired modulation index or ratio of signal-power-to-average-power out of the laser of the digital signal. If the difference voltage is below threshold, then the laser modulation control block provides a signal on a line 62 to increase the qain of the signal in the laser driver 20. An opposite effect occurs if the difference voltage is above threshold. In the driver, both the digital and analog ~ignals are adjusted proportionately, so that the relative modulation indices set up for the two signal types is maintained.
Turning now to Fig. 3, a detailed illustration is shown of one way to construct a digital portion of the laser driver 20 of Fig. 2 for handling the relatively low-speed digital data input signal on the line 16. That signal is first terminated by a resistor 70 and capacitor 72 in parallel, which helps with proper switching of a transistor 74 to prevent pulsewidth distortion. The transi~tor 74 is sourced~by~a VCC voltage at a node 76 at +5V. The collector volt~ge is ~iltered by a capaoitor pair 78 in parallel, and a series of resistors 79 18 employed for the purpose of level conversion before be~ng buffered by a buffer stage 80, which also serves to convert the driving signal to a driving signal having negative excursions. This was do~e for the particular embodiment shown because of the particular laser selected, which needs to be driven negatively. This, of course, need not be the case~
2 ~ 3 An emitter follower section 82 follows the buffer stage 80 and further level converts the input to get closer to a negative 5V suited to the particular laser diode 12 we selected. A buffer section 84 buffers the output of the emitter follower section 82 and is itself followed by a lowpass filter section 86 which passes ~ignals, for example in the range of 0-20 MHz. Thi8 is not the same as the lowpass filter 28 shown in Fig. 2, but i8 merely provided to eliminate higher freguency components from the digital signal which would otherwise cause distortions in the analog video ~ignal, to be multiplexed with the digital at node 102.
The lowpass filter 86 is followed by a further conversion section 88 which places the most negative lS excursion of the filtered signal almost down to -5V ~o that a minimal DC current will be provided by this section.
For given signal excursion or swing at the base of transistor 90, the resistor 91 sets the modulation current for the digital signal in the laser 12.
The light output 24 from the laser diode 12 is detected by the bacX facet 26 thereof, and the detected signal i~ provided on the line 30, as described above in - connection with Fig. 2. Although a lowpass filter 28 is shown in Fig. 2, for the particular case illustrated, it wa~ found not necessary ,to include such a lowpass filter, since the capacitance oP the diode itsel~ plus the input resistance of the transistor 154 clrauit was ~u~ficient}y great to provide an effective lowpass filter, ln this particular case.
In connection with the de~cription of Fig. 4 below, it will be 6een that the output thereof is provided on a line 100 to a summing node 102 shown in Fig. 3, where the output of the video circuit of Fig. 4 is summed with the current contributed by the digital portion illustrated in - ~ .
. .
~ 3 ~1 3 907-111 Fig. 3. This effectively forms a frequency-division multiplexing node for multiplexing the low-frequency digital signals with the high-frequency video ~ignals.
The multiplexed signal thus modulates the diode 12.
Turning now to Fig. 4, an illustration i8 shown of video circuitry for a laser driver 20 embodiment, according to the present invention. The high-speed RF
signals 18 of Fig. 2 are shown at the upper left of Fig.
4 as an input signal to a voltage controlled attenuator 104 to keep the video level at a constant level as controlled by a signal on a line 106, which ~s in turn controlled by the feedback signal on the line 62 shown in both Fig. 2 and Fig. 4 (from the laser ~odulation control 56 to be disclosed in more detail below in connect~on with Fig. S).
An output signal on a line 106 from the voltage controlled attenuator 104 is filtered by a highpass filter 108 for getting rid of any low frequency components that might otherwise corrupt the digital signals to be ~oined with the video signals on the line 100, as shown summed at the junction 102 in Fig. 3.
The signal on the line 106 is also provided to a series of resistors 109, 110 and a capacitor 112, ~hich together serve the purpose of presenting an impedance 2S which prevents any influence of the aontrol circuitry on the video ~ignal path 106. In other words, resistors 109, 110 and the capa¢itor 112 have values selected su~h that the impedance presented to the main llne 106 i8 greater than ten times the characteristic impedance of the main line 106. A diode 114 (configured as a back diode to minimize temperature drift effects) and capacitor 116 serve the purpose of doing average power detection. The capacitor 116 also acts in concert with a resistor 118 as a pre-integrator to prevent instantaneous high peaks from being presented to an integrator 120 2 ~ 3 '. ~ 907~
which integrates a signal on a line 122, to provide an integrated output signal on a line 124. The integrator is with reference to a reference signal on a line 126, whereby the integrator 120 tries to zero the difference between the signal on the line 122 and the signal on the line 126. After the integrator 120, stages 128, 130 perform both gain and level shifting by moving the DC
swing of a signal on line 132 into a range that the voltage-controlled attenuator 104 needs as a control voltage, i.e., between 0 and -5V.
The dif~erential amplifier stage 130 drives the difference between the input signal on the line 132 and an input signal on a line 134 to zero. The signal on the line 134 is provided by a signal conditioninq stage 136 responsive to the feedback signal on the line 62 from Fig. 5.
Fig. 5 shows the laser bias and AGC control part of Fig. 2. A voltage regulator 150 i8 responsive to the -5V
on line 92 for providi~g a regulated -2.5V on a line 152.
At equilibrium, the voltag~ on the line 34 sits at -1.25V, and the amount of swing is determined by the way the ~odulation index is set up.
A transistor 154 is responsive at its collector to the ~5V on the line 76 and provides a current through a pair o~ resistors 156, 158, which have a connecting node 160 which, at equilibrium, 6it8 at -2.5V. The peak detector 36a and valley detector 36b o~ Fig. 2 are shown in one embodiment in Fig. 5. A buf~er operational amplifier 162 provides the captured peak signal on the line 38a, which is held by a circuit 164 having a resistor 166 and a capacitor 168 with values chosen ao as to have a time constant longer than the longest expected time between transitions of the digital input signal, which may be unbalanced in the sense of not having a 50 percent duty cycle. Thus, for a case where the longest ` :.
: :
~v ~J 3 1 ~) time between transitions is on the order of 180 nanoseconds, the resistive value may be chosen to be 162 Kohm, while the capacitor may be about 33 picofarad.
Similar values can be chosen for a resistor 170 and a capacitor 172 in a circuit 1~4 having a purpose of holding the peaX or valley of the Gignal on the line 160.
An operational amplifier 176 provides the valley signal on the line 38b to the averager 40, which is responsive to both the signal on the line 38b and to the signal on the line 38a for finding the midpoint. A differential amplifier 180 compares the reference signal on the line 48 to the average signal on the line 44, as previously discussed in connection with Fig. 2. The output of the differential amplifier lB0 is the signal on the line 52 shown in Fig. 2 as a feedback sig~al for the laser driver. This signal is used to drive a transistor 181.
For a given signal voltage at the base of transistor 181, a DC or bias current is set by resistor 181a and is then summed through line 182 at node 102 with the video and digital modulation currents passing through the laser diode 12.
The signal on the line 38a is a signal representing the latest peak value of the input signal. It is provided not only to the voltage follower 40 of the average detector, but also the difference detector 42 which i8 responsive also to ,the signal on the line 38b for providing the difference signal on the line 54 to a comparator 190, which compaxes the difference signal on the line 54 to the reference signal on the line 58 and provides the fee~back ~ignal on the line 62 to the video portion of the laser driver, as shown in Fig. 4. The signal on the line 62 is also used at the gate of an FET
192 used as a voltage-controlled resistor in the digital portion of the laser driver circuit of Pig. 3. The 3S signal changes the resistance of the FET in accordance 2 ~ ~ 3 ~3 `` ~ 907-111 with changes in the difference in the peak and valley, therefore changing the voltage division ration of the digital signal after transistor 80 in Fig. 3.
Although the invention has been 6hown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additional in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.
Claims (11)
1. A method for maintaining constant light output for varying efficiencies and operating points of a laser diode modulated by a modulating signal, comprising the steps of:
sensing the light output and providing a sensed signal having a magnitude indicative thereof;
providing, in response to the sensed signal, a bias current feedback control signal for controlling a bias current provided to the laser diode; and providing, in response to the sensed signal, a modulation current amplitude feedback control signal for controlling the modulation current amplitude used to modulate the bias current.
sensing the light output and providing a sensed signal having a magnitude indicative thereof;
providing, in response to the sensed signal, a bias current feedback control signal for controlling a bias current provided to the laser diode; and providing, in response to the sensed signal, a modulation current amplitude feedback control signal for controlling the modulation current amplitude used to modulate the bias current.
2. The method of claim 1, wherein the varying efficiencies are due to varying temperatures.
3. The method of claim 1, wherein the varying operating points are due to variations in duty cycle of the modulating signal at least partly in digital form.
4. The method of claim l, wherein the bias current feedback control signal is provided according to a midpoint of peaks of the sensed signal.
5. The method of claim 1, wherein the modulation current amplitude feedback control signal is provided according to a difference in magnitudes between peaks of the sensed signal.
6. The method of claim 1, wherein the modulating signal comprises a relatively low-speed digital data signal frequency-division multiplexed with one or more relatively high-speed signals.
7. The method of claim 6, wherein the high-speed signals are analog video signals.
8. Apparatus for maintaining constant light output for varying efficiencies and operating points of a laser diode modulated by a modulating signal, comprising:
means responsive to the light output for providing a sensed signal having a magnitude indicative thereof;
means for providing, in response to the sensed signal, a bias current feedback control signal for controlling a bias current provided to the laser diode;
means for providing, in response to the sensed signal, a modulation current amplitude feedback control signal for controlling the modulation current amplitude used to modulate the bias current; and laser driver means, responsive to the bias current feedback control signal and the modulation current amplitude feedback control signal and to the modulating signal for providing the constant light output.
means responsive to the light output for providing a sensed signal having a magnitude indicative thereof;
means for providing, in response to the sensed signal, a bias current feedback control signal for controlling a bias current provided to the laser diode;
means for providing, in response to the sensed signal, a modulation current amplitude feedback control signal for controlling the modulation current amplitude used to modulate the bias current; and laser driver means, responsive to the bias current feedback control signal and the modulation current amplitude feedback control signal and to the modulating signal for providing the constant light output.
9. Apparatus of claim 8, further comprising:
a laser diode driver (20), responsive to a low-speed digital data signal (16), a high-speed RF signal (18), a bias feedback signal (52) and a modulation feedback signal (62), for providing a driving signal (102);
a laser diode (12), responsive to the driving signal (102), for providing a constant light output signal (22) and a monitoring light output signal (24);
a back facet monitor diode (26), responsive to the monitoring light output signal (24), for providing a sensed signal (30);
peak detection means (36a), responsive to the sensed signal (30), for providing a peak signal (38a) having a magnitude indicative of a positive peak amplitude of the sensed signal;
valley detection means, responsive to the sensed signal (30), for providing a valley signal (38b) having a magnitude indicative of a negative peak amplitude of the sensed signal;
averager means (40), responsive to the peak and valley signals (38a, 38b), for providing a midpoint signal (44) having a magnitude indicative of a midpoint between the positive and negative peak signals;
difference detector means (42), responsive to the peak and valley signals (38a, 38b), for providing a difference signal (54) having a magnitude indicative of a difference between the positive and negative peak signals;
laser bias control means (46), responsive to the midpoint signal (44) and to a bias reference signal (48), for providing the bias feedback signal (52); and laser modulation control (56), responsive to the difference signal (54) and to a modulation reference signal (58), for providing the modulation feedback signal (62).
a laser diode driver (20), responsive to a low-speed digital data signal (16), a high-speed RF signal (18), a bias feedback signal (52) and a modulation feedback signal (62), for providing a driving signal (102);
a laser diode (12), responsive to the driving signal (102), for providing a constant light output signal (22) and a monitoring light output signal (24);
a back facet monitor diode (26), responsive to the monitoring light output signal (24), for providing a sensed signal (30);
peak detection means (36a), responsive to the sensed signal (30), for providing a peak signal (38a) having a magnitude indicative of a positive peak amplitude of the sensed signal;
valley detection means, responsive to the sensed signal (30), for providing a valley signal (38b) having a magnitude indicative of a negative peak amplitude of the sensed signal;
averager means (40), responsive to the peak and valley signals (38a, 38b), for providing a midpoint signal (44) having a magnitude indicative of a midpoint between the positive and negative peak signals;
difference detector means (42), responsive to the peak and valley signals (38a, 38b), for providing a difference signal (54) having a magnitude indicative of a difference between the positive and negative peak signals;
laser bias control means (46), responsive to the midpoint signal (44) and to a bias reference signal (48), for providing the bias feedback signal (52); and laser modulation control (56), responsive to the difference signal (54) and to a modulation reference signal (58), for providing the modulation feedback signal (62).
10. The apparatus of claim 9, further comprising current-to-voltage level conversion means (32), responsive to the sensed signal (30), for providing the sensed signal (30) in converted form.
11. The apparatus of claim 9, further comprising lowpass filter means, responsive to the sensed signal (30) for providing a low-pass filtered sensed signal (30).
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/898,702 US5268916A (en) | 1992-06-15 | 1992-06-15 | Laser bias and modulation circuit |
| US07/898,702 | 1992-06-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2098343A1 true CA2098343A1 (en) | 1993-12-16 |
Family
ID=25409914
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002098343A Abandoned CA2098343A1 (en) | 1992-06-15 | 1993-06-14 | Laser bias and modulation circuit |
Country Status (7)
| Country | Link |
|---|---|
| US (2) | US5268916A (en) |
| EP (1) | EP0574816B1 (en) |
| JP (1) | JPH0685363A (en) |
| AT (1) | ATE143184T1 (en) |
| CA (1) | CA2098343A1 (en) |
| DE (1) | DE69304806T2 (en) |
| ES (1) | ES2094415T3 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5541759A (en) * | 1995-05-09 | 1996-07-30 | Microsym Computers, Inc. | Single fiber transceiver and network |
Families Citing this family (37)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5268916A (en) * | 1992-06-15 | 1993-12-07 | Alcatel Network Systems, Inc. | Laser bias and modulation circuit |
| JPH0795160A (en) * | 1993-09-20 | 1995-04-07 | Fujitsu Ltd | Method for modulating response signal of optical amplifier |
| US5402433A (en) * | 1994-01-05 | 1995-03-28 | Alcatel Network Systems, Inc. | Apparatus and method for laser bias and modulation control |
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| US5726437A (en) * | 1994-10-27 | 1998-03-10 | Fuji Xerox Co., Ltd. | Light intensity control device |
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| US5963570A (en) * | 1997-05-12 | 1999-10-05 | At&T Corp. | Current control for an analog optical link |
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| US6137522A (en) * | 1998-01-07 | 2000-10-24 | Xerox Corporation | Raster output scanner exposure control for bias and run levels in a multiple diode system |
| JP3085274B2 (en) * | 1998-01-19 | 2000-09-04 | 日本電気株式会社 | Optical transmitter |
| US6049073A (en) * | 1998-03-27 | 2000-04-11 | Eastman Kodak Company | Control circuit for a stabilized laser |
| JPH11344689A (en) * | 1998-06-03 | 1999-12-14 | Hitachi Ltd | Solid-state laser device |
| US6549310B1 (en) | 1999-01-08 | 2003-04-15 | International Business Machines Corporation | Fiber optic data link module with built-in link diagnostics |
| US7181146B1 (en) | 2001-01-17 | 2007-02-20 | Optical Communication Products, Inc. | Self-adjusting data transmitter |
| US6560258B1 (en) | 2001-04-17 | 2003-05-06 | Analog Devices, Inc. | Direct-coupled laser diode driver structures and methods |
| WO2003017441A1 (en) * | 2001-08-03 | 2003-02-27 | Infineon Technologies Ag | Method and device for adjusting a laser |
| SE523137C2 (en) * | 2001-09-07 | 2004-03-30 | Optillion Ab | Laser modulation control |
| US7212747B2 (en) * | 2002-06-10 | 2007-05-01 | Matsushita Electric Industrial Co., Ltd. | Optical transmission device and optical transmission method for transmitting a burst radio signal |
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| JP4205916B2 (en) * | 2002-09-03 | 2009-01-07 | パナソニック株式会社 | Extinction ratio compensation laser drive circuit and optical communication device |
| US6928094B2 (en) * | 2002-12-16 | 2005-08-09 | Intel Corporation | Laser driver circuit and system |
| ATE424640T1 (en) | 2003-01-08 | 2009-03-15 | Tecey Software Dev Kg Llc | DEVICE AND METHOD FOR MEASURING DYNAMIC LASER SIGNALS |
| US7142574B2 (en) * | 2003-05-21 | 2006-11-28 | Intel Corporation | Laser driver circuit and system |
| US7027685B2 (en) * | 2003-08-20 | 2006-04-11 | The Boeing Company | Apparatus and method for fiber optic link with built-in test |
| US7418015B2 (en) * | 2004-02-23 | 2008-08-26 | Finisar Corporation | System and method for control of optical transmitter |
| ATE489750T1 (en) * | 2004-04-21 | 2010-12-15 | Tecey Software Dev Kg Llc | METHOD AND APPARATUS FOR IMPROVED LASER PERFORMANCE COMPENSATION THROUGH DIGITAL SIGNAL PROCESSING |
| JP2005317666A (en) * | 2004-04-27 | 2005-11-10 | Sumitomo Electric Ind Ltd | Laser driving circuit |
| US20050271100A1 (en) * | 2004-06-04 | 2005-12-08 | Keith Everett | System and method for controlling optical sources, such as laser diodes, and computer program product therefor |
| US7505692B2 (en) * | 2004-08-31 | 2009-03-17 | Cisco Technology, Inc. | System and method for optical transmission |
| TWI287340B (en) * | 2004-12-07 | 2007-09-21 | Ind Tech Res Inst | Laser driver with automatic power control |
| US7639001B2 (en) * | 2006-01-17 | 2009-12-29 | The Boeing Company | Built-in test for high speed electrical networks |
| JP4973005B2 (en) | 2006-05-24 | 2012-07-11 | 日立電線株式会社 | Laser control apparatus and control method thereof |
| DE102009049000A1 (en) * | 2009-10-09 | 2011-04-14 | Bktel Communications Gmbh | Method and device for optical transmission of an AC signal |
| WO2023046578A1 (en) | 2021-09-21 | 2023-03-30 | Signify Holding B.V. | An optical wireless communication system |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4355395A (en) * | 1978-04-10 | 1982-10-19 | British Telecommunications | Injection lasers |
| DE2841433C2 (en) * | 1978-09-22 | 1983-08-25 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Bias current regulation of laser diodes |
| US4277846A (en) * | 1979-12-27 | 1981-07-07 | Bell Telephone Laboratories, Incorporated | Circuit for stabilizing the output of an injection laser |
| US4317236A (en) * | 1980-02-25 | 1982-02-23 | Bell Telephone Laboratories, Incorporated | Laser digital transmitter |
| FR2494514A1 (en) * | 1980-11-14 | 1982-05-21 | Lignes Telegraph Telephon | DEVICE FOR STABILIZING THE OUTPUT POWER OF A TRANSMITTER MODULE FOR AN OPTICAL FIBER TRANSMISSION SYSTEM |
| JPS6245086A (en) * | 1985-08-22 | 1987-02-27 | Oki Electric Ind Co Ltd | Laser diode drive circuit |
| EP0347202A3 (en) * | 1988-06-14 | 1991-03-20 | Brother Kogyo Kabushiki Kaisha | Excitation system for a semiconductor laser device |
| JP2706262B2 (en) * | 1988-07-12 | 1998-01-28 | キヤノン株式会社 | Semiconductor laser driver |
| JP2612608B2 (en) * | 1988-10-20 | 1997-05-21 | キヤノン株式会社 | Semiconductor laser driver |
| US5018154A (en) * | 1989-09-12 | 1991-05-21 | Brother Kogyo Kabushiki Kaisha | Semiconductor laser drive device |
| JPH03216363A (en) * | 1990-01-22 | 1991-09-24 | Fuji Photo Film Co Ltd | Apparatus for driving semiconductor laser |
| US5268916A (en) * | 1992-06-15 | 1993-12-07 | Alcatel Network Systems, Inc. | Laser bias and modulation circuit |
-
1992
- 1992-06-15 US US07/898,702 patent/US5268916A/en not_active Expired - Fee Related
-
1993
- 1993-06-09 ES ES93109253T patent/ES2094415T3/en not_active Expired - Lifetime
- 1993-06-09 AT AT93109253T patent/ATE143184T1/en not_active IP Right Cessation
- 1993-06-09 EP EP93109253A patent/EP0574816B1/en not_active Expired - Lifetime
- 1993-06-09 DE DE69304806T patent/DE69304806T2/en not_active Expired - Lifetime
- 1993-06-14 CA CA002098343A patent/CA2098343A1/en not_active Abandoned
- 1993-06-15 JP JP5144030A patent/JPH0685363A/en active Pending
- 1993-11-24 US US08/158,166 patent/US5488621A/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5541759A (en) * | 1995-05-09 | 1996-07-30 | Microsym Computers, Inc. | Single fiber transceiver and network |
Also Published As
| Publication number | Publication date |
|---|---|
| US5268916A (en) | 1993-12-07 |
| JPH0685363A (en) | 1994-03-25 |
| EP0574816B1 (en) | 1996-09-18 |
| ATE143184T1 (en) | 1996-10-15 |
| US5488621A (en) | 1996-01-30 |
| DE69304806T2 (en) | 1997-02-06 |
| DE69304806D1 (en) | 1996-10-24 |
| EP0574816A1 (en) | 1993-12-22 |
| ES2094415T3 (en) | 1997-01-16 |
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| EEER | Examination request | ||
| FZDE | Discontinued |