CA2325881A1 - Apparatus and method for compensation of chromatic dispersion in optical fibers - Google Patents
Apparatus and method for compensation of chromatic dispersion in optical fibers Download PDFInfo
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- CA2325881A1 CA2325881A1 CA002325881A CA2325881A CA2325881A1 CA 2325881 A1 CA2325881 A1 CA 2325881A1 CA 002325881 A CA002325881 A CA 002325881A CA 2325881 A CA2325881 A CA 2325881A CA 2325881 A1 CA2325881 A1 CA 2325881A1
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
- G02B6/2706—Optical coupling means with polarisation selective and adjusting means as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters
- G02B6/2713—Optical coupling means with polarisation selective and adjusting means as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters cascade of polarisation selective or adjusting operations
- G02B6/272—Optical coupling means with polarisation selective and adjusting means as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters cascade of polarisation selective or adjusting operations comprising polarisation means for beam splitting and combining
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/14—Mode converters
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
- G02B6/2753—Optical coupling means with polarisation selective and adjusting means characterised by their function or use, i.e. of the complete device
- G02B6/278—Controlling polarisation mode dispersion [PMD], e.g. PMD compensation or emulation
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29371—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion
- G02B6/29374—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion in an optical light guide
- G02B6/29376—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion in an optical light guide coupling light guides for controlling wavelength dispersion, e.g. by concatenation of two light guides having different dispersion properties
- G02B6/29377—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion in an optical light guide coupling light guides for controlling wavelength dispersion, e.g. by concatenation of two light guides having different dispersion properties controlling dispersion around 1550 nm, i.e. S, C, L and U bands from 1460-1675 nm
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2513—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion
- H04B10/2525—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion using dispersion-compensating fibres
Abstract
A dispersion compensation device uses at least two chromatic dispersion compensation fibers to compensate for chromatic dispersion present in an optical communication system. Two dispersion orders can be corrected using appropriate lengths of two serially coupled compensation fibers having different dispersion characteristics. The device can compensate for N
additional orders of dispersion by using N additional compensation fibers with unique dispersion characteristics. The device can be coupled directly to a transmission fiber.
additional orders of dispersion by using N additional compensation fibers with unique dispersion characteristics. The device can be coupled directly to a transmission fiber.
Description
APPARATUS .AND METHOD FOR COMPENSATION OF CHROMATIC DISPERSION
IN OPTICAL FIBERS
Cross-Reference to Related Applications This application claims priority to provisional U.S. patent application number 60/079,423 which was filed March 26, 1998, provisional U.S. patent application number 60!089,350 which was filed Junc 15, 1998 and provisional U.S. patent application number 601091,026 which was filed Junc 29, 1998 and incorporates by reference U.S. patent applications "Transverse Spatial Mode Transformer for Optical Communication" (attorney docket no. LCM-001) and "Optical Communication System with Chromatic Dispersion Compensation" (attorney dockEt no. LCM-002) filed concurrently herewith.
Field of the Invention The invention relates to fiber optic telecommunication systems and more specif'xcally to chromatic dispersion compensation in such systems.
Background of the Invention The tendency of a pulse of light propagating through an optical fiber to broaden is a result of the fact that different wavelengths of light pass through the fiber at ditfenat speeds. This speed differential which causes the pulse to broaden is termed chromatic dispersion. Chromatic dispersion presents a problem in modern optical communication systems ba~xuse the tendency of light pulses to broaden as they propagate down the fiber causes the closely spaced light pulses to overlap in time. This overlap can have an undesirable effect since it restricts hew closely spaced the pulses can be. This in turn limits the data bandwidth of the optical fiber.
There are many characteristics of dispersion. First order dispersion is the rate of change zo of index of refraction with respect to wavelength in the fiber. First ordex dispersion is also referred to as group velocity. Second order dispersion is the rate of change of the fixst order dispersion with respect to wavelength. Second order dispersion producxs the pulse broadening.
Third order dispersion is the raft of chauage of broadening with respect to a change in wavelength. This is often refermd to as the dispersion slope.
Several solutions have been proposed to mitigaat~ee the effects of dispersion is tzansmission fibers. One technique involves the use of a compensating optical fiber having an appropriate RECT1FlED SHEET (RULE 91 ) ~
~------'- ~~cket No.: LCM-003PC Ca o232sssi Zooo-o9-Zs length and which has a dispersion that is opposite to the dispersion characteristic of the transmission fiber. The result is dispersion in the transmission fiber is substantially matched and canceled by the total dispersion in the compensating fiber. While this technique offers a solution to the dispersion problem, it may be impractical in actual use because of the attenuation due to the required length of the compensating fiber. In such a case, the total transmission length of the fiber is significantly increased thereby increasing the signal attenuation in the fiber. Furthermore, it may be di~cult to find a fiber of the desired length with the required dispersion properties.
It is also difficult to design a fiber having a changing index of refraction across the 1o diameter of the fiber (the fiber index profile) that will compensate simultaneously for the second and third dispersion orders. It is even more difficult to control the material properties of such fibers even in the most accurate fabrication process necessary to produce such fibers.
In addition, the process of fabricating the single compensating chromatic dispersion fiber is expensive and generally not practical.
15 When a pulse of light is transmitted through an optical fiber, the energy follows a number of paths which cross the fiber axis at different angles. A group of paths which cross the axis at the same angle is known as a mode. Sometimes it is necessary to limit or control the number of modes used in a transmission system. The fundamental mode LPoi in which light passes substantially along the fiber axis is often used in high bandwidth transmission 2o systems using optical fibers commonly referred to as single mode fibers.
The dispersion properties of high order modes have been investigated at length. There is a dependence of high order mode dispersion on wavelength and on the properties of the fiber. By properly designing the fiber index profile it is possible to make the dispersion slope be positive, negative or zero. It is also possible to make the magnitude of the dispersion be 25 negative, zero or slightly positive. Using these two properties one can either control or compensate for the dispersion in any transmission fiber.
Systems have been developed to take advantage of higher order modes to compensate for dispersion in a typical optical communication system. In such systems it has been necessary to first convert the lower order fundamental mode of the light to a higher order 3o ' spatial mode. This is accomplished using longitudinal mode conversion.
Prior art methods for mode conversion are known as longitudinal mode conversion and are based on introducing a periodic perturbation along the fiber axis. The length of each period and the number of periods in AMENDED SHEET
IN OPTICAL FIBERS
Cross-Reference to Related Applications This application claims priority to provisional U.S. patent application number 60/079,423 which was filed March 26, 1998, provisional U.S. patent application number 60!089,350 which was filed Junc 15, 1998 and provisional U.S. patent application number 601091,026 which was filed Junc 29, 1998 and incorporates by reference U.S. patent applications "Transverse Spatial Mode Transformer for Optical Communication" (attorney docket no. LCM-001) and "Optical Communication System with Chromatic Dispersion Compensation" (attorney dockEt no. LCM-002) filed concurrently herewith.
Field of the Invention The invention relates to fiber optic telecommunication systems and more specif'xcally to chromatic dispersion compensation in such systems.
Background of the Invention The tendency of a pulse of light propagating through an optical fiber to broaden is a result of the fact that different wavelengths of light pass through the fiber at ditfenat speeds. This speed differential which causes the pulse to broaden is termed chromatic dispersion. Chromatic dispersion presents a problem in modern optical communication systems ba~xuse the tendency of light pulses to broaden as they propagate down the fiber causes the closely spaced light pulses to overlap in time. This overlap can have an undesirable effect since it restricts hew closely spaced the pulses can be. This in turn limits the data bandwidth of the optical fiber.
There are many characteristics of dispersion. First order dispersion is the rate of change zo of index of refraction with respect to wavelength in the fiber. First ordex dispersion is also referred to as group velocity. Second order dispersion is the rate of change of the fixst order dispersion with respect to wavelength. Second order dispersion producxs the pulse broadening.
Third order dispersion is the raft of chauage of broadening with respect to a change in wavelength. This is often refermd to as the dispersion slope.
Several solutions have been proposed to mitigaat~ee the effects of dispersion is tzansmission fibers. One technique involves the use of a compensating optical fiber having an appropriate RECT1FlED SHEET (RULE 91 ) ~
~------'- ~~cket No.: LCM-003PC Ca o232sssi Zooo-o9-Zs length and which has a dispersion that is opposite to the dispersion characteristic of the transmission fiber. The result is dispersion in the transmission fiber is substantially matched and canceled by the total dispersion in the compensating fiber. While this technique offers a solution to the dispersion problem, it may be impractical in actual use because of the attenuation due to the required length of the compensating fiber. In such a case, the total transmission length of the fiber is significantly increased thereby increasing the signal attenuation in the fiber. Furthermore, it may be di~cult to find a fiber of the desired length with the required dispersion properties.
It is also difficult to design a fiber having a changing index of refraction across the 1o diameter of the fiber (the fiber index profile) that will compensate simultaneously for the second and third dispersion orders. It is even more difficult to control the material properties of such fibers even in the most accurate fabrication process necessary to produce such fibers.
In addition, the process of fabricating the single compensating chromatic dispersion fiber is expensive and generally not practical.
15 When a pulse of light is transmitted through an optical fiber, the energy follows a number of paths which cross the fiber axis at different angles. A group of paths which cross the axis at the same angle is known as a mode. Sometimes it is necessary to limit or control the number of modes used in a transmission system. The fundamental mode LPoi in which light passes substantially along the fiber axis is often used in high bandwidth transmission 2o systems using optical fibers commonly referred to as single mode fibers.
The dispersion properties of high order modes have been investigated at length. There is a dependence of high order mode dispersion on wavelength and on the properties of the fiber. By properly designing the fiber index profile it is possible to make the dispersion slope be positive, negative or zero. It is also possible to make the magnitude of the dispersion be 25 negative, zero or slightly positive. Using these two properties one can either control or compensate for the dispersion in any transmission fiber.
Systems have been developed to take advantage of higher order modes to compensate for dispersion in a typical optical communication system. In such systems it has been necessary to first convert the lower order fundamental mode of the light to a higher order 3o ' spatial mode. This is accomplished using longitudinal mode conversion.
Prior art methods for mode conversion are known as longitudinal mode conversion and are based on introducing a periodic perturbation along the fiber axis. The length of each period and the number of periods in AMENDED SHEET
these longitudinal converters must be determined accurately according to the wavelength, the strength of the perturbation, and the modes involved. By constructing a longitudinal mode converter it is possible to achieve good efficiency in transferring the energy from one mode to the other in a limited spectral bandwidth. This spectral property has been used in Dense Wavelength Division Multiplexing (DWDM) applications in telecommunications for other applications.
Unfortunately, this technique is accompanied by significant energy attenuation and it cannot be used over broad spectral bandwidths.
Another deficiency associated with longitudinal mode converters is related to the fact that after the conversion, only a single mode should be present in the fiber. It can be difi~cult to discriminate between desired modes and undesired modes having almost the same group velocities because unwanted modes can appear at the output of the converter. As the modes propagate, modal dispersion occurs and the pulse broadens. Generally, longitudinal mode converters introduce significant energy attenuation and noise. Therefore, a trade-off must be made between having broad-spectrum capability and the demand for converting the original mode to a pure, single, high-order mode.
One such longitudinal mode converter is discussed in patent number 5,802,234.
Here, a single mode transmission fiber carries the LPoI to a longitudinal mode converter. Before conversion in this system, however, it is necessary to couple the single mode transmission fiber to a multimode fiber while maintaining the signal in the basic LPoI mode. This coupling is typically di~cult to achieve without signal degradation and any misalignment or manufacturing inaccuracies can result in the presence of higher order modes. It is desirable that only the LPoI
mode propagate initially in the multimode fiber in order to avoid significant noise that degrades the system performance and typically such coupling results in the propagation of additional modes.
The present invention overcomes the disadvantages of longitudinal mode converters and previous attempts to control dispersion in a fiber optic system.
Summary of the Invention The present invention relates to an apparatus and method for chromatic dispersion compensation of optical systems. The apparatus and method make use of multiple chromatic dispersion compensation optical fibers. The number of orders of dispersion that can be corrected increases with the number of compensation fibers in the apparatus.
Specifically, N orders of dispersion can be corrected by serially coupling N chromatic dispersion compensation optical fibers.
In one embodiment, the present invention features a chromatic dispersion compensation module which includes a first and second dispersion compensation fiber. The optical signal is dispersion compensated by each compensation fiber. In one embodiment, one compensation fiber compensates for first order chromatic dispersion and the other compensation fiber compensates for second order chromatic dispersion. In another embodiment, at least one of the compensation fibers is optical coupled to a transmission fiber.
In another aspect, the invention features a method of compensating for chromatic dispersion in an optical system which includes the steps of receiving an optical signal from a transmission fiber, injecting the optical signal into a first compensation fiber and dispersion compensating the optical signal. The method includes the additional steps of injecting the optical signal exiting the first compensation fiber into a second compensation fiber, additionally compensating the optical signal, and injecting the optical signal into a second transmission fiber.
Brief Description of the Drawings These and other advantages of the invention may be more clearly understood with reference to the specification and the drawings, in which:
FIG. 1 is a block diagram of an embodiment of a typical fiber optic transmission system known to the prior art;
FIG. 2 is a block diagram of an embodiment of the fiber optic transmission system of the present invention including a chromatic dispersion compensation fiber module;
FIG. 3 is a block diagram of an embodiment of the chromatic dispersion compensation fiber module shown in FIG. 2 showing transverse mode transformers and a chromatic dispersion compensation fiber;
FIG. 4 is a block diagram of another embodiment of the chromatic dispersion compensation fiber module of the present invention showing transverse mode transformers and two chromatic dispersion compensation fibers;
FIG. 5 is a highly schematic diagram of an embodiment of a transverse mode transformer shown in FIG. 3;
~~~--~~w'~'-'~cketNo.: LCM-003PC ca o232sssi 2000-o9-2s 25-04-2000 ~ U S 009906479 FIG. 6a is a block diagram of an alternative embodiment of a fiber optic transmission system of the current invention with the leading transmission fiber replaced by a transmission source;
FIG. 6b is a block diagram of an alternative embodiment of a fiber optic transmission system of the current invention with the receiving transmission fiber replaced by a detector;
FIG. 7a is a graph of the intensity as a function of position along the diameter of a fiber in an ideal case;
FIG. 7b is a graph of the intensity as a function of position along the diameter of the fiber after transformation to the LPo2 mode;
FIG. 8 is a graph of the relative energy in the higher order mode relative to the LPQ1 mode for an element optimized for operation at a wavelength of 1550nm in an ideal case;
FIG. 9 is a block diagram of an alternative embodiment of a transverse mode transformer using two phase elements;
FIG. l0a is a highly schematic diagram of an alternative embodiment of the present invention showing two chromatic dispersion compensation fibers used for multiple order dispersion compensation;
FIG. l Ob is a highly schematic diagram of an alternative embodiment of the present invention showing two chromatic dispersion compensation fibers sandwiching a single mode transmission fiber used for multiple order dispersion compensation;
2o FIG. l la - 1 le are graphs of different solution spaces showing relative design characteristics resulting from the use of first and second order dispersion;
FIG. 12a-12c are illustrations of alternative embodiments of the transverse mode transformer shown embedded in a fiber optic transmission system;
FIG. 13a-13c are graphs of the amplitude versus position plot of the pulse across the diameter of the fiber before, during and after mode transformation;
FIG. 14 is an illustration of an alternative embodiment of the current invention using a polarization beamsplitter and a polarization combiner;
FIG. 15 is a schematic diagram of a single bulk component that can be used to replace the discrete bulk optical components in the embodiment shown in FIG. 14;
3o FIG. 16 shows a representation of the polarization of propagating modes through the element described in FIG. 15;
AMENDED SHEET
FIG. 17 shows a representation of the polarization of propagating modes using a birefringent element;
FIG. 18 is a block diagram of an alternative embodiment of the current invention designed to eliminate the sensitivity of the system to polarization mode dispersion by using a circulator and a Faraday mirror; and FIG. 19 is a block diagram of an alternative embodiment of the current invention designed to eliminate the sensitivity of the system to polarization mode dispersion without using a circulator.
FIG. 20a-20c are diagrams of alternative embodiments of a transverse mode transformer using internal reflection.
Detailed Description of the Invention A typical optical fiber transmission system known in the prior art is shown in FIG. 1.
Such a system includes a signal transmitter 2 in optical communication with a single mode fiber (SMF) 3 which is in turn in optical communication with a signal receiver 4.
(Other components common to optical fiber systems, such as amplifiers, circulators, isolators, etc. are not shown.) A
signal is transmitted from the transmitter 2 into the fiber 3 where it propagates some distance.
Depending on the length and other properties of the fiber, significant signal attenuation and dispersion can occur in the fiber. The receiver 4 acquires the attenuated signal as it exits the fiber 3.
A basic configuration of the system of the present invention is presented in FIG. 2. A
transmitter 2 transmits an optical signal into a communication fiber 3. The communication fiber 3 introduces dispersion that requires compensation. The chromatic dispersion compensation module 10 compensates for signal dispersion introduced by the communication fiber 3 before propagating the signal into a receiver 4.
An embodiment of the chromatic dispersion module 10 is shown in FIG. 3. A
signal propagating in a single mode fiber (SMF} 3 enters a mode transformer 28 which converts the basic lower order spatial mode, generally LPo~, to a higher order spatial mode, generally LPo2, that propagates in a special chromatic dispersion compensating fiber 30. The chromatic dispersion compensation fiber (DCF) 30 is designed to compensate for the first order dispersion of the signal. A second chromatic dispersion compensation fiber 31 with different compensation properties may be coupled to the first chromatic dispersion compensation fiber 30 in order to ~cketNo.: LCM-003PC Ca o232sssi 2000-09-2s US 009906479 _7_ compensate for dispersion slope as shown in FIG. 4. If required, more than two chromatic dispersion compensation fibers may be used to compensate even higher order dispersion or alternatively for mode filtering applications. Once compensation is complete, the signal is then converted back to the lower order mode by a second mode transformer 28' and emerges from the chromatic dispersion compensation module 10 in the single mode fiber 3'.
The mode transformer 28 of the present invention is a bi-directional transverse mode transformer. It can be used to convert a lower order spatial mode to a higher order spatial mode. Conversely, the same transverse mode transformer 28 can be used to convert a higher order spatial mode to a lower order spatial mode. Unlike prior mode transformers which used 1o the longitudinal axis of the fiber to accomplish longitudinal mode conversion, the present transverse mode transformer uses transverse properties of the wavefront of the light to mode convert by selectively altering the phase of at least one portion of the wavefront. One embodiment of a transverse mode transformer is shown in FIG. 5. A transverse phase element 58 arranged perpendicular to the longitudinal axis of the fiber is used to accomplish mode transformation. A pulse of light propagates in a single mode fiber SO
with a small diameter core 54. The pulse broadens into an expanded region 56 as it emerges from the fiber. As the pulse passes through the transverse phase element 58 the phase distribution of the pulse is changed. The phase element 58 can consist of a spatially selective phase element which alters the phase of points on the wavefront as a function of their transverse position. A
focusing lens 62 focuses the pulse back into the special chromatic dispersion compensation fiber 64, shown as having a broader core 66 simply for explanatory purposes.
In one embodiment the lens 62 is a compound lens. In another embodiment, gradient index (GRIN) lenses are used. The phase element 58 can be any spatially selective phase element, including but not limited to, lenses, mirrors, gratings, electro-optic devices, beamsplitters, reflective elements, graded indexed materials and.photolithographic elements.
Phase transformation can be achieved using the properties of spherical aberration inherent in optical lenses. After a wavefront passes through a lens, it will experience spherical aberration. The resulting distorted wavefront can be used with or without a phase element 58 in the transverse mode transformer 28 of the present invention to transform the 3o spatial mode of the original wavefront to a higher order spatial mode.
AMENDED SHEET
w---w'-'-'-cketNo.: LCM-003PC ca o232sssi Zooo-o9-Zs _g_ FIG. 6a depicts a system in which a transmission source 24 replaces the optical fiber 3 shown in the embodiment in FIG. 4. Here the system does not require an input transmission fiber and retains all the functionality and advantages of the present invention. The transmission source 24 injects an optical signal directly into the chromatic dispersion compensation module 10 where it is pre-compensated before being received by the transmission fiber 3'. Precompensation can be desirable when the transmission fiber 3' has a known dispersion that requires compensation.
FIG. 6b describes a system in which a detector 36 replaces the transmission fiber 3' shown in the embodiment in FIG. 4. Here the system does not require an exit transmission 1 o fiber 3' and the functionality of the system is not affected. In this case the optical signal propagates in the optical fiber 3 before being compensated by the chromatic dispersion compensation module 10. Once the signal is down converted by mode transformer 28', it is detected directly by detector 36. This method can conserve energy since there will not be fiber coupling losses exhibited before the detector.
The physical mechanism of the transverse mode transformation presented in this invention is explained with reference to FIGS. 13a to 13c. (FIGS. 13a to 13c share the same horizontal scale.) Figure 13a illustrates the gaussian-like amplitude distribution of mode LPo, in a single mode fiber, wherein the horizontal axis represents the transverse position across the diameter of the fiber in arbitrary units and the vertical axis represents the amplitude 2o in arbitrary units. In one embodiment, the transverse phase element 58 (FIG. 5) introduces a step function to the wavefront 20 of the pulse such that the center region 20a of the wavefront is retarded with respect to the outer region 20b of the wavefront 20.
Therefore, the inner region 20a .and the outer region 20b of the wavefront 20 will differ in phase by 180°. After propagation and.transformation, the resulting distribution 22 shown in FIG.
13c enters the chromatic dispersion compensation fiber 64 (see FIG. 5). More than ninety percent of the transverse intensity distribution in the LPo, mode (see FIG. 7a) is present in the LPoz mode (see FIG. 7b) after transformation. The remaining energy is distributed among higher order modes which are not supported by the special chromatic dispersion compensation fiber 64.
Therefore, the fiber will contain substantially a single high order mode (LPoz). The same process, but in the reverse order, occurs in the second mode transformer 28' at the opposite end of the compensation fiber 64. This technique can also be applied to convert between other spatial modes.
AMENDED SHEET
'-~w----'-'W cketNo.: LCM-003PC CA o232sssi Zooo-o9-Zs One of the advantages of this transverse transformation mechanism is its high efficiency over a broad spectrum. FIG. 8 shows the residual energy in the LPo~
mode for an element optimized for operation at 1550nm. The horizontal axis represents the wavelength of the pulse in nanometers, and the vertical axis represents the ratio between the energy remaining in the low order mode to the total energy of the pulse. Less 'than one half of a percent of the pulse energy is left in the lowest order mode over greater than 1 OOnm of spectral range.
In order to further improve the transformation efficiency it is possible to use multiple phase elements 58" and 58" as shown~in FIG. 9. The pulse emerging from fiber 50 is 1o collimated by lens 62', then it passes through the two phase elements 58' and 58" and is finally focused by lens 62" into a special chromatic dispersion compensation fiber 64. This technique reduces longitudinal sensitivity in the placement of the phase elements. The design of phase elements 58' and 58" can be based on a coordinate transformation technique for converting between spatial modes. The first phase element 58' is designed to have local phase~changes across the pulse. Each local phase change redirects (i.e., steers) a small section of the wavefront 20 to a predetermined coordinate on the second phase element 58". As a result, a predetermined intensity pattern is generated at the second phase element 58". The second phase element also induces local phase changes across the wavefront so that the resulting wavefront 20 with predetermined intensity and phase distributions at the second 2o element 58" yields the desired spatial mode.
Another embodiment of the chromatic dispersion compensation module 10 of the present invention is shown in FIG. 10a. This embodiment may be used with transverse mode transformers 28, but is not limited to their use. Any means that propagates a pulse with a higher order mode into an optical coupler 6 can use the invention. After the higher order pulse passes through optical coupler 6, the pulse then enters the first chromatic dispersion compensation fiber (DCF~) 8 which is designed to compensate for the dispersion of the communication fiber 3. DCF, 8 is spliced to a second dispersion compensation fiber (DCFZ) 9 through a splice 12. DCF2 9 is designed to have minimal second order dispersion at the point where the dispersion slope is maximum. By properly choosing the design parameters, a 3o minimal length of DCF, 8 and DCFZ 9 is required to compensate for dispersion. DCF~ 8 and DCF2 9 can be designed to operate with the basic LPoI mode as long as they have different dispersion characteristics. The order in which DCF, 8 and DCFZ 9 are arranged can be changed. Generally, more chromatic dispersion compensation fibers are required as the number of dispersion orders to be compensated increases.
AMENDED SHEET
~-~--------'-''~cketNo.: LCM-003PC ca o232sssi 2000-o9-2s The chromatic dispersion compensated pulse passes into the outgoing optical transmission fiber 5' at splice 14. FIG. lOb illustrates another embodiment of the invention. A single mode fiber is sandwiched between two dispersion compensation fibers. Any number of combinations can be realized without detracting from the essence of the invention.
Graphs of possible solutions using the chromatic dispersion compensation fibers of the present invention are shown in FIGS. l la-l le. The horizontal axes represent the second order dispersion, and the vertical axes represent the second order dispersion slope (i.e., third order dispersion). The dispersion compensation introduced by the chromatic dispersion compensation fibers is presented as arrow 24. FIG. 11 a represents an ideal system, where the to desired dispersion solution is presented as the point 20. By choosing the proper length of chromatic dispersion compensation fiber; the desired results are achieved.
Unfortunately, in conventional communication systems it is difficult to change the relationship between the dispersion orders. Moreover, it is difficult to even predict this relationship before fabrication of the compensation fiber is completed. In addition, this relationship varies strongly 15 according to fabrication processes. Therefore, if the desired amount of dispersion compensation presented at point 20 is displaced as illustrated in FIG. 1 lb, it is impossible to achieve the desired compensation. It is possible, however, to increase the length of the DCF
in order to add length 26 to the arrow 24, so that the actual magnitude of dispersion is . increased and the resulting dispersion 27 will approximate the desired dispersion 20.
20 By combining two or more different fibers it is possible to achieve a variety of dispersion properties. The dispersion properties of DCF, 8 and DCFZ 9 in FIG.
l0a are represented as 32 and 34 in FIG. l lc. The area 36 represents the solution space of dispersion compensation which can be achieved by proper combination of the two fibers DCF, 8 and DCFZ 9.
25 FIG. 11 d represents an example of such a combination. Using a combination of two or more DCFs, one can compensate for higher orders of dispersion. In order to achieve better coverage of the dispersion possibilities it is desirable to increase the angle between the arrows 32 and 34 in FIG. 1 lc. It is difficult to achieve this result by using~conventional single mode DCFs, however, high order mode-dispersion compensation fibers (HOM-DCF) can achieve 3o more than 90 degrees difference between two different DCFs as presented in FIG. 1 le. This system is insensitive to the exact properties of the DCFs, because changing the length of the fibers can compensate for any deviation in the result.
AMENDED SHEET
" ~cketNo.: LCM-003PC Ca o232sssi Zooo-o9-Zs -11- .
FIG. 12a depicts an alternative embodiment of the transverse mode transformer of the present invention and shows a connection, between two fibers, designed to modify the wavefront. Both fibers include a core 10 and cladding 11. The face 14 of the transmission fiber 7 can be perpendicular to the face of the dispersion compensation fiber 8 or at a small angle to the DCF 8 in order to eliminate reflection noise. The end face of at least one of the f hers has a predetermined binary pattern 16. The pattern 16 can be etched onto the fiber or be in optical communication with the fiber. The pattern is designed to redistribute a gaussian wavefront such as that corresponding to the LPo, mode as depicted in FIG. 7a to the LPo2 mode as depicted in Fig. 7b. In order to achieve an instantaneous change of the wavefront, to the height of the binary pattern is set in one embodiment to 1.5 microns.
This height is much smaller than the 'Rayleigh range', which is approximately 50 microns in a conventional fiber.
The Rayleigh range is defined as nr2/~, where r is the radius of the wavefront and ~, is the wavelength of the light.
FIG. 12b depicts an embodiment in which the fibers 7, 8 are in contact with each other in order to reduce the relative motion and losses. FIG. 12c depicts the same architecture as in FIG. 12b except that a transparent material (for example the cladding itself) fills the gap 17.
In this architecture the height of the pattern 16" can be larger. If the relative refractive index difference between the filled gap 17 and the pattern 16" is set to 4%, then the pattern height is set to 13 microns. This height is still smaller than the 'Rayleigh range'.
2o The width of the wavefront in a fiber is of the order of microns. Since modern photolithographic methods can achieved sub-micron resolution, photolithography can be used to create the desired pattern on the face of the fiber.
Just as photolithography makes it is possible to accurately etch or coat the desired pattern on the edge of the fiber, multiple lithographic processes make it possible to approximate any continuous pattern. Accurate alignment of the fiber core to the desired pattern can be achieved by illuminating the fiber through the core.
Another method for creating a pattern 16 on the end face of a fiber is to attach a short (i.e., a few tenths of microns in length) fiber having the desired pattern 16.
It can also be done by attaching a long fiber to the fiber end face and cutting it to the desired length. This 3o method is more convenient and less expensive in mass production.
An internally reflective spatial mode transformer 190 of the present invention is illustrated in FIG. 20a. The gaussian beam emerging from the end of a single mode fiber 3 includes a AMENDED SHEET
" ~cketNo.: LCM-003PC Ca o232sssi Zooo-o9-Zs =12-center portion 192 and outer portions 1,94. The gaussian beam,192, 194 and 194' enters the 'spatial mode transformer 190 where only the outer portions 194 are reflected from an internal surfaces 196 and 196' back into the center portion 192 so that the interference between the portions 192, 194 and 194' results in a wavefront similar to that of the LPo~
mode. The resulting wavefront passes through one or more lenses 198 which couple the wavefront into a high order mode fiber 8. The internal surfaces 196 and 196' can be made from a variety of reflectors including, but not limited to, metallic reflective materials and refractive index interfaces (e.g., a segment of optical fiber having a core-cladding interface). FIG. 20b illustrates an internally reflective spatial mode transformer 190 attached to the single mode to fiber 3. In another embodiment shown in FIG. 20c, a fiber-based spatial mode transformer 190' is disposed between the ends of the two fibers 3 and 8. The mode transformer 190' includes a short segment of optical fiber with an expanded core 200 of high refractive index.
The cores of the two fibers,3 and 8 can be expanded in order to improve the coupling efficiency between spatial modes.
t 5 The transverse transformation process is insensitive to the polarization of the propagating pulse. However, in many applications it is necessary to introduce different phase shifts to the different polarizations of the pulse. This can be desirable because the polarization of the LPo~ mode in the single mode fiber can be different from that of the higher order modes such as the TEo~ mode. FIG. 14 depicts an embodiment for such an application.
2o In this embodiment a collimating lenses 88, a polarization beamsplitter 92,,and a combiner 96 are conventional bulk elements. Special mirrors 100 and 102 perform the transverse mode transformation. These mirrors 100 and 102 are designed to introduce phase changes to the reflected wavefronts. One way of achieving this is by etching patterns on the mirrors themselves. In another embodiment, the transverse mode transformer 28 is constructed as a 25 single bulk component 109 as shown in FIG. 15. The incident optical beam 110 is split into two orthogonally polarized beams 111 and 113 by a polarization beamsplitter 115. Each beam is then reflected by total internal reflection from sides 114, and recombined at polarization beamsplitter 115 into a single output beam 112.
The effect of this element 109 on the polarization of the light passing through it is 30 illustrated in FIG. 16. An arbitrarily polarized pulse 120 is split to its two orthogonal polarization components 124a and 124b by the polarization beamsplitter 115 (not shown).
The phase of each component 124a and 124b is changed by the phase elements on the mirrors 114 of FIG. 15 resulting in altered components 128a and 128b. A polarization beamsplitter 115 (not shown) combines the components 128a and 128b into a AMENDED SHEET
cketNo.: LCM-003PC CA o232sssi Zooo-o9-Zs single annular distribution 132. The orientation of the phase elements on the mirrors I 14 which are used to generate the altered components 128a and 128b into a can be rotated so that all LP" modes can be generated separately. As a result, only a single mode propagates in the fiber DCF 8 of FIG. 14. One advantage is that a polarization-maintaining fiber is not required.
If the polarization of the incident pulse is known (after a polarizer or a polarizing splitter) then it is possible to transform its polarization to match that of the high order modes in the fiber. This polarization transformation can be done with a fine transverse grating. For example, the polarization of the LPo, mode (the lowest order mode), which is basically linear 1o and uniform across the mode, can be transformed to an azimuthal one (as that of the TEoI) by using a transverse grating with a varying local period.
Alternatively, a birefringent element can be used. FIG. 17 represents a physical description of the process of transforming a linear polarization towards angular polarization by using a retardation plate. The linear polarization 140 passes through a waveplate having primary axes oriented at an angle to the orientation of the linear polarization 142. The height of the plate is designed to have an angular dependence according to the equation H,(r,6)=
D/(2n)6, where D is defined as the depth for which the birefringence waveplate is not changing the orientation of linear polarization. . The resulting polarization 144 is shown in FIG. 17. However, this wavefront may have a residual angular phase. Therefore, another 2o non-birefringent element 146 is used to compensate for any residual angular phase. This element introduces the negative angular phase. This phase can be presented as H2(r,6)=-F/(2~)8, where F is calculated according to the residual angular phase. The same effect can be achieved also by using two retardation waveplates having opposite angular phases and their primary axis oriented at opposite angles to the linear polarization.
The transverse phase elements can be implemented in a few configurations according to the requirements of the complete system. FIG. 18 represents one embodiment of a system according to the present invention system designed to eliminate the sensitivity of the system to polarization mode dispersion. The light propagating in a single mode fiber 3 enters a circulator 160 or a coupler (not shown). Then the light passes through the transverse mode 3o transformer 162. The light is propagated as a higher order mode in the dispersion.
compensation fiber 164. A Faraday mirror 166 then reflects the light. After the light has passed again through the dispersion compensation fiber 164 and transverse mode AMENDED SHEET
transformer 162, the circulator 160 separates the outgoing light for propagation through fiber 3' from the incoming light propagating through fiber 3.
However, in many applications circulators 160 are not desired because of their expense and complexity. Couplers (i.e., beamsplitters) are also undesirable because they introduce an inherent 50% loss. FIG. 19 represents a configuration in which a circulator or coupler is not needed. The light is separated into its orthogonal polarizations by the polarization sputter 172.
Then, each polarization passes through a Faraday rotator 174 imparting a 45° polarization rotation to the polarization and then through a phase element 178. A
polarization conserving special fiber 180 or an elliptical special fiber 180 is oriented at 45°
so it is parallel to the transmitted polarization. The influence of the two Faraday rotators 174 cancels the rotation introduced by the special fiber 180. As a result, the two polarizations return to their original state and are combined at the polarizer 172 in the same orientation. As the two polarizations are counter-propagating in the special fiber 180, they have the same orientation.
Therefore, they will be combined without time difference.
Thus, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover alI of the generic and specific features of the invention described herein.
Unfortunately, this technique is accompanied by significant energy attenuation and it cannot be used over broad spectral bandwidths.
Another deficiency associated with longitudinal mode converters is related to the fact that after the conversion, only a single mode should be present in the fiber. It can be difi~cult to discriminate between desired modes and undesired modes having almost the same group velocities because unwanted modes can appear at the output of the converter. As the modes propagate, modal dispersion occurs and the pulse broadens. Generally, longitudinal mode converters introduce significant energy attenuation and noise. Therefore, a trade-off must be made between having broad-spectrum capability and the demand for converting the original mode to a pure, single, high-order mode.
One such longitudinal mode converter is discussed in patent number 5,802,234.
Here, a single mode transmission fiber carries the LPoI to a longitudinal mode converter. Before conversion in this system, however, it is necessary to couple the single mode transmission fiber to a multimode fiber while maintaining the signal in the basic LPoI mode. This coupling is typically di~cult to achieve without signal degradation and any misalignment or manufacturing inaccuracies can result in the presence of higher order modes. It is desirable that only the LPoI
mode propagate initially in the multimode fiber in order to avoid significant noise that degrades the system performance and typically such coupling results in the propagation of additional modes.
The present invention overcomes the disadvantages of longitudinal mode converters and previous attempts to control dispersion in a fiber optic system.
Summary of the Invention The present invention relates to an apparatus and method for chromatic dispersion compensation of optical systems. The apparatus and method make use of multiple chromatic dispersion compensation optical fibers. The number of orders of dispersion that can be corrected increases with the number of compensation fibers in the apparatus.
Specifically, N orders of dispersion can be corrected by serially coupling N chromatic dispersion compensation optical fibers.
In one embodiment, the present invention features a chromatic dispersion compensation module which includes a first and second dispersion compensation fiber. The optical signal is dispersion compensated by each compensation fiber. In one embodiment, one compensation fiber compensates for first order chromatic dispersion and the other compensation fiber compensates for second order chromatic dispersion. In another embodiment, at least one of the compensation fibers is optical coupled to a transmission fiber.
In another aspect, the invention features a method of compensating for chromatic dispersion in an optical system which includes the steps of receiving an optical signal from a transmission fiber, injecting the optical signal into a first compensation fiber and dispersion compensating the optical signal. The method includes the additional steps of injecting the optical signal exiting the first compensation fiber into a second compensation fiber, additionally compensating the optical signal, and injecting the optical signal into a second transmission fiber.
Brief Description of the Drawings These and other advantages of the invention may be more clearly understood with reference to the specification and the drawings, in which:
FIG. 1 is a block diagram of an embodiment of a typical fiber optic transmission system known to the prior art;
FIG. 2 is a block diagram of an embodiment of the fiber optic transmission system of the present invention including a chromatic dispersion compensation fiber module;
FIG. 3 is a block diagram of an embodiment of the chromatic dispersion compensation fiber module shown in FIG. 2 showing transverse mode transformers and a chromatic dispersion compensation fiber;
FIG. 4 is a block diagram of another embodiment of the chromatic dispersion compensation fiber module of the present invention showing transverse mode transformers and two chromatic dispersion compensation fibers;
FIG. 5 is a highly schematic diagram of an embodiment of a transverse mode transformer shown in FIG. 3;
~~~--~~w'~'-'~cketNo.: LCM-003PC ca o232sssi 2000-o9-2s 25-04-2000 ~ U S 009906479 FIG. 6a is a block diagram of an alternative embodiment of a fiber optic transmission system of the current invention with the leading transmission fiber replaced by a transmission source;
FIG. 6b is a block diagram of an alternative embodiment of a fiber optic transmission system of the current invention with the receiving transmission fiber replaced by a detector;
FIG. 7a is a graph of the intensity as a function of position along the diameter of a fiber in an ideal case;
FIG. 7b is a graph of the intensity as a function of position along the diameter of the fiber after transformation to the LPo2 mode;
FIG. 8 is a graph of the relative energy in the higher order mode relative to the LPQ1 mode for an element optimized for operation at a wavelength of 1550nm in an ideal case;
FIG. 9 is a block diagram of an alternative embodiment of a transverse mode transformer using two phase elements;
FIG. l0a is a highly schematic diagram of an alternative embodiment of the present invention showing two chromatic dispersion compensation fibers used for multiple order dispersion compensation;
FIG. l Ob is a highly schematic diagram of an alternative embodiment of the present invention showing two chromatic dispersion compensation fibers sandwiching a single mode transmission fiber used for multiple order dispersion compensation;
2o FIG. l la - 1 le are graphs of different solution spaces showing relative design characteristics resulting from the use of first and second order dispersion;
FIG. 12a-12c are illustrations of alternative embodiments of the transverse mode transformer shown embedded in a fiber optic transmission system;
FIG. 13a-13c are graphs of the amplitude versus position plot of the pulse across the diameter of the fiber before, during and after mode transformation;
FIG. 14 is an illustration of an alternative embodiment of the current invention using a polarization beamsplitter and a polarization combiner;
FIG. 15 is a schematic diagram of a single bulk component that can be used to replace the discrete bulk optical components in the embodiment shown in FIG. 14;
3o FIG. 16 shows a representation of the polarization of propagating modes through the element described in FIG. 15;
AMENDED SHEET
FIG. 17 shows a representation of the polarization of propagating modes using a birefringent element;
FIG. 18 is a block diagram of an alternative embodiment of the current invention designed to eliminate the sensitivity of the system to polarization mode dispersion by using a circulator and a Faraday mirror; and FIG. 19 is a block diagram of an alternative embodiment of the current invention designed to eliminate the sensitivity of the system to polarization mode dispersion without using a circulator.
FIG. 20a-20c are diagrams of alternative embodiments of a transverse mode transformer using internal reflection.
Detailed Description of the Invention A typical optical fiber transmission system known in the prior art is shown in FIG. 1.
Such a system includes a signal transmitter 2 in optical communication with a single mode fiber (SMF) 3 which is in turn in optical communication with a signal receiver 4.
(Other components common to optical fiber systems, such as amplifiers, circulators, isolators, etc. are not shown.) A
signal is transmitted from the transmitter 2 into the fiber 3 where it propagates some distance.
Depending on the length and other properties of the fiber, significant signal attenuation and dispersion can occur in the fiber. The receiver 4 acquires the attenuated signal as it exits the fiber 3.
A basic configuration of the system of the present invention is presented in FIG. 2. A
transmitter 2 transmits an optical signal into a communication fiber 3. The communication fiber 3 introduces dispersion that requires compensation. The chromatic dispersion compensation module 10 compensates for signal dispersion introduced by the communication fiber 3 before propagating the signal into a receiver 4.
An embodiment of the chromatic dispersion module 10 is shown in FIG. 3. A
signal propagating in a single mode fiber (SMF} 3 enters a mode transformer 28 which converts the basic lower order spatial mode, generally LPo~, to a higher order spatial mode, generally LPo2, that propagates in a special chromatic dispersion compensating fiber 30. The chromatic dispersion compensation fiber (DCF) 30 is designed to compensate for the first order dispersion of the signal. A second chromatic dispersion compensation fiber 31 with different compensation properties may be coupled to the first chromatic dispersion compensation fiber 30 in order to ~cketNo.: LCM-003PC Ca o232sssi 2000-09-2s US 009906479 _7_ compensate for dispersion slope as shown in FIG. 4. If required, more than two chromatic dispersion compensation fibers may be used to compensate even higher order dispersion or alternatively for mode filtering applications. Once compensation is complete, the signal is then converted back to the lower order mode by a second mode transformer 28' and emerges from the chromatic dispersion compensation module 10 in the single mode fiber 3'.
The mode transformer 28 of the present invention is a bi-directional transverse mode transformer. It can be used to convert a lower order spatial mode to a higher order spatial mode. Conversely, the same transverse mode transformer 28 can be used to convert a higher order spatial mode to a lower order spatial mode. Unlike prior mode transformers which used 1o the longitudinal axis of the fiber to accomplish longitudinal mode conversion, the present transverse mode transformer uses transverse properties of the wavefront of the light to mode convert by selectively altering the phase of at least one portion of the wavefront. One embodiment of a transverse mode transformer is shown in FIG. 5. A transverse phase element 58 arranged perpendicular to the longitudinal axis of the fiber is used to accomplish mode transformation. A pulse of light propagates in a single mode fiber SO
with a small diameter core 54. The pulse broadens into an expanded region 56 as it emerges from the fiber. As the pulse passes through the transverse phase element 58 the phase distribution of the pulse is changed. The phase element 58 can consist of a spatially selective phase element which alters the phase of points on the wavefront as a function of their transverse position. A
focusing lens 62 focuses the pulse back into the special chromatic dispersion compensation fiber 64, shown as having a broader core 66 simply for explanatory purposes.
In one embodiment the lens 62 is a compound lens. In another embodiment, gradient index (GRIN) lenses are used. The phase element 58 can be any spatially selective phase element, including but not limited to, lenses, mirrors, gratings, electro-optic devices, beamsplitters, reflective elements, graded indexed materials and.photolithographic elements.
Phase transformation can be achieved using the properties of spherical aberration inherent in optical lenses. After a wavefront passes through a lens, it will experience spherical aberration. The resulting distorted wavefront can be used with or without a phase element 58 in the transverse mode transformer 28 of the present invention to transform the 3o spatial mode of the original wavefront to a higher order spatial mode.
AMENDED SHEET
w---w'-'-'-cketNo.: LCM-003PC ca o232sssi Zooo-o9-Zs _g_ FIG. 6a depicts a system in which a transmission source 24 replaces the optical fiber 3 shown in the embodiment in FIG. 4. Here the system does not require an input transmission fiber and retains all the functionality and advantages of the present invention. The transmission source 24 injects an optical signal directly into the chromatic dispersion compensation module 10 where it is pre-compensated before being received by the transmission fiber 3'. Precompensation can be desirable when the transmission fiber 3' has a known dispersion that requires compensation.
FIG. 6b describes a system in which a detector 36 replaces the transmission fiber 3' shown in the embodiment in FIG. 4. Here the system does not require an exit transmission 1 o fiber 3' and the functionality of the system is not affected. In this case the optical signal propagates in the optical fiber 3 before being compensated by the chromatic dispersion compensation module 10. Once the signal is down converted by mode transformer 28', it is detected directly by detector 36. This method can conserve energy since there will not be fiber coupling losses exhibited before the detector.
The physical mechanism of the transverse mode transformation presented in this invention is explained with reference to FIGS. 13a to 13c. (FIGS. 13a to 13c share the same horizontal scale.) Figure 13a illustrates the gaussian-like amplitude distribution of mode LPo, in a single mode fiber, wherein the horizontal axis represents the transverse position across the diameter of the fiber in arbitrary units and the vertical axis represents the amplitude 2o in arbitrary units. In one embodiment, the transverse phase element 58 (FIG. 5) introduces a step function to the wavefront 20 of the pulse such that the center region 20a of the wavefront is retarded with respect to the outer region 20b of the wavefront 20.
Therefore, the inner region 20a .and the outer region 20b of the wavefront 20 will differ in phase by 180°. After propagation and.transformation, the resulting distribution 22 shown in FIG.
13c enters the chromatic dispersion compensation fiber 64 (see FIG. 5). More than ninety percent of the transverse intensity distribution in the LPo, mode (see FIG. 7a) is present in the LPoz mode (see FIG. 7b) after transformation. The remaining energy is distributed among higher order modes which are not supported by the special chromatic dispersion compensation fiber 64.
Therefore, the fiber will contain substantially a single high order mode (LPoz). The same process, but in the reverse order, occurs in the second mode transformer 28' at the opposite end of the compensation fiber 64. This technique can also be applied to convert between other spatial modes.
AMENDED SHEET
'-~w----'-'W cketNo.: LCM-003PC CA o232sssi Zooo-o9-Zs One of the advantages of this transverse transformation mechanism is its high efficiency over a broad spectrum. FIG. 8 shows the residual energy in the LPo~
mode for an element optimized for operation at 1550nm. The horizontal axis represents the wavelength of the pulse in nanometers, and the vertical axis represents the ratio between the energy remaining in the low order mode to the total energy of the pulse. Less 'than one half of a percent of the pulse energy is left in the lowest order mode over greater than 1 OOnm of spectral range.
In order to further improve the transformation efficiency it is possible to use multiple phase elements 58" and 58" as shown~in FIG. 9. The pulse emerging from fiber 50 is 1o collimated by lens 62', then it passes through the two phase elements 58' and 58" and is finally focused by lens 62" into a special chromatic dispersion compensation fiber 64. This technique reduces longitudinal sensitivity in the placement of the phase elements. The design of phase elements 58' and 58" can be based on a coordinate transformation technique for converting between spatial modes. The first phase element 58' is designed to have local phase~changes across the pulse. Each local phase change redirects (i.e., steers) a small section of the wavefront 20 to a predetermined coordinate on the second phase element 58". As a result, a predetermined intensity pattern is generated at the second phase element 58". The second phase element also induces local phase changes across the wavefront so that the resulting wavefront 20 with predetermined intensity and phase distributions at the second 2o element 58" yields the desired spatial mode.
Another embodiment of the chromatic dispersion compensation module 10 of the present invention is shown in FIG. 10a. This embodiment may be used with transverse mode transformers 28, but is not limited to their use. Any means that propagates a pulse with a higher order mode into an optical coupler 6 can use the invention. After the higher order pulse passes through optical coupler 6, the pulse then enters the first chromatic dispersion compensation fiber (DCF~) 8 which is designed to compensate for the dispersion of the communication fiber 3. DCF, 8 is spliced to a second dispersion compensation fiber (DCFZ) 9 through a splice 12. DCF2 9 is designed to have minimal second order dispersion at the point where the dispersion slope is maximum. By properly choosing the design parameters, a 3o minimal length of DCF, 8 and DCFZ 9 is required to compensate for dispersion. DCF~ 8 and DCF2 9 can be designed to operate with the basic LPoI mode as long as they have different dispersion characteristics. The order in which DCF, 8 and DCFZ 9 are arranged can be changed. Generally, more chromatic dispersion compensation fibers are required as the number of dispersion orders to be compensated increases.
AMENDED SHEET
~-~--------'-''~cketNo.: LCM-003PC ca o232sssi 2000-o9-2s The chromatic dispersion compensated pulse passes into the outgoing optical transmission fiber 5' at splice 14. FIG. lOb illustrates another embodiment of the invention. A single mode fiber is sandwiched between two dispersion compensation fibers. Any number of combinations can be realized without detracting from the essence of the invention.
Graphs of possible solutions using the chromatic dispersion compensation fibers of the present invention are shown in FIGS. l la-l le. The horizontal axes represent the second order dispersion, and the vertical axes represent the second order dispersion slope (i.e., third order dispersion). The dispersion compensation introduced by the chromatic dispersion compensation fibers is presented as arrow 24. FIG. 11 a represents an ideal system, where the to desired dispersion solution is presented as the point 20. By choosing the proper length of chromatic dispersion compensation fiber; the desired results are achieved.
Unfortunately, in conventional communication systems it is difficult to change the relationship between the dispersion orders. Moreover, it is difficult to even predict this relationship before fabrication of the compensation fiber is completed. In addition, this relationship varies strongly 15 according to fabrication processes. Therefore, if the desired amount of dispersion compensation presented at point 20 is displaced as illustrated in FIG. 1 lb, it is impossible to achieve the desired compensation. It is possible, however, to increase the length of the DCF
in order to add length 26 to the arrow 24, so that the actual magnitude of dispersion is . increased and the resulting dispersion 27 will approximate the desired dispersion 20.
20 By combining two or more different fibers it is possible to achieve a variety of dispersion properties. The dispersion properties of DCF, 8 and DCFZ 9 in FIG.
l0a are represented as 32 and 34 in FIG. l lc. The area 36 represents the solution space of dispersion compensation which can be achieved by proper combination of the two fibers DCF, 8 and DCFZ 9.
25 FIG. 11 d represents an example of such a combination. Using a combination of two or more DCFs, one can compensate for higher orders of dispersion. In order to achieve better coverage of the dispersion possibilities it is desirable to increase the angle between the arrows 32 and 34 in FIG. 1 lc. It is difficult to achieve this result by using~conventional single mode DCFs, however, high order mode-dispersion compensation fibers (HOM-DCF) can achieve 3o more than 90 degrees difference between two different DCFs as presented in FIG. 1 le. This system is insensitive to the exact properties of the DCFs, because changing the length of the fibers can compensate for any deviation in the result.
AMENDED SHEET
" ~cketNo.: LCM-003PC Ca o232sssi Zooo-o9-Zs -11- .
FIG. 12a depicts an alternative embodiment of the transverse mode transformer of the present invention and shows a connection, between two fibers, designed to modify the wavefront. Both fibers include a core 10 and cladding 11. The face 14 of the transmission fiber 7 can be perpendicular to the face of the dispersion compensation fiber 8 or at a small angle to the DCF 8 in order to eliminate reflection noise. The end face of at least one of the f hers has a predetermined binary pattern 16. The pattern 16 can be etched onto the fiber or be in optical communication with the fiber. The pattern is designed to redistribute a gaussian wavefront such as that corresponding to the LPo, mode as depicted in FIG. 7a to the LPo2 mode as depicted in Fig. 7b. In order to achieve an instantaneous change of the wavefront, to the height of the binary pattern is set in one embodiment to 1.5 microns.
This height is much smaller than the 'Rayleigh range', which is approximately 50 microns in a conventional fiber.
The Rayleigh range is defined as nr2/~, where r is the radius of the wavefront and ~, is the wavelength of the light.
FIG. 12b depicts an embodiment in which the fibers 7, 8 are in contact with each other in order to reduce the relative motion and losses. FIG. 12c depicts the same architecture as in FIG. 12b except that a transparent material (for example the cladding itself) fills the gap 17.
In this architecture the height of the pattern 16" can be larger. If the relative refractive index difference between the filled gap 17 and the pattern 16" is set to 4%, then the pattern height is set to 13 microns. This height is still smaller than the 'Rayleigh range'.
2o The width of the wavefront in a fiber is of the order of microns. Since modern photolithographic methods can achieved sub-micron resolution, photolithography can be used to create the desired pattern on the face of the fiber.
Just as photolithography makes it is possible to accurately etch or coat the desired pattern on the edge of the fiber, multiple lithographic processes make it possible to approximate any continuous pattern. Accurate alignment of the fiber core to the desired pattern can be achieved by illuminating the fiber through the core.
Another method for creating a pattern 16 on the end face of a fiber is to attach a short (i.e., a few tenths of microns in length) fiber having the desired pattern 16.
It can also be done by attaching a long fiber to the fiber end face and cutting it to the desired length. This 3o method is more convenient and less expensive in mass production.
An internally reflective spatial mode transformer 190 of the present invention is illustrated in FIG. 20a. The gaussian beam emerging from the end of a single mode fiber 3 includes a AMENDED SHEET
" ~cketNo.: LCM-003PC Ca o232sssi Zooo-o9-Zs =12-center portion 192 and outer portions 1,94. The gaussian beam,192, 194 and 194' enters the 'spatial mode transformer 190 where only the outer portions 194 are reflected from an internal surfaces 196 and 196' back into the center portion 192 so that the interference between the portions 192, 194 and 194' results in a wavefront similar to that of the LPo~
mode. The resulting wavefront passes through one or more lenses 198 which couple the wavefront into a high order mode fiber 8. The internal surfaces 196 and 196' can be made from a variety of reflectors including, but not limited to, metallic reflective materials and refractive index interfaces (e.g., a segment of optical fiber having a core-cladding interface). FIG. 20b illustrates an internally reflective spatial mode transformer 190 attached to the single mode to fiber 3. In another embodiment shown in FIG. 20c, a fiber-based spatial mode transformer 190' is disposed between the ends of the two fibers 3 and 8. The mode transformer 190' includes a short segment of optical fiber with an expanded core 200 of high refractive index.
The cores of the two fibers,3 and 8 can be expanded in order to improve the coupling efficiency between spatial modes.
t 5 The transverse transformation process is insensitive to the polarization of the propagating pulse. However, in many applications it is necessary to introduce different phase shifts to the different polarizations of the pulse. This can be desirable because the polarization of the LPo~ mode in the single mode fiber can be different from that of the higher order modes such as the TEo~ mode. FIG. 14 depicts an embodiment for such an application.
2o In this embodiment a collimating lenses 88, a polarization beamsplitter 92,,and a combiner 96 are conventional bulk elements. Special mirrors 100 and 102 perform the transverse mode transformation. These mirrors 100 and 102 are designed to introduce phase changes to the reflected wavefronts. One way of achieving this is by etching patterns on the mirrors themselves. In another embodiment, the transverse mode transformer 28 is constructed as a 25 single bulk component 109 as shown in FIG. 15. The incident optical beam 110 is split into two orthogonally polarized beams 111 and 113 by a polarization beamsplitter 115. Each beam is then reflected by total internal reflection from sides 114, and recombined at polarization beamsplitter 115 into a single output beam 112.
The effect of this element 109 on the polarization of the light passing through it is 30 illustrated in FIG. 16. An arbitrarily polarized pulse 120 is split to its two orthogonal polarization components 124a and 124b by the polarization beamsplitter 115 (not shown).
The phase of each component 124a and 124b is changed by the phase elements on the mirrors 114 of FIG. 15 resulting in altered components 128a and 128b. A polarization beamsplitter 115 (not shown) combines the components 128a and 128b into a AMENDED SHEET
cketNo.: LCM-003PC CA o232sssi Zooo-o9-Zs single annular distribution 132. The orientation of the phase elements on the mirrors I 14 which are used to generate the altered components 128a and 128b into a can be rotated so that all LP" modes can be generated separately. As a result, only a single mode propagates in the fiber DCF 8 of FIG. 14. One advantage is that a polarization-maintaining fiber is not required.
If the polarization of the incident pulse is known (after a polarizer or a polarizing splitter) then it is possible to transform its polarization to match that of the high order modes in the fiber. This polarization transformation can be done with a fine transverse grating. For example, the polarization of the LPo, mode (the lowest order mode), which is basically linear 1o and uniform across the mode, can be transformed to an azimuthal one (as that of the TEoI) by using a transverse grating with a varying local period.
Alternatively, a birefringent element can be used. FIG. 17 represents a physical description of the process of transforming a linear polarization towards angular polarization by using a retardation plate. The linear polarization 140 passes through a waveplate having primary axes oriented at an angle to the orientation of the linear polarization 142. The height of the plate is designed to have an angular dependence according to the equation H,(r,6)=
D/(2n)6, where D is defined as the depth for which the birefringence waveplate is not changing the orientation of linear polarization. . The resulting polarization 144 is shown in FIG. 17. However, this wavefront may have a residual angular phase. Therefore, another 2o non-birefringent element 146 is used to compensate for any residual angular phase. This element introduces the negative angular phase. This phase can be presented as H2(r,6)=-F/(2~)8, where F is calculated according to the residual angular phase. The same effect can be achieved also by using two retardation waveplates having opposite angular phases and their primary axis oriented at opposite angles to the linear polarization.
The transverse phase elements can be implemented in a few configurations according to the requirements of the complete system. FIG. 18 represents one embodiment of a system according to the present invention system designed to eliminate the sensitivity of the system to polarization mode dispersion. The light propagating in a single mode fiber 3 enters a circulator 160 or a coupler (not shown). Then the light passes through the transverse mode 3o transformer 162. The light is propagated as a higher order mode in the dispersion.
compensation fiber 164. A Faraday mirror 166 then reflects the light. After the light has passed again through the dispersion compensation fiber 164 and transverse mode AMENDED SHEET
transformer 162, the circulator 160 separates the outgoing light for propagation through fiber 3' from the incoming light propagating through fiber 3.
However, in many applications circulators 160 are not desired because of their expense and complexity. Couplers (i.e., beamsplitters) are also undesirable because they introduce an inherent 50% loss. FIG. 19 represents a configuration in which a circulator or coupler is not needed. The light is separated into its orthogonal polarizations by the polarization sputter 172.
Then, each polarization passes through a Faraday rotator 174 imparting a 45° polarization rotation to the polarization and then through a phase element 178. A
polarization conserving special fiber 180 or an elliptical special fiber 180 is oriented at 45°
so it is parallel to the transmitted polarization. The influence of the two Faraday rotators 174 cancels the rotation introduced by the special fiber 180. As a result, the two polarizations return to their original state and are combined at the polarizer 172 in the same orientation. As the two polarizations are counter-propagating in the special fiber 180, they have the same orientation.
Therefore, they will be combined without time difference.
Thus, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover alI of the generic and specific features of the invention described herein.
Claims
Claims We claim:
1. A chromatic dispersion compensation module operative on at least one optical signal, comprising a plurality of optical fibers characterized in that each optical fiber in said plurality of optical fibers compensates for a different dispersion order, and at least one of said optical fibers operates on said optical signal substantially in a high order spatial mode.
Claims 2 through 4 have been canceled.
Claims 5 through 9 have been canceled.
Claims 10-19 have been canceled.
Claims 20 through 25 have been canceled.
Claims 26 through 32 have been canceled.
Claims 33 and 34 have been canceled.
-20a-35. The chromatic dispersion compensation module of claim 1 wherein said high order spatial mode is the LP02 mode.
36. The chromatic dispersion compensation module of claim 1 wherein at least one of said optical fibers is a single mode fiber.
37. The chromatic dispersion compensation module of claim 1 wherein one of said dispersion orders corresponds to zero-th order dispersion.
38. The chromatic dispersion compensation module of claim 1 wherein one of said dispersion orders corresponds to dispersion slope.
39. The chromatic dispersion compensation module of claim 1 wherein one of said dispersion orders corresponds to second order dispersion.
40. The chromatic dispersion compensation module of claim 1 further comprising a mode transformer for converting said optical signal from a lower order spatial mode to said high order spatial mode.
41. The module of claim 1 further comprising a transmission fiber optically coupled to a first optical fiber in said plurality of optical fibers.
42. The module of claim 1 further comprising a transmission fiber optically coupled to a last optical fiber in said plurality of optical fibers.
43. A chromatic dispersion compensation module operative on at least one optical signal, comprising a plurality of optical fibers characterized in that each optical fiber in said plurality of optical fibers compensates for a different linear combination of dispersion orders, and at least one of said optical fibers operates on said optical signal substantially in a high order spatial mode.
44. A method for compensating for multiple orders of dispersion of at least one optical signal by a plurality of optical fibers, the method being characterized by the steps of:
receiving said optical signal having multiple orders of dispersion; and -20b-transmitting said optical signal through said plurality of optical fibers, wherein at least one of said optical fibers in said plurality of said optical fibers operates on said optical signal substantially in a high order spatial mode, wherein each optical fiber of said plurality of optical fibers compensates for a different dispersion order.
45. The method of claim 44 wherein said multiple orders of dispersion comprises at least second order dispersion.
46. The method of claim 44 wherein said multiple orders of dispersion comprises at least dispersion slope.
47. The method of claim 44 further comprising the step of converting said optical signal from a first mode substantially to a second higher order mode.
48. The method of claim 47 wherein said second higher order mode is the LP02 mode.
49. The method of claim 44 further comprising the steps of receiving said optical signal from a transmission fiber and transmitting said first optical signal through said plurality of said optical fibers.
50. The method of claim 44 wherein said compensation corresponds substantially to the opposite value of said multiple orders of dispersion.
51. The method of claim 44 further comprising the steps of transmitting said optical signal from said plurality of optical fibers through a transmission fiber.
52. The method of claim 51 wherein each optical fiber in said plurality of optical fibers pre-compensates for a different dispersion order from said transmission fiber.
53. A method for compensating for multiple orders of dispersion of at least one optical signal by a plurality of optical fibers, the method being characterized by the steps of:
receiving said optical signal having multiple orders of dispersion; and -20c-transmitting said optical signal through said plurality of optical fibers, wherein at least one of said optical fibers in said plurality of said optical fibers operates on said optical signal substantially in a high order spatial mode, wherein each optical fiber in said plurality of optical fibers compensates for a different linear combination of dispersion orders.
54. The method of claim 53 wherein each optical fiber in said plurality of optical fibers pre-compensates for a different linear combination of dispersion orders from said transmission fiber.
1. A chromatic dispersion compensation module operative on at least one optical signal, comprising a plurality of optical fibers characterized in that each optical fiber in said plurality of optical fibers compensates for a different dispersion order, and at least one of said optical fibers operates on said optical signal substantially in a high order spatial mode.
Claims 2 through 4 have been canceled.
Claims 5 through 9 have been canceled.
Claims 10-19 have been canceled.
Claims 20 through 25 have been canceled.
Claims 26 through 32 have been canceled.
Claims 33 and 34 have been canceled.
-20a-35. The chromatic dispersion compensation module of claim 1 wherein said high order spatial mode is the LP02 mode.
36. The chromatic dispersion compensation module of claim 1 wherein at least one of said optical fibers is a single mode fiber.
37. The chromatic dispersion compensation module of claim 1 wherein one of said dispersion orders corresponds to zero-th order dispersion.
38. The chromatic dispersion compensation module of claim 1 wherein one of said dispersion orders corresponds to dispersion slope.
39. The chromatic dispersion compensation module of claim 1 wherein one of said dispersion orders corresponds to second order dispersion.
40. The chromatic dispersion compensation module of claim 1 further comprising a mode transformer for converting said optical signal from a lower order spatial mode to said high order spatial mode.
41. The module of claim 1 further comprising a transmission fiber optically coupled to a first optical fiber in said plurality of optical fibers.
42. The module of claim 1 further comprising a transmission fiber optically coupled to a last optical fiber in said plurality of optical fibers.
43. A chromatic dispersion compensation module operative on at least one optical signal, comprising a plurality of optical fibers characterized in that each optical fiber in said plurality of optical fibers compensates for a different linear combination of dispersion orders, and at least one of said optical fibers operates on said optical signal substantially in a high order spatial mode.
44. A method for compensating for multiple orders of dispersion of at least one optical signal by a plurality of optical fibers, the method being characterized by the steps of:
receiving said optical signal having multiple orders of dispersion; and -20b-transmitting said optical signal through said plurality of optical fibers, wherein at least one of said optical fibers in said plurality of said optical fibers operates on said optical signal substantially in a high order spatial mode, wherein each optical fiber of said plurality of optical fibers compensates for a different dispersion order.
45. The method of claim 44 wherein said multiple orders of dispersion comprises at least second order dispersion.
46. The method of claim 44 wherein said multiple orders of dispersion comprises at least dispersion slope.
47. The method of claim 44 further comprising the step of converting said optical signal from a first mode substantially to a second higher order mode.
48. The method of claim 47 wherein said second higher order mode is the LP02 mode.
49. The method of claim 44 further comprising the steps of receiving said optical signal from a transmission fiber and transmitting said first optical signal through said plurality of said optical fibers.
50. The method of claim 44 wherein said compensation corresponds substantially to the opposite value of said multiple orders of dispersion.
51. The method of claim 44 further comprising the steps of transmitting said optical signal from said plurality of optical fibers through a transmission fiber.
52. The method of claim 51 wherein each optical fiber in said plurality of optical fibers pre-compensates for a different dispersion order from said transmission fiber.
53. A method for compensating for multiple orders of dispersion of at least one optical signal by a plurality of optical fibers, the method being characterized by the steps of:
receiving said optical signal having multiple orders of dispersion; and -20c-transmitting said optical signal through said plurality of optical fibers, wherein at least one of said optical fibers in said plurality of said optical fibers operates on said optical signal substantially in a high order spatial mode, wherein each optical fiber in said plurality of optical fibers compensates for a different linear combination of dispersion orders.
54. The method of claim 53 wherein each optical fiber in said plurality of optical fibers pre-compensates for a different linear combination of dispersion orders from said transmission fiber.
Applications Claiming Priority (9)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US7942398P | 1998-03-26 | 1998-03-26 | |
| US60/079,423 | 1998-03-26 | ||
| US8935098P | 1998-06-15 | 1998-06-15 | |
| US60/089,350 | 1998-06-15 | ||
| US9102698P | 1998-06-29 | 1998-06-29 | |
| US60/091,026 | 1998-06-29 | ||
| US09/249,920 | 1999-02-12 | ||
| US09/249,920 US6339665B1 (en) | 1998-03-26 | 1999-02-12 | Apparatus and method for compensation of chromatic dispersion in optical fibers |
| PCT/US1999/006479 WO1999049340A2 (en) | 1998-03-26 | 1999-03-26 | Apparatus and method for compensation of chromatic dispersion in optical fibers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2325881A1 true CA2325881A1 (en) | 1999-09-30 |
Family
ID=27491471
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002325881A Abandoned CA2325881A1 (en) | 1998-03-26 | 1999-03-26 | Apparatus and method for compensation of chromatic dispersion in optical fibers |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US6339665B1 (en) |
| EP (1) | EP1064572A2 (en) |
| JP (1) | JP2002507874A (en) |
| AU (1) | AU3114699A (en) |
| CA (1) | CA2325881A1 (en) |
| IL (1) | IL138715A0 (en) |
| WO (1) | WO1999049340A2 (en) |
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| WO1999042892A1 (en) | 1998-02-19 | 1999-08-26 | Massachusetts Institute Of Technology | Photonic crystal omnidirectional reflector |
| WO2000022466A1 (en) | 1998-10-14 | 2000-04-20 | Massachusetts Institute Of Technology | Omnidirectional multilayer device for optical waveguiding |
| US6442320B1 (en) * | 1999-04-16 | 2002-08-27 | Lasercomm Inc. | Limited mode dispersion compensating optical fiber |
| WO2000070378A1 (en) * | 1999-05-17 | 2000-11-23 | The Furukawa Electric Co., Ltd. | Optical fiber and optical transmission line comprising the optical fiber |
| JP3557134B2 (en) * | 1999-09-28 | 2004-08-25 | 富士通株式会社 | Optical transmitting apparatus, wavelength division multiplexing optical signal generation method, and channel expansion method |
| GB9929344D0 (en) | 1999-12-10 | 2000-02-02 | Univ Bath | Improvements in or relating to photonic crystal fibres |
| US6792209B1 (en) * | 1999-12-22 | 2004-09-14 | At&T Corp. | Method and system for reducing non-linear cross talk in low dispersion optical fiber |
| US6453102B1 (en) | 2000-02-07 | 2002-09-17 | Corning Incorporated | Dispersion compensating module and mode converter, coupler and dispersion compensating optical waveguide therein |
| US6628872B2 (en) * | 2000-03-13 | 2003-09-30 | Sumitomo Electric Industries, Ltd. | Dispersion compensator and optical transmission system |
| DE50110551D1 (en) * | 2000-05-06 | 2006-09-07 | Thorlabs Gmbh | EMULATOR FOR PMD SECOND ORDER |
| DE10033820A1 (en) | 2000-07-12 | 2002-02-07 | Adalbert Bandemer | Apparatus to emulate a polarization mode dispersion, of the second order, has a unit which can turn its main polarization axis between the output and input of a polarization splitter/combiner |
| WO2001092931A2 (en) * | 2000-05-31 | 2001-12-06 | Corning Incorporated | Dispersion slope compensating optical fiber |
| CN1489712A (en) | 2001-01-25 | 2004-04-14 | �ź㴫 | Photonic crystal optical waveguides having tailored dispension profiles |
| CN1268950C (en) | 2001-01-25 | 2006-08-09 | 全波导通信公司 | Low-loss photonic crystal waveguide having large core radius |
| JP2004521379A (en) | 2001-01-31 | 2004-07-15 | オムニガイド コミュニケーションズ インコーポレイテッド | Electromagnetic mode conversion of photonic crystal multimode waveguide |
| US6943935B2 (en) | 2001-03-16 | 2005-09-13 | Corning Incorporated | Dispersion-managed cable for raman-assisted transmission |
| US6628859B2 (en) | 2001-03-22 | 2003-09-30 | Triquint Technology Holding Co. | Broadband mode converter |
| WO2002089363A1 (en) * | 2001-04-27 | 2002-11-07 | Ciena Corporation | Method and system for providing dispersion and dispersion slope compensation |
| JP3908923B2 (en) * | 2001-05-01 | 2007-04-25 | 日本電信電話株式会社 | Optical component, optical component design method, and optical module |
| US6816659B2 (en) * | 2001-06-29 | 2004-11-09 | Pirelli Cavi E Sistemi S.P.A. | Unit for compensating the chromatic dispersion in a reconfigurable manner |
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| FR2838261B1 (en) * | 2002-04-05 | 2004-07-09 | Cit Alcatel | DISPERSION COMPENSATION FIBER USING HIGHER ORDER MODE |
| US6993228B2 (en) * | 2003-08-13 | 2006-01-31 | Corning Incorporated | Dispersion compensated optical fiber transmission system and module including micro-structured optical fiber |
| JP2006145757A (en) | 2004-11-18 | 2006-06-08 | Fujitsu Ltd | Dispersion compensator |
| US8822905B2 (en) * | 2011-09-16 | 2014-09-02 | Alcatel Lucent | Optical mode couplers for multi-mode optical fibers |
| CN103513327B (en) * | 2013-09-11 | 2016-01-27 | 江苏南方通信科技有限公司 | A kind of method for making of bend-insensitive multimode optical fiber |
| FR3025957B1 (en) | 2014-09-11 | 2016-12-23 | Cailabs | CHROMATIC DISPERSION COMPENSATION DEVICE AND METHOD |
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-
1999
- 1999-02-12 US US09/249,920 patent/US6339665B1/en not_active Expired - Fee Related
- 1999-03-26 WO PCT/US1999/006479 patent/WO1999049340A2/en not_active Application Discontinuation
- 1999-03-26 JP JP2000538255A patent/JP2002507874A/en not_active Withdrawn
- 1999-03-26 IL IL13871599A patent/IL138715A0/en unknown
- 1999-03-26 AU AU31146/99A patent/AU3114699A/en not_active Abandoned
- 1999-03-26 EP EP99912881A patent/EP1064572A2/en not_active Withdrawn
- 1999-03-26 CA CA002325881A patent/CA2325881A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO1999049340A3 (en) | 1999-11-25 |
| AU3114699A (en) | 1999-10-18 |
| US6339665B1 (en) | 2002-01-15 |
| US20020001430A1 (en) | 2002-01-03 |
| WO1999049340A2 (en) | 1999-09-30 |
| IL138715A0 (en) | 2001-10-31 |
| EP1064572A2 (en) | 2001-01-03 |
| JP2002507874A (en) | 2002-03-12 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| FZDE | Discontinued |