WO2002027364A2 - Tunable grating-based dispersion compensator - Google Patents
Tunable grating-based dispersion compensator Download PDFInfo
- Publication number
- WO2002027364A2 WO2002027364A2 PCT/US2001/030216 US0130216W WO0227364A2 WO 2002027364 A2 WO2002027364 A2 WO 2002027364A2 US 0130216 W US0130216 W US 0130216W WO 0227364 A2 WO0227364 A2 WO 0227364A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- grating
- optical waveguide
- dispersion compensator
- tapered region
- inner core
- Prior art date
Links
Classifications
-
- 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
- G02B6/29304—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 by diffraction, e.g. grating
- G02B6/29305—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 by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
- G02B6/29313—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 by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response
- G02B6/29314—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 by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response by moving or modifying the diffractive element, e.g. deforming
-
- 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
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02195—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating
- G02B6/022—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating using mechanical stress, e.g. tuning by compression or elongation, special geometrical shapes such as "dog-bone" or taper
-
- 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
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02195—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating
- G02B6/02204—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating using thermal effects, e.g. heating or cooling of a temperature sensitive mounting body
-
- 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
- G02B6/29379—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 characterised by the function or use of the complete device
- G02B6/29392—Controlling dispersion
- G02B6/29394—Compensating wavelength dispersion
Definitions
- the present invention relates to dispersion compensators, and more particularly to a tunable dispersion compensator based on a Bragg grating that allows the dispersion characteristics of a Bragg grating element to be tuned.
- Fiber Bragg gratings can be used as effective filter elements in a range of applications in optical communications networks.
- the dispersion characteristics of a communication link are crucial in determining performance and transmission fidelity.
- Gratings, particularly chirped gratings can be used effectively for dispersion compensation.
- the ability to tune the dispersion introduced by a grating element is important in providing an adjustable element for performance optimization.
- All-optical networks in which communications signal are dynamically routed in the optical domain.
- One of the issues that affect the ability of network engineers to increase transmission distances & data rates is signal impairments.
- One of the important parameters of a link is the dispersion of the system, which can create a serious deleterious effect on the signal quality in a high-Gbit optical transmission systems such as 10 Gbits/s and 40 Gbits/s.
- FIG. 1 depicts a known optical transmission system 10.
- Optical data 12 which is generated by a laser transmitter 14, is transmitted along a fiber link 16, that may or may not contain optical amplifiers and other devices (that may in themselves be dispersive) to a receiver 18.
- the optical data is transmitted along the fiber link 16, that may or may not contain optical amplifiers and other devices (that may in themselves be dispersive) to a receiver 18.
- the optical data is transmitted along the fiber link 16 that may or may not contain optical amplifiers and other devices (that may in themselves be dispersive) to a receiver 18.
- the differential group delay in a signal can be compensated for by the use of an appropriately chirped grating 22.
- the light (or received bit stream) 20 from the fiber link 16 is coupled though a circulator 24 to a chirped grating 22.
- the chirped grating 22 has a bandwidth B and length L. The chirping of the grating 22 results in a strong group delay that can be chosen to be equal to, but opposite to that of the fiber link 16.
- the differential group delay for a wavelength component reflected from the front of the grating compared to one reflected from the rear of the grating is ⁇ 1000 ps. If the grating has a bandwidth of 1 nm, then it's effective dispersion is 1000 ps/nm.
- the grating 22 has to be designed to match a given dispersion induced group delay error in a communications link. Summary of the Invention
- An object of the present invention is to provide a tunable dispersion compensator having a Bragg grating that allows the dispersion characteristics of a Bragg grating element to be tuned.
- an optical waveguide includes an outer cladding disposed about an inner core.
- a portion of the cladding of the waveguide includes a tapered region.
- the cladding has a minimum cross-sectional dimension of 0.3 mm.
- a chi ⁇ ed grating is written in the inner core of the tapered region of the cladding.
- a tunable dispersion compensator in accordance with another embodiment of the present invention, includes an optical waveguide having an outer cladding disposed about an inner core. A portion of the cladding has a tapered region. The cladding has a minimum cross-sectional dimension of 0.3 mm. A chirped grating is written in the inner core of the tapered region of the cladding.
- FIG. 1 is a block diagram of an optical transmission system including a Bragg grating-based dispersion compensator that is known in the art
- FIG. 2 is a side view of a tunable dispersion compensating device in accordance with the present invention
- FIG. 3 is a side view of a grating element of a tunable dispersion compensating device having a chi ⁇ ed grating written in a first "sense" in accordance with the present invention
- FIG. 4 is a graphical representation of the chi ⁇ rate of the grating element of FIG. 3 as the grating is longitudinally compressed;
- FIG. 5 is a graphical representation of the reflectivity profile of the grating element of FIG. 3 when no compressional load is applied;
- FIG. 6 is a graphical representation of the reflectivity profile of the grating element of FIG. 3 when a compressional load is applied;
- FIG. 7 is a side view of a grating element of a tunable dispersion compensating device having a chi ⁇ ed grating written in a second "sense" in accordance with the present invention
- FIG. 8 is a graphical representation of the chi ⁇ rate of the grating element of FIG. 7 as the grating is longitudinally compressed;
- FIG. 9 is a side view of an alternative embodiment of a grating element in accordance with the present invention.
- FIG. 10 is a side view of an alternative embodiment of a grating element in accordance with the present invention.
- a tunable dispersion compensating device generally shown as
- the 100 comprises an optical Bragg grating element 102, best shown in FIG. 3.
- the grating element 102 is a bulk or large diameter waveguide, having an outer cladding 104 disposed about an inner core 106.
- the grating element may be etched, grounded or machined to form a generally "dog bone" shape, wherein the end portions 108 of the grating element has a larger diameter than the center portion 110 disposed therebetween.
- a chi ⁇ ed grating 112 is written or impressed within the portion of the core 106 disposed in the center portion 110 of the grating element 102.
- the center portion 110 is machined into a tapered form to allow different stresses to be applied along the grating length when the grating element 102 is compressed longitudinally by force F.
- the cross-sectional area of the center portion 110 of the grating element 102 is gradually reduced from one value to a second value in a linear fashion.
- the outer diameter of the center portion tapers from one end to the other as a function of the square rot of the distance such that longitudinal compression of the element results in a linear increase in wavelength tuning of the chi ⁇ ed grating 112 along its length.
- the grating element 102 depicted in FIG. 3 wherein the sense of the chi ⁇ ed grating 112 results in the Bragg wavelength increasing from left to right as depicted.
- the spacing of the gratings at the wide end of the center portion of the grating element is greater than the spacings of the gratings at the narrower end.
- the physical taper in the grating element 102 results in the longer wavelength having a higher sensitivity to compression load than the shorter wavelengths. Consequently, referring to Fig. 4, as the grating element is compressed longitudinally by force F, the grating chi ⁇ rate 114 a-c decreases.
- FIG. 5 shows that the chi ⁇ bandwidth 113 of the grating element 102 is relatively wide, when no compressional load is applied.
- FIG. 6 shows that the chi ⁇ ed bandwidth 115 of the grating 102 is reduced and the center wavelength 0 is shifted to ⁇ d , when a compressional load is applied.
- the original chi ⁇ may be written into the grating element 102 in the opposite sense, wherein the sense of the. chi ⁇ ed grating results in the Bragg wavelength increasing from right to left as depicted.
- the spacing of the gratings at the wide end of the center portion 112 of the grating element 102 is less than the spacings of the gratings at the narrower end.
- the physical taper in the grating element results in the shorter wavelengths having a higher sensitivity to compression load than the longer wavelengths. Consequently, referring to FIG. 8, as the grating is compressed longitudinally by force F, the grating chi ⁇ rate 120a-c increases. Conversely to the grating element of FIG.
- one limitation of this approach is the compressional tuning also tunes or shifts the overall center wavelength ⁇ co of the grating 112. This can cause an issue if the grating bandwidth does not overlap that of the signal at all times and over it's tunable range. This can be compensated by thermal tuning of the grating element, as shown in broken lines at 121 in FIG. 6. Thermal tuning would allow correction of any center wavelength caused by compressional tuning. Thermal tuning could be effected using either heating elements or peltier (TEC) cooler/heater elements 122, as shown in FIG. 2.
- TEC peltier
- the optical grating element 102 of the tunable dispersion compemsating device 100 is disposed within a compressing device or housing 124.
- the grating element comprises silica glass (SiO2) having the appropriate dopants, as is known, to allow light to propagate along the inner core, and has an outer diameter (d) of at least 0.3mm.
- the grating element 102 may be formed by using fiber drawing techniques now know or later developed that provide the resultant desired dimensions for the core and the outer dimensions, similar to that disclosed in co-pending US Patent Application, Serial No. 09/455,868 entitled "Large Diameter Optical Waveguide, Grating, and Laser".
- the grating element 102 may then be etched, grounded or machined to form the "dogbone” shape.
- a pair of fibers or "pigtails" 126 may be attached to the ends of the grating element by known techniques, such as epoxy or glass fusion.
- the optical grating element 102 may be formed by heating, collapsing and fusing a glass capillary tube to a fiber by a laser, filament, flame, etc., as is described in copending US Patent Application, Serial No. 9/455,865, entitled “Tube-Encased Fiber Grating", which is inco ⁇ orated herein by reference.
- Other techniques may be used for collapsing and fusing the tubes to the fiber, such as is discussed in US Patent No. 5,745,626, entitled “Method For And Encapsulation Of An Optical Fiber", to Duck et al., and/or US Patent No.
- the chi ⁇ ed Bragg grating 112 is written (embedded or imprinted) into the inner core 106 of the grating element 102.
- the Bragg grating 112 reflects a portion of the light as indicated by a line 128, and passes the remaining wavelengths of the incident light (within a predetermined wavelength range), as indicated by a line 130.
- the chi ⁇ ed grating 112, as is known, is an aperiodic variation in the effective refractive index and/or effective optical abso ⁇ tion coefficient of an optical waveguide, such as that described in US Patent No. 4,725,110 and 4,807,950, entitled “Method for Impressing Gratings Within Fiber Optics", to Glenn et al; and US Patent No. 5,388,173, entitled “Method and Apparatus for Forming Aperiodic Gratings in Optical Fibers", to Glenn, which are hereby inco ⁇ orated by reference to the extent necessary to understand the present invention.
- any wavelength-tunable grating or reflective element 112 embedded, written, etched, imprinted, or otherwise formed in the inner core 106 may be used if desired.
- the term “grating” means any of such reflective elements.
- the optical grating element 102 may be made of any glass, e.g., silica, phosphate glass, or other glasses, or made of glass and plastic, or solely plastic.
- An actuator 132 such as a piezoelectric actuator, axially compresses the grating element 102 within the compression device or housing 124, as indicated by arrows 134. Accordingly, the PZT actuator 132 provides a predetermined amount of force to compress the grating element 102, and thereby tune the grating 112 to a desired center wavelength. In response to a control signal generated by a controller 136 via conductor 138, the PZT actuator 132 is energized to provide the appropriate compression force necessary to tune the grating element to the desired chi ⁇ (i.e., bandwidth and center wavelength of reflectivity profile) of the grating 112.
- chi ⁇ i.e., bandwidth and center wavelength of reflectivity profile
- the controller 136 adjusts the expansion and retraction of the actuator 132 in response to a displacement sensor 140 that provides feedback representative of the strain or compression of the grating element 102 to form a non-optical closed-loop control configuration.
- a displacement sensor 140 that provides feedback representative of the strain or compression of the grating element 102 to form a non-optical closed-loop control configuration.
- light 12 propagating through the network or device is not used to provide feedback for the tuning of the grating 112.
- the displacement sensor 140 includes a pair of capacitive elements 142, similar to that disclosed in co-pending US Patent Application, Serial No.
- the controller measures the capacitance between the capacitive plates 144; and provides a sensed signal via conductors 146, indicative of the measured capacitance, to the controller 136.
- the gap between the parallel capacitive plates 144 will vary, thereby causing the capacitance to change correspondingly.
- the change in capacitance may be directly or inversely proportional to the change in the chi ⁇ of the grating 112, depending on the sense of the chi ⁇ ed grating.
- the invention has been described with respect to using a capacitor to measure the gap distance, it should be understood by those skilled in the art that other gap sensing techniques may be used, such as inductive, optical, magnetic, microwave, time-of- flight based gap sensors. Moreover, the scope of the invention is also intended to include measuring or sensing a force applied on or about the compressive element, and feeding it back to control the compression tuning of the optical structure. While the embodiment of the present invention described hereinbefore includes means to provide feedback of the displacement of the grating element 54, one should recognize that the grating units may be accurately and repeatedly compressed/tuned to allow the grating unit to operate in an open loop mode.
- the grating 112 may be tuned by mechanically stressing (i.e. tension, bending) the grating elements 102.
- mechanically stressing i.e. tension, bending
- the grating 112 has been described as being within a grating element 102 in the form of a bulk waveguide, one will appreciate that the grating may be written into a fiber, wherein the grating may be toned thermally or mechanically (compression or tension).
- FIG. 9 shows another embodiment of a grating element 160 similar to the grating element 102 of Fig. 3. Contrary to grating element 102, the taper of the center portion 110 of grating element 160 is linear and the grating 162 is periodic. Consequently, as the grating elements are longitudinally compressed, the grating becomes variably chi ⁇ ed and provides a quadratic chi ⁇ in the grating.
- Fig. 10 shows yet another embodiment of a grating element 170 similar to the grating element 102 in Fig. 3. Contrary to grating element 102, the grating 172 of grating element 170 is periodic such that the grating becomes linearly chi ⁇ ed as the grating element 170 is longitudinally compressed.
- the dimensions and geometries for any of the embodiments described herein are merely for illustrative pu ⁇ oses and, as much, any other dimensions may be used if desired, depending on the application, size, performance, manufacturing requirements, or other factors, in view of the teachings herein.
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Chemical & Material Sciences (AREA)
- Dispersion Chemistry (AREA)
- Mechanical Light Control Or Optical Switches (AREA)
- Light Guides In General And Applications Therefor (AREA)
- Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP01977205A EP1322979A2 (en) | 2000-09-28 | 2001-09-27 | Tunable grating-based dispersion compensator |
JP2002530887A JP2004510195A (en) | 2000-09-28 | 2001-09-27 | Tunable dispersion compensator with diffraction grating |
AU2001296341A AU2001296341A1 (en) | 2000-09-28 | 2001-09-27 | Tunable grating-based dispersion compensator |
CA002424032A CA2424032A1 (en) | 2000-09-28 | 2001-09-27 | Tunable grating-based dispersion compensator |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US67545500A | 2000-09-28 | 2000-09-28 | |
US09/675,455 | 2000-09-28 |
Publications (2)
Publication Number | Publication Date |
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WO2002027364A2 true WO2002027364A2 (en) | 2002-04-04 |
WO2002027364A3 WO2002027364A3 (en) | 2003-03-06 |
Family
ID=24710569
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/US2001/030216 WO2002027364A2 (en) | 2000-09-28 | 2001-09-27 | Tunable grating-based dispersion compensator |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP1322979A2 (en) |
JP (1) | JP2004510195A (en) |
AU (1) | AU2001296341A1 (en) |
CA (1) | CA2424032A1 (en) |
WO (1) | WO2002027364A2 (en) |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1996026458A2 (en) * | 1995-02-22 | 1996-08-29 | Pirelli Cavi S.P.A. | Chirped optical fibre grating |
WO2000037969A2 (en) * | 1998-12-04 | 2000-06-29 | Cidra Corporation | Compression-tuned bragg grating and laser |
EP1024376A1 (en) * | 1999-01-26 | 2000-08-02 | Lucent Technologies Inc. | Optical grating device with variable coating |
-
2001
- 2001-09-27 AU AU2001296341A patent/AU2001296341A1/en not_active Abandoned
- 2001-09-27 JP JP2002530887A patent/JP2004510195A/en active Pending
- 2001-09-27 CA CA002424032A patent/CA2424032A1/en not_active Abandoned
- 2001-09-27 EP EP01977205A patent/EP1322979A2/en not_active Withdrawn
- 2001-09-27 WO PCT/US2001/030216 patent/WO2002027364A2/en not_active Application Discontinuation
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1996026458A2 (en) * | 1995-02-22 | 1996-08-29 | Pirelli Cavi S.P.A. | Chirped optical fibre grating |
WO2000037969A2 (en) * | 1998-12-04 | 2000-06-29 | Cidra Corporation | Compression-tuned bragg grating and laser |
EP1024376A1 (en) * | 1999-01-26 | 2000-08-02 | Lucent Technologies Inc. | Optical grating device with variable coating |
Non-Patent Citations (2)
Title |
---|
PUTNAM M A ET AL: "Fabrication of tapered, strain-gradent chirped fibre Bragg gratings" ELECTRONICS LETTERS, IEE STEVENAGE, GB, vol. 31, no. 4, 16 February 1995 (1995-02-16), pages 309-310, XP006002436 ISSN: 0013-5194 * |
SHIN D ET AL: "Design and implementation of PCB-type capacitance displacement sensor collocated with magnetic bearings" SENSORS AND ACTUATORS A, ELSEVIER SEQUOIA S.A., LAUSANNE, CH, vol. 71, no. 3, 1 December 1998 (1998-12-01), pages 223-229, XP004140100 ISSN: 0924-4247 * |
Also Published As
Publication number | Publication date |
---|---|
JP2004510195A (en) | 2004-04-02 |
AU2001296341A1 (en) | 2002-04-08 |
WO2002027364A3 (en) | 2003-03-06 |
CA2424032A1 (en) | 2002-04-04 |
EP1322979A2 (en) | 2003-07-02 |
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