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US 6,330,383 B1Granted
Disperson compensation by using tunable nonlinearly-chirped gratings
AssigneeUniversity of Southern California
InventorsJin-Xing Cai, Kai-Ming Feng, Alan E. Willner, Jiangde Peng, Sanggeon Lee, Reza Khosravani
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Abstract
A nonlinearly chirped fiber grating for achieving tunable dispersion compensation, dispersion slope compensation, polarization mode dispersion, chirp reduction in directly modulated diode lasers, and optical pulse manipulation. A dynamical dispersion compensation mechanism can be implemented in a fiber communication system based on such a nonlinearly chirped fiber grating.
Claims80
A device, comprising:
- a wave-guiding element having an optic axis and adapted to transport optical energy along said optic axis;
- a first grating formed in said wave-guiding element along said optic axis to have a varying grating period that changes as a nonlinear function of a position along said optic axis so as to change relative time delays of different spectral components in said optical energy;
- a second grating formed in said wave-guiding element along said optic axis to have a grating period that is different than said varying grating period,
- wherein said first grating and said second grating spatially overlap each other in said wave-guiding element and operate in combination to produce a plurality of reflection bands centered at different wavelengths.
1 more element
A device, comprising:
- a wave-guiding element having an optic axis to transport optical energy along said optic axis, said wave-guiding element having a refractive index that varies along said optic axis according to a combination of a first spatial modulation and a second spatial modulation, wherein said first spatial modulation is an oscillatory variation with a nonlinearly-chirped period along said optic axis and said second spatial modulation is a periodic modulation with a period different than said nonlinearly-changing period;
- and
- a control unit engaged to said wave-guiding element and operable to change a property of said first spatial modulation in said wave-guiding element along said optic axis,
- wherein said first and second spatial modulations in said refractive index operate in combination to produce a plurality of reflection bands at different wavelengths and to change relative time delays of reflected optical signals of different wavelengths.
1 more element
A device for changing relative time delays of different wavelength channels in a wavelength-division-multiplexed (WDM) optical signal, comprising:
- a WDM unit operable to output a WDM signal;
- an optical routing unit, connected to said WDM unit to receive said WDM signal;
- a dispersion-compensating unit, connected to said optical routing unit to receive said WDM signal and operable to change dispersions of different wavelength channels in said WDM signal to produce a modified WDM signal, said dispersion-compensating unit comprising:
- a wave-guiding element having an optic axis to transport optical energy along said optic axis, said wave-guiding element having a spatial variation pattern along said optic axis according to a combination of a first spatial modulation and a second spatial modulation, wherein said first spatial modulation is an oscillatory variation with a nonlinearly-chirped period along said optic axis and said second spatial modulation is a periodic modulation with a period different than said nonlinearly-changing period;
- and
- a control unit engaged to said wave-guiding element and operable to change a property of said wave-guiding element along said optic axis,
- wherein said first and second spatial modulations in said refractive index operate in combination to produce a plurality of reflection bands at different wavelengths and to change relative time delays of reflected optical signals of different wavelengths.
4 more elements
A device operable to change relative time delays of two different polarizations in an optical signal, comprising:
- a wave-guiding element having an optic axis to transport optical energy along said optic axis and configured to exhibit birefringence for polarizations along first and second axes that are substantially perpendicular to said optic axis;
- a grating formed in said wave-guiding element along said optic axis to have a varying grating period that changes nonlinearly along said optic axis to change relative delays in reflected spectral components in said optical energy,
- wherein said grating and said birefringence operate in combination to reflect two polarizations of said optical energy along said first and said second axes at different locations along said optic axis to cause a delay between said two polarizations.
A device, comprising a plurality of nonlinearly-chirped fiber gratings connected with one another to respectively receive different wavelength channels in an optical wavelength-division-multiplexed (WDM) signal, said fiber gratings respectively configured to reflect optical signals within specified, different spectral bandwidths to produce different delays in different reflected wavelength channels so that a modified WDM signal comprising said reflected wavelength channels has reduced dispersion, wherein each fiber grating comprises:
- a segment of optical fiber having a fiber grating formed along said fiber, said fiber grating having a grating period that nonlinearly changes along said fiber to effect different delays at different positions for reflected optical waves of different wavelengths that are Bragg phase-matched, within a selected spectral bandwidth;
- and
- a fiber control unit, engaged to said fiber grating and configured to change a property of said fiber grating to produce a change in relative delays of said reflected optical waves at said different wavelengths.
A fiber device, comprising:
- a fiber structured to include a fiber core to guide optical energy along said optical core;
- a fiber grating formed in said fiber core to include a spatial variation pattern along said fiber core which combines a first spatial modulation and a second spatial modulation that spatially overlap each other, said first spatial modulation including an oscillatory variation with a nonlinearly-chirped period along said fiber core and said second spatial modulation including a periodic modulation with a period different than said nonlinearly-changing period, wherein said fiber grating is operable to interact with said optical energy to produce a plurality of reflection bands at different wavelengths;
- and
- a control unit engaged to said fiber and operable to control said spatial variation pattern of said fiber grating to change relative time delays of reflected optical signals of different wavelengths in different reflection bands.
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A method for compensating dispersion in an optical WDM system, comprising:
- directing a WDM signal with a plurality of WDM channels at different WDM wavelengths into a fiber which has a fiber grating, said fiber grating having a spatial variation pattern formed of a first spatial modulation and a second spatial modulation that spatially overlap each other, said first spatial modulation including an oscillatory variation with a nonlinearly-chirped period along said fiber and said second spatial modulation including a periodic modulation with a period greater than said nonlinearly-changing period, wherein said fiber grating is operable to interact with said optical energy to produce a plurality of reflection bands at different wavelengths;
- monitoring dispersion in said WDM signal to produce a monitor signal indicating the dispersion;
- and
- adjusting said fiber grating to make a change in said spatial variation pattern according to the monitor signal to change relative time delays of different reflected spectral components in said WDM signal to reduce the dispersion.
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A method for compensating time-varying polarization-mode dispersion in optical fibers, comprising:
- directing an optical signal from a fiber transmission system into a fiber grating which is formed in a fiber with optical birefringence for polarizations along first and second axes that are substantially perpendicular to said fiber, said fiber grating having a nonlinear spatial pattern with a nonlinearly-chirped grating period along said fiber;
- using the optical birefringence along the first and the second axes to produce different delays in reflected signals of different polarizations along the first and the second axes;
- and
- adjusting the nonlinear spatial pattern in said fiber grating to tune relative delays of different spectral components in each polarization state and to shift the wavelength of each reflected spectral component to compensate for time-varying polarization-mode dispersion in said fiber transmission system.
1 more element
Dependencies are inferred from the claim text.