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US 6,654,105 B2Granted
Cross-correlating PMD detector
AssigneeCorning Applied Technologies Corporation
InventorsFeiling Wang, Xiao-Li Li, Yingyin Zou, Wei Hu
Life of this patent
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Abstract
A polarization mode dispersion center (306) measures PMD impairment through the cross-correlation of optical pulses. A second variable phase retarder plate (504) is oriented with polarization eigenstates at preferably 45 degree angle with respect to those eigenstates of a first variable phase retarder plate (502) to provide controllable phase retardations that can be varied and measured as an indication of PMD impairment.
Claims18
A polarization mode dispersion (PMD) detector for measuring PMD impairment through the cross-correlation of optical pulses of a light wave for controlling one or more polarization transformers and a plurality of differential group delay elements in a PMD compensator, the detector comprising:
- a first variable phase retarder having a first controllable phase retardation exerted between a pair of orthogonal polarization components of the light wave in a fast axis and a slow axis of the first variable phase retarder;
- a second variable phase retarder oriented at a 45-degree angle with respect to the first variable phase retarder such that the second variable phase retarder has polarization eigenstates oriented at a 45-degree angle with respect to the polarization eigenstates of the first variable phase retarder, the second variable phase retarder having a second controllable phase retardation exerted between a pair of orthogonal polarization components of the light wave in a fast axis and a slow axis of the second variable phase retarder,
- wherein the first and second variable phase retarders each comprises a solid-state ferroelectric variable waveplate having electrode pairs for the application of applied voltages that facilitate the application of variable electric fields perpendicular to the light propagation direction, the electric field in each of the waveplate defining the direction of the slow axis in each of the waveplate and causing the first phase retardation and the second phase retardation that are independently controlled through the applied voltages across the electrode pairs;
- a linear polarizer optically coupled to the second variable phase retarder, the polarizer having a polarization direction parallel to the first variable phase retarder;
- a low-speed photodetector optically coupled with the polarizer for sensing the intensity of the light wave transmitted through the linear polarizer as a measure of PMD impairment through the cross-correlation of optical pulses of the light wave;
- and
- a controller for varying the first controllable phase retardation of the first variable phase retarder and for varying the second controllable phase retardation of the second variable phase retarder to minimize the measure of PMD impairment and for controlling the at least one polarization transformer and the plurality of differential group delay elements, in response to the measure of PMD impairment.
4 more elements
A polarization compensator for compensation of polarization mode dispersion (PMD)-induced distortion of a light wave in transmission fibers of an optical transmission system, the compensator comprising:
- a plurality of differential group delay elements for adjusting PMD values;
- at least one polarization transformer for coupling the light wave to the plurality of differential group delay elements to provide endless compensation of the PMD-induced signal distortion such that the at least one polarization transformer has sufficient degrees of freedom, image-forming the two PSPs of the fiber being compensated onto the PSPs of the plurality of differential group delay elements, without settling at a local minimum of the overall PMD;
- a polarization mode dispersion detector for measuring PMD-induced impairment through the cross-correlation of optical pulses of the light wave, the detector comprising:
- a first variable phase retarder having a first controllable phase retardation exerted between a pair of orthogonal polarization components of the light wave in a fast axis and a slow axis of the first variable phase retarder;
- a second variable phase retarder oriented at a 45-degree angle with respect to the first variable phase retarder, the second variable phase retarder having a second controllable phase retardation exerted between a pair of orthogonal polarization components of the light wave in a fast axis and a slow axis of the second variable phase retarder
- wherein the first and second variable phase retarders each comprises a solid-state ferroelectric variable waveplate having electrode pairs for the application of applied voltages that facilitate the application of variable electric fields perpendicular to the light propagation direction, the electric field in each of the waveplate defining the direction of the slow axis in each of the waveplate and causing the first phase retardation and the second phase retardation that are independently controlled through the applied voltages across the electrode pairs;
- a linear polarizer optically coupled to the second variable phase retarder, the linear polarizer having a polarization direction parallel to the first variable phase retarder;
- a low-speed photodetector optically coupled with the polarizer for sensing the intensity of the light transmitted through the linear polarizer;
- and
- a controller for varying the first controllable phase retardation of the first variable phase retarder and for varying the second controllable phase retardation of the second variable phase retarder to minimize the measure of PMD impairment and for controlling the at least one polarization transformer and the plurality of differential group delay elements, in response to the measure of PMD impairment such that the endless compensation of the PMD-induced signal distortion results.
7 more elements
A method for detecting polarization mode dispersion (PMD) impairment, the method comprising the steps of:
- providing first and second variable phase retarders each comprising a solid-state ferroelectric variable wavep late having electrode pairs for the application of applied voltages that facilitate the application of variable electric fields perpendicular to the light propagation direction, the electric field in each of the waveplate defining the direction of the slow axis in each of the waveplate and causing the first phase retardation and the second phase retardation that are independently controlled through the applied voltages across the electrode pairs;
- varying a first controllable phase retardation exerted between a first pair of orthogonal polarization components of the light wave in a fast axis and a slow axis of a the first variable phase retarder;
- orienting the second variable phase retarder at a 45-degree angle with respect to the first variable phase retarder;
- varying a second controllable phase retardation exerted between a second pair of orthogonal polarization components of the light wave in a fast axis and a slow axis of the second variable phase retarder;
- linear polarizing the first and second pairs of orthogonal polarization components of the light wave that are aligned at a 45-degree angle with each other in a polarized direction parallel to the first pair for cross-correlating the optical pulses of the light wave;
- sensing the intensity of the cross-correlation as a measure of PMD impairment;
- and
- controlling the first controllable phase retardation of the first and second variable phase retarders to minimize the measure of PMD impairment and for controlling at least one polarization transformer and a plurality of differential group delay elements, in response to the measure of PMD impairment.
5 more elements
Dependencies are inferred from the claim text.