A distortion analyzer for generating a distortion signal based on an input signal. For example, the distortion signal may be generated by adding a first signal corresponding to the entire spectrum of the input signal to a second signal corresponding to a low-frequency component of the input signal and then subtracting from the result of addition a third signal corresponding to a specific frequency band of the input signal. The effect of polarization mode dispersion that an optical signal experiences as it propagates through an optical transmission fiber may be compensated for at a receiver using a birefringent compensator, in which the distortion analyzer continuously examines the signal outputted by the compensator and supplies the distortion signal to the compensator, which causes the compensator to reduce the effect of such polarization mode dispersion based on the level of the distortion signal.
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a divisional of U.S. patent application Ser. No. 09/465,152, now U.S. Pat. No. 6,330,375B1, filed on Dec. 16, 1999, the teachings of which are incorporated herein by reference.
A polarization scrambler and a polarization mode dispersion (PMD) compensation system compensate for PMD on an active optic fiber. The polarization scrambler scrambles a state of polarization of an optical signal that carries user information. The PMD compensation system then receives the optical signal over the active optic fiber. The PMD compensation system measuring a differential group delay and principal states of polarization of the PMD in the active optic fiber. The PMD compensation system then determines a modification of the optical signal based on the differential group delay and the principal states of polarization of the PMD. The PMD compensation system modifies the optical signal in the active optic fiber to compensate for PMD based on the determination of the modification. The PMD compensation system then transmits the optical signal. By measuring the differential group delay and the principal states of polarization, the PMD compensation system adapts to changes in the PMD in the active optic fiber.
A method and apparatus for utilizing tunable differential group delay with at least a component of a fiber optic transmission system includes providing a tunable differential group delay system that is optically connected to a component of the fiber optic transmission system. The tunable differential group delay system is then controlled to insert differential group delay into the component of the fiber optic transmission system.
The present invention relates to a spectrometer module comprising an input, for receiving an incoming optical signal, a variable differential group delay (DGD) element, for applying a variable birefringence retardation to said incoming optical signal, and a detector unit for detecting the power of a signal exiting said variable DGD element, having a defined state of polarization. It also relates to a monitor module, a monitoring unit and a monitoring system, comprising such a spectrometer module for use in monitoring an optical network. Further, the invention relates to a spectrometer device, for spectrometry purposes, comprising a spectrometer module as stated above.
A polarization stabilizing device and method based on controlling the phase retardation of a pair of variable phase retarders with a controller such that the first of the variable retarders has its phase retardation switched between first and second values whenever the phase retardation of the second of the variable retarders reaches an upper or a lower limit. The upper and lower limits of the second retarder and the first and second values of the first retarder are chosen so that discontinuities in the power of the output optical signal are avoided when the first variable retarder is switched, thereby providing endless polarization stabilization using phase retarders that themselves have only limited retardation ranges.
