Abstract: An automatic polarization controller is described that includes an optical input that receives a polarization multiplexed optical pulse train that comprises a first and a second polarized optical pulse train. A dither modulation signal is superimposed on at least one of the first and the second polarized optical pulse trains. A polarization transformer transforms an input polarization state of the polarization multiplexed optical pulse train to an output polarization state in response to a control signal that is applied to a control input of the polarization transformer. A polarization selective element receives the transformed polarization multiplexed optical pulse train and passes a polarized optical pulse train including the dither modulation signal. A detector receives the polarized optical pulse train including the superimposed dither modulation signal and generates a signal that is proportional to the amplitude of the dither modulation signal.

Abstract: An apparatus and method for dynamically optimizing performance in a communication channel are described. The communication channel can be part of a high-speed digital network such as the Internet and can be a dense wavelength-division multiplexed (DWDM) optical communication channel. The DWDM signal includes forward error correction (FEC) information which is added to the DWDM signal and is used within the DWDM optical layer to monitor transfer errors in the data. Error correction statistics generated as a result of analysis of the FEC information in the data in accordance with the invention are used in generating an adjustment to and/or optimizing performance of the system. An adjust signal used in generating and making the adjustment is generated using FEC error correction statistics. In one embodiment, the adjust signal is a feedback signal transferred back to the transmission end of the channel.

Abstract: An apparatus and method for monitoring performance of a communication channel or link are described. Errors in the transfer of data are detected and corrected using forward error correction (FEC). The FEC statistics are monitored to determine conditions related to performance of the system. For example, the number of errors corrected by the FEC can be monitored over predetermined periods of time. Using this approach, certain fading errors which tend to correct themselves over time without intervention can be identified, and costly, time consuming troubleshooting and repair efforts can be avoided. By monitoring the types of errors being corrected, i.e., one-bits or zero-bits, certain particular conditions, such as coherent crosstalk, can be identified. Also, monitoring the FEC statistics, particularly numbers of errors corrected, permits identification of system performance degradation at extremely low error rates, such that a Q-measurement for the system is generated.

Abstract: An exemplary system and method for differential group delay compensation are provided that include a method for differential group delay compensation of an optical signal that increases overall bandwidth and reduces the bit-error-rate of a fiber optic transmission system. The method includes generating a translated polarization signal by translating the wavelength of either or both of a leading polarization signal and a trailing polarization signal of an optical signal. The wavelength(s) is translated by an amount that is related to the delay between the leading polarization signal and the trailing polarization signal. The translated polarization signal may then be introduced, along with the other polarization signal, to an optical fiber, such as a dispersion compensating fiber with high chromatic dispersion, that has the optical property of a group delay that varies with wavelength. This results in the generation of a differential group delay compensated optical signal.