Constrained continuous phase modulation and demodulation in an optical communications system

摘要

A transmitter in an optical communications system includes a digital signal processor for processing a data signal to generate a sample stream encoding successive symbols in accordance with a constrained phase modulation scheme having a constellation of at least two symbols and a modulation phase constrained to a phase range spanning less than 4π. A digital-to-analog converter converts the sample stream into a corresponding analog drive signal. A finite range phase modulator modulates a phase of a continuous wavelength channel light in accordance with the analog drive signal, to generate a modulated channel light for transmission through the optical communications system. A receiver in the optical communications system includes an optical stage for detecting phase and amplitude of the modulated channel light and for generating a corresponding sample stream, and a digital signal processor for processing the sample stream to estimate each successive symbol of the modulated channel light.

主权项

1. A receiver for use in an optical communications system, the receiver comprising:
an optical stage configured to detect phase and amplitude of a modulated channel light received through the optical communications system to generate a corresponding multi-bit digital sample stream, wherein the modulated channel light comprises a stream of symbols defined by a constrained phase modulation scheme having a constellation of at least two symbols and in which a modulation phase is constrained to a phase range spanning less than 4π; and a digital signal processor configured to process the multi-bit digital sample stream to recover an estimate of each successive symbol of the modulated channel light, the digital signal processor comprising:
a dispersion compensator configured to process the multi-bit digital sample streams to compensate dispersion impairments of the received modulated channel light;a 2×2 Multiple Input Multiple Output (MIMO) channel equalizer configured to process dispersion compensated sample streams output from the dispersion compensator to compensate polarization impairments of the received modulated channel light; anda feedback loop configured to steer the 2×2 MIMO channel equalizer using estimated values of received data symbols as a target, wherein the feedback loop comprises:
a programmable target filter configured to filter the estimated values of received data symbols to generate a target signal;a comparator configured to generate an error signal based on the target signal and an output of the 2×2 MIMO channel equalizer; anda coefficient calculator configured to calculate a set of equalization coefficients for the 2×2 MIMO channel equalizer based on the error signal.