Feedback-controlled coherent optical receiver with electrical compensation/equalization

An optical coherent receiver comprising:

• a series connected subsystem successively including an input signal processor driving an optical coupler, the latter driving a post coupler optical processor, the latter driving a balanced optical-to-electrical (OE) converter, the latter driving an RF processor, the latter driving a baseband RF/EDC (Electronic Dispersion Compensation/Equalization) processor, the latter providing an RF output signal from said receiver;
• a first closed loop subsystem including a peak detector connected between said RF processor and said post coupler optical processor;
• a second closed loop subsystem including a frequency and phase lock network (FPL) driven by said RF processor, an optical local oscillator (LO) driven by the said FPL, and an optical LO processor driven by said optical LO, said optical LO processor driving said optical coupler;
• a third closed loop subsystem including said RF processor driving an autoscan, the latter driving said optical LO;
• said input signal processor being operative for receiving and processing a modulated optical input signal to provide a stable polarized optical output signal Esig;
• said optical coupler being independently receptive of Esig, and an optical reference signal ELO, for providing a plurality of output signals each of which are a combination of Esig and ELO, and each of which are phase shifted from one another;
• said post coupler optical processor being independently receptive of said plurality of output signals from said optical coupler, respectively, for both processing these signals via included fiber stretching means for equalizing the path lengths thereof and providing the same as a plurality of path length equalized optical output signals, and for providing an optically derived RF feedback signal to said optical coupler for causing the ratios between any two of the plurality of output signals therefrom to be of a given value;
• said balanced optical-to-electrical (OE) converter being receptive of said plurality of path length equalized optical output signals, for converting these signals into at least one RF output signal;
• said RF processor being receptive of said at least one RF output signal for providing a first RF feedback signal that is peak detected via said peak detector to drive said fiber stretching means of said post coupler optical processor to maintain the equalization of said plurality of path length equalized optical signals, for further providing a second RF feedback signal to said autoscan for driving the latter to produce an output signal therefrom for temperature correcting said optical LO, for further providing a third RF feedback signal to drive said frequency and phase lock module to control the phase and frequency of said optical LO, whereby the phase of the latter is locked to the phase of said optical input signal, and for providing a baseband output signal;
• said baseband RF/EDC processor being receptive of said baseband output signal for processing the same to compensate for both noise and transmission impairments of this signal, and for producing the RF output signal of said receiver;
• said peak detector being receptive of an RF signal from said RF processor, for providing a control output signal representative of the peak of the RF output signal, for controlling said post coupler optical processor to insure optimal coupling ratio;
• said FPL being receptive of an RF error signal from said RF processor, for providing a drive output signal for controlling said optical LO to align its frequency/phase to the modulated input signal;
• said optical LO being operative to produce an optical output signal for driving said optical LO processor to produce said ELO reference signal;
• and
• said autoscan being receptive of a filtered IF signal from said RF processor for detecting, tracking, and locking onto said optical input signal.