Patent ID: 7460793

Claim:
A coherent optical detection system receiving an incoming optical signal in an optical communications network, said system comprising: a local oscillator emitting light; a phase diverse hybrid for generating two replicas of the incoming signal and two replicas of the local oscillator light, said phase diverse hybrid combining the first replica of the incoming optical signal and the first replica of the local oscillator light into a first output and combining the second replica of the incoming optical signal and the second replica of the local oscillator light into a second output and wherein said local oscillator does not have to be phase locked to the incoming optical signal; wherein the phase relationship between the optical signal and the local oscillator light in the first output is different from 0 degrees and different from 180 degrees compared to the phase relationship between the local oscillator light and the optical signal in the second output and the state of polarization of the optical signal relative to the local oscillator light in the first output is not orthogonal to the state of polarization of the optical signal relative to the local oscillator light in the second output; and two photodetectors communicating with the phase diverse hybrid, wherein said two photodetectors receive optical signals from the two outputs and convert them to electrical signals; the electrical signals received by the two photodetectors are digitized by two A/D converters to create digital values; and a digital signal processor multiplies the digital values from the two A/D converters by two coefficients and sums them to form a complex number, then multiplies the complex number by a rotating phase factor to provide a complex representation of the envelope of the electric field of the incoming optical signal or a component of the complex representation of the envelope of the electric field of the incoming optical signal, the rotating phase factor having a frequency and a phase equal to estimates of the frequency and the phase of the incoming optical signal with respect to the local oscillator light.