Coherent optical receiver with linear XOR phase detection and frequency down-conversion

A novel optical coherent receiver architecture for linear optical phase modulation based on mixed signal circuit concepts is presented. This approach relies on heterodyne optical-to-RF down-conversion and linear RF phase demodulation using an XOR gate, generating a linear phase response over +/-pi/2 modulation depth. Adding digital frequency division by a factor n before the phase detector increases the linear range n-fold. Further, the coherent receiver is shown to perform frequency down-conversion in a linear manner. A first proof-of-principle discrete components demonstration has been performed to verify the frequency division architecture.