All-Optical Coherent Receiver with Feedback and Sampling

To obtain higher linearity in an analog photonic link, a novel coherent receiver design with feedback is proposed and demonstrated, where the linearity and signal-to-noise-ratio (SNR) tradeoff associated with a traditional phase demodulator can be eliminated. The local phase modulator in the feedback loop of the receiver tracks the phase change of the incoming signal and reduces the effective swing of the phase demodulator, leading to better linearity without reducing the strength of the transmitted signal. Thus, the SNR of the demodulated signal can be preserved while the linearity is improved. Up to 22.8 dB increase in spur free dynamic range (SFDR) is demonstrated. This novel receiver design is all-optical in the sense that no electrical loop amplifier is necessary. In order to operate the link at carrier frequencies beyond the loop bandwidth, an optical sampling technique is employed to downconvert the signal to the baseband. With feedback in the receiver, 14.1 dB of SFDR improvement is obtained experimentally in the sampled operation