Monolithic integration of high linearity attenuated counter-propagating optical phase-locked loop coherent receiver

Introduction: Coherent phase modulated RF/photonic links have been proposed [1, 2] to realise high dynamic range analogue optical links, which require the use of an optical phase-locked loop (OPLL) as a linear phase demodulator. Through feedback, the OPLL forces the output phase response of a local optical phase modulator to mirror the phase of an incoming optical signal. Since high loop gain and wide bandwidth are required for efficient phase tracking, the OPLL must have an extremely short loop delay to ensure feedback stability. This can be realised using an attenuated counter-propagating (ACP) configuration [2], which eliminates the phase delays from the optical phase modulators and photodetectors in the OPLL. Integration of the ACPOPLL on a single chip is necessary so that the propagation delays arising from optical signal routing and the electrical feedback are minimised. In this Letter, we describe the first monolithically integrated ACPOPLL PIC on an indium phosphide (InP) material platform. We present preliminary results that demonstrate the highest spurious-free dynamic range (SFDR) reported for a single-chip OPLL coherent receiver.