Optical polarisation-diversity homodyne receiver with local laser - incorporates two homodyne reception branches with frequency regulated by threshold logic selecting branch with stronger signal

摘要

Polarisation beamsplitters (PS1,PS2) in the optical signal (SE) and local laser (LL) channels are associated with acousto-optical modulators (AOM1,AOM2) and 3 dB couplers (K1,K2) feeding p-i-n diode pairs (D1,D2;D3,D4) followed by photocurrent amplifiers (FV1,FV2). High-pass filtered components are multiplied (M1,M2) by coeffts. from peak rectifier-digitisers and threshold logic (BG1,BG2). Low-pass filtered components are amplified (VCA) and switched (S1-S3) into phase-locked loops (PLL) for modulator control based on the stronger of the two inputs. ADVANTAGES - Local laser frequency and phase control instabilities with weak input signals are prevented, and oscillation time is shortened with less tringent demands on loop gain.