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

摘要

A polarisation beamsplitter (PS) divides the optical signal (SE) between two 3dB couplers (K1,K2) associated with respective local lasers (LL1,LL2), 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 (MB1,MB2). Low-pass filtered components are amplified (VCA) and switched (S1,S2) into phase-locked loops (PLL) for laser frequency and phase control based on whichever branch provides the input. ADVANTAGES - Local laser frequency and phase control instabilities with weak input signals are prevented, and oscillation time is shortened with less stringent demands on loop gain.