Sensitivity degradation of an optical (2*2) and a (3*3) phase diversity ASK receiver due to gain imbalance and nonideal phase relations of the optical hybrid

The sensitivity penalty due to phase and gain imbalance for a (2*2) and a (3*3) optical homodyne phase diversity amplitude-shift keying (ASK) receiver is investigated for the shot-noise-limited case. It is shown that both types of imbalance lead to a time varying character of the bit error rate (BER) types of imbalance and the phase mismatch. The calculation of the BER is performed as a function of the threshold value. It is shown that for an optimized threshold value, the phase diversity ASK receivers can tolerate rather large amounts of gain imbalance, namely approximately +or-10%, and a phase mismatch of approximately +or-10 degrees for the (2*2) receiver and approximately not=15 degrees for the (3*3) receiver without an excessive sensitivity degradation (<2 dB).<
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