Carrier recovery and filtering in optical BPSK heterodyne systems disturbed by phase noise from external cavity semiconductor lasers

Performance analysis of direct-detection optical DPSK systems using a dual-detector optical receiver

“…In such receiver the dc currents 'dcl and 'dc2 cancel when subtracted, so that the output current i(t) is only due to the cross-product of the optical fields in the two branches of the interferometer. Neglecting the excess noise due to laser intensity fluctuations, th power spectral density (PSD) of n0(t), can be written as N0= 2q(Id1+Jd2) (10) where q is the charge of the electron. The PSDs of n1(t) and n2(t) add because they are generated by different photodiodes and thus are independent.…”