Phase noise insensitive coherent optical heterodyne CPFSK receiver with limiter discriminator detector

A coherent optical heterodyne CPFSK receiver with a limiter discriminator (LD) detector, which cannot be degraded by the quantum phase noise of lasers when the frequency deviation ratio h is equal to unity is proposed. The receiver can give the same bit error rate as the ideal digital DPSK system. The expression ¹/₂ exp (-SNR) can be considered the upper bound of the minimum error rate of CPFSK-LD detector.