Comparison of optical BPSK and QPSK heterodyne lightwave systems

A comparative study of the coherent optical binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) heterodyne communication receivers is presented. First, both receivers are analyzed assuming two systems with a 0.5 dB and 2.5 dB power penalty. The analysis is performed in terms of laser linewidth, bit rate signal power and phase error for the same bit error rate 10^-10. The sensitivities of the two types of receivers are compared. Second, calculations of the signal to noise ratio (SNR) optimum, probability of bit error with cycle slippage and non-cycle slippage for both systems are presented. Finally, the comparison in terms of BER versus number of photons/bit (E_pb) for different laser linewidth/bit rates and bit error rate 10^-3 and 10^-1 are presented. It is shown that the QPSK receiver requires a larger amount of power than the BPSK receiver to achieve the same performance. At the power penalty of 0.5 dB, the QPSK systems are impractical while the BPSK system performs well