Accurate computations of the nonlinear phase noise and BER in DPSK modulation-balanced direct detection high-speed optical fiber communication systems

This article analyzes the nonlinear phase noise caused by an amplified spontaneous-emission of erbium-doped optical fiber amplifier and self-phase modulation (SPM) in a differential phase-shift keying modulation- balanced direct detection optical fiber communication system. Using numerical methods, the characteristic function of the differential nonlinear phase noise \({\cos (\Delta \varphi)}\) in the received electrical current of signals and the accurate computation formula of the BER are achieved when SPM is dominant comparing to cross phase modulation and four wave mixing. The result is verified by a simulation of a 40-Gbit/s transmission system.