Optimum system design for CPFSK heterodyne delay demodulation system with DFB LDs

Abstract

An optimum system configuration for an optical continuous-phase frequency-shift-keying (CPFSK) heterodyne delay demodulation system with distributed feedback laser diodes (DFB LD's) was investigated. The optimum modulation index was indicated by evaluating the LD phase noise effect and the IF noise effect. The IF noise effect was investigated in detail, considering noise conversion effect through delay demodulation. In the case of IO-MHz IF beat spectral width, it is indicated that the modulation index rn = 1.5 is optimum for a 1.2-Gbit/s system. With this optimum modulation index of m = 1.5, a 204-km long span transmission experiment, with -41.5-dBm receiver sensitivity, has been successfully carried out. The feasibility of using stand-alone DFB LD's for a high sensitivity CPFSK delay demodulation system has been confirmed through this experiment.

Performance of Reed-Solomon Codes in CPFSK Coherent Optical Communications

“…2. We assume that the required IF bandwidth covers 95% signal power and can be approximated as B IF = ( m+-l R b [3]. It is seen that / Π9\ there exists an optimum code rate I r = --I for which the BER is minimum.…”

“…The error rate for the delay demodulation can be expressed as [3] 2 τ • exp [ -(2n +1) 2 πΔντ] · cos where = is the modulation index parameter, T τ = is the delay time, 2m…”

“…With consideration of stability and practicability, frequency-shift-keying (FSK) systems attract much interest. Especially, the continuous-phase frequency-shift-keying (CPFSK) optical heterodyne with delay demodulation is most attractive, because it provides for direct modulation of laser diodes, needs reasonable linewidth requirements [2], and has compact power spectral density [3]. Since the CPFSK delay demodulation scheme uses signal light phase information, high receiver sensitivity is expected.…”

An Accurate Analysis of the CPFSK System by Considering the Correlation between Discrete Samples in Post-Detection Filtering

“…The earlier analysis is concentrated on tight IF filtering and approximates the noise at the decision gate to be a Gaussian process [4][5][6]. Later analysis not using the Gaussin approximation was developed [7][8][9].…”