Novel Vestigial Sideband Modulation Scheme to Enhance the SNR in Radio Over Fiber Systems

Abstract

The optical single sideband (OSSB) scheme is a common choice in radio over fiber system for compensating chromatic dispersion (CD) but it suffers from low signal to noise ratio (SNR).We present the novel technique for SNR improvement using unequal sideband intensity based modulation scheme, we name it optical vestigial sideband modulation scheme (OVSB). To analyze such scheme we use the series Mach-Zehnder modulator (MZM) and phase modulator (PM) configuration. In this configuration by operating MZM at quadrature point and properly tuning the PM index the individual intensity of the first order sidebands and higher order harmonics can be controlled independent to each other.The optimum operating point of PM for maximizing the SNR can be identified by reducing the harmonic distortion and increasing the first order sidebands power. We experimentally validated the proposed OVSB scheme generation method and provide its theoretical proof. We evaluate the symbol error rate (SER) performance using 4QAM signal for OSSB and OVSB and show the improved performance of OVSB scheme compared to OSSB scheme. We also discuss the harmonic distortion behavior of the series MZM and PM configuration.