Spectrally Efficient SSB Optical OFDM Signal Using Balanced Detection

Abstract

Orthogonal frequency division multiplexing (OFDM) has already gained importance in the field of optical communications with the increasing popularity of Radio-over-Fiber (RoF) technique. In this paper, generation of optical OFDM (OOFDM) signal using both direct and external intensity modulation that can be detected using direct-detection receivers is presented. Direct intensity modulation is performed using Vertical Cavity Surface Emitting Laser (VCSEL) whereas external modulation is done using Mach-Zehnder Modulator (MZM). These modulation schemes are tested using vector modulation format, i.e., quadrature amplitude modulation (QAM) that are used to modulate the orthogonal subcarriers, thus generating an OFDM signal. The performance of the system with different orders of QAM is compared based on the error vector magnitude (EVM) of the received constellation. The change in EVM is studied for the increase in the transmission distance of the signal. OOFDM systems using MZM showed better results compared to the system using VCSEL.