Chapter 7 - Various Types of Optical OFDM

Abstract

This chapter illustrates the optical orthogonal frequency-division multiplexing (OFDM) variations according to their underlying techniques and applications. One of the major strengths of the orthogonal frequency-division multiplexing (OFDM) modulation format is its rich variation and ease of adaption to a wide range of applications. In wireless systems, OFDM has been incorporated in wireless local area network. Coherent optical OFDM (CO-OFDM) represents the ultimate performance in receiver sensitivity, spectral efficiency, and robustness against polarization dispersion, but it requires the highest complexity in transceiver design. The synergies between coherent optical communications and OFDM are twofold. OFDM brings coherent systems computation efficiency and ease of channel and phase estimation. The coherent systems bring OFDM a much-needed linearity in RF-to-optical (RTO) up-conversion and optical-to-RF (OTR) down-conversion. Consequently, a linear transformation is the key goal for the OFDM implementation. It is apparent that the challenges for CO-OFDM implementation are to obtain a linear RTO up-converter and linear OTR down converter. It has been proposed and analyzed that by biasing the Mach–Zehnder modulators (MZMs) at null point, a linear conversion between the RF signal and the optical field signal can be achieved.