Photonic circuit topologies for optical OFDM and nyquist WDM

Photonic circuits are the key to advanced functionality in future optical systems, as they efficiently process terabit/s data streams. This paper reviews how photonic circuit topologies have evolved to support high-spectral efficiency modulation formats, including: All-Optical Optical Frequency Division Multiplexing (AO-OFDM), Discrete Fourier Transform Spread OFDM (DFT-S-OFDM), Nyquist Wavelength Division Multiplexing, (NWDM), Orthogonal Time Division Multiplexing (OrthTDM, OTDM), chirped-OFDM and quasi-Nyquist signals. The importance of the order of components such as modulators, delays and filters within these circuits is stressed, as simple changes to the circuit topology have significant impacts on the spectra of the signals, and the required bandwidths of the modulators.