Optical processing and manipulation of wavelength division multiplexed signals

This chapter describes optical processing concepts that allow for simultaneous manipulation of multiple wavelength channels in a single or few optical processing units. This offers a potential for collective sharing, among the channels, of the energy associated with the processing, thus lowering the required processing energy per channel. Optical processing allows for ultra-broadband processing, thus increasing the potential energy savings, and could play a role in flexible networks by e.g. converting wavelength grids, modulation or signal formats. This chapter will describe means to regenerate multiple wavelength channels for improved transmission performance, compress or magnify the wavelength grid for better bandwidth utilisation, as well as means to complement the optical signal processing with its digital cousin. In particular, we will describe optical time lenses and phase-sensitive amplifiers, and optical phase conjugation paired with digital probabilistic shaping. The chapter will also give an overview of efficient nonlinear materials that could support these advanced optical signal processing schemes.