Basic Building Blocks and Techniques

Abstract

Programmable integrated photonics (PIP) relies on designing suitable basic building blocks (BBBs) able to carry elementary signal processing operations and interconnection hardware architectures that offer very high spatial regularity. The most popular BBBs proposed so far are based on elementary 2×2 tunable photonics coupling components capable of providing independent setting of the power coupling ratio. Additionally, they are based on the phase shift experienced by the incoming signals from two input waveguides in their transition to the two output waveguide ports of the device. This chapter deals primarily with these components. First, it considers the basic matrix methods required to describe their operation, either standalone or in combination with others to form more complex structures. Next, it describes the main technology approaches for the implementation of BBBs, including 3dB Mach–Zehnder tunable couplers, directional couplers, and beamsplitters, followed by how these BBBs are employed to build up a tunable basic unit (TBU), which is the elementary constituent of waveguide mesh circuits. It concludes by describing the devices and techniques relevant in multiport devices, and discusses the equivalence between mode conversion and linear optics matrix transformations and the universal linear combiner.