ABSTRACT
This chapter presents the background principles of multiport programmable optical processors which are a mesh of 2 × 2 reconfigurable Mach-Zehnder interferometers (MZIs) in different topologies. It demonstrates how the unitary transformation matrix of a given application is decomposed for programming such MZI-based optical processors. Additionally, a phase-error- and loss-tolerant MZI-based optical processor for optical neural networks (ONNs) is investigated. The structure has a diamond shape mesh with a set of additional MZIs compared to the commonly used Reck mesh. The additional MZIs in the Diamond mesh make its topology more symmetric yielding higher robustness to phase error and insertion loss of the MZIs, and provide extra degrees of freedom in the weight matrix optimization of the ONNs during training. The main subject of this chapter is to investigate such MZI-based optical processors, which allows for the design and implementation of more efficient and practical MZI-based optical processors that better cope with inevitable fabrication processes imperfections and experimental imperfections. The demonstration of these analyses is significant since it can be used to implement any universal MZI-based field-programmable structure to serve as optical computational accelerator, which can be experimentally configured for a given application.
