Fundamental Building Blocks for Scalable Photonic Programmable Processors.

Photonics technology is emerging as a key enabler, complementing electronics in next-generation applications by offering greater bandwidth, lower latency and improved energy efficiency. Silicon photonic programmable processors bring these advantages to a solid-state platform, providing compact form factors and low power consumption, although the scalability of densely integrated circuits is still under active investigation. In this article, we present a comprehensive study of the essential photonic components required for large-scale integration of silicon photonic processors, covering both design and experimental demonstration. We analyse and optimise the fundamental building blocks-including splitters, phase shifters, and crossings-and experimentally validate their scalability through wafer-scale characterisation. To finish, we illustrate the impact at the circuit level in a 4 × 4 optical switch loaded with high-speed transmission and discuss the remaining challenges for large-scale integration.