On-chip Optical Phase Monitoring in Multi-Transverse-Mode Integrated Silicon-based Optical Processors

TL;DR

This paper presents a novel on-chip optical phase monitoring method in multi-transverse-mode silicon photonics, enabling programmable optical processing without conventional phase detection, by converting phase information into measurable optical power differences.

Contribution

It introduces a new integrated design that uses mode-sensitive phase shifters and mode conversion to measure optical phase directly, eliminating the need for coherent detection.

Findings

First on-chip implementation of optical phase monitoring in multi-mode silicon photonics.

Demonstrates effective phase measurement through mode-dependent power variation.

Enables fully integrated programmable optical processors.

Abstract

We design a Multi-Transverse-Mode Optical Processor (MTMOP) on 220 nm thick Silicon Photonics exploiting the first two quasi-transverse electric modes (TE0 and TE1). The objective is to measure the optical phase, required for programming the optical processor, without use of conventional optical phase detection techniques (e.g., coherent detection). In the proposed design, we use a novel but simple building block that converts the optical phase to optical power. Mode TE0 carries the main optical signal while mode TE1 is for programming purposes. The MTMOP operation relies on the fact that the group velocity of TE0 and TE1 propagating through a mode-sensitive phase shifter are different. An unbalanced Mach-Zehnder interferometer (MZI) consists of a mode-sensitive and mode-insensitive phase shifters in the two arms. We set the bias of the phase shifters so that TE0 propagating in the two arms constructively interfere while this will not be the case for TE1. Hence, we detect the phase shift applied to TE0 by measuring the variation in the optical power of TE1. To the best of our knowledge, this design is the first attempt towards realizing a programmable optical processor with fully integrated programming unit exploiting multimode silicon photonics.