Si-waveguide-based optical power monitoring of 2$\times$2 Mach$\unicode{x2013}$Zehnder interferometer based on InGaAsP/Si hybrid MOS optical phase shifter

TL;DR

This paper introduces a simple, CMOS-compatible optical power monitoring scheme for a 2x2 Mach–Zehnder interferometer using InGaAsP/Si hybrid MOS phase shifters and a Si waveguide photodetector, enabling real-time power monitoring without additional loss.

Contribution

The paper presents a novel in-line optical power monitoring method for integrated photonic switches using hybrid MOS phase shifters and a Si waveguide photodetector, demonstrating practical implementation.

Findings

Effective real-time power monitoring demonstrated

No excess optical insertion loss introduced

Compatible with existing CMOS fabrication processes

Abstract

Transparent in-line optical power monitoring in Si programmable photonic integrated circuits (PICs) is indispensable for calibrating integrated optical devices such as optical switches and resonators. A Si waveguide (WG) photodetector (PD) based on defect-mediated photodetection is a promising candidate for a transparent in-line optical power monitor owing to its simplicity and ease of integration with a fully complementary metal-oxide-semiconductor (CMOS)-compatible process. Here, we propose a simple optical power monitoring scheme for a 2$\times$2 Mach$\unicode{x2013}$Zehnder interferometer (MZI) optical switch based on InGaAsP/Si hybrid MOS optical phase shifters. In the proposed scheme, a low-doped p-type Si WG PD with a response time of microseconds is utilized as a transparent in-line optical power monitor and the ground terminal of the MOS optical phase shifter is shared with that of the Si WG PD to enable the simple monitoring of the output optical power of the MZI. Based on this scheme, we experimentally demonstrate that the output optical power of a 2$\times$2 MZI can be simply monitored by applying a bias voltage to the Si slabs formed at the output WGs of the MZI without excess optical insertion loss.