Automated control strategy for setting and stabilization of photonic circuits

TL;DR

This paper introduces a Wheatstone bridge-based control system for real-time stabilization and calibration of integrated photonic circuits, offering high sensitivity, temperature insensitivity, and voltage-based measurement to improve optical device performance.

Contribution

It presents a novel on-chip Wheatstone bridge configuration for stable, real-time control of photonic devices, reducing noise and simplifying circuit design compared to traditional methods.

Findings

High sensitivity to optical power changes

Temperature insensitivity of the bridge configuration

Enables automatic re-tuning of photonic interferometers

Abstract

In this paper, we propose the Wheatstone bridge configuration for enabling real-time and closed-loop stabilization and calibration of photonic devices integrated on chip. The measurement of the optical power propagating in a waveguide is achieved by leveraging the photo-thermal resistance variation of one of the resistors that comprise a bridge, which is either part of the waveguide or in close contact with the waveguide. The voltage generated by a monitor is applied through a processing unit to preceding actuators with a view to locking a system at the desired signal level. As all the "resistors" consisting of the Wheatstone bridge are placed on a single material platform in proximity to each other, the bridge is insensitive to temperature variations. Consequently, it functions exclusively as a monitor for the optical power propagating in a waveguide. Due to the high sensitivity of the monitor, automatic re-tuning of the Mach-Zehnder interferometer can be achieved with a recovery time defined by the material properties of the bridge "resistor". The material platform and arrangement can be implemented for both monitoring and activating the actuators, which makes the proposed system an attractive candidate for closed-loop control of optical devices. Furthermore, in contradistinction to the majority of monitors and photodetectors, which provide electrical current as an outcome of measuring an optical signal, the proposed circuit provides voltage, thereby eradicating the necessity to convert current to voltage at a later stage. This serves to firstly streamline the entire circuit and secondly contribute to a substantial diminution in the noise level in the circuit.