Digital laser frequency control and phase stabilization loops for a high precision space-borne metrology system

TL;DR

This paper presents the design and testing of fully digital control loops for laser frequency stabilization and phase locking in a space-based optical metrology system, enhancing performance and flexibility.

Contribution

It introduces a fully digital control system for laser stabilization in space, enabling easier implementation, calibration, and improved performance over traditional analog methods.

Findings

Successful implementation of digital control loops for laser stabilization.

Enhanced system performance and noise handling capabilities.

Ability to accurately characterize system transfer functions.

Abstract

We report on the design, implementation and characterization of fully digital control loops for laser frequency stabilization, differential phase-locking and performance optimization of the optical metrology system on-board the LISA Pathfinder space mission. The optical metrology system consists of a laser with modulator, four Mach-Zehnder interferometers, a phase-meter and a digital processing unit for data analysis. The digital loop design has the advantage of easy and flexible controller implementation and loop calibration, automated and flexible locking and resetting, and improved performance over analogue circuitry. Using the practical ability of our system to modulate the laser frequency allows us to accurately determine the open loop transfer function and other system properties. Various noise sources and their impact on system performance are investigated in detail.