Optical Frequency Locked Loop for long-term stabilization of broad-line DFB lasers frequency difference

TL;DR

This paper demonstrates a digitally tunable optical frequency locked loop that stabilizes the frequency difference of broad-line DFB lasers over long periods with high precision, robustness, and ease of optimization.

Contribution

It introduces a novel integrated phase-frequency detector-based OFLL design with a simple optimization method and demonstrates long-term stabilization over a 4-15 GHz range.

Findings

Achieved < 0.5 Hz long-term stability over 1000 seconds.

Successfully stabilized frequency offsets from 4 to 15 GHz.

System response closely matches theoretical predictions.

Abstract

We present an experimental realization of the Optical Frequency Locked Loop (OFLL) applied to long-term frequency difference stabilization of broad-line DFB lasers. The presented design, based on an integrated phase-frequency detector chip, is digitally tunable in real-time, robust against environmental perturbations and compatible with commercially available laser current control modules. We present a simple model and a quick method to optimize the loop for given hardware using only simple measurements in time domain and approximate laser linewidth. We demonstrate frequency stabilization for offsets encompassing entire 4-15 GHz capture range. We achieve < 0.5 Hz long-term stability of the beat note frequency for 1000 s averaging time. Step response of the system as well as phase characteristics closely adhere to the theoretical model.