Synchronization of frequency combs by optical injection

TL;DR

This paper demonstrates a method to synchronize and stabilize dual optical frequency combs using optical injection locking, significantly improving signal quality and simplifying data processing for integrated spectrometers.

Contribution

The authors introduce a novel optical injection locking technique to fully phase-stabilize dual frequency combs, enabling coherent averaging and reducing data complexity.

Findings

Dual combs can be synchronized via optical injection locking.

The method stabilizes the offset frequencies, resulting in periodic and stable signals.

Enhanced SNR and reduced data size achieved through coherent averaging.

Abstract

Optical frequency combs based on semiconductor lasers are a promising technology for monolithic integration of dual-comb spectrometers. However, the stabilization of the offset frequency fceo remains a challenging feat due the lack of octave-spanning spectra. In a dual-comb configuration, the uncorrelated jitter of the offset frequencies leads to a non-periodic signal resulting in broadened beatnotes with a limited signal-to-noise ratio (SNR). Hence, expensive data acquisition schemes and complex signal processing are currently required. Here, we show that the offset frequencies of two frequency combs can be synchronized by optical injection locking, which allows full phase-stabilization when combined with electrical injection. A single comb line isolated via an optical Vernier filter serves as Master oscillator for injection locking. The resulting dual-comb signal is periodic and stable over thousands of periods. This enables coherent averaging using analog electronics, which increases the SNR and reduces the data size by one and three orders of magnitude, respectively. The presented method will enable fully phase-stabilized dual-comb spectrometers by leveraging on integrated optical filters and provides access for measuring and stabilizing fceo.