# Synchronization of two DFB lasers using frequency-shifted feedback for microwave photonics

## TL;DR

This paper demonstrates the effective synchronization of two DFB lasers using frequency-shifted feedback, enabling stable phase locking over a broad parameter range for microwave photonics applications.

## Contribution

It introduces a novel experimental setup and confirms through modeling that strong cross-injection reduces phase sensitivity, advancing laser synchronization techniques.

## Key findings

- Successful frequency difference locking over broad parameters
- Mitigation of phase sensitivity with strong cross-injection
- Observation of bounded-phase oscillations

## Abstract

The phase synchronization of two semiconductor DFB lasers submitted to both frequency-shifted cross-injection and self-feedback is investigated, both numerically and experimentally. A dedicated setup based on monolithic DFB lasers permits to effectively lock the frequency difference of the two lasers on an external reference over a broad range of parameters. In agreement with a delayed rate equation model, it is shown that the sensitivity of the locking to the optical feedback phases is mitigated by using strong cross-injection, thus paving the way to applications for microwave photonics. Other synchronization dynamics can also be observed, such as bounded-phase oscillations.