Continuously tunable coherent pulse generation in semiconductor lasers

TL;DR

This paper demonstrates a monolithic semiconductor laser capable of continuously tuning its repetition rate from 4 to 16 GHz using spatiotemporal gain modulation, enabling fully tunable chip-scale lasers and frequency combs.

Contribution

It introduces a novel method for continuous tuning of laser repetition rates via microwave-induced gain modulation, overcoming traditional cavity mode limitations.

Findings

Achieved continuous tuning of repetition rate from 4 to 16 GHz.

Generated frequency combs with tunable mode spacings.

Produced coherent pulse trains with adjustable repetition rates.

Abstract

In a laser, the control of its spectral emission depends on the physical dimensions of the optical resonator, limiting it to a set of discrete cavity modes at specific frequencies. Here, we overcome this fundamental limit by demonstrating a monolithic semiconductor laser with a continuously tunable repetition rate from 4 up to 16 GHz, by employing a microwave driving signal that induces a spatiotemporal gain modulation along the entire laser cavity, generating intracavity mode-locked pulses with a continuously tunable group velocity. At the output, frequency combs with continuously tunable mode spacings are generated in the frequency domain, and coherent pulse trains with continuously tunable repetition rates are generated in the time domain. Our results pave the way for fully tunable chip-scale lasers and frequency combs, advantageous for use in a diverse variety of fields, from fundamental studies to applications such as high-resolution and dual-comb spectroscopy.