Ring resonator enhanced mode-hop-free wavelength tuning of an integrated extended-cavity laser

TL;DR

This paper introduces a novel method to extend the continuous, mode-hop-free wavelength tuning range of integrated diode lasers using ring resonators, achieving a six-fold increase while maintaining ultra-narrow linewidths.

Contribution

The authors present a technique that allows a long-cavity laser to have a tuning range comparable to a short cavity, without sacrificing linewidth quality.

Findings

Achieved 0.22 nm (28 GHz) tuning range, six times the cavity's free-spectral range.

Maintained ultra-narrow linewidth of 2.2 kHz in the extended tuning.

Demonstrated the method on a hybrid InP-Si3N4 diode laser covering 120 nm.

Abstract

Extending the cavity length of diode lasers with feedback from Bragg structures and ring resonators is highly effective for obtaining ultra-narrow laser linewidths. However, cavity length extension also decreases the free-spectral range of the cavity. This reduces the wavelength range of continuous laser tuning that can be achieved with a given phase shift of an intracavity phase tuning element. We present a method that increases the range of continuous tuning to that of a short equivalent laser cavity, while maintaining the ultra-narrow linewidth of a long cavity. Using a single-frequency hybrid integrated InP-Si3N4 diode laser with 120 nm coverage around 1540 nm, with a maximum output of 24 mW and lowest intrinsic linewidth of 2.2 kHz, we demonstrate a six-fold increased continuous and mode-hop-free tuning range of 0.22 nm (28 GHz) as compared to the free-spectral range of the laser cavity.