Electro-optically tunable single-frequency lasing from neodymium-doped lithium niobate microresonators

TL;DR

This paper demonstrates a neodymium-doped lithium niobate whispering gallery mode laser that is electro-optically tunable over 3.5 GHz, offering stable, single-frequency operation suitable for integrated photonics applications.

Contribution

It introduces a novel electro-optically tunable single-frequency laser using neodymium-doped lithium niobate microresonators with suppressed higher-order modes for stable operation.

Findings

Achieved 3.5 GHz tuning range with 68 V voltage

Maintained frequency stability better than 20 MHz over 30 minutes

Demonstrated stable single-mode lasing with 6% power variation

Abstract

Tunable light sources are a key enabling technology for many applications such as ranging, spectroscopy, optical coherence tomography, digital imaging and interferometry. For miniaturized laser devices, whispering gallery resonator lasers are a well-suited platform, offering low thresholds and small linewidths, however, many realizations suffer from the lack of reliable tuning. Rare-earth ion-doped lithium niobate offers a way to solve this issue. Here we present a single-frequency laser based on a neodymium-doped lithium niobate whispering gallery mode resonator that is tuned via the linear electro-optic effect. Using a special geometry, we suppress higher-order transverse modes and hence ensure single-mode operation. With an applied voltage of just $68\,$V, we achieve a tuning range of $3.5\,$GHz. The lasing frequency can also be modulated with a triangular control signal. The freely running system provides a frequency and power stability of better than $\Delta\nu =20\,$MHz and 6%, respectively, for a 30 minute period. This concept is suitable for full integration with existing photonic platforms based on lithium niobate.