Wideband current modulation of diode lasers for frequency stabilization

TL;DR

This paper introduces a high-bandwidth current modulation technique for diode lasers that enables stable, wideband frequency modulation with minimal phase lag, suitable for advanced laser stabilization applications.

Contribution

A novel current modulation scheme with a dedicated source and impedance matching that achieves flat transfer function up to 100 MHz, enhancing laser frequency stabilization capabilities.

Findings

Phase lag less than 90° up to 25 MHz

Gain flatness of ±3 dB from DC to 100 MHz

Improved phase noise of 42 mrad_rms in optical phase-locked loop

Abstract

We present a current-modulation technique for diode-laser systems that is specifically designed for high-bandwidth laser-frequency stabilization and wideband frequency modulation with a flat transfer function. It consists of a dedicated current source and an impedance-matching circuit both placed close to the laser diode. The transfer behaviour of the system is analysed under realistic conditions employing an external-cavity diode laser (ECDL) system. We achieve a phase lag less than 90$\deg$ up to 25 MHz and a gain flatness of $\pm$ 3 dB in the frequency range of DC to 100 MHz while the passive stability of the laser system is not impaired. The potential of the presented current modulation scheme is demonstrated in an optical phase-locked-loop between two ECDL systems resulting in an improved phase noise of 42 mrad$_{rms}$. The design files are available as an open-source project.