From ultra-noisy to ultra-stable: Optimization of the optoelectronic laser lock

Abstract

We demonstrate the direct locking of a 820 kHz linewidth semiconductor distributed feedback laser to a high finesse, compact, and ultrastable reference cavity using the optoelectronic (OEO) laser locking method, resulting in cavity thermal noise-limited phase noise performance. We compare the OEO lock to the standard Pound–Drever–Hall method, demonstrating several new aspects and advantages of the OEO lock in attaining low phase noise from noisy lasers, including reducing the residual laser noise by more than 140 dB compared to its free-running level at a 10 Hz offset. In addition, we introduce a new RF feedforward noise-correction scheme that transfers the stability of the ultrastable reference cavity to an optical frequency comb even if the cavity-stabilized laser itself has high residual noise. We also reveal an OEO lock state that is capable of extremely high levels of laser noise rejection using feedforward, exceeding current theoretical models by ∼15 dB. By combining compact laser sources with sub-1 ml volume and ultrastable optical cavities, this work enables extremely compact and robust ultrastable laser systems with applications in low phase noise microwave generation, sensing, and satellite ranging.