Cavity length control for Fourier domain mode locked (FDML) lasers with μm precision

In highly dispersion compensated Fourier domain mode locked (FDML) lasers, an ultra-low noise operation can only be achieved by extremely precise and stable matching of the filter tuning period and light circulation time in the cavity. We present a robust and high precision closed-loop control algorithm and an actively cavity length controlled FDML laser. The cavity length control achieves a stability of similar to 0.18 mHz at a sweep repetition rate of similar to 418 kHz which corresponds to a ratio of 4x10(-10). Furthermore, we prove that the rapid change of the cavity length has no negative impact on the quality of optical coherence tomography using the FDML laser as light source. (c) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement