On acceleration sensitivity of 2  μm whispering gallery mode-based semiconductor self-injection locked laser

While whispering gallery mode resonators are well known for their low acceleration sensitivity, there has not been much published experimental research on the subject. We performed environmental sensitivity tests of a 2 μm semiconductor distributed feedback (DFB) laser, self-injection locked to a high-Q crystalline whispering gallery mode resonator. Measured acceleration sensitivity of the laser is below 5×10^-11  g^-1 in the 1-200 Hz frequency bandwidth and thermal sensitivity does not exceed 12  MHz/°C. The laser's frequency noise is below 50  Hz/Hz^1/2 at 10 Hz, reaching 0.4  Hz/Hz^1/2 at 400 kHz. The instantaneous linewidth of the laser is improved by nearly 4 orders of magnitude compared to the free-running DFB laser and is measured to be 50 Hz at 0.1 ms measurement time. The Allan deviation of the laser frequency is on the order of 10^-9 from 1 to 1000 s. All these features make the laser attractive for metrology applications involving low-noise 2 μm seed lasers.