Laser frequency noise characterisation using high-finesse plano-concave optical microresonators

Characterising laser frequency noise is essential for applications including optical sensing and coherent optical communications. Accurate measurement of ultranarrow linewidth lasers over a wide frequency range using existing methods is still challenging. Here we present a method for characterising the frequency noise of lasers using a high finesse plano-concave optical microresonator (PCMR) acting as frequency discriminator. To enable noise measurements at a wide range of laser frequencies, an array of PCMRs was produced with slight variations of thickness resulting in a series of discriminators operating at a series of periodical frequencies. This method enables measuring the frequency noise over a wide linewidth range (15Hz to <100MHz) over the 1440nm-1630nm wavelength range. To assess the performance of the method, four different lasers were characterised, and the results were compared to the estimations of a commercial frequency noise analyser.