Frequency noise measurement and its uncertainty estimation of an optical frequency comb using a delay line interferometer

Abstract

We describe frequency noise measurements for an optical frequency comb by using a delayed self-heterodyne method with a Michelson-type fiber-optic delay line interferometer without a low-noise reference laser. We measured the frequency noise power spectral densities (PSDs) for free-running and frequency-stabilized comb modes and estimated the uncertainties of the measurement results. For example, for the frequency-stabilized comb, the measured frequency noise PSD and its uncertainty were 23 dBHz2 Hz−2 and 0.66 dB, respectively, at a Fourier frequency of 10 kHz. We also measured the frequency noise PSDs of the comb modes by the conventional method using an ultrastable reference laser and compared the results with those that we measured with the delayed self-heterodyne method. The measurement results that we obtained with the two methods were consistent within their uncertainties, which shows that the delayed self-heterodyne method provides high reliability. This combined with its simplicity and user-friendliness suggest that the method has the potential to become a standard frequency noise measurement approach for frequency combs.