Dynamic spectroscopic characterization for fast spectral variations based on dual asynchronous undersampling with triple optical frequency combs

A dynamic spectroscopic characterization scheme for fast spectral variations based on dual asynchronous undersampling with triple optical frequency combs is proposed and demonstrated here. The tri-comb scheme leverages two of the combs to simultaneously sample the fast spectral variations applied to the third comb. The repetition rate differences for both pairs of combs are relatively small, in order to maintain sufficiently large spectral measurement ranges. The corresponding sampling rates could be much slower than a fast time-varying spectral modulation to be measured. Nevertheless, despite of the frequency ambiguity in the undersampled dual-comb results, it is shown that it is possible to identify the original frequency of spectral variations based on the difference in the undersampled frequency domain information. Experimental results show that our scheme can increase the frequency demodulation range by at least two orders of magnitude while retaining the accuracy and spectral measurement range of similar DCS schemes. Demonstration based on a tri-comb mode-locked fiber laser is carried out to measure the dynamic spectral response from a fiber Bragg grating (FBG), to which up to 110 kHz of vibration is applied. This scheme could further extend the capability of dual-comb spectroscopic techniques, and it also illustrates the potential of the low-complexity multi-comb laser source for novel yet practical applications.