Ultra-flat optical frequency comb generation based on amplitude modulator and Gaussian band-stop filter

A new scheme to generate ultra-flat optical frequency comb (OFC) with tunable frequency spacing is proposed and demonstrated based on an amplitude modulator driven by a digital periodic square-wave signal. A Gaussian band-stop filter is used to adjust flatness of the comb lines that generated from the amplitude modulator. The frequency spacing is adjusted by changing the period of the square-wave signal. The theoretical analysis model of the scheme is established and the relationship between the modulation index of the amplitude modulator and the flatness and power of OFC is studied. Through experiment simulations, it is shown that high-quality OFCs with the number of 32, 64, 128 comb lines, the tunable frequency spacing, and the flatness of 0.3 dB can be achieved.