20 ∼ 120 GHz microwave photonics waveform generation by spatial spectral filtering of a 10 GHz mode-locked laser

We demonstrate a simple method to generate a high speed pulse train from a relatively low speed pulse source by spatial spectral filtering using a pulse shaper. For spectral filtering, we build a simple line-by-line pulse shaper with 5 GHz resolution at 1.55 μm, where we use a grating, collimating lens, and intensity mask. By applying a 10 GHz mode-locked spectral comb to the shaper, we generate relatively stable 20 ~ 120 GHz pulse trains with 10 GHz step. The characteristics of generated pulse trains are examined quantitatively by measuring optical spectra, time-domain waveforms, auto correlation traces, and radio-frequency spectra.