Largely chirped microwave waveform generation using a silicon-based on-chip optical spectral shaper

We design and fabricate a novel silicon-based optical spectral shaper for the generation of a largely chirped microwave waveform. The optical spectral shaper has a Mach-Zehnder interferometer structure in which multiple micro-ring resonators are cascaded. By controlling the radii of the rings, the spectral response of the spectral shaper can be controlled to have a largely increasing or decreasing free spectral range, which is needed for the generation of a largely chirped microwave waveform based on spectral shaping and wavelength-to time (SS-WTT) mapping. The proposed optical spectral shaper is fabricated using a CMOS compatible process with 193-nm deep ultraviolet lithography. By using such an optical spectral shaper in an SS-WTT mapping system, a largely chirped microwave waveform with a bandwidth of 15.55 GHz and a chirp rate of 17.2 GHz/ns is demonstrated.