Independently Tunable Dual-Band Linearly-Chirped Microwave Waveforms Generation on a Silicon Photonic Chip

We propose a photonic approach for generation of independently tunable dual-band linearly-chirped microwave waveforms (LCMWs) based on a Fourier-domain mode-locked opto-electronic oscillator (FDML-OEO). The FDML-OEO is implemented with the use of an independently-tunable dual-passband on-chip microwave photonic filter (MPF) realized by phase modulation to intensity modulation (PM-IM) conversion. In the integrated PM-IM implementation, an optical filter with a tunable dual-passband is a key component that incorporates two separated racetrack microring resonators (MRRs) with an ultra-narrow bandwidth. A metallic micro-heater is placed on top of each MRR for resonance wavelength tuning when a driving signal is applied. When the periods of the two applied driving signals match the round-trip time of the OEO loop simultaneously, Fourier-domain mode locking is reached, and dual-band LCMWs can be generated. Thanks to independently tuning of each MRR, each sub-band of the dual-band LCMW generated by the FDML-OEO is independently tunable in terms of central frequency, signal bandwidth and chirp rate. A silicon-based ultrahigh-Q dual-bandpass optical filter chip is fabricated and characterized. With the use of the fabricated chip, the generation of dual-band LCMWs is demonstrated, of which each sub-band can be tuned in the central frequency from 7.5 to 12.5 GHz, the bandwidth from 0.5 to 1.5 GHz, and the chirp rate with positive or negative value. The proposed integrated independently tunable dual-band LCMW generation system features great advantage of waveform tunability, which is potential to be widely used in multi-band multi-functional radar systems applications.