Generation of complementary linear frequency-modulated microwave signals based on an on-chip Sagnac dual-loop spectral shaper

A spectral shaper based on the cooperative operation of a grating-assisted contra-directional coupler (GACDC) and a Sagnac dual-loop is proposed and experimentally demonstrated. The Sagnac dual-loop shares a single segment of chirped grating and generates positively and negatively chirped signals, reducing the number of required grating components by half compared with conventional approaches. A 2 × 2 multimode interference (MMI) coupler is adopted at the output port to realize an interferometric combination, enabling the simultaneous output of two-channel chirped spectra with complementary phase and balanced amplitude. The device is fabricated on a standard 220 nm silicon-on-insulator (SOI) platform. Using the spectral shaping and wavelength-to-time mapping (SS-WTTM) technique, a pair of complementary linear frequency-modulated (LFM) microwave signals is generated. The test results show that the bandwidths of the two output signals are approximately 23 GHz, with corresponding time-bandwidth products (TBWP) of 48.3 and 50.6, the chirp rates reach 11.8 GHz/ns and 11.6 GHz/ns, and the pulse compression ratios are 117 and 114, respectively. The two-channel signals exhibit negative correlation characteristics, and the experimental results show good agreement with the simulation results.