Silicon Photonics for Microwave Photonics Applications

We provide an overview of recent work on developing integrated microwave photonic subsystems in silicon photonics for generating chirped microwave waveforms as well as for providing optical true time delay. First, we describe on-chip spectral shapers based on Bragg gratings (BGs), including a distributed Fabry-Pérot cavity, a Michelson interferometer incorporating identical chirped BGs, and a Sagnac loop incorporating a chirped BG, for use in wavelength-to-time mapping systems. The performance of these on-chip spectral shapers is compared to those based on microring resonators as well as fiber or free-space configurations. Second, we consider the development of an index variable optical true time delay line (OTTDL) using subwavelength grating (SWG) waveguides. For SWG waveguides of the same length, incremental delays can be obtained by tailoring the group index via control over the duty cycle. We compare the performance of SWG waveguide OTTDLs to other length variable implementations in silicon.