Integration of Photonic Crystal Splitter and Slow Light Waveguide for a Microwave Photonic Filter

We theoretically investigate an ultracompact integration of a photonic crystal (PC) splitter and a slow-light waveguide for a microwave photonic filter. We realize the filter characteristics with a free spectrum range of 130 GHz and a notch depth of 10 dB, and the whole length is only 24.8 μm with the use of a slow-light PC waveguide as a delay line. The splitter is fabricated with the delay line using a U-shaped waveguide. In addition, the coupling efficiency between slow-light waveguide and U-shaped waveguide has been increased from 10% to 62% with an optimized linear taper structure. The proposed microwave photonic filter can be applied in the 60-GHz Radio-over-Fiber (RoF) system.