High performance and tunable optical pump-rejection filter for quantum photonic systems

Integrated photonic circuits have become an attractive platform for the quantum information processing, paving the way for quantum information management with scalable device. In this context, silicon photonics represents the most mature technology to implement the quantum system functionalities, due to its large scalability and compatibility with CMOS technology. Efficient photon-pairs sources based on Spontaneous Four-Wave Mixing (SFWM) and high-performance photodetector have been already demonstrated. The efficient detection of photon-pairs requires a pump filter at the photodetector, preserving the signal-idler pair. Thus, filters with high Extinction Ratio (ER), low Insertion Loss (IL) and narrow rejection Bandwidth (BW) are needed. Here, we propose the design of an ultra-high-performance rejection filter, based on a silicon dual-loaded single input/output Mach-Zehnder Interferometer (MZI), with one branch coupled to a Ring Resonator (RR) and the other to three serially coupled RRs forming a Coupled Optical Resonator Waveguide (CROW). Very high performance (ER = 150.55 dB, IL = 0.104 dB, BW = 0.243 nm), within a footprint of 60 µm × 160 µm, has been calculated, demonstrating its suitability for an efficient suppression of the pump signal. The filter response is also thermo-optically tuneable in a 6 MHz range, with a reconfigurability time of about 8 µs.