Ultraflat bandpass, high extinction, and tunable silicon photonic filters

We report on the design and the demonstration of silicon photonic ultrafiat bandpass filters with low insertion loss and high out-of-band rejection for an operation near the 1550 nm wavelength band. These filters are based on cascading low (2nd) order Ring-Assisted MachZehnder Interferometer (RAMZI) filter stages. The cascade design enables high out-of-band rejection while keeping the unit cells of each stage low order to be more tolerant to fabrication imperfections. The characterization of filters shows an insertion loss of similar to 1 dB, an in-band ripple of <0.1 dB, an out-of-band rejection of >50 dB for a filter 3-dB bandwidth of similar to 1.1 nm, and tunable up to similar to 6 nm. We also investigate the filter's spur-free dynamic range at high input optical powers, which is important for RF photonics applications, and quantify a dynamic range of >60 dB for a laser power as high as similar to 11.6 mW sent to the filter. Such integrated filters are promising for applications in pump wavelength rejection in four-wave mixing photon pair generation, and in RF antenna remoting where multiple RF signals are carried on different coarse wavelengths to be separated. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

This article reports on the design and demonstration of silicon photonic ultraflat bandpass filters with low insertion loss and high out-of-band rejection. The filters are cascaded low-order Ring-Assisted Mach-Zehnder Interferometer (RAMZI) filter stages, enabling high rejection of out-of-band signals while maintaining low-order unit cells for tolerance to fabrication imperfections. The filters have low insertion loss, minimal in-band ripple, and a wide tunable range. The study also investigates the filters' dynamic range at high input optical powers, which is important for RF photonics applications.