Compact Tunable Resonance Filters with Ultra-Broad Rejection for Silicon Photonics

This paper reports a novel design of compact tuneable resonance filter with a highly extinguished and ultra-broad out-of-band rejection in CMOS compatible silicon photonics technology platform. The proposed device is designed with two identically apodized distributed grating structures for guided Fabry-Pérot resonant transmissions in a silicon on insulator rib waveguide structure. The device design parameters are optimized by theoretical simulation for a low insertion loss singly-resonant transmission peak at a desired wavelength.  However, the devices were fabricated (using in-house facilities) to demonstrate multiple resonant transmission peaks along with a singly-resonant one.  We observed that a device length of as low as ∼35 𝜇m exhibits a rejection band as large as ∼60 nm with an extinction of ∼40 dB with respect to the resonant wavelength peak at 𝜆𝑟∼1550 nm (FWHM ∼80 pm, IL∼2 dB). The experimental results have been shown to be closely matching to our theoretical simulation and modelling results. As expected from the theoretical prediction, the trend pertaining to the trade-off between passive insertion loss and Q-value of the resonances has been observed depending on the device parameters. The thermo-optic tuning characteristics of resonant wavelengths have been obtained by integrating microheaters in the cavity. The resonance peak has been tuned at a rate of 96 pm per mW of consumed thermal power. The thermo-optic switching response has been measured to be in the order of ~5 𝜇s. As a potential application, noise associated with an amplified pump wavelength (𝜆𝑃∼1550 nm) has been shown to be suppressed by ∼15 dB (up to the detector noise floor) which can be investigated further for large-scale integrated quantum photonic circuits. The demonstrated device can also be explored further for many other applications such as modulation, add-drop multiplexing, sensing etc.