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 ð?œ‡m exhibits a rejection band as large as ∼60 nm with an extinction of ∼40 dB with respect to the resonant wavelength peak at ð?œ†ð?‘Ÿâˆ¼1550 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 ð?œ‡s. As a potential application, noise associated with an amplified pump wavelength (ð?œ†ð?‘ƒâˆ¼1550 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.Â

This paper presents an integrated optical signal processor (OSP) design using CMOS-compatible silicon photonics technology, offering a tunable RF bandpass filter (5G/6G frequency range) with a programmable bandwidth and symmetric out-of-band rejection. The OSP is comprised of two identical microring resonators cascaded with a common bus waveguide, in 220 nm silicon-on-insulator substrate. The ring resonators are designed with low-loss rib waveguide structures (supporting fundamental and first-order TE-like modes) to ensure relatively lower propagation losses and to obtain high-Q resonances. The single-mode bus waveguide is designed to facilitate the desired range of coupling strengths via thermo-optic tuning. Four thermo-optic phase shifters are integrated to tune the resonant wavelengths and the Q-values of the individual microring resonators. The four phase shifters could be programmed to obtain desired optical filter characteristics of the fabricated OSP chip. The RF filter experiments were carried out using an off-chip laser source (λ ~ 1550 nm), a phase modulator (3-dB BW = 10 GHz) and a photodetector (3-dB BW = 26.5 GHz). The central frequency of the RF bandpass filter could be tuned upto 8 GHz in our experimental setup. The 3-dB (20-dB) bandwidth of the filter was tuned from 0.84 GHz (2.77 GHz) to 1.8 GHz (5.47 GHz) with a symmetric out-of-band rejection > 20 dB (above noise level). Even though the fabricated OSP chip has the potential to realize filter response beyond 50 GHz, the observed tuning range is limited by the efficiency of the thermo-optic phase-shifters, and the bandwidth of phase modulator/photodetector used in our experiments.