Narrowband, Single-Channel, Wavelength-Tunable, SOI Reflector Based on a Bent Grating-Coupled Microring With an Inline Nanobeam

We propose a novel narrowband, single-channel, wavelength-tunable, silicon photonic reflector based on a compact grating-coupled microring (MRR) incorporating an inline nanobeam. A bent grating-assisted contra-directional coupler (CDC) is used for the wavelength-selective coupling between the bus and ring waveguides of the MRR to allow only a single resonant mode to be excited. The nanobeam acts as an ultra-compact, broadband, inline mirror which enables coupling between the counter-propagating modes in the MRR, thereby generating backward-traveling resonant light. The combination of the grating-assisted CDC and the nanobeam ultimately results in the single-channel reflection response of the MRR. The proposed reflectors developed on silicon-on-insular (SOI) platforms were fabricated and experimentally characterized. Ultra-narrow reflection bandwidths of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>15 pm and large side-lobe suppression ratios of up to 16.8 dB were demonstrated, and single-channel responses were observed over broadband wavelength ranges (60 nm). The thermal tuning of the reflector wavelength was also validated. Anticipated applications include sensing, laser engineering, and optical communications.