Mid-infrared tunable Vernier filter on a germanium-on-insulator photonic platform

We demonstrate the operation of a tunable Vernier filter at a mid-infrared wavelength of approximately 1.95 mu m. To enable efficient tuning through the thermo-optic effect, the filter is implemented on a germanium (Ge)-on-insulator photonic platform. Heat is generated from an overlaying metal heater line to induce the thermo-optic effect to tune the filter output without incurring excessive loss. Owing to the higher thermo-optic coefficient of Ge, the tunability of a single microring resonator is 0.083 nm/mW or 0.175 nm/degrees C, which is approximately twofold higher than that of silicon. Through the implementation of the Vernier effect by cascading two microring resonators, the tunability of the filter is increased to 0.753 nm/mW or 1.487 nm/degrees C, which is more than ninefold higher than that of a single microring resonator. (c) 2019 Optical Society of America