Mid-infrared thermo-optic modulators in SoI

We report experimental results for thermo-optic modulators in silicon-on-insulator (SoI) material operating at the wavelength of 3.8 µm. These devices are based on asymmetric Mach-Zehnder interferometers (MZIs) with aluminum heaters placed above one MZI arm. The SoI rib waveguides with 400-nm Si device layer thickness are used. Devices with conventional straight MZI arm and spiral MZI arm geometries are investigated. Straight-arm MZIs exhibited higher modulation depths, of up to 30.5 dB, whereas spiral-arm MZIs required smaller switching powers, as low as 47 mW. Measured -3 dB bandwidths were up to 23.8 kHz and did not vary significantly with device configuration