MEMS enabled suspended silicon waveguide platform for long-wave infrared modulation applications

Abstract Long-wave infrared (LWIR, 6–14 µm) is an important wavelength range as it covers abundant vibrational molecular fingerprints that can be used for gas/liquid sensing and absorption spectroscopy. Silicon waveguide-based passive photonic devices that offer advantages toward chip-scale miniaturization of photonic integrated circuits (PIC) and photonic sensors in LWIR have been explored. However, the modulation of Si-based guided-wave propagation in LWIR remains less reported. Here, we demonstrate a MEMS tunable directional coupler operating at a long-wave infrared wavelength range (6.4–7 µm) using suspended Si waveguides with subwavelength gratings. Leveraging the membrane transfer technology, the whole photonic waveguide device membrane is transferred onto a receiver substrate with a cavity that allows sufficient displacement for MEMS electrostatic actuation. The proposed device experimentally achieved an optical attenuation of −14.25 dB with 90 V DC bias voltage, while having a response time of 177 µs. In addition, the demonstration of using such a device for computational spectroscopy has been validated.