A photonic integrated circuit-based optomechanical mid-IR bolometer

In recent years, a new class of bolometers based on mechanical spectroscopy has been proposed as an alternative route capable of surpassing the performance of state-of-the-art mid-infrared detectors. In this approach, the absorption-induced temperature change is measured through mechanical frequency shifts. We report on design, fabrication and characterization of an on-chip integrated optomechanical mid-IR bolometer. The device is composed of a silicon nitride trampoline mechanical resonator, suspended above a Si₃N₄ photonic integrated circuit (PIC). The optomechanical coupling via the near-field interaction, allows for shot noise limited detection of the motion of the trampoline and measurement of its frequency shifts. The trampoline resonator also features a Platinum structure, enhancing the mid-IR absorption efficiency. We demonstrate broadband mid-IR absorption spectroscopy using our device at modulation speeds exceeding 1 kHz. In this regime, the detection is limited by shot noise and the speed is limited by the thermal response of the resonator. Our work combines ultra-low-loss Si₃N₄ PICs, noise characterization techniques in optomechanics and mid-IR optics for realizing the next generation of mid-IR sensor.