Sensitive Infrared Detection via Optomechanical Spring Sensing

We theoretically propose achieving sensitive, low-noise, and fast detection of incoherent thermal photons at room temperature using an optomechanical spring sensing principle. Briefly speaking, our detection mechanism is based on monitoring the mechanical frequency of a coherent optomechanical oscillator (OMO), which critically depends on the number of intracavity near-infrared photons. The incoming free-space mid-infrared signal changes the intracavity photon number of the near-infrared resonator through an optical frequency conversion process, and the resulting shift in the OMO frequency is optically read out. A key advantage of this active sensing approach is that the extremely narrow linewidth of the OMO greatly increases detection sensitivity, leading to a noise-equivalent power of 0.1 pW/Hz. Meanwhile, the intrinsic response time of our detection mechanism is mostly limited by the mid-infrared resonator lifetime, which can be as short as a few nanoseconds. Our proposed method, based on mature photonic integrated circuit platforms, can potentially scale up to multipixel arrays for thermal imaging applications.