Two‐Photon Nanomachining of a Micromechanically Enhanced Optical Cavity Sensor on an Optical Fiber Tip

Abstract

Herein, a two‐photon nanostructuring process that is employed to monolithically integrate dynamic three‐dimensional (3D) micromechanical features into Fabry–Pérot cavity (FPC) sensors on an optical fiber tip is demonstrated. These features represent a breakthrough in the integration and fabrication capabilities of micro optomechanical devices and systems. The demonstrated dynamic optical surface enables directional thin‐film deposition onto obscured areas. The rotation of the dynamically movable mirror to deposit a thin reflective coating onto the inner surfaces of a FPC with curved geometry is leveraged. The reflective coating in conjunction with the dynamically rotatable mirror greatly improves the quality factor of the FPC and enables a new class of highly integrated multipurpose sensor systems. A unique open cavity geometry on an optical fiber tip is used to demonstrate temperature and refractive index sensing with sensitivities of 2045 ± 39 nm/RIU and 366 ± 22 pm °C−1, respectively. A gold reflective coating sputtered onto the inner surfaces of the FPC improves the quality factors of the cavity by more than 800%. This technology presents a path forward for utilizing 3D design freedom in micromechanically enhanced optical systems to facilitate versatile processing and advantageous geometries beyond the current state of the art.