Slightly Tapered Optical Fiber With Inner Air-Cavity as a Miniature and Versatile Sensing Device

A long-standing goal of optical fiber sensors is the development of a miniature and versatile optical fiber device, which is capable of performing multiple sensing functions, and supporting a simple and efficient system. Here, we demonstrate an elegant way of achieving such a device by use of an inner air-cavity in a slightly tapered optical fiber. Owing to the small size of only a few tens microns and inner cavity structure, a spatially precise "point sensing" with high sensitivity and good robustness can be readily achieved. The refractive index, strain, and temperature sensitivities obtained are similar to 1060 nm/RIU (refractive index unit), 22.5 pm/mu epsilon, and 80 pm/degrees C, respectively. The inner air-cavity-based device is flexible, ultracompact, versatile, and highly efficient, which provides a promising new way for a wide range of optical fiber sensing applications.