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Since 1966, when K. C. Kao and G. A. Hockham proposed the idea of low-optical-loss glass fibers, the invention of ultralow-loss silica optical fibers has contributed to the rapid development of numerous fields, including communications, sensing, lasing, and imaging. The unique properties of optical fibers, including their small size, ultrahigh aspect ratio, high mechanical robustness, immunity to electromagnetic interference, and high biocompatibility, facilitate their application in various environments such as remote distances, confined spaces, and even harsh environments with extremes of temperature, pressure, corrosion, and electromagnetic field.

We present a novel refractometric sensor based on a coated all-coupling optical-fiber-nanowire microcoil resonator which is robust, compact, and comprises an intrinsic fluidic channel. We calculate the device sensitivity and find its dependence on the nanowire diameter and coating thickness. A sensitivity as high as 700 nm/RIU and a refractive index resolution as low as 10^-10 are predicted.

We present an ultra-small all-silica high temperature sensor based on a reflective Fabry-Perot modal interferometer (FPMI). Our FPMI is made of a micro-cavity (~4.4 μm) directly fabricated into a fiber taper probe less than 10 μm in diameter. Its sensing head is a miniaturized single mode-multimode fiber configuration without splicing. The sensing mechanism of FPMI is the interference among reflected fundamental mode and excited high-order modes at the end-faces. Its temperature sensitivity is ~20 pm/°C near the wavelength of 1550 nm. This kind of sensor can work in harsh environments with ultra-large temperature gradient, but takes up little space because of its unique geometry and small size.

We experimentally demonstrated a refractometric sensor based on a coated optical microfiber coil resonator. It is robust, compact, and comprises an intrinsic fluidic channel. A sensitivity of about $40\mathrm{nm}$ /RIU (refractive index unit) has been measured, in agreement with predictions.