Abstract
A new type of polymer and silica connection is proposed. A tapered SMF- 28 silica optical fiber tip is fabricated using a CO2 laser by focusing and stretching the fiber. The tapered silica tip is inserted in one of the holes of a microstructured polymer optical fiber using a 3D alignment system. Using a supercontinuum source, the spectrum is observed after one and after two connections. The polymer fiber is characterized in curvature while using the previous connection.

Abstract
A microfiber knot resonator integrated in an abrupt taper-based Mach-Zehnder interferometer was used for simultaneous measurement of temperature and refractive index. This compact structure was fabricated using only CO2 laser processing. The transmission spectrum is the combination of the microfiber knot resonator and the Mach-Zehnder interferometer responses. The two different components of the transmission spectrum (the microfiber knot resonator and the MachZehnder interferometer components) present different sensitivities when subjected to physical or chemical parameters. A characterization in temperature, refractive index, and sodium chloride (NaCl) concentration was performed. A simple matrix method was used for simultaneous measurement of temperature and refractive index.

Abstract
A fiber Bragg grating was inscribed in an abrupt fiber taper using a femtosecond laser and phase-mask interferometer. The abrupt taper transition allows to excite a broad range of guided modes with different effective refractive indices that are reflected at different wavelengths according to Bragg's law. The multimode-Bragg reflection expands over 30 nm in the telecom-C-band. This corresponds to a mode field overlap of up to 30% outside of the fiber, making the device suitable for evanescent field sensing. Refractive index and temperature measurements are performed for different reflection peaks. Temperature independent refractive index measurements are achieved by considering the difference between the wavelength shifts of two measured reflection peaks. A minimum refractive index sensitivity of 16 +/- 1 nm/RlU was obtained in a low refractive index regime (1.3475-1.3720) with low influence of temperature (-0.32 0.06 pm/degrees C). The cross sensitivity for this structure is 2.0 x 10(-5) RlU/degrees C.. The potential for simultaneous measurement of refractive index and temperature is also studied.

Abstract
A sensing structure based on a cleaved silica microsphere is proposed for temperature sensing. The microsphere was cleaved using focused ion beam milling. The asymmetry in the structure introduced by the cut generates not only new cavities but also random interferometric reflections inside the microsphere. These two spectral components can be separated using low-pass and high-pass filters, respectively. The sensor response to temperature can be extracted from the cavities' component using a correlation method. The device achieved a temperature sensitivity of -10.8 +/- 0.2 pm/degrees C between 30 degrees C and 80 degrees C. The same effect is impossible to be obtained in a normal uncleaved microsphere. The random interferometric component did not provide any information on temperature using the same analysis. However, when changing the temperature, a new and completely distinct reflection spectrum with no apparent correlation with others at different temperatures was achieved.

Abstract

Abstract
In this work, an alternative method of coupling light into microstructured polymer fibers is presented. The solution consists in using a fiber taper fabricated with a CO2 laser. The connection is formed by inserting a tapered silica tip into the holes of a microstructured polymer fiber. This alternative method is duly characterized and the feasibility of such fiber connection to enable the polymer fiber as a displacement sensor is also demonstrated. © 2018 by the authors.