Abstract
Two different sensing structures based on a hollow microsphere Fabry-Perot cavity are proposed. The hollow spheroidal cavities are fabricated resorting only to fusion splicing. The first structure is based on a hollow microsphere located at the fiber end and works as a probe sensor. The structure was subjected to lateral load pressure and presents a sensitivity of 1.56 +/- 0.01 nm/N. The second proposed sensor relies on an in-line hollow microsphere. The sensing structure allows the detection of lateral loading, with a sensitivity of 2.62 +/- 0.02 nm/N, as well as strain detection, with a sensitivity of 4.66 +/- 0.03 pm/mu epsilon. The two proposed sensors present similar response when subjected to temperature and have low thermal sensitivity.

Abstract
This work presents a multimode interference-based fiber sensor in a cavity ring-down system for sensing temperature-induced refractive index (RI) changes of water. The sensing head is based in multimodal interference (MMI) and it was placed inside the fiber loop cavity of the CRD system. A modulated laser source was used to send pulses down into the fiber loop cavity and an erbium-doped fiber amplifier (EDFA) was placed in the fiber ring to provide an observable signal with a reasonable decay time. The behavior of the sensing head to temperature was studied due to its intrinsic sensitivity to said parameter - a sensitivity of -1.6 10(-9) s/C was attained. This allowed eliminating the temperature component from RI measurement of water and a linear sensitivity of 580 mu s/RIU in the RI range of 1.324-1.331 was obtained.

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
The use of a polymer fiber as a refractive index sensor is proposed. A fiber Bragg grating is inscribed near the fiber tip and the fiber is cut shorter thus creating a Fabry-Perot cavity. The reflections between the fiber Bragg grating and the fiber end-face create a Fabry-Perot interferometer. The sensor was characterized to refractive index changes at constant temperature and to temperature at constant refractive index using a fast Fourier transform analysis of the interference signal. The sensor revealed a sensitivity of-1. 94 RIU-1 with a resolution of lx10(-3)RITJ and low sensitivity to temperature, with a cross sensitivity to temperature of 3. 6x10(-4)RIU/degrees C.

Abstract
The possibility of using polymer fiber as a refractive index sensor is presented. The sensor is based on a Fabry-Perot interferometer formed at the tip of the polymer fiber. The interference is granted due to reflections between a fiber Bragg grating and the fiber end-face. The sensor was characterized to refractive index changes at constant temperature using a fast Fourier transform analysis of the interference signal. A sensitivity of -1.94 RIU-1 was achieved with a resolution of 1 x 10(-3) RIU and a cross sensitivity to temperature of 1 x 10(-4) RIU/degrees C

Abstract
Optical Y-junction power splitters owe their inherent broadband spectral behavior to their design. However, depending on the fabrication technique employed, asymmetries in the junction might arise, perturbing its performance; this is the case in femtosecond laser written Y-junctions where one arm is typically written over the top of the other. In this letter, the spectral behavior of Y-junctions fabricated in fused silica by the femtosecond laser direct writing technique was analyzed and optimized for the first time, to the best of our knowledge. The junction arms output power balance as well as the corresponding spectral flatness between 1300 and 1600 nm is substantially increased by the implementation of an initial separation between the arms at the junction diverging point, enabling the manufacturing of balanced broadband Y-junctions.