Abstract
The detection of dissolved carbon dioxide (dCO(2)) is made possible through a colorimetric effect that occurs in a sensitive membrane. The reaction with dCO(2) changes the pH of the membrane causing a small difference in its colour which results in a characteristic absorbance spectrum band near 435 nm. A sensing platform based on this effect was developed and tested in gaseous and in aqueous environments. It is a combination of a bundle of large core fibre optics (with diameters above 200 mu m) with light emission diodes (LEDs) in the visible range of the spectrum, a silicon photodetector and a polymer membrane sensitive to CO2. A variation in the absorption of 3 / %VV was obtained in the range from 0 to 1.6 % of gaseous CO2 with an estimated response time below 60 seconds.

Abstract
A Mach-Zehnder interferometer was created from a cavity milled in the taper region next to a microfiber knot resonator. A focused ion beam was used to mill the cavity with 47.8 mu m in length. The microfiber knot resonator was created from an 11 mu m diameter taper, produced using a filament fusion splicer. After milling the cavity, the microfiber knot resonator spectrum is still visible. The final response of the presented sensor is a microfiber knot resonator spectrum modulated by the Mach-Zehnder interference spectrum. A preliminary result of -8935 +/- 108 nm/RIU was obtained for the refractive index sensitivity of the cavity component in a refractive index range of n = 1.333 to 1.341. Simultaneous measurement of refractive index and temperature using this combined structure is a future goal.

Abstract
A compact sensing structure using two distinct optical devices, a microfiber knot resonator and an abrupt taper-based Mach-Zehnder interferometer (MZI), is presented. The device was fabricated using only CO2 laser processing. The transmission spectrum presents two different components with different sensitivities to different physical and chemical parameters. The sensor was characterized in temperature and refractive index. For temperature sensing in water, the MZI component presents a sensitivity of -196 +/- 2 pm/degrees C while the microfiber knot resonator (MKR) component shows a sensitivity of 25.1 +/- 0.9 pm/degrees C, for water temperature variations of 12 degrees C. Sensitivities of 1354 +/- 14 nm/RIU and -43 +/- 4 nm/RIU were achieved for refractive index sensing for the MZI and the MKR components, respectively, in a refractive index range from 1.32823 to 1.33001. The matrix method was used for the simultaneous measurement of temperature and refractive index.

Abstract
This work reports a multimode interference-based fiber sensor in a cavity ring-down system (CRD) for sensing temperature-induced refractive index (RI) changes of water. The sensing head is based in multimodal interference (MMI) and it is 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 -1.6x10(-9) mu s/degrees 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. The use of a MMI fiber sensor in the proposed CRD configuration allowed achieving a sensitivity similar to 4-fold than that obtained with a tilted fiber Bragg grating and similar to 2-fold than that when a micrometric channel inscribed in the fiber was used.

Abstract
A sensor based on Fabry-Perot interferometry with a hollow microsphere cavity embedded in a 3D printed structure is proposed. The sensor was tested for lateral loading and temperature, showing promising results. By imprintring the sensor on the structure, the dynamic range of application is severely increased enabling the application of the sensor in harsh environments.

Abstract
A Fabry-Perot based sensor with two coupled hollow microspheres is presented. The sensor was fabricated using fusion splicing techniques, enabling a low-cost, highly reproducible, production. The coupling of the two microspheres gives rise to a highly sensitive strain sensor, reaching a sensitivity of 4.07 pm/mu epsilon. The allsilica composition leads to a low thermal sensitivity, making the proposed structure suitable applications in environments with varying external conditions.