Abstract
We propose a fiber-based environmental sensor that exploits the reflection-phase-shift tunability provided by the use of layered coatings composed of dielectric slabs spaced by conducting membranes. A transfer-matrix study is done in a simplified theoretical model, for which an enhanced sensitivity of the reflection interference pattern to the output medium is demonstrated, in the typical refractive index range of liquid media. An experimental configuration using a cascaded Fabry-Perot microcavity coated by a graphene oxide/polyethylenimine (GO/PEI) multilayered structure is demonstrated. Its cost-effective chemical production method makes graphene oxide-based hybrid coatings excellent candidates for future real-life sensing devices.

Abstract
Two distinct optical fibers for endoscope-based configurations are demonstrated and studied in this work. The fibers used for the experiment consist of: a conventional singlemode fiber (SMF 28e) and a hollow core photonic crystal fiber (HC-PCF) based on silica. Two studies that allowed the characterization of these fibers, according to their optical output power and when subjected to curvature, were carried out. The intensity power profile was also analysed in relation to the propagation distance, transversal displacement and incidence angle. After this study it can be concluded that the most suitable solution for the endoscope is the HC-PCF fiber working as a transmission probe. For the proof of concept of the fiber-based endoscope, a cleaved multimode fiber (MMF) tip was used as a reception probe and its reflection efficiency was also analysed.

Abstract
Demonstration of a fiber-integrated non-volatile reconfigurable metasurface providing high-contrast group delay dispersion switching functionality is reported, which may be engineered to operate at wavelengths across the near-infrared (telecoms) band. Light-induced amorphous-crystalline phase switching in a chalcogenide (germanium antimony telluride) metasurface, only a fraction of a wavelength thick, fabricated on the end-facet of a single-mode optical fiber, enables intensity and phase modulation of the guided wave at metasurface designated bands. Such devices present a range of opportunities in fiberized remotely programmable phase/intensity multiplexing and dynamic dispersion compensation for emerging telecommunications and data storage/processing applications, including in photonic neural network and neuromorphic computing architectures.

Abstract
The potential of evanescent Mach-Zehnder interferometers, embedded in Eagle2000 substrates, as refractive index sensors was assessed. For that, femtosecond laser direct writing and wet etching were used to fabricate and expose the sensing arm at the surface of the glass substrate, while keeping the reference arm buried. From the analysis of the structures' spectral response, we found that the wavelength shift of the different order peaks increased greatly for refractive indices nearing that of the glass, indicating a greater overlap between the guided mode's evanescent field and the external medium. Therefore, a maximum sensitivity of 10271 nm/RIU was obtained at a refractive index of 1.491. The sensitivity in the refractive index range of water-based solutions was, on the other hand, limited to 446 +/- 39 nm/RIU. Due to the geometry of the device, applications with films deposited at the surface of the substrate and PDMS based microfluidic channels can be explored.

Abstract
Optical waveguides were fabricated at the surface of Eagle2000 glass substrates, using femtosecond laser direct writing and wet etching, and their potential as intensity-modulated refractometers was assessed. Through the analysis of their broadband spectral response to different refractive index oils, we observed that mode mismatch is present when the guided mode reaches the surface of the substrate and interacts with the external medium, thus enabling the use of such optical waveguides in refractive index sensing. Refractive indices equal to or greater than that of the substrate also induced a coupling mechanism that was shown not to be suitable in these devices. The device's wavelength of operation was found to be tunable by controlling the distance between the surface and the center of the optical waveguide. However, the sensitivity was seen to diminish by increasing the latter, being nonexistent for distances greater than 5.5 mu m. In this study, the maximum sensitivity values were found for a surface to core center distance between 1 and 2 mu m, in the biological range, and 2.5 to 3 mu m, for a refractive index nearing that of the substrate. Accordingly, maximum sensitivities of approximate to 25 dB/RIU and approximate to 1200 dB/RIU were found between 1.300 < n(D)(25)degrees(C) < 1.400 and 1.490 < n(D)(25)degrees(C) < 1.500, respectively.

Abstract
Low loss optical waveguides are the key component for the fabrication of more complex integrated optics devices. In most works related to femtosecond laser written waveguides, the values presented give results at a single wavelength or in a narrow wavelength band; but some applications in optical sensing, for example, would benefit from waveguides having good propagation properties in a larger wavelength range. This paper presents results that allow one to gain insight into the major loss mechanisms present in laser written waveguides in two different types of glasses (fused silica and Eagle 2000 glass) and the dependence of those on the fabrication parameters. Finally, an example of application of broadband operating waveguides is given.