A highly sensitive temperature sensor based on an all-fiber Sagnac loop interferometer combined with metal-filled side-hole photonic crystal fiber (PCF) is proposed and demonstrated. PCFs containing two side holes filled with metal offer a structure that can be modified to create a change in the birefringence of the fiber by the expansion of the filler metal. Bismuth and indium were used to examine the effect of filler metal on the temperature sensitivity of the fiber-optic temperature sensor. It was found from measurements that a very high temperature sensitivity of $-9.0\mathrm{nm}/°\mathrm{C}$ could be achieved with the indium-filled side-hole PCF. The experimental results are compared to numerical simulations with good agreement. It is shown that the high temperature sensitivity of the sensor is attributed to the fiber microstructure, which has a significant influence on the modulation of the birefringence caused by the expansion of the metal-filled holes.

A fibre optic Bragg grating sensor to measure the strain in the chest of patients is described. The sensor provides a new method to measure ventilatory movements and it can also determine the respiratory frequency spectrum. The apparatus uses a fixed optical filter reference scheme to reduce the overall cost and is able to detect respiratory movements with frequency components up to 10 Hz. Ventilatory signals were acquired from slow breathing, with 500 ml inspiration volume, to fast, with a reduced volume of 60 ml, respiration. The sensor described here can be used to trigger the pulse burst of electrically assisted ventilation processes or to monitor high frequency oscillatory ventilation.

In this paper, we propose and numerically analyze a novel design for a high sensitivity refractive index (RI) sensor based on long-range surface plasmon resonance in H-shaped microstructured optical fiber with symmetrical dielectric–metal–dielectric waveguide (DMDW). The influences of geometrical and optical characteristics of the DMDW on the sensor performance are investigated theoretically. A large RI analyte range from 1.33 to 1.39 is evaluated to study the sensing characteristics of the proposed structure. The obtained results show that the DMDW improves the coupling between the fiber core mode and the plasmonic mode. The best configuration shows 27 nm of full width at half maximum with a resolution close to 1.3 × 10 ${}^{-5}$ nm, a high sensitivity of 7540 nm/RIU and a figure of merit of 280 RIU ${}^{-1}$ . Additionally, the proposed device has potential for multi-analyte sensing and self-reference when dissimilar DMDWs are deposited on the inner walls of the side holes. The proposed sensor structure is simple and presents very competitive sensing parameters, which demonstrates that this device is a promising alternative and could be used in a wide range of application areas.

In this paper, multi-plasmon resonances in microstructured optical fibers (MOFs) are proposed and analyzed as a methodology to achieve surface-plasmon-resonance (SPR) sensors with a wide refractive index (RI) detection range and as a multi-analyte sensing technique. For this purpose, the influence of multi-plasmon excitations on the performance of SRP sensors based on suspended core microstructured optical fibers (SCFs) with three and four holes was studied theoretically. A large analyte RI range from 1.33 to 1.39 was evaluated to investigate the sensing performance of the SCF-based SPR sensors. The results indicate that the excitation of higher order SPP modes could be an alternative to achieve SPR sensors with a wide analyte RI range and competitive resolution. We found that the shape of the fiber core and the metallized surface have a significant effect on the plasmonic excitation spectra. We also found that multi-plasmon excitations have potential for multi-analyte sensing and self-reference. This paper can provide a reference for developing MOF-based SPR sensors.

In this work, a new approach based on the use of a one-dimensional photonic crystal (1DPC) made of dielectric layers with alternating refractive indexes deposited inside a photonic crystal fiber (PCF) is proposed as a suitable platform for the excitation of Bloch surface waves (BSWs). The presence of an additional dielectric layer on the 1DPC modifies the local effective refractive index, enabling a direct manipulation of the BSWs. In particular, we investigate BSW resonance conditions in a 1DPC of alternating layers of TiO₂ and SiO₂ deposited inside a three-hole suspended-core PCF to design an ultra-wide range refractive index sensor in the near infrared. The obtained simulation results indicate that BSW sensors based on PCF could be an alternative to surface plasmon resonance (SPR) sensors, with a ultrahigh sensing figure-of-merit, which might facilitate applications in high-resolution refractive index sensing.

With the goal of ultimate control over the light propagation, photonic crystals currently represent the primary building blocks for novel nanophotonic devices. Bloch surface waves (BSWs) in periodic dielectric multilayer structures with a surface defect is a well-known phenomenon, which implies new opportunities for controlling the light propagation and has many applications in the physical and biological science. However, most of the reported structures based on BSWs require depositing a large number of alternating layers or exploiting a large refractive index (RI) contrast between the materials constituting the multilayer structure, thereby increasing the complexity and costs of manufacturing. The combination of fiber–optic-based platforms with nanotechnology is opening the opportunity for the development of high-performance photonic devices that enhance the light-matter interaction in a strong way compared to other optical platforms. Here, we report a BSW-supporting platform that uses geometrically modified commercial optical fibers such as D-shaped optical fibers, where a few-layer structure is deposited on its flat surface using metal oxides with a moderate difference in RI. In this novel fiber optic platform, BSWs are excited through the evanescent field of the core-guided fundamental mode, which indicates that the structure proposed here can be used as a sensing probe, along with other intrinsic properties of fiber optic sensors, as lightness, multiplexing capacity and easiness of integration in an optical network. As a demonstration, fiber optic BSW excitation is shown to be suitable for measuring RI variations. The designed structure is easy to manufacture and could be adapted to a wide range of applications in the fields of telecommunications, environment, health, and material characterization.