This study presents the development and validation of a fibre Bragg gratings (FBGs)-based sensor system for the assessment of strain in the midpalatal suture in subjects using rapid palatal expanders (RPEs). The ex-vivo experiments were made by means of positioning two RPEs in a porcine palatal region. The RPEs used were the Hyrax, a tooth-borne expander and MARPE (microimplant-assisted rapid palatal expansion), a bone-borne expander. In order to define the regions in the palatal region for the sensors positioning, a finite-element analysis was performed in a porcine head subjected to the loadings caused by an RPE. In addition, a strain transfer model was used to obtain a correction coefficient that approximates the strain estimated by the FBG to the actual strain in the structure under shear and normal stress. Results show high linearity in the sensors characterisation tests with the advantages of compactness, intrinsic safe operation and multiplexing capabilities of FBGs. In the RPE analysis, a higher strain was estimated in the anterior region, which is in accordance with the simulation and previously reported results, where MARPE showed a higher strain (with an exponential pattern) than Hyrax as the number of activations increase.

In optical fibre communication system, improved modulation schemes have been proposed to increase capability and high bit rate transmission. One such technique is optical duobinary modulation, which can able to broadcast high-speed optical signals over bandwidth-limited channels. The conventional modulation schemes employ the non-return-to-zero modulation and return-to-zero modulation technique. These schemes decrease spectrum width and increase the dispersion tolerance. However, the effect of inter-symbol inference presents between the pulses. These techniques give a reduced performance for high bit rate transmissions and transmission over long distances. Hence in this work, the implementation of duobinary modulation improves the performance of optical communication along with the provision of enhanced security through bio-inspired chaos masking scheme. The bio-inspired chaos-masking scheme generates the security key using the spider security pattern generator to provide improved security. The parameters of the proposed technique are analysed for different transmission rates and the performance improvement is validated.

In this work, the authors review different design setups of polarisation beam splitters (PBSs) developed in Si₃N₄ platforms. They analyse different approaches based on directional couplers and interferometers. Then the authors present the design and simulation results of a PBS based on two cascaded multi-mode interferometers that operate in the whole C-band. Finally, the authors compare the devices in terms of insertion loss, extinction ratio, bandwidth, footprint and fabrication tolerances.

The authors analyse a method, which leads to an efficient and precise algorithm for synthesising coaxial, optical fibre couplers of arbitrary modal electric-field distributions. Their purpose is to design a fibre optic index profile supporting two pre-selected mode fields such that their interference transfers all the optical power spatially from the core region to a cladding part of the optical fibre completely. To deal with this problem, they apply inverse transmission-line techniques. Using the desired electric field, they work inversely and synthesise the appropriate refractive index profile of the couplers with excellent crosstalk. They envisage one can apply this technique to design fibre optic coaxial components acting as filters in sensing and numerous other applications.

The authors present a new method for determining the optical properties of arbitrary refractive index elliptical core fibres. The method applies the elliptic cylindrical coordinate system to Maxwell's equations and appropriately, using Fourier Transforms, operated on an elliptical core optical fibre waveguide, derives a flexible algorithm, which can be used to determine the optical properties of elliptical fibre waveguides. By dividing the fibre into a series of uniform consecutive thin dielectric layers transversely across the elliptical cross section with suitable transforming functions representing voltage and current themselves based on the electromagnetic field components, leads to transverse transmission line equations. The resonance frequencies of the cascaded matrices determine the mode propagation constants. The analysis leads to a numerical algorithm for calculating the exact modes of propagation constants. The method is analytically exact and computationally accurate, leading to algorithmic implementation, without making use of Mathieu functions which are solutions for step index waveguide. The advantage of this work is also the fact that it can be applied to arbitrary refractive index profiles. They present results of modal diagrams for various fibre ellipticities and also apply this method to determine the birefringence of graded index profile fibres and mode cut-off frequencies.

This study presents a Brillouin distributed sensor (BDS) with high spatial resolution for the monitoring of temperature and strain simultaneously. Fourier deconvolution (FD), Fourier regularised deconvolution (FRD), and Fourier regularised denoising deconvolution (FRDD) algorithms have been explored to measure the Brillouin backscattered power using the optical time-domain reflectometry technique. The improvement of temperature and strain resolutions along with the spatial resolution using the FRDD algorithm is observed for 50 km sensing range. The numerical simulation process of the proposed sensing system has been simultaneously incorporated to extract temperature and strain information. The simulation results show that the temperature and strain resolutions are observed as 5°K and 138 μɛ, respectively, using FRDD compared with the FD algorithm which shows temperature and strain resolutions as 54°K and 1588 μɛ, respectively, at a 50-km distance. A high spatial resolution of 9 m is observed of the proposed BDS over the sensing range of 50 km using the FRDD algorithm. In addition, the denoising capability of the proposed FRDD algorithm is validated using the experimentally obtained Rayleigh backscattered signal.

Fibre Bragg Grating (FBG) sensor is a new sensor with numerous advantages. How to apply in the safety monitoring of landslide engineering is still in experiment and research stage. Here, FBG is used to monitor the landslide process of the gravel soil pile. Before monitoring experiment, the article first tests FBG packaging and burying effect by two tests in lab, one is sand pile landslide test which proves vertical buried is feasible and the other is loading test on the steel bar sensor which proves the wavelength change of FBG on steel bar sensor has a good linear relationship with the loading change. Then, buried the steel bar sensor in the gravel soil slope after simple encapsulation. Stress and strain monitoring results of grating sensors are obtained in landslide which is formed through the simulation of excavation construction. The experimental data show that through correct embedding FBG sensors can effectively monitor the stress–strain change of the slope. FBG provides a new way for the landslide early warning.

Compared with the traditional electrical resistance strain gauge, the fibre Bragg grating (FBG) is a new material that can be used to produce the strain sensor, which has many advantages such as convenient installation, low temperature drifting, less signal interference and higher transmitted quality. In this study, FBG sensor system configuration, design principle, numerical simulation and loading tests for the FBG strain gauge are expatiated extensively. At the last, one-axial and three-axial strain gauges are produced and some conclusions have been put forward. So the FBG strain gauge can meet the precision of the structure monitoring and replace the traditional sensors.

Optical fibers have demonstrated, against all early predictions, that their geometry is extremely well-suited for handling high optical powers. However, over the years, many refinements have been done to the basic structure of these waveguides to allow guiding and generating high-powers. As a result of this development the fibers employed in high-power laser systems differ significantly from those typically used in other fields such as telecommunications and/or sensors. Therefore, this chapter is devoted to describing and explaining the main intricacies of those optical fiber designs presently used for high-power operation. In this context, the main goal of this chapter is that the reader gets an overview of the different fiber designs and building blocks of high-power optical fibers. The chapter is divided into three main parts: a brief historical overview of the evolution of this technology, a description of the main constituents of fibers for high-power operation (including the core, the pump cladding and materials), and, finally, an outlook in which novel trends in the design of these waveguides are briefly described.

The thermal response of packaged biconic taper filter with a free spectral range of 1.7 nm is investigated over a temperature range of 0–70°C. The filter length dependence with temperature is estimated from the spectral offset. This device presented thermal stability of 3 × 10⁻³ nm/°C, measured at λ ₀ = 1550 nm.