[INVITED] Developments in optical fibre sensors for industrial applications

The development of intrinsic optical fiber pH sensors based on fluorescence from novel coumarin dyes which are covalently immobilized onto the distal end of the fiber is described. The sensors provide response in the pH range of 0.5 − 6 with good stability over 24 h. The response time of the sensors is approximately 25 s. The sensors show no sensitivity to ionic strength (IS) and have excellent photostability

Amplified spontaneous emission-based technique for simultaneous measurement of temperature and strain by combining active fiber with fiber gratings

This article reports on an optical fiber-based sensing system for carrying out the simultaneous measurement of temperature and strain. The sensor design is based on the combination of active dopedoptical fiber and fiber gratings. Erbium/ytterbium co-doped fiber is used to meet the requirements for both high temperature responsivity and small sensor size to address smart structure applications. The temperature dependence of the amplified spontaneous emission power under different pump wavelengths is used as the basis of the sensor and an optical reference to enhance the measurement resolution is discussed. The feasibility of this technique for simultaneous measurement of temperature and strain is demonstrated

Fiber-Bragg-Grating-Based Sensor System to Measure Battery State of Charge Based on a Machine Learning Model

Real-time monitoring of the state of charge (SOC) of the batteries used in a wide variety of applications is becoming increasingly important, especially given the impetus by the current targets towards “net-zero”. In this research, an advanced approach was used involving fiber Bragg grating (FBG)-based sensors that were developed and implemented for the measurement of the key parameters required to ensure optimum battery performance. In this work, one of the biggest challenges to assess (and then map) the data from the sensor system developed is tackled in order to better understand the key parameters of the battery in an efficient and improved way. It is well known that the relationship between the changes in the resonance wavelength of the FBGs used in the sensor system, arising due to change in the electrical parameters of the battery, is complex and dependent on several different factors. In this work, this effect was evaluated by coupling the sensor data to a data-driven regression model approach that was developed for the measurement of the SOC of the batteries used, and this was obtained directly and conveniently from the FBG data. In this comprehensive study, FBG-based sensors were fabricated and then installed onto the battery, which then was subjected to a range of charging–discharging cycles, following which the electrical parameters of the battery were estimated from recorded data using a black-box machine learning (ML) model. Data-driven regression algorithms were employed for the training of the black-box model. The efficiency of the estimation of the SOC of the battery from the FBG-based sensor data was found to be high, at 99.62% (R2 values of Estimated SOC and True SOC line), creating a very satisfactory result for this key measurement. Thus, the work shows the robustness of the FBG-based sensor system combined with the neural network algorithm as an effective way to evaluate the electrical parameters of the battery, which is particularly important, as no physical/electrochemical/electrical model of the system is thus required

3D-printed Tilt Sensor based on an embedded Two-mode Fiber Interferometer

A 3D-printed tilt fiber sensor using a two-mode fiber interferometer (TMFI) as the sensing mechanism has been demonstrated. The TMFI was constructed by splicing single-mode fibers (SMF28s) at both ends of a two-mode fiber (TMF) to generate a comb-like interference spectrum that is sensitive to bending. A 3D-printed cantilever with a weight attached to one end was used to induce bending as the structure was tilted and by embedding the TMFI onto the 3D printed cantilever, different tilt angles can be measured, as a result of the bending of the fiber. The TMFI exhibited a linear response towards the tilt angles, θ, with a responsivity of 1 × 10-2 nm/deg at negative θ (0 to -90°) and 5 × 10-3 nm/deg at positive θ (0 to 90°), respectively. The sensor was able to detect small angle changes in increments as small as 1° and it performs better than embedded FBG sensors. The tilt sensor proposed has a small form factor and simple design, as well as being cost-effective and light-weight, thus showing significant potential for a variety of civil engineering applications

Generation of periodic surface structures on silica fibre surfaces using 405 nm CW diode lasers

Periodic surface structures have been observed on the end surfaces of synthetic silica fibres when they are exposed to long-term irradiation with light from a 405 nm CW diode laser. The surface structures are generated when the laser power is at a level which is three magnitudes of order lower than that of the damage threshold. They exhibit multiple bends, break-ups and bifurcations, unlike interference patterns but rather like the effect caused by short-pulsed laser irradiation on wide band-gap insulators. The detailed investigation undertaken in this work has concluded that the key parameters that contribute to the generation of the surface structures are power density, surface roughness, polarisation direction and the presence of ultraviolet defect centres

Optical fibre-based sensor technology for humidity and moisture measurement: Review of recent progress

Humidity and moisture sensing is becoming increasingly important in industry and through a wide spectrum of applications and a review of research activity in the field across a range of technologies was presented previously by some of the authors. Recognizing the major developments in the last few years, especially in the field of fibre optic humidity and moisture sensing, this paper aims to extend that approach to review and categorize recent progress in the optical fibre field for the measurement of humidity and moisture and examine, as a result, the breadth of applications that now are being discussed