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Optical fibers are a key component in modern photonics, where conventionally used polymer materials are derived from fossil-based resources, causing heavy greenhouse emissions and raising sustainability concerns. As a potential alternative, fibers derived from cellulose-based materials offer renewability, biocompatibility, and biodegradability. In the present work, we studied the potential of carboxymethyl cellulose (CMC) to prepare optical fibers with a core-only architecture. Wet-spun CMC hydrogel filaments were cross-linked using aluminum ions to fabricate optical fibers. The transmission spectra of fibers suggest that the light transmission window for cladding-free CMC fibers was in the range of 550–1350 nm, wherein the attenuation coefficient for CMC fibers was measured to be 1.6 dB·cm–1 at 637 nm. CMC optical fibers were successfully applied in touch sensing and respiratory rate monitoring. Finally, as a proof-of-concept, we demonstrate high-speed (150 Mbit/s) short-distance signal transmission using CMC fibers (at 1310 nm) in both air and water media. Our results establish the potential of carboxymethyl cellulose-based biocompatible optical fibers for highly demanding advanced sensor applications, such as in the biomedical domain. publishedVersion

The safety level of curtain wall panel will gradually decrease with the increase in service time due to the aging of materials, corrosion and looseness of fasteners. Therefore, the deformation monitoring analysis of building curtain wall based on optical fiber sensing technology was proposed. In this paper, the relationship between the stable state of the curtain wall panel and its dynamic characteristic parameters was studied. For this purpose, the optical fiber sensing technology into the deformation monitoring of the curtain wall was introduced, and the optical fiber sensing model of the stability of the glass curtain wall with the input layer content and hidden layer content was established. Moreover, the remote, rapid and accurate quantitative evaluation of the safety state of the curtain wall panel was realized to complete the deformation monitoring analysis of the curtain wall. The experimental results showed that the optical fiber sensing model can effectively monitor the stability of glass curtain wall, and the monitoring effect of building curtain wall using optical fiber sensing technology was better.

With the development of information transmission, there is an increasing demand for state monitoring of fiber-optic communication networks to improve the security and self-healing ability of the network. Distributed optical fiber sensing is one of the most attractive methods because it can achieve real-time detection of the whole network without additional sensing heads. However, when the sensing network is introduced into the communication network, the failure probability should be efficiently suppressed with limited sensing resources. In this paper, the fuzzy logic system is used to evaluate the impact of different sensing resource allocation on optical cable network quality. The link failure probability and path failure probability under the condition of uniform and non-uniform sensing resource allocation are simulated and analyzed, respectively. As shown in the analysis results, the failure probability under non-uniform allocation is significantly lower than under uniform allocation. In this paper, we discussed and addressed the allocation of the optical fiber sensing and communication integrated (OFSCI) network with the limited sensing resource for the first time. The results are helpful to develop an allocation strategy for optical fiber sensing and a communication integrated network with a higher robustness.

On the basis of the photoelectric properties and hydrophilicity and multimode interference of Graphene Oxide (GO), this study proposes an all-fiber humidity sensor. Two core-offset regions are constructed with a fiber fusion splicer, and a GO film is coated on a single-mode fiber (SMF) between the core-offset regions to form a humidity-sensitive Mach–Zehnder interference structure. As the external humidity environment changes, the refractive index of the GO changes, and the light in the SMF is modulated by humidity. External humidity is measured by detecting the changes in the wavelength of the transmission spectrum of the sensing structure. A saturated salt solution is used to build a stable humidity environment. The sensitivity of the sensor is 0.05 nm/% relative humidity (RH) at 35.3%–95.8% RH, and the linear relationship between the characteristic wavelength and RH is 88%. In addition, the linear relationship between the light intensity and the RH of the sensor at a single wavelength at 1571 nm is analyzed, and the linearity is 97.45%. According to this finding, photoelectric conversion is used to convert the light intensity signal into a voltage signal. The data are processed by a computer to achieve the real-time and visual monitoring of the humidity environment. The fiber optic humidity sensor proposed in this work has a simple structure, simple production, low cost, and high sensitivity. This work provides a new method for humidity sensing.

Optical fiber sensing technology has developed rapidly since the 1980s with the development of the optical fiber and fiber optical communication technology. It is a new type of sensing technology that uses light as a carrier and optical fiber as a medium to sense and transmit external signals (measurands). Distributed fiber optical sensors (DFOS) can continuously measure the external physical parameters distributed along the geometric path of the optical fiber. Meanwhile, the spatial distribution and change information of the measured physical parameters over time can be obtained. This technology has unmatched advantages over traditional point-wise and electrical measurement monitoring technologies. This paper summarizes the state-of-the-art research of the application of the distributed optical fiber sensing technology in geo-engineering in the past 10 years, mainly including the advantages of DFOS, the challenges in geo-engineering monitoring, related fundamental theoretical issues, sensing performance of the optical sensing cables, distributed optical fiber monitoring system for geo-engineering, and applications of optical fiber sensing technology in geo-engineering.

The weak direct current (DC) signals detected and converted by the photodetector are output to the mobile phone by voltage/frequency switching, and the signals are processed by the mobile phone APP and audio conversion module. The photodetector is equipped with the automatic switching function to design an optical power meter and detect weak signals. Meanwhile, the optical cable identification system is analyzed and combined with the optical power meter to generate an optical fiber sensing network to improve the weak alternating current (AC) signal detection. This network needs data fusion in sensor nodes’ data collection. The cluster routing protocol is introduced and combined with the back propagation neural network (BPNN) to propose a method suitable for this photoelectric transmission and improve the information fusion and accuracy. In the experiment, the optical power meter is output in gears first, and the output waveforms are normal. The photodiode’s optical power is adjusted to obtain different frequencies on the oscilloscope. In the proposed optical fiber sensing network, weak AC signals are amplified significantly, and different optical fiber lines can be distinguished in the optical cables. The proposed information collection method can reduce network communication and node energy consumption.

Optical fiber sensing systems have been widely developed for several fields such as biomedical diagnosis, food technology, military and industrial applications and civil engineering. Nowadays, the growth and advances of optical fiber sensors (OFS) are focused on the development of novel sensing concepts and transducers as well as sensor cost reduction. This review provides an overview of the state-of-the-art of OFS based on sol–gel materials for diverse applications with particular emphasis on OFS for structural health monitoring of concrete structures. The types of precursors used in the development of sol–gel materials for OFS functionalization to monitor a wide range of analytes are debated. The main advantages of OFS compared to other sensing systems such as electrochemical sensors are also considered. An interdisciplinary review to a broad audience of engineers and materials scientists is provided and the relationship between the chemistry of sol–gel material synthesis and the development of OFS is considered. To the best of the authors’ knowledge, no review manuscripts were found in which the fields of sol–gel chemistry and OFS are correlated. The authors consider that this review will serve as a reference as well as provide insights for experts into the application of sol–gel chemistry and OFS in the civil engineering field.

Purpose The purpose of this paper is to establish a strain prediction model of mining overburden deformation, to predict the strain in the subsequent mining stage. In this way, the mining area can be divided into zones with different degrees of risk, and the prevention measures can be taken for the areas predicted to have large deformation. Design/methodology/approach A similar-material model was built by geological and mining conditions of Zhangzhuang Coal Mine. The evolution characteristics of overburden strain were studied by using the distributed optical fiber sensing (DOFS) technology and the predictive model about overburden deformation was established by applying machine learning. The modeling method of the predictive model based on the similar-material model test was summarized. Finally, this method was applied to engineering. Findings The strain value predicted by the proposed model was compared with the actual measured value and the accuracy is as high as 97%, which proves that it is feasible to combine DOFS technology with machine learning and introduce it into overburden deformation prediction. When this method was applied to engineering, it also showed good performance. Originality/value This paper helps to promote the application of machine learning in the geosciences and mining engineering. It provides a new way to solve similar problems.

We demonstrate distributed measurement of the polarization beat length along single-mode optical fibers (SMFs) using slope-assisted Brillouin optical correlation-domain reflectometry (BOCDR) with high spatial resolution, long measurement range, high sampling rate, and single-end accessibility. The beat lengths of SMFs wound on mandrels with radii of 10.5, 7.5, and 3.4 cm are measured to be 36.0, 18.2, and 3.7 m, respectively, which agree well with theoretical calculations. This indicates that a unique beyond-nominal-resolution effect of slope-assisted BOCDR does not influence the measurement. Subsequently, distributed beat length measurement is demonstrated using an SMF comprising two sections wound on mandrels with different radii (10.5 and 3.4 cm).

Mode excitations in D-shaped multimode fiber are analyzed in detail in terms of the effect of launch offset, polishing depth, and length of the D-shaped section. Based on the analysis, specklegrams from D-shaped multimode fiber structures are proposed to be applied in refractive index sensing. Glycerol solutions with different concentrations were used to study the relationship between the zero-mean normalized cross-correlation coefficient (ZNCC) of fiber output specklegrams and the surrounding refractive index. Responses of different D-shaped fiber structures are investigated and compared. For all of the structures, regular gradual changes of the ZNCC for each specklegram with the refractive index are found in a wide refractive index range of 1.352-1.444, which shows the feasibility of refractive index sensing. A high sensitivity being 10.47 RIU−1 is obtained by the structure with the polishing depth being $18~\mu \text{m}$ and length being 5cm. The proposed refractive sensing scheme is easy to realize with wide measurement range and high flexibility.

Multicore fiber (MCF) which contains more than one core in a single fiber cladding has attracted ever increasing attention for application in optical sensing systems owing to its unique capability of independent light transmission in multiple spatial channels. Different from the situation in standard single mode fiber (SMF), the fiber bending gives rise to tangential strain in off-center cores, and this unique feature has been employed for directional bending and shape sensing, where strain measurement is achieved by using either fiber Bragg gratings (FBGs), optical frequency-domain reflectometry (OFDR) or Brillouin distributed sensing technique. On the other hand, the parallel spatial cores enable space-division multiplexed (SDM) system configuration that allows for the multiplexing of multiple distributed sensing techniques. As a result, multi-parameter sensing or performance enhanced sensing can be achieved by using MCF. In this paper, we review the research progress in MCF based distributed fiber sensors. Brief introductions of MCF and the multiplexing/de-multiplexing methods are presented. The bending sensitivity of off-center cores is analyzed. Curvature and shape sensing, as well as various SDM distributed sensing using MCF are summarized, and the working principles of diverse MCF sensors are discussed. Finally, we present the challenges and prospects of MCF for distributed sensing applications.

In practical engineering applications, the real-time monitoring of structural physical field is very important, which requires overall performance improvements on the Brillouin optical fiber sensing, including fast measurement, quick data demodulation and small amount of data storage. A novel Brillouin optical time-domain analysis (BOTDA) scheme has been proposed based on compressed sensing and pattern recognition algorithms, which paves the way for the real time Brillouin optical fiber sensing. In order to test the sensing performance, the Brillouin gain spectrum is measured by the traditional fast BOTDA, where the frequency step and span are 4 MHz and 500 MHz, respectively. By employing the proposed algorithms, the strain information is directly obtained with only 35% of the full data, verifying the feasibility of real-time measurements.

We have proposed n-shape elastomers for enhancing sensitivity of acoustic signal detection. The simulation results show that such n-shape elastomers with cantilever-like structure can be deformed by sound wave pressure, showing great potential of high sensitivity sensor head in distributed optical fiber sensing system.

We present a high-speed fiber Bragg grating interrogator based on an active Sagnac interferometer and phase-generated-carrier demodulation performed in real time by a low-cost FPGA system. The system has 280kHz detection bandwidth and 1MS/s sampling rate, and implements a multitone-mixing scheme to reduce distortion.

We study the influence of the fiber Bragg grating (FBG)'s bandwidth on the performance of the long distance point sensing system based on random fiber laser. The results show that the optical signal-to-noise ratio (OSNR) decreases gradually when the bandwidth of the FBG increases by simulation, under the same pump power, which is demonstrated by the experiment. This work could provide a reference for designing a long-distance optical fiber sensing system.

Refereed/Peer-reviewed A multiplexed fiber sensor is proposed based on Fabry-Perot interferometers formed by serially splicing C-shaped and single mode fibers. We first demonstrate multiplexed refractive index sensing by independently filling and measuring sodium chloride (NaCl) solutions with different concentrations in a two-cavity system. The results show minimal cross-talk between the two interferometers. The dual-cavity interferometric sensor was then applied to biochemical sensing by utilizing polyelectrolyte layer by layer self-assembly followed by the biotin-streptavidin binding mechanism. The proposed sensor solves an important problem in biochemical sensing by providing an ability to simultaneously measure a negative control, critical for reducing false positive measurements.

In this paper we propose a novel type of highly-birefringent and ultra-wideband low-loss photonic crystal fiber (PCF) incorporating elliptical holes in the cladding and rhombic holes located along the transversal axes. The PCF is simulated and analyzed with finite-difference time-domain method. The properties of PCFs were investigated for various distribution, shape and size of air holes. For the optimized PCF design the birefringence reaches 8 × 10−3 at 1550 nm and the confinement loss is as low as 5 × 1 0 − 4 dB/km with single mode operation in an ultra-broad transmission band (500 nm–1800 nm). Furthermore, the single mode and single polarization transmission could be achieved in this PCF at longer wavelengths beyond 1600 nm. This kind of PCF has potentials in optical long haul communication and optical fiber sensing.

The design idea and complete system design scheme of crack monitoring system based on fiber micro-bending principle are proposed. The simulation test platform of crack monitoring system is constructed, which provides theoretical and technical guarantee for crack monitoring test based on fiber sensing. A crack monitoring technique based on oblique fiber optic sensing network is proposed, and the angle of skew between the fiber and the crack is equal to 60. Time is the best sensor network deployment solution. The technical method has the advantages of simple process, low cost, easy implementation, and ability to realize distributed measurement. A crack monitoring technology based on microbend sensitized fiber sensor head is proposed. The quantitative relationship between optical loss and crack width of sensitized fiber sensor network is established, and microbend sensitized fiber sensor head is designed and fabricated. The technical method can accurately locate and accurately measure concrete cracks under the condition of unknown crack direction, and the test precision reaches 0.05 mm, which is completely suitable for high-precision and distributed monitoring of concrete cracks, and can be used in concrete bridges and dams. Widely promoted and applied in crack monitoring such as tunnels.

Optical fiber sensing (OFS) systems can be used to accurately measure temperature, strain, pressure, and other physical parameters by detecting the change in the field of lightwave. As they are used in more application areas, a new type of OFS with the ability of providing multi-dimensional, highly sensitive, ultra-fine, and real-time measurement is necessary. This is possible with the application of digital coherent optical technologies in the OFS systems. In this paper, we show that many aspects of OFS systems can be replaced or enhanced by digital coherent optical technologies. For example, digital optical frequency comb (DOFC) can replace the sweeping laser source, and the digital coherent optical receiver can replace the direct detection receiver to enable simultaneous detection of all the dimensions of lightwave. Based on these techniques, we present our research progresses on OFS with multi-dimensional, real-time, ultra-fine spectral analysis, and single-shot Brillouin optical time-domain analysis based DOFC for distributed OFS. We show that the OFS systems can be bought to a whole new level with the capabilities of real-time time–frequency analysis, ultra-fine spectral resolution, and ultra-low sensitivity. Opportunities and challenges of using digital coherent optical technologies in OFS systems are also discussed.

Interferon-gamma (IFN-γ), a proinflammatory cytokine, has been used as an early indicator of multiple infectious diseases or tumors. In order to explore the detection capability of a commonly used anti-IFN-γ aptamer, a simple target induced strand-displacement aptasensing strategy was tested by introducing three different complementary strands and two different signal/quencher pairs. The Texas red/BHQ2-based sensor showed the best affinity constant (Kd) of 21.87 ng mL−1. It was found that the strand-displacement aptasensing strategy was impacted by the complementary position and length of the complementary strands. Additionally, the hybridization chain reaction (HCR) amplification strategy was introduced, yielding a 12-fold improved sensitivity of 0.45 ng mL−1. In order to further explore the sensing platform for spatially localized cytokine detection, the Texas red/BHQ2-based strand-displacement aptasensor was successfully fabricated on the 3D optical fiber surface to achieve a deployable sensing device for monitoring IFN-γ based on the fluorescence spots counting strategy. Finally, the three developed aptasensing strategies (strand-displacement strategy, HCR amplification strategy, 3D optical fiber aptasensor) were applied for detection of IFN-γ secreted by PBMCs with comparable results to those of ELISA. The deployable 3D optical fiber aptasensor with the superior sensitivity is potential to be used for detection of spatially localized IFN-γ in vivo.

The optical fiber acoustic sensing system is suitable for long-distance monitoring of the acoustic signals generated by the external disturbances. According to the continuity of sensing units, quasi-distributed and distributed optical fiber acoustic sensing technologies are differentiated to meet different application requirements. On the one hand, the recent progress of Fabry-Perot interferometer (FPI) focusing on the diaphragm material, and the research hotspots in the field of the continuous Fiber Bragg grating (FBG) array are firstly reviewed. On the other hand, Mach-Zehnder interferometry (MZI), Michelson interferometry (MI), and Sagnac interferometry (SI) have rapidly developed in the aspect of the demodulation algorithm optimization with the purpose of the sensing performance improvement. Moreover, the current primary research works of the phase-sensitive optical time-domain reflectometer ( $\varphi $ -OTDR) are the signal-to-noise ratio improvement and the mixed optical structure design. Finally, this paper presents an overview of the recent advances of optical fiber acoustic sensing system in the application domains of military defense, structural health monitoring, petroleum exploration, and development.

The monitoring of mine pressure, division of vertical zoning of the overburden, discrimination of key stratum structure of the overburden and monitoring of advanced abutment pressure are still the main research problems in the field of coal mining. Therefore, the promotion of development of a monitoring technology of mining-induced rock mass deformation has important research value in the mining field. There are many problems to be solved in the application of optical fiber sensing (OFS) to deformation monitoring, such as the corresponding relationship between actual deformation and optical parameters, the coupling relationship between the optical fiber and rock mass and the reasonable division of vertical zoning of the overburden. In this study, a quantitative index of coupling action between the mining rock mass and optical fiber is put forward, and the coupling coefficient of different vertical zonings is quantitatively analyzed and discussed. Based on this, five different media in contact with optical fiber are proposed. The relationship between the strain curve form, the development height of the fracture zone and the activity of key stratum is established. It is of great academic value and research significance to establish a characterization system of displacement, deformation and structural evolution of overlying strata based on optical fiber sensing technology.

Distributed sensors have become a great advantage for Structural Health Monitoring (SHM) as they allow for the multiple points measurement using a single sensor. Nevertheless, the installation of this technology can be time-consuming and have an impact on the overall cost of the project. For this reason, this paper explores the application of different techniques for embedding fiber optic cable into textile for Distributed Optical Sensors which could greatly reduce the installation time. This embedding also provides the ability to design sensors with different patterns that enable monitoring structures like pipelines, bridges, and others. In this paper we have identified an embedding technique that does not damage the fiber optic cable. Additionally, the sensors were tested to study their response to temperature and strain by using Brillouin Optical Time Domain Amplification (BOTDA) interrogation technique.

In this paper, we demonstrate the refractive index (RI) sensing properties of long-period fiber gratings (LPFGs) at 2 μm. The RI sensing properties of the resonant dips of LP03, LP04, LP05, and LP06 cladding modes operating at 2 μm have been studied, respectively. The sensitivity of resonant dip of LP06 mode operating at 2 μm could reach -670 nm/RIU and - 15483.9 nm/RIU in the RI region of 1.3500-1.4500 and 1.4500-1.4624, respectively, which is higher than that of the resonant dip of lower-order cladding modes. Furthermore, the RI sensitivity can be achieved higher with the longer resonance wavelength. The proposed LPFGs-based RI sensor has potential for the next generation optical fiber sensing systems.

This paper introduces an implementation of a system allowing to denoise the intensity data sensed by a DAS system before analyzing it through a convolutional neural network for train tracking. The results obtained showed that it is possible to track a train by focusing only on the magnitude of signals without caring out complex treatments.

A novel polarization-based forward transmission system without signal fading is proposed for vibration detection. This system promises potential application in perimeter security and physical parameters measurement.

The use of two phase shifted supermode interferometers is proposed for precision optical fiber sensing. The advantage of such interferometers for sensing include sensitivity enhancement, easy implementation, simple interrogation, and compactness. Some sensors are demonstrated.

In recent years, artificial neural networks (ANNs) have been increasingly used to enhance the performance of optical fiber sensors for the distributed measurement of strain and temperature. This paper reviews ANN-based approaches for improved and accelerated raw data processing, denoising, as well as higher-level tasks such as event recognition and classification.

An optical fiber sensing system with a frequency shifting loop monitor phase perturbations applied to a transducer in an optical fiber. A sensitivity below 4 µrad/Hz^(1/2) in a 20 kHz – 2 MHz bandwidth is obtained.

Nowadays, optical fiber sensing is an emerging and versatile technology thanks to continuous advances in micro/nanofabrication techniques as well as the application of new nanomaterials. Novel optical fibers combined with a new generation of nanostructured coatings are enabling the development of enhanced optical fiber sensors, for chemical, environmental, and biological applications. Consequently, there is an increasing interest of these fiber-based devices for the monitoring of physical parameters such as temperature, relative humidity, refractive index, strain, and bending, among others, providing higher sensitivity ratios, better detection limits, and improving other sensing parameters. This chapter covers the most used techniques and new trends for the design and nanofabrication of enhanced physical fiber sensors in the last few years. Likewise, an overview of the most relevant applications and an outlook of the optical fiber-based sensing approach for physical parameters is presented.

A single code sequence designed by a genetic searching algorithm is proposed to enhance the signal-to-noise ratio of Brillouin distributed sensors without hardware modification, enabling high-performance and cost-effective sensing over a 200-km-loop setup.

We propose a cost-effective method for temperature measurement range changing of the Ethernet-based optical fiber sensing system, and also show experimental results about the temperature measurement range changeability with a variable optical attenuator.

Conventional polarization-sensitive optical fiber sensors (POFS) sometimes can hardly detect external disturbances at some special locations where the polarization state of light has little change with the fixed analyzer. This phenomenon is the so-called polarization-induced signal fading that leads to alarm missing in the forward transmission POFS system and deteriorates locating accuracy in the polarization optical time-domain reflectometry system. To eliminate the fading phenomenon and maintain the high sensitivity along the whole sensing fiber, we propose a forward transmission polarization-sensitive optical fiber sensing scheme using polarization-maintaining fiber with the slow axes 45° aligned splicing at both the input and detection ends. Theoretical and experimental results indicate that the system works at the most sensitive state and the signal fading phenomenon is eliminated. This system promises potential applications in perimeter security and physical parameters measurement.

Due to environmental loads, fatigue effects, corrosion and material aging and other factors, the surface of high-speed railway bridge cables will inevitably be damaged, which affects the safety of the bridge. Therefore, a method for detecting surface defects of high-speed railway bridge cables based on optical fiber sensing technology is proposed. Secondly, based on the theory of high-speed fiber-optic sensor, the defect of the bridge is detected and detected by the method of neural network. The results show that: under the application of the proposed method, the defect judgment is accurate, and the type identification is also accurate, which provides a reference for bridge safety and health monitoring.

In recent years, the use of phase change energy storage and thermal insulation building materials has gradually expanded. In order to effectively control the use effect of phase change energy storage and thermal insulation building materials, a quality control method for phase change energy storage and thermal insulation building materials based on optical fiber sensing technology is proposed. Complete the selection of optical fiber sensor components to achieve high-precision collection and processing of building material data. The main evaluation basis is obtained by using extension set theory, and the data association degree of building material quality is studied. The comprehensive evaluation analysis method is used to complete the quality evaluation and control of building materials. So far, the design of the quality control method for phase change energy storage thermal insulation building materials based on optical fiber sensing technology is completed. Through the comparison of experiments, it can be seen that this method has a better quality control effect than the traditional method of phase change energy storage insulation building materials.

Industry is currently in a period of great expansion, the so-called “Industry 4.0”. It relies on the development of new sensor technologies for the generation of systems capable of collecting, distributing and delivering information. Particularly, on Chemical and Biochemical industries, the development of portable monitoring devices can improve many process parameters, like safety and productivity. In this work, the design of a smartphone-based optical fiber sensing platform for the online assessment of fed-batch fermentation systems is reported. The setup is comprised of a smartphone equipped with a 3D-printed case and an application for analyzing the pixel intensity, which is correlated to the broth refraction index (function of sucrose concentration). A sensitivity of 85.83 RIU-1 (refractive index unit) was verified, and the sensor performance was compared to a handheld refractometer and to model predictions. It showed to be a reliable, portable and low-cost instrument for online monitoring bioreactors, easily reproducible on-site by simply printing it.