Search

Optical fiber biochemical sensing technology, as a cutting‐edge, multidisciplinary, and universal sensing technology, is gradually becoming the research focus in the field of biochemical sensing. They enjoy distinctive characteristics such as high cost‐effectiveness, flexibility, resistance to electromagnetic interference, and small size and can be used to detect biochemical analytes at ultra‐low concentrations with ultra‐low sample consumption, even when these biochemical analytes are in hard‐to‐reach environments. An aptamer is a DNA or RNA oligonucleotide fragment with a high affinity for the target selected from random sequences. Due to their advantages of simple synthesis, low cost, good stability, good specificity, and strong affinity, they are gradually becoming ideal recognition elements and may replace antibodies as next‐generation target receptors. Therefore, aptamers, as functional materials, are integrated into optical fiber sensors, which are called optical fiber aptasensors, providing new opportunities for the construction of high‐performance and intelligent biochemical sensors. This article aims to review the recent research progress of fiber‐optic aptamer biochemical sensors, with a focus on their sensing mechanisms and applications. Finally, based on the existing deficiencies of fiber‐optic aptamer biochemical sensors and practical requirements, their future development trends are briefly discussed. [ABSTRACT FROM AUTHOR]

Fiber optic sensors based on surface plasmon resonance (SPR) have demonstrated outstanding performance in biomedical, environmental monitoring, public safety, and other aspects, which provide powerful platforms for qualitative detection and quantitative analysis of molecular interactions. Among them, multichannel fiber optic SPR sensor has become a core tool in parallel detection scenarios due to the superiorities of compensating for nonspecific binding and environmental fluctuations and implementing multianalyte determination. The realization methods of multichannel sensing revolve around fiber microstructures, enhancement by materials, and hybrid fiber. The applications of multichannel fiber optic SPR sensors are demonstrated in sensing of liquid refractive index (RI), RI and temperature, biochemical molecules, and physical parameters. This review thoroughly analyzes and compares the structure, excitation effect, sensing performance, and the advantages and disadvantages of each type of multichannel fiber optic SPR sensor. Even though there are still some challenges, such as insufficient sensing channels and difficulty in fabrication, in their advancement, efforts in multidiscipline including developing high‐performance sensitive films and innovating micro–nano fabrication processes will overcome these bottlenecks. Lastly, the future development directions of multichannel fiber optic SPR sensors from principle, structure, and material aspects are discussed. [ABSTRACT FROM AUTHOR]

• A sensitive temperature sensor based on PDMS sensitized fiber MZI is first proposed. • In-situ thermal monitoring of polyacrylamide hydrogel gelation process is realized. • The gelation law and mechanism of polyacrylamide hydrogel are analyzed. • This technology is expected to monitor the thermal information in reaction processes. Real-time and in-situ monitoring the gelation temperature information of the polyacrylamide hydrogel is of great significance for revealing its reaction kinetics information and regulating the performance and quality. In this paper, based on PDMS sensitized in-fiber Mach-Zehnder interferometer (MZI), a sensitive temperature sensor with a temperature sensitivity of 10.22 nm/℃ is proposed, which is used for in-situ thermal monitoring of the gelation process of polyacrylamide hydrogel. By establishing the gelation thermal curve, it is demonstrated that the gelation process mainly includes four stages: initial lag, rapid gelation, cooling stage and stabilization stage. Among them, the rapid gelation stage is the most critical, which shows the heat released in the gelation process and the gelation time. In addition, experimental results confirmed that with the increase of monomer and crosslinker concentration, the heat released during the gelation process gradually increases, but the gelation time is almost unaffected. Since the proposed PDMS sensitized MZI sensor has the advantages of miniaturization, high sensitivity, intrinsically safe, etc., it can be further extended to other dynamic reaction processes for real-time monitoring of temperature information. [ABSTRACT FROM AUTHOR]

• Machine learning has significantly enhanced optical fiber sensor performance. • Reviewed the latest progress in machine learning applied to optical fiber sensors. • More comprehensive classification introduction from point/discrete sensors, distributed sensors, image processing, and others. • A comprehensive overview of machine learning methods applied to optical fiber sensors was provided. In recent years, with the increasing demand for intelligent society, intelligent photonics has developed rapidly. Machine learning (ML), as a subset of artificial intelligence (AI), has played an important role in the intelligent evolution of optical fiber sensors. Its impact extends beyond enhancing sensor performance by introducing innovative problem-solving approaches. Specifically, ML algorithms have become instrumental in signal demodulation and elevating the efficacy of discrete and distributed sensors, and have also greatly promoted the development of optical fiber speckle pattern processing. This paper presents the latest advancements in ML-based optical fiber sensors, outlines the problems faced by conventional demodulation methods and the common ML algorithms applied in optical fiber sensors, and emphasizes key applications. Additionally, this paper delves into the challenges and future development of this emerging research direction. [ABSTRACT FROM AUTHOR]

A fiber-optic pH sensor, based on layer-by-layer (LBL) self-assembly and surface plasmon resonance (SPR) technology, is proposed and experimentally confirmed. This article proposes poly (diallyldimethylammonium chloride) (PDDA) as the pretreatment solution for the surface of the gold film and the highly sensitive polyacrylic acid/chitosan (PAA/CS) self-assembled nanomembrane as the pH-sensitive film. It has been experimentally verified that the sensor can detect pH from 3.18 to 11.84 and it exhibits a high average sensitivity of 32.31 nm/pH in this range. In addition, experiments have confirmed that the sensor has attractive stability, repeatability, and hysteresis characteristics. [ABSTRACT FROM AUTHOR]

Optofluidic, as an emerging technology that combines photons and microfluidics, has become a powerful, intelligent, and universal sensing platform in the field of bio‐chemical sensing. Optical fiber optofluidic (OFOF), as a branch of optofluidic technology, has stimulated a host of remarkable achievements in the field of bio‐chemical sensing due to its superiority of compact structure, immunity to electromagnetic interference, low sample consumption, high sensitivity, and real‐time dynamic response. In this paper, an overview of OFOF bio‐chemical sensors is presented. The OFOF system architectures are introduced and some advanced functional materials and coating technologies that can be utilized in the OFOF sensing platform to achieve high‐performance biochemical sensing are summarized. Research progress and current status of OFOF bio‐chemical sensors based on various sensing mechanisms are summarized and analyzed, with emphases on their sensing principles, sensing structures, sensing applications, advantages, and disadvantages. Lastly, the existing challenges and future development trends of OFOF biochemical sensors are briefly discussed. [ABSTRACT FROM AUTHOR]

A reflective optical fiber nickel ion (Ni2+) sensor based on surface plasmon resonance (SPR) and surface ion imprinting was proposed and demonstrated. The sensor is made of multimode optical fiber with a core diameter of 600 $\mu \text{m}$ and coated with a gold film for an exciting SPR effect. To realize highly sensitive and highly selective detection of Ni2+, graphene oxide (GO) and Ni2+-imprinted Chitosan (IP-CS) are subsequently combined on the sensor surface. The GO can not only act as the intermediate binder between the Au film and the CS but also increase the sensitivity of the sensor. The Ni2+ holes on the IP-CS can realize the specific capture of Ni2+. The experimental results show that the sensitivity of the sensor to Ni2+ is 5.220 nm/[lg(mg/L)] with a limit of detection of $2.393\times 10^{-3}$ mg/L, and the selectivity of the sensor is significantly improved after imprinting. Besides, the sensor has good stability and repeatability, and fast responsiveness. [ABSTRACT FROM AUTHOR]

A fiber optic ethanol gas sensor with ZnSnO 3 hollow cube/nano-TiO 2 composite coating based on ultraviolet (UV) radiation sensitization was proposed, which can realize high sensitivity, high selectivity, and fast ethanol gas sensing at room temperature. The probe adopted a simple single-mode fiber (SMF)-multi-mode fiber-SMF structure. The ZnSnO 3 /TiO 2 gas-sensitive film was coated on the sensing area by dip-coating method. Experiment results show that the probe sensitized by UV radiation has a linear sensitivity of 3.85 pm/ppm for ethanol gas at 0–250 ppm, which is about 6.6 times more sensitive than the probe without UV radiation (0.582 pm/ppm). In addition, the probe with UV radiation has good time measurement stability, a fast response time (response time is about 20 s, recovery time is about 60 s), and excellent ethanol gas selectivity. This study proves that UV radiation is an effective method to increase the sensitivity of gas sensing. This is also the first application of ZnSnO 3 /TiO 2 composite material in fiber optic sensors. Combined with the advantages of fiber optic sensing, it shows anti-electromagnetic interference, micro size, high sensitivity, high selectivity, fast response, and remote sensing. • A Fiber optic room temperature ethanol sensor was proposed and fabricated. • The TiO2/ZnSnO3 composite material was firstly applied in fiber optic sensors. • Under the UV radiation, the probe behaves good stability, fast response, excellent selectivity. [ABSTRACT FROM AUTHOR]

A new type of two-channel surface plasmon resonance (SPR) sensor based on hollow-core fiber (HCF) for simultaneous measurement of seawater salinity and temperature was presented in this article. One of the SPR channels that are excited on the outer surface of the HCF with Au film coating was used to measure the seawater salinity, while another SPR channel that is excited on the inner surface of the HCF with Ag film coating and polydimethylsiloxane (PDMS) infiltration was used for seawater temperature measurement at the same time. The experimental results showed that the salinity sensitivity and temperature sensitivity of the sensor could reach 0.3769 nm/‰ and −0.956 nm/°C, respectively. This demonstrated that the two-channel SPR sensor not only showed the possibility in the simultaneous measurement of two parameters with high sensitivity, excellent stability, small size, and high mechanical strength but also shed new light on the multiparameter measurement fields and the development of lab-in-fiber sensors. [ABSTRACT FROM AUTHOR]

A new type of two-channel surface plasmon resonance (SPR) sensor based on hollow-core fiber (HCF) for simultaneous measurement of seawater salinity and temperature was presented in this article. One of the SPR channels that are excited on the outer surface of the HCF with Au film coating was used to measure the seawater salinity, while another SPR channel that is excited on the inner surface of the HCF with Ag film coating and polydimethylsiloxane (PDMS) infiltration was used for seawater temperature measurement at the same time. The experimental results showed that the salinity sensitivity and temperature sensitivity of the sensor could reach 0.3769 nm/‰ and −0.956 nm/°C, respectively. This demonstrated that the two-channel SPR sensor not only showed the possibility in the simultaneous measurement of two parameters with high sensitivity, excellent stability, small size, and high mechanical strength but also shed new light on the multiparameter measurement fields and the development of lab-in-fiber sensors. [ABSTRACT FROM AUTHOR]

Highlights • The sensing head is a non-adiabatic tapered fiber. • The sensor is encapsulated in a liquid-infiltrated glass microtube. • The sensor has low cost, high sensitivity and good mechanical strength. Abstract A non-adiabatic tapered fiber sensor was fabricated, and its applications in refractive index (RI) and temperature sensing were investigated in both theory and experiment. The experiment results demonstrated that the tapered fiber sensor with a diameter of 8 μm had RI sensitivity as high as 1800 nm/RIU and temperature sensitivity of about −300 pm/°C. Then, taking advantage of its high refractive index sensitivity property, an improved temperature sensor structure was proposed by encapsulating it in a glass microtube and filling the microtube with high thermo-optical coefficient liquid. This improved sensor structure showed a higher temperature sensitivity of around −900 pm/°C. The improved sensor structure is simple, low cost and easily fabricated. Besides, this temperature sensor has high sensitivity, good mechanical strength and strong anti-disturbance ability. [ABSTRACT FROM AUTHOR]

A novel, highly sensitive dual-parameter sensor based on tandem-interferometric arrangement of Fabry–Pérot interferometer and Mach–Zehnder interferometer (MZI) has been designed and implemented in this paper. The sensor is composed of a single-mode fiber (SMF), hollow-core fiber, no-core fiber (NCF), and photonic crystal fiber (PCF). Those can simultaneously form a Fabry–Pérot interferometer and a MZI. The both interferometers are able to measure strain. Meanwhile, the PCF was filled with liquid crystal to measure electric field intensity. Hence, simultaneous measurement of electric field and strain can be achieved. The sensitivities of electric field and strain can reach up to 10.5 nm/(kV/mm) and 1.25 pm/ $\mu \varepsilon $ , respectively. [ABSTRACT FROM PUBLISHER]

A review for optical fiber sensors based on fiber ring laser (FRL) demodulation technology is presented. The review focuses on the principles, main structures, and the sensing performances of different kinds of optical fiber sensors based on FRLs. First of all, the theory background of the sensors has been discussed. Secondly, four different types of sensors are described and compared, which includes Mach–Zehnder interferometer (MZI) typed sensors, Fabry–Perot interferometer (FPI) typed sensors, Sagnac typed sensors, and fiber Bragg grating (FBG) typed sensors. Typical studies and main properties of each type of sensors are presented. Thirdly, a comparison of different types of sensors are made. Finally, the existing problems and future research directions are pointed out and analyzed. [ABSTRACT FROM AUTHOR]

Optical fiber surface plasmon resonance (SPR) sensors have proven their particular advantages in chemical and biological sensing over conventional detection methods. By analyzing the principle of biochemical optical fiber SPR sensor, it is concluded that the main reason affecting the sensitivity of the sensor is the structure of the optical fiber sensor and the functional material. This paper briefly introduces the structural design of optical fiber sensors and focuses on the classification of optical fiber sensitive materials according to the principle of enhancing SPR effect. The latest applications of optical fiber SPR sensors in biochemistry in recent years are classified and summarized. The potential and obstacles in the current research are compared and analyzed. Finally, the possible direction of the sensor in the future is discussed. [ABSTRACT FROM AUTHOR]

A review for optical fiber hydrogen sensors based on palladium (Pd) and tungsten oxide (WO 3 ) thin films is presented, with specific focus on the measurement methods, probe structures, and sensing properties of different sensors. Firstly, the theoretical models behind the optical fiber hydrogen sensors, as well as their practical limitations, are addressed. Secondly, four mainstream measurement methods, including intensity, fiber Bragg grating (FBG), interferometer, surface plasmon resonance (SPR), which have been proposed to sense the physicochemical properties variations of sensitive thin films when exposed to hydrogen, are reviewed. Then, the advantages and disadvantages of all the above measurement methods are also discussed and compared. Finally, the existing problems and future prospects of optical fiber hydrogen sensors are pointed out. [ABSTRACT FROM AUTHOR]

In this paper, a new optical fiber hydrogen(H 2) sensor based on a self-assembled microbottle resonator was proposed. The self-assembled microbottle was simply obtained by coating the single-mode fiber (SMF) with an internal composite material layer of palladium-tungsten trioxide (Pd-WO 3) that was sensitive to H 2 and an outer organic polymer material layer of polydimethylsiloxane (PDMS) with a significant thermal response. The microbottle resonator was further fabricated by coupling a tapered fiber with the self-assembled microbottle to excite whispering gallery mode (WGM). When the WGM resonator is exposed to H 2 , H 2 molecules penetrate the PDMS and undergo redox reaction with the Pd-WO 3. After the PDMS absorbs the reaction heat, its volume and refractive index will change, along with the wavelength shift of the WGM resonator. Therefore, a simple and low-cost H 2 sensor is realized by observing the shift of resonance wavelength. Experimental results showed that the hydrogen sensor had a maximum sensitivity of − 3.091 nm/% at 25 ℃. And the resonance wavelength just shifted a small distance when the relative humidity increased from 22.87 % to 84.59 % or the temperature rose from 20.2 ℃ to 30 ℃, which indicated the sensor had preferable resistance to disturbances of external humidity and temperature. • A simple and low-cost optical fiber H2 sensor was proposed with high sensitivity of − 3.091 nm/%. • The self-assembled microbottle was simply fabricated by coating Pd-WO 3 and PDMS on a fiber in sequence. • The sensor has preferable resistance to disturbances of external humidity and temperature. [ABSTRACT FROM AUTHOR]

This article theoretically and experimentally characterizes single-mode fiber bending losses and associated sensing. As the bending radius decreased, the losses increased significantly, and shock phenomena were observed in the loss curve. Theoretical analysis shows that these processes were caused by coupling between fundamental models spreading in the optical fiber and whispering gallery mode spreading in the cladding and coating layers. Based on the principles of single-mode fiber bending losses, a loss modulator was designed to bend the single-mode fiber and produce losses due to external displacement. A displacement-loss model was constructed and the results were consistent with the theoretical analysis. The displacement resolving power of the loss modulator was 1 µm. The displacement measurement was from 0–350 µm, resulting in losses from 0–25 dB. [ABSTRACT FROM PUBLISHER]

A plug-and-play surface plasmon resonance (SPR) dual-parameter optical fiber biosensor is reported, in which Au film was firstly coated on the fiber surface for exciting SPR and the end half of the Au film was modified with Au nanoparticles to generate double SPR resonance valleys. For simultaneous detecting of glucose and cholesterol concentrations, modified P-mercaptophenylboronic acid (PMBA) and β-cyclodextrin (β-CD) were subsequently coated on the surface of sensor probe. Due to the cis-diol structure of glucose, it can interact with PMBA, leading to a red shift of one SPR resonant valley, whose maximum wavelength shift is 11.228 nm in the range of 0–1.7 mM glucose concentration. On the same time, the cholesterol molecules can realize the host-guest combination with β-CD, leading to a red shift of another SPR resonant valley, and the maximum wavelength shift is 18.893 nm in the cholesterol concentration range of 0–300 nM. The detection limits of the sensor to glucose and cholesterol are 0.00078 mM and 0.012 nM, respectively. The enhances the practical value of the dual-parameter sensor. Both theory and experiment results verify the feasibility of the "plug-and-play" sensor to measure the dual biomass of glucose and cholesterol with ultra-low detection limit and good selectivity. The proposed method provides a huge research value for the optical fiber sensor in multi-parameter measurement. • A highly-sensitive and reflective optical fiber SPR biosensor was proposed for dual-parameter measurement. • Glucose and cholesterol concentrations could be simultaneously measured by one sensor. • Au nanoparticles were coated on the sensor to adjust the resonant wavelength and enhance the sensor sensitivity. • The cross-sensitivity between glucose and cholesterol could be neglected by selecting PMBA and β-CD as sensitive materials. • The sensor has an ultra-low detection limit and excellent selectivity for detecting low concentrations of glucose and cholesterol. [ABSTRACT FROM AUTHOR]

□ A novel simultaneous method of strain and temperature measurement based on a polarization maintaining fiber Bragg grating loop mirror is proposed and demonstrated. The sensing head was composed of a fiber loop mirror and a section of fiber Bragg grating made of a polarization maintaining fiber. The Bragg wavelengths of the fiber grating in the polarization maintaining fiber were along slow and fast axis showing different sensitivities to strain and temperature with the interferometric peak wavelength of the fiber loop mirror. By monitoring the shifts of the Bragg wavelength and interferometric peak of the fiber loop mirror, with its temperature sensitivity of 0.1167 nm/°C and strain sensitivity of 0.0093 nm/μϵ, a temperature measurement resolution about 0.009°C and a strain measurement resolution of 1.08 μϵ was achieved theoretically and experimentally. [ABSTRACT FROM AUTHOR]

• The SCPCF with high mechanical strength and four air holes were used to form modal interferometer. • Seawater temperature and salinity can be simultaneously measured in one integrated all-fiber sensor. • The proposed structure has the advantages of high mechanical strength and simple manufacturing process. • The temperature sensitivity of 1.486 nm/°C and salinity sensitivity of 2.495 nm/‰ were realized. An optical fiber sensor for simultaneous measurement of seawater temperature and salinity was designed and implemented based on a lateral offset Modal interferometer (MI) using a suspended core photonic crystal fiber (SCPCF). The MI was made by fusing single mode fiber and multimode fiber (SMF-MMF) structures with a lateral offset SCPCF coated with UV adhesive film on the inner wall. In the experiment, the response of the sensor to the change of seawater temperature and salinity was measured respectively. The results have shown that the temperature sensitivity of 1.486 nm/°C was obtained within the temperature range from 5 °C to 45 °C and the salinity sensitivity of 2.495 nm/‰ was obtained within the salinity range from 0‰ to 50‰. The sensor resolves the problem of cross-sensitivity between seawater temperature and salinity and provides a simple structure with low cost and high sensitivity. [ABSTRACT FROM AUTHOR]

The main structures of the gas absorption cell, including small graded-index lens type, Bragg fiber type, photonic crystal type, etc., are compared in this article. Also, different principles of the gas absorption cell were discussed in detail in order to improve the sensitivity of the optical gas sensor. The study showed that the structure of gas cells plays a key role in the improvement of the sensitivity of optical gas sensors. The end of the article discusses the future direction of the development of the gas cell. [ABSTRACT FROM PUBLISHER]

[Display omitted] • A simple and reflective optical fiber sensor was proposed for high-sensitive measurement of Hg2+ concentration. • The Hg2+ could mismatch with T-T base pairs in DNA to form T-Hg2+-T structure. • The sensor behaved good sensitivity, stability and selectivity. • The sensor behaved low detection limit. A reflective optical fiber surface plasmon resonance (SPR) sensor was proposed to measure the concentration of mercury ions (Hg2+). The specific single-stranded DNA was modified on the optical fiber sensing surface coated with Au film by the combination of covalent bond and charge adsorption. The Hg2+ can mismatch with T-T (thymine-thymine) base pairs in single-stranded DNA to form T-Hg2+-T structure, which led to the change of refractive index in sensing area and the wavelength shift of SPR spectrum. The measurement results showed that when the concentration of Hg2+ increased from 0 μM to 13 μM, the resonance spectrum shifted by 14.26 nm. In the linear range between 1–8 μM, the measurement sensitivity of the sensor could reach 1.51 nm/μM. The limit of detection (LOD) was found to be 0.28 μM. Besides, the sensor showed good stability, selectivity and reusability. [ABSTRACT FROM AUTHOR]

With the increasing of water pollution problems, detection of heavy metal ion concentration in water environment becomes significant. Optical fiber sensor, with its particular advantages of small-size, anti-electromagnetic interference, chemical inertness, remote and real-time monitoring ability, has become an ideal platform for detection of heavy metal ion concentration. In this paper, we briefly review the current research progress of heavy metal ion sensors based on optical fiber technology. Five main measurement methods are described, including optical absorbance method, fiber grating method, modal interference method, plasmonic method, and fluorescence method. The sensing mechanisms, sensing structures, sensing materials, and sensing characteristics of different kinds of measurement methods are introduced and summarized. Furthermore, the advantages and disadvantages of each measurement method are analyzed. Finally, the future development directions of optical fiber heavy metal ion sensors are also discussed. [ABSTRACT FROM AUTHOR]

In this paper, we design an in-fiber two-parameter sensor with multimode fiber (MMF)-Au film coated hollow fiber (HCF)-MMF structure, which can simultaneously excite Surface Plasmon Resonance (SPR) effect and Multimode Interference (MMI) effect. A composite material of Au nanoparticles/β-cyclodextrin (AuNPs/β-CD) is deposited on the surface of the Au film coated HCF to realize highly-sensitive measurement of cholesterol concentration. Here, the AuNPs can not only enhance the measurement sensitivity of the SPR sensor, but also increase the numbers of combination sites of β-CD and cholesterol. Then, to solve the cross-sensitivity problem between temperature and cholesterol, the glycerin is selected as a temperature-sensitive material to fill into the inner channel of the HCF, making the MMI sensor sensitive to temperature, and finally realizing the simultaneous measurement of cholesterol concentration and temperature. The experimental results demonstrate that the wavelength shift of the SPR and the MMI are 12.7 nm and 7.9 nm, respectively, when the cholesterol concentration changes from 0 to 500 nM. The temperature sensitivity of the SPR and the MMI are −0.9 nm/°C and 2.64 nm/°C, respectively, in the temperature range of 30°C–46 °C. In addition, the sensor shows good recognition ability of cholesterol molecules in serum environment, with good stability, selectivity and repeatability, and has broad application prospects in the biomedical field. An optical fiber sensor with SPR + MMI double effect superimposed is fabricated by collapse-welding method. The AuNPs/β-CD composite is synthesized by reduction method and connected to the sensing region by covalent bond to identify cholesterol molecules. In addition, hollow fiber filled with glycerin is an excellent temperature-sensitive material that can be used for temperature sensing. Based on the above design, cholesterol concentration and temperature can be measured simultaneously by demodulation of mixed sensing signals. [Display omitted] • An MMF–HCF–MMF fiber structure was proposed for simultaneously exciting SPR and MZI. • A composite material of AuNPs/β-CD was utilized for highly sensitive measurement of cholesterol concentration. • The glycerol was filled into the HCF for highly sensitive measurement of temperature. • The proposed sensor possesses high sensitivity, excellent stability and selectivity. [ABSTRACT FROM AUTHOR]

An optical fiber ammonia (NH 3) sensor based on multi-mode interference (MF) and anti-resonance (AR) principle is proposed, which can detect the NH 3 and increase the function of temperature measurement to avoid the influence of ambient temperature. The sensor is made of single-mode fiber (SMF) - hollow core fiber (HCF) - SMF - coreless fiber (NCF) -SMF welding, wherein NCF deposited graphene oxide gas response coating by dip-coating method. HCF and NCF can excite AR valley and MF valley simultaneously in the same spectrum. Experimental results show that for NH 3 gas sensing, MF valley exhibits a NH 3 sensitivity of 3.28 pm/ppm with a response time of 60 s and a recovery time of 30 s, while AR valley is not sensitive. For temperature sensing, MF valley and AR valley are sensitive to temperatures of − 12.63 pm/℃ and 15.57 pm/℃, respectively. The simultaneous detection of NH 3 and temperature can be realized through spectral demodulation. The gas sensor offers several advantages, including straightforward preparation, cost-effectiveness, and low operating temperature. Most importantly, it solves the problem of temperature interference that is often ignored in fiber optic gas sensors, and the hybrid fiber structure is suitable for many multi-parameter measurement occasions and has important practical application significance. • A novel sensing technique based on anti-resonance and multi-mode interference superposition is proposed. • A micro-optical fiber optic sensor with two-parameter recognition capability is developed. • The simultaneous detection of ammonia and temperature is realized. • The problem of temperature cross sensitivity which is common in gas sensor is solved effectively. • The multi-parameter detection capability of this hybrid fiber structure makes it very potential for a variety of practical applications. [ABSTRACT FROM AUTHOR]

The observation of seawater salinity and temperature is indispensable for sustainable development and utilization of marine resources. In this research, a simple and low-cost single-mode fiber (SMF) - no-core fiber (NCF) - SMF structure based on Mach-Zehnder interference (MZI) is proposed to measure two variables with the assistance of an artificial neural network (ANN). In contrast to traditional wavelength linear fitting, direct matching of the entire spectrum to the variables through machine learning analysis effectively improves the accuracy of the output predictions. Specifically, mean absolute errors of salinity and temperature reduce from 1.540‰ to 0.808‰ and from 1.061 ℃ to 0.154 ℃, respectively. The relaxation of the light source and the optical spectrum analyzer (OSA) requirements, the fluctuation of salinity or temperature, the disturbance of environmental parameters will all not weaken the demodulation performance of the new method. Furthermore, the accuracy of the predicted results on the new probes demonstrates the adaptability of the demodulation approach. Importantly, ANN can simultaneously demodulate two parameters from a single spectrum, avoiding the cross-sensitivity problem in traditional methods. The strategy is highly generalizable and promising to be extended to any other parameters measured by optical fiber sensors. [Display omitted] • The SNS sensor combined with ANN is proposed to measure salinity and temperature. • This way relaxes instrumentation requirements and resists environmental disturbances. • The presented demodulation system has certain applicability to the new probe. • The cross-sensitivity problem of dual-parameter demodulation is overcome. [ABSTRACT FROM AUTHOR]

• A physical stretching method for preparing PDMS-based fiber structure is reported. • The PDMS fiber is coupled with two multimode fibers by adhesion, forming an interferometer. • The PDMS fiber based interferometer sensor has good sensitivity to VOC gases. • The sensor has merits of simple preparation, high sensitivity, good tensile properties, and humidity resistance. In this paper, a method for preparing polydimethylsiloxane (PDMS)-based fiber structure was reported and its performance for volatile organic compound (VOC) gas sensing was demonstrated. The PDMS fiber prepared by the physical stretching method was coupled at the end faces of two multimode fibers by adhesion, forming an inter-mode interferometer. The PDMS was not easily dislodged after curing, which contributes to the strong robustness of the whole structure. When the PDMS optical fiber is exposed to VOC gas environment, PDMS will adsorb VOC gas molecules, resulting in changes in its refractive index and volume, which shifts the wavelength of inter-mode interference. Experiments show that the sensor has good sensitivity to VOC gases such as acetone, ethanol, and methanol. In the concentration range of 0–400 ppm, the sensitivity reaches 14.84 pm/ppm, 13 pm/ppm, 4.39 pm/ppm, 7.37 pm/ppm, and 5.99 pm/ppm for acetone, ethanol, methanol, toluene, and ether respectively. The proposed sensor has excellent characteristics such as simple preparation, high sensitivity, good tensile properties, and humidity resistance, which indicates that the sensor has some potential for VOC gas detection. [ABSTRACT FROM AUTHOR]

• This review shows the advanced and relevant technical specifications of fiber optic detection technology for VOC gas. • This review summarizes the gas-responsive materials and some advanced film deposition techniques of fiber optic VOCs sensors. • This review presents the sensing principles, performance, and applications of fiber optic VOC gas sensors. • This review discusses the existing challenges and potential applications of fiber optic VOCs sensors. • This review can help to keep the reader informed of the latest advances in the field. Most volatile organic compounds (VOCs) are toxic, carcinogenic, and mutagenic, and can have serious effects on human health and the ecological environment. Therefore, the detection and identification of VOCs have an urgent need in both indoor and outdoor environments. Fiber optic sensors, as intrinsically safe, miniature, portable, immune to electromagnetic interference, and easy to remote sensing and multiplexing sensing technology, are utilized in VOC gas sensing promising to provide new approaches to overcome the limitations of conventional gas sensing systems. This review assesses recent research advances in fiber optic VOC gas sensors, including various sensing principles, gas-responsive materials, new techniques for sensing material deposition, structures, and applications. Fiber optic VOC gas sensors are classified and discussed based on different principles. In addition, this paper extensively reviews the recent advances in fiber optic VOC gas sensors and discusses the strategies and approaches to further their development. [ABSTRACT FROM AUTHOR]

Graphene as a novel material has laid a foundation for its applications in optical fiber sensors, due to its unique properties, especially the optical properties. On the other hand, optical fiber sensors have received world-wide attention due to their high sensitivity, small size, good anti-electromagnetism disturbance ability and other potential advantages. In this paper, the developments of graphene in the applications of optical fiber sensors were reviewed from four aspects. Firstly, the common preparation methods of graphene were introduced. Next, the optical properties of graphene have been concluded. And then, some typical optical fiber chemical and biological sensors based on graphene, such as temperature sensors, biological sensors and gas sensors, were reviewed. It was shown that graphene had a great potential in the optical fiber sensing technology. Furthermore, the deficiencies and challenges of the graphene in the applications of optical fiber sensors were analyzed. In a whole, the unique advantages of graphene have present their versatility and importance in the application fields of optical fiber sensors. [ABSTRACT FROM AUTHOR]

• A highly-sensitive and reflective glucose sensor was proposed and demonstrated. • The GOD was uniformly and firmly fixed on the surface of the metal film through covalent binding method. • The proposed sensor head is reflective, which is suitable for remote sensing. A reflective optical sensor based on surface plasmon resonance (SPR) was proposed to measure the glucose concentration. The gold film was sputtered on the surface of plastic cladding optical fiber to excite SPR and reflect light at the same time, making the SPR sensor highly sensitive to the variation of surrounding refractive index. Then, glucose oxidase (GOD) was adopted as the sensitive film of glucose and covalently bonded on the gold film. The enzymatic reaction between the GOD and the glucose led to the change of refractive index around the optical fiber sensor, and then cause a shift of the SPR spectrum. Therefore, the glucose concentration could be obtained by monitoring the shift of the resonance wavelength. Experimental results showed that the measurement sensitivity of the SPR sensor could reach 85.4 nm/(mg/mL) (for glucose concentration) with good selectivity and stability, which has great potential application in biomedicine and human health monitoring. [ABSTRACT FROM AUTHOR]