Long-Period Fiber Grating (LPFG)-based biosensors operate on the fundamental principle that changes in the surrounding refractive index (SRI) can be translated into measurements of resonance wavelength shifts or variations in transmission loss. Through continued exploration of writing method for LPFGs, various gratings with special structures and novel functions have been designed and developed garnering increasing attention in the realm of novel optic devices. Currently, the fabrication of LPFGs primarily involves altering the effective refractive index of the fiber core using methods such as the mask method and holography, which result in a permanent change in the refractive index of the fiber core. However, this paper explores a method of fabricating dynamic LPFGs based on the principle of acousto-optic effect, whose applications could be more convenient in certain cases. The propagation of ultrasonic waves within the fiber optic induces periodic elastic strain of the fiber, leading to corresponding changes in the fiber’s refractive index over time and space. By modulating the characteristics of the ultrasound, various types of LPFGs can be generated. The feasibility of this method is verified through experiments, and two special gratings, namely dynamic phase-shifted long-period fiber grating and dynamic chirped long-period fiber grating, are fabricated based on the variations in ultrasonic characteristics. This development presents a new technique for addressing fiber optic sensing requirements and opens avenues for future applications such as the detection of immunoglobulin, bacteria, DNA, blood antibody analysis and other targets.
Using phase mask technology, the method of online preparation of wire-drawing tower grating (DTG) under single pulse laser was studied. the self-prepared DTG separately tested its breaking strength, the consistency of hundreds of identical gratings (center wavelength and reflectivity), and the temperature response of thousands of gratings in a single fiber. The results show that under the optimal process, the mechanical strength of DTG is not only consistent with the original fiber, but also relatively 6% higher than that of FBG; the isotropic grating at different positions, the center wavelength is stable within 80pm, and the reflectance difference is less than 3dB, and the temperature response consistency is very high. Therefore, the proposed single-pulse laser based on the phase mask to prepare the drawing tower grating can fully meet the requirements of the internet of things for large-capacity, fast response, long-distance, densely distributed fiber sensor network technology.
We demonstrate a sensing network with 5000 identical ultraweak fiber Bragg gratings (uwFBGs) at equal separations of 100 mm based on optical frequency domain reflectometry. The fiber is 510-m long and includes 5000 uwFBGs with a reflectivity of 0.02% and with identical peak reflection wavelengths of ∼1553.9 nm. With an applied strain from 0 to 600 μϵ on the uwFBGs, this system can unambiguously distinguish the shifts in the wavelengths and the locations of the uwFBGs. Compared with a traditional FBG interrogation method, this technique achieves a high-spatial resolution and a large number of multiplexed uwFBGs. The distinct advantages of the proposed sensor network make it an excellent candidate for distributed strain sensing measurements.
A new structure sapphire fiber Fabry-Perot (F-P) high-temperature sensor based on sapphire wafer was proposed and fabricated. The sensor uses the sapphire fiber as a transmission waveguide, the sapphire wafer as an Fabry-Perot (F-P) interferometer and the new structure of “Zirconia ferrule-Zirconia tube” as the sensor fixing structure of the sensor. The reflection spectrum of the interferometer was demodulated by a serial of data processing including FIR bandpass filter, FFT (Fast Fourier Transformation) estimation and LSE (least squares estimation) compensation to obtain more precise OPD. Temperature measurement range is from 20 to 1000°C in experiment. The experimental results show that the sensor has the advantages of small size, low cost, simple fabrication and high repeatability. It can be applied for longterm, stable and high-precision high temperature measurement in harsh environments.
We demonstrate a high spatial resolution multiplexing scheme for fiber Bragg grating (FBG) sensors based on single-arm frequency-shifted interferometry (SA-FSI). The SA-FSI system uses an incoherent broadband source, a slow detector, and an electro-optic modulator (EOM). By sweeping the frequency of EOM and taking the fast Fourier transform (FFT) of the interference signal, we resolved the locations of FBGs distributed both in parallel and in series along fiber links despite their reflection spectral overlap. Eighteen weak FBGs (~5% reflectivity) separated by ~0.1 m were clearly resolved experimentally, sweeping EOM modulation frequency in the range of 2-11 GHz.
We propose and demonstrate a miniature Fabry-Perot (F-P) interferometric sensor based on a hollow glass microsphere (HGM) for highly sensitive temperature measurement. The sensor head is fabricated by sticking a HGM on the end face of a single-mode fiber, and it consists of a short air F-P cavity between the front and the rear surfaces of the HGM. A sensor with 135.7280-μm cavity length was tested for temperature measurement from -5 °C to 50 °C. The obtained sensitivity reached up to 24.5 pm/°C and the variation rate of the HGM- F-P’s cavity length was2.1 nm/°C. The advantages of compact size, easy fabrication and low cost make the sensor suitable for highly sensitive temperature sensing.
We propose a novel glucose fiber optic sensor combining a thinned cladding fiber Bragg grating (ThFBG) with glucose oxidase (GOD). By immobilizing GOD on the surface of a ThFBG, the fabricated sensor can obtain a high specificity to glucose. Because of the evanescent field, the sensor is very sensitive to the ambient refractive index change arising from the catalytic reaction between glucose and GOD. A four-level fiber model was simulated and verified the precision of the sensing principle. Two methods, glutaraldehyde crosslinking method (GCM) and 3-aminopropyl triethoxysilane covalent coupling method (ATCCM), were experimentally utilized to immobilize GOD. And sensor fabricated with the method ATCCM shows a measurement range of 0-0.82 mg/mL which is better than the sensor fabricated with the method GCM with measurement range of 0-0.67 mg/mL under the same condition. By using ATCCM to immobilize GOD with different concentrations, three sensors were fabricated and used for glucose measurement by monitoring the Bragg wavelength (λb) shifts, the results indicate a good linear relationship between wavelength shift and glucose concentration within a specific range, and the measurement range increases as GOD concentration increases. The highest sensitivity of sensor reaches up to 0.0549 nm/(mg.mL-1). The proposed sensor has distinct advantages in sensing structure, cost and specificity.
The latest progress of our lab in recent 10 years on the area of bridge structural health monitoring (SHM) based on optical fiber sensing technology is introduced. Firstly, in the part of sensing technology, optical fiber force test-ring, optical fiber vibration sensor, optical fiber smart cable, optical fiber prestressing loss monitoring method and optical fiber continuous curve mode inspection system are developed, which not only rich the sensor types, but also provides new monitoring means that are needed for the bridge health monitoring system. Secondly, in the optical fiber sensing network and computer system platform, the monitoring system architecture model is designed to effectively meet the integration scale and effect requirement of engineering application, especially the bridge expert system proposed integration of sensing information and informatization manual inspection to realize the mode of multi index intelligence and practical monitoring, diagnosis and evaluation. Finally, the Jingyue bridge monitoring system as the representative, the research on the technology of engineering applications are given.
A novel gas senor combined fiber cavity ring-down (CRD) with frequency-shifted interferometry (FSI) is proposed and demonstrated. Compared to the conventional fiber CRD techniques, the CRD decay transient was originated from continuous-wave light as a function of the distance transmitted in the cavity, therefore this method needs neither pulsed light nor fast detection. As a proof-of-concept experiment, we employed a micro-optical gas cell as the sensing element and measured different concentrations of acetylene samples. The experimental results show that the FSI-CRD system has a resolution of 0.15798%/dB, and it provides a simple and cost-effective scheme for gas sensing.
A novel magnetic field sensor consisting of magnetic fluid (MF) and etched highly birefringent fiber loop mirror (Hi-Bi FLM) is proposed in the paper. The sensor is based on the etched FLM interferometer by using the property of the controllable refractive index of MF under external magnetic field. The refractive index of MF is changed by a tunable magnetic field and the resonant dip wavelength produced by the FLM shifts correspondingly. The magnetic field intensity can be measured by detecting wavelength shift. High sensitivity of 11.31pm/Oe and a resolution of 0.1Oe are obtained for the proposed magnetic field sensor.
Aiming at exiting linear temperature fire detection technology including temperature sensing cable, fiber Raman scattering, fiber Bragg grating, this paper establish an experimental platform in cable tunnel, set two different experimental scenes of the fire and record temperature variation and fire detector response time in the processing of fire simulation. Since a small amount of thermal radiation and no flame for the beginning of the small-scale fire, only directly contacting heat detectors can make alarm response and the rest of other non- contact detectors are unable to respond. In large-scale fire, the alarm response time of the fiber Raman temperature sensing fire detector and fiber Bragg grating temperature sensing fire detector is about 30 seconds, and depending on the thermocouples’ record the temperature over the fire is less than 35℃ in first 60 seconds of large-scale fire, while the temperature rising is more than 5℃/min within the range of ± 3m. According to the technical characteristics of the three detectors, the engineering suitability of the typical linear heat detectors in cable tunnels early fire detection is analyzed, which provide technical support for the preparation of norms.
We report our research on the development of a gas detection system for environmental application. The CO2 concentration of a remote site is detected with near-infrared laser spectroscopy. Light from a thermal-tuning DFB laser, whose wavelength is close to 1.57 μm, is delivered to/from the remote gas cell via silica optical fiber. The low transmission attenuation of 0.2 dB/km promises long distance CO2 sensing in the length of the gas cell in our experiment is 20 cm only, and detection accuracy of CO2 is 1%.
KEYWORDS: Signal processing, Data processing, Signal to noise ratio, Signal attenuation, Error analysis, Sensors, Absorption, Fiber optics sensors, Optical fibers, Fiber Bragg gratings
This paper develops a program to process the ring-down signal automatically finding peaks and calculating decay rate.
The program is tested by simulated data and analyzes the error under different SNR. Experimental system is set up to
acquire ring-down signal that is processed by data processing program.
We reported a high-sensitivity CO2 gas sensing system based on wavelength scanning absorption spectroscopy. A
distributed feedback (DFB) laser was used as the light source in the system, whose wavelength was thermally tuned, by a
thermoelectric cooler (TEC), to scan around one CO2 absorption line near 1572nm. Scanning of the absorption line
spectrum is performed over a glass CO2 gas cell, 16.5 cm long with collimated optical fiber connectors. Different
concentrations of CO2 were prepared by a high-precision gas flow control meter and sealed within the gas cell. A self-designed
detection and amplification circuit was employed for absorption spectrum detection. The circuit implements
background-cancellation with a two tier amplification scheme. By cancelling the high background signal, we can
improve the CO2 sensitivity by about two orders of magnitude compared with commonly used direct detection methods
with high background signals. Reducing the high DC signal permits isolated amplification of the absorption line
spectrum. Absorption spectra of different CO2 concentrations were measured, and the results demonstrated sensing
capability of 100% to <0.1% concentrations of CO2. This sensing system is expected to be used in conjunction with a
wireless CO2 sensor network for large area CO2 monitoring. Given the very lower power consumption of the DFB laser
and the detection circuit this sensing system offers a solution for affordable long term CO2 monitoring for reliable
storage in carbon sequestration.
In this paper, a new complex sensing film containing both optical indicator and enzyme was prepared and its sensing
properties were studied, using cellulose acetate (CA) as the carrier and tris (2,2'-blpyridyl) dichloro-ruthenium (II)
hexahydrate (Ru(bpy)3Cl2) as the indicator. The cross-linking method was used to immobilize glucose oxidase (GOD).
The immobilization conditions were optimized: the concentration of sodium periodate as 0.2 M and the reaction time as
30 min, those for ethanediamine as 0.03 M and 2.5 hours, those for GA as 1.5% (v/v) and 2 hours, those for GOD as 35
mg/ml and 21h. The optimal temperature and pH value for the catalytic properties of the sensing film are 38 °C and 7.0,
respectively. A fiber optic glucose sensor with this complex sensing film has been studied. The results show that its
detecting range is 100-600 mg/dl and its response time is less than 20 seconds.
A novel fiber optic biosensor for the determination of nitric oxide based on vicinal diaminobenzozcridine (VDABA)
fluorescent probe was designed and fabricated. The reaction conditions between VDABA and NO, which include
concentration of VDABA, temperature and pH, were studied in-depth. The sensitivity of VDABA for NO detection
under the optimum conditions and its optical properties were also investigated. The fluorescence responses were
concentration-dependent and a good linear relationship (R2=0.9863) was observed over the range 1.8×10-6 to 9×10-6
mol/L NO, the regression equation was F = 3.8889[NO] (mol/L)+217.2. Besides, a complex sensitive film embedding
VDABA in cellulose acetate (CA) was prepared, and a fiber optic NO biosensor was fabricated using this film. Then the
change of fluorescence phase shift of this biosensor was studied preliminarily by means of the lock-in technology.
In this paper, Glucose oxidase (GOD) was immobilized on a novel silica membrane. The multifunctional sensing
membrane was prepared by sol-gel method. GOD was immobilized on the aminated silica surfaces by glutaraldehyde
cross-linking method. The fiber optical glucose sensor based on fluorescence quenching was designed and fabricated
using lock-in amplifying technology to realize the detection of glucose concentration. The experimental results show that
a linear range between phase delay φ and the glucose concentration of the solution was observed in the concentration
range of 100 to 600 mg/dl and the detection limit is 50mg/dl, the sensor can meet the demand of clinical application. The
response time of the sensing membrane was about 15s. The experimental results demonstrated that this biosensor with
the multifunctional sensing membranes has high sensitivity, repeatability, good stability and fast response.
There are great amount of information in the safety monitoring of huge structures and equipments and many kinds of
sensors with promising long-term stability will be needed. Fiber Bragg grating (FBG) sensing technology is an effective
means to realize the safety monitoring of huge structures and equipments. In this paper, the typical problems in the
engineering application of safety monitoring of huge structures and equipments using FBG sensing technology have
been analyzed. The key technologies of its engineering application have been studied, including FBG detecting
technology in the harsh environment with high temperature and huge strain, the multipoint monitoring technology with
huge capacity, and the demodulating technology. On that basis, several kinds of FBG sensing methods and products
have been developed. The application examples of these products in a number of huge structures and equipments such
as bridges, tunnels, huge rotating machines, and oil tanks have been presented, which will be helpful to the settlement of
the related technical problems.
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