Showing papers in "Photonic Sensors in 2015"

Polyimide-coated fiber Bragg grating for relative humidity sensing

Abstract: A fiber-optic humidity sensor has been fabricated by coating a moisture sensitive polymer film to the fiber Bragg grating (FBG). The Bragg wavelength of the polyimide-coated FBG changes while it is exposed to different humidity conditions due to the volume expansion of the polyimide coating. The characteristics of sensors, including sensitivity, temporal response, and hysteresis, were improved by controlling the coating thickness and the degree of imidization during the thermal curing process of the polyimide. In the relative humidity (RH) condition ranging from 11.3% RH to 97.3% RH, the sensitivity of the sensor was about 13.5 pm/% RH with measurement uncertainty of ±1.5% RH.

FBG based high sensitive pressure sensor and its low-cost interrogation system with enhanced resolution

Abstract: A fiber Bragg grating (FBG) pressure sensor with high sensitivity and resolution has been designed and demonstrated The sensor is configured by firmly fixing the FBG with a metal bellows structure The sensor works by means of measuring the Bragg wavelength shift of the FBG with respect to pressure change From the experimental results, the pressure sensitivity of the sensor is found to be 906 pm/psi, which is approximately 4000 times as that of a bare fiber Bragg grating A very good linearity of 9986% is observed between the Bragg wavelength of the FBG and applied pressure The designed sensor shows good repeatability with a negligible hysteresis error of ± 029 psi A low-cost interrogation system that includes a long period grating (LPG) and a photodiode (PD) accompanied with simple electronic circuitry is demonstrated for the FBG sensor, which enables the sensor to attain high resolution of up to 0025 psi Thermal-strain cross sensitivity of the FBG pressure sensor is compensated using a reference FBG temperature sensor The designed sensor can be used for liquid level, specific gravity, and static/dynamic low pressure measurement applications

Enhancement of the Sensitivity of Gas Sensor Based on Microstructure Optical Fiber

Abstract: This paper proposes the design and characterization of microstructure optical fiber for gas sensing applications. The aim is to detect toxic and colorless gases over a wide transmission band covering 0.80 µm to 2.00 µm wavelength. Numerical investigation is carried out by using the finite element method (FEM). The numerical study shows that sensitivity of the proposed sensor is moderately increased by introducing four non-circular holes around the defected core of photonic crystal fiber and the confinement loss is also reduced. Furthermore, we confirm that increasing the diameter of central air core and size of the non-circular holes can improve the relative sensitivity and the confinement loss is reduced by increasing the diameter of air holes in the cladding. The enhancement of the relative sensitivity is more than 27.58% (0.1323 to 0.1688) at the wavelength λ=1.33µm that is the absorption line of methane (CH4) and hydrogen fluoride (HF) gases. The confinement loss of the fiber is 1.765×10-8 dB/m.

Early Warning Smartphone Diagnostics for Water Security and Analysis Using Real-Time pH Mapping

Abstract: Early detection of environmental disruption, unintentional or otherwise, is increasingly desired to ensure hazard minimization in many settings. Here, using a field-portable, smartphone fluorimeter to assess water quality based on the pH response of a designer probe, a map of pH of public tap water sites has been obtained. A custom designed Android application digitally processed and mapped the results utilizing the global positioning system (GPS) service of the smartphone. The map generated indicates no disruption in pH for all sites measured, and all the data are assessed to fall inside the upper limit of local government regulations, consistent with authority reported measurements. This implementation demonstrates a new security concept: network environmental forensics utilizing the potential of novel smartgrid analysis with wireless sensors for the detection of potential disruption to water quality at any point in the city. This concept is applicable across all smartgrid strategies within the next generation of the Internet of Things and can be extended on national and global scales to address a range of target analytes, both chemical and biological.

Optimization Study on Graphene-Coated Microfiber Bragg Grating Structures for Ammonia Gas Sensing

Abstract: The excitation of the surface field and evanescent enhancement in the graphene have shown sensitive to the refractive index of surrounding media and potential applications in high-sensitivity biochemical sensing. In this paper, we investigate the graphene-coated microfiber Bragg gratings (GMFBGs) with different diameters for ammonia gas sensing. The maximum sensitivity with 6 pm/ppm was achieved experimentally when the microfiber’s diameter was about 10 μm. Moreover, by adjusting the diameter of the GMFBG, the sensing performance of the GMFBGs could be optimized. Experimental results indicated that GMFBGs with the diameter of 8 μm − 12 μm would show the characteristics of the high sensitivity, relative low attenuation, and large dynamic range.

Long-range displacement sensor based on SMS fiber structure and OTDR

Abstract: This paper presents a long-range displacement measurement method by using a single-multi-single mode (SMS) fiber structure, attached to a flexible plate between two permanent poles and the optical time domain reflectometer (OTDR)-based interrogator. The SMS fiber structure sensors are prepared with two different configurations, i.e. straight and sinusoidal configurations. It is demonstrated that the displacement sensor can perform a displacement measurement with a range from 0 mm to 150 mm with a resolution of 0.159 mm. The sinusoidal configuration provides a better sensitivity than the straight configuration. The proposed sensor offers a low cost, and it can be implemented for quasi-distributed displacement measurement which is suitable for civil structure monitoring.

Intelligent detection and identification in fiber-optical perimeter intrusion monitoring system based on the FBG sensor network

Abstract: A real-time intelligent fiber-optic perimeter intrusion detection system (PIDS) based on the fiber Bragg grating (FBG) sensor network is presented in this paper. To distinguish the effects of different intrusion events, a novel real-time behavior impact classification method is proposed based on the essential statistical characteristics of signal’s profile in the time domain. The features are extracted by the principal component analysis (PCA), which are then used to identify the event with a K-nearest neighbor classifier. Simulation and field tests are both carried out to validate its effectiveness. The average identification rate (IR) for five sample signals in the simulation test is as high as 96.67%, and the recognition rate for eight typical signals in the field test can also be achieved up to 96.52%, which includes both the fence-mounted and the ground-buried sensing signals. Besides, critically high detection rate (DR) and low false alarm rate (FAR) can be simultaneously obtained based on the autocorrelation characteristics analysis and a hierarchical detection and identification flow.

Study on the non-contact FBG vibration sensor and its application

Abstract: A non-contact vibration sensor based on the fiber Bragg grating (FBG) sensor has been presented, and it is used to monitor the vibration of rotating shaft. In the paper, we describe the principle of the sensor and make some experimental analyses. The analysis results show that the sensitivity and linearity of the sensor are −1.5 pm/μm and 4.11% within a measuring range of 2 mm–2.6 mm, respectively. When it is used to monitor the vibration of the rotating shaft, the analysis signals of vibration of the rotating shaft and the critical speed of rotation obtained are the same as that obtained from the eddy current sensor. It verifies that the sensor can be used for the non-contact measurement of vibration of the rotating shaft system and for fault monitoring and diagnosis of rotating machinery.

Research on pressure tactile sensing technology based on fiber Bragg grating array

Abstract: A pressure tactile sensor based on the fiber Bragg grating (FBG) array is introduced in this paper, and the numerical simulation of its elastic body was implemented by finite element software (ANSYS). On the basis of simulation, fiber Bragg grating strings were implanted in flexible silicone to realize the sensor fabrication process, and a testing system was built. A series of calibration tests were done via the high precision universal press machine. The tactile sensor array perceived external pressure, which is demodulated by the fiber grating demodulation instrument, and three-dimension pictures were programmed to display visually the position and size. At the same time, a dynamic contact experiment of the sensor was conducted for simulating robot encountering other objects in the unknown environment. The experimental results show that the sensor has good linearity, repeatability, and has the good effect of dynamic response, and its pressure sensitivity was 0.03 nm/N. In addition, the sensor also has advantages of anti-electromagnetic interference, good flexibility, simple structure, low cost and so on, which is expected to be used in the wearable artificial skin in the future.

A coal mine multi-point fiber ethylene gas concentration sensor

Abstract: Spontaneous combustion of the coal mine goaf is one of the main disasters in the coal mine. The detection technology based on symbolic gas is the main means to realize the spontaneous combustion prediction of the coal mine goaf, and ethylene gas is an important symbol gas of spontaneous combustion in the coal accelerated oxidation stage. In order to overcome the problem of current coal ethylene detection, the paper presents a mine optical fiber multi-point ethylene concentration sensor based on the tunable diode laser absorption spectroscopy. Based on the experiments and analysis of the near-infrared spectrum of ethylene, the system employed the 1.62 μm (DFB) wavelength fiber coupled distributed feedback laser as the light source. By using the wavelength scanning technique and developing a stable fiber coupled Herriot type long path gas absorption cell, a ppm-level high sensitivity detecting system for the concentration of ethylene gas was realized, which could meet the needs of coal mine fire prevention goaf prediction.

Fiber-optic Fabry-Perot hydrogen sensor coated with Pd-Y film

Abstract: A fiber-optic Fabry-Perot hydrogen sensor was developed by measuring the fringe contrast changes at different hydrogen concentrations. The experimental results indicated that the sensing performance with the Pd-Y film was better than that with the Pd film. A fringe contrast with a decrease of 0.5 dB was detected with a hydrogen concentration change from 0% to 5.5%. The temperature response of the sensor was also measured.

Photovoltaic Properties of Thermally-Grown Selenium-Doped Silicon Photodiodes for Infrared Detection Applications

Abstract: In this work, the photovoltaic properties of selenium-doped silicon photodiodes were studied. Influence of illumination of the impurity absorption range on the current-voltage and spectral characteristics of the fabricated device were considered. The photoresponse dependencies on the electric intensity, current, and radiation power at the sample were observed. Results obtained in this work showed that the current-sensitivity of the fabricated structures at the forward bias was rather higher than that of photoresistors. The photosensitivity and detectivity were up to 2.85×10−16W·Hz−1/2 and 2.1×1011cm·Hz1/2W−1, respectively.

Study on the algorithm of vibration source identification based on the optical fiber vibration pre-warning system

Abstract: One of the key technologies for optical fiber vibration pre-warning system (OFVWS) refers to identifying the vibration source accurately from the detected vibration signals. Because of many kinds of vibration sources and complex geological structures, the implement of identifying vibration sources presents some interesting challenges which need to be overcome in order to achieve acceptable performance. This paper mainly conducts on the time domain and frequency domain analysis of the vibration signals detected by the OFVWS and establishes attribute feature models including an energy information entropy model to identify raindrop vibration source and a fundamental frequency model to distinguish the construction machine and train or car passing by. Test results show that the design and selection of the feature model are reasonable, and the rate of identification is good.

Resolution enhancement of optical surface plasmon resonance sensor using metamaterial

Abstract: In this paper, we present and discuss a path to extend the enhancement of the resolution of an optical surface plasmon resonance (SPR) sensor. Basically, our approach is to combine bi-metamaterial layers to design the SPR sensor. The calculation shows that the proposed SPR sensor structure has a preference over the conventional SPR sensors and bimetallic SPR sensors since it gives a much sharper reflectance dip and can achieve considerable sensitivity improvement when compared to the recently reported investigations. The effects of the metamaterial permittivity, permeability, and thickness on the reflectance curve are studied. It is also seen that metamaterial layers improve the field of the proposed SPR structure, which may provide a novel tool to significantly enhance the sensitivity and resolution of the sensors.

Long period fiber grating based refractive index sensor with enhanced sensitivity using Michelson interferometric arrangement

Abstract: The long period fiber grating (LPFG) is widely used as a sensor due to its high sensitivity and resolution. However, the broad bandwidth of the attenuation bands formed by the mode coupling between the fundamental core mode and the cladding modes constitutes a difficulty when the device is used as a conventional sensor. To overcome this limitation, a Michelson interferometer-type sensor configuration has been developed, using an LPFG grating pair formed by coating a mirror at the distal end of the LPFG. This sensor configuration is more convenient to use and is able to overcome the limitations of the single LPFG based sensor as the shifts in the attenuation bands being more easily detectable due to the formation of the sharp spectral fringe pattern in the LPFG based Michelson interferometer. In this work, I studied the LPFG based Michelson interferometer as the refractive index sensor and discussed the sensitivity enhancement of the LPFG based Michelson interferometer as a refractive index sensor by employing higher order cladding modes and by reducing the cladding radius. The results demonstrated the HE17 mode with a cladding radius of 62.5 μm, in the range of surrounding refractive index (SRI) of 1–1.45, and its resonant peak showed a wavelength shift of 26.99 nm/RIU. When the cladding region was further reduced to 24 μm, the resonant peak showed a wavelength shift of 569.88 nm/RIU, resulting in a sensitivity enhancement of nearly 21 times. However, as the cladding region was etched further, then the HE17 order cladding mode and higher mode would be cut off. Therefore, the implementation of high sensitivity for SRI sensing with the reduced cladding in the LPFG based Michelson interferometer is dependent on the proper combination of the cladding radius and cladding mode order.

An extrinsic fiber Fabry-Perot interferometer for dynamic displacement measurement

Abstract: A versatile fiber interferometer was proposed for high precision measurement. The sensor exploited a double-cavity within the unique sensing arm of an extrinsic-type fiber Fabry-Perot interferometer to produce the quadrature phase-shifted interference fringes. Interference signal processing was carried out using a modified zero-crossing (fringe) counting technique to demodulate two sets of fringes. The fiber interferometer has been successfully employed for dynamic displacement measurement under different displacement profiles over a range of 0.7 μm to 140 μm. A dedicated computer incorporating the demodulation algorithm was next used to interpret these detected data as well as plot the displacement information with a resolution of λ/64. A commercial displacement sensor was employed for comparison purposes with the experimental data obtained from the fiber interferometer as well as to gauge its performance, resulting in the maximum error of 2.8% over the entire displacement range studied.

Design of Mach-Zehnder Interferometer and Ring Resonator for Biochemical Sensing

Abstract: We proposed a compact design of an optical biochemical sensor based on the Mach-Zehnder interferometer (MZI), which was coupled by a ring resonator (RR) as a sensing tool. The sensor sensitivity has been determined by power difference at the output ports. The sensor enhancement has been optimized by numerically evaluating the geometrical parameters of the MZI and RR. A great sensor sensitivity depicted by Fano resonance characteristic has been demonstrated as a function of the round trip phase in the range of 4×10−4 − 4×10−4, which was changed by the presence of the sample solution in the sensing area. This optimum sensitivity has been obtained for the values of two coupling coefficients of the MZI κ1 = κ2 = 0.5/mm and the coupling coefficient between the MZI arm and RR κR = 0.5/mm. Furthermore, a good profile of sensitivity exchange has been exhibited by inducing the direct current voltage to the coupling region of κR. Finally, the output power transmission of the ring-coupled arm was depicted as a function of tunable κR.

Design of a surface plasmon resonance sensor based on grating connection

Abstract: Nowdays, the study of measurement of the biological field focuses on the research of improving surface plasmon resonance (SPR) in the fields of integration and detection sensitivity. We designed a kind of grating connected surface plasmon resonance sensor. Theoretically, we analyzed the wave vector and the effective refractive index relations with the diffraction grating structure. Then we obtained the nanoparticles enhancement SPR structure with a resolution 10 times higher than that of traditional SPR sensors. Also, we used the finite-difference time-domain (FDTD) analysis and simulation which showed that it was obvious with coupling effect by the nanoparticles enhancement SPR structure that the reflectance spectral bandwidth results validated the structure significantly which improved the sensitivity. Experimental results showed that the dynamic response of the designed sensor reached 10−6 RIU (refractive index unit). This study has the certain significance to long-distance and special sensing applications.

Rockfall hazard alarm strategy based on FBG smart passive net structure

Abstract: In order to realize working state remote monitoring for a passive net, alarm timely and correctly for the rockfall invasion, and solve the disadvantages in the existing means, such as needing power supply in situ, vulnerability to electromagnetic interference and environmental climate impact, a smart passive net structure based on the optical fiber sensing technology was designed which equipped with intercepting and sensing functions. The wire rope net as one part of the smart passive net was weaved with two kinds of optical fiber sensing elements, namely, fiber Bragg grating (FBG) perimeter severity sensors and optical fiber monitoring net with each end of the tail fiber containing an FBG probe. Based on the proposed smart structure, a combination alarm strategy for rockfall was proposed, which can distinguish transmission bug, whether the rockfall invasion or net broken occurs. Through a designed simulation test, the effectiveness of the proposed alarm strategy was certificated.

Ammonia sensing system based on wavelength modulation spectroscopy

Abstract: A sensing system in the near infrared region has been developed for ammonia sensing based on the wavelength modulation spectroscopy (WMS) principle. The WMS is a rather sensitive technique for detecting atomic/molecular species, presenting the advantage that it can be used in the near-infrared region by using the optical telecommunications technology. In this technique, the laser wavelength and intensity were modulated by applying a sine wave signal through the injection current, which allowed the shift of the detection bandwidth to higher frequencies where laser intensity noise was typically lower. Two multi-pass cells based on free space light propagation with 160 cm and 16 cm of optical path length were used, allowing the redundancy operation and technology validation. This system used a diode laser with an emission wavelength at 1512.21 nm, where NH3 has a strong absorption line. The control of the NH3 gas sensing system, as well as acquisition, processing and data presentation was performed.

Simultaneous measurement of one dimensional bending and temperature based on Mach-Zehnder interferometer

Abstract: A simple and compact optical fiber directional bending vector sensor with simultaneous measurement of temperature based on the Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The device consists of a piece of photonic crystal fiber (PCF) sandwiched between two single mode fibers (SMFs) with a lateral offset splicing. It shows the capacity for recognizing positive and negative directions. Within a curvature range of -7.13 m-1 to 7.13 m-1, the bending sensitivities of two resonant dips with opposite fiber orientations are obtained to be 0.484 nm/m-1 and 0.246 nm/m-1, respectively. This simple MZI is formed by invoking interference between LP01 and LP21 core modes, which leads to that the sensor is not sensitive to ambient refractive index (ARI). The temperature sensitivity has also been investigated. Two dips have obviously different sensitivities on the temperature and bending, so two parameters of both curvature and temperature can be distinguished and measured simultaneously by constructing a matrix and using one simple model interferometer.

Self-Compensating Displacement Sensor Based on Hydramatic Structured Transducer and Fiber Bragg Grating

Abstract: An optical fiber displacement sensor with a large measuring range for simultaneous displacement and temperature measurement is presented in this paper. We developed a specific transducer based on the piston and hydraumatic structure to realize a large displacement measurement, which combined the large measuring range and high precision into a single sensor system. The spectrum showed two reflection peaks used to compensate for cross-sensitivity in the displacement detection. This displacement sensor can linearly work in a large measuring displacement range greater than 45 mm with a high sensitivity of 0.036 nm/mm. The sensor we reported can be developed for real-time displacement monitoring in many industrial environments such as the mechanical shape or liquid level monitoring.

Low velocity impact localization system using FBG array and MVDR beamforming algorithm

Abstract: This paper proposes an impact localization system based on the fiber Bragg grating (FBG) array and minimum variance distortionless response (MVDR) beamforming algorithm. The linear FBG array, which contains seven FBG sensors, is used for detecting impact signals. Morlet wavelet transform is applied for extracting narrow-band signals of impact signals. According to the MVDR beamforming algorithm, the system realizes single-impact and multi-impact localizations. The localization system is verified on a 500 mm×500 mm×2 mm carbon fiber reinforced polymer (CFRP) plate for single-impact and multi-impact localizations. The average locating error and the maximum locating error are 6.8 mm and 9.9 mm, respectively.

Study of Modeling Aspects of Long Period Fiber Grating Using Three-Layer Fiber Geometry

Abstract: The author studied and demonstrated the various modeling aspects of long period fiber grating (LPFG) such as the core effective index, cladding effective index, coupling coefficient, coupled mode theory, and transmission spectrum of the LPFG using three-layer fiber geometry. Actually, there are two different techniques used for theoretical modeling of the long period fiber grating. The first technique was used by Vengsarkar et al who described the phenomenon of long-period fiber gratings, and the second technique was reported by Erdogan who revealed the inaccuracies and shortcomings of the original method, thereby providing an accurate and updated alternative. The main difference between these two different approaches lies in their fiber geometry. Venserkar et al used two-layer fiber geometry which is simple but employs weakly guided approximation, whereas Erdogan used three-layer fiber geometry which is complex but also the most accurate technique for theoretical study of the LPFG. The author further discussed about the behavior of the transmission spectrum by altering different grating parameters such as the grating length, ultraviolet (UV) induced-index change, and grating period to achieve the desired flexibility. The author simulated the various results with the help of MATLAB.

OFDR based distributed temperature sensor using the three-channel simultaneous radio-frequency lock-in technique

Abstract: Weak signal detection for single-mode fiber-optic distributed temperature sensor (DTS) is a key technology to achieve better performance. A hybrid technique combining the incoherent optical frequency domain reflectometry (IOFDR) and the three-channel simultaneous radio-frequency (RF) lock-in amplifier (LIA) is presented to improve the signal-to-noise ratio (SNR) of the measured spontaneous Raman backscattered light. The field programmable gate array (FPGA) based RF-LIA is designed with a novel and simple structure. The measurement frequency range is achieved from 1 kHz to 100 MHz. Experimental results show that the backscattered light signal of picowatt level can be detected with high SNR. With a 2.5 km single-mode fiber, a 1064 nm laser source, and the measurement time of 500 s, this sensing system can reach a spatial resolution of 0.93 m and a temperature resolution of about 0.2°C.

Fiber Bragg Grating Sensor Network Optimization

Abstract: This study introduces the optimization of the fiber Bragg grating (FBG) network and the load identification. Current researches on the optimal placement and reliability of the FBG network and the static load identification are generally analyzed. And then, the optimal placement of sensors and reliability of the FBG network are studied. Through the analysis of structural response characteristics, the general rules of sensors placement in structural static response parameters monitoring are proposed. The probability calculation is introduced, and the numerical analyses of the FBG sensor network reliability of several simple topologies are given.

A kind of biomolecular probe sensor based on TFBG surface plasma resonance

Abstract: This paper reports the application of the biomolecular probe sensor based on the tilted fiber Bragg grating (TFBG) surface plasma resonance (SPR) which can recognize the specificity of the specific molecule by depositing sensitive biological membrane outside the active golden layer. The method of self-assembly was used to make the fixed sensitive biological membrane to achieve the best effect in the experiment. To illustrate the specific recognition of the DNA molecule, the TFBG-SPR biosensor was exposed to complementary DNA solutions with the concentration of 0.1 mmol/L and 0.05 mmol/L, respectively. The resonance wavelength of the TFBG-SPR biosensor increased gradually, indicating that the hybridization with the complementary DNA molecules changed the effective refractive index in the vicinity of the golden layer. Furthermore, the results illustrated the feasibility of the biomolecular probe sensor based on the TFBG surface plasma resonance for detecting the specific molecule.

Design of fiber magnetic field sensor based on fiber Bragg grating Fabry-Perot cavity ring-down spectroscopy

Abstract: A novel fiber magnetic sensor based on the fiber Bragg grating Fabry-Perot (FBG-FP) cavity ring-down technique with pulse laser injection is proposed and demonstrated theoretically. A general expression of the intensity of the output electric field is derived, and the effect of the external magnetic field on the ring-down time is discussed. The results show that the output light intensity and the ring-down time of the FBG-FP cavity are in the inverse proportion to the magnitude of the external magnetic field. Our results demonstrate the new concept of the fiber magnetic sensor with the FBG-FP cavity ring-down spectroscopy and the technical feasibility.

Large dynamic range SPR measurements using a ZnSe prism

Abstract: A large dynamic index measurement range (n = 1 to n = 1.7) using surface plasmon resonance (SPR) shifts was demonstrated with a ZnSe prism at 632.8 nm, limited by the available high index liquid hosts. In contrast to borosilicate based SPR measurements, where angular limitations restrict solvent use to water and require considerable care dealing with Fresnel reflections, the ZnSe approach allows SPR spectroscopies to be applied to a varied range of solvents. An uncertainty in angular resolution between 1.5° and 6°, depending on the solvent and SPR angle, was estimated. The refractive index change for a given glucose concentration in water was measured to be n = (0.114 ± 0.007) /%[C6H12O6]. Given the transmission properties of ZnSe, the processes can be readily extended into the mid infrared.

Effect of wavelength on metrological characteristics of non-holographic fiber specklegram sensor

Abstract: In this paper, we report some results about the effects of varying the wavelength in a structure of a non-holographic fiber specklegram sensor. In these arrangements, the speckle pattern produced by a multi-mode optical fiber is coupled to the asingle-mode optical fiber with lower numerical aperture, which produces a filtering effect that can be used as an optical transduction mechanism. The influence of the wavelength on the sensor performance is evaluated by changing the laser wavelength, and a strong effect on the linearity and reproducibility of its response is found. Lasers emitting at 1310 nm, 1550 nm, and 1625 nm are used.