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Temperature-Compensated Interferometric High-Temperature Pressure Sensor Using a Pure Silica Microstructured Optical Fiber
Abstract
We present a high-temperature interferometric pressure sensor using a simple-design and easy-to-fabricate pure silica four-hole novel microstructured optical fiber. The asymmetric geometry of the fiber allows hydrostatic pressure to induce stress at the optical fiber core, which converts to an interferometric shift. The large core of the fiber supports the propagation of several modes. Multimode interference created between different pairs of modes is used to sense the temperature and pressure change. The use of pure silica fiber is motivated by the ability of this fiber to operate up to high temperature as dopant diffusion is avoided. The sensor is demonstrated to measure pressure at a temperature up to 800 °C. We demonstrate temperature compensation using a Fourier approach to monitor different interference pairs and their phase response to pressure and temperature change. Experimental results show that the sensor has a linear response and excellent stability with a detection limit of 8.86 kPa at 800 °C temperature. This simple, compact, and potentially low-cost sensor is promising for harsh environment applications to improve quality control, operation efficiency, and safe working conditions.
... We recently applied multimode interference to pressure measurement at high temperature utilising a pure silica based four-hole asymmetric shaped microstructured optical fiber. Using the fabricated pressure sensing fiber (PSF) we created a reflection mode multimode interferometer and demonstrated stable pressure measurement up to 800 • C [33]. ...
... Fig. 1 shows a schematic diagram demonstrating the multimode interferometer created by splicing single mode polarization-maintaining (PM) fiber with multimode PSF. The in-house fabricated PSF proposed by Reja et al. [33] has an elliptical shaped core having major and minor axis diameters of 17.5 µm and 7 µm, respectively, allowing it to have relatively large numerical aperture and thus multimode guidance. The fabrication details of the PSF and numerical analysis of the pressure induced stress and resulting refractive index change across the fiber core are reported by Reja et al. [33]. ...
... The in-house fabricated PSF proposed by Reja et al. [33] has an elliptical shaped core having major and minor axis diameters of 17.5 µm and 7 µm, respectively, allowing it to have relatively large numerical aperture and thus multimode guidance. The fabrication details of the PSF and numerical analysis of the pressure induced stress and resulting refractive index change across the fiber core are reported by Reja et al. [33]. The schematic in Fig. 1 illustrates how multimode interference is formed from a two-point sensor consisting of PM-PSF-PM-PSF-PM fiber. ...
We demonstrate a multipoint optical fiber pressure sensor for high temperature operation using multimode interference. Each sensing element consists of a four-hole asymmetric multimode fiber acting as the pressure sensing fiber, spliced between two standard polarization-maintaining single mode fibers. Multiple sensing elements are serially connected for multipoint pressure sensing and demultiplexing is achieved using Fourier analysis. The spatial frequency associated with each sensing element is separated by having distinct optical path lengths. The pure silica material of the sensing fiber enables high-temperature operation. As a proof of concept, we demonstrate two-point pressure sensing at a temperature up to 900 °C with negligible crosstalk between the sensing elements and good stability. Our demonstrated sensor has potential applications in heavy industry where spatially resolved measurements of pressure at high temperature may lead to improvements in efficiency and safety.
... Environment applications to improve quality control, operation efficiency, and safe working conditions. [24] A POF Smart Carpet was built by Avellar et al. [10]. It was based on one POF arranged parallel to the walking direction in between two polyethylene layers, 60 cm wide and 2 m long. ...
... The static and dynamic calibration test indicated that the sensor's linearity, repeatability, and hysteresis within the 1 MPa pressure range were 4.33%, 1.9%, and 2.8%, respectively, and that the resonant frequency was 8.97 MHz. Reja et al. [24] presented a high-temperature interferometric pressure sensor using pure silica four-hole microstructured optical fiber. The large core of the fiber supported the propagation of several modes. ...
Background:
In the last ten years, the design and implementation of Optical Fiber Sensors (OFS) in biomedical applications have been discussed, with a focus on different subareas, such as body parameter monitoring and control of assistive devices.
Materials and methods:
A scoping review was performed including scientific literature (PubMed/Scopus, IEEE and Web of Science), patents (WIPO/Google Scholar), and commercial information.
Results:
The main applications of OFS in the rehabilitation field for preventing future postural diseases and applying them in device controllers were discussed in this review. Physical characteristics of OFS, different uses, and applications of Polymer Optical Fiber pressure sensors are mentioned. The main postures used for posture monitoring analysis when the user is sitting are normal position, crooked back, high lumbar pressure, sitting on the edge of the chair, and crooked back, left position, and right position. Additionally, it is possible to use Machine Learning (ML) algorithms for posture classification, and device control such as Support Vector Machine, k-Nearest Neighbors, etc., obtaining accuracies above 97%. Moreover, the literature mentions wheelchair controllers and Graphical User Interfaces using pressure maps to provide feedback to the user.
Conclusions:
OFS have been used in several healthcare applications as well as postural and preventive applications. The literature showed an effort to implement and design accessible devices for people with disabilities and people with specific diseases. Alternatively, ML algorithms are widely used in this direction, leaving the door open for further studies that allow the application of real-time systems for posture monitoring and wheelchairs control.
... One of the main reasons that MOFs have become such an important new technology is that the hole structure can be designed to fabricate fibres that have very special optical properties. This is fundamental in a wide array of applications including communication networks [1], high-temperature and pressure sensors [4,5,6], chemical sensing [7,8,9], and biological sensing such as DNA detection [10,11,12]. Nevertheless, the optical properties can depend very sensitively on the geometry of the internal structure of the fibre and hence achieving very high tolerances in the manufacturing process is paramount. ...
In the fabrication of optical fibres, the viscosity of the glass varies dramatically with temperature so that heat transfer plays an important role in the deformation of the fibre geometry. Surprisingly, for quasi-steady drawing, with measurement of pulling tension, the applied heat can be adjusted to control the tension and temperature modelling is not needed. However, when pulling tension is not measured, a coupled heat and fluid flow model is needed to determine the inputs required for a desired output. In the fast process of drawing a preform to a fibre, heat advection dominates conduction so that heat conduction may be neglected. By contrast, in the slow process of extruding a preform, heat conduction is important. This means that solving the coupled flow and temperature modelling is essential for prediction of preform geometry. In this paper we derive such a model that incorporates heat conduction for the extensional flow of fibres. The dramatic variations in viscosity with temperature means that this problem is extremely challenging to solve via standard numerical techniques and we therefore develop a novel finite-difference numerical solution method that proves to be highly robust. We use this method to show that conduction significantly affects the size of internal holes at the exit of the device.
... However, the resistance and capacitance of the signal processing circuit are not significantly affected. If the transmitted signal is not processed, it will affect the control accuracy [33,34]. It is difficult to meet the precision requirements simply by adding hardware compensation to the sensor. ...
In order to meet the latest requirements for sensor quality test in the industry, the sample sensor needs to be placed in the medium for the cold and hot shock test. However, the existing environmental test chamber cannot effectively control the temperature of the sample in the medium. This paper designs a control method based on the support vector machine (SVM) classification algorithm and K-means clustering combined with neural network correction. When testing sensors in a medium, the clustering SVM classification algorithm is used to distribute the control voltage corresponding to temperature conditions. At the same time, the neural network is used to constantly correct the temperature to reduce overshoot during the temperature-holding phase. Eventually, overheating or overcooling of the basket space indirectly controls the rapid rise or decrease in the temperature of the sensor in the medium. The test results show that this method can effectively control the temperature of the sensor in the medium to reach the target temperature within 15 min and stabilize when the target temperature is between 145 °C and −40 °C. The steady-state error is less than 0.31 °C in the high-temperature area and less than 0.39 °C in the low-temperature area, which well solves the dilemma of the current cold and hot shock test.
... Meanwhile, these fibers are fabricated under high temperature (∼1900 • C). After the annealing process, the produced fiber structure can show good long-term stability for gas pressure monitoring [20,21]. ...
A highly sensitive inline gas pressure sensor based on the hollow core Bragg fiber (HCBF) and harmonic Vernier effect (VE) is proposed and experimentally demonstrated. By sandwiching a segment of HCBF between the lead-in single-mode fiber (SMF) and the hollow core fiber (HCF), a cascaded Fabry–Perot interferometer is produced. The lengths of the HCBF and HCF are precisely optimized and controlled to generate the VE, achieving a high sensitivity of the sensor. Meanwhile, a digital signal processing (DSP) algorithm is proposed to research the mechanism of the VE envelope, thus providing an effective way to improve the sensor’s dynamic range based on calibrating the order of the dip. Theoretical simulations are investigated and matched well with the experimental results. The proposed sensor exhibits a maximum gas pressure sensitivity of 150.02 nm/MPa with a low temperature cross talk of 0.00235 MPa/ $^\circ$ ∘ C. All these advantages highlight the sensor’s enormous potential for gas pressure monitoring under various extreme conditions.
... The optical fiber pressure sensor is small in size, has anti-electromagnetic interference and high-temperature resistance [15,16] to overcome the above problems. For example, Fei Feng reported an optical fiber Fabry-Perot pressure sensor [17] as having a maximum linearity error of 1% in the temperature range of 20-400 • C; Mohammad Istiaque Reja developed a pure silica micro-structured optical fiber pressure sensor which can tolerate temperatures up to 800 • C [18]. However, the fiber Fabry-Perot cavity used for pressure sensing is sensitive to temperature changes, which causes unwanted output besides pressure change. ...
Due to material plastic deformation and current leakage at high temperatures, SOI (silicon-on-insulator) and SOS (silicon-on-sapphire) pressure sensors have difficulty working over 500 °C. Silicon carbide (SiC) is a promising sensor material to solve this problem because of its stable mechanical and electrical properties at high temperatures. However, SiC is difficult to process which hinders its application as a high-temperature pressure sensor. This study proposes a piezoresistive SiC pressure sensor fabrication method to overcome the difficulties in SiC processing, especially deep etching. The sensor was processed by a combination of ICP (inductive coupled plasma) dry etching, high-temperature rapid annealing and femtosecond laser deep etching. Static and dynamic calibration tests show that the accuracy error of the fabricated sensor can reach 0.33%FS, and the dynamic signal response time is 1.2 μs. High and low temperature test results show that the developed sensor is able to work at temperatures from −50 °C to 600 °C, which demonstrates the feasibility of the proposed sensor fabrication method.
Optical fiber pressure sensing is of significant interest for industrial process monitoring and acoustic sensing. However, the direct detection of pressure changes along an optical fiber with minimal crosstalk is a significant challenge due to the low stress-optic coefficient of glass and interferences from temperature, bending, and strain. Here we demonstrate that deep learning combined with microstructured optical fiber specklegram sensing is an effective approach to overcoming environmental crosstalk for the challenging application of pressure sensing. Specklegrams created from multimode interference are inherently sensitive to both the measurand of interest and other environmental perturbations. By employing a deep neural network, namely a multi-layer perceptron, we show that the environmental crosstalk of the specklegram based pressure sensor can be mitigated. Furthermore, we demonstrate the practical implementation of the machine learning based pressure sensor where we need to continuously update the model. We show that the network can learn and reject environmental disturbances and predict pressure values correctly through continuous training updates. This technique approaches the instrument error of our calibration pressure gauge, with an error below 3 kPa over a range of 1 MPa.
We built a fiber-optic hydrophone using a multimode microstructured pressure-sensitive fiber with a multi-fiber fanout. A neural network is used for signal post-processing and achieved better results than a commercial electric hydrophone.
We demonstrate a fiber-optic hydrophone using a multimode microstructured pressure-sensitive optical fiber, which has a sensitivity comparable to a commercial electric hydrophone and 14 to 17 dB improvement over conventional single mode and multimode optical fiber. We then configure the pressure-sensitive fiber with a multi-fiber fan-out output where each output channel encodes different coupling from the pressure-sensitive fiber’s modal interference pairs. Thus, each channel has a different response to both the acoustic wave and environmental noise. We use a neural network model as the signal processing module to combine the acoustic signals from the multiple fiber channels to reconstruct the original signal. By combining the channels, the neural network model can effectively reduce crosstalk from environmental noise. We then demonstrate the ability to reconstruct complex audio signals using several classical music symphonies.
The temperature resolution of Fiber Optic Sensor is greatly limited by background noise. In this paper, we propose a noise suppression method, based on variational mode decomposition (VMD), to enhance the temperature resolution. The VMD algorithm is employed to decompose the original signal into several intrinsic mode function (IMF) components, each limited by a certain bandwidth. We calculate the correlation coefficient between each IMF component and the original sensing signal, and filter out IMFs with correlation coefficients less than the average, which primarily contain noise signal. The IMFs with correlation coefficients greater than the average are retained for signal reconstruction. The experimental and comparative results demonstrate the exceptional performance of the proposed algorithm in denoising temperature signals, effectively removing background and environmental noise while preserving temperature information. Furthermore, by analyzing the power spectrum of the temperature signal before and after noise suppression, we observe that the proposed algorithm can achieve a temperature resolution of 10
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°C, which is two orders of magnitude higher than that before noise suppression (10
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°C). These results validate the efficacy of our method in reducing system noise and improving the accuracy and reliability of interferometric temperature sensors.
High-temperature pressure sensors can be widely used in industries with high-temperature working conditions, such as aerospace, automotive, petroleum industry and fire protection. Pressure sensors with excellent sensing performance and high-temperature tolerance will have broad application prospects in harsh environments. This review summarizes the research progress of high-temperature pressure sensors from aspects ranging from materials and working mechanisms to temperature compensation methods. Finally, challenges and trends in the field are briefly discussed. It is expected to benefit the scientific research community and promote further research and applications of high-temperature sensors.
Polymer or Plastic Optical Fiber sensors (POFs) and Fiber Bragg Grating sensors (FBGs) have gained increasing popularity in biomedical engineering (BME) applications over the past decades due to their unique properties such as compact size, lightweight, wide dynamic range, biocompatibility, electromagnetic and radio frequency interference immunity, high strain sensitivity, and multiplexing capabilities. The POF sensor flexibility, low Young’s modulus (sensitivity to mechanical changes), higher elastic limits, and higher impact resistance make it suitable for instrumentation requirements in medical devices and biological analysis and measurements. Medical applications for POFs and FBGs have been demonstrated by developing instruments, gait assistance devices, wearables, and biosensors. This paper presents an ambitious review of the current state of the art of POF and FBG-based measuring techniques based on optical multicore fibers (MCF) or multiple optical single-core fibers with embedded FOS sensors. It comprehensively analyses how various sensor variants have been used in medical, healthcare, and remote sensing applications. The review comprises a range of aspects, which include: (I) research methodology; (II) an overview of POF and FBG sensing technology; (III) applications of POFs and FBGs in BME applications; (IV) current state and future trends of POFs and FBGs in the field of BME. The BME applications discussed include applications of POFs and FBGs in; (1) physiological parameter monitoring; (2) biomechanics; (3) foot plantar pressure assessment; (4) gait assistance wearable devices and rehabilitation robotics; (5) joint angle measurement and human movement assessment; (6) health diagnosis; (7) robotic medical microsurgery; and (8) temperature monitoring during thermal ablation treatment.
Owing to their unique structural design and strong light-matter interaction, microstructure optical fibers (MOFs) emerge as a promising platform for optical sensing. When MOF-based sensors are perturbed, the acquired spectrum data are scrambled that significantly limits their practical application. To overcome this challenge, a functionalized MOF enabled by deep learning-based data analytics is proposed and experimentally demonstrated to realize temperature sensing in the presence of external perturbations. Under different temperature states, the trained deep learning model can effectively extract features from the collected signal data and achieve highly accurate recognition of complex speckle patterns. Experimental results show that the speckle recognition accuracy of the deep learning model reaches 98.64% and 100% in the presence and absence of external perturbations, respectively. The approach herein can be extended to other MOF-based sensing systems with regular or irregular speckle patterns for detecting various measurands. And moreover, the MOF integrated with an optical neural network possesses several desirable features such as high recognition accuracy, anti-interference capability and simplified configuration, showing great potential toward realizing the smart monitoring applications in the aspects of healthcare, industry, and environmental engineering..
We propose and demonstrate a suspended fiber-optic Fabry–Pérot interferometer for sensitivity-improved high-pressure measurement. A thin-cladding fiber (TCF) is inserted into a silica capillary wherein the end faces of the TCF and single-mode fiber form a suspended FP structure. The sensitivity of the sensor is determined by the air microcavity length
L
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and capillary length
L
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. The sensitivity can be controlled by changing the
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/
L
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ratio. A capillary with inner and outer diameters of 100 μm and 150 μm, respectively, was used to experimentally demonstrate this sensitivity enhancement. The
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ratio was increased from 13.4 to 114.6 and the sensitivity increased from -361.41 pm/MPa to -2975.21 pm/MPa were achieved. In the pressure measurement range of 0–80 MPa, the uncertainty in pressure measurement of the packaged sensor was 0.03%. The sensor has the advantages of small size, simple structure, remarkable accuracy, large range, together with a much suppressed temperature cross-sensitivity, approximately 0.0011 MPa/°C.
We present a novel strain sensor based on a hybrid Fabry–Perot interferometer (HFPI), which is mainly constructed by a cascade of a suspended-core fiber (SCF) and a hollow-core fiber (HOF) between two single-mode fibers (SMFs). When the optical path length (OPL) is matched to some extent, the reflection spectrum of the proposed HFPI demonstrates dense periodic Fabry–Perot interferometer (FPI) fringes tailored with a widely expanded envelope, the dip or peak of which responds swiftly to the strain due to the Vernier effect and the strain response difference between the SCF and the HOF. Through optimizing the parameters, one can achieve a magnified strain sensitivity up to −91.41 pm/
$\mu \varepsilon $
ranging from 0 to
$1800~\mu \varepsilon $
. The strain sensitivity is much higher than that of the single HOF FPI structure or the single SCF FPI structure. Moreover, a theoretical model has been established to explain the principle of the proposed HFPI based on the Vernier effect and the ways to further improve the sensitivity. By adding a fiber Bragg grating (FBG), the temperature can also be interrogated by demodulating the envelope peak of the HFPI and the peak of the FBG. The proposed structure has the advantages of high sensitivity, large dynamic range, temperature discrimination ability, and compact size, providing potential from personal human health perception to public structure health monitoring.
A fiber twist angle sensor has been theoretically proposed and experimentally verified by employing a fiber Sagnac loop interferometer based on a self-made eccentric dual-core fiber. The asymmetry of the dual-core fiber structure made the deformation of the fiber more obvious under the action of twist and enabled the designed sensor to identify the direction of twist angle. A clockwise (CW) and counterclockwise (CCW) rotation of a 5-cm-long eccentric dual-core fiber in the Sagnac loop generated a phase difference, which induced a red or blue shift of the interference spectrum, and the purpose of twist angle sensing was achieved by monitoring the spectral shift. The size of the twisted object should be larger than 5 cm, so that the sensor can be placed on the surface of the object to measure the twist deformation. In the measuring range from −90° to 90°, the twist angle-based sensitivity and twist rate-based sensitivity of the designed sensor were, respectively, investigated in CW and CCW directions: the former was 45.2 pm/° in CCW direction (−90° to 0°) and 12 pm/° in CW direction (0°–90°), and the latter was 129.49 pm/(rad/m) in CCW direction (–31.4 to 0 rad/m) and 34.38 pm/(rad/m) in CW direction (0–31.4 rad/m). The satisfactory sensitivity, stability, and repeatability make it a competitive alternative in twist angle sensing region, which can be widely used in engineering, biomedical, and other twist angle sensitive fields.
In this Letter, we report on a fiber-optic Fabry–Perot interferometric pressure sensor with its external diaphragm surface thinned and roughened by a femtosecond laser. The laser-roughened surface helps to eliminate outer reflections from the external diaphragm surface and makes the sensor immune to variations in the ambient refractive index. The sensor is demonstrated to measure pressure in a high-temperature environment with low-temperature dependence.
We propose a high-temperature sensor based on a suspended-core microstructured optical fiber (SCMF). The sensor is constructed by fusion splicing a piece of SCMF between two sections of multimode fibers (MMFs) which act as light beam couplers. The multimode interference is formed by the air cladding modes and the silica core modes in the SCMF. Fast Fourier transform is adapted to filtering the raw transmission spectra of the MMF-SCMF-MMF structure. The wavelength shift of the dominant spatial frequency is monitored as the temperature varies from 50 °C to 800 °C. The sensitivities of 31.6 pm/°C and 51.6 pm/°C in the temperature range of 50 °C-450 °C and 450 °C-800 °C are respectively achieved. Taking advantage of the compact size, good stability and repeatability, easy fabrication, and low cost, this proposed high-temperature sensor has an applicable value.
An extrinsic Fabry-Pérot interferometric (EFPI) sensor created at the tip of an optical fiber is presented for high-pressure measurement. The sensor, with a diameter of 125 μm, is fabricated exclusively in pure silica fiber, which makes it suitable for applications in high-temperature environments. The EFPI cavity of the sensor is formed by fusion splicing, cleaving, polishing, and femtosecond laser micromachining. Experimental studies show that the sensor exhibits high stability and good linearity over a pressure range of 10 MPa under high-temperature conditions (up to 800°C). This sensor offers great potential for use in high-temperature applications.
A compact dual-cavity Fabry–Perot interferometer (DC-FPI) sensor is proposed and demonstrated based on a hollow-core photonic bandgap fiber (HC-PBF) spliced with a hollow-core fiber (HCF). The HC-PBF, which has low transmission loss, was used as the first FPI cavity and also acted as a bridge between the lead-in single-mode fiber and the HCF. The HCF was used as the second FPI cavity and also acted as a micro gas inlet into the first FPI cavity. A DC-FPI sensor with different cavity lengths of 226 and 634 μm in the first FPI and the second FPI was created. Both gas pressures ranging from 0–10 MPa and temperatures ranging from 100–800°C were measured using the DC-FPI sensors together with a fast Fourier transform and phase-demodulation algorithm. Experimental results showed that the first FPI cavity was gas pressure sensitive but temperature insensitive, while the second FPI cavity was temperature sensitive but gas pressure insensitive. A high gas pressure sensitivity of 1.336 μm/MPa and a temperature sensitivity of 17 nm/°C were achieved in the DC-FPI sensor. Moreover, the cross sensitivity between the gas pressure and temperature was calculated to be ∼ − 15 Pa / ° C and ∼ 0.3 ° C / MPa . The proposed DC-FPI sensors provide a promising candidate for the simultaneous measurement of high pressures and high temperatures at some precise locations.
The femtosecond laser-induced fiber Bragg grating is an effective sensor technology that can be deployed in harsh environments. Depending on the optical fiber chosen and the inscription parameters that are used, devices suitable for high temperature, pressure, ionizing radiation and strain sensor applications are possible. Such devices are appropriate for aerospace or energy production applications where there is a need for components, instrumentation and controls that can function in harsh environments. This paper will present a review of some of the more recent developments in this field.
We demonstrate a novel type of distributed optical fiber acoustic sensor, with the ability to detect and retrieve actual temporal waveforms of multiple vibration events that occur simultaneously at different positions along the fiber. The system is realized via a dual-pulse phase-sensitive optical time-domain reflectometry, and the actual waveform is retrieved by heterodyne phase demodulation. Experimental results show that the system has a background noise level as low as 8.91 × 10 − 4 rad / √ Hz with a demodulation signal-to-noise ratio of 49.17 dB at 1 kHz, and can achieve a dynamic range of ∼ 60 dB at 1 kHz (0.1 to 104 rad) for phase demodulation, as well as a detection frequency range from 20 Hz to 25 kHz.
We propose and experimentally demonstrate, for the first time to our knowledge, high temperature fiber sensing using the multimode interference effect within a suspended-core microstructured optical fiber (SCF). Interference fringes were found to red-shift as the temperature increased and vice versa. Temperature sensing up to 1100°C was performed by measuring the wavelength shifts of the fringes after fast Fourier transform (FFT) filtering of the spectra. In addition, phase monitoring at the dominant spatial frequency in the Fourier spectrum was used as an interrogation method to monitor various temperature-change scenarios over a period of 80 hours. Our proposed high temperature fiber sensor is simple, cost-effective, and can operate at temperatures beyond 1000°C.
We demonstrate a new approach to high temperature sensing using femtosecond laser ablation gratings within silica suspended-core microstructured optical fibers. The simple geometry of the suspended-core fiber allows for femtosecond laser processing directly through the fiber cladding. Pure silica glass is used, allowing the sensor to be used up to temperatures as high as 1300°C while still allowing the fibre to be spliced to conventional fiber. The sensor can also be wavelength division multiplexed, with three sensors in a single fiber demonstrated.
This paper reports on a new kind of temperature sensor operating over an extremely large temperature range at high monitoring speeds. The sensor utilizes fiber Bragg gratings inscribed into multimode single crystalline Sapphire fibers, basically providing temperature control via an optical reflection signal. The gratings operate up to 1900 °C, which is the highest temperature determined using Bragg grating so far, and allow signal processing with a temperature resolution better than ±2 K. The sensor uniquely provides fast dynamic temperature monitoring at an unprecedented rate of 20 Hz. Overall, fiber Bragg grating inside Sapphire fibers provide a new base for precise high-temperature measurement with key advantages such as signal multiplexing, large temperature bandwidth and insensitivity to electromagnetic fields.
This investigation describes a detailed analysis of the fabrication and testing of optical fibre pressure and temperature sensors (OFPTS). The optical sensor of this research is based on an extrinsic Fabry–Perot interferometer (EFPI) with integrated fibre Bragg grating (FBG) for simultaneous pressure and temperature measurements. The sensor is fabricated exclusively in glass and with a small diameter of 0.2 mm, making it suitable for volume-restricted bio-medical applications. Diaphragm shrinking techniques based on polishing, hydrofluoric (HF) acid and femtosecond (FS) laser micro-machining are described and analysed. The presented sensors were examined carefully and demonstrated a pressure sensitivity in the range of sp = 2–10 nmkPa and a resolution of better than ΔP = 10 Pa (0.1 cm H2O). A static pressure test in 38 cmH2O shows no drift of the sensor in a six-day period. Additionally, a dynamic pressure analysis demonstrated that the OFPTS never exceeded a drift of more than 130 Pa (1.3 cm H2O) in a 12-h measurement, carried out in a cardiovascular simulator. The temperature sensitivity is given by k=10.7
pmK, which results in a temperature resolution of better than ΔT = 0.1 K. Since the temperature sensing element is placed close to the pressure sensing element, the pressure sensor is insensitive to temperature changes.
The fabrication, characterization and encapsulation of a fiber optic temperature sensor based upon a micro Fabry–Perot (F-P) cavity is presented. The F-P cavity is formed between a reflective in-fiber metallic splice and the air-fiber boundary at the end of the sensor. A change in temperature modifies the optical cavity length, and this is observed as a change in the reflected interference spectrum. The sensor has been demonstrated for high-temperature measurement up to 1100 °C. The stability of the sensor system is ∼10 °C over a period exceeding 300 h at 1100 °C. Furthermore, a sealed capillary is used as a protective enclosure.
Femtosecond laser written Bragg gratings have been written in exposed-core microstructured optical fibers with core diameters ranging from 2.7 µm to 12.5 µm and can be spliced to conventional single mode fiber. Writing a Bragg grating on an open core fiber allows for real-time refractive index based sensing, with a view to multiplexed biosensing. Smaller core fibers are shown both experimentally and theoretically to provide a higher sensitivity. A 7.5 µm core diameter fiber is shown to provide a good compromise between sensitivity and practicality and was used for monitoring the deposition of polyelectrolyte layers, an important first step in developing a biosensor.
Figure 2 in a previous Letter [ Opt. Lett. 38, 4609 (2013)] was incorrect and is modified here.
Longitudinal and transverse wave velocities, six kinds of elastic parameters (Young, shear and bulk moduli, Lamè parameter, Poisson's ratio and acoustic wave velocity anisotropy factor) and dilational and shear internal frictions of a fused quartz have been simultaneously measured over a temperature range 298 1674 K, by an ultrasonic pulse sing-around method. These elastic moduli, Lamè parameter and Poisson's ratio increase with increasing temperature, suggesting enhancement of rigidity for mixed mode II mode III shear by crystallization on heating. The 840 and 1110 K peaks in dilational friction might be related to phase transition of alpha-quartz/beta-quartz and beta-quartz/beta2-tridymite. For shear friction, the 390 and 1360 K peaks would be attributed to beta1/beta2-tridymite and glass phase transitions, respectively.
Detailed studies on fiber optic pressure and temperature sensors for oil down-hole applications are described in this paper. The sensor head is an interferometric based fiber optic senor in which the air-gap will change with the pressure or temperature. For high-speed applications, a novel self-calibrating interferometric/intensity-based (SCIIB) scheme, which realizes compensations for both the light source drift and the fiber loss variation, was used to demodulate the pressure (or temperature) signals. An improved white light system was developed for sensor fabrication. This system is also used as the signal demodulation system providing very high resolution. Experiment results show that the SCIIB system achieves 0.1% accuracy with a 0-8000psi working range for the pressure sensor and a 0-600 degree(s)C working range for the temperature sensor. The resolution of the white light system is about +/- 0.5 nm with a dynamic range up to 10 micrometers. The long -term testing results in the oil site are also presented in this paper.
We describe novel Bragg grating sensors based on single mode fiber made with side air holes. Measurements made at 12 kpsi and 100 C produced enhanced sensitivity and reduced thermal dependence compared to normal fiber Bragg gratings.
A fiber-optic strain sensor is demonstrated by using a short length of polarization-maintaining photonic crystal fiber (PM-PCF) as the sensing element inserted in a Sagnac loop interferometer. Spectrum shift in response of strain with a sensitivity of 0.23 pm/με is achieved, and the measurement range, by stretching the PM-PCF only, is up to 32 mε. Due to the ultralow thermal sensitivity of the PM-PCF, the proposed strain sensor is inherently insensitive to temperature, eliminating the requirement for temperature compensation.
An optical fiber twist sensor is proposed by using solidcore lowbirefringence photoniccrystalfiber(LB-PCF)-based Sagnac interferometer. The twist effects on the fiber are theoret- ically analyzed. The results show that the dip wavelength of the transmission spectrum shifts with the twist angle with a high sen- sitivity and resolution of 1.00 nm and 0.01 , respectively. The sensor is also insensitive to environmental temperature change with an ultralow thermal dependent coeffiecient of 0.5 pm C. Index Terms—Birefringence, low-birefringence photonic crystal fiber, optical fiber twist sensor, Sagnac interferometer.
Many proposed microfluidic biosensor designs are based on the measurement of the resonances of an optical microcavity. Fluorescence-based resonators tend to be simpler and more robust than setups that use evanescent coupling from tuneable laser to probe the cavity. In all sensor designs the detection limits depend on the wavelength resolution of the detection system, which is a limitation of fluorescence-based devices. In this work, we explore the ultimate resolution and detection limits of refractometric microcavity sensor structures. Because many periodic modes are collected simultaneously from fluorescent resonators, standard Fourier methods can be best suited for rapid and precise analysis of the resonance shifts. Simple numerical expressions to calculate the ultimate sensor resolution and detection limits were found, and the results compared to experiments in which the resonances of fluorescent-core microcapillaries responded to various sucrose concentrations in water.
In this paper a fibre optic sensor is developed and tested to measure pressure and temperature under simulated wellbore conditions. The sensor consists of a miniature all-silica fibre optic Extrinsic Fabry-Perot Interferometer (EFPI) sensor which has a novel embedded Fibre Bragg Grating (FBG) reference sensor element to determine both pressure and temperature at the point of measurement. The sensor head is completely fabricated from fused-silica components, i.e. completely made of glass, utilizing a 200μm outer diameter silica glass fibre, a silica glass capillary and a Single-Mode FBG. All silica-glass components were spliced together using a conventional fusion splicer to obtain a robust sensor structure.
Because of their small size, passive nature, immunity to electromagnetic interference, and capability to directly measure physical parameters such as temperature and strain, fiber Bragg grating sensors have developed beyond a laboratory curiosity and are becoming a mainstream sensing technology. Recently, high temperature stable gratings based on regeneration techniques and femtosecond infrared laser processing have shown promise for use in extreme environments such as high temperature, pressure or ionizing radiation. Such gratings are ideally suited for energy production applications where there is a requirement for advanced energy system instrumentation and controls that are operable in harsh environments. This paper will present a review of some of the more recent developments.
For many industrial applications, corrosion is a life-limiting phenomenon and therefore requires careful consideration and rigorous experimental testing before structural materials can be reliably deployed, particularly in harsh chemical environments. The traditional approach to measuring corrosion requires exposing many samples to the intended environment and then extracting them individually at discrete intervals for postexposure characterization. This approach does not provide a high degree of temporal resolution, nor does it provide any real-time information regarding dynamic changes in corrosion rates. Developing an online corrosion monitor capable of surviving harsh chemical environments could provide valuable information regarding the structural health of components and changing process conditions that could accelerate corrosion. To this end, a corrosion sensor was developed based on a pressure-driven Fabry-Pérot cavity (FPC). This sensor uses a pressure control system to internally pressurize the FPC formed between the sensor’s housing and a metal-embedded singlemode optical fiber. Simultaneous measurement of the change in FPC length using low-coherence interferometry and the applied pressure enables the calculation of the relative changes in the sensor’s diaphragm thickness due to corrosion on its outer surface. Measurements were made
in situ
while actively corroding the sensor and were validated against surveillance specimens that were corroded simultaneously. The uncertainties in the measured corrosion were analyzed using error propagation of the uncertainties in the measured pressures and displacements and were found to be <1% of the initial diaphragm thickness.
We experimentally demonstrated two high-sensitivity high-temperature sensors based on in-line Michelson interferometers with the array of microspheres, which were fabricated by a simple fusion splicing technique. The devices have the highest temperature sensitivity of 0.139 nm/°C and 0.166 nm/°C, respectively, within the temperature region between 100 °C and 800 °C. The increase in the number of microspheres can improve temperature sensitivity while reducing the size of the sensor has been proved. It can be a new way to improve the performance of high-temperature fiber-optic sensors.
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 paper proposes poly (diallyldimethylammonium chloride) PDDA as the pretreatment solution for the surface of the gold film and the highly sensitive 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 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.
A highly sensitive humidity sensor with low temperature sensitivity is proposed and demonstrated using a polyvinyl alcohol coating tapered fiber. The taper fiber is highly sensitive to the environmental medium due to its microscale diameter. Thus, a humidity sensor can be prepared by plating a polyvinyl alcohol moisture sensitive film in a tapered region. The experimental results show that the sensor has a high humidity sensitivity of 0.1194 nm/%RH but with a relatively low temperature sensitivity of 0.029 nm/°C. Thus, the sensor can eliminate temperature interference and achieve accurate measurement of environmental humidity. At the same time, the sensor has excellent reversibility, stability and advantages common to optical fiber sensors, such as small size, antielectromagnetic interference and remote measurement.
High-temperature measurements are of significant importance in various harsh-environment engineering fields, such as fossil fuel production, and the metallurgical and aviation industries. In recent years, there is a steady trend to shift from conventional electronic sensors to optical fiber sensors for high-temperature applications. In particular, optical fiber sensors are small in size, immune to electromagnetic interference, readily applicable for remote sensing, have high elasticity, and incorporate capabilities for multiplexing and distributed sensing. However, commonly used fused silica optical fiber sensors exhibit severe limitations at ultrahigh temperatures due to significantly degraded optical and mechanical properties at temperatures >1000 °C. The excellent optical transparency, thermal and chemical stability, mechanical robustness, and high melting temperature (~2040 °C) of single-crystal sapphire fibers (SFs) make them a strong candidate for sensing applications in high-temperature environments. Translation of the sensing schemes from mature silica fiber sensors to SF sensors has undergone tremendous growth and advancements in the past two decades. However, hurdles to the development of a near-term deployable SF sensing system have proven persistent due to the highly multimodal nature of SFs. This article reviews sensing techniques that have been implemented with SFs recently. The aim is to provide a comprehensive summary of past research on SF sensing systems. Perspectives on further research into the challenging yet promising arena are also discussed.
This article reports a novel optical fiber extrinsic Fabry-Perot interferometer (EFPI) for probing pressure changes with subpascal (~0.1 Pa, ~1.45 × 10
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup>
psi) resolution. The principal idea of the sensor is to employ a traditional C-shaped Bourdon tube as a mechanical transducer that is coupled to a highly sensitive EFPI device. The cavity of the EFPI device is formed between a gold-coated mirror, mounted to a concave section of the Bourdon tube, and the endface of an optical fiber mounted at the base section of the Bourdon tube. Based on this design, the pressure-induced deflections of the Bourdon tube are directly correlated with the changes in cavity length of the EFPI, which can be determined by analyzing the interference signals. An experiment based on probing hydrostatic pressure changes induced by the addition of single water droplets to a test chamber was performed to quantify the measurement resolution of the proposed sensor because an apparatus for producing exceedingly small, stable, and reproducible pressure changes does not exist. Compared with conventional optical fiber pressure sensors, the proposed pressure sensor requires a simple fabrication process and can be used to measure pressure changes with high sensitivity (~23.5 μm/kPa, cavity length change/pressure change). Moreover, the sensitivity and resolution of the pressure sensor can be flexibly adjusted using Bourdon tubes designed for different dynamic ranges (e.g., 0-70 MPa, 0-10152 psi). It is believed that the proposed novel pressure sensor has the potential to find a wide range of applications that require precise instrumentation.
In this manuscript, we fabricated and tested a series of extrinsic fiber Fabry-Perot interferometric acoustic sensors based on corrugated silver diaphragms. These diaphragms were fabricated through a simple and low-cost method. The corrugations were firstly etched on the silicon surface permanently and then transferred to the silver diaphragm with the help of photoresist as the sacrificial layer. Sensors with different corrugation depths were fabricated. Experimental results showed the same trend with theoretical results on the mechanical sensitivities of the fabricated corrugated diaphragms, which first increased and then decreased with the increase of the corruption’s depth. Other characteristics of the fabricated optical acoustic sensors based on corrugated silver diaphragms were also tested in details. The proposed fabrication method of the corrugated diaphragm showed the advantages of simplicity and low-cost, and the acoustic sensors showed high-sensitivity, which was suitable for weak acoustic’s sensing.
Fiber optics is the elective technology for sensing temperatures in harsh environments. Among the possible exploitable working principles, fiber Bragg gratings are the most widespread implementation for their excellent balance between system complexity and performance. However, despite they are well known and established, so far metrological investigations have been limited to cases in which the sensor is used in uniform temperature conditions. This paper analyzes the response of commercial fiber Bragg gratings employed as temperature sensors in applications that imply large temperature gradients, such as in laser based thermal treatments of solid tumors. A theoretical model of the sensor is implemented first and then used to evaluate its response in non-uniform temperature distributions. The model results are experimentally validated by means of a liver phantom and comparisons between different grating configurations, such as single or multiplexed with different lengths, are made.
We have demonstrated a novel scheme for simultaneous measurement of temperature and refractive index by using an exposed core microstructured optical fiber (ECF). The ECF allows for high sensitivity to refractive index due to the small exposed-core, while being supported by a standard fiber diameter cladding making it robust compared to optical micro-fibers. The sensor combines a fiber Bragg grating (FBG) inscribed into the core of the ECF and a multimode Mach-Zehnder interferometer (MZI). Both the FBG and MZI are sensitive to refractive index (RI) and temperature through a combination of direct access to the evanescent field via the exposed-core, the thermo-optic effect and thermal expansion. The FBG and MZI respond differently to changes in temperature and RI, thus allowing for the simultaneous measurement of these parameters. In our experiment RI sensitivities of 5.85 nm/RIU and 794 nm/RIU, and temperature sensitivities of 8.72 pm/°C and -57.9 pm/°C, were obtained for the FBG and MZI respectively. We demonstrate that a transfer matrix approach can be used to simultaneously measure both parameters, solving the problem of temperature sensitivity of RI sensors due to the high thermo-optic coefficient of aqueous samples.
We present a comparison of four different grating-based optical fiber high temperature sensors. Three of the sensors are commercially available and include a heat treated, twisted (chiral) pure-silica microstructured optical fiber, a femtosecond laser written Bragg grating in a depressed cladding single mode fiber and a regenerated fiber Bragg grating. We compare these to an in-house fabricated femtosecond laser ablation grating in a pure-silica microstructured optical fiber. We have tested the sensors in increments of 100°C up to 1100°C for durations of at least 24 hours each. All four sensors were shown to be operational up to 900°C, however the two sensors based on pure-silica microstructured fiber displayed higher stability in the reflected sensor wavelength compared to the other sensors at temperatures of 700°C and higher. We further investigated high temperature stability of silica suspended-core fibers with femtosecond laser inscribed ablation gratings, which show improved stability up to 1050°C following thermal annealing. This investigation can be used as a guide for selecting fiber types, packaging, and grating types for high temperature sensing applications.
In this paper, we present a miniature fiber-optic Fabry-Pérot interferometric pressure sensor based on an in-situ printed fiber-top air cavity. With an in-house optical 3D μ-printing setup, a suspended SU-8 diaphragm with light scatter is directly printed on the end face of standard single-mode optical fibers to form a sealed air Fabry-Pérot cavity. The fabricated Fabry-Pérot micro-interferometer shows a linear response to the change of pressure with a sensitivity of 2.93 nm/MPa in the range of 0 ∼ 700 kPa. The response of the sensor to the change of temperature in the range from 30 °C to 65 °C is measured to be ∼38 pm/°C. Such an ultra-small fiber-optic pressure sensor has remote monitoring capability and is promising for for a great number of measurement and testing applications ranging from miniature manometers to bioprobes.
We report a novel type-II photonic crystal fiber Bragg grating for high temperature applications. The Bragg grating is inscribed in a low-loss in-fiber structure named suspended-core photonic microcell, which is post-processed from commercial pure-silica photonic crystal fiber. Grating samples with core diameters of about 4 $\mu$ m were made by using a focused near-infrared femtosecond laser and a phase mask, and then tested in a tube furnace from room temperature to about 1200°C. The thermal response of the Bragg resonant wavelength was measure to be about 12 pm/°C and 16 pm/°C, respectively, at the temperature of 100°C and 1000°C. The grating spectrum remained stable in a 10-hour isothermal annealing at 1000°C and started decaying at about 1120°C with the rate of about 0.02 dB/min. This type of grating possesses flexibilities in both waveguide and grating structure design, exhibits good high temperature performance, hence would be promising platform for building wavelength-division-multiplexed fiber sensors and tunable devices with wide working temperature range. IEEE
We present a research to determine the long-term stability of intrinsic Fabry-Perot (F-P) optical fibre sensors in high temperature environments. In-fibre sensors were created in 125μm diameter single mode fibre (Corning SMF28 Ultra) and a 125μm diameter PCF ESM-12B pure SiO $_2$ fibre spliced to a SMF28 fibre with a low reflectivity Cr layer at the interface. The outcome is a low finesse optical cavity either formed by a short length of Ge doped SMF fibre, or a short length of pure and undoped SiO $_2$ core PCF fibre. We demonstrate the manufacturing technique required for these intrinsic FP sensors as well as the stability of their optical characteristics at temperatures up to the range of 850°C to 1050°C . We report on the effect of annealing on stability after exposing sensors to temperatures of 1000°C above nominal working temperatures. In the temperature range above 900°C we observe increasing levels of non-reproducible drift characteristics. Stability is demonstrated up to 1000°C . After extended exposure of sensors to high temperatures we observe deviations from the initial smooth second order response of phase versus temperature which has been attributed to a change in core diameter in the fibre leading to the sensor at the distal end due to Ge diffusion at the high temperatures. The down lead is exposed to over a length of 17 cm. The dopant diffusion of an SMF28 ultra fibre has been studied using Energy Dispersive X-rays analysis (SEM/EDX), to measure the radial distribution of Ge concentration before and after being heated for a period of 100 days.
The small dimensions of optical fiber sensors are of particular interest to biological applications, given the ability to penetrate relatively inaccessible regions. However, conventional optical fibers are larger than biological material such as cells, and thus there is a need to further miniaturize fiber sensors. Here we present the fabrication of ultra-small Fabry-Perot cavities written into optical micro-fibers using focused ion beam milling. We have fabricated cavities as small as 2.8 μm and demonstrated their use for sensing of both bulk refractive index and thin-layer coatings. In order to achieve sensitive measurements we interrogate at visible wavelengths with a broadband detection system, thereby reducing the free spectral range of the interferometer relative to the measurement bandwidth, increasing the number of interference fringes, and allowing for the implementation of the Fourier shift method.
In this paper, a review of microstructured optical fiber (MOF) sensors is given. Various kinds of MOFs are described and their sensing applications are summarized. Two main types of MOF sensors in terms of grating-based and interferometry-based are reviewed. In particular, several types of microstructured optical fibers designed for sensing applications in our works are demonstrated, including the measurement of physical parameters, e.g. pressure, strain, torsion, temperature, and the detection of biomedical parameters such as refractive index and microfluidic flow rate. The basic design principles of MOF sensors based on fiber Bragg grating and interferometers are given. Comparisons of the performances of the fibers and sensors are also conducted according to the relevant topics.
Abstract This work presents a novel biosensor using the multimode interference effect in an exposed core microstructured optical fiber (ECF). In this work biotin molecules are immobilized onto the ECF core surface to serve as the capturing probe for streptavidin, the target molecules. Since each distinct guided mode in the ECF interacts with the surrounding medium differently, the interference between any two specific modes will experience a fringe shift (or phase change) upon a change in the refractive index (RI) of the surrounding medium, or a localized RI change on the surface of the ECF core as a result of a biological binding event. In our experiment, the interferometric sensing platform was realized by splicing a section of ECF with lead-in and lead-out single mode fibers (SMFs). An interference pattern is obtained in the transmission spectrum as the result of multiple excited modes (excited and re-collected at the lead-in and lead-out splicing points) propagating in the ECF with different propagation constants. The interference pattern is non-uniform, indicating that there are more than two modes involved. Fast Fourier transform (FFT) is used to separate individual interference patterns that contribute to this complex spectrum and monitor their phase changes upon RI variation of the surrounding medium. In this way multiple RI sensitivities can be realized because each spatial frequency possesses a distinct sensitivity with respect to the surrounding RI. The operation of this device was validated by measuring the phase changes that occur when the sensing platform was subjected to solutions of different RIs or functionalized with different molecules. A biosensor was demonstrated based on this novel platform using biotin as the capturing probe to specifically detect streptavidin with low non-specific adsorption. The proposed platform is reliable, cost-effective, and offers a potential label-free biosensing alternative to the widely used surface plasmon resonance (SPR) technique.
A self-enclosed fiber-optic Fabry–Perot (F–P) cavity is created by splicing a single-mode fiber to a photonic crystal fiber (PCF) with a precise hole micromachined by a 157-nm laser at the end face of the PCF. Furthermore, such a F–P cavity is etched chemically and its high-temperature and pressure responses are investigated experimentally. The pressure sensitivity is $sim 54.7$ pm/MPa and the temperature sensitivity is $sim 0.45$ pm/°C. The proposed sensor could offer some excellent features such as good high-temperature stability, low cross-sensitivity between pressure and temperature, ease of mass-production, making it attractive for pressure measurement under high-temperature.
A fiber Fabry-Perot (F-P) interferometer and a fiber Bragg grating (FBG) based pressure and temperature multiplexing sensor system is presented. This system is designed for high-temperature oil well down-hole permanent monitoring of pressure and temperature. Connecting a FBG temperature sensor and a F-P pressure sensor in series in the sensor head, the sensor system combines the advantages of simple structure of FBG for temperature sensing and high accuracy and low-temperature cross-sensitivity of F-P pressure sensor. Experimental results showed that the temperature measurement accuracy of 0.5degC and the long-term drift of the air gap of the F-P pressure sensor at 300degC is less than 0.1% within 300 h time span. This indicates that a long-term pressure measured accuracy of 0.03 MPa has been achieved in pressure gauge range of 0-30 MPa and in temperature variation range between 18degC to 300degC.
A matrix of synthetic fused silica samples with OH contents from 30 to 1300ppm and of a fictive temperature from 1000 to 1300°C has been characterized regarding their thermal expansion with high precision. The thermal expansion increases with fictive temperature and drops with OH content. Although fictive temperature and OH are coupled due to the influence of OH on the relaxation of the network, an independent influence of the OH content on thermal expansion has been observed. This may provide a deeper insight into the impact of impurities incorporated into the fused silica network.
A thermally insensitive pressure measurement up to 300 degree C was demonstrated utiliz ing fiber Bragg gratings written onto a side -hole single mode fiber. The resulting temperature sensitivity is about 300 times lower than normal FBGs.
The current status of optical fiber sensors is reviewed. The optical fiber sensors have certain advantages that include immunity to electromagnetic interference, lightweight, small size, high sensitivity, large bandwidth, and ease in implementing multiplexed or distributed sensors. Strain, temperature and pressure are the most widely studied measurands and the fiber grating sensor represents the most widely studied technology for optical fiber sensors. Fiber-optic gyroscopes and fiber-optic current sensors are good examples of rather mature and commercialized optical fiber sensor technologies. In this paper, among the various fiber-optic sensor technologies, especially, technologies such as fiber grating sensors, fiber-optic gyroscopes, and fiber-optic current sensors are discussed with emphasis on the principles and current status. Today, some success has been found in the commercialization of optical fiber sensors. However, in various fields they still suffer from competition with other mature sensor technologies. However, new ideas are being continuously developed and tested not only for the traditional measurands but also for new applications. 2003 Elsevier Science (USA). All rights reserved.
Crystallization rates were measured in vacuum, dry nitrogen, and water-saturated nitrogen atmospheres from 1300° to 1540°C. In all cases the observed rates were linear. Three reactions appeared to contribute to crystallization: the intrinsic crystallization, the impurity effect of H2O vapor, and furnace contamination. Enhancement of crystallization by both water vapor and furnace contamination is attributed to the breaking of silicon—oxygen bonds of the glass structure. Competitive adsorption mechanisms were proposed to characterize the adsorption of water and impurity species. The activation energy for apparent intrinsic crystallization was 134 kcal/mole; the activation energy for crystallization in H2O vapor was 77 kcal/mole.
The feasibility of a biosensor for DNA detection based on suspended-core photonic crystal fibers is investigated. The possibility of functionalization of the hole surface, which allows DNA strand binding, is demonstrated, along with the selective detection of DNA through hybridization of immobilized peptide nucleic acid probes with their full-complementary and mismatched DNA segments.
The photoelastic constants and their dispersion for visible light were determined for two samples of vitreous silica, Corning and Herasil No. 1. The results for the mercury green line, 546 mμ, are quoted here. The photoelastic constants were 4.22×10<sup>-13</sup> (d/cm<sup>2</sup>)<sup>-1</sup> (ordinary ray) and 3.56×10<sup>-13</sup> (d/cm<sup>2</sup>)<sup>-1</sup> (extraordinary ray). From the ratio of Poisson's ratio to Young's modulus 0.216×10<sup>-12</sup> (d/cm<sup>2</sup>)<sup>-1</sup> and Young's modulus 0.76×10<sup>12</sup> (d/cm<sup>2</sup>), which were also determined, there were calculated the pressure coefficient of refractive index 0.909×10<sup>-12</sup> (d/cm<sup>2</sup>)<sup>-1</sup> and the elasticity volume coefficient of refractive index V dN/dV=0.34. Comparison of these results with those reported for other glasses indicates that the oxygen ions of vitreous silica are more deformable then the oxygen ions of other siliceous glasses. In vitreous silica about ⅓ of the volume change accompanying an elastic dilatation arises from the dilatation of the oxygen ions. A comparison is also made with the results reported for corresponding thermally induced effects. It indicates that (a) during a thermal dilatation of a siliceous glass, the oxygen ion undergoes a dilatation which in the case of most siliceous glasses causes an equivalent dilatation of the body, but which in the case of vitreous occurs internally instead, and (b) in crystal quartz no appreciable dilatation of the oxygen ion occurs during a thermal dilatation. The thermal dilatation of the oxygen ion in the glasses would thus seem related to its strained bond configuration.
A temperature-insensitive fiber bending sensor is demonstrated by using a special optical fiber with cladding-mode resonance. The special fiber with a pure silica core and a fluorine-doped silica inner cladding shows strong cladding-mode resonance. The single-mode fiber (SMF)-special fiber-SMF is proposed as a sensor head to monitor the cladding-mode resonance. The response of the resonant spectrum exhibits high sensitivity to bending curvature and inherent insensitivity to temperature. The proposed special fiber bending sensor is simple and inexpensive.
We report on temperature sensors based on regenerated fiber Bragg gratings (RFBGs) for measurements up to 1100. The annealing process required to regenerate such gratings makes the optical fiber too delicate, thus making an adequate packaging necessary. Prior to the grating regeneration the optical fiber is protected with a ceramic tube which in turn is shielded with a thick metal casing. We have performed a thorough characterization of the thermo-optical response of both packaged and unpackaged RFBG sensors placing especial attention on possible residual hysteresis after several temperature cycling tests. The response and recovery times of packaged sensors were found to be, respectively, ~9 s and ~ 22 s.
We present thermally regenerated fiber Bragg gratings in air-hole microstructured fibers for high-temperature, hydrostatic pressure measurements. High-temperature stable gratings were regenerated during an 800 °C annealing process from hydrogen-loaded Type I seed gratings. The wavelength shifts and separation of grating peaks were studied as functions of external hydrostatic pressure from 15 to 2400 psi, and temperature from 24 °C to 800 °C. This Letter demonstrates a multiplexible pressure and temperature sensor technology for high-temperature environments using a single optical fiber feedthrough.