Geometrical analysis of an optical fiber bundle displacement sensor

The performance of a multifiber optical lever was geometrically analyzed by extending the Cook and Hamm model [Appl. Opt. 34, 5854-5860 (1995)] for a basic seven-fiber optical lever. The generalized relationships between sensitivity and the displacement detection limit to the fiber core radius, illumination irradiance, and coupling angle were obtained by analyses of three various types of light source, i.e., a parallel beam light source, an infinite plane light source, and a point light source. The analysis of the point light source was confirmed by a measurement that used the light source of a light-emitting diode. The sensitivity of the fiber-optic lever is inversely proportional to the fiber core radius, whereas the receiving light power is proportional to the number of illuminating and receiving fibers. Thus, the bundling of the finer fiber with the larger number of illuminating and receiving fibers is more effective for improving sensitivity and the displacement detection limit.     

Optical position sensor using fluorescent fiber and longluminescent source

A novel method is proposed to implement a sensor for the measurement of an object size or position. It uses an adjustable-length fluorescent optical fiber and a large luminescent source. A physical model is developed, showing how to combine different measurements in order to reject the influence of possible drifts such as source intensity variations. Experimental results are presented, and good agreement with the theoretical model is obtained. Theoretical and experimental values of the resolution are given. A computer simulation to analyze the influence of the system parameters is reported     

Optical sensor array and integrated light source

We report a new, solid-state, integrated optical array sensor platform. The optical sensor array and integrated light source (OSAILS) is demonstrated for quenchometric O2 detection. The OSAILS requires low voltages (3-5 V dc), it is stable (< or = 5% RSD over the course of several hours of continuous operation), it is reproducible and reversible (< or =3% RSD), it exhibits a rapid response time (<30 s), and it provides good detection limits (0.2% O2). The OSAILS opens the door to a number of new optical sensor array strategies.     

Optical zooming interferometer for subnanometer positioning using an optical frequency comb

A high-precision positioning stage based on an optical zooming interferometer is proposed. Two external-cavity diode lasers, stabilized to a femtosecond optical frequency comb, are used as optical sources. The zooming principle is demonstrated, and the positioning resolution of 0.2 nm is achieved. The positioning accuracy was partly evaluated.     

Confocal microscopy using variable-focal-length microlenses and an optical fiber bundle

The use of variable-focal-length (VFL) microlenses can provide a way to axially scan the foci across a sample by electronic control. We demonstrate an approach to coupling VFL microlenses individually to a fiber bundle as a way to create a high-throughput aperture array with a controllable aperture pattern. It would potentially be applied in real-time confocal imaging in vivo for biological specimens. The VFL microlenses that we used consist of a liquid-crystal film sandwiched between a pair of conductive substrates for which one has a hole-patterned electrode. One obtains the variation of the focal length by changing the applied voltage. The fiber bundle has been characterized by coupling with both coherent and incoherent light sources. We further demonstrate the use of a VFL microlens array in combination with the fiber bundle to build up a confocal system. The axial response of the confocal system has been measured without mechanical movement of the sample or the objective, and the FWHM is estimated to be approximately 16 microm, with asymmetric sidelobes.     

Analytical and experimental studies on asymmetric bundle fiber displacement sensors

A fiber-optic displacement sensor (FODS) is theoretically and experimentally studied using an asymmetrical bundled fiber. The bundled fiber consists of two parallel fibers with different core radial ratios (CRRs) to achieve different sensitivity and dynamic range for displacement measurements. Both analytical modeling and experimental observations show that the linear range and sensitivity can be adjusted by controlling the CRR between transmitting and receiving fibers. This increases the flexibility of the sensor, which can be used for precise non-contact sensing applications.     

Optical fiber relative-humidity sensor with polyvinyl alcohol film

We describe a fiber-optic relative-humidity (RH) sensor comprising a moisture-sensitive overlay on a single-mode side-polished fiber. The hygroscopic polymeric material deposited was polyvinyl alcohol (PVA), which proved to have good adherence and stability. The film reached a fast equilibrium with atmospheric moisture (in less than 1 min), inducing changes in the output optical power of approximately 10 dB for the 70%-90% RH range. To yield a low-cost device, single-mode standard communication fibers were used; therefore all the components of the sensor can be commercial, mass-produced telecommunication devices. The experimental results obtained are consistent with the expected behavior of the system; the output power decreases because of losses in the polished region of the fiber as the refractive index of its external medium approaches the fiber core value. Because the external medium is PVA film, its refractive index changes in response to its water content.     

Remote fluorescence imaging of dynamic concentration profiles with micrometer resolution using a coherent optical fiber bundle

Dynamic concentration profiles within the diffusion layer of an electrode were imaged in situ using fluorescence detection through a multichannel imaging fiber. In this work, a coherent optical fiber bundle is positioned orthogonal to the surface of an electrode and is used to report spatial and temporal micrometric changes in the fluorescence intensity of an initial fluorescent species. The fluorescence signal is directly related to the local concentration of a redox fluorescent reagent, which is electrochemically modulated by the electrode. Fluorescence images are collected through the optical fiber bundle during the oxidation of tris(2,2'-bipyridine)ruthenium(II) to ruthenium(III) at a diffusion-limited rate and allow the concentration profiles of Ru(II) reagent to be monitored in situ as a function of time. Tris(2,2'-bipyridine)ruthenium(II) is excited at 485 nm and emits fluorescence at 605 nm, whereas the Ru(III) oxidation state is not fluorescent. Our experiments emphasize the influence of two parameters on the micrometer spatial resolution: the numerical aperture of optical fibers within the bundle and the Ru(II) bulk concentration. The extent of the volume probed by each individual fiber of the bundle is discussed qualitatively in terms of a primary inner-filter effect and refractive index gradient. Experimentally measured fluorescence intensity profiles were found to be in very good agreement with concentration profiles predicted upon considering planar diffusion and thus validate the concept of this new application of imaging fibers. The originality of this remote approach is to provide a global view of the entire diffusion layer at a given time through one single image and to allow the time expansion of the diffusion layer to be followed quantitatively in real time.     

Simulation, implementation, and analysis of an optical fiber bundle distance sensor with single mode illumination

A simulation model for an optical fiber bundle distance sensor with a single mode fiber as the illumination fiber and a multimode fiber as the receiving fiber is presented. Approximating the illumination light exiting the single mode fiber as having a Gaussian intensity profile, a closed-form solution of the reflected light coupled into the receiving fiber was derived. A distance sensor was implemented and the measured sensor outputs were compared with the simulation data to verify the theoretical model. The performance of the distance sensor with different design parameters was analyzed. Design guidelines for achieving desired sensor performances are suggested.     

Design and operation of a thermal sensor with micrometer-spatial resolution

We have developed a simple superconducting thin film device that can be used as either a thermometer or a thermal conductivity sensor. Over a narrow range the device has somewhat better temperature resolution than a conventional germanium thermometer, but its main advantage is that it has very high spatial resolution. The fabrication and operation of the device are described, together with preliminary results of experiments in which it is used to study liquid⁴He very nearT . Potential improvements are also discussed.     

Temperature sensor using an optical fiber coupler with a thin film

A temperature sensor was demonstrated and fabricated by coating thermosensitive film around a fiber coupler. Based on the multicladding equivalent method, the coated fiber coupler was simplified to a conventional one. With the high thermo-optical coefficient of organic-inorganic solgel material, a good sensing result was achieved. The range of temperature measured is from -50 to 100 degrees C. The resonant wavelength has a shift of about 25 nm. A sensitivity of 0.17 nm/degrees C is achieved. With the advantages of having a simple structure and being unaffected by the instability of the light source, the proposed fiber coupler temperature sensor will find wide applications.     

Surface plasmon resonance sensor using an optical fiber with an inverted graded-index profile

A new optical fiber sensor based on surface plasmon resonance is described. It uses an optical fiber with an inverted graded-index profile. A theoretical analysis of the optical propagation when a point light source was used and a computation of the optical power transmitted by the fiber were performed. Experiments were carried out to measure changes of the transmitted power caused by refractive-index variations of the surrounding dielectric medium. Both the simulation and experiments have shown that the sensor exhibits high sensitivity for changes of the surrounding medium in a refractive index range from 1.33 to 1.39.     

Optical fiber sensor for electric field and electric charge using low-coherence, Fabry-Perot interferometry

An optical fiber sensor for electric field and electric charge, based on the deflection of a small cantilever, has been developed. When the sensor head is placed in an electric field, induced charging produces deflection of the cantilever, which is measured using low-coherence, Fabry-Perot interferometry. The sensor has been used to measure the electric field in the vicinity of a Van de Graaff generator, in the range 135-650 V/cm. The measured deflections are in good agreement with the predictions of a simple model equating the electrostatic and mechanical forces acting on the cantilever.     

Optical fiber magnetic field sensor based on multi-mode fiber and core-offset structure

A magnetic field sensor based on a magnetic fluid (MF)-coated intermodal interferometer is proposed and experimentally demonstrated. It is fabricated by a core-offset structure between two segments of multi-mode fibres (MMF), a spherical structure is formed in the end of the second segment MMF. The core-offset section can be used to excite the core mode to the cladding, then the core and cladding modes will interference at the spherical structure due to the optical path difference caused by the refractive index difference. Two interference valleys of the interferometer integrated with MF under different magnetic field intensities have been experimentally analysed. The experimental results exhibit that the sensor possesses a magnetic field sensitivity of ?0.187 nm/mT by monitoring the wavelength shift at the magnetic field intensity from 0 to 20mT, and the optical power attenuation at specific wavelength with a magnetic field has a maximum sensitivity of 0.228 dB/mT.     

Optical temperature sensor and thermal expansion measurement using a femtosecond micromachined grating in 6H-SiC

An optical temperature sensor was created using a femtosecond micromachined diffraction grating inside transparent bulk 6H-SiC, and to the best of our knowledge, this is a novel technique of measuring temperature. Other methods of measuring temperature using fiber Bragg gratings have been devised by other groups such as Zhang and Kahrizi [in MEMS, NANO, and Smart Systems (IEEE, 2005)]. This temperature sensor was, to the best of our knowledge, also used for a novel method of measuring the linear and nonlinear coefficients of the thermal expansion of transparent and nontransparent materials by means of the grating first-order diffracted beam. Furthermore the coefficient of thermal expansion of 6H-SiC was measured using this new technique. A He-Ne laser beam was used with the SiC grating to produce a first-order diffracted beam where the change in deflection height was measured as a function of temperature. The grating was micromachined with a 20 microm spacing and has dimensions of approximately 500 microm x 500 microm (l x w) and is roughly 0.5 microm deep into the 6H-SiC bulk. A minimum temperature of 26.7 degrees C and a maximum temperature of 399 degrees C were measured, which gives a DeltaT of 372.3 degrees C. The sensitivity of the technique is DeltaT=5 degrees C. A maximum deflection angle of 1.81 degrees was measured in the first-order diffracted beam. The trend of the deflection with increasing temperature is a nonlinear polynomial of the second-order. This optical SiC thermal sensor has many high-temperature electronic applications such as aircraft turbine and gas tank monitoring for commercial and military applications.     

Unbalance and harmonics detection in induction motors using an optical fiber sensor

In this work, a new method for the detection of the negative effects of a particular unbalanced voltage and inverter harmonics on the performance of an induction motor using fiber sensors is proposed. Supplying a three-phase induction motor with unbalanced voltages causes an oscillating electromagnetic torque that generates vibrations, increased losses, efficiency reduction, and an extra temperature rise that leads to a reduction on insulation life of the machine. A new in-line fiber etalon accelerometer has been designed to detect these vibrations in the range DC-500 Hz. The in-line fiber etalon scheme used provides high robustness and stability, giving enough sensitivity to monitor the low-frequency and low-amplitude oscillations in the stator of the machine that exist in a voltage unbalance situation. To prove this claim, a 1.5-kW squirrel cage induction motor is analyzed under different unbalance levels. It is shown that a precise unbalance factor can be detected without accessing to the electric part of the machine and an accurate monitoring can be obtained using the high-resolution analysis proposed.     

Stress optical fiber sensor using light coupling between two laterally fused multimode optical fibers

A stress optical fiber sensor was manufactured and tested. It uses light coupling between two parallel and laterally fused, all-silica multimode optical fibers along a cladding length of a few centimeters. This sensor is dedicated to the measurement of high values of stress. A theoretical model was developed using the mode coupling and the perturbation theory to calculate the global coupling coefficient of light. A serial optical fiber sensor network interrogated by the time-division multiplexing method was realized and tested. The major applications of this sensor are control and monitoring of civil engineering structures and concretes.     

应变、温度、位移测量光纤光栅传感器的研究

本文介绍了集成式Bragg光纤光栅(FBGI)传感器的结构及其应用该传感器测量应变、温度、位移的基本原理.利用FBGI和相干性干涉信号解调方法实现了用一个传感器同时测量三个参量.实验结果表明温度精度达±1℃,应变精度为±30u ε,位移分辨率达1nm,测量重复性好.     

Development of light composite materials with low coefficients of thermal expansion

Abstract

Composite materials based on aluminium are used in different fields where weight, thermal expansion, and thermal stability are key requirements. The aim of the present study was to develop a universal method and scientific approach for evaluating the design of lightweight, Al matrix composites with low coefficients of thermal expansion (CTE) and high dimensional stability, and to produce such composites using the vacuum plasma spray (VPS)process. The methodology is general and could be applied to other composite systems. The VPS-produced Al and Al alloy 6061 based composites were reinforced with a variety of ceramic particles including Si₃N₄, B₄C, TiB₂, and 3Al₂O₃.2SiO₂. These composites have low CTE values ((12–13)×10^-6 K^-1), similar to that of steel, and high dimensional stability (capable of keeping dimensions stable with changes in temperature). They have low porosity (98–99%dense) and a uniform distribution of the strengthening particles. Hot rolling of the VPS-formed composites, followed by heat treatment, resulted in a significant improvement in the mechanical properties. Deformed and heat treated 6061 based composites, containing 20 wt-%TiB₂ and 40 wt-%3Al₂O₃?2SiO₂, showed excellent mechanical properties (ultimate tensile strength 210–250 MPa, elongation >4%).