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We analyzed the electromagnetic performance of a novel optical switch in a form of microelectromechanical (MEMS) device with a thin metallic microplate reflector supported by four flat metallic springs on its sides. The reflector tilts under the electrostatic actuation in two planes and part of its initially flat surface acquires some curvature. In this way the reflector steers the optical input beam to one of up to eight positions corresponding to the output ports and focuses the optical beam on this port. We evaluated analytically the reflector displacement against the actuator driving voltage under realistic parameters of the optical switch. Then we obtained the reflector tilt and curvature under nominal actuator driving voltage by means of numerical modeling of the switch with the commercial design and simulation software CoventorWare®. In addition, we looked at a possibility of reducing the switch driving voltage at the expense of spring stiffness. Our results confirm the possibility of optical switching with this novel device.

Fiber optic light guides can be used as indicators (witness devices) of the emergence of cracks in masonry composed of construction-grade ceramic bricks. In this study, we experimentally investigated the relationship between the type and size of the fiber optic light guide and the size of the crack opening that caused fiber breakage by physically modeling a crack opening on a special stand. Two sizes of multimode fiber optic light guides with quartz core and cladding and poly(methyl methacrylate) (acrylic) coating were studied in detail. The results are useful for the practical implementation of the proposed method in automatic optoelectronic crack detection systems for brick buildings and structures.

We describe an experiment to access the onset of cracks in brick structural elements by means of arrays of the optical fibers attached to the surface of the elements. The opening of a crack leads to the fracture of the optical fiber that crosses the crack, thus witnessing its appearance. The detection of cracks of a width of about 1 mm was successfully conducted with the communications-grade multimode silica optical fibers. The optical transmission of all optical fibers of the array was continuously monitored by means of the multichannel optical transmitter and receiver. Our results demonstrate that the optical fibers served as reliable indicators of structural damage in form of cracks to brick masonry. We consider some practical aspects of implementing this method for monitoring the appearance of cracks in brick masonry buildings, which present structural risks.

We describe a sensor system for damage detection in concrete structures after extreme events such as earthquakes. The system employs large array of optical fibres (up to 256 fibres) that are either embedded in, or bonded to the surface of the structural element or elements under test. A structural damage (cracks or complete failure) results in breaking of one or several optical fibres and sharp decrease in their optical transmission. The fibres are interrogated using a matrix-type optical fibre circuit with 16 optical transmitters and 16 optical receivers that operate in the TDM mode. This type of system can be used for monitoring of large arrays of other intensity-type optical sensors.

We present a layout and operational characteristics of an optical switch that performs a cyclic switching of an input port to multiple output ports by means of a metal-clad optical fibre cantilever in oscillatory motion at its natural resonance frequency. The oscillatory motion of the fibre is produced by the force of the alternating electric or magnetic field. The switch is intended for use in large arrays of fibre-optical sensors with binary-type amplitude modulation of optical signals, such as employed in liquid-level measurement and structural damage detection.

We present theoretical and experimental results for a fiber optic refractometric sensor employing a semi-ellipsoidal sensing element made of polymethyl methacrylate. The double internal reflection of light inside the element provides sensitivity to the refractive index of the external analyte. We demonstrate that the developed sensor, operating at a wavelength of 632 nm, is capable of measurement within a wide range of refractive indices from n=1.00 to n=1.47 with sensitivity over 500 dB/RIU. A comparison of the developed sensor with two more complex refractometric sensors, one based on tapered optical fiber and the other based on suspended-core microstructure optical fiber, is presented.

We present an analytical nonlinear adiabatic theory of the microwave electron device that we call the Autophase Microwave Tube (AMT). In contrast to the well-known Traveling Wave Tube (TWT), the AMT exploits a highly efficient non-synchronous beam-wave interaction for the amplification (or generation) of the HF electromagnetic waves, and, differently from klystron and such hybrid devices as twystron, it employs a continuous beam-wave interaction. Because of these distinctive features, the AMT presents a special class of microwave electron devices, which feature very high electronic efficiency (which tends to 100%) and large bandwidth. Here, we develop the theory that allows one to find the profiles of static longitudinal electric or magnetic field (or both) over the device length, which yield negligible de-bunching together with highly efficient amplification (generation) of the HF electromagnetic wave. The analysis of electron motion in the bunch is performed by means of Lyapunov stability theory. The numerical example illustrates the possibility of achieving the electronic efficiency of AMT as high as 92%. We compare different autophase regimes in the AMT and show that the profiling of the longitudinal static magnetic focusing field in the helix AMT with the non-azimuthally symmetric wave has many advantages with respect to other regimes.

The cause for the decrease in light transmission in optical fibers embedded in reinforced concrete beams with flexural deformation was investigated. It was determined that optical fibers in such beams have multiple bends as a result of chaotic movement of gravel particles during the shrinkage of the concrete mixture. The results of field and model experiments are presented, which indicate that the probable reasons for the decrease in light transmission in optical fibers embedded in reinforced concrete beams, observed when the latter are bent, are local changes in the parameters of the optical fibers in regions with sharp bends accompanying beam deformation.

We present results of an ongoing study of structural health monitoring of concrete elements by means of arrays of telecommunications-grade optical fibers embedded in such elements. In this work, we show a possibility of using this technique for monitoring the transverse displacement of the reinforced concrete beams under flexural loading. We embedded a number of multimode silica-core/polymer-clad/polymer-coated optical fibers in a mold with preinstalled reinforcing steel bars and fresh concrete mix. Then the concrete was compacted and cured. Some optical fibers were broken during the fabrication process. The fiber survival rate varied with concrete grade, compacting technique and optical fiber type. The fibers that survived the fabrication process were employed for the monitoring. They were connected to the optical transmitter and receiver that formed a part of a larger measurement system. The system continuously measured the optical transmission of all optical fibers while the reinforced concrete beams were subjected to incremental transverse loading. We observed a quasi-linear decrease in optical transmission in all optical fibers of the array vs. the applied load and respective flexural displacement. Although the underlying phenomena that lead to such a variation in optical transmission are not clear yet, the observed behavior might be of interest for assessing the transverse displacement of the reinforced concrete beams under flexural loading.

This paper presents a prototype optical-fibre refractometric liquid-level sensor which can access the static and dynamic levels of liquid nitrogen in large cryogenic systems. This version of the sensor is intended for use in various tests of cryogenic systems such as used in rocketry, during the design stage. The sensor employs a vertical linear array of 140 highly sensitive optical-fibre refractometric transducers. The liquid-level measurement range is 1.6 m with a resolution of up to 5 mm. The optical transducers are multiplexed using a matrix-type optical-fibre network which employs a robust level tracking algorithm. This type of sensor can be used for measuring the level of other cryogenic liquids such as liquid hydrogen.

We investigated the attainable stability of the monofilar-helix traveling wave tube (TWT) with respect to the parasitic backward-wave oscillation under periodic magnetic focusing. We accounted for the effect of the electron beam rotation in the nonhomogeneous focusing magnetic field, magnetic field amplitude and periodicity, and the specific coupling of the electron beam with the synchronous harmonics of the electromagnetic wave existing on the slow-wave circuit. This specific coupling takes place in the monofilar-helix TWT only and decreases its stability with respect to the parasitic backward-wave oscillation in comparison to other types of helix TWT. For the purpose of this analysis, we developed further the linear two-dimensional (2-D) multiwave theory of the helix TWT described in our previous work . In this theory, we account for space charge fields by means of waveguide excitation model based on the direct solution of Maxwell equations. Differently from , the present version of our theory allows for accounting of the coupling of the synchronous 0th spatial harmonic (forward employed for the amplification) and -1st (parasitic backward) harmonic of the circuit wave with the electron beam in the monofilar-helix TWT. By numerical modeling, we obtained quantitative data on the starting conditions for the parasitic backward-wave oscillation in the typical monofilar-helix TWT in the intersection point of the dispersion curves of these two harmonics. The described coupling mechanism does not exist in the bifilar-helix TWT. Therefore, the TWT with the bifilar helix is more stable with respect to the parasitic backward-wave oscillation than the TWT having the monofilar helix. These theoretical results correlate with the existing experimental evidence. The results of the present study, in particular, explain why the backward-wave oscillation suppression by tailoring of the focusing magnetic field has a significant effect in the bifilar-helix TWT but does not work in the monofilar-helix TWT.

An optical-fibre sensor system is presented for monitoring void fraction distribution in a spacecraft's gas and propellant centrifuge separator. The system could be used at the separator development stage or for monitoring, during ground tests, the elements of the spacecraft propulsion system. Our sensor system employs an array of point optical-fibre refractometric transducers installed in the form of several linear radial arrays on the separator rotating blades. We employed a small-size hemispherical optical detection element as the transducer and we optimized its parameters through numerical ray-tracing. The aim is to minimize the effect of the thin film of liquid that forms on the transducer's surface in this application. The features of this sensor system are: (1) an efficient matrix-type multiplexing scheme, (2) the installation of the main optoelectronic unit of the sensor in a hermetically sealed container inside the separator tank located on the rotating shaft and (3) the spark-proof and explosion-proof design of the sensor circuits and elements. The sensor is simple, reliable, low-cost and is capable of withstanding the factors involved during operation of the propulsion system such as cryogenic temperatures and chemically aggressive liquids. The novel elements and design concepts implemented in this sensor system can also find applications in other sensors for spacecraft propulsion systems and also in a variety of optical-fibre sensors used in scientific research and industry.

We analyzed the resonant coupling in the low-refractive-index sensor based on a directional coupler implemented in a microstructured optical fiber with a composite core and the parallel analyte channel in the form of a hollow-core waveguide. We showed the possibility of an 8-fold increase in the analyte channel radius that is equivalent to a 64-fold increase in its cross section, in comparison to the existing design. With an increase in the analyte channel radius, the resonance frequencies of the composite core mode and the satellite waveguide modes shift to longer wavelengths, while the dispersion curves of the high-order modes of the satellite waveguide tend to merge and their resonances become less pronounced than the resonances of the low-order modes. With an increase in the analyte channel radius from 2 to 16 μm, the sensor sensitivity increases by 40% and the detection limit becomes lower by a factor of 2. Such an increase in the analyte channel radius also eliminates the need in a high-pressure pump for filling the channel with analyte and thus makes this sensor much more practical than was previously thought.

We investigated experimentally the response of the fiber-optical refractometric sensor with semi-cylindrical plastic detection element under different polarization states of the input light. Our results demonstrate that the state of polarization of light in such sensor has a significant effect on the sensor response to external refractive index. This property can be exploited, in particular, for adjusting the form and linearity of the sensor response in situations when such adjustment cannot be achieved by modification of the sensor geometrical parameters and material constants.

This work focuses on the results and analyses performed on long-period optical-fiber gratings (LPFG) designed for use as refractometric sensors. The study was conducted with non-uniform LPFG specially designed for refractometric applications. First, LPFG transmission spectra were calculated for nominal period, propagation constant of the cladding mode and phase shift between the adjacent LPFG sections. Then, a random variation of the above parameters was introduced and the effect of this variation on the transmission spectrum of the LPFG, with the external refractive index as parameter, was evaluated. Finally, a change in the resonant wavelength against the external refractive index was investigated under random variation of parameters. We have found that in some long-period fiber grating refractometric sensors fabrication tolerances should as stringent as 0.2 % of nominal parameter. The methodology of tolerance analysis and quantitative data obtained in this work might be useful in establishing tolerances for fabrication parameters of long-period fiber grating refractometric sensors.

An optical-fiber sensor system for structural health monitoring of concrete elements such as beams and columns is presented. The system employs arrays of conventional optical fibers embedded in the concrete elements as crack sensors. Twelve types of optical fibers as well as several embedding techniques have been tested for this role. The survival rate of optical fibers embedded in concrete could be as high as 80%. The loss of fibers during the embedding process was acceptable provided that the number of fibers in the array had redundancy. The optical transmission of all fibers in the array was monitored in a time-division multiplexed mode at a high repetition rate, in the kHz range. The monitoring scheme allowed a quasi-continuous data acquisitions of large optical fiber arrays. A sharp decrease in the optical transmission of one or more optical fibers was a clear indicator of the development of cracking in the element subjected to flexural loads. The system was successful in detecting not only the initiation but also the propagation of cracks in concrete elements subjected to incremental flexural loading. In this work, the relation between the mechanical properties of the optical fibers and their behavior for the described application is discussed. Also, considerations towards a rational design of the system are proposed. The damage detection system may be used for the mapping and monitoring of cracks in concrete elements. The simplicity of the operation and relatively low cost of the proposed system make it a great candidate for applications in structural health monitoring of critical elements in civil infrastructure.

We studied the effectiveness of design projects in teaching Telecommunications Engineering to undergraduate students. The projects consisted in designing and prototyping of relatively complex electronic or optoelectronic devices. The distinctive feature of these projects was their real-world interdisciplinary nature. We discuss the requirements for educationally effective projects and describe the technical and educational results that we achieved. The recommendations that we derive are applicable to teaching electrical, electronic, and telecommunications engineering to undergraduate students.

We describe the design and implementation of a laboratory with virtual and real exercises for optical devices course. We have introduced such a laboratory in teaching telecommunications engineering at the National Autonomous University of Mexico. The laboratory complements the optional theoretical optical devices course of forty-eight (48) hours that we offer to the students of the next-to-last 8th semester of the aforementioned career. A combination of virtual and real exercises, and remote access to some real exercises allow us to provide effective laboratory training to a large number of students with limited quantity of real laboratory equipment.

We present an optical fiber liquid-level sensor which employs an array of plastic optical fibers coupled to a single semicylindrical refractometric detection element of plastic. The sensor measures the level of liquids in a discrete way and also is capable of discriminating between different liquids (such as gasoline and water) in a tank or reservoir.

We present a novel optical fiber refractometric sensor with semi-cylindrical optical detection element. A pair of the multimode optical fibers is attached symmetrically to the element’s flat plane. The optical coupling of the two fibers due to internal reflection of light from the element’s cylindrical surface is sensitive to the refractive index of the surrounding medium. We exploit several internal reflections in series and partial focusing of the optical beam by the element’s cylindrical surface to achieve enhanced sensitivity to the refractive index of the surrounding medium and reduced intrinsic optical loss in the transducer. We show theoretically that the transducer, in particular, can discriminate between the air and gasoline. We also present experimental data obtained with plastic detection element, which confirm our theoretical results. A vertical array of such transducers employing a relatively long single semi-cylindrical detection element can access the level of gasoline in automobile tanks.

This paper describes a fiber-optic level indicator designed to detect the liquid interface in the liquid-hydrogen storage tanks. The considerations which led to the choice of the particular fiber-optic sensor and the construction of the measurement system are discussed. A fiber-optic refractometric transducer with the detection element of ellipsoidal form was developed which features a step-like response to the external refractive index in the narrow interval of this quantity between unity (gas) and 1.0974 (liquid hydrogen). The fiber-optic inputs to the storage system secure the reduced heat ingress in the liquid-hydrogen in comparison to sensors with electrical wires. The fiber-optic transducer features small dimensions, is strong mechanically, and supports multiple cycles of cooling to 20 K and heating to the ambient temperature. The device successfully indicated the level of liquid interface in a liquid-hydrogen storage tank under the maximum excess pressure in the tank of 4 MPa. The paper discusses a number of prospective applications of the developed fiber-optic transducer in the liquid-hydrogen storage systems.

This paper presents an optical fibre sensor which can access the refractive index of the external liquid absorptive media. The sensor employs an evanescent-field intensity-type transparent dielectric detection element of hemispherical form. For this detection element, the effect of absorption of the external media on the measurement results was quantified. In order to reduce the measurement errors caused by finite absorption of the external media, we incorporated an absorption-sensitive optical cell in series with the detection element in the sensor. We describe the new measurement procedure that allows one to reduce the errors caused by the finite absorption of the external media.

We present a prototype optical-fiber liquid-level sensor for measuring the static and dynamic level of liquid nitrogen in large cryogenic hydraulic systems. This version of sensor is intended for use for various tests of the cryogenic hydraulic systems at their design stage. The sensor employs a total of 140 highly sensitive optical-fiber point detectors of liquid in a form of vertical linear array. The liquid level measurement range is of 1.6 m, a vertical resolution is up to 5 mm. The optical detectors of liquid are multiplexed by means of matrix-type optical fiber network, which operates under robust level-tracking algorithm. A sensor of this type can be used for measuring the level of other cryogenic fluids.

We present a mathematical linear 2D model of the interaction of the synchronous forward and backward harmonics of the electromagnetic wave, existing in the slow-wave circuit, with the electron beam in a monofilar-helix traveling-wave tube (TWT) under periodic permanent magnetic (PPM) focusing. We accounted for the effect of the electron beam alternating rotation in the PPM focusing field, magnetic field amplitude and periodicity, and the specific coupling of the electron beam with the circuit wave. This coupling takes place in the monofilar-helix TWT only and decreases its stability with respect to the parasitic backward-wave oscillation in comparison to other types of helix TWT.

Small-size lesions to cerebral cortex induced by the CO2 laser have found applications in neurophysiology for anatomical-functional mapping of the brain functions by areas. The advantage of this new technique in comparison to traditional ones (mechanical, electrical and chemical methods) consists in the possibility of making well-controlled lesions of small and repeatable size to cerebral cortex. In this work, we employed numerical and physical modelling to study the effect of the CO2 laser beam diameter and power density on the ablation rate, size and shape of the laser-induced lesions. Our study showed that the existing linear mathematical model of the laser-induced ablation is sufficiently correct only for the case of relatively shallow lesions. For large penetration depths, the mathematical model of laser-tissue interaction that accounts for the exponential decay of laser power density with penetration depth gave better agreement with the experiment than the existing linear model.

Distributed optical fiber sensor systems are prospective candidates for the environmental pollution monitoring over large industrial sites. Among particular optical probes that are attractive for this application are the refractometric ones. However, despite all previous work on this subject, the performance limit of these probes, especially in case of the micro-optical of fiber-optical design, is not yet established. To clarify this point, computer simulations dealing with the response of the novel paraboloidal-shaped micro-optical probe to small changes in the refractive index of the surrounding media are presented. The relative sensitivity concept, which is the ratio of the probe output in two different media, is introduced. The relative sensitivity is proposed as an objective basis for the comparison of refractometric probes.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this article we describe an optoelectronic sensor for assessing the level of light petrochemical products in technological tanks at the oil refmeries. This sensor employs the multi-element vertical array of discrete micro-opticalrefractometric transducers. The transducers are made of silica glass and have the conical shape. In the air, each transduceroperates as a tiny retro-reflector that optically couple together two multimode optical fibers. The optical coupling in the transducer is due to the internal reflection at the conical surface. The amount of the coupling depends on the refractive index ofthe surrounding media. In a fluid, the total internal reflection vanishes and the coupling becomes negligibly small. The number of immersed transducers is a measure of the fluid level in the reservoir. Because of the significance of the transducer transmission function, it is evaluated in detail under various combinations of the geometrical parameters of the micro-opticalstructure and connecting optical fibers. The numerical ray tracing shows that the form of the transmission function can bemodified by change of some geometrical parameters ofthe structure.This discrete level-sensor yields both a large measurement range and high resolution. Also, the optical measurementprinciple secures the spark-proof and explosion-proof operation. In addition, the probe is resistant to the chemical corrosion.Several innovations offer a competitive advantage to the users.The particular device described in this paper is designed to measure the top level of liquid propane-butane in the filledor almost filled technological tanks at the oil refineries. However, the solutions described here may find applications in avariety of fiber-optic liquid-level sensors employing large transducer arrays.Key words: Optical fiber sensors, refractometry, fluid detection, liquid level measurement

New laser-based technique for anatomical-functional study of the medial prefrontal cortex (MPFC) of the brain of experimental animals (rats) is presented. The technique is based on making accurate well-controlled lesions to small MPFC and subsequent observing behavioral alterations in the lesioned animals relative to control ones. Laser produces smaller and more accurate lesions in comparison to those obtained by traditional methods, such as: mechanical action, chemical means, and electrical currents. For producing the brain lesions, a 10 W CO2 CW laser is employed for reasons of its sufficiently high power, which is combined with relatively low cost-per-Watt ratio. In our experience, such power rating is sufficient for making MPFC lesions. The laser radiation is applied in a form of pulse series via hollow circular metallic waveguide made of stainless steel. The waveguide is of inner diameter 1.3 mm and 95 mm long. The anesthetized animals are placed in stereotaxic instrument. Via perforations made in the skull bone, the MPFC is exposed to the laser radiation. Several weeks later (after animal recuperation), standard behavioral tests are performed. They reveal behavioral changes, which point to a damage of some small regions of the MPFC. These results correlate with the histological data, which reveal the existence of small and accurate MPFC lesions. The present technique has good prospects for use in anatomical- functional studies of brain by areas. In addition, this technique appears to have considerable promise as a treatment method for some pathologies, e.g. the Parkinson's disease.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In many applications of Laser Doppler Velocimetry object velocity varies with time within soniemore or less wide range. Large variations present a problem for signal processing. This difficulty may bereduced in the proposed new Laser Doppler Velocimeter which utilise the periodic polyharmonic spatialprobe field. The probe field is formed by the holographic technique employing the periodic wavefrontmodulator and the field-forming hologram. By proper selection of the parameters of these components,the probe field with pronounced high-order spatial harmonic content is obtained. This results in thepresence of several Doppler frequency harmonics in the output signal, for the single value of objectvelocity. One of these harmonics is used for velocity determination. The choice of a particular harmonic depends on how well it fits into the frequency range of the instrument's electronics. If the object velocity becomes too small or too large, some other Doppler frequency harmonic which now fits betterinto the instrument frequency range is used for further processing and velocity determination.

This paper treats electro-physiological effects of the low- level laser irradiation of blood (LBI). The data presented here are based on the observation of almost 200 patients suffering from the acute disruption of coronary blood circulation, unstable angina pectoris and myocardial infarction. Statistically significant changes of the electro-physiological characteristics were observed in the group of 65 patients, treated by the LBI. In particular, the significant 6 percent extension of the effective refractory period was observed. The electrical situation threshold has increased by 20.6 percent. The significant changes of some other important electro-physiological characteristics were within the range of 5-15 percent. In this paper, the data obtained on the LBI effectiveness are compared also with the results obtained on 94 patients who in addition to the standard anti-angina therapy were treated by the autohaemo- transfusion performed simultaneously with the UV-light irradiation of the transfused blood. The results obtained demonstrate the significant positive effect of the low energy LBI. The electrophysiological data obtained have good correlation with observed anti-arrhythmic effect of the LBI. This is proved by the data obtained on the electro- physiological characteristics of the cardiovascular system and by other clinical data on the experimental and control group of patients. In the course of this research the exact effect of the low level LBI was established. LBI led to the pronounced positive changes in electro-physiological characteristics of the cardiovascular system of the patients, it also led to the pronounced anti-arrhythmic effect.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Ray-tracing has found important applications in the analysis of optical systems. In this work, a special modification of the ray-tracing method is applied to the analysis of several different micro-optical structures, used as probes for refractive index measurements, with the aim of obtaining the structure that is practical and acceptable from the technological point of view. The structure which is studied here is a small size solid retroreflector of special shape and complex inner constitution. It serves to couple together a pair of optical fibers. One of these fibers is connected to the light source, the other one to the photometer. The operation of this structure as the refractometric sensor is based on the frustrated total internal reflection in the retroreflector, which is formed by the structure's surface. Therefore, the structure's internal reflectivity depends on the refractive index of the surrounding media. This media may be either a gas or a fluid. By use of this structure, the refractive index of the surrounding media can be determined, and the type of the particular fluid may be disclosed. However, for better performance, the sensor's shape has to be optimized taking into consideration the particular parameters of the optical elements and materials used for the sensor, and the refractive index value of the particular fluid. Because of some singularities of the problem, the special ray-tracing algorithm has been developed for the analysis of this structure. This algorithm has proved to be effective for the theoretical optimization of the structure used as refractometric optical sensor.

Statistically significant results on positive effects of low-energy intercardiac blood irradiation, based on observation of 354 patients suffering from Q-MI, are presented. The He-Ne laser and a catheterized flexible fiber-optic lightguide were used to perform the blood irradiation. The data obtained make it possible to draw a conclusion that the positive clinical effect of the laser blood irradiation is realized via stress-limiting mechanisms.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fiber-optic sensors are attractive for biomedical applications primarily because of their non- electrical and non-conductive nature. This secures the safety of use and immunity to electromagnetic interference. In addition to these advantages, the optical-fiber level-sensor presented here has a small size, high accuracy, and fast time response. The sensor probe is chemically passive and can be easily sterilized. These features make the sensor attractive for numerous applications in physiology, biochemistry and medicine. The level-sensor presented here is a multipoint discrete optical-fiber device employing an array of small-size liquid- sensitive optical refractometric transducers of new type. The array of such transducers is connected via multi-fiber optical cable to the optoelectronic transmitter-receiver unit of the sensor. It performs an intelligent quasi-continuous level monitoring of a fluid. The sensor accuracy, resolution and level measurement range depend on the array length and the total number of the transducers employed. In case of the most close spacing of the transducers, the sensor level-resolution is better than plus or minus 0.2 mm.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present the results of a theoretical numerical analysis of transmission characteristics of a fiber optic refractometric transducer with a hemispherical glass detection element. In this transducer, the internal reflection of light from the element's spherical surface depends on the refractive index of the surrounding medium. We examine the effects of the transducer's geometrical and optical parameters and its refractive index on the transmission function, its nonlinearity, and the transducer's sensitivity to the refractive index of the surrounding medium. We show that through a proper choice of the transducer's material and geometrical parameters, it is possible to obtain a transmission function of any necessary span over a wide interval of the refractive index of the surrounding medium (from n = 1.0 to 1.7), and to modify the form of the transmission function from a linear one to a steplike one in virtually the same device. This permits us to use the proposed transducer for two contrasting applications: assessing the refractive index, and discriminating between two liquids or between air and a liquid, as in the detection of liquids, level measurement, etc. In addition, it is possible to adjust the transducer input range to the refractive index of a particular fluid (or fluids) of interest.

We present the results of a theoretical numerical analysis of a novel fiber optic refractometric transducer. It consists of a hemispherical glass detection element and a pair of the multimode optical fibers attached symmetrically to the element's flat equatorial plane. The internal reflection of light from the element's spherical surface is sensitive to the refractive index of the surrounding medium. We exploit several internal reflections in series and the focusing of the beam by the element's spherical surface to achieve enhanced sensitivity to the refractive index of the surrounding medium and reduced intrinsic optical loss in the transducer. We present the data on the effect of transducer's parameters on its transmission function. We show that the transducer can operate in a relatively wide range of the refractive index of the surrounding medium (we show this for the interval n = 1.0 to n = 1.45). We also present experimental data confirming our theoretical results.