Extrinsic Fiber-optic Sensor Research Articles

Direct contact evanescent wave absorption enabled fiber optic refractive index sensor operating in the dynamic range of 20 °C to 60 °C

The study of refractive index provides the complete picture of material bodies with reference to their major properties like physical, chemical, optical, etc., and hence decides the behavior of the material body at macro level. Measurement of refractive index in small volume samples using a U-shaped extrinsic fiber optic sensor based on the principle of direct contact evanescent wave absorption can be employed to detect such information. In order to obtain such measurements, a U-shaped glass probe connected between a light transmitter and an optical detector using two PCS multimode optical fibers of the same diameters (200/230 μm) was developed and investigated in the present study. Liquid mixtures prepared using Toluene and Acetic acid taking at different proportions making total volume equivalent to 20 ml employing a two burette system. When the liquid mixtures are applied on the U-shaped probe the light reaching the detector from the source was shown varying depending upon the refractive index of the mixture. The changes in the transmitted power spectra were measured as a function of absorption of higher order evanescent wave modes at various refractive index values at different temperature levels ranging from 20 °C to 60 °C of the mixture and by repeating the experiment with various operating wavelengths (630 nm, 660 nm, 820 nm & 850 nm). The calibrated curves were plotted, which can be used to determine the refractive index of liquids at various temperatures with high degree of accuracy, precision and sensitivity measurements, exploiting all the benefits offered by the optical fiber communication systems.

Comprehensive Study and Experimental Validation of U-shaped Probe Extrinsic Fiber Optic Sensor for the Measurement of Refractive Index at Various Temperatures using a Tunable Light Source

Extensive detection performances due to sensitivity to external and internal perturbations in the fiber structure makes the optical fiber sensors highly superior over the conventional sensors. The fiber optic sensors with clad removed fibers at some portion along its length play a vital role in the determination of refractive index of various liquids at several wavelengths and at several temperatures. In the present paper a refractive index sensor has been developed to investigate the performance and experimental validation in the measurement of R.I. values of liquids at various temperatures using a tunable light source capable of emitting light at the wavelengths of 630nm, 660nm, 820nm and 850nm. The U-shaped glass probe connected between the tunable light source and an optical detector using two multimode PCS fibers of 200/230μm, acts as a clad removed portion of the sensor which is called as sensing zone or sensing region. In the working principle of the sensor, the U-shaped glass rod immersed into each mixture prepared with the combination of Toluene and Acetonitrile, the light launched from the source reaching the detector was noted at various temperatures and by tuning the wavelength of the source to 630nm, 660nm, 820nm and 850nm. From the data obtained, the sensor was calibrated to measure the refractive index of various liquids at different temperatures and wavelengths. Exploiting all the advantages offered by the fiber optic communication systems, the sensor was expected to be rugged, robust, reliable, and durable offering the sensitivity in the range of the order of 10-5.

Precision-Microfabricated Fiber-Optic Probe for Intravascular Pressure and Temperature Sensing.

Small form-factor sensors are widely used in minimally invasive intravascular diagnostic procedures. Manufacturing complexities associated with miniaturizing current fiber-optic probes, particularly for multi-parameter sensing, severely constrain their adoption outside of niche fields. It is especially challenging to rapidly prototype and iterate upon sensor designs to optimize performance for medical devices. In this work, a novel technique to construct a microscale extrinsic fiber-optic sensor with a confined air cavity and sub-micron geometric resolution is presented. The confined air cavity is enclosed between a 3 μm thick pressure-sensitive distal diaphragm and a proximal temperature-sensitive plano-convex microlens segment unresponsive to changes in external pressure. Simultaneous pressure and temperature measurements are possible through optical interrogation via phase-resolved low-coherence interferometry (LCI). Upon characterization in a simulated intravascular environment, we find these sensors capable of detecting pressure changes down to 0.11 mmHg (in the range of 760 to 1060 mmHg) and temperature changes of 0.036 °C (in the range 34 to 50 °C). By virtue of these sensitivity values suited to intravascular physiological monitoring, and the scope of design flexibility enabled by the precision-fabricated photoresist microstructure, it is envisaged that this technique will enable construction of a wide range of fiber-optic sensors for guiding minimally invasive medical procedures.

U-shaped Glass Rod as Key Construction Material in the Extrinsic Fiber Optic Sensor to Determine Various Parameters of Liquids at the Operating Wavelength of 660nm

The growth of fiber optic communications and optoelectronics industries has revolutionized two major product areas over the past 50years. The industry of optical fiber revolutionized the telecommunication with reliable links by offering greater performance. Laser printers, Compact disk systems, Laser pointers, Bar code devices are some of the products revolutionized by optoelectronics industries. The optoelectronic technology and fiber optic communication technology have been used in the progress of optical fiber sensing technology. In the present work a novel sensing technique has been used in the configuration of an advanced sensor using two 200/230μm PCS fibers of 50cm each in length, a SciTech power meter, laser light source of 660nm and a U-shaped borosilicate glass rod of specific dimensions. The combination of two volatile liquids (Toluene and 1-Butanol) have been chosen as test liquids to calibrate the sensor having the capability of measuring the various parameters of liquids either transparent or dark in the various dynamic ranges at room temperature (30°C). The sensor has been analyzed on the lines of its geometrical parameters and sensitivity aspects. This sensor is expected to play a major role in future industrial, medical, military, civilian, scientific and consumer applications by providing higher sensitivities, reliability, ruggedness and other advantages in comparison with conventional sensors.

Multifunctional Extrinsic Fiber Optic Sensor to Measure Various Parameters of Liquids at the Operating Wavelength of 660nm Employing a U-Shaped Glass Rod as a Sensing Element

Fiber Optic sensor technology has become more popular since early 1970’s during which the mechanism of losses from optical fibers was exploited to construct a new class of fiber optic sensors and systems. A novel fiber optic sensor has been developed by connecting a U-shaped glass element of specific dimensions between a light source of 660nm wavelength and an optical power detector by using a couple of PCS optical fibers of 200/230μm diameters of core and cladding respectively. The sensor can be employed to measure several parameters such as Refractive Index, Density, Viscosity, Ultrasonic Velocity, Molar Volume, Molar Refraction, Dielectric Constant, Acoustic Impendence, Adiabatic Compressibility, Viscous Relaxation Time, Intermolecular Free Length, Absorption Coefficient, Gibb’s Free Energy, Free Volume, Internal Pressure and their excess parameters of Toluene and tert-Butanol mixtures at 30℃ temperature and at the operating wavelength of 660nm

Extrinsic Fiber-Optic Sensor for Detection of Saliva pH

Measurements of pH are important in industry, agriculture, medicine, etc. Two main principles, namely electrochemical and optical ones, have been employed in pH meters and sensors. This paper is aimed at the development of extrinsic fiber-optic sensors of saliva pH. Such sensors have already been used for monitoring pH changes caused by biological processes. In this paper, fiber-optic sensors consisted of inlet and outlet silica fibers transmitting light from a halogen lamp to a sample cell and then to a diode-array spectrometer. Two types of sample cells were used; namely a silica cell with a measurement path of 10 mm, and a special silica capillary cell with a hole diameter of 0.07 mm and measurement path up to 40 mm. This capillary, produced at the Institute, consists of a Bragg mirror applied onto the inner silica capillary wall. Both the sensors were calibrated by using Sorensen buffers with bromothymol blue and a commercial pH meter. The calibration curves were used for the determination of pH of saliva samples collected from one healthy person at different times. It has been found that the fiber-optic sensors provide us with lower pH values than the pH meter. This result can be explain by effects of saliva components on bromothymol blue spectra. By using a correlation line between pH values measured by the sensors and those from the pH meter the sensor reliability of about 0.3 pH units can be estimated.

Fiber optic sensor for heart rate detection

The principle of operation, design aspects, experimentation and performance of an extrinsic fiber optic sensor using fiber optic displacement sensor for the measurement of amplitude and frequency of heart rate signal is presented and investigated. The displacement sensor consists of fiber optic transmitter, fiber optic bundled probe and photodiode detector and an artificial electrocardiogram (ECG) signal is used in the testing. The sensitivity of the sensor is found to be 0.002mV/μm and thus it is capable of measuring heart rate from 50bpm to 300bpm with linearity more than 99%. The simplicity of the design, high degree of sensitivity, dynamic range and the low cost of the fabrication make it suitable for real field applications. Moreover, accuracy and reliability are the excellent pay-offs of this fiber optic sensor.

Compensation for Temperature-Dependence of the Faraday Effect by Optical Activity Temperature Shift

This paper presents a robust fiber-optic magnetic field, or electric current sensor with temperature compensation. The compensation is based on the optical activity temperature dependence of a Bi12GeO20 crystal. A novel measuring head for this extrinsic fiber-optic sensor is developed. Optical path for temperature measurement passes between optical paths, used to sense the magnetic field, thus ensuring proper temperature sampling. Measurement accuracy is improved from 0.8% to 0.2%.

Simulation and experimental studies of an extrinsic fiber optic sensor for liquid refractometry

The working of a fiber optic sensor for sensing of refractive index of liquids based on intensity modulation is studied in detail. Mathematical modeling and simulation for the intensity of light collected by parallel, flat-tipped, dual fiber probe immersed in liquids of different refractive index are carried out. The model consists of transmitting fiber, receiving fiber, reflector and liquid medium of different refractive index. A cone of light emerges out of the transmitting fiber gets reflected in the form of cone of light toward receiving fiber. This cone of angle gets modified in accordance with refractive index of the liquid medium. The output intensity may be determined by considering the overlap area between the receiving fiber core and cross-section of reflected cone emitted by the image of a transmitting fiber. The proposed model takes into account various effects such as numerical aperture of fiber, change of refractive index of liquid medium, and scattering effect. Finally experimental results are compared with simulated ones.

Measurement of Phase Boundaries of Hydrocarbon Mixtures Using Fiber Optical Detection Techniques

In this paper we present a novel technique for experimental determination of dew and bubble points of oils and gases under reservoir conditions. Extrinsic fiber optic sensors mounted on an 80-mL titanium equilibrium cell are part of the measurement setup. Formation of a new phase in the sample confined within the cell is sharply indicated by the creation of characteristic changes in the fiber optic signal. This allows for precise detection of dew and bubble point conditions. The entire apparatus is transportable and can easily be carried to field locations for quick and accurate studies of bottom hole samples. Phase behavior measurements (dew and bubble points) of three model systems and a real reservoir fluid are presented.

Spectrometric Temperature Measurement Using a Zinc Selenide-Based Fiber-Optic Sensor

An extrinsic fiber-optic sensor for temperature monitoring based on the spectral shift of ZnSe has been developed. The calibration model is based on wavelength position data rather than intensity, eliminating the need for measurement of the input light intensity and making it robust with respect to lamp and detector fluctuations. The wavelength accuracy necessary to obtain quality results with this method was achieved on a low-cost spectrometer by combining the sensor output with light from a mercury lamp that enabled realtime correction data to be acquired simultaneously with the spectral shift of the ZnSe. The results on this economically priced system were similar to those from a more expensive, more wavelength stable spectrometer that did not require wavelength correction. In both cases, the standard error of prediction (SEP) for temperatures in the 25–70 °C range was initially around 0.2 °C. After two weeks, the SEP increased to around 0.4–0.5 °C.

Alignment considerations in extrinsic fiber-optic sensors

The performance of a fiber-optic sensor and its overall cost depend on the packaging of the sensor. Alignment of different optical, optoelectronic, and mechanical components is a key problem in the package design of a fiber-optic sensor. An intensity based fiber-optic sensor that can be used as a refractive-index or displacement sensor is considered as a case study in analyzing the effects of alignment on the performance of a fiber-optic sensor. Alignability of this sensor package is defined and calculated, taking into account the coupling efficiency and effects of various misalignments. Guidelines for making the package so that the fiber-optic sensor works more efficiently are developed from our calculations.