Optical Fiber Refractometer Research Articles

Fiber-optic interferometric refractometer for deep-water studies of sea water

A fiber-optic interferometric refractometer is proposed for precise monitoring of the refractive index of sea water at depths of 30–100 m by means of a measuring probe controlled automatically from onboard by underwater equipment.

Temperature-compensated optical fiber Michelson refractometer

Fiber optic interferometric refractometers usually possess large temperature sensitivities, especially those based on individual long-period gratings. This work introduces a compound-cavity Michelson interferometer that uses mode coupling in a long-period grating to establish the two optical paths in a single fiber, and therefore presents a compact sensor for in vivo refractive index measurement. Successful operation of the athermal refractometer was demonstrated experimentally by comparing its phase shift due to temperature-dependent changes of the refractive index of the analyte with refractive index readings from a temperature-controlled Abbe refractometer.

Optical sensor based on ultrathin films of δ-form syndiotactic polystyrene for fast and high resolution detection of chloroform

In this work are analyzed the performances of an optoelectronic sensor based on a sensitive nanoscale film of semicrystalline syndiotactic polystyrene (sPS) with a nanoporous crystalline phase developed for fast and high resolution detection of chloroform. In particular, the change of the polymer refractive index due to chloroform sorption into the polymer layer when the sensor is exposed to CHCl3 has been used as transduction property. Reflectance measurements have been performed using a fiber optic refractometer, coated with nanometric sPS film at very low pressure of chloroform, demonstrating high sensitivity and fast-time response combined with excellent reversibility. Mass sorption experiments have also been performed on the same polymeric material with an electronic microbalance at the same conditions at which the optical sensor has been characterized. This allowed a quantitative correlation between the mass of the analyte sorbed within the polymer layer and the refractive index variation, which has been found to be essentially independent of the temperature.

An high sensitivity optical sensor for chloroform vapours detection based on nanometric film of δ-form syndiotactic polystyrene

A film of syndiotactic polystyrene (sPS) in the nanoporous crystalline δ form has been used for the detection of chloroform in the vapor phase at very low concentration The variation of the refractive index due to the chloroform sorption within the polymer has been used as transduction property. Reflectivity measurements by a fiber optic refractometer, coated with a nanometric (73 nm) film has been performed at very low pressure of chloroform (between 0.2 and 5 Torr) at three different temperatures (35, 49 and 56 °C). Mass sorption experiments have been concurrently performed with an electronic microbalance operating in the same conditions of the optical sensor. Major result from the gravimetric tests is that the analyte is mainly adsorbed into the nanoporous phase where the penetrant molecules can be hosted with a certain selectivity based on both size exclusion and host guest interactions. The quantitative correlation between the mass of analyte sorbed within the polymer layer and the refractive index variation has been observed to be temperature independent. A phenomenological equation based on the Lorentz–Lorenz law has been proposed to describe the effect of the chloroform uptake including both concentration and polarizability changes on the refractive index of the sensible layer.

Optoelectronic refractive index measurements: application to smart processing

In the last decade, polymeric-based composites, in light of their low weight/mechanical strength ratio, have been widely used in many industrial areas, such as automotive, aeronautic, and aerospace areas. Because of the dependence of their properties on the manufacturing stage, real-time monitoring of the processing stage has been indicated as the key point for improving the quality and reducing manufacturing process costs through an intelligent control of the manufacture itself. To this aim, optimal monitoring systems should be non-intrusive, real-time, and able to measure a physical property changing during the process development. Refractive index is a suitable state parameter being directly correlated to the material density. In this work, the assessment of the performances of a fiber-optic refractometer has been presented. Experimental results demonstrate the capability of the sensor system to monitor the cure kinetics of a polymeric thermoset and to measure its glassy transition temperature.

Development of an optical refractometer by analysis of one-dimensional photonic bandgap structures with defects.

A theoretical analysis of an optical fiber photonic-bandgap-based refractometer is presented. The design is based on a quarter-wave reflector with one defect. By modifying both the real and the imaginary parts of the index of refraction of the defects we begin to change either the frequency or the amplitude of the localized optical mode. So we could fabricate a specific optical fiber refractometer by combining all the variables: index of refractive index of the defects and the rest of layers, thickness of the defect, number of layers, etc. to yield a large set of design possibilities, for example, detecting wider or thinner ranges of refractive indices, or controlling the detection accuracy. Some rules for the practical implementation of the refractometer are given.

Polarization Insensitive Fiber-Optic Refractometer based on a Side-polished Fiber Coupler with a Thick Glass Waveguide

Side-polished single-mode fiber covered with a thick planar-glass-waveguide is studied as a polarization-insensitive fiber-optic refractometer The properties of the device are very sensitive to the index variation of an upper cladding on top of the overlay waveguide. We investigate the spectral response, the polarization properties, and the relationship between the shift in coupling wavelength and the index variation of an upper cladding layer Index resolutions of the order of 10-4 have been achieved.

Differential optical fiber refractometer based on a path-matching differential interferometer with temperature compensation: erratum

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Yu-Lung Lo and Chin-Ho Chuang, "Differential optical fiber refractometer based on a path-matching differential interferometer with temperature compensation: erratum," Appl. Opt. 41, 5015-5015 (2002) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

An evanescent-coupling plastic optical fibre refractometer and absorptionmeter based on surface light scattering

To the best of our knowledge, an evanescent-coupling plastic optical fibre (POF) refractometer and absorptionmeter, based on surface light scattering, is described for the first time. The sensing elements were manufactured by machining random roughness, using side-polishing technique. Coarser polishing leads to stronger surface light scattering, allowing measurements of refraction index smaller than the fibre cladding value. The same device also works as an absorptionmeter, where refractive and absorptive mechanisms may compete with each other.

Differential optical fiber refractometer based on a path-matching differential interferometer with temperature compensation

We present a new approach for the development of a highly stable optical fiber refractometer based on a path-matching differential interferometer. Exploiting a single-channel phase tracker and new synthetic heterodyne demodulations, one can eliminate the thermal drift on a piezoelectric transducer stack as a phase modulator by subtraction. A transducer in a differential Fabry-Perot refractometer is designed to compensate for the thermal effects not only from thermal expansion but also from the thermo-optic effect. The experimental data show that the refractive-index change in the sensing system can be kept at a level of approximately 5 x 10(-4) without serious variations for a 1-h period of long-term monitoring associated with a temperature variation of from 25 to 50 degrees C. Accordingly, the proposed new system can be easily implemented and used as a long-term monitoring system for medical care applications such as monitoring patients during drug injection.

Polarimetric optical fiber refractometer

An optical fiber refractometer based on a photometric return-path birefringence sensor is proposed. For measuring the refractive index, the phase shift between polarization components on total internal reflection inside a refractometric prism is used. Several kinds of refractometric prism are described. It is shown that a refractive-index sensitivity of 0.0001 and higher for a wide range of index values is attainable.

New synthetic-heterodyne demodulator for an optical fiber interferometer

A new algorithm for modulating a PZT stack using a sinewave signal instead of a saw-tooth signal was developed in order to resolve the flyback problem in a PZT driver. An improved synthetic heterodyne demodulator circuit was designed and arranged to interrogate the output signal from an interferometric sensor with a sinewave modulation (phase-generated carrier). The depth of modulation, or a gain amplifier in the circuit design, was adjusted such that the standard heterodyne signal could be formed. The result is a conventional PM-modulated carrier that can be demodulated using standard techniques, followed by a lock-in amplifier or a phase meter, to recover the phase shift in the sensing information. Implementing it into a path-matching differential interferometer for the signal modulation validates this new method. As compared to the conventional technique, modulating the PZT stack in a saw-tooth signal, this technique supplies a wider modulated frequency and, therefore, a wider frequency response in a sensing system. Finally, the new synthetic heterodyne is applied to a differential optical fiber refractometer for measuring the refractive index change. A lock-in amplifier is chosen as the demodulator to extract the phase shift. Therefore, the resolution of this sensing system is 7.52/spl times/10/sup -7/ refractive index unit for a 120-/spl mu/m length of the sensing cavity.

SPR fibre sensor sensitised by fluorosiloxane polymers

A simple SPR optical fibre sensor working with a monochromatic light source and based on resonance in a stabilised silver film is presented here. It can be used either as an optical fibre refractometer, in the range of refractive index: 1.355–1.405 with a sensitivity of 4.5×10 −5, or as a chemical vapour sensor. For the detection of vapours of chlorinated hydrocarbon compounds and of aromatic compounds, the sensitive part of the fibre is coated with fluorosiloxane polymers. Detection limits of 3000 ppm were obtained for trichloroethylene and of 180 ppm for xylene. The sensitivities of detection of the optical fibre sensor coated with fluorosiloxane polymers are discussed. For the chlorinated hydrocarbon compounds, the difference between the refractive indices of the solvent and the polymer is the predominant factor. For aromatic compounds whose boiling temperature is higher, the condensation effect in the porosity of the polymer is predominant.

Developing stable optical fiber refractometers using PMDI with two-parallel Fabry–Perots

The paper presents a new approach to developing an optical fiber refractometer. The objective of the study is to come up with a relatively inexpensive but reliable optical refractometer that can be used to measure the change of refractive index in a resolution of 10 −5 and to work in a dynamic range up to 6×10 −3 at a DC frequency of up to 100 Hz. It is known that the phase modulations of optical fiber sensors are very sensitive to external disturbances, especially to the effects of thermal drifts or vibrations. A cancellation technique to compensate the effect of variation on a PZT stack is proposed in this paper to stabilize the system. Two parallel Fabry–Perot sensing cavities corresponding to two path-matching cavities for read-out systems are employed to form path-matching differential interferometries (PMDI). One Fabry–Perot cavity is used as sensing head, and the other as reference sensor. As a result, the experimental data show that the change of refractive index of a so designed sensing system can be kept in at the level of 10 −4 without any serious variations even for a 3-h long-term monitoring. Accordingly, the proposed new system can be easily implemented and used as a long-term monitoring system in a medical care environment.

Fiber-optic interference refractor for investigating aqueous media

A circuit of a modified laser fiber-optic interference refractometer is described. Using the modified refractometer it is possible to measure the absolute indices of refraction of water at depths down to 10 m in an automatic mode. The capabilities of the modified design are discussed and the measurement error is estimated.

Laser interference refractometer for investigating water surface layers

The special features involved in making accurate refractometer investigations of surface layers in water reservoirs are discussed. A fiber-optic laser interference refractometer scheme is proposed for such investigations and the accuracy of its readings is estimated.

Monochromatic excitation of surface plasmon resonance in an optical-fibre refractive-index sensor

A simple and inexpensive refractive-index sensor is described. The transducer is a multimode optical fibre which has been metallized with gold on the sensing area. The principle of this sensor is based on surface plasmon excitation at the metal/dielectric interface. This set-up, which uses monochromatic incident light, can work as an optical-fibre refractometer or as a refractive-index-variation optical-fibre sensor, in a range between 1.33 and 1.40. This sensor can detect a refractive-index variation around 10 −4 and can measure a refractive index with an accuracy around 2 × 10 −4.

Quantitative evaluation of skin surface lipids by a fiber-optic refractometer

A method to quantitatively evaluate the skin surface lipids by the use of a fiber-optic refractometer is described. The method exploits the fact that the skin surface lipids tend to make the light propagating inside the fiber core refracted into the surrounding medium thus decreasing the sensor output. The applicability of the sensor is examined by comparison with a traditional gravimetric technique using a balance. Optical measurement results obtained from the forehead of a volunteer are related to the results by gravimetry, which indicates there is a strong correlation between them. The practicality of the sensor is also confirmed by a bilateral symmetry test where data taken from both sides of the forehead are related, giving a correlation coefficient of 0.883.

Measurement of Flow Rate in a Thin Elastic Tube Using Miniaturized Fiberoptic Refractometer.

A tracer method using a miniaturized fiberoptic refractometer as a measurement of flow rate in a thin elastic tube was proposed. In this paper, the sensing principle and construction of this refractometer, which is capable of being inserted in to a thin tube, are described. Using this refractometer, an experimental study was performed on the possibility of measurement of flow rate in a thin tube. A theoretical study was also carried out to clarify the measurement error.

Skin hydration state estimation using a fiber-optic refractometer

A U-shaped fiber-optic refractometer is used to estimate the hydration state of human skin. The validity of the sensor in this application has been investigated by comparing the sensor output with the conductance of the skin to a high-frequency electrical current of 3.5 MHz, which has been reported to be a good measure of the skin hydration state. Results indicate that there is a relatively close relationship between the optical sensor output and the electrical conductance. A water sorption-desorption test conducted to confirm the above relationship has revealed that the fiber-optic probe can provide a convenient means for estimating the skin hydration state in an easy manner.