Design. Fabrication and Characterization of Fiber Optic Sensors for Physical and Chemical Applications

Advent of lasers together with the advancement in fiber optics technology has revolutionized the sensor technology. Advancement in the telemetric applications of optical fiber based measurements is an added bonus. The present thesis describes variety of fiber based sensors using techniques like micro bending, long period grating and evanescent waves. Sensors to measure various physical and chemical parameters are described in this thesis.

Two-section fiber optic Raman polarizer for high-speed transmission systems

We report on a theoretical study of polarization impairments in periodically spun fiber Raman amplifiers. Based on the Stochastic Generator approach we have derived equations for polarization dependent gain and mean-square gain fluctuations. We show that periodically spun fiber can work as a Raman polarizer but it suffers from increased polarization dependent gain and gain fluctuations. Unlike this, application of a depolarizer can result in suppression of polarization dependent gain and gain fluctuations. We demonstrate that it is possible to design a new fiber Raman polarizer by combining a short fiber without spin and properly chosen parameters and a long periodically spun fiber. This polarizer provides almost the same polarization pulling for all input signal states of polarization and so have very small polarization dependent gain. The obtained results can be used in high-speed fiber optic communication for design of quasi-isotropic spatially and spectrally transparent media with increased Raman gain. © 2011 IEEE.

Periodic nonlinear Fourier transform for fiber-optic communications, Part II:eigenvalue communication

In this paper we propose the design of communication systems based on using periodic nonlinear Fourier transform (PNFT), following the introduction of the method in the Part I. We show that the famous "eigenvalue communication" idea [A. Hasegawa and T. Nyu, J. Lightwave Technol. 11, 395 (1993)] can also be generalized for the PNFT application: In this case, the main spectrum attributed to the PNFT signal decomposition remains constant with the propagation down the optical fiber link. Therefore, the main PNFT spectrum can be encoded with data in the same way as soliton eigenvalues in the original proposal. The results are presented in terms of the bit-error rate (BER) values for different modulation techniques and different constellation sizes vs. the propagation distance, showing a good potential of the technique.

Design and Development of Fiber Optic Sensors for Trace Detection of Certain Environmental Pollutants

In recent years,photonics has emerged as an essential technology related to such diverse fields like laser technology,fiber optics,communication,optical signal processing,computing,entertainment,consumer electronics etc.Availabilities of semiconductor lasers and low loss fibers have also revolutionized the field of sensor technology including telemetry. There exist fiber optic sensors which are sensitive,reliable.light weight and accurate devices which find applications in wide range of areas like biomedicine,aviation,surgery,pollution monitoring etc.,apart from areas in basic sciences.The present thesis deals with the design,fabrication and characterization of a variety of cost effective and sensitive fiber optic sensors for the trace detetction of certain environment pollutants in air and water.The sensor design is carried out using the techniques like evanescent waves,micro bending and long period gratings.

Dispersion-dominated nonlinear fiber-optic channel

We propose to apply a large predispersion (having the same sign as the transmission fiber) to an optical signal before the uncompensated fiber transmission in coherent communication systems. This technique is aimed at simplifica- tion of the following digital signal processing of nonlinear impairments. We derive a model describing pulse propagation in the dispersion-dominated nonlinear fiber channel. In the limit of very strong initial predispersion, the nonlinear propagation equations for each Fourier mode become local and decoupled. This paves the way for new techniques to manage fiber nonlinearity.

Prediction of subcutaneous fatty acid composition from ham of CLA fed boars and gilts using a NIRS fiber optic probe

The aim of this work was the use of NIR technology by direct application of a fiber optic probe on back fat to analyze the fatty acid composition of CLA fed boars and gilts. 265 animals were fed 3 different diets and the fatty acid profile of back fat from Gluteus medius was analyzed using gas chromatography and FT-NIR. Spectra were acquired using a Bruker Optics Matrix-F duplex spectrometer equipped with a fiber optic probe (IN-268-2). Oleic and stearic fatty acids were predicted accurately; myristic, vaccenic and linoleic fatty acids were predicted with lower accuracy, while palmitic and α-linolenic fatty acids were poorly predicted. The relative percentage of fatty acids and NIR spectra showed differences in fatty acid composition of back fat from pigs fed CLA which increased the relative percentage of SFA and PUFA while MUFA decreased. Results suggest that a NIR fiber optic probe can be used to predict total saturated and unsaturated fatty acid composition, as well as the percentage of stearic and oleic. NIR showed potential as a rapid and easily implemented method to discriminate carcasses from animals fed different diets.

Comparative Performance of Two Fiber Optic Ammonia Sensors Employing Different Sensing Materials

The design and fabrication of fiber based ammonia sensors employing Bromothymol blue and Chitosan as sensing elements are presented in this paper. In the presence of ammonia gas the absorption of Bromothymol blue changes while in the case of Chitosan the refractive index changes which in turn modulates the intensity of light propagating through a fiber.

A microbent fiber optic pH sensor

Optical fiber sensors developed for measuring pH values usually employ an unclad and unstrained section of the fiber. In this paper, we describe the design and fabrication of a microbent fiber optic sensor that can be used for pH sensing. In order to obtain the desired performance, a permanently microbent portion of a plastic optic fiber is coated with a thin film of dye impregnated sol–gel material. The measurements are simultaneously carried out in two independent detection schemes viz., the bright field detection configuration for detecting the core modes and dark field detection configuration, for detecting the cladding modes. The results of measurements of core mode-power and cladding mode-power variation with change in pH of a solution surrounding the coated portion of the fiber is presented. This paper thus demonstrates how a bare plastic fiber can be modified for pH sensing in a simple and cost effective manner.

A fiber optic smart sensor for studying the setting characteristics of various grades of cement

A simple, effective and inexpensive fiber optic sensor for investigating the setting characteristics of various grades of cement is described. A finite length of unsheathed multimode optical fiber laid inside the cement mix, is subjected to stress during the setting process. The microbends created on the fiber due to this stress directly influence the intensity of light propagating through the fiber. Continuous monitoring of such variations in the light output transmitted through the fiber gives a clear measure of the setting characteristics of the cement mix, thus providing a simple and elegant technique of great practical importance in the field of civil engineering. The smart fiber optic sensor described above can be incorporated into a building during the construction process itself so that continuous monitoring of the deterioration process for the entire life time of the building can be carried out.

A Comparative Study of Fiber Optic Humidity Sensors Based on Chitosan and Agarose

A comparative study of two biopolymer based fiber optic humidity sensors is presented in this paper. Sensing elements Agarose and Chitosan swells in the presence of water vapour and undergoes changes in refractive index and modulates the intensity of light propagating through a fiber with Agarose or Chitosan as cladding.

Design and development of an LED based fiber optic evanescent wave sensor for simultaneous detection of chromium and nitrite traces in water

The design and development of a cost-effective, simple, sensitive and portable LED based fiber optic evanescent wave sensor for simultaneously detecting trace amounts of chromium and nitrite in water are presented. In order to obtain the desired performance, the middle portions of two multimode plastic clad silica fibers are unclad and are used as the sensing elements in the two arms of the sensor. Each of the sensor arms is sourced by separate super bright green LEDs, which are modulated in a time-sharing manner and a single photo detector is employed for detecting these light signals. The performance and characteristics of this system clearly establish the usefulness of the technique for detecting very low concentrations of the dissolved contaminants.

A fiber optic concentration sensor

A simple fiber optic concentration sensor based on the coupling of light f rom one fiber to another through a solution is discussed. The operational characteristics of the sensor are illustrated by taking the solutions of potassium permanganate and fast green dye as samples.The extrinsic type sensor described here shows linearity at lower concentrations.

High sensitivity fiber optic angular displacement sensor and its application for detection of ultrasound

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fluorometric fiber optic drop sensor for atmospheric hydrogen sulfide

A fluorometric technique based on a liquid drop excited from its interior by an optical fiber is described for the measurement of low concentrations of atmospheric hydrogen sulfide (H2S). A drop of alkaline fluorescein mercuric acetate (FMA) solution is suspended in a flowing air sample stream and serves as a renewable sensor. An optical fiber contained within the conduit that forms the drop, brings in the excitation beam; the fluorescence emission is measured by an inexpensive photodiode positioned close to the drop. As H2S in the sample is collected by the alkaline drop, it reacts rapidly with FMA resulting in a significant decrease in fluorescence intensity, proportional to the concentration of H2S sampled. The chemistry of this uniquely selective reaction has been well established for many years, the present technique permits a simple fast inexpensive near real-time measurement with very little reagent consumption. Even without prolonged sampling/preconcentration steps, limits of detection (LODs) in the double digit ppbv range is readily attainable. (C) 1997 Elsevier B.V. B.V.

Geometrical parameter analysis of a high-sensitivity fiber optic angular displacement sensor

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)