Fiber optical sensors

Optical Fibers. Pure and doped fused siHca fibers have replaced copper lines in the telecommunication area. Eused siHca fibers are used in laser surgery, optical sensor appHcation, and laser welding (see Sensors). Optical-fiber-tethered weapons such as fiber-optics-guided (EOG) missiles are another potential appHcation for fused siHca (249,250) (see Eiberoptics). 

Keywords Photonic bandgap fibers Bragg fibers Resonant optical sensors Optical fiber sensors Plasmonics Plasmonic sensors... 

In addition to these catalytic sensors, optical fibers also provide the prerequisites for the construction of affinity sensors. In the classical example, a glucose sensor [220], the lectin con-canavalin A, is covalently attached to the internal wall of a membrane stitched on the tip of the fiber, and it binds by affinity the fluorescein-labelled macromolecule dextran. The in-... 

Fiber-optic chemical sensors are composed of a sensing material and a transducer. The transducer converts the recognition and sensing events obtained by the sensing materials into a response such as an optical signal. Optical measurements can provide rapid, sensitive, and nondestructive analysis of many important compounds. In fiberoptic chemical sensors, optical fibers are used to transmit the optical signal to the measurement device, enabling a remote detection of the analyte in the sample. The use... 

J. Dakin and B. Culshaw, Optical Fiber Sensors, Vol. I, Principles and Components, Artech House, London, 1988. 

Benjamin, R.F., F.J. Mayer, and R.L. Maynard (1984), Microshell-Tipped Optical Fibers as Sensors of High-Pressure Pulses in Adverse Environments, in Eiber Optics in Adverse Environments 11, Proc. SPIE, 506 (edited by R.A. Green well),... 

In real curvature sensors, a vibrating membrane mirror is placed at the telescope focus, followed by a collimating lens, and a lens array. At the extremes of the membrane throw, the lens array is conjugate to the required planes. The defocus distance can be chosen by adjusting the vibration amplitude. The advantage of the collimated beam is that the beam size does not depend on the defocus distance. Optical fibers are attached to the individual lenses of the lens array, and each fiber leads to an avalanche photodiode (APD). These detectors are employed because they have zero readout noise. This wavefront sensor is practically insensitive to errors in the wavefront amplitude (by virtue of normahzing the intensity difference). 

FIGURE 8.4 Configurations for several different kinds of optieal fiber sensing systems are shown. The eommon faetor in all these systems is the use of an optical fiber as an integral element in the system, either to earry light to and from diserete sensors (often referred to as optrodes), or as sensitive elements themselves (intrinsie fiber sensors). Courtesy, AT T Bell Laboratories. 

The complex where L = CgHsC = CCgHs [134] was also used to develop an optical fiber sensor as the complex changes color from dark yellow to pale yellow. The sensor... 

With the complex where L = pyridine an optical nanosensor was developed [135-137], the method used to fix the vapochromic material to the optical fiber was the electrostatic self assembling method (ESA) and the light source used was an 850 nm LED. The sensor was tested for two different alcohols (ethanol and methanol) and it was possible to distinguish between different concentrations. It was also possible to discriminate between the two different alcohols. 

The complex obtained when L = 2,2 -bipyridine was used in the development of an optical fiber sensor that works in the reflection mode [138]. The sensor response for three different VOCs with four different concentrations each was studied and it was shown that the sensor responded to the three VOCs and that it was possible to distinguish between the different concentrations. 

Laguna, M., Bariain, C., Garrido, J., Mafias, l.R. and Romeo, 1. (2001) Optical fiber sensor for volatile organic vapors. Patent WO-047936. 

Bariain, C Matias, I.R., Fdez-Valdivielso, C Elosiia, C Luquin, A., Garrido, J. and Laguna, M. (2005) Optical fiber sensors based on vapochromic gold complexes for environmental applications. Sensors and Actuators B, 108, 535—541. 

Measurement by means of a wall optical sensor The thickness of a film and the slope of its free surface can also be measured by means of a wall optical sensor, as proposed by Ohba et al. (1984). This sensor consists of a cluster of seven optical fibers mounted flush with the wall (Fig. 3.33). A laser beam passed through the central fiber is reflected by the free surface onto the other fiber tips, which collect the light and transmit it to two photodiodes. The light intensities received by these two detectors enable the film thickness and the inclination angle to be determined. 

In context with methane detection during offshore oil drilling, another infrared fiber optic methane sensor was reported25. The detector comprises 3 main units a microcomputer-based signal processing and control unit, a nonconducting fiber optic gas sensor, and an optical fiber cable module. The system operates at an absorption line of methane where silica fibers have very low losses. 

Resonant photoacoustic gas spectrometry was adapted to fiber optic sensor technology32 as early as in 1984. A Mach-Zehnder arrangement was combined with a resonant photoacoustic cell for gap analysis. The pollutant gas NO2 was detectable in a concentration of 0.5 ppm. In a smart optical fiber hydrogen sensor, the fiber is coated with palladium metal which expands on exposure to hydrogen. This changes the effective optical path length of the fiber, which is detected by interferometry33. 

Kautsky 1931 first oxygen sensor (non-fiber optic) based on dynamic quenching of the phosphorescence of adsorbed dyes... 

As the potential of optical fiber probes for pH measurements was rapidly recognized, several other articles appeared within a few years75 83. Most were reflectance-based, and Seitz reported the first fluorescent pH sensors84, 78. The article by Janata85 on whether pH optical sensors can really measure pH is another "must" in the early literature since it points to aspects hardly addressed in pH sensor work. 

Rogers A.J., Distributed optical-fiber sensors, J. Phys. D Appl. Phys. 1986 19 2237. 

Inaba H., Chan K., Ito H., All-optical remote gas sensor system over a 20 km range based on low-loss optical fibers in the near infrared region, Proc. SPIE-Int. Soc. Opt. Eng. 1984 514 211. 

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