Fiber light guides

The phenomenon of total internal reflection plays a basic role in the construction of fiber light guides, i.e., thin fibers made up of transparent materials (Figure 6.4) if an optic ray enters the guide, it will be unable to abandon it, propagating inside to its end because any incident angle for it will be larger Pc because of the small fiber diameter. 

Cleaning fabrics, quartz rods for light guide fibers, residues in microelectronics Removal of monomers, oligomers, and solvent from polymers Fractionation... 

Another early fiber optic refractive "sensor" was the one for measurement of temperature and salinity variations of sea water31. The sensing region consisted of a partly uncovered light guide. It detects salinity variations in water of known temperature, and temperature variations in water of known salinity with an accuracy of +/- 2 g/L and 1 °C, respectively, at NaCl concentrations of 300 g/L. 

Figure 18. Method of coating ultratransparent light guide fibers of silica with polymer films for strength and stability.

Figure 19. Influence of UV radiation as polymerization agent on the subsequent total photon attenuation in silica fibers, as a function of wavelength in nanometers. When no absorption of the UV is arranged lowest losses are assured. (The loss expressed in decibels per kilometer is a modern figure of merit for light guide...

As evidence of light guide fiber stabilization and control through processing refinement, plot of frequency of failure against the tensile strength (in hundreds of thousands pounds per square inch) shows extraordinary uniformity for the control system compared to wide distribution of failures from surface defects and other variations in a conventional fiber... 

Surface fluorescence of NADH/NADPH can be recorded continuously with a DC fluorimeter and correlated with changes in experimental conditions. A mercury arc lamp (with a 340-375 nm filter in front) is used as a hght source for fluorescence excitation. The fluorescence response of reduced NADH/NADPH was measured at 450-510 nm. The DC fluorimeter and the Hg arc lamp are connected to the kidney by a trifurcated fiber optics light guide. NADH/NADPH fluorescence emission can be corrected for changes in tissue opacity by a 1 1 subtraction of reflectance changes at 340-375 nm from the fluorescence. To determine NADH/NADPH redox state of the total surface area of kidney cortex and to evaluate whether certain areas were insufficiently perfused, fluorescence photographs of the total surface area were taken. The study demonstrated that the surface fluorescence method is simple and provides specific information about the mitochondrial oxidation-reduction state. 

The light transmission technique is most frequently used for the determination of average bubble size in gas-liquid dispersion. It has the advantages of quick measurement and on-line operation. The probes are usually made of mirror-treated glass rods (Vermeulen et al., 1955), internally blackened tubes with mirrors (Calderbank, 1958), or fiber optic light guide (Hong and Lee, 1983). 

Fig. 7 Set-up for time-resolved imaging of 96-microwell plate formats, a Fast gateable CCD-camera, b Optical emission filter, c Light-guiding adapter, consisting of 96 optical fibers, d 96-microwell plate (black with transparent bottom), e Optical excitation filter, f Pulseable LED array with 96 light emitting diodes...

An oxygen sensor array using these principles was developed by Liebsch et al. [60]. A modification of the applied imaging set up is illustrated in Fig. 7. It consists of a CCD camera with a fast mechanical shutter, an array of 96 pulsed LEDs, a computer-steered pulse generator, a constant power supply, a light-guiding adapter with 96 optical fibers, and the corresponding excitation and emission filters. 

In the following, the light guiding properties will be discussed that are important for optical fibers and that possibly impose some constraints on the preparation process. 

For the light guiding effect of optical fibers it is important to have a core with a refractive index somewhat larger than that of the airrounding cladding. Therefore the core normally consists of silica doped with other oxides to increase the refractive index. In the following we therefore discuss the simultaneous deposition of silica and germania in the silica tube. 

If the spectrum of the fluorescence should be measured the photomultiplier is replaced by a spectrometer. In this case the generated light is coupled into a multimode fiber and guided to the spectrometer. 

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