Claddings polymers

Polymers also play a role in the case of specialized optical equipment, where the different parts are connected by silica fibers. This applies, for example, to instruments used for spectroscopic process analysis, i.e., for real-time control of chemical processes [91]. To prevent physical damage, the fibers are coated with poly(vinyl chloride) or acrylate-based polymers. Fibers coated with polyimide withstand temperatures up to 350 °C. 

Schaffert, Electrophotr aphy, 2nd Edition, Focal Press, London (1975). 

Borsenbergei D. S. Weiss, Organic Photoreceptors for Xerography, Dekkei  

Schein, Electrophotography and Development Physics, 2nd Edition, Lapladan Press, Morgan Hills, CA, USA (1996). 

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The simplest case of fibre structure is the step-index one, characterized by a constant circular refractive index profile in the core and polymer cladding of lower refractive index (Figure 3). The refractive indexes of the core and cladding depend on the materials used. The cores of these structures can be prepared from melts as well as from preforms without radial and azimutal variations of the refractive index. To obtain suitable mechanical... 

Yuan J, El-Sherif MA, MacDiarmid AG, Jones W (2001) Fiber optic chemical sensors using modified conducting polymer cladding. Proc SPIE 4205 170-179... 

Figure 2.14. Schematic diagram of a drawing machine for producing polymer-clad, fused silica open tubular columns.

This relationship ensures that the critical angle of incidence of the interface is not exceeded and that total internal reflection occurs (Levi, 1980). Typical values of NA for fused SiOj fibers with polymer cladding are in the range of 0.36-0.40. The typical values of = 14° used to insert the beam of the biomedical laser into the fiber is much smaller than those values ( 21-23°) corresponding to typical NA values. The maximum value of the propagation angle a typically used in biomedical laser systems is i 4.8°. 

For etch and fill, we once again begin by depositing metal onto a substrate for the ground plane. A 5-/xm passive polymer cladding layer is spin cast over the metal... 

Fluorescence is excited by laser (e.g. argon), and the back-scattered fluorescent light picked up by the fibre and analysed by spectrometry and photon-counting techniques. Where a single fibre is used to carry both the exciting and fluorescent light, the natural fluorescence in the fibre can limit the lower detection limit (3 x 10 ) for Rhodamine B dye detected by a 600/im polymer-clad silica fibre (33). This can be overcome using two separate fibres. 

Measurements with evanescent wave spectroscopy have been made, using both glass slides as a waveguide and optical fibres such as polymer-clad silica (PCS) fibre without the cladding. 

Extrusion also allows the fabrication of core/clad preforms. Savage et al. successfully reported the coextrusion of a Ge-As-Se preform and its subsequent fiber drawing [152], The coextrusion technique produces preforms with optimum core/clad interface quality. Fibers with optical losses of 1.7 dB/m at 6.0 pm were fabricated. Recently Abouraddy et al. have extended the technology by coextruding composite macroscopic preforms made of two ChG materials and a thermoplastic polymer cladding [153], yielding mechanically robust fibers. 

Single infrared fibers can be used as ATR probes and sensors in a wide variety of applications. Fibers are also used as waveguides to transfer radiation from the spectrometer to a remote location. Most often, chalcogenide fibers are used in bundles rather than single fibers. To reduce the attenuation found in polymer-clad fibers, the fibers are clad with another chalcogenide of lower refractive index than the core. As chalcogenide cladding has very low absorption, the attenuation can be reduced to as low as 0.1 dB... 

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