Optical fibres focusing light

The prevalently used waveguides are optical fibres. Fibre technology is standard in the UV to near-IR, but also some fibres for light transport in the mid-IR have been developed. An overview of different IR fibre materials and their characteristic performance parameters is given in Table 1. More details can be found in a number of reviews focused on the material properties of IR transmitting optical fibres26 31. For some applications, as an alternative to optical fibres also hollow waveguides may be used. 

The study focuses on a main issue regarding the longitudinal light coUeclion and propagation — thanks to an optical fibre-based textile — of sunrays having random incidence. The developed textile should present an optimal compromise between performance and weight. Because of its complexity, this main issue is subdivided. 

Figure 11.5 Schematics of the active OCT imaging catheter, where an optical fibre is scanned by the polymer actuator and a lens focuses the light at the imaging plane. The reflected light is collected by the same optical fibre and processed by the OCT system.

Experimental equipment for X-ray diffraction methods has improved enormously in recent years. CCD detectors and focusing devices (Goepel mirror) have drastically reduced the data acquisition time. Cryogenic systems have been developed which allow structural studies to be extended down to the liquid helium temperature range. These developments have had important implications for SCO research. For example, fibre optics have been mounted in the cryostats for exploring structural changes effected by light-induced spin state conversion (LIESST effect). Chaps. 15 and 16 treat such studies. 

For the purpose of visually inspecting the interior of a vessel, tank or barrel which is classified as zone 0, light generated by a zone 1 luminaire, which is located outside the vessel in zone 1, is brought into zone 0 via a fibre optics bundle. In the luminaire, the light is focused on the aperture of the fibre optics bundle by means of a condensor lens (Figs 11.1 and 11.2). 

A miniaturized spectrometer with CCD array for mounting on a printed circuit card inside the electronics has been developed for a film thickness monitor (18, 19). Light from the input fibre is focused by a 40 mm achromatic lens on to a blazed reflection grating with 300 lines/mm. A 50-element CCD array gives a spectral resolution of 10 nm. The spectrometer is 10 mm thick and 80 mm long. Spectrometers made by integrated optics have also been suggested (20). 

High-performance fibres have historically been difficult to analyse by transmission FT-IR spectroscopy. Until a few years ago, the analysis of samples smaller than 25 pm was virtually impossible even with an IR microscope because the visible light portion did not have sufficient depth of field to focus the sample, and diffraction effects would result in a sloping baseline and stray light. Filament physical geometry, especially for highly orientated samples, causes optical aberrations resulting in band distortions that can lead to poor spectral quality. 

In situ measurements in industry must be extrapolated to on-plant monitoring. The feasibility of using fibre optic coupling between the Raman experiment and the FT interferometer has been demonstrated. For on-line use special designed probes can withstand up to 300°C and 15,000 psi. Because Raman light can remotely be focused, it is even possible to measure in a non-invasive mode (for example through a specified reactor window). A portable process Raman analyser enables both in-line and at-line measurements. 

Spherical ball lenses have been used as collimators in fibre optic connectors. Sapphire spheres with a high refractive power are industrially produced in a wide range of diameters (Sandoz SA, Cugy, Switzerland Rubis Precis, Charquemont, France). Light emitted from a fibre can be focused with this lens type onto the sample site (Figure 12A). Rol found a maximal performance when the ratio of the back surface distance to the fibre and the radius of the... 

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