Optical fibre silica

Silica is the more conventional material used for fibre manufacturing. The optical fibre telecommunications concentrated the main efforts for waveguide... 

The construction of the optoelectronic interface can be based on a silicon photodiode since analytical and reference wavelengths are from the visible and the IR regions, respectively. The signals can be filtered out by optical filters (then two photodiodes are required) or one photodiode can be synchronised with modulation waves of the LEDs used. Finally, silica optical fibres can be used as light waveguides. The choice between single fibre or bundle is determined by the application of the sensor. 

From the spectral attenuation curve of an optical fibre drawn from Optran-UV (Figure 6) it can be seen that the losses are relatively high, but still acceptable (of the order of dB/m in the UV) for practical sensing. Refractive index of silica is 1.457 at 633 nm and falls down with increasing wavelength. 

Optical fibres composed of plastics are also transparent in the visible spectral region but optical losses reach 102 - 103 dB/km13. Their refractive index varies from 1.35 to 1.6 depending on the kind of polymer used (e.g. polymethymethacrylate PMMA -1.49). The chemical resistance is much worse than that of silica fibres and thermal stability is incomparable. On the other hand, low temperature processes of plastic fibre preparation allow us mix the starting polymer with organic dyes which enables the production of luminescent fibres suitable e.g. for fluorescence-based sensing13. 

Over the last several years, the number of studies on application of artificial neural network for solving modeling problems in analytical chemistry and especially in optical fibre chemical sensor technology, has increase substantially69. The constructed sensors (e.g. the optical fibre pH sensor based on bromophenol blue immobilized in silica sol-gel film) are evaluated with respect to prediction of error of the artificial neural network, reproducibility, repeatability, photostability, response time and effect of ionic strength of the buffer solution on the sensor response. 

The pH optical fiber sensor without any pH-sensitive dye was also described70. Porous silica layer made by the sol-gel method was cladded onto optical fibre core and was exploited as the optical transducer. Acid-base properties of silica surface caused that the surface charge of silica changed with pH of the solution. For example saturation of the sol-gel layer with cations leads to an increase of the electron density of the film, hence, the refractive index of the film. Since the surface charge of silica depends on pH, the refractive index of silica film varies also with pH. Thus, changes of... 

Carbon dioxide gas (CO2) exhibits a set of relatively strong absorption bands at approximately 2 pm, which coincides with the infra-red edge of the transmission band of silica optical fibres (see Figure 6). These absorption... 

Optical fibres need to be free of impurities such as transition metal ions (see Chapter 8) and conventional methods of preparing silica glasses are inadequate. The sol-gel process is one way of forming fibres of sufficient purity (chemical vapour deposition. Section 3.7, is another). These processes use volatile compounds of silicon which are more easily purified, for example by fractional distillation, than silica. It is possible to produce silica fibres using a method similar to that studied in the nineteenth century, but with the geldrying time reduced from a year to a few days. Liquid silicon alkoxide (Si(OR)4), where R is methyl, ethyl, or propyl, is hydrolysed by mixing with water. 

The core of silica optical fibres contains some B2O3, Ge02, and P2O5. How do these impurities increase the refractive index ... 

Silica-based glasses Si02 with 10% GeOj Optical fibres for communication... 

It is ironic to consider the III-V nitrides, the premier materials for short wavelength blue and UV emitters, as sources of infrared light. However, Er-doped GaN is of interest for making electrically pumped, temperature insensitive, broad band and compact optical amplifiers or sources of 1.54 pm light. Applications include long-haul communication systems (amplifiers), local area networks (50/50 splitters) and sources (lasers) for transmission in silica-based optical fibres. 

Kiang, K., Erampton, K., Monro, T. et al., Extruded single mode non-silica glass holey optical fibres, Electron. Lett., 38, 546, 2002. 

Two methods for the covalent immobilization of single-stranded DNA onto fused silica optical fibres using various linkers for the development of biosensors were reported by Krull and co-workers [22]. One method involved a hydrophobic and the other a hydrophilic spacer arm and it was determined which linker would provide the best immobilization efficiency, hybridization kinetics, and minimal non-specific adsorption to the surface. 

Silica 100% Si02 Very low coefficient of thermal expansion Optical components, laboratory ware, optical fibre... 

An instantaneous pulse of wavelength 1000 60 pm is introduced into a silica optical fibre. What will be the pulse spread in km after 1 second The refractive indices of silica are as follows n(400 nm) = 1.47000 n(average) = 1.46265 (700nm) = 1.45530. 

Arthur, C. L, and Pawliszyn, J., 1990, Solid-phase microextraction with thermal desorption used fused silica optical fibres. Anal. Chem. 62 2145-2148. 

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