Substrate 708 INDEX

Figures 13(a) and 13(b) illustrate the intensity distributions for two environment/substrate combinations, namely air/glass and water/glass. It can be concluded that the dipole located at a dielectric surface preferably radiates into the higher refractive index substrate at angles close to the critical angle. The intensity radiated into the environment is, on the other hand, relatively small. Yet it is this fraction of the fluorescence intensity that forms the basis of the sensor signal in conventional systems such as the optical biosensor...

Waveguide Sensors Using Low Index Substrates Reverse Waveguide Configuration... 

More detailed analysis shows that the application of the low refractive index substrates not only increases the penetration depth into the cover media, but also since the mode profile is reversed places a larger portion of the electromagnetic power flowing in the waveguide structure into the cover media, thus increasing the sensor sensitivity for refractive index variations in the cover solution9 15. 

The RM device consists of a high-index substrate ( 1 mm thick lead glass, = 1.72825), a thin low-index spacer (about 1000 nm of magnesium fluoride or silica) and a very thin monomode waveguiding layer (about 100 nm of titanium oxide, zirconium oxide, hafnium oxide or silicon nitride). It can be used to monitor re-... 

In situ FTIR " also had to overcome serious difficulties in its application to electrochemical problems. Unlike ellipsometry, where the wavelengths used are in a region of low solvent absorbance, IR is strongly absorbed by most familiar organic solvents and most particularly by water. This leads inevitably either to thin-layer cells or the development of internal reflection techniques. The former has the advantage of simplicity in interpreting spectral data, but it severely limits the type of electrochemistry that can be carried out. The latter requires not only a suitable high-refractive index substrate, such as Ge or Si, but also an adherent very thin layer of metal as the electrode. Technically this is difficult to fabricate so that the metal layer is continuous, and a substantial lateral resistance is inevitable. 

Despite the gains in internal quantum efficiency, the overall efficiency is still less than 19%. As much as 80% of the photons produced cannot get out because of the high index of refraction of the polymer material. Approaches such as texturing the surface of the glass, index matching or using low index substrate materials, and the use of arrays of microlenses have made increases in the extraction efficiency. 

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