Light coupling

However, this coupling method might not be suitable for sensor systems used outside the laboratory, since the pressure of the prism on the waveguide needs to be reproduced with high precision. 

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Polypyridine ruthenium (II) chelate complex [Ru (Bpy) ] is known to participate in a photoredox reaction on excitation with visible light, coupled with the... 

An absorption spectrum is a plot that shows how well dilferent frequencies of light couple to excitations in the sample. It is conventional to convert the units for frequency (v) from Hertz to wave numbers (cm-1) by dividing v by the speed of light (c). IR frequencies are characteristic of certain bonds in molecules and can thus be used to identify species on surfaces. Correlation charts are available which permit assignments of particular molecular species to certain IR frequencies. 

Fig. 5.5 Experimental setup. The diode laser is frequency scanned by one waveform generator, while the other controls the modulation. The light couples from a tapered fiber into and back out of microsphere WGMs, and the throughput is detected. A polarizing beamsplitter (PBS) separates throughput of the two polarizations. A diode pumped solid state laser can be used as an external heat source for the microsphere, and the vacuum chamber allows control over the ambient pressure. Reprinted from Ref. 5 with permission. 2008 International Society for Optical Engineering...

Core mismatch between two fiber segments can also cause part of the core-mode light coupled into the cladding modes. Based on this mechanism, CCMI sensors... 

In another approach, two cascaded microstructure-collapses on a photonic crystal fiber are intentionally introduced by C02 laser or electric arc heating31. In this way, the mismatch of core size along the fiber causes light coupling between the core and cladding modes. 

Fig. 15.4 Two common light coupling elements used for waveguides (a) a prism and (b) a grating...

Fig. 18.3 (a) Top view of LC ARROW chip (b) Cross sectional view of liquid core section showing light coupling between liquid and solid cores... 

Abstract A new dif active device for light coupling between a planar optical waveguide... 

Gas-phase photoacoustic detection of propane in N2 was attempted on a Si chip. In this method, a modulated light beam is incident on the sample. If the wavelength of the modulated light couples to an energy transition in a gas, the gas absorbs the modulated light resulting in periodic gas expansions and contractions, which are manifested as an acoustic wave. This wave can be detected by a microphone. In contrast to conventional absorption spectroscopy, the sensitivity of photoacoustic spectroscopy scales inversely with dimension, and hence this method is favored in the microscale. This is because photoacoustic spectroscopy is a differential technique in which the absorption is measured as the intensity per unit surface area [796],... 

Optical activity, that is, rotation of the plane of polarized light coupled with unequal absorption of the right- and left-circularly polarized components, is a property of a molecule (or an entire three-dimensional array of atoms or molecules) that is not superposable on its mirror image. When the number of molecules of one type exceeds the number of those that are their nonsu-perposable mirror images, a net optical activity results. To predict when optical activity will be possible, it is necessary to have a criterion to determine when a molecule and its mirror image will not be identical, that is, superposable. 

Fig. 8 Light coupling methods into waveguides, (a) Grating coupling, (b) prism coupling, (c) front-face coupling via optical lens (d) front-face coupling via optical fiber...

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