Waveguides, planar

Figure C2.15.12. (a) TE and (b) TM modes for tire dielectric planar waveguide.

Figure 10-11. The sample is a 290 nm thin film of LPPP deposited on a BK7 substrate. A planar waveguide glass/polymer/air is formed since the polymer film has the highest index of refraction. The resulting intensity profile of the guided TE waveguide mode for the sample is shown on the right hand side. Only one guided mode is supported.

Figure 10-15 shows the output vs. input energy relation with a clear threshold at a pump pulse energy of approximately 1.5 nJ. This value is an order of magnitude lower than the threshold for the observation of ASE in simple planar waveguides, i.e. without distributed feedback but prepared with the same conjugated polymer. 

A novel fiber optic sensor concept using antibody-antigen reactions at a glass-liquid interface was reported by Daehne146. The reaction of antibodies immobilized onto the surface of fused silica fiber optic or planar waveguides with antigens in solution was detected by interaction with the evanescent wave. By detecting in-line fluorescence, the measurement of human IgG is described. 

In addition, the integration of modem optical technology and electrochemical techniques for sensing applications appears to be a powerful new approach. A new type of optoelectrochemical sensor for chlorine, based on an electrochromic thin-film sensing layer placed on top of a planar waveguide, has demonstrated the applicability of this combined approach. 

There are several types of optical waveguides - planar waveguides and cylindrical waveguides (optical fibers). Basic optical waveguide geometries are shown in Figure 1. 

Let us investigate light propagation in a planar waveguide consisting of three media with the refractive indices i < n2> 3 and a waveguide layer thickness d (Figure 2). 

Rowe-Taitt C.A., Hazzard J.W., Hoffman K.E., Cras J.J., Golden J.P., Ligler F.S., Simultaneous detection of six biohazardous agents using a planar waveguide array biosensor, Biosensors and Bioelectronics 2000 15 579-589. 

Figure 2 is a simplified illustration of mode propagation within a planar waveguide. 

The absorption-based platforms described previously employed evanescent wave interrogation of a thin sensing layer coated onto a planar waveguide. A sensitivity enhancement strategy for optical absorption-based sensors based on planar, multimode waveguides was developed recently by us18. The objective was to apply this theory to the development of low-cost, robust and potentially mass-producible sensor platforms and the following section outlines the assumptions and predictions of this theoretical model. 

While planar optical sensors exist in various forms, the focus of this chapter has been on planar waveguide-based platforms that employ evanescent wave effects as the basis for sensing. The advantages of evanescent wave interrogation of thin film optical sensors have been discussed for both optical absorption and fluorescence-based sensors. These include the ability to increase device sensitivity without adversely affecting response time in the case of absorption-based platforms and the surface-specific excitation of fluorescence for optical biosensors, the latter being made possible by the tuneable nature of the evanescent field penetration depth. 

Deposition of sensor layers is possible on fibre Flow-through cell allowing the optics, planar waveguides, and test strips simultaneous exposure of the membrane to... 

As an alternative to planar waveguiding structures we report here the fabrication of crystal cored fibres in which it is possible to maintain uniform guide dimensions over long lengths. These fibres with organic crystal core material having large second order non-linearity could be used for miniaturization of visible laser sources and realization of parametric amplifiers for optical communications. 

Fig. 13.2 Different types of evanescent sensors, (a) a planar waveguide (b) a polished optical fiber (c) an MNF taper...

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