Planar waveguides glass

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.

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. 

Typical of sodium-containing glasses such as ZBLAN or BIG-Na, another way to increase the refractive index is to substitute Li+ for Na+ ions, despite the lower polarizability of lithium ions because of their small size. Actually, Li+ ions are so small that they induce a local collapse of the glassy network resulting in an increase of the densification and of the refractive index [10,24,25]. This property is utilized for the elaboration of fluoride glass planar waveguides by ionic exchange, as described in Sec. 5.3. 

Using planar waveguides made out of Hydex glass, one study demonstrated detection of 500 nM bulk concentration of 24-base target oligonucleotides [30], The surface of the resonator in this case is treated with an epoxysilane compound that reacted with amine-modified probe nucleotides. However, this particular study includes no characterization of limits of detection. 

In the case of planar waveguides the amount of ions exchanged in the glass can be estimated by measuring their refractive index profile n(x). The x coordinate is calculated here into the glass (on the surface x = 0) to the direction perpendicular to its surface. This profile can also be described theoretically using the normalized concentration u(x) of admixture ions introduced into the glass - see equation (5). 

Figure 13. Comparison of refractive index profiles of planar waveguides produced in soda-lime glass doped with ions Ag (a) or (b) with the refractive index profiles produced in BK-7 glass doped with ions Ag (c) or (d).

Rogoziriski R., Electrodijfusion processes with the conversion of polarization direction of electric field in the formation of planar waveguide structures using ion exchange technique in glass, Optica Applicata, 28 (4), 331-343 (1998). 

Figure 35. Propagation of a confinid light ray within a planar waveguide mounted on a substrate Most substrate materials are glasses or crystals with a refractive index of 1.4-2.4. and the cover material is air the thickness of the film ranges from 0.1 to several micrometers, a) Cover, n - n b) Film, n = /if c) Substrate, n = //.,...

---