Reverse waveguide

Several techniques can be employed to couple an optical beam propagating in free space into a thin-film optical waveguide. Grating coupling and prism coupling (Fig. 15.4) are briefly outlined here, since these methods are applied in actual reverse waveguide and MCLW configurations, respectively. 

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

Fig. 15.6 Comparison of the cover penetration depths (a) and cover RI sensitivities (b) of conventional and reverse waveguides (marked with RW) for the zeroth and first order TE and TM modes. Reprinted from Ref. 34 with permission. 2008 Elsevier...

Fig. 15.8 Comparison of resonant peak position (a) and peak amplitude (b) transduction for a grating coupled reverse waveguide. Reprinted from Ref. 36 with permission. 2008 American Institute of Physics...

Living Cell Detection Using Nanoporous-Silica-Supported Reverse Waveguides... 

The grating-coupled nanoporous-silica-supported reverse waveguide chip was also applied for monitoring the attachment and spreading of Human Dermal Fibroblast cells to the surface16. As in the bacteria experiments, the waveguide surface was coated with a thin layer of poly-L-lysine layer to improve cell attachment and spreading. 

A new one-dimensional mierowave imaging approaeh based on suecessive reeonstruetion of dielectrie interfaees is described. The reconstruction is obtained using the complex reflection coefficient data collected over some standard waveguide band. The problem is considered in terms of the optical path length to ensure better convergence of the iterative procedure. Then, the reverse coordinate transformation to the final profile is applied. The method is valid for highly contrasted discontinuous profiles and shows low sensitivity to the practical measurement error. Some numerical examples are presented. 

Optical sensors (Figure 1) can be defined as devices for optical monitoring of physical parameters (pressure1, temperature2, etc.) or (bio)chemical properties of a medium by means of optical elements (planar optical waveguides or optical fibres). Chemical or biochemical fibre-optic sensors3 are small devices capable of continuously and reversibly recording the concentration of a (bio)chemical species constructed be means of optical fibres. 

Horvath R., Pedersen H.C., Demonstration of reverse symmetry waveguide sensing in aqueous solutions, Appl. Phys. Lett. 2002 81 2166-2168. 

Skivesen, N. Horvath, R. Pedersen, H. C., Multimode reverse symmetry waveguide sensor for broad range refractometry, Opt. Lett. 2003, 28, 2473 2475... 

Fig. 8.5 A scanning electron micrograph of a silicon dioxide mold with reverse patterns the left and right trenches create a bus and a microring waveguides, respectively. The high aspect ratio protruded wall between trenches is used to stamp out a narrow coupling gap. Reprinted from Ref. 42 with permission. 2008 American Vacuum Society...

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. 

Horvath, R. Skivesen, N. Larsen, N. B. Pedersen, H. C., Reverse symmetry waveguide for optical biosensing, In Frontiers in Chemical Sensors. Novel Principles and Techniques Orellana, G. Moreno Bondi, M. C., Eds. Springer Series on Chemical Sensors and Biosen sors Springer, Berlin, 2005, Vol. 3, 279 301... 

The KTP chips are individually immersed in a molten bath of a mixture of RbNOs and Ba(N03)2. Within this bath, the Rb ions diffuse into the unmasked portions of the KTP chip, while the K ions diffuse out of the substrate and into the bath, shown in the illustration in figure 6. In the diffused regions, the rubidium ions increase the index of refraction relative to the undiffused KTP and thus form the optical waveguide. Note that due to the presence of barium, there is an increase in the index of refraction and the ferroelectric domain in the diffused region is reversed and hence the term chemical poling is used for this process. 

Figure 5.20 — Reversible flow-through optical waveguide gas sensors using a reagent immobilized on the inner walls of the tube for the determination of moisture (water) (A) and sulphur dioxide (B). For details, see text. (Reproduced from [64] and [65] with permission of the American Chemical Society and Elsevier Science Publishers, respectively).

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