Waveguides total internal reflection

Fig. 2. Waveguide stmcture showiag the total internal reflection of light. The diameter, is 50 p.m for a standard multimode system, 62.5 p.m for a large...

A hollow waveguide (HWG) is essentially a hollow tube that transports light from one end to the other either by multiple mirror reflection or by total internal reflection. The hollow structure gives them several advantages (i) a high power threshold, (ii) low insertion losses, (iii) no end reflections, (iv) a small beam divergence, (v) robustness and - especially important for sensor applications - (vi) a wide spectral transmission range. 

As the mode propagates within the waveguide by total internal reflection, its exponentially decaying evanescent tail extends into both cover and substrate layers over a distance that is characterised by the penetration depth, dp. The extent to which the evanescent field penetrates the cover layer is of vital importance to the operation of evanescent-wave-based sensors. The penetration depth can be calculated from Equation (1) and is typically of the order of the wavelength of the propagating light. 

Figure 2. Regular reflectance Replication of Snellius law for reflected and refracted radiation at interface in dependence on the refractive indices of the media adjacent to this interface, demonstrating total internal reflectance and evanescent field, exciting fluorophores close to the waveguide or even surface plasmon resonance.

Fig. 9.1 Cross section of a simple three layer slab waveguide, and a plot of the fundamental mode intensity profile. Light rays (dashed line) in the waveguide are confined by total internal reflection at the core cladding interfaces...

Fig. 10.3 Total internal reflection in a three layer waveguide structure. n, (i C, F, S) indicates the refractive index of layer i of the waveguide structure, % > nc s dF is the thickness of the core layer...

Figure 19. (a) Cross-sectional view of the calculated field distribution in a total internal reflection (TIR) coupler in a 2 pm SOI waveguide, and (b) an etched TIR structure in SOI. 

Optical waveguides generally confine light by means of the total internal reflection (TIR) effect, which is accomplished at the interfaces of a high refractive index dielectric medium (core) surrounded by a lower refractive index medium (cladding and substrate) (Fig. 5) [48,49]. 

Table 2 Different materials employed in the fabrication of total internal reflection (TIR) and antiresonant reflecting optical waveguide (ARROW) waveguides...

The actual situation in a dielectric waveguide is somewhat more complicated because when a beam is totally internally reflected, the optical field actually penetrates a finite distance into the lower index material, and the reflected beam experiences a phase shift that depends on both angle and polarization. These effects complicate calculations of the mode characteristics, and split each mode into two modes with orthogonal polarizations, but the simple zigzag picture is adequate for most qualitative considerations (13). 

Wellman AD, Sepaniak MJ (2007) Multiplexed, waveguide approach to magnetically assisted transport evanescent field fluoroassays. Anal Chem 79 6622-6628 Loete F, Vuillemin B, Oltra R et al (2006) Application of total internal reflection fluorescence microscopy for studying pH changes in an occluded electrochemical cell development of a waveguide sensor. Electrochem Commun 8 1016—1020... 

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