Silicon waveguides

Fig. 9.7 The effective index change induced by the adsorption of a 2 nm thick molecular layer with index n 1.5, calculated as a function of core thickness for the TM mode propagating in glass, polymer, silicon nitride, and silicon waveguides. The right vertical axis shows the equiva lent modal sensitivity...

Fig. 9.12 Top view of folded path waveguide layouts using (a) a double spiral and (b) a grid configuration. Both images are taken using an InGaAs infra red camera while X 1550 nm light is coupled into the silicon waveguide chip...

Fig. 9.16 The calculated output spectrum of a silicon waveguide ring resonator sensor at critical coupling (t a) and for t 0.8a. The assumed ring radius is R 150 pm...

Fig. 9.17 Silicon waveguide ring resonators employing (a) a directional coupler (DC), and (b) a multimode interference (MMI) coupler, as viewed from above using a scanning electron micro scope...

Schmidt, B. Almeida, V. Manolatou, C. Preble, S. Lipson, M., Nanocavity in a silicon waveguide for ultrasensitive nanoparticle detection, Appl. Phys. Lett. 2004, 85, 4854 4856... 

Planar waveguides can be differentiated depending on the fabrication techniques employed those fabricated by the deposition of layers onto a substrate (such as silica on silicon waveguides) and those fabricated by means of diffusion techniques, by generating an area of a higher refractive index than the rest of the substrate, such as titaniumdithium niobate waveguides (Fig. 6). 

Rong G, Najmaie A, Sipe JE, Weiss SM (2008) Nanoscale porous silicon waveguide for label-free DNA sensing. Biosens Bioelectron 23 1572-1576... 

Fig. 2 Propagation velocity estimates for silica (a) and gold nanoparticles (b) on a silicon waveguide. U bs and UscM represent the absorption and scattering components of Eq. 10, and Uo is the summation of the two. Velocities...

Fig. 4 Electromagnetic force on a particle as a function of position. Gradient force calculated for 600 and 400 nm spherical glass particles on a silicon waveguide.

Porous Silicon Waveguides for Small Molecule Detection... 

Here we focus on the capabilities of a porous silicon waveguide biosensor for the detection of small molecules. The porous silicon waveguide, shown schematically in Figure 3a, consists of two porous silicon layers. Light is trapped in the top, high refractive index layer, based on total internal reflection at the interfaces with air and the bottom, low refractive index porous silicon... 

Figure 4 shows the relationship between the porous silicon waveguide resonance shift and electric field interaction with biomolecules, in this case 24-base pair DNA, inside the porous silicon waveguide. In this first order analysis (25, 24), the total power of the field and its distribution remains constant while... 

Calculations have been performed to estimate the detection limit of the porous silicon waveguide biosensor based on the percent of optical power interacting with biomolecules in the waveguide (25). The sensor is capable of detecting pictogram quantities of small molecules in a 1 mm surface area. The detection limit depends on the number of probe molecules immobiUzed on the pore walls, the size of the biomolecules relative to the size of the pores, and the efficiency at which the probe molecules capture the target species. 

Figure 4. The response of the porous silicon waveguide sensor upon exposure to biomolecules depends on the percent of the optical field interacting with the molecules. The inset shows the field distribution in the waveguide with the majority of the field inside the porous silicon (LP = low porosity layer, HP = high porosity layer) where biomolecules may be captured. Therefore, even if only a few biomolecules are present in the waveguide, they can be detected...

Figure 5. Experimental measurement of porous silicon waveguide resonance after several functionalization steps and exposure to either (a) complimentary DNA, (b) non-complimentary DNA, or (c) buffer solution. The small shift due to DNA hybridization is easily within the resolution of the prism coupler rotation stage of0.002°. (d) Histogram summarizing the selectivity of the porous silicon waveguide sensor to 24 base pair DNA. DNA hybridization (complimentary DNA shift) can be clearly distinguishedfrom the low level of non-specific binding (mismatch DNA shift) and the noise floor of the measurement system...

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