Fig. 1. Four-layer planar waveguide structure with embedded thin metal layer of silver (Ag).

Fig. 2. Mode profile in transverse XY plane as obtained in (a) analytical calculation and (b) FEM using Comsol Multiphysics 4.3a. We used the values ns=1.453374, nf=1.7264, nc=1.33, df=500  nm, dm=50  nm, and λ=630  nm. RI of silver is calculated with the help of Eq. (6).

Fig. 3. Propagation of fundamental TM mode (Hy) at λ=630  nm. (a) XZ plane projection. (b) Three-dimensional representation from Comsol Multiphysics 4.3a. We used the values ns=1.453374, nf=1.7264, nc=1.33, df=500  nm, dm=50  nm, and λ=630  nm.

Fig. 4. Schematic diagram of stratified medium. Gray layer indicates metal layer and white layer indicates dielectric layer.

Fig. 5. Effective permittivity of the (a) real part and (b) imaginary part of the stratified layer. We took the values dsf=70  nm, dsm=30  nm, and εsd=1.42. εx, solid line; εz, broken line.

Fig. 6. Schematic diagram of the modified plasmonic waveguide. The hashed layers are the metal layers.

Fig. 7. Propagation of fundamental TM mode (Hy) at λ=630  nm. (a) XZ plane projection. (b) Three-dimensional representation from Comsol Multiphysics 4.3a. We used the values ns=1.453374, nf=1.7264, nc=1.33, df=500  nm, dm=50  nm, and λ=630  nm. RI of silver is calculated with the help of Eq. (6). The thickness of dielectric layer is 55 nm and the metal layer is 25 nm in the stratified layer.

Fig. 8. Variation of λres with nclad for different εsd (=n2 dielectric) modified waveguide with df=590  nm, dm=80  nm, nf=1.7264, and ns=1.453374.

Fig. 9. Variation of absorption loss of the fundamental TM mode with wavelength for various analyte indices. We used the values ns=1.453374, nf=1.7264, df=650  nm, dm=73  nm, εsd=2.0164, dsf=55  nm, and dsm=28  nm.

Fig. 10. Comparison of absorption loss between four-layer integrated Kretschmann waveguide with bulk metal layer and loaded with stratified layer. We choose nanalyte=1.33. Both waveguides are optimized to achieve maximum absorption loss.

Fig. 11. Variation of absorption loss of the proposed sensor with gold used in stratified layer. We used the values ns=1.453374, nf=1.7264, df=610  nm, dm=73  nm, εsd=2.0164, dsf=60  nm, and dsm=28  nm. RI of gold is calculated with the help of Eq. (6).