Refractive indices effective

Fig. 3.5 Effective refractive index of the LP02 LP08 cladding modes vs. the SRI in HRI coated fiber with (a) 150 nm (b) 200 nm (c) 250 nm, and (d) 300 nm thin overlays...

The coupling coefficients vs. the SRI are reported in Fig. 3.6 b-d for overlay thicknesses of 200, 250, 300 nm, respectively, always with the same coating index of 1.578. From these figures, it can be clearly inferred that increasing the overlay thickness the coupling coefficients curves shift toward lower SRIs as it happens for the effective refractive index curves. 

Fig. 3.8 Effective refractive index sensitivity to overlay RI changes vs. overlay thickness for different cladding modes...

The presence of the HRI coating induces an increase in the effective refractive index of the cladding modes and thus a decrease in the resonance wavelengths. In addition, the spatial shift of the cladding mode field profile toward the HRI overlay promotes a decrease of the overlap integral with the core mode and so of the transmission loss peak. The subsequent evaporation of the solvent molecules from the nano-cavities results in a reduction of its refractive index. This explains the partial... 

When chloroform was added, the equilibrium response of the sensor progressively decreased. This is probably related to the combination of the nonlinear behavior of the effective refractive index of the coupled cladding mode on the overlay refractive index with the nonlinear relationship between adsorbed mass of... 

Fig. 10.1 Binding event between analyte and receptor molecules occurring at the core cover interface of a three layer waveguide structure within the evanescent region of a guided mode. NeS indicates the effective refractive index of the fundamental guided mode...

Here, P0 is the input transmission power, and the parameters yc and ya are the coupling and attenuation parameters, respectively. They are expressed through the attenuation constant, a, the circumference, S, the effective refractive index, n, and the coupling coefficient, k, as follows ... 

In Sect. 15.2 we concluded that refractive index variation in the aqueous cover media shifts the effective refractive index of the waveguide modes. Thus, by monitoring on-line the effective refractive index, the refractive index change can be followed. This is the basic principle of waveguide sensing. 

Various sensor arrangements depend on the actual way how the shift in the mode s effective refractive index is followed. In order to design a sensitive waveguide sensor and to quantify the refractive index changes, the effective refractive index has to be connected with the physical parameters of the waveguide. To this end, one needs to solve the Maxwell s equations using the appropriate boundary conditions10. 

When a grating is used to excite the modes, usually the waveguide film is periodically modulated at the film/cover or film/substrate (or at both) interface (Fig. 15.4b). The incident beam illuminates this grating and one of the diffraction orders will excite the modes. The mode s effective refractive index can be calculated from the so-called grating equation10,30. 

In both cases, the incident angle is monitored using a goniometer or a CCD and converted to effective refractive index values using the above equations. 

Fig. 15.5 Cover penetration depth as a function of the effective refractive index. Using a substrate with RI less than the RI of the aqueous cover solution, the penetration depth into the aqueous cover can be tuned up to infinity. While using glass as a substrate with RI of 1.53 the probing depth has a maximum value around 180 nm, using a light wavelength of 633 nm...

In order to achieve guiding in the deposited polyelectrolyte adlayer, the effective refractive index of the guided mode N must be lower than the RI of the adlayer, A. 

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