Fig. 1. Cross section of the simulation model (50  μm×50  μm) comprising a GaAs/AlGaAs waveguide with a 6 μm AlGaAs layer (optical buffer), a 6 μm GaAs layer (actual waveguide), and a 20 μm thick GaAs substrate. The width (w), the thickness of the absorbed layer (dl) simulating an analyte, and the refractive index of the outer medium (no) were varied during the simulations.

Fig. 2. Dependence of the modal behavior on the width of the waveguide (A) for the amide region (1800–1600  cm−1), and (B) for the carbohydrate region (1200–1000  cm−1). (C) The fundamental guided TM00 mode of a 5 μm wide waveguide, and (D) the first-order TM01 mode of a 11 μm wide waveguide at a wavelength at 1700  cm−1 are also illustrated.

Fig. 3. Exponential fit of the effective refractive index of a 13 μm wide waveguide at a wavelength at 1100  cm−1 as a function of the absorbing analyte layer thickness.

Fig. 4. Linear fit of the effective refractive index of a 5 μm wide waveguide at a wavelength at 1700  cm−1 as a function of the refractive index of the outer medium.

Fig. 5. (Top) Normalized electric field component along the center axis of a waveguide versus the waveguide width. Inset illustrates the waveguide section of the simulated electric field for a 5 μm wide waveguide at 1700  cm−1. (Bottom) Magnified view of the electric field above the waveguide surface (i.e., the evanescent field).