Spatial distribution of light fields in a silicon conical waveguide

The spatial distribution of monochromatic light fields is studied in a tapered silicon fibre with the subwavelength aperture. The lowest-order electric TM₀₁ mode is analysed theoretically in a cone with perfectly reflecting metal walls filled with a light absorbing medium. Exact formulas and approximate expressions are obtained for a medium with the complex permittivity, which describe the spatial dependences of the electric and magnetic energy densities inside the cone. The behaviour of the field at the waveguide exit is analysed for the aperture diameter as small as ~1/30 of the wavelength. The main attention is devoted to the transmission coefficients of the probe, which were calculated for a wide range of its geometrical parameters in the wavelength region from 400 to 830 nm. It is found that silicon provides a substantial increase in the output light energy density at the optical probe end both in the IR and visible spectral regions compared to glass.