Abstract
Facet reflections at the waveguide-air interface for strongly-guiding
waveguides with sub-wavelength scale dimensions do not follow the usual Snell's
law. Significant amount of reflected power can be channeled into higher order
modes as well as radiation modes. This paper shows for the first time how
the exact analytical solution of the facet reflection can be obtained by using
a new technique based on Fourier analysis and perturbative series summation
without the need for approximation or iteration. The proposed analysis enables
the distribution of power reflected into various guided and radiation modes
to be readily computed. Through this technique, a spectral overlapping criterion
and a coupling matrix are derived that analyze effectively the power distribution
among all the strongly and weakly-coupled radiation modes in an end-facet
reflection. Accurate pre-determination of the number of radiation modes for
efficient computation without compromising resultant accuracy is achieved.
More importantly, the anomalous wave reflection behaviors at the facet of
a strongly-guiding waveguide are presented. These include anomalous high radiation
modes coupling as a function of cladding refractive index not reported before.
This paper further includes an exemplary illustration of the analysis based
on a symmetric planar nano-waveguide with high refractive index contrast for
both TE and TM polarization under fundamental incident mode.
© 2012 IEEE
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