Abstract
Materials in the terahertz (THz) region have high refractive indices, thus leading to
significant Fresnel reflection loss. We present a step-by-step 2-D THz antireflection grating
design procedure using thin film theory and coupled-coefficient-matrix method. A thin film with
desirable properties is first optimized by genetic algorithm, and a ‘translation’ from thin film
to multilevel grating is then implemented with the coupled-coefficient-matrix method. A final
smoothing step leads to a square-pyramidal-frustum grating. Using rigorous coupled-wave analysis,
we demonstrate a subwavelength square-pyramidal-frustum grating based on silicon producing
broadband (0.5 to 5 THz) and efficient (transmittance>95%) polarization-independent
antireflection effects. The grating parameters are evaluated, showing that our design is resistant
to parameter deviations such as grating depth and incidence angle.
© 2013 IEEE
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