Design of antireflection gratings with approximate and rigorous methods

Abstract

High-spatial-frequency gratings can be used as an alternative to thin-film antireflection coatings to reduce the reflectivity at the boundary between two different media. In the case of one-dimensional gratings, the conditions on the grating structure can be approximately determined by the effective medium theory (EMT) in combination with the thin-film theory. For two-dimensional gratings, which can be used to reduce the polarization sensitivity, a corresponding EMT does not exist. We present an estimation of the effective permittivity of two-dimensional gratings. The range of validity of the antireflection grating design by the EMT is determined by the use of rigorous electromagnetic theory. Beyond the validity of EMT, rigorous theory is used to design antireflection gratings with a maximized feature size.

Fabrication and Analysis of Three-Layer All-Silicon Interference Optical Filter with Sub-Wavelength Structure toward High Performance Terahertz Optics

“…3 shows the effective refractive indices of layers #1:SWS and #3:SWS for each orthogonal linear polarization as a function of wavelength. The effective refractive indices exhibit wavelength dispersion, signifying that zeroth-order EMT [12] is no longer valid at shorter wavelength regions. Diffraction, however, does not occurred in the wavelength regions (λ = 16-200 µm).…”

“…We introduce SWS layers to control the refractive indices of each interference layer. According to the effective medium theory (EMT) [12], a SWS layer behaves as a homogenous medium layer with an effective refractive index. Recently, SWS surfaces were being used widely for optical elements following the fast developments in micro-fabrication technologies [13].…”

Broadband Antireflective Properties of Inverse Motheye Surfaces

“…It is easily deduced from (3) and (4) that if the grating periods, and , are small compared to the incident wavelength only the diffractive order will propagate in reflection (i.e., all other diffractive orders will be evanescent). This condition is written mathematically as (5) In this work we are interested in generating only zeroth order AR surfaces thus the conditions given by (5) must be enforced.…”

Architectures and Devices for Millimeter Wave Imaging

“…Unfortunately, implementing this same approach at millimeter wavelengths can be challenging since finding materials with the desired dielectric constants is difficult. An alternative method, originally developed for designing AR surfaces in visible and infrared applications, uses a multi-level subwavelength grating fabricated directly on the surface of a dielectric (1)(2)(3). This technique was biologically inspired by the sub-wavelength surface pattern on the cornea of the common insects including many moths and many butterflies.…”