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Theory and measurement of optical properties of two-dimensionally structured surfaces

Effective Medium Theory (EMT) developed by Rytov was successfully applied to obtain the effective refractive index of sub-wavelength, periodic, one-dimensional structures. Here, an algorithm to solve such bi-dimensional structures is proposed. This provides an approximate method for solving the reflectance and transmittance of two-dimensional structures that are periodic, providing that the radiation wavelength is much smaller than the structure’s periods.

The method starts from the EMT for 1D structures and is applied to solve 2D periodic sub-wavelength structures by considering the latter problem as a superposition of two 1D problems. Such a method is highly useful, considering the long computational time required by the more accurate Rigorous Coupled-Wave Analysis (RCWA) now in use. The theory of the optical properties for normal incidence of inhomogeneous media with two-dimensional periodicity has been developed, based on effective index methods.

A software code has been developed to simulate optical properties of sub-wavelength structures. The theory avoids the approximation made by Ritov, and the calculations are exact. A software code has been written in Visual Basic. This programming language permits a friendly interface with the user, where the parameters can be easily modified. The software allows inclusion of absorbing structures, having an arbitrary number of layers. In this way, arbitrary profiles can be simulated. Also, the code includes the possibility of different angles of incidence, as well as treating separately both polarisations.

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Reported by

Universidad Autónoma de Madrid
Depto. Física de Materiales - Universidad Autónoma de Madrid
28049 Madrid
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