Antireflection structured (ARS) surfaces on GaAs substrates for application with normally incident, randomly polarized, 10.6-microm-wavelength radiation are designed and analyzed. Both one-dimensional (1-D) and two-dimensional (2-D) multilevel profiles are examined with special attention given to multilevel approximations of 1-D triangular and 2-D pyramidal profiles. The 1-D profiles are designed by using second-order effective medium theory (EMT), as we have found zeroth-order EMT to be insufficient when ARS surfaces are designed for use with optically dense materials, e.g., most materials used in the infrared spectral region. We analyze both 1-D and 2-D profiles by using rigorous coupled-wave analysis and find that the more levels the profile contains, the better the ARS surface's response to bias angles, wavelength detunings, and errors in etch depth. Although both 1-D and 2-D profiles can efficiently suppress reflections for unpolarized light, 2-D gratings are advantageous when randomly polarized light is of interest.

A novel thoretical treatment of antireflection-structured surfaces possessing general one-dimensional continuous profiles is presented. Closed-form solutions for the field reflection coefficients of these antireflection-structured surfaces are obtained through the use of effective medium theory and tapered transmission-line theory. Two specific surface profiles (sinusoidal and triangular) are analyzed in detail. Both the sinusoidal and triangular profiles are found to exhibit low reflectances over a broad range of angles and wavelengths. Results obtained with effective medium theory and transmission-line theory are compared with results obtained through the application of rigorous coupled-wave analysis.

No abstract

We report a new class of high-dispersion immersed diffraction gratings for which the reflective nature of the diffraction is provided by the phenomenon of total internal reflection (TIR) regardless of grating tooth shape. Thus, the component can be fabricated from a single dielectric material and requires no metallic or dielectric film layers for high reflection diffraction efficiency. With the absence of metallic absorption, diffraction efficiencies of these TIR gratings can reach more than 99% for 15-20-nm spectral bandwidths, making them suitable for many laser-based technologies.

It is generally accepted that diffractive elements designed for multiwavelength operation require deep surface-relief profiles. We show, however, that thin diffractive elements can be designed to operate with more than one wavelength. A novel, to our knowledge, optimization technique is introduced for this purpose. The maximum phase delay is limited to only a few multiples of 2pi, and the element can implement different functions for different wavelengths. Examples with fan-out gratings are discussed.