Two-dimensional Grating Structures Research Articles

Efficient electromagnetic analysis of two-dimensional finite quasi-random gratings for quantum well infrared photodetectors

In this work, a recently developed full-wave electromagnetic analysis technique is applied to the simulation of two-dimensional finite quasi-random gratings for quantum well infrared photodetectors. This steepest descent fast multipole method is a mathematically rigorous technique that permits the rapid and accurate solution of the electric field integral equation governing scattering from a quasi-planar structure. In the present application, it enables the efficient and accurate simulation of scattering by finite two-dimensional grating structures interfacing with GaAs. Grating absorption is predicted by evaluating the scattered optical electric field component at the device layer along the growth direction. Numerical examples illustrating the functional dependence of the absorption on grating parameters and wavelength are discussed. The simulation approach presented here should prove to be a useful tool for the a priori design of novel aperiodic, quasi-random and rough surface two-dimensional gratings for infrared imaging applications.

Fabrication of arrays of large step-free regions on Si(001)

In this letter we describe a method for producing large areas of Si(001) surfaces which are (i) free of atomic steps and (ii) arranged in regular patterns on the wafer. The first step is the fabrication of a two-dimensional grating structure using e-beam lithography and reactive ion etching. This grating is then annealed within the appropriate temperature window in ultrahigh vacuum to produce the desired array of (001) step-free regions. We illustrate the success of the method through the use of low-energy electron microscopy for a few repeat spacings on test structures each extending over a 3×3 mm2 area. Alternative processing steps are discussed as well as application to submicron device technology.

Optimal design for antireflective tapered two-dimensional subwavelength grating structures

Techniques for the design of continuously tapered two-dimensional (2D) subwavelength surface-relief grating structures for broadband antireflection surfaces are investigated. It has been determined that the Klopfenstein taper [ Proc. IRE44, 31 ( 1956)] produces the optimum graded-index profile with the smallest depth for any specified minimum reflectance. A technique is developed to design the equivalent tapered subwavelength surface-relief grating structure by use of 2D effective-medium theory. An optimal Klopfenstein tapered 2D subwavelength grating is designed to reduce the Fresnel reflections by 20 dB over a broad band from an air–substrate (ns = 3.0) interface. The performance is verified by use of both a 2D effective-medium-theory simulation algorithm and rigorous coupled-wave analysis. These structures are also shown to achieve this low reflectance over a wide field of view (θFOV > 110°). The pyramidal spatial profile, which has generally been assumed to produce the optimal broadband antireflection grating structure, is shown to require a significantly larger depth to achieve the same performance as a Klopfenstein-designed tapered antireflection grating structure.

Sol-Gel Processed Inorganic and Organically Modified Composites for Nonlinear Optics and Photonics

ABSTRACTThe newly emerging field of Nonlinear Optics and Photonics offers tremendous opportunities for material scientists. In this paper, chemical processing using the sol-gel method is described for the preparation of new composite materials of both a silica glass and a V2O5 gel with a wπ conjugated polymer poly-p-phenylene vinylene up to 5d% by weight. The composite films show highly improved optical quality with large third-order nonlinear optical coefficients, the latter from the conjugated polymer. Optical waveguiding through the film has been achieved. Nonlinear optical studies using femtosecond degenerate four wave mixing and power dependent waveguide coupling have been successfully performed. Also, to investigate the use of such films for optical recording, a two-dimensional grating structure has successfully been produced.