Design Of Diffractive Elements Research Articles

Paraffin Diffractive Lens for Subterahertz Range—Simple and Cost Efficient Solution

Novel optical materials and manufacturing methods are especially important in the fast growing terahertz (THz) market, where new solutions for shaping and redirecting of radiation are widely investigated. An innovative method of manufacturing refractive and diffractive optical elements (DOEs) for THz spectral range using commercially available and cost-effective devices and materials is presented. The 3D-printing method is used to produce molds, which are then filled with paraffin. The optical elements obtained with this method outperform many commercial ones, especially in higher frequencies. Moreover, a different diffractive element design (as kinoforms of higher order) is proposed to match the resolution limitations of 3-D printing.

Iterative design of diffractive elements made of lossy materials.

Diffractive surface relief elements made of lossy materials exhibit phase-dependent absorption, which not only reduces the efficiency but also distorts the signal if the surface profile is realized on the basis of a phase-only design. We introduce an extension of the iterative Fourier transform algorithm, which accounts for such phase-dependent absorption, and present examples of its application to the design of diffractive beam splitters. The operator required for taking absorption into account is chosen to maximize the efficiency of the found design.

Design of diffractive lenses for focusing surface plasmons

We present a method of designing diffractive optical elements for transforming and focusing surface plasmons. The method is based on a phase modulation of the surface plasmon provided by the dielectric block with varying geometric parameters located on the interface. The problem of SP diffraction by a dielectric block is solved using the rigorous coupled wave analysis. We demonstrate that the modulation can be implemented not only by changing the length of the dielectric block at fixed height, but also by changing the height at fixed length as well as by simultaneous changing of both parameters. The height modulation and combined height–length modulation are believed to be considered for the first time. As an example, the design of diffractive elements for focusing surface plasmons is considered. It is demonstrated that combining the height and length modulations allows us to increase the diffraction efficiency by more than 10%.

Design of diffractive elements at millimeter wavelengths using subwavelength cylindrical microstructures

AbstractWe describe a design methodology for synthesizing diffractive elements based on two‐dimensional subwavelength cylindrical microstructures. We combine a numerical and experimental approach to demonstrate that by varying the diameter, pitch, and depth of subwavelength cylindrical occlusions in a homogenous substrate it is possible to produce multiphase diffractive elements. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1880–1884, 2007; Published online in Wiley Inter‐Science (www.interscience.wiley.com). DOI 10.1002/mop.22571

Diffractive element design for resonant scanner angular correction: a beam retardation approach

A new approach for designing diffractive optical corrective elements with zooming capability to convert nonlinear sinusoidal scanning into linear scanning is proposed. Such a device will be useful for linearizing the angular scan of a resonant mirror scanner. The design methodology is to create a graded index of a refraction device as the reference design with its index of refraction parameters based on beam retardation through propagation in an inhomogeneous medium. The diffractive element is designed by utilizing a binarizing algorithm of the accumulated phase from transmission through the refractive element. In contrast to a prior approach, which was introduced based on the beam propagation through inhomogeneous media, the new approach takes beam diameters into consideration. This makes both the refractive element and its associated diffractive element more robust against beam fanning.

Diffractive element design for resonant scanner angular correction

We propose an optical corrective element with zooming capability to convert nonlinear sinusoidal scanning into linear scanning. Such a device will be useful for linearizing the angular scan of a resonant mirror scanner. The design methodology is to create a graded index of refraction device as the reference design, with its index of refraction parameters based on the propagation of an electromagnetic field in inhomogeneous media. The algorithm for converting this refractive element to the corresponding binary diffractive version is also presented. Design and simulation data are shown.

Effects of abrupt surface-profile transitions in nonparaxial diffractive optics.

It is shown that the failure of the thin-element approximation of diffractive optics may, in the first approximation, be attributed to local diffraction effects caused by the abrupt vertical transitions in binary surface-relief profiles. We determine the field disturbance caused by a single-step transition (of given height) by rigorous diffraction theory. Associating such a disturbance with each individual transition point in the profile, we obtain a computationally efficient refinement of the thin-element approximation for the analysis and design of diffractive elements in the nonparaxial domain. The results agree well with those obtained by global application of rigorous diffraction theory, provided that the smallest features in the binary profile are larger than approximately one optical wavelength.

Optimized quantization for diffractive phase elements by use of uneven phase levels

Many applications of diffractive phase elements involve the calculation of a continuous phase profile, which is subsequently quantized for fabrication. The quantization process maps the continuous range of phase values to a limited number of discrete steps. We present a new scheme with unevenly spaced levels for the design of diffractive elements and apply it to the design of intracavity mode-selecting elements. We show that this modified quantization can produce significantly better results than are possible with a regular or even the bias-phase-optimized quantization scheme that we reported here earlier. In principle this process can be employed to a greater or lesser extent in any quantization process, allowing the fabrication of diffractive elements with much improved performance.

Irregular spot array generator with trapezoidal apertures of varying heights

Design of diffractive elements with trapezoidal apertures of varying heights is proposed, which provides closer-to-arbitrary-shape apertures for generating irregular spot array. The number of apertures is much less than that required by the previous approach with trapezoidal apertures of fixed height.

On pixel-oriented structure parametrization for design of diffractive elements

In two dimensions the design of paraxially operating diffractive elements is typically based on a pixel-oriented parametrization of the structure of the element. Various algorithms have been suggested to optimize such a set of parameters in order to obtain a diffractive element with satisfying optical properties. In particular projection-type algorithms such as the iterative Fourier transform algorithm have been proven to be well adapted to this kind of parametrization. Because of the significant progress which has been made in the availability of computer memory the number of pixels is no longer a serious bottleneck of a pixel-oriented parametrization and therefore the benefit of projection-type algorithms has been increased in recent years. This is demonstrated by comparing designs of diffractive elements as they can be obtained by different methods. Moreover, an additional constraint for projection-type algorithms is described and implemented which allows the control of the minimum feature size of the structure of the diffractive element independent of the chosen pixel size. In general this is necessary to maintain the validity of the scalar approximation for a design which is based on the pixel-oriented parametrization.

On pixel-oriented structure parametrization for design of diffractive elements

On pixel-oriented structure parametrization for design of diffractive elements

Application of optimization algorithms to the design of diffractive optical elements for custom laser resonators

We report what we believe to be the first applications of numerical optimization algorithms to the design of diffractive elements that customize the fundamental mode profile of a laser system. Standard design techniques treat these elements as specific phase-conjugation devices, which leads to performance loss when they are quantized to permit fabrication. Numerical optimization can account for quantization of the element to increase the effective performance. Also, it is shown that allowing a slight increase in the intrinsic loss of the cavity can substantially increase the fidelity of the fundamental mode of the customized cavity. The good discrimination qualities of the mode-selection elements are shown to be unaffected by this process.

Rigorous electromagnetic analysis of diffractive cylindrical lenses

A novel two-region formulation of the rigorous electromagnetic boundary element method (BEM) is developed and applied to practical diffractive cylindrical lenses of continuous profile and with discrete levels (32, 8, and 2). The performance of these diffractive lenses is presented for incident waves of TE and TM polarization, for a range of beam profiles, and for normal and nonnormal incidence. An optimum width of the Gaussian beam is determined. The BEM is shown to be accurate and versatile, providing the numerical and graphical results that are needed for analysis and design of diffractive elements.

Design strategy of diffractive elements with prescribed diffraction angles in non-paraxial region

Diffractive elements designed on the basis of scalar diffraction theory are confined to paraxial optical functions. The reason s the limited range of validity of scalar theory. To overcome this restriction, the design must be performed using rigorous electromagnetic theory, which is able to handle arbitrary feature sizes. However, the optimization concepts for the design of diffractive elements in the paraxial domain fail, when they are applied to rigorous design in the non-paraxial domain. The reason for this failure is discussed and a modified strategy is presented to design diffractive elements in the non-paraxial domain. Multiple beam splitters with prescribed diffraction angles are synthesized.