We present an algorithm for the design of 1D binary-phase subwavelength lenses that uses a hybrid finite element-boundary element method to model vector diffraction and a simulated quenching routine to perform the optimization. The hybrid method offers several advantages over other analysis techniques in terms of both computational efficiency and storage requirements. To facilitate the rapid convergence of the design, we use two subwavelength lenses, which we designed based on scalar techniques, as initial inputs to the algorithm. The designs produced by both lenses are presented.

We apply a 2D hybrid finite element-boundary element method to the analysis of diffractive optical elements (DOEs). We use the finite element method to solve Helmoltz's equation in the interior of a DOE and use the boundary element method, a Green's function approach, to determine the field exterior to the DOE. We couple the two methods at the DOE surface by enforcing field continuity conditions. We use the hybrid method to analyze the diffraction from a binary-phase lens that has subwavelength features and an eight level diffractive lens.

A direct-search method for the computer design of phase holograms is presented. It is a general method not restricted to any particular optical geometry. The optimization of the hologram is carried out by examining the effect of small changes made to the hologram phase distribution on the image complex amplitude distribution. The effect of the changes is calculated using an approximation to the Fresnel-Kirchhoff integral. Binary phase hologram designs and simulated reconstructions of image intensity distributions are presented.

Dammann gratings are binary phase diffractive optical elements that may be used to split an incoming beam of light into a one- or two-dimensional array of beams. The 1D gratings can be designed for different numbers of diffraction orders (N). For a given value of N there are 2^(N-1 possible 1D solutions. Each solution is distinguished by a particular sign combination of the phases of the diffraction orders and is obtained by optimizing the N adjustable length elements in the grating design. The number of iterations required and the likelihood of converging on a solution is strongly dependent upon the starting point of the iterative process. In an effort to produce an efficient way of designing the gratings for larger N, a methodology to select the starting point was developed. The relationship between efficiency and sign combination of the phases was studied to determine which phase combinations were most likely to produce higher efficiency solutions.

Optical systems utilizing diffractive optics often are non-rotationally symmetric systems. Use of a 3D element based modeling paradigm instead of a conventional surface based approach can make set up and perturbation studies of systems with diffractive optics more straightforward and reliable. This is demonstrated using planar optical interconnect systems for examples.

The analysis and the design of diffractive optical elements beyond the paraxial domain that contain wavelength-scale features must be based on the rigorous electromagnetic theory, i.e. on the solution of Maxwell's equations without introducing deliberate approximations present in scalar theories. In this paper we given an overview of various rigorous diffraction analysis methods and describe in more detail a Fourier-expansion eigenmode method that we call the BKK method. We apply exact diffraction theory to the analysis and the design of conventional diffractive elements as well as to the synthesis of several novel types of components.

The scattering of plane wave incident on multilayer structure, refractive index in each layer being a function of one lateral dimension in layers plane, is considered in symbolic vector- operator form. In this framework a S-matrix propagation algorithm is developed, which rigorously eliminates backscattering from solution procedure. In the case of grating layers with unique-period refractive indices the S-matrix propagation algorithm is implemented with Fourier-transform technique of numerical solution. Stability upon increasing truncation order, layers depths and number, and a high-precision holding of power conservation test within the S-matrix propagation are found. Convergence issue for Fourier-transform implementation in TM polarization is recapitulated and a new recipe of its using is suggested. The examples of optimal designs are considered.

We introduce a novel polarizing beam splitter that uses the anisotropic spectral reflectivity (ASR) characteristics of a high spatial frequency multilayer binary grating. By combining the form birefringence effect of a high spatial frequency grating with the resonant reflectivity of a periodic multilayer structure, the ASR characteristics for the two orthogonal linear polarizations are obtained. Such ASR effects allow us to design an optical element that is transparent for TM polarization but reflective for TE polarization. The properties of the polarizing beam splitter are investigated using rigorous coupled-wave analysis. The design results show that an ASR polarization beam splitter can provide a high polarization extinction ratio for optical waves from a wide range of incident angles and a broad optical spectral bandwidth. Such ASR polarizing beam splitters are uniquely suitable for image processing and optical interconnection applications.

Resonant grating filters based on 2D gratings are investigated experimentally. A two-layer structure, which consists of a uniform guiding layer and a grating layer, is used to achieve a symmetric, low-sideband resonance that is suitable for narrow-band filter applications.

We propose a new method to design and optimize a Diffractive Optical Element (DOE) that performs a quasi-synchronous optical clock distribution within a glass slab bounded onto an MCM substrate, by internal reflections. This design avoids clock skew at very high frequencies, even for non-symmetrical detector placements, and does not need any slab back side element alignments. The method is based on a phase retrieval algorithm that propagates wavefronts by the mean of two different numerical kernels between n different spatial planes. We propose also a method to optimize the detector placement on the MCM module, in order to have the DOE design to work efficiently. We have simulated the effects of typical fabrication and packaging tolerances on the performances of the overall system. A 16 phase level demonstrator is being fabricated on Thomson LCR's MCM specifications and will be tested.

The diffractive optical element (DOE) is modeled as an aspherical thin lens with infinitely large index which can be implemented in commercial lens design software. The corresponding relation between the aspherical coefficient and the DOE phase profile is studied. Broad-band achromatic doublet and triplet designs in the visible wavelength region are discussed to show the design principles. Trade-offs using hybrid doublet or triplet to correct chromatic aberrations are analyzed. In addition, third order aberrations and design freedoms of the DOE and refractive glass thin lenses are compared. For a hybrid design with DOE lens required to be hosted on a flat surface, it is shown that the glass selection for the hosting lens can be used to reduce coma and maintain the same image qualities as the all glass design. Finally, a hybrid 20X 0.5 microscope objective lens is designed and compared with the all refractive optical element design, both approaches achieve similar imaging qualities. It is shown that the hybrid design approach reduces the number of optical elements, other advantages of this design include no high dispersion glasses used and a much more compact optical system.

To solve a special task of laser-beam material treatment, a new diffractive element was designed, fabricated and investigated, which converts a given single-mode CO₂-laser beam into a ring-shaped intensity distribution in the working plane. This was accomplished by application of refined ray-tracing methods and an enhanced micro technology using e-beam generated masks. Relevant steps of calculation and manufacturing of these masks are outlined. First results of measured intensity distribution demonstrate a good conformity with results of computer simulations.

A cost-effective way of producing prototype multi-level phase diffractive optical elements is discussed. It is based on combining multiple projects on a single wafer to spread the non- recurring engineering costs over many users thereby reducing the cost. In this paper we discuss issues of cost versus design that were encountered in a multi-project foundry offered by Honeywell.

With the present trends toward miniaturization, the demand for complex optical elements with surface features is increasing. If these complex optical elements, such as diffractive optics, are fabricated in glass they should be superior to plastic, both in optical quality and environmental stability. Currently diffractive optics are manufactured by either photolithographic methods or single point diamond turning, and neither technique lends itself to high volume, low-cost manufacturing diffractive optics in glass. In recent years advances in the sol-gel process have made it possible to replicate fine-patterned surfaces in high purity silica glass by a molding technique. This paper reviews the results to date of the replication of the following different types of diffractive optics: (1) binary grating, (2) blazed grating, (3) hybrid diffractive/refractive optical element, and (4) plano kinoform.

Micro-optics such as diffractive optics and computer generated holograms are essential components for modern optical design. To reduce their unit fabrication cost we describe a method of reproducing micro-optics in quantities. A true gray-level mask was fabricated in High Energy Beam Sensitive (HEBS)-Glass by means of a single e-beam direct write step. This gray-level mask was used in a optical contact aligner to print a multilevel Diffractive Optical Element (DOE) in a single optical exposure. A chemically assisted ion beam etching process has been used to transfer the DOE structure from the resist into the substrate.

We present an overview of the physics of holographic grating formation and electro-optical switching in a unique polymer-dispersed liquid crystal material. Anisotropic counter-diffusion of liquid crystal (LC) molecules and monomers during holographic recording appears to produce conditions favorable for distorting phase-separated sub-micrometer LC droplets into prolate ellipsoids with major axes along the grating vector. A simple shaped-droplet mechanical model yields results in good agreement with optical diffraction data for polarization properties and switching fields as well as response and relaxation times, as long as droplets can be assumed to be positive uniaxial domains. Normal surface anchoring of LC molecules is likely in these systems, based on NMR data, and this tends to strongly influence the effective refractive index and birefringence of the droplets.

Microtags are microscopic computer-generated holograms with 130-nm features and are mass- producible with EUVL. This fabrication method renders microtags difficult to counterfeit. Applications include tagging and tracking of microprocessors, memory chips, currency, and credit cards.

True time-delay beam steering in optical domain for phased-array antenna application using multiplexed substrate guided wave propagation is introduced. Limitations of practical true- time-delays are discussed. Aspects on making holographic grating couplers are considered. Finally, experimental results on the generation of 25 GHz broadband microwave signals by optical heterodyne technique and 1-to-30 massive substrate guided wave optical fanout with an uniform fanout intensity distribution are presented.

Fine-grained polymer dispersed liquid crystals have recently become available for electrically switchable holographic elements. We explore applications of this novel material to switchable focus diffractive lenses. Several fabrication approaches, holographic and non-holographic, are demonstrated and compared with respect to design flexibility, diffraction efficiency, switching dynamic range, and optical quality. It appears possible to shift optical power between widely separated focal points with a modulation ratio 100:1 on a 10 - 50 microsecond(s) time scale.

Switched optical elements (SOE's) are an emerging class of optical devices. These dynamically addressed optical elements utilize transmissive or reflective structures incorporating a material that exhibits an electrically variable index of refraction. When an electric field is applied to the resulting composite structure, a range of predetermined optical characteristics emerge--spatially modulating, diffracting or redirecting light in a controlled manner. Thus, the effect that the device has on an incident wavefront may be controlled by varying the applied electric field. Although not yet in widespread commercial use, these devices could expand the range of applications for holographic optical elements and diffractive optical elements through a new capability, that of real-time control of the optical function of an optical element. A number of diffractive SOE structures will be discussed here as well as some of the technical and engineering issues that affect the performance of switchable optical elements for use in commercial products.

Holographic gunsights were first demonstrated in the mid 1970s by researchers at the Environmental Research Institute of Michigan (ERIM) under contracts with the Air Force and the Army. The sights utilized He-Ne gas lasers and were designed for use with large weapons systems. With the advent of low cost visible laser diode, ERIM formed a new company, EOTech, to develop, manufacture and market a holographic gun sight for small arms. A hologram is used to reconstruct the image of a reticle pattern that appears at the target plane. Unlike red-dot sights, virtually any reticle pattern, 2D or 3D, can be formed. The design challenges include an opto-mechanical package that is compact, light weight and low cost which can withstand recoils up to 4,000 Gs and provide fine elevation/windage pointing adjustments, and optics that are aberration-free and stable over a wide temperature range. Manufacturing challenges include the mass production of high quality holographic optics at low cost and the precision alignment of the very low f/number optics.

Shift multiplexing is a holographic storage method implemented with spherical wave reference beams. We present the main properties of shift multiplexing, compare it with angle multiplexing, and describe the design of a holographic 3D disk system that is capable of storing 12.4 bits/micrometers ² using this method.

Diffractive optics allow for increased optical performance, decreased size and weight, and decreased systems costs in numerous applications. Many types of optics can be fabricated using diffractive surfaces which are not possible or not cost competitive, using standard refractive lenses. Diffractive optics technology has been developed at Kodak to the point where low cost, mass produced, plastic molded diffractive optics are available on a commercial basis for internal and external use. Rotationally symmetric, aspheric, refractive/diffractive hybrid lenses have been injection molded in 100,000 part test runs and the lenses demonstrated consistent quality throughout the test. In this paper we will discuss design, analysis and fabrication of diffractive optics for some typical applications. These applications include diffractive hybrid achromats for visual applications such as, fixed focus and zoom camera lenses, camera viewfinders, diffractively achromatized laser diode objectives, asymmetric anamorphic diffractive concentrating and spectral filtering lenses for a rangefinding and autofocus applications, the use of diffractive optics in high quality, grayscale laser writers for beam deflection and F(theta) lenses, the use of an array of diffractive elements as concentrating lenses that also separate the incident light into its component colors for CCD array applications. Examples of Kodak fabricated injection molded diffractive hybrid achromats will be analyzed for surface figure and optical performance. Diffractive laser beam deflectors and F(theta) lenses and their production as plastic molded parts will also be discussed. Finally, measurements of diffraction efficiency of molded diffractive optics fabricated at Kodak will be discussed.

A single optical element capable of both wavelength dispersion and imaging would be useful for implementing compact imaging spectrometers. We have fabricated a hybrid refractive/diffractive element that accomplishes these goals. The element is a plano-convex glass lens with a reflective diffractive surface fabricated on the planar side. The diffractive surface combines a blazed grating and several forms of aberration correction. The surface relief profile was fabricated in poly-methyl methacrylate (PMMA) by direct-write electron beam (E-beam) lithography followed by a single development step. The 8.2 mm X 8.2 mm exposure pattern was corrected for both the nonlinear dose response of the PMMA and the E-beam proximity effect. Surface characterization by atomic force microscopy revealed that the grating blaze profile was linear, although the grating was overetched. Optical characterization included diffraction efficiency measurements, knife-edge spot size measurements, and CCD spot irradiance profiles at multiple wavelengths and field positions. The measured spot and field sizes translate to a resolution of 65 wavelength channels in the 400 to 700 nm band of interest and 128 spots along the imaging direction for a 10 mm entrance slit.

The wavelength scaling of an f# 2.5 off axis HOE from 488 nm to 1064 nm has been done. We canceled large induced astigmatism, and other higher order aberrations using a combination of 1 curved reflector, 1 cylindrical lens and one Null CGH bonded to the cylindrical lens. The task was made more difficult by a requirement to fill a 404 nm round aperture and make it focus to a 53 micron diameter spot at the 1/e clip level. The design procedure, the construction sequence and the measured results are presented as a work in progress.

One limitation of diffractive optical elements (DOEs) or zone plate lenses is abundant chromatic aberration. A previous report described a novel system that exploits this typically unwanted effect to create an Image Spectrometer [Lyons 1995]. A DOE performs the imaging and provides the dispersion necessary to separate a multispectral target into separate spectral images. A CCD is stepped or scanned along the optical axis recording a series of these spectral images. This paper reports on the DOE that was fabricated, simulated and implemented in a visible DOIS prototype. The data from this prototype can be interpolated to predict the performance of fieldable DOIS systems that can be designed to operate at ultraviolet, visible or infrared [Hinnrichs 1995] wavelengths for multispectral and hyperspectral imaging in medicine, forensics, industrial and environmental monitoring, as well as military applications.

This paper describes an application of holographic to product diffusers with different optical properties. We report on holographic diffusers for making uniform the infrared source radiation patterns with a variable dispersion angle. The holographic recording geometry provides control over the angular dispersion characteristics of the diffuser. Multiple-lobe and multiple-spot holographic diffusers with 3D scattering patterns have been fabricated. The scattering pattern is achieved by recording a diffuser. We provide some details on the recording set-up and procedure. We discuss some holographic properties of DuPont holographic recording films used in this application. Measurements of the scattering properties are presented for diffusers made in DuPont holographic recording films. For a holographic multiple-spot diffuser, the optical channel frequency response was measured and compared with an opal glass diffuser.

A combination grating is the diffractive relief structure resulting from the superposition of at least two gratings. For the case of two combined gratings, whose individual profiles are described by function f₁ and f₂, the resultant surface relief profile is described by f₁ + f₂. Typical examples are crossed gratings. Experimental and theoretical results for different combination gratings are presented, including examples which cannot be produced using standard holographic or ruling techniques. The applications include diffractive optical variable devices, which are applied to documents as visual high-security features.

Dynamic free-space optical routing system is experimented by a holographic crossbar with single-stage switching architecture. For dynamic operation, electrically addressed liquid- crystal spatial light modulator and diffraction gratings are used in place of passive holograms. Diffraction gratings are consisted of regular cells and have multiple phase delays. This pixelated kinoform phase grating array displayed on SLM deflects a input beam toward a wanted direction or splits a input beam into many beams and then steers them to desired positions. Each grating array is combined with three periods of grating which is constructed by 32 X 32 pixels with equally space phase levels. This system has higher efficiencies and superior characteristics of beam split, and produces asymmetric output beam pattern. In this system, input ports are 3 X 3 and output ports are 5 X 5. It operates at high speed as dynamic free-space optical switch and leads low optical losses.

A new photopolymer holographic recording material based on cationic ring-opening polymerization avoids limitations of conventional holographic photopolymers resulting from the free radical chemistry typically employed. The effects of oxygen, moisture, and component characteristics on holographic recording characteristics are described. Sensitivities greater than 0.1 cm²/mJ and refractive index modulations greater than 5 X 10^-3 are achievable with negligible changes in the physical dimensions (volume change as low as 0.4%) of the imaged material. Linear recording is observed for exposure fluence up to 20 mJ/cm². Good Bragg selectivity consistent with the imaged thickness is observed, and both the angular response and the diffraction efficiency are stable in these materials without the need for post-imaging fixing procedures.