Binary blazed reflection gratings.

A reflection grating with a binary surface profile is presented that has high diffraction efficiency. The measured intensity for the + 1st diffracted order was 77%. The binary grating is composed of a minilattice with feature sizes comparable with the wavelength of the incident light. The overall structure is designed in such a way that it imitates a conventional blazed grating. The grating also has interesting polarization properties. The main part of the TE-polarized light is diffracted into the 1st diffracted order, and most of the TM-polarized light remains in the 0th diffracted order. The measurements of the grating are compared with rigorous diffraction theory and found to be in reasonable agreement.

Dielectric binary blazed gratings.

Artificial index gratings, which are composed of binary microstructures of sizes less than the incident wavelength, are analyzed as functions of the filling factor or duty cycle of the microstructures. Different models for calculating the optimum duty cycles to produce high blazed diffraction efficiency are compared. Blazed binary grating designs in a material with a refractive index n = 2 show theoretical diffraction efficiencies as high as η = 80%. In the semiconductor material silicon, which has a refractive index n = 3.4, theoretical diffraction efficiencies as high as η = 70% are predicted.

Diffractive beam splitter for laser Doppler velocimetry.

A miniaturized sensor head for the optical measurement of velocities of fluids based on laser Doppler velocimetry is demonstrated. Holographic optical elements mounted on a glass substrate are used for beam splitting and deflection. Volume holograms in dichromated gelatin exhibit good optical efficiency (75% transmission of a cascade of two holographic optical elements). With diffractive devices one can achieve achromatic behavior that makes the sensor insensitive to wavelength drifts or mode hopping of a semiconductor laser.

Upper bound on the diffraction efficiency of phase-only fanout elements.

For one-dimensional binary-phase [(0, pi) and (0, non-pi)] fanout elements and for one-dimensional continuous or multilevel quantized phase fanout elements, an upper bound on diffraction efficiency is presented for fanouts ranging from 2 to 25. The upper bound is determined by optimizing with respect to the array phase the upper bound on diffraction efficiency for a coherent array. To determine the upper bound for binary-phase gratings, restrictions on the array phase are imposed. For fanouts that are >5, the upper bound on the diffraction efficiency for continuous phase fanouts ranges between 97 and 98%; for (0, pi)-binary-phase fanouts the upper bound ranges between 83 and 84%; and for (0, non-pi)-binary-phase, between 87 and 88%.

Concept for an optical bus-type interconnection network.

A concept for parallel optoelectronic bus-type interconnections (many participants-many participants) is given. The choices between multimode and single-mode fan-ins in free-space optical systems are discussed. When one single space-invariant multiple beam-splitting system is used for fan-out and fan-in simultaneously, the energy requirements for communications scale with 2N (for N participants on each busline), which is compared with N(2) for space-variant systems. A simple demonstration experiment with a Dammann grating used as a multiple beam splitter is shown, and in a design example the theoretical performance is discussed.

Possibilities and limitations of space-variant holographic optical elements for switching networks and general interconnects.

Space-variant optical elements are necessary for realizing optical interconnects of arbitrary design. For such applications, planar holographic optical elements offer the highest degree of flexibility and ease of production; however their diffraction-based operation gives rise to chromatic aberrations. Here estimates for the number of independent space-variant interconnects, their spatial tolerances, and their wavelength stability are considered for close-cascade, and related, geometries.

Artificial distributed-index media fabricated by zero-order gratings.

Zero-order gratings are grating structures with a period that is small compared with the wavelength of light. Only the directly transmitted or reflected light, the zero diffraction order, is nonevanescent and propagates in a distance from the grating. Thus the grating behaves like a slab of ordinary homogeneous material with an effective refractive index. By varying the material composition, i.e., by variation of the duty cycle of the grating, the effective refractive index can be changed. A grating with variable duty cycle therefore behaves like a material with distributed index. Based on such artificial materials, distributed-index elements are proposed. The physical principle is demonstrated with water waves.

Array generation with lenslet arrays.

Lenslet arrays can be used as phase gratings, having many diffraction orders with equal intensity. Applications are multiple imaging and illumination of arrays of optical or optoelectronic devices in digital optics. The homogeneity of the intensities within the array can be improved by using field lenslets. The basic theory as well as experiments with diffractive and with graded index lenses are shown.

Holographic quarterwave plates.

Quarterwave plates can be made as holographic gratings in positive photoresist. We studied the effect of the grating period and relief depth on the phase retardation and on the rotation of the polarization of the transmitted light. Experiments were performed with gratings of different periods, which also exhibit an antireflection property.

Optical design of programmable logic arrays.

Regular free-space interconnects such as the perfect shuffle and banyan provided by beam splitters, lenses, and mirrors connect optical logic gates arranged in 2-D arrays. An algorithmic design technique transforms arbitrary logic equations into a near-optimal depth circuit. Analysis shows that an arbitrary interconnect makes little or no improvement in circuit depth and can even reduce throughput. Gate count is normally higher with a regular interconnect, and we show cost bounds. We conclude that regularly interconnected circuits will have a higher gate count compared with arbitrarily interconnected circuits using the design techniques presented here and that regular free-space interconnects are comparable with arbitrary interconnects in terms of circuit depth and are preferred to arbitrary interconnects for maximizing throughput.

Array illuminator based on phase contrast.

An array illuminator converts a uniformly wide beam losslessly into an array of bright spots. These spots provide the necessary illumination for microcomponents such as optical logic gates or bistable elements. Such elements may serve as devices in a 2-D discrete parallel processor. We propose an array illuminator with a phase grating on its front end. The phase grating is illuminated uniformly and then converted into an amplitude image by means of a phase contrast setup. The bright spots of the amplitude image are to be used for illuminating the array of microdevices of a digital optical computer.

Accuracy of phase shifting interferometry.

The accuracy of phase shifting interferometers is impaired by mechanical drifts and vibrations, intensity variations, nonlinearities of the photoelectric detection device, and, most seriously, by inaccuracies of the reference phase shifter. The phase shifting procedure enables the detection of most of the errors listed above by a special Lissajous display technique described here. Furthermore, it is possible to correct phase shifter inaccuracies by using an iterative process relying solely on the interference pattern itself and the Fourier sums used in phase shifting interferometry.

Map transformations by optical anamorphic processing.

A map transformation is a willful geometrical distortion of an image. Examples are rotation, shearing, and local stretching of the coordinate system. We describe an optical setup that performs a map transformation by spatial filtering with two phase-only filters. The system is able to perform in x- and y-linear distortions (e.g., shears) as well as certain x- and y-nonlinear distortions. The distorting filters introduce no aberrations. The object may radiate coherently, incoherently, or partially coherently. Some experimental results are presented.