The use of computer aided design (CAD) techniques in micro-optics is suggested in an effort to make the development of optics similar to the development of integrated VLSI electronics. The numerical simulation of integrated micro-optic systems is described as one part of a CAD system. Wave-optical and ray tracing approaches can be used for the analysis. Results are shown for the simulation of an integrated imaging system.
An interactive CAD system for a computer-generated hologram (CGH) is developed to produce many kinds of CGHs in the form of Postscript files, G-code files for NC machines, and HPGL files. These files can later be sent to a laser printer and also a laser beam lithography system. The laser beam lithography system developed has a writing area of 200 mmA approximately 200 mm with 0.5E m positional accuracy. By using the LBL system, some CGHs for optical interconnection and kinoforms are optimized with the simulated annealing algorithm.
A numerical encoding method for digital holography is described. The method directly encodes both the amplitude and phase of a complex number using pure phase transmission. Fabrication techniques are discussed and experimental results are presented that demonstrate the feasibility of this encoding method.
We consider 1-D and 2-D error diffusion (ED), modulated error diffusion, random encoding, and direct quantization computer generated hologram (CGH) encoding schemes. Multilevel (L transmittance levels), macro pixel (N2 CGH pixels per sample) and one CGH pixel per sample, and amplitude and phase encodings are considered. Three diverse applications (matrix-vector processors, spectrum analyzers, and general interconnections for neural nets etc.,) are considered. We find random encoding is best for matrix-vector macro pixels (due to the high local accuracy required, i.e., the fact that one matrix cell maps to one output point), modulated ED (or ED) is best for spectrum analyzers (where good global signal representation is required), and multilevel ED is needed for complex lenses and interconnections (where a very complex global function is required).
We present a new algorithm for the design of phase-only gratings. In general, a successful grating design will shape the relative intensities of the diffracted orders while simultaneously maximizing the light contained in the orders of interest. This iterative algorithm achieves both of these goals. Solutions typically have efficiencies of .90 to 1.00 and can be made arbitrarily close to the desired intensity profile. Convergence to a solution is quick for small numbers of orders (about 20) and the performance of the final solution is fairly independent of the starting point.
To reduce design complexity, the designers of two-dimensional array generators typically assume that the desired array is separable in two-dimensions. However, optical symbolic substitution systems and optical morphological systems require processing elements capable of generating arbitrary two-dimensional arrays. Techniques for designing array generators capable of realizing two-dimensional arbitrary arrays are discussed herein and include modification of the replicating function used to produce the grating, modification of the geometry of the basic period, and a combination of the two techniques. The replicating function is modified using three techniques: the multiplication of each replica by a phase term, the use of intercolumnar shifts, and the use of a nonrectilinear replication grid, for example, a hexagonal grid. The use of a nonrectangular base period, for example, hexagonal or circular, is also capable of changing the geometry of the output array. Using a combination of these techniques it is possible to reduce the complexity of the design problem yet produce nonseparable source arrays.
For one-dimensional binary phase [(0,π) and (0,non-π)] array generators and for one-dimensional continuous or multilevel quantized phase array generators, an upper bound on diffraction efficiency is presented for fan-outs ranging from 2 to 25. The upper bound is determined by optimizing, with respect to array phase, the upper bound on diffraction assuming a coherent array. To determine the upper bound for binary phase gratings restrictions on array phase are imposed. For fan-outs greater than five, the upper bound on diffraction efficiency for continuous phase fan-outs ranges between 97% and 98%; for (0,π)-binary phase fan-outs the upper bound ranges between 83% and 84%; and for (0,non-π)-binary phase, between 87% and 88%.
It has been shown previously that an optical analysis based on a ray trace can prove to be beneficial in the design of binary type phase holograms, because the optical path of each ray must be taken into account. Binary elements converted directly from thick, classical designs to Fresnel/binary equivalent without a redesign will probably have reduced performance. Furthermore, the phase prescription developed by sophisticated lens design programs may not be manufacturable. A simple design example is presented in order to illustrate natural and manufacturing constraints.
We present results characterizing the effects of processing errors on the performance of staircase kinoforms, commonly known as `binary optical devices.' Diffraction efficiency and modulation transfer function data are given for various types of processing errors present in staircase kinoforms of a f/10 Fresnel phase lens having two, four, and eight phase levels. Processing errors include etch depth, linewidth, and mask alignment. Processing errors, especially mask alignment, are shown to have the greatest impact on diffraction efficiency and very little effect on image quality.
We have calculated the angle-resolved scattering from several phase only Fresnel zone plates (lenses) and Dammann gratings (beam splitters). We simulate manufacturing errors by random perturbations of the surface-relief pattern, and calculate the irradiance in the far-field by evaluating the Fresnel diffraction integral. Scattering from perturbations of the etch depth is found to be proportional to the square of the ratio of the perturbation divided by the wavelength. Random perturbations of the pattern edges in Fresnel zone plates causes more scattering with shorter wavelengths than with longer wavelengths, but in Dammann gratings this scattering is independent of wavelength. Scattering increases for either small apertures or small f-numbers; but does not depend on either the number of levels in a Fresnel zone plate, the pattern in a Dammann grating, or the form of the probability distribution function.
The subject matter of this report is the analysis of the dependence of the diffraction efficiency of volume phase gratings on the state of polarization of the read-out wave. I revise the derivation of the two-wave coupled-wave theory starting from Maxwell's equations. The new formulation of the theory differs from the well-known results of Kogelnik's theory mainly in three aspects: (1) The new theory incorporates the effect of form birefringence caused by the layered structure of the refractive index profile. (2) The dephasing parameter which describes the dephasing between the read-out wave and the signal wave has a definite parity. Consequently, the new theory is invariant under the reciprocity transformation of optics. (3) The grating strength for the p-polarization depends not only on the read-out geometry but on the profile of the refractive index as well.
Star couplers are general fan-in/fan-out devices with each individual input furnishing equal light to all outputs. After a brief look at the thermodynamics of star couplers, we describe three distinct types of holographic star couplers: (1) a single-mode coupler with predictable loss, (2) a lossless multimode coupler, and (3) an agile star coupler that reconfigures according to our desire.
Teledyne Brown Engineering designed, fabricated and tested an infrared telescope using only spherical mirror elements. Aberrations were corrected with a binary optic pattern etched onto a germanium lens. The telescope is an F/3, off-axis Gregorian design with no obscuration. The field-of-view (FOV) is 4x8 degrees and it operates in the 8 to 12 micron waveband, with an entrance pupil of 5 cm. The telescope demonstrates that a single binary optical element can correct a significant amount of both pupil- and field-dependent aberrations introduced by tilted spherical mirrors, while maintaining a broad wavelength band of operation. The line spread functions, measured at 10 microns on the telescope, coincided very well with theoretical line spread functions generated by a commercial lens design code.
We propose the application of computer-generated Fourier domain holograms to wavefront synthesis and manipulation in integrated optics. In particular, we describe the use of such diffractive optical elements to split a guided plane wave into several equal-intensity output waves. Gratings with fan-out to 6, 7, and 8 are demonstrated with about +/- 25% (approximately +/- 1 dB) array uniformities.
Phase-only filters that maximize the output signal-to-noise ratio (for colored noise input) are presented. These optimal POFs are then tested with the help of simulations to illustrate their ability to detect targets in natural backgrounds.
The calculation of filters in optical pattern recognition can benefit from the progress made in digital holography. Various calculation methods and theoretical statements that are of importance in optical filtering are provided by digital holography. This is illustrated for the inverse filter.
This paper presents recent developments in volume holography, applicable to chip-to-chip, board-to-board, and processor-to-processor multiwavelength wavelength division multiplexing (WDM) interconnects (and data links) from both subsystem and component points of view.
A new concept polarizer using a birefringent diffraction grating has been developed. The operating principles and fabricated polarizer characteristics are described. The fabricated element has more than 20 dB extinction ratios for both polarization lights which are sufficient for use in optical disk heads. The polarizer is easily mass manufactured by the planar batch process. A holographic optical element that is combined with this polarizer function is proposed. Applications of the holographic optical element for an optical disk read/write head are also described.
We describe a computer generated hologram (CGH) to produce the Hough transform (HT) with a new output format that eliminates the ambiguity and noise caused by overlapping outputs in the Hough space. The new format HT CGH is designed and fabricated as a multilevel phase CGH which greatly increases the light efficiency and requires less space bandwidth product (SBWP) compared with amplitude HT CGHs reported previously. New format HT phase CGHs have been fabricated and tested in the laboratory and these results are presented. Optical laboratory data obtained using these CGHs are presented for multitarget tracking of point targets.
The application of a ray-tracing methodology to computer-generated hologram (CGH) as a special imaging lens is presented. The design is based on a relatively analytic solution involving the minimization of the mean-squared wavefront deviation of the output wavefront, i.e., by using the optimization techniques one might use a computer program to determine the hologram phase transfer function which exhibits minimum aberration of the output wavefront. We design the special imaging lens of the CGH to extend the field of view of the optical system. It demonstrates much lower aberrations than the comparable spherical image lens of the CGH. We use the ray-tracing equations to determine the image properties of the system. Some experimental results are shown.
A shared aperture using only reflective optics for two coherent beams with different wavelengths is desired. Beams that share an aperture are colinear, and they have the same transverse phase profile across the aperture as their respective sources. A shared aperture system composed entirely of reflective phase gratings is presented here. Using the Talbot effect that is observed in Fresnel diffraction from periodic objects, the phase of the beams is preserved, and the efficiency of the system is maximized. An experimental Talbot shared aperture system using HeNe and HeCd beams has an efficiency of 88.1% for the HeNe beam and 70.3% for the HeCd beam. These measured efficiencies agree well with computer simulations.
A single hybrid refractive/diffractive lens element is designed to replace the multiple refractive cylindrical lenses present in the parallel readout optical disk system. The new system has less elements, simplified alignment, and significantly reduced aberrations. Experimental results are presented.
A holographic disk scanner for a laser vision sensor that can locate objects under hazardous conditions has been developed. The laser vision system utilizes a CO2 laser with a wavelength of 10.6 micrometers , and has excellent transmission characteristics through an environment of smoke and flames. In designing the holographic disk scanner, the diffraction efficiencies were calculated for substrate materials and grating profiles while considering the relationship between the grating period and the groove depth. Based on the calculations, surface-relief transmission gratings were fabricated using germanium (Ge) as a substrate, thereby obtaining a maximum diffraction efficiency of 62.9%. Using the gratings, a ten-facet holographic disk scanner was constructed. By rotating the scanner at 6000 rpm, high-speed image construction of 7 frames/sec, a resolution of 10 cm, and a field of vision of +/- 4 degree(s) were accomplished.
Holographic notch filters (HNF) are replacing dielectric filters in certain optical systems that incorporate single line laser sources. HNF characteristics, physical structure, specification, benefits, and customer acceptance are described for laser spectroscopy and laser surgery applications.
In this contribution, new computer-generated diffractive optical elements are proposed that are able to concentrate an incident beam into line segments of various lengths, arbitrary inclination in respect to the optical axis, as well as any distribution of the longitudinal intensity. The approach is based on the energy conservation principle taken in the scope of the geometrical optics approximation and equations of the paraxial ray tracing. Hyperbolic zone plate, linear zone plate, conical zone plate, as well as elements focusing light into the segment of the optical axis are shown to be limiting cases of the proposed elements.
Volume phase holographic gratings provide the high diffraction efficiency often required from holographic optical elements. In order to provide wide angular bandwidth, high index modulation is also required. A new addition to the family of Du Pont holographic photopolymer films has significantly higher index modulation for the grating spacings typical of holographic transmission elements. In this paper, the recording of volume phase transmission gratings in this holographic photopolymer is described. The dependence of holographic properties on exposure conditions, grating characteristics, and processing are discussed. The performance characteristics of holographic optical elements produced in this material are also presented.
Holographic optical elements (HOEs) are produced in a variety of materials for a wide range of applications. An ideal holographic recording medium for holographic notch filters would be capable of high index modulation, produce high optical densities, exhibit low scatter, haze, and absorption, and be able to survive harsh environments. None of the currently available recording media possess all of the above characteristics; thus the material selected must suit the application requirements. This paper discusses experimental results regarding the holographic and optical properties of two holographic recording materials: dichromated gelatin (DCG), and Du Pont HRF-700 photopolymer. The strengths and limitations of the two materials, as applied to notch filters, are discussed, and data are presented showing the fundamental characteristics of each.
We describe the formation and selected properties of composites made from DMP-128 transmission holograms and the nematic liquid crystal E7. Analysis of the liquid crystal structure in the composites by polarizing microscopy, refractive index measurements, and differential scanning calorimetry produced two primary observations. (1) Treatment of the interior surface of the porous holograms controls the nature of the liquid crystal alignment; both planar and homeotropic alignment is possible for the E7 composites. (2) Incorporation of E7 into DMP composites significantly reduces its degree of order compared to that for a standard nematic cell.
In this paper, the real-time effect as well as other primary properties of nongelatin dichromated (NGD) holographic recording film are presented briefly. A real-time diffraction efficiency (RTDE) of up to 25% has been obtained in experiment.
In this paper we present an antihumidity dichromated gelatin holographic recording material called AHDCG. It possesses the good optical performances of common dichromated gelatin (DCG). The holograms produced by this material, under common laboratory circumstances (RH > 80 usually), have been kept for more than one year without degradation in efficiency. The method of making this material, the surface structure, and its holographic properties are presented.
In this paper it is presented that holographic optical elements (HOEs) generated by computer are copied on nongelatin dichromated holographic films (NGD) [1,2], which has a characteristic of controlling groove profile and copying easily etc. This may be a new method to fabricate HOEs with continuous phase modulation. The diffraction efficiency of the HOEs on NGD, e.g., NGDHOE, has been increased over three times comparing with that of original CGH reduced—photographed and bleached. The depth of relief patterns can be controlled by exposure. It is indicated that ti'e final NGDHOE can be used as a master of embossment directly in plastic film. This would be an efficient way that to produce cheaper and lighter weight HOEs in large scale. KEYWORDS: CGH, NGD, HOE, etching, blazing grating
This paper proposes a new transducer for displacement measurement, which realizes proportional error measurement using a holograghic optical element (HOE) to process optical information. The principle of the transducer is analyzed theoretically. The experiment results and schematic diagram used for making the HOE are given.
Results of the investigations of holographic diffraction grating (with spatial frequencies from 600 to 3600 mm-I) production processes on the thin- film light-sensitive systems As2S3-Ag,As2Se3-Ag,GeSe2-Ag and thin film layers As2S3,As2Se3 and GeSe2 are presented in this report. Experimental investigations and model calculations of relief formation processes on such resist media were carried out. The possibility of composite relief production in chalcogenide vitreous semiconductor (ChVS) metal structures with the help of photodoping and photostimulated solubility changes in ChVS is shown. Diffraction efficiency η dependencies from exposition, wavelength, developing conditions, and additional uniform exposure were investigated. Ways of optimizing such parameters are shown. The η spectral and angular dependencies of the gratings were studied, and results of electronmicroscopic groove profile investigations are presented. Holographic gratings with 70 - 85% efficiency for polarized light and stray light level approximately 10-6 were produced.
A new photo-lithographic imaging (PLI) method to produce high efficiency volume phase-only CGH has been developed. PLI technique utilizes Du Pont proprietary materials and processes to replicate a binary intensity CGH, recorded on a chrome photomask-master, into a dry photopolymer. By changing the refractive index of the photopolymer in the imaged areas the intensity modulated pattern in the chrome photomask-master is converted into a volume phase modulated pattern with a single lithographic step. This technique was used to fabricate a variety of computer generated holographic optical element (CGHOE), such as on-axis and off- axis Fresnel zone plates and array illuminators. Diffraction efficiencies up to 98% were observed for a CGHOE consisting of a 10 X 10 array of off-axis Fresnel zone plates. Such CGHOEs can be fabricated on a variety of substrates and in different configurations, providing substantial technological and economical advantages over existing conventional manufacturing techniques for diffractive binary CGHOEs.