Dorian Kermisch

Fourier spectrum of halftone images

An analytic expression has been developed that can be used for computing the Fourier spectrum of any halftone image as a function of the original continuous-tone image and the halftone process. This result takes into account the nonlinear effects of the threshold step in the halftone process. Although the result is general and can be applied to any original image, in some cases of periodic images the Fourier components of the halftone image are particularly easy to compute. We show important differences between spectra of halftone images and scanned or sampled images. In halftone images, significant image detail is maintained at spatial frequencies greater than half of the screen frequency and aliasing or moire patterns depend upon object contrast and upon the halftone function differently from similar patterns which occur in scanned or sampled imagery.

Nonuniform Sinusoidally Modulated Dielectric Gratings

A simple, three-dimensional, holographic grating consists of a sinusoidally modulated dielectric slab. The assumption that the modulation index, δ, is constant is at most a first-order approximation. Usually, the light beams used in making the grating are attenuated inside the recording material, hence δ varies within the dielectric slab. From known solutions for the electromagnetic field diffracted by a uniform dielectric grating, solutions for the case when δ is not constant are found, first for a lossless and then for a lossy dielectric grating. The effective modulation index of the grating at exactly Bragg-angle incidence is given by the averaged value of δ over the slab thickness.

Image Reconstruction from Phase Information Only

A quantitative analysis of the effect on image reconstruction of discarding the amplitude information contained in a wavefront reflected by a diffusely reflecting, coherently illuminated surface is given. The image reconstruction from a phase record alone is analyzed for the perfect and imperfect phase-matching cases.

Partially coherent image processing by laser scanning

We describe a class of image-processing optical systems, based on a laser scanner, whose output is an electronic video signal from a simple photodetector. We show that certain image-processing properties of these systems are exactly equivalent to the properties of conventional, partially coherent, image-processing optical systems. These systems are of interest when we want to combine optical image processing with further electronic processing. Some applications, such as electronic read out of phase-encoded images, are discussed.

Principle of equivalence between scanning and conventional optical imaging systems

The principle of equivalence between the imaging properties of scanning and conventional imaging systems has been proven in the past by assuming scalar sources of radiation and isotropic media. We prove here its general validity for optical systems with vector, electromagnetic sources of radiation and any optically nonactive media.

Efficiency of Photochromic Gratings

A method for computing the diffraction efficiency of photochromic, transmission holographic gratings is developed. The nonuniform exposure through the depth of the material is taken into account. The efficiency depends strongly on the modulation of the refractive index. The diffraction efficiency of some typical photochromic gratings is calculated, and efficiencies of up to 10% are predicted.

Image formation mechanism in the γ-ruticon

The gamma-ruticon is an image buffer device that has already been described in the literature. We present here the theory of its image formation mechanism and derive the total device image transfer function. We show that we can separate the ruticon imaging mechanism into three distinct and independent parts: the photo-conductor mechanism that produces an electrostatic image; the elastomer mechanism that transforms the electrostatic image into a surface relief image; and the optical readout mechanism that translates the surface relief image into a conventional image. The influence of each of these mechanisms on the characteristics of the final image is investigated.

Prism‐waveguide coupling efficiency for waveguides with an arbitrary refractive‐index profile

Using the WKB approximation, we generalize Ulrich’s solution to the optimum coupling efficiency of a prism‐waveguide coupler, so that it can be applied to a waveguide with an arbitrary refractive‐index profile. As an example, we give an analytic solution to a waveguide having an exponential refractive‐index profile.

Visualization Of Large Variation Phase Objects

A hybrid optical-electronic method for the display of large variation phase objects is described. It displays a conventional image whose local irradiance (or density) is proportional to the phase of the object. The method requires a much simpler optical system than previously proposed methods.

A Practical Integrated Optics Device

We present the theory and experimental results of the performance of an integrated optics device that is composed of a prism-waveguide dual coupler. In the device, a circular and collimated beam of light is coupled into a LiNb03 Ti indiffused waveguide, with an efficiency of 94%, propagates 1 cm. in the waveguide, where electrodes can process the optical signal, and then the guided light is coupled out by the same prism with the same high efficiency. After presenting the theory, which is applicable to any type of waveguide, we show the experimental results that demonstrate the high efficiency throughput, and the high degree of collimation of the emerging beam.