Gal Shabtay

Tunable birefringent filters - optimal iterative design.

More than 50 years ago, B. Lyot and later on I. Solc introduced new types of optical filters called birefringent filters. Such filters take advantage of the phase shifts between orthogonal polarization to obtain narrow band filters. It requires birefringent wave plates for introducing phase retardation between the two orthogonal components of a linearly polarized light that correspond to the fast and slow axes of the birefringent material. In this paper we present new methods and architectures that generalize the Lyot-Ohman and Solc filters for optimally synthesizing an arbitrary all-optical filter by defining an error metric and minimizing it with simulated annealing. We also suggest the use of the electro-optic effect for controlling the retardation of individual elements that make up the tunable filter. Such a filter could be used for instance for realizing a dynamically tunable optical add/drop multiplexer in a telecommunication system.

Significance of phase and amplitude in the Fourier domain

We add new thoughts and aspects to the importance of phase and amplitude in the Fourier domain. We show how very similar objects react radically differently if, in the Fourier domain, either the phase was lost completely or the amplitude was modified to be constant. We also discuss the great influence of symmetry on the relative significance of the Fourier amplitude and of the Fourier phase. We show how changing the value of one pixel in some objects completely changes the significance of the Fourier phase and amplitude.

DISPLAY OF SPATIAL COHERENCE

The mutual-intensity function plays a major role in characterizing quasi-monochromatic, partially coherent optical signals. We demonstrate an optical system for displaying the mutual intensity of a one-dimensional input beam. The experimental system is based on the fact that the mutual intensity of a signal can be expressed as the ensemble averaging of a cross-correlation operation between two related optical signals. The setup consists of a Sagnac interferometer followed by an optoelectronic joint transform correlator. Experimental results demonstrate the capabilities of the mutual-intensity analyzer.

Encoding technique for design of zero-order (on-axis) Fraunhofer computer-generated holograms

Diffractive optical elements able to generate zero-order (on-axis) distributions with phase as well as amplitude distributions are described. The proposed elements are surface relief plates, i.e., phase-only elements, that are based on the concept of computer-generated masks followed by common etching processes. The encoding method assumes fixed spatial partitioning of the cell and a phase-only value allocated to each subelement. The reconstructed amplitude and phase distributions contain imperfections (noise) resulting from the encoding process. Methods of error reduction and improvements are provided.

SYNTHESIS OF SPATIAL COHERENCE

The mutual intensity function plays a major role in characterizing quasi-monochromatic, partially coherent optical signals. We propose to use the mutual intensity as a carrier of information to avoid speckle noise in coherent illumination systems and to permit the use of complex functions that are prohibited spatially incoherent sources. To do this we require methods for encoding the information as a coherence function. An optical system for synthesizing a beam with a given mutual intensity function is proposed. The optical system permits the synthesis of any desired mutual intensity function. The illumination is supplied by a quasi-monochromatic, spatially incoherent source. Experimental results demonstrate the performance of this system for several cases.

Modified morphological correlation based on bit-map representations

Pattern recognition with high discrimination can be achieved with a morphological correlator. A modification of this correlator is carried out by use of a binary slicing process instead of linear thresholding. Although the obtained correlation result is not identical to the conventional morphological correlation, it requires fewer calculations and provides even higher discrimination. Two optical experimental implementations of this modified morphological correlator as well as some experimental results are shown.

ITERATIVE ALGORITHM FOR DETERMINING OPTIMAL BEAM PROFILES IN A THREE-DIMENSIONAL SPACE

A new, to our knowledge, iterative algorithm for achieving optimization of beam profiles in a three-dimensional volume is presented. The algorithm is based on examining the region of interest at discrete plane locations perpendicular to the propagation direction. At each such plane an intensity constraint is imposed within a well-defined transverse spatial region of interest, whereas the phase inside that region as well as the complex amplitude outside the region is left unchanged from the previous iteration. Once the optimal solution is found, the mask that generates the desired distribution can be readily implemented with a planar diffractive optical element such as a computer-generated hologram. Several computer simulations verified the utility of the proposed approach.

Magneto-optic-based devices for polarization control

In this paper we present a number of measurements of the magneto-optic (MO) polarization rotation effect in MO glasses. We then show three design concepts of MO based devices that are of interest for optical communications applications. The first device is a tunable optical polarization controller, the second is a polarization filter that passes through only a specific point on the Poincare sphere and the third is a MO Fabry–Perot resonator that enhances the MO effect and can be used inside an all-optical switch or as part of a polarization coding module.

Optimal synthesis of three-dimensional complex amplitude distributions.

The synthesis of three-dimensional (3-D) light distributions is important for many applications. For example, in scanning applications it is preferable that the scanning beam preserve its characteristics over a large distance to yield elongated scanning range. It is evident that any 3-D light distribution must satisfy the wave equation or, in second-order approximation, the Fresnel diffraction formula. Thus many desirable 3-D light distributions may not be realizable. We propose a single optical element (OE) that synthesizes a physical beam within a certain 3-D region. The OE provides the optimal physical beam in comparison with a desired one in the sense of minimal mean-square error.

High-efficiency arbitrary array generator

Implementation of a beam-shaping system, whereby an arbitrary array of spots is generated, is proposed. The suggested beam-shaping generator, which is based on the Gerchberg-Saxton algorithm, contains two phase-only filters and thus yields a very-high-power throughput. The flexibility of the suggested approach is demonstrated with some computer simulations.