Michael R. Feldman

Comparison between optical and electrical interconnects based on power and speed considerations.

Conditions are determined for which optical interconnects can transmit information at a higher data rate and consume lc3s power than the equivalent electrical interconnections. The analysis is performed for free-space optical intrachip communication links. Effects of scaling circuit dimensions, presence of signal fan-out, and the use of light modulators as optical signal transmitters are also discussed.

Iterative encoding of high-efficiency holograms for generation of spot arrays

An iterative discrete on-axis encoding method for computer-generated holograms (termed IDO encoding) has been developed. The binary IDO method employs simulated annealing to optimize the hologram phase delay and reduce sensitivity to fabrication tolerances. Computer-simulation results indicate that binary phase IDO encoding is capable of generating two-dimensional spot arrays with diffraction efficiencies larger than 70%. An experimentally fabricated hologram, designed to account for a 6% manufacturing hologram thickness tolerance, produced a 3 x 3 array of spots with 59% diffraction efficiency. The binary IDO algorithm can be employed to encode arbitrary images with twofold rotation symmetry.

Holographic Optical Interconnects For VLSI

This paper introduces new applications and design trade-offs anticipated for free-space optical interconnections of VLSI chips. New implementations of VLSI functions are described that use the capability of making optical inputs at any point on a chip and take advantage of greater flexibility in on-chip signal routing. These include n-port addressable memories, CPU clock phase distribution, hardware multipliers, and dynamic memory refresh, as well as enhanced testability. Fault tolerance and production yields may be improved by reprogramming the optical imaging system to circumvent defective elements. These attributes, as well as those related to performance alone, will affect the design methodology of future VLSI ICs. This paper focuses on identifying the design issues, their possible solutions, and their impact on VLSI design tech-niques and, finally, presents some preliminary measurements on various sys-tem components.

Implementation of optical interconnections for VLSI

This paper reports on the progress in implementing optical interconnections for VLSI. Four areas are covered: 1) the holographic optical element (HOE), 2) the laser sources, 3) the detectors and associated circuits forming an optically addressed gate, and 4) interconnection experiments in which five gates are actuated from one source. A laser scanner system with a resolution of 12 µm × 20 µm has been utilized to generate the HOEs. Diffraction efficiency of the HOE and diffracted spot size have been measured. Stock lasers have been modified with a high-frequency package for interconnect experiments, and buried heterostructure fabrication techniques have been pursued. Measurements have been made on the fabricated photodetectors to determine dark current, responsivity and response time. The optical gates and the overall chip have been driven successfully with an input light beam, as well as with the optical signal interconnected through the one to five hologram.

Computer generated holographic optical elements for optical interconnection of very large scale integrated circuits

The use of computer generated holographic elements for implementation of free-space optical interconnection of very large scale integrated circuits is presented. The design of the holographic optical elements is based on laser source divergence, source to hologram spacing, signal fanout, and resolution of the hologram recorder. The results of a computer simulation of diffraction from the hologram are compared with the analytically predicted results, particularly to confirm the effect of spatial sampling on the performance of an on-axis interferogram hologram. Measurements taken using transmission absorption and transmission phase holograms in photographic emulsion, as well as reflective surface relief holograms on silicon, are compared to predicted results. Performance benefits expected from extension of the design process to holograms fabricated using electron-beam lithography are discussed.

Optimum encoding of binary phase-only filters with a simulated annealing algorithm

A simulated annealing algorithm is introduced to encode binary phase-only filters optimally for image recognition. Similar patterns that cannot be distinguished with conventional filter encoding methods are clearly distinguished with the optimized filter. The computational requirements for optimizing the filter are not excessive.

Spatial-light-modulator-based electro-optical imaging system

We describe a novel electro-optical system that can image objects over a long range of distance without involving any mechanical movement.

Computer aided design of computer generated holograms for electron beam fabrication

Computer Aided Design (CAD) systems that have been developed for electrical and mechanical design tasks are also effective tools for the process of designing Computer Generated Holograms (CGHs), particularly when these holograms are to be fabricated using electron beam lithography. CAD workstations provide efficient and convenient means of computing, storing, displaying, and preparing for fabrication many of the features that are common to CGH designs. Experience gained in the process of designing CGHs with various types of encoding methods is presented. Suggestions are made so that future workstations may further accommodate the CGH design process.

Comparison of binary encoding schemes for electron-beam fabrication of computer generated holograms

The suitability of various binary encoding methods for electron-beam recording of computer generated holograms is systematically evaluated. Subjected to the limitations of computing resources, a set of criteria is established according to which these encoding schemes are evaluated and compared. This comparison can be used to determine the optimum encoding method for desired wavefront properties.