Steven P. Levitan

Pipelined communications in optically interconnected arrays

Abstract Two synchronous multiprocessor architectures based on pipelined optical bus interconnections are presented. The first is a linear pipeline with enhanced control strategies which make optimal use of the available communication bandwidth of the optical bus. The second is a two-dimensional architecture in which processors are placed in a square grid and interconnected to one another through horizontal and vertical pipelined optical buses. These architectures allow any two processors to communicate with each other using one (for the linear case) or two (for the two-dimensional case) pipelined bus cycles. Further, they permit all processors to have simultaneous access to the buses using slots within a pipelined cycle. We show that the architectures have simple control structures and that well-known processor interconnections, e.g., the complete binary trees and the hypercube networks, can be efficiently embedded in them. These architectures have an effectively higher bandwidth than conventional bus configurations and appear to be good candidates for a new generation of hybrid optical-electronic parallel computers.

Coincident pulse techniques for multiprocessor interconnection structures.

We present several optical interconnection structures which support communication requirements unique to multiprocessor systems, namely, broadcasting, multicasting, simulcasting, and multiport memory access. The structures are based on guided wave time division multiplexed channels and use coincident pulse techniques to optically demultiplex individual bits at selected destinations. We describe 1-and 2-D structures which are appropriate for processor to processor interconnections and for processor to memory interconnections, respectively.

Reliability optimization models for embedded systems with multiple applications

Summary and Conclusions-This paper presents four models for optimizing the reliability of embedded systems considering both software and hardware reliability under cost constraints, and one model to optimize system cost under multiple reliability constraints. Previously, most optimization models have been developed for hardware-only or software-only systems by assuming the hardware, if any, has perfect reliability. In addition, they assume that failures for each hardware or software unit are statistically independent. In other words, none of the existing optimization models were developed for embedded systems (hardware and software) with failure dependencies. For our work, each of our models is suitable for a distinct set of conditions or situations. The first four models maximize reliability while meeting cost constraints, and the fifth model minimizes system cost under multiple reliability constraints. This is the first time that optimization of these kinds of models has been performed on this type of system. We demonstrate and validate our models for an embedded system with multiple applications sharing multiple resources. We use a Simulated Annealing optimization algorithm to demonstrate our system reliability optimization techniques for distributed systems, because of its flexibility for various problem types with various constraints. It is efficient, and provides satisfactory optimization results while meeting difficult-to-satisfy constraints.

Digital integrated circuit testing using transient signal analysis

A novel approach to testing CMOS digital circuits is presented that is based on an analysis of I/sub DD/ switching transients on the supply rails and voltage transients at selected test points. We present simulation and hardware experiments which show distinguishable characteristics between the transient waveforms of defective and non-defective devices. These variations are shown to exist for CMOS open drain and bridging defects, located both on and off of a sensitized path.

Sensitivity enhancement of fiber Bragg gratings to transverse stress by using microstructural fibers

We present simulation and experimental results of fiber Bragg grating responses to transverse stress in microstructure fibers. The grating wavelength shifts and peak splits are studied as a function of external load and fiber orientation. Both simulation and measurement results indicate that the sensitivity of grating sensors to the transverse stress can be enhanced by a factor of eight in a two-hole fiber over that in a standard fiber.

CMOS supporting circuitries for nano-oscillator-based associative memories

“Let physics do computing” is a promising approach to new-paradigm computing in the beyond CMOS era. Building associative memories based on the physics of nano oscillators, in particular, presents a lot of potential for intelligent information processing. In this paper, we discuss how CMOS supporting circuitries can interface the fabric of nano oscillators with digital computing world. Using CMOS ring oscillators to emulate the nano oscillator behavior, how to produce the associative memory function and to use it for image recognition is demonstrated by HSPICE simulation.

Non-Boolean associative architectures based on nano-oscillators

Many of the proposed and emerging nano-scale technologies simply cannot compete with CMOS in terms of energy efficiency for performing Boolean operations. However, the potential for these technologies to perform useful non-Boolean computations remains an opportunity to be explored. In this talk we examine the use of the resonance of coupled nano-scale oscillators as a primitive computational operator for associative processing and develop the architectural structures that could enable such devices to be integrated into mainstream applications.

Optoelectronic buses for high-performance computing

Modern computer buses are typically organized by the three functions of data transfer, addressing, and arbitration/control. In this paper we present a fiber-based bus design which provides optical solutions for each of these functions. The design includes an all-optical addressing system, based on coincident pulse addressing, which eliminates the latency contribution and bandwidth limitation associated with electronic address decoding. The control system uses time-of-flight relationships between a priority chain and a feedback waveguide to implement fully distributed asynchronous and self-timed bus arbitration. >

Designing communicating colonies of biomimetic microcapsules.

Using computational modeling, we design colonies of biomimetic microcapsules that exploit chemical mechanisms to communicate and alter their local environment. As a result, these synthetic objects can self-organize into various autonomously moving structures and exhibit ant-like tracking behavior. In the simulations, signaling microcapsules release agonist particles, whereas target microcapsules release antagonist particles and the permeabilities of both capsule types depend on the local particle concentration in the surrounding solution. Additionally, the released nanoscopic particles can bind to the underlying substrate and thereby create adhesion gradients that propel the microcapsules to move. Hydrodynamic interactions and the feedback mechanism provided by the dissolved particles are both necessary to achieve the collective dynamics exhibited by these colonies. Our model provides a platform for integrating both the spatial and temporal behavior of assemblies of “artificial cells,” and allows us to design a rich variety of structures capable of exhibiting complex, cooperative behavior. Due to the cell-like attributes of polymeric microcapsules and polymersomes, material systems are available for realizing our predictions.

Demonstration of a multichannel optical interconnection by use of imaging fiber bundles butt coupled to optoelectronic circuits

Through five experiments, we demonstrate and characterize the basic functionality of imaging fiber bundles for optoelectronic chip-level interconnections. We demonstrate the transmission of spot arrays with spot sizes and a spot pitch roughly equal to 2 and 4 times the core pitch, respectively. We show that optoelectronic integrated circuits, including sources and detectors, can be butt coupled directly to fiber bundles without any additional optical elements. We demonstrate a 16-channel interconnect with -23 dB of cross talk, and we characterize the most significant optical loss mechanism. Finally, we show how imaging fiber bundles can be used to implement more complex interconnection structures by an example of a hybrid-bonded structure that implements a low-cost, high-connectivity solution for more advanced system architectures.