Anis Husain

Optical interconnections for massively parallel architectures

This paper presents a study of board-level interconnection requirements for highly parallel and massively parallel computing. Analytical models of the I/O bandwidth of popular interconnection networks have been developed and show that current electronic technologies are poor in supporting the necessary I/O density and bandwidth. Optical interconnects appear to offer greater potential in meeting these I/O requirements. Several possible optical implementations of interconnecting a network of electronic processors are compared. The use of polymer waveguides appears to offer the best solution compatible with existing multiboard system architectures.

Polymer Waveguide-Based Optical Backplane for Fine-Grained Computing

The interconnection requirements of fine-grained computing are examined and compared to the requirements of coarser grained, multiplexed systems. Specifications for the interconnection medium are developed and compared to the performance of available optical source and interconnection components. The use of polyimide waveguides for both applications is considered and the probable architecture of a multiboard fine-grained system is described.

Optical interconnect of digital integrated circuits and systems

Conventional interconnect and switching technology is rapidly becoming a critical issue in the realization of systems using silicon-based VHSIC/VLSI chips or GaAs integrated circuits. Optical interconnect technology promises to enhance performance significantly, provide relief from the pinout problem, decrease implementation complexity, and provide improvements to the flexibility and real-time reconfigurability of these systems. Furthermore, by releasing the bandwidth constraints on interconnects, the full processing speed capabilities of silicon logic could be exploited to improve system throughput dramatically. This paper outlines the key issues involved in implementing optical interconnects and the impact of exploiting this concept on the architecture of digital systems.

Progress and status of guided-wave optical interconnection technology

Optical interconnects at the cabinet-to-cabinet, board-to-board, and multichip module-to- multichip module levels will enable future avionics systems requirements to be met by eliminating undesirable compromises associated with electrical interconnects. Fiber optics is the well established medium of choice for cabinet-to-cabinet applications, while planar polymeric interconnects are required at the backplane level. Significant advances have been made in demonstrating practical polymer interconnects compatible with existing board fabrication principles, however both waveguide loss and interfaces to optoelectronic components require further improvement before the technology is broadly applicable.

Collaborative Beamfocusing Radio (COBRA)

A Ziva team has recently demonstrated a novel technique called Collaborative Beamfocusing Radios (COBRA) which enables an ad-hoc collection of distributed commercial off-the-shelf software defined radios to coherently align and beamform to a remote radio. COBRA promises to operate even in high multipath and non-line-of-sight environments as well as mobile applications without resorting to computationally expensive closed loop techniques that are currently unable to operate with significant movement. COBRA exploits two key technologies to achieve coherent beamforming. The first is Time Reversal (TR) which compensates for multipath and automatically discovers the optimal spatio-temporal matched filter to enable peak signal gains (up to 20 dB) and diffraction-limited focusing at the intended receiver in NLOS and severe multipath environments. The second is time-aligned buffering which enables TR to synchronize distributed transmitters into a collaborative array. This time alignment algorithm avoids causality violations through the use of reciprocal buffering. Preserving spatio-temporal reciprocity through the TR capture and retransmission process achieves coherent alignment across multiple radios at ~GHz carriers using only standard quartz-oscillators. COBRA has been demonstrated in the lab, aligning two off-the-shelf software defined radios over-the-air to an accuracy of better than 2 degrees of carrier alignment at 450 MHz. The COBRA algorithms are lightweight, with computation in 5 ms on a smartphone class microprocessor. COBRA also has low start-up latency, achieving high accuracy from a cold-start in 30 ms. The COBRA technique opens up a large number of new capabilities in communications, and electronic warfare including selective spatial jamming, geolocation and anti-geolocation.

Guided-Wave Optical Interconnects For VLSI Systems

Electrical interconnect technology is becoming the major limitation in the realization of high-performance computing machines. The use of optical interconnections promises to alleviate key interconnect bottlenecks such as pinout, fanout, wiring density, and communication bandwidth. We present results of work on guided-wave optical interconnect circuits for eventual use within and between multichip packages. Low-loss integrated optical waveguides (<0.5 dB/cm), right-angle waveguide corner bends (<0.4 dB/cm), right-angle waveguide crossovers (<0.2 dB), and right-angle 1:2 waveguide branches (<0.5 dB) are presented.

Optical interconnects for parallel processing

Analytical modeling and practical experience reveal that interconnection networks for large-scale parallel architectures are severely limited by the I/O bandwidth of electrical interconnects. Optical interconnects offer far greater potential in meeting these bandwidth demands. The development of an operational 1024x1024 polyimide waveguide perfect shuffle network and high-density modulator arrays demonstrate how optics can meet this challenge. Further optical switching networks would be possible with the development of single-mode 2x2 waveguide switches. We envisage as feasible the insertion of active optical interconnection networks in future large-scale parallel architectures using integrated arrays of waveguide modulators photodetectors switches and interconnects.

Collaborative Beamfocusing Radios (COBRA): A reciprocity based distributed beamforming system

Collaborative Beamfocusing Radios (COBRA) enables an ad-hoc collection of distributed commercial off-the-shelf software defined radios to coherently time align and beamform to a remote radio through dynamic RF channels associated with movement. COBRA uses reciprocal buffering, a causal implementation of the Time Reversal (TR) algorithm; leveraging RF channel reciprocity to cancel out channel impairments synchronizing a set of distributed transmitters into a phase coherent array to obtain N2 gain at a intended target. COBRA has been demonstrated aligning multiple commercial software-defined radios at up to 5.6 GHz carriers, using only quartz oscillators.

Computational imaging for aberrated optics (CIAO): experimental results

This paper presents experimental results obtained with Ziva Corp.’s image processing approach called Computational Imaging for Aberrated Optics (CIAO), which is a multi-image deconvolution algorithm. CIAO enhances the performance of imaging systems by accommodating wavefront error. This accommodation allows the designer to improve system performance or reduce system cost. CIAO has been successfully tested in a wide field of view imaging system, which has significant aberrations. These experimental results show CIAO restoration of high quality images from highly blurred images. Specifically, CIAO allows the pupil to open <50% beyond the diffraction limited aperture, which allows more light capture and higher cut-off resolution.