Dawei Huang

Three-dimensional optoelectronic stacked processor by use of free-space optical interconnection and three-dimensional VLSI chip stacks

We present a demonstration system under the three-dimensional (3D) optoelectronic stacked processor consortium. The processor combines the advantages of optics in global, high-density, high-speed parallel interconnections with the density and computational power of 3D chip stacks. In particular, a compact and scalable optoelectronic switching system with a high bandwidth is designed. The system consists of three silicon chip stacks, each integrated with a single vertical-cavity-surface-emitting-laser-metal-semiconductor-metal detector array and an optical interconnection module. Any input signal at one end stack can be switched through the central crossbar stack to any output channel on the opposite end stack. The crossbar bandwidth is designed to be 256 Gb/s. For the free-space optical interconnection, a novel folded hybrid micro-macro optical system with a concave reflection mirror has been designed. The optics module can provide a high resolution, a large field of view, a high link efficiency, and low optical cross talk. It is also symmetric and modular. Off-the-shelf macro-optical components are used. The concave reflection mirror can significantly improve the image quality and tolerate a large misalignment of the optical components, and it can also compensate for the lateral shift of the chip stacks. Scaling of the macrolens can be used to adjust the interconnection length between the chip stacks or make the system more compact. The components are easy to align, and only passive alignment is required. Optics and electronics are separated until the final assembly step, and the optomechanic module can be removed and replaced. By use of 3D chip stacks, commercially available optical components, and simple passive packaging techniques, it is possible to achieve a high-performance optoelectronic switching system.

Free-space parallel multichip interconnection system

A parallel data-communication scheme is described for interchip communication with free-space optics. We present a proof-of-concept and feasibility demonstration of a practical modular packaging approach in which free-space optical interconnect modules can be simply integrated on top of an electronic multichip module (MCM). Our packaging architecture is based on a modified folded 4-f imaging system that is implemented with off-the-shelf optics, conventional electronic packaging techniques, and passive assembly techniques to yield a potentially low-cost packaging solution. The prototype system, as built, supports 48 independent free-space channels with eight separate laser and detector chips, in which each chip consists of a one-dimensional array of 12 devices. All chips are assembled on a single ceramic carrier together with three silicon complementary metal-oxide semiconductor chips. Parallel optoelectronic (OE) free-space interconnections are demonstrated at a speed of 200 MHz. The system is compact at only 10 in.(3) (~164 cm(3)) and is scalable because it can easily accommodate additional chips as well as two-dimensional OE device arrays for increased interconnection density.

Optomechanical design and characterization of a printed-circuit-board-based free-space optical interconnect package

We present a proof of concept and a feasibility demonstration of a practical packaging approach in which free-space optical interconnects (FSOIs) can be integrated simply on electronic multichip modules (MCMs) for intra-MCM-board interconnects. Our system-level packaging architecture is based on a modified folded 4f imaging system that has been implemented with only off-the-shelf optics, conventional electronic packaging, and passive-assembly techniques to yield a potentially low-cost and manufacturable packaging solution. The prototypical system as built supports 48 independent FSOI channels with 8 separate laser and detector chips, for which each chip consists of a one-dimensional array of 12 devices. All the chips are assembled on a single substrate that consists of a printed circuit board or a ceramic MCM. Optical link channel efficiencies of greater than 90% and interchannel cross talk of less than -20 dB at low frequency have been measured. The system is compact at only 10 in.3 (25.4 cm3) and is scalable, as it can easily accommodate additional chips as well as two-dimensional optoelectronic device arrays for increased interconnection density.

Cross talk and ghost talk in a microbeam free-space optical interconnect system with vertical-cavity surface-emitting lasers, microlenses, and metal–semiconductor–metal detectors

A diffraction-based beam-propagation model is used to study optical cross talk in microbeam free-space optical interconnection (FSOI) systems. The system consists of VCSELs, microlenses, and metal-semiconductor-metal (MSM) detectors, with the detectors modeled as amplitude gratings with low contrast ratio (based on experimental results). Different possible cross-talk sources are studied. Results show that, in an optimized system, the cross talk caused by diffractive scattering is not an issue. However, in such systems the principal reflection from a MSM detector surface creates two problems: VCSEL coupling and ghost talk. The coupling of the reflected beam into the VCSELs may cause power oscillation (and increase the bit error rate), whereas ghost talk will limit the distance-bandwidth product of the interconnect system. This optical system is also abstracted in hspice together with the laser driver and receiver circuits to analyze ghost talk in this system. Results show that at high speed (1 Gbit/s or more) these effects negatively affect system performance.

Comparative study of very short distance electrical and optical interconnects based on channel characteristics

This paper presents a comparative study for very short distance (less than 1 meter) electrical and optical interconnects in terms of channel characteristics. We also predict when and where optical interconnect may replace their electrical counterpart.

Analysis of free-space optical interconnects for the three-dimensional optoelectronic stacked processor

Performance of free-space optical interconnect for the three-dimensional optoelectronic stacked processor (3DOESP) has been analyzed. The wave propagation in the optical interconnection system has been investigated by utilizing rigorous scalar diffraction theory. The effects of ghost talk caused by the superposition of the delayed reflections of the original signal due to the multiple propagation of the wave between the vertical-cavity surface-emitting laser (VCSEL) and metal-semiconductor-metal (MSM) detector have been analyzed. The conducted study indicates that even in the presence of significant amount of ghost talk a high performance free-space optical interconnect can be realized in this system by employing a receiver architecture that allows for DC level adjustment of the signal at the input of the transimpedance amplifier stage.

Three-dimensional optoelectronic crossbar switch

High-speed operation of free-space optical interconnect for a three-dimensional optoelectronic crossbar switching has been analyzed. System architecture, transmitter and receiver design are presented. The effect of ghost talk caused by the superposition of the delayed reflections of the original signal due to the multiple propagation of the wave between the vertical-cavity surface-emitting laser (VCSEL) and metal-semiconductor-metal (MSM) detector has been analyzed. The study indicates that even in the presence of significant amount of ghost talk a high performance free-space optical interconnect can be realized in this system by employing a receiver architecture that allows for DC level adjustment of the signal at the input of the transimpedance amplifier stage.

Can optical interconnects be sufficiently parallel to support the needs of computer systems

The level of parallelism required for computer interconnects represents significant opportunities and serious challenges for optical interconnects. In this presentation, we will discuss several challenges and present some potential optical interconnect solutions.

Free-space optical interconnection of 3D optoelectronic VLSI chip stacks

Large-scale computer and data-communication systems have reached a bottleneck in performance in recent years due to the limitations of electronic interconnections for data transfer. One potential solution is based on the use of optoelectronic device arrays for free space optical interconnects. In this paper, we present the design and implementation of a 16 X 16 3D distributed optoelectronic crossbar switch.

Parallel three-dimensional free-space optical interconnection for an optoelectronic processor

A hybrid scalable optoelectronic crossbar switching system that uses global parallel free-space optical interconnects and three-dimensional (3D) VLSI chip stacks is presented. The system includes three 3D chip stacks with each consisting of 16 VLSI chips. A single 16 X 16 VCSEL/MSM detector array is flip-chip bonded on top of the chip stack. Each chip supports 16 optical I/Os at 1 Gb/s. For the free-space optical interconnection between the chip stacks, a novel folded hybrid micro/macro optical system with a concave reflection mirror has been designed. The optics module can provide a high resolution, large field of view, high link efficiency, and low optical crosstalk. It is also symmetric and modular. Off-the- shelf macro-optical components are used. The concave reflection mirror can significantly improve the image quality and tolerate a large misalignment of the optical components. Scaling of the macrolens can be used to adjust the interconnection length between the chip stacks. The optical system is analyzed based on ray-tracing and scalar diffraction theory. The impact of Ghost talk on high-speed optical interconnection is studied. For system packaging, only passive alignment is required. Optics and electronics are separated until final assembly step, and the optomechanic module can be removed and replaced. By using 3D chip stacks, commercially available optical components and simple passive packaging techniques, it is possible to achieve a high-performance optoelectronic switching system.