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“Optoelectronic-VLSI System Integration for Digital Information Processing”
by Sunkwang Hong
December 2002
Optoelectronic-VLSI systems can provide high-bandwidth multimedia applications and real-time parallel processing using the complementary properties of electronics and optics. Optics has many advantages in high-speed data transfer including inherent low crosstalk and low power, while electronics is more suitable for logic functions and integrated circuitry. In this research, we present designs and demonstrations of optoelectronic-VLSI systems based on two different approaches: a modular integration, and a monolithic integration. Both approaches deal with the optimal integration of optoelectronic devices for high-speed, high-throughput network communications and data processing.
We have designed and tested a modular optoelectronic-VLSI system called Translucent Smart Pixel Array (Transpar). The system includes a field-programmable gate array (FPGA), a transimpedance amplifier (TIA) receiver, and an interlaced array of 4 _ 4 vertical-cavity surface-emitting lasers (VCSELs) and metal-semiconductor-metal (MSM) detectors. The FPGA allows for reconfigurable networks and processors, thus Transpar can implement dynamic novel network protocols. The components are mounted on a printed circuit board (PCB) for testing of various optical interconnection techniques. Bulk lenses, diffractive optical elements (DOEs) and fiber image guides (FIGs) were tested and compared as interconnection techniques for the Transpar system. A detailed wave-propagation simulation for the FIGs is presented and compared with experimental results. The effect of optical crosstalk and minimization of the overall power dissipation are also considered.
One technique for the monolithic integration of mixed-signal integrated circuits with optoelectronics is Ultra-thin Silicon-on-Sapphire (UTSi) technology. UTSI has low parasitic capacitance and enables different optical and electrical components to be integrated with ordinary complementary metal-oxide semiconductor (CMOS) circuits using standard fabrication processes. It is well suited for low-cost and high-performance optical data communication systems. The sapphire substrate of UTSi is highly transparent to the propagation of light from VCSELs and simplifies the packaging. We have designed and tested four different UTSi chips for evaluation and testing of integration of optoelectronic components. These chips contain VCSEL drivers, receiver circuitry, clock generators, frequency dividers, and voltage controlled oscillators. Flip-chip bonding is used to combine VCSEL and detector arrays with the UTSi CMOS circuits. The architecture and system performance of each chip is tested and discussed.