Optical interconnects for neural and reconfigurable VLSI architectures

The increasing transistor density in very large-scale integrated (VLSI) circuits and the limited pin number in the off-chip communication lead to a situation described as interconnect crisis in microelectronics. Optoelectronic VLSI (OE-VLSI) circuits using short-distance optical interconnects and optoelectronic devices like microlaser, modulator, and detector arrays for optical off-chip sending and receiving offer a technology to overcome this crisis. However, in order to exploit efficiently the potential of thousands of optical off-chip interconnects, an appropriate VLSI architecture is required. We show for the example of neural and reconfigurable VLSI architectures that fine-grain architectures fulfill these requirements. An OE-VLSI circuit realization based on multiple quantum-well modulators functioning as two-dimensional (2-D) optical input/output (I/O) interface for the chip is presented. Due to the parallel optical interface, an improvement of two to three orders of magnitude in the throughput performance is possible compared to all-electronic solutions. For the optical interconnects, a planar-integrated free-space optical system has been designed leading to an optical multichip module. Such a system has been fabricated and experimentally characterized. Furthermore, we designed and manufactured fiber arrays, which will be the core element for a convenient test station for the 2-D optoelectronic I/O interface of OE-VLSI circuits.