Multistage Sorting Module With VCSEL Based Free-space Optical Interconnects

Abstract

Free-space optical ir erconnects promise highly parallel implementations of multistage interconnection networks (MINs) for sorting and switching applications. The largest network demonstrated so far [ l ] had 1,024 channels in parallel, ran at a clock rate of 100 kHz, and was based on SEED devices [2]. The practical difficulties associated with the employment of SEED devices (tight wavelength and temperature tolerances, complex optical systems for the modulator type devices) motivate us to investigate the use of active light emitting devices. In particular, the novel vertical cavity surface emitting laser (VCSEL) [3] is a promising candidate for free-space optical interconnects. In this paper, we present the first demonstration of a MIN which employs VCSEL based optical interconnects. Figure 1 shows schematically the MIN we have implemented. Six switching stages, each consisting of four parallel 2x2 crossbar switching nodes, are interconnected in a non-local way. In our system, the numbers to be sorted are represented in binary format and are synchronously fed into the network with most significant bits leading. The control of the network is distributed. Each node compares the two numbers arriving at its input ports in a bitsequential way and routes the greater number through the upper, the smaller number through the lower output port [4]. From another point of view, the network performs a core function of a self-routing packet switch. The network sorts according to the leading bits (address headers), and it delivers the trailing bits (payloads) to the corresponding destination ports.