System Issues Relating To Laser Diode Requirements For VLSI Holographic Optical Interconnects

Abstract

Laser requirements and limitations for VLSI optical interconnect networks employing computer-generated holograms are discussed from a system point of view. For architectures with a collimating lens at the laser and a collector lens at the detector, the restrictions on laser wave-length stability are typically ± 10 A (thus requiring the laser's temperature to be regulated to approximately ± 5°C to 10°C). Diffraction limitations are shown to restrict the density of interconnects to the 104/cm2 range from many architectures (in particular, "space variant" architectures), rather than the 107/cm2 to 108/cm2 range frequently cited for "space invariant" architectures. Architectures with a mixture of space variance and invariance can lead to intermediate densities. Some architectures require low threshold, high efficiency lasers, whereas others require very high output power with much less concern for threshold and efficiency. A network with 3000 point-to-point interconnects per square centimeter, each transmitting at a 500 Mbit rate with a 10-11 bit-error rate, is analyzed. The best system performance is obtained if wavelength stabilized high power (10 W) laser arrays are available. Monolithic integration is discussed, and the need for uniform and/or tunable emission wavelength may be the greatest challenge in this area.