Fibers and waveguides function as the ``wires'' for optical interconnects, with fibers being similar to copper wires and waveguides similar to microstrips and striplines. Commercially available fiber optic networks are now being used for computer-to-computer interconnects and computer-to-peripheral connections. As the need grows for higher performance systems, guided optical interconnects will start to see use within the computer, possibly as far down into the packaging hierarchy as MCM-to-MCM (multichip module, or wafer-to-wafer).
Electrical interconnects achieve some bandwidth enhancement through
time division multiplexing (TDM) and spatial multiplexing (e.g., ribbon
cables). But the immense bandwidth available in optical waveguides
(THz) has opened up additional avenues to bandwidth
enhancement for optical interconnects, namely, wavelength division
multiplexing (WDM) and subcarrier multiplexing (SCM). This added
capability could be critical for TeraFLOPS systems due to parallelism
requirements that could exceed one million channels. Novel schemes for
combining spatial multiplexing with TDM, WDM, and SCM for optical
interconnection may be needed.