Analysis of intrachip electrical and optical fanout

We examine the benefits of electrical isolation in intrachip optical signaling. We calculate the delay and energy metrics of an optical interconnect with fanout driving an electrical load. By examining fanout and including load drivers into delay equations, we make a shift from the general trend of looking at optical interconnects as a replacement for long parasitic wires. Our calculations show that optical fanout provides a large improvement in an Etau2 (energy delay squared) metric and improves performance even at very short intrachip distances. The break-even length corresponds to the wiring length of 250 minimum-size inverters that are compactly laid out. These results provide a compelling reason to further examine the implementation of optical interconnects.