Optical interconnects to silicon CMOS

There are even greater problems for off-chip interconnects than on-chip ones. It is possible to break long on-chip interconnects up using on-chip repeater amplifiers, but that approach is very inconvenient off of the chip. Consequently, off-chip interconnects are a particularly attractive first implementation of optical interconnects to silicon chips. Optical interconnects are interesting for many reasons other than this scaling argument. They are immune to electromagnetic interference and crosstalk, they provide voltage isolation, they can have very low loss, and. they allow use of free-space optics, imaging many light beams from one chip to another. Historically a great impediment to integrating optical interconnects with CMOS was the absence of suitable optical output devices. Fortunately there are now two devices that may be able to fill this role - quantum-well modulator diodes, and vertical cavity surface emitting lasers (VCSELs).