content: A major issue for moving forward with increasing transistor density has been heat. As you move electrons through material (Copper, silicon, etc) you generate heat. It's not a huge amount per transistor, but when you pack a billion of them together you get a lot of heat - hence the need for big heatsinks and integrated fans. Another note, is that electricity traveling through copper moves at about 2/3 the speed of light. With optical computing, that heat is no longer generated due to electrons moving around. Your information moves twice at c instead of 2/3c and to top it off, you're now looking at speeds easily in the Terahertz range.  Optical computing started out in the 60's, but fell by the wayside because it's really, really hard. Now, though, it looks like the technology is there and with electrical computing starting to hit physical boundaries, I think we'll see a resurgence.