Light-emitting diodes (LEDs) are a cornerstone of consumer tech. They make thin-and-light TVs and smartphones possible, provide efficient household, handheld, and automobile illumination, and, of course, without LEDs your router would not have blinkenlights. Thanks to some engineers from MIT, though, a new diode looks set to steal the humble LED’s thunder. Dubbed a diode for light, and crafted using standard silicon chip fabrication techniques, this is a key discovery that will pave the path to photonic (as opposed to electronic) pathways on computer chips and circuit boards.
In electronics, a diode is a gate that only allows electrons to pass in one direction (and with an LED, it also emits light at the same time). In this case, the diode for light — which is made from a thin layer of garnet — is transparent in one direction, but opaque in the other. Garnet is usually hard to deposit on a silicon wafer, but the MIT researchers found a way to do it — and that’s really the meat of this discovery.
Basically, it’s now possible, with regular chip-fab tools, to create an integrated silicon circuit with optical, rather than electronic, interconnects — both internally, and between other chips. Photons, moving through the kind of transparent metamaterials that would be required to make such a circuit, move a lot faster than electrons. Furthermore, optical channels, through wavelength-division multiplexing, can carry a lot more data than electric signals. At the moment, hundreds of copper wires connect the CPU, northbridge, and memory — with on-chip photonic controllers, a motherboard might only have 10 or 20 channels.
In the near term, though, garnet-on-silicon chips are likely to be used in networking — first in backbone routers, which are physically huge and very power hungry because of the current size of optical switching hardware, and then hopefully at home and in the office (100Gbps home networks!) Then, once the size of MIT’s diode for light is scaled down — it’s currently around 400nm long, some 20 times larger than a transistor — we might begin to see photonic circuits in computers.
Read more at MIT