The drive to make faster and faster computers just got a huge optical jump! University of Pennsylvania researchers have made a quantum leap in designing new-age gates for use in new age computers. These gates are controlled by light!
Computers of today are made out of gates that are switched on and off by electrical signals. The crucial speed involved in the switching speeds of these gates is the velocity at which electrons (or other charge carriers) travel inside the substrate that make up the gate. In other words, how fast you can switch a gate on and then off and then on again depends on how fast the electrons feel the changing electric field and travel back and forth. All of this can be greatly accelerated if we use light signals and not electric ones!
So here is the first photonic switch, all made out of cadmium sulphide nanowires. The team of researchers consists of an associate professor Ritesh Agarwal and graduate student Brian Piccione, from the Department of Material Sciences, Pennsylvania University.
They are carrying forward their earlier research finding, when they found that cadmium sulphide (CdS) nanowires is the perfect substance on which to attempt such a thing. Cadmium sulphide exhibits very strong light-matter coupling. This simply means that there exist mechanisms within the substrate that can control the way light behaves within the material.
How they did it
What they did was cut a gap in a CdS nanowire. Light was then shone on one of the sections. This light is perfectly transmitted down the length of the nanowire. Now, the team shone another light on the second part of the nanowire. This, believe it or not, cuts off the light that was already going through the nanowire. This phenomenon is called destructive interference. So now, you have a gate which you can turn on or off by shining light on the second part. All you need to do, in principle, is to measure the intensity of light coming out the second part of the wire.
And that’s it!
This is a basic switch. With switches you can make gates. With gates you can design a computer.
One of the basic types of gates is the so called NAND (Not AND) gate. The NAND gate can be used to construct any other gate. A NAND gate returns a high signal (‘1’) if either or both of the inputs is zero, and zero if both inputs are one. The team has built such a device using two CdS nanowires.
The paper appears in Nature Nanoscience: http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2012.144.html