Researchers Create First All Optical Nanowire NAND Gate

mhore writes "Researchers at the University of Pennsylvania have created the first all optical, nanowire-based NAND gate, which paves the way towards photonic devices that manipulate light to perform computations. From the release: 'The research team began by precisely cutting a gap into a nanowire. They then pumped enough energy into the first nanowire segment that it began to emit laser light from its end and through the gap. Because the researchers started with a single nanowire, the two segment ends were perfectly matched, allowing the second segment to efficiently absorb and transmit the light down its length.' The gate works by shining light on the nanowire structure to turn on and off information transported through the wire. The research appeared this month in Nature Nanotechnology (abstract)."

Wrong direction

[nurb432]

I think we are wasting the potential of future optics if we think in binary, as this team is doing.

Optics scream for multilevel logic.

Re:Wrong direction

[perl6geek]

I've worked two years on a PHD thesis involving all-optical signal processing (though I worked on all-optical signal regeneration, not logical gates), and one of my conclusions is that multi-level is an order of magnitude more challenging than two values. The reason is that if you do multiple processing steps, you usually get some random fluctations, so you need to have components that fix that, i.e. fix to a certain level. Now you have basically two options, you can encode your information in the phase or in the amplitude/power. In the case of power levels you can use something like nonlinear loop mirrors, but they have the problem that they change the power ratio level between the states. In the case of phase encoded signals, a you can use a saturated phase-sensitive amplifier (for example two symmetric pumps), but they require quite high powers, and you have to injection-lock the pumps to compensate phase drifts, and they still only work for two levels. There is exactly one scheme that works for multiple levels (see http://eprints.soton.ac.uk/336325/1.hasCoversheetVersion/Thesis.pdf [soton.ac.uk] for a PHD thesis about it), but it turns phase noise into amplitude noise, so you need an amplitude regenator after it. So, binary logic is plenty of challenge to get working; once that's establish, we can still think about multiple levels.

Re:Density and No True Off

[mark-t]

Photons have an interesting property over electrons, however. A photon's motion does not produce an external field which will affect the trajectory taken by others that passes close to it. Electrons do.