Light-based computers in development | Hacker News Reader

Light-based computers in development

kutv.com

27 pointsparwell15 comments

> The key advantage of light, made of photo[n]s, is it’s the fastest thing you can use to transfer information according to the professor.

I wish people would stop spreading this exaggeration. ~~Electrons~~ Electronic signals move at 0.66c. In practice 1c is unlikely to provide the most significant gains.

The key benefit is actually the energy efficiency that the article barely mentions, as well as massive reduction of interference within circuits (which is why you have to up the CPU voltage when you overclock).

I have to nitpick because that's a very frequent misconception as well: electrons, in fact, move very slowly in metals and semiconductors (a few cm/s at best). It's the electromagnetic waves that move so fast (depending on the material, it's going to be anywhere between 0.5c and 0.9c in most everyday appliances), but the electrons themselves are really slow.

I always went with this:

Principle of physics is that Light and Electricity are the SAME THING. Electricity is just Light guided along wires. [http://scienceline.ucsb.edu/getkey.php?key=2910]

Than the following link shows that electricity moves about 1/100 the speed of light in wires:

Light travels through empty space at 186,000 miles per second. The electricity which flows through the wires in your homes and appliances travels much slower: only about 1/100 th the speed of light. Part of the reason is that light is massless; it has no weight, whereas the electricity flowing in the wires is made up of a stream of electrons, all of which have some small amount of weight. In addition, the electrons flowing through the wires constantly bump into the atoms of the wire, which slows them down considerably. If you were to take the electrons out of the wire and make them flow through space (which is essentially what you do when you make a spark), they can move faster, but no matter what, they cannot move as fast light. [Light travels through empty space at 186,000 miles per second. The electricity which flows through the wires in your homes and appliances travels much slower: only about 1/100 th the speed of light. Part of the reason is that light is massless; it has no weight, whereas the electricity flowing in the wires is made up of a stream of electrons, all of which have some small amount of weight. In addition, the electrons flowing through the wires constantly bump into the atoms of the wire, which slows them down considerably. If you were to take the electrons out of the wire and make them flow through space (which is essentially what you do when you make a spark), they can move faster, but no matter what, they cannot move as fast light. [Light travels through empty space at 186,000 miles per second. The electricity which flows through the wires in your homes and appliances travels much slower: only about 1/100 th the speed of light. Part of the reason is that light is massless; it has no weight, whereas the electricity flowing in the wires is made up of a stream of electrons, all of which have some small amount of weight. In addition, the electrons flowing through the wires constantly bump into the atoms of the wire, which slows them down considerably. If you were to take the electrons out of the wire and make them flow through space (which is essentially what you do when you make a spark), they can move faster, but no matter what, they cannot move as fast light.[http://scienceline.ucsb.edu/getkey.php?key=2910]]

Thanks, edited to clarify.

You're welcome :).

You're right that there's a pretty limited benefit to simple signal transmission, but when it comes to switching and capacitance, there could very well be more significant gains.

The main problem is still getting strong optical nonlinearity to build optical only transistors. Right now best case 1 in 100 photons will be affected by most "switches". There's been some research using various resonators to enhance the nonlinearities, but that's really the big problem to solve right now.

There's also scaling issues - we have 20nm electrical switches, which is almost 50 times smaller than the wavelength of visible light, so you either need to go to deep UV or confine light to area much smaller than the free-space wavelength, which presents its own challenges.

My personal interest in optical computing is mainly in building optical quantum computers, in which case the cost/size/power of solving these challenges could be well worth it due to the scaling advantages of multi-qubit entanglement. Classical optical computing does not really seem that worth it if we need to build computer chips that are 1000 times bigger and run each operation on average 10^8 times to get a valid result, although the clock speed and power benefits would be nice.

This is what gets my juices going: http://arxiv.org/abs/1207.1619

All-optical Reservoir Computing

If efficiency is vastly improved, we can stack the layers and increase frequency by quite a bit. Even if the processor becomes a 10cm x 10cm x 10cm cube, it's okay as a proof of concept.

It's an interesting approach to overcome the inherient limitations of electron based circuits.

Again, right now 1 in 100 photons will interact with an optical switch. This effect multiplies with each level of transistors. This means you have to "run" your circuit potentially something like 10^100 times to get all of the transistors in your path to work on the same photon.

That's pretty rough.

> Light-based computers in development, to be millions of times faster

When will we see this millions time faster computers commercially available?

Maybe around the time when the thousands-times faster internet and 100 times larger batteries from articles I read years ago are available...

Are you being optimistic or pessimistic? It's only been 15-20 years since 56kb dialup was the norm, and Tesla are doing pretty well at the moment.

Not pessimistic about technology, but about exaggerated article titles :)

it's research and it's still valuable, even though yours truly might not yet be able to buy it at fry's yet.

some research might become available on the end-user, some won't. Often HN worthy stuff isn't really end-user though.

For me personally, it's good enough if it manages to inspire and interest others.

Soon I hope, I want to write software that runs a million times as slow.

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