Liquid Crystals and Lasers

Wan2Be writes "A new kind of glass pane that quickly switches from transparent to diffracting and back again. The change is triggered by applying an electric field, so the pane could easily be controlled by the electric signals of a computer, offering a powerful new way to steer beams of light."

Comments

Too slow for communications

[hbackert]

LCs are very slow compared to what is nowadays the speed bits traveling along a glass fibre. I cannot see a useful way of using it directly to redirect or modulate laser light. Maybe indirectly (like in getting rid of reflections), but this technology is still slow compared to what you can do with real crystals. Those are unfortunately very delicate objects (humidity is bad, bad, bad) and pretty expensive and you cannot make large ones (but you do not need to as laser light is usually small area-wise).

So unless someone shows me a useable way to use this technology, I will put it in the box Interresting technology with no current use with Internet attached to it to make it seem more interresting than it is.

Re:Too slow for communications

[x00101010x]

You are correct, too slow for communications.

However, many areas of manufacturing these days use lasers, and these would be plenty fast for those applications. They would also get rid of moving parts, which is great since many manufacturing environments contain large amounts of airborne debris which require anything with moving parts to me continually maintained/replaced.

So, maybe not fast enough for communication, but fast enough for other things. Also, given enough time, it could catch up with desirable data speeds..

Re:Too slow for communications

[js7a]

given enough time, it could catch up with desirable data speeds

Liquid crystals are really slow. You really have to struggle to get 35 ms switching out of them, which is what the movie people want. These diffraction switches are a lot faster, but I doubt they'll ever get faster than 0.5 ms.

The basic problem is that you're dealing with long strands of polymers which orient themselves almost but predictably not quite parallel to each neighboring polymer strand, unless a current is flowing, in which case they just align strictly parallel to each other. It takes time, lots of time, for the reconfiguration to occur, because it is a fundamentally mechanical process.

The article cited did a horrible job IMHO of representing the underlyng science. The regularity of the crystal droplets has nothing to do with the new effect -- which is using a thinner layer of liquid crystals to difract instead of polarize, which requires thicker LCs. The droplet regularity is an artifact of the thinness, not a cause of the essential property as is purported.

Re:Too slow for communications

[shamino0]

LCs are very slow compared to what is nowadays the speed bits traveling along a glass fibre. I cannot see a useful way of using it directly to redirect or modulate laser light.

LCs are definitely too slow to be used for something like modulation or per-packet switching, given current data rates (an OC-192 fiber carries approximately 10Gbps, or one bit per 0.1ns).

But there are other uses. It is still useful for pure optical circuit-switching applications, where you want software to set up an optical circuit that will not change for a long time (hours, days, maybe even years) until it is explicitly reprovisioned or rerouted.

This is currently done with very small electro-mechanical parts that can optically redirect light from each input fiber to the appropriate output fibers. A system that can do it using a diffracting LC (such as that described in the article) would be able to do it with no moving parts - greatly increasing reliability. It would probably also be faster, although that's less important for this application, given the large amounts of time that the optical circuits are likely to remain established.

Depending on how precise they can control the diffraction, it might even be possible for one LC to diffract multiple wavelengths in different ways, and be able to control them individually. If this can be accomplished, it makes Wave Division Multiplexing (WDM - where multiple optical circuits are carried on one fiber using multiple wavelengths) easier to implement, since you would no longer have to separate the wavelengths into separate fibers before switching them.

Re:I hate to break it to you...

[Smidge204]

Ah, but that's just turning opaque. This stuff doesn't turn opaque, it refracts. This allows for not just blocking the light but reaiming/controlling it as well.

Very similar concept, almost identical process, but quite a difference overall.

If you bother to RTFA, it says:

"The big difference between what we do and what has been done before is that older-style glass panes contain a random distribution of drops and drop sizes ... without any order in the drop size and spacing, these older liquid crystal systems simply scatter light in all directions ... In our case, ... we're able to steer light in specific directions"
=Smidge=