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...

[Anonvmous Coward]

" Similar technology has been available for years (I remember when it was first becoming commercially available in the early to mid nineties). In fact, there are offices with conference rooms with entire walls made of these types of windows."

Anybody remember Star Tours in either Disney Land or Disney World? (Is that ride still there?) When you enter the main building and see R2D2 and C3PO working on a transport, look to the right and up. You'll see a big movie screen composed of a few small squares of semi-transparent glass. If you look carefully, you can see the glass go from clear to foggy in a pre-programmed pattern.

I was 12 when I noticed that. Man, I can't believe 13 years have gone by and I still remember that.

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=

Could be useful for holographic storage

[Krellan]

Something that can aim a beam of light without needing a moving part could be very useful for holographic storage.

I hope this development can help with improving holographic storage. Someday, the hard drive will reach its limit, and people will grow tired of the noise and reliability problems....

Weird Science

[DerekLyons]

A quote from the article;

Link and colleagues aren't sure what they're going to find when they shine light through several stacked-up layers of these ordered droplets ... that's what's so exciting about doing it! It might split the light up into a rainbow, like a prism, or it might affect the light in a totally unexpected way.

This verges awfully close to being junk science. If you don't have some expectations to compare results to, or some theory of what the results are likely to be, it's awful hard to come up with valid results. Having something other than your expectations occur is OK, as is having your theory be wrong. That's how science advances, by figuring out how and why you were wrong. Bad science happens when the opposite occurs, when you handwave away results that don't meet your theory, or rig results and experiments, or when you assume something you don't understand is something it isn't. (Pons and Fliechmann made all of these mistakes and more.)

Re:Weird Science

[RobertB-DC]

This verges awfully close to being junk science. If you don't have some expectations to compare results to, or some theory of what the results are likely to be, it's awful hard to come up with valid results.

I agree with your point, especially when the article goes on to say:

But first they need to find reliable ways to arrange the droplets into various 3-dimensional patterns. This is where low gravity comes in handy. Weightlessness greatly simplifies making 3-D structures from fluid droplets...

To a technical reader, it looks suspiciously like a hammer (weightless environment) looking for a nail (ooh, multilayer refracting LCDs!).

One thing to remember, though, is that "Science @ NASA" is not targeted at technically savvy folks like we /.ers. The site's home page says as much:

The Science Directorate at NASA's Marshall Space Flight Center sponsors the Science@NASA web sites. The mission of Science@NASA is to help the public understand how exciting NASA research is and to help NASA scientists fulfill their outreach responsibilities.

The article we're dissecting here wasn't designed to explain LCDs in accurate technical detail, nor was it supposed to present the pros and cons of the technology. It's clearly written to "help the public understand how exciting NASA research is" -- and nothing else.

IIRC, the Science @ NASA info used to be a little more in depth. Then, a funding squeeze nearly killed the website altogether. Apparently, the only way they were able to get funding for this basic communications vehicle was to direct it at the least common denomonator. I used to get their email updates, but I dropped them quite a while back -- I think because the articles lost their tech-geek appeal.

Great thing for rear windows on cars

[tjstork]

Or driver side mirrors. As soon as some SUV does the brights on you, just turn your windows to black...

Re:Great thing for rear windows on cars

[henrygb]

... or for a variable sun roof. The Maybach 62 - a Mercedes for people with too much money - has an adjustable rear roof. "The laminated glass pane on the inside has an intermediate layer in the form of a liquid crystal membrane of conductive polymer plastic. The membrane has a cable connection to a control unit which generates an AC output of 90 volts. Switching the power on arranges the crystals in the plastic membrane in such a way that the glass becomes transparent and allows daylight into the rear of the Maybach 62 over its entire area. The special feature is that as soon as the AC voltage is switched off, the liquid crystals lose their transparent arrangement and the light is fragmented in all directions. The glass becomes opaque and filters the daylight to produce a pleasant, diffused glow, with only approx. 76 per cent reaching the interior. This electrically controlled transparency has its world premiere in the Maybach 62. Thanks to this unique roof technology the rear passengers in this luxury motor car can decide in accordance with their mood or the weather conditions whether to enjoy a bright interior flooded with daylight in which to admire an exclusive, panoramic view of the scenery, or whether to relax beneath a semi-transparent glass dome."

transparent to reflective

[greywire]

is there any kind of LCD or other material that can go from reflective to transparent?

I have an invention idea that requires such a thing.

It also would need to be able to switch pretty rapidly...

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

[jafuser]

I didn't catch that in particular, but Innoventions (at Epcot) used to have some home tech exhibit where they had windows which were 5 or 6 feet tall by 1 or 2 feet wide which transitioned between clear and opaque using liquid crystals.