Optical Switches Go Acoustic

It’s time to add another weird technology to the list of potential switching fabrics that could revolutionize Internet backbones.

We’ve already had tiny tilting mirrors, liquid crystals, and ink-jet printer bubbles. Now we’re about to get acousto-optical switches, ones that use sound waves to deflect beams of light from one fiber to another.

Like other technologies in this space, acousto-optical switches aren’t new. They’re already used in lab equipment, projectors for movie screens, and all manner of optical widgets. Now, however, a couple of companies are developing full-scale telecom switches based on the same technology.

One is Gooch and Housego PLC http://www.goochandhousego.com, an established manufacturer of acousto-optical devices based in Ilminster in the UK. It's quoted on the AIM (Alternative Investment Market), London's equivalent of Nasdaq’s OTC Bulletin Board, under the ticker symbol of GHH.

The other is Light Management Group http://www.lmgr.net (whose web site was down at press time), a manufacturer of outdoor advertising screens based on acousto-optical technology. It’s headquartered in Burlington, Ontario, and its shares are traded on Nasdaq’s Bulletin Board under the ticker symbol of LMGR.

The share price of both of these companies see-sawed violently earlier this year, as speculators (over)reacted to news of their respective projects.

In Gooch and Housego’s case, its chairman referred to a “breakthrough” in the development of its switch in the company’s annual report. It was picked up by a national newspaper, and Gooch and Housego’s share price rocketed from 80-85 pence to £6 (about $9) in February. The company then issued a statement saying that it was a long way from producing a commercial product, and its share price sunk back. It was trading at £2.02 this morning (June 20).

It’s been a similar story at Light Management Group. Its stock shot up from 12 cents at Christmas to $17 in February, when the company announced its optical switch developments. Since then, it’s sunk back to around $3.50. (It’s been climbing today, following a news announcement not connected with the company’s switch developments.)

In both cases, investors have contacted Light Reading, asking what's going on. So, here’s the score:

Why acousto-optical switching?

The technology has two big plus points, according to its promoters. First, there are no moving parts -- and thus nothing to jam, break, or wear out, as is the case with MEMS (micro-electro-mechanical systems), the technology behind the tiny tilting mirrors being used in most all-optical switch developments at the moment.

Second, acousto-optical switches have very low losses. The sound waves that switch the light also re-energize it, unlike other optical switching technologies.

The downsides? Acousto-optical switches are relatively slow. They take around 10 microseconds to switch from one wavelength to another, which rules them out for handling packet-by-packet routing and raises a question mark over whether they could be used for automatically re-routing wavelengths around failures.

Acousto-optical switches can also be expensive to make, according to Eddie Young, president of Neos Technologies Inc. http://www.neostech.com, a manufacturer of a wide range of acousto-optical devices. Neos makes a switch for lab use but hasn’t developed one for use in telecom networks. At least a couple of other companies – Brimrose http://www.brimrose.com and Intra-Action Corp. http://www.intraaction.com - are in a similar position to Neos. They make acousto-optical switches, but not for telecom applications.

Here’s the scoop on the two companies that are taking the plunge:

Light Management Group

This outfit is adapting its existing laser screen technology, which works by moving a laser beam carrying different colors across a screen in the same way that a cathode ray tube paints a TV picture – step by step, row by row, like knitting.

The laser beam is shone through two special crystals, one for controlling horizontal movement and the other for controlling vertical movement. The deflection angle is controlled by transmitting sound waves through the crystal. The frequency of the sound wave controls the angle of deflection and the volume of the sound wave controls the light’s intensity. The science behind this effect is complicated and best left to boffins.

Light Management Group already makes devices that project light beams onto screens using 256 horizontal movements in 256 rows – a total of 65,536 different positions. The same technology can be used to produce a 256 x 256 port switch, according to Don Iwacha, the company’s president.

However, it isn’t quite as simple as that, because the light isn’t all going in one direction, as it is in the projector system. It has to come in on one port and go out on another, which is equivalent to light starting from one location on the screen and being bounced back onto another location. Quite how Light Management Group achieves this isn’t clear. It’s also unclear how this setup would deal with contention – having to handle several connections between input and output ports at the same time, without blocking any of them.

Light Management Group has already demonstrated the concept behind its planned switch and is now building a “commercial prototype” for delivery by the end of the year, according to Iwacha. He emphasizes that it won’t be a complete switch. It will be a subsystem that OEMs can incorporate in commercial products.

Gooch and Housego

This company’s developments are being kept under wraps, but “Pablo”, an investor in the company, has helped Light Reading track down some intriguing information.

Gooch and Housego isn’t using crystals to divert beams of light from one output port to another. It’s using a fiber invention patented by staff at the Opto-electronics Research Laboratories at the University of Southampton – an outfit which coincidentally announced its own startup, Southampton Photonics Inc., last week (see Fiber Components Excite VCs).

Here’s the big picture: This development makes use of devices called “fused couplers,” which comprise two pieces of fiber that are fused together at one point, rather like Siamese twins. The fusing is done in a special way so that light of a certain wavelength jumps from one fiber to the other, while other wavelengths continue on the original fiber.

In the early 90s, Southampton University came up with a way of using these passive splitters to make active switches, using sound waves. In this case, the sound wave is pumped into the fiber in much the same way as secondary lasers pump in light to boost signals in optical amplifiers. Some of the sound’s energy is transferred to the light, with the result that a different-frequency light jumps across the divide into the adjoining fiber. That’s switching in an elementary form, and it is what’s covered in the above patent.

Gooch and Housego won’t say how far it’s got towards using this technology to make a real switch. Financial director Ian Bayer emphasizes that it’s a research project that may or may not come to something. He points out that Gooch and Housego, unlike startups, has an established business (with P/E ratio of 22) that’s growing at more than 40 percent a year. Investors should focus on this, says Bayer. The research project "is a bonus", he adds.

By Peter Heywood, International Editor, Light Reading, http://www.lightreading.com
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