Trellis Photonics (www.trellis-photonics. com) expects to begin next month beta tests of an optical switch based on electroholography, which the company says is a fundamental breakthrough in material science that could rock the world of high-tech.
Electroholography, for which the company holds the patent, is the only optical switching method that is solid state and wavelength-specific. This results in a variety of economic, network management and speed benefits as compared with other optical switching methods, says Trellis CEO Tim Cahall.
The technology, developed by Trellis director and co-founder Aharon Agranat to offer a computer representation of a human brain, uses holograms inside crystals to steer individual wavelengths in nanoseconds. Other popular optical switching technologies, such as Micro-electromechanical Systems (MEMS), do it in millionths of a second, according to Trellis.
With electroholography, the crystals are arranged in rows and columns, like a garden trellis. Light travels through them until voltage is applied to, for example, a crystal with a hologram written for red. Zap it with voltage, and the red is individually routed.
About 90 percent of the light hitting a specific crystal is switched; the other 10 percent serves a monitoring function. It also allows for power balancing of wavelengths traveling together on a single fiber.
Cahall explains that other optical switching methods including movable mirrors, aka MEMS; heated waveguides; ink-jet bubbles; and solid crystals are optomechanicals, and therefore have moving parts and move atoms.
On the other hand, Electroholography moves only electrons. The optomechanicals are "white light switchers," which means that they switch light only in one color, whereas electroholography switches multiple colors of light.
Lucent Technologies Inc. (www.lucent. com) and Nortel Networks Ltd. (www. nortelnetworks.com) use MEMS technology. Corning Inc. (www.corning.com) and JDS Uniphase Corp. (www.jdsuniphase.com) employ MEMS and liquid crystals. Agilent Technologies Inc. (www.agilent.com) has embraced bubbles technology. None of the large companies has adopted acousto- or thermo-optics to date, according to Cahall.
With the movable mirrors method, a device shines light in a mirror and moves the angle of that mirror to reflect light to a different mirror, thus directing the signal to a different path. Crystals work much the same way, but instead of mirrors, the crystal method employs light polarization techniques. With the ink-jet method, bubbles are within a waveguide, and light passes through it and across the glass where a capillary of oil acts as a mirror to reflect light to a different waveguide.
In addition, two non-optomechanical options include acousto-optic and thermo- optic switching, but these use waveguides, which Cahall describes as fiber inside glass. He adds that they are not wavelength-specific.
Today's typical optical systems (not employing optical switches) only can run 10 billion bits per second, but the industry employs DWDM to increase that to around 40 billion bits per second, says Cahall.
"If you switch all light in a fiber together, you can have 40 [billion bits] coming in one place and ending in one place. But you want to add and drop, meaning you have to access different colors," says Cahall. "With other [optical switching] technologies, you have to put a filter in front of the switch to pull out colors of light, and they lose as much light as they would traveling through 20 miles of fiber. So power is lost, and there is a need for regeneration."
Then a carrier can do switching between different fibers, he says. But because the colors of light were taken from different fibers and put on a single fiber, the different wavelengths are powered differently, so an additional optical attenuator is needed for each different wavelength on that fiber to adjust its power. That means 40 different optical attenuators per fiber--adding cost, complexity and maintenance, says Cahall.
Plus, carriers then need to remultiplex the traffic. And there's no way to do network management for all that traffic, he adds.
A Different Method
Electroholography, however, is wavelength-specific, so it doesn't require the filters and antennuators. It does all the muxing in the switching fabric, rather than requiring separate boxes for the multiplexing function.
Electroholography also provides a network-management feature not found in other solutions, says Cahall.
Trellis uses the half decibel of light that can't be switched, but is optically identical to the given signal to allow the network operator to do a CRC, or cyclic redundancy check, on a signal at any point in the network. CRC allows the network operator to validate the bit stream and check for possible corruption.
The Trellis Intelligent Lambda Switch, offering 240 wavelengths, is expected to be in betas at the end of June. General availability, plus 480-, 960- and 1920-wavelength models, is slated for the end of the year.
