'Optochips' swing open a new door for improving optical products
By ROBERT PEASE
Research at the University of Southern California (USC) and the University of Washington has yielded impressive results in achieving speed and capacity increases for optical applications. New polymers were substituted for traditional lithium niobate to create new "optochips," or polymeric electro-optic modulators, that can outperform today's standard modulators by a factor of 10 times or more in terms of information-processing speed.
The optochips are microscopic de vices that perform functions such as translating electrical signals-television, computer, telephone, and radar-into optical signals at rates up to 100 Gbits/sec. The major advantages are in frequency response and power consumption.
"The new polymers allow a much larger frequency response, which translates into a higher bit rate for digital communications or larger bandwidth for RF [radio frequency] analog communications," says James Bechtel, senior vice president at IPITEK, a fiber-optic systems manufacturer in Carlsbad, CA, that is testing the new devices. "But the main significance is the very low drive voltage-less than 1 V compared to around 5 V used in comparable devices today.
"The power consumption is the square of this half-wave voltage. So if you decrease the driver voltage by a factor of five, you lower your power consumption by a factor of 25. The polymers are also more readily adaptable to heterogeneous integration with other material than lithium niobate is," adds Bechtel.
Lithium-niobate crystals used in today's electro-optic modulators require a power source of 5 V or more to operate, creating problems due to heat generation that, in turn, results in a loss of signal in the data stream. Using less voltage enables data-transmission rates to increase dramatically. Since the new polymers require less than 1 V, less heat is generated and data rates can be increased 10-fold.
Electro-optic modulators are devices that serve as a bridge between electronics and fiber-optic equipment. The new polymers promise a new generation of large-capacity devices with very low noise and very-low-power consumption.
Although the recent announcement of this enabling technology centered on optical modulators, the new polymers are causing quite a stir among manufacturers of integrated optic devices. The optochips are viewed by many as a major breakthrough that could lead to more efficient routing switches, sensors, directional couplers, and other optical-networking devices.
USC electrical engineer William Steier, who collaborated with Larry Dalton, a chemist at the University of Washington, and other researchers, dubbed the optochip technology as "the Holy Grail the people in the fiber-optic business have been looking for." That would put the technology in the category of dense wavelength-division multiplexing (DWDM), which may be a bit premature until more tests and trials are successfully completed.
"There's still work to be done, but I think it's a very exciting announcement," says Bechtel. "We don't have all the answers yet, and there's still a lot of testing to be done, but the preliminary results indicate this is a pretty significant breakthrough in material science. As a result, it's also a pretty significant breakthrough in integrated optics."
There are a number of applications for the technology in telecommunications, says Bechtel, including long-distance, high-speed communications. For cable TV, the technology could be applied in the super trunks and long-distance cable transmitters that are primarily external modulator devices, such as Mach-Zehnder modulators used for very-high-speed digital and cable-TV trunks.
The interest of several major optical equipment manufacturers has been peaked, but although they may be making plans for commercial development, most aren't willing to show their hands at this point. Polymer integrated optics, however exciting, has to endure the same maturing process as other enabling technologies. But it's a safe bet that some companies are heading to their respective drawing boards to research and develop ways to apply it in new products. The promising outlook for large-scale production and fabrication, similar to that of electronic integrated circuits, should also equate to low costs for the optochips and related new devices.
"I think the thrust of additional research will be in manufacturability and long-term reliability," says Bechtel. "The basic idea of how to make [these devices] is already well established. But we still need to do some manufacturing engineering to get to the point of making these devices in large quantities."
At IPITEK, for example, Bechtel says the company intends to use the devices for its own transport systems and expects other vendors to do likewise. He expects the technology to eventually evolve into a very competitive new market.
"I think the data market is growing faster than the demand for memory grew in the computer industry," says Bechtel. "So the Internet is driving the expansion of fiber-optic communications and other types of communications at a pretty hefty rate. This is one step in helping that growth continue."
Companies such as IPITEK have already successfully tested prototype devices, and products that incorporate the polymer-based devices could be sold in limited quantities very soon. Most believe it will be a year or two before the higher-capacity devices are ready for the marketplace.
"At IPITEK, we could have sold prototype products that have already undergone testing by other people, but we haven't done that," says Bechtel. "We're just not ready and want to do some more testing, including further development of the manufacturing technology. But I think in one or two years, they will be available in significant volume."
The new polymer research, paid for by grants from the National Science Foundation, the U.S. Air Force Office of Scientific Research, and the Office of Naval Research, is aimed at developing new materials based on the principles of condensed-matter theory. Although this latest breakthrough significantly affects the fiber-optic telecommunications industry, other properties of the polymer materials, such as a resistance to radiation, are sparking interest in the space and satellite communities.