A new circuit that combines electrical and optical components could speed the deployment of fiber-optic networks to homes, which would usher in a host of new services, including Internet-protocol television. The technology is currently being developed by a handful of companies in both the United States and Japan.
Today, fiber-to-the-home (FTTH) is available in only about 15 U.S. cities, as well as some urban areas in Japan, Korea, and China, in part because it takes a huge investment of time and money to build all the infrastructure: to dig new trenches, to lay new fiber, and to install the fiber utility box on homes.
But there’s another hold up: it’s expensive to manufacture and deploy all the individual optic-fiber devices, called “triplexers,” that must be affixed to houses. These triplexers, which come into play where the fiber connects to the home, contain the electrical and optical components that guide and collect the data-carrying photons that become Web pages, telephone calls, or video.
While new technology may do little to solve the problem of ditch-digging, it could make it much cheaper to produce triplexers, by integrating multiple functions onto a single chip. This technology, called a planar lightwave circuit (PLC), is already used in some fiber network applications. But there it integrates only optical components – for applications such as triplexers, the chip needs to incorporate both electrical and optical components.
The optical structures in a triplexer, the waveguides and filters, direct the incoming information and split the photons delivered through the fiber-optic pipes into two wavelengths (1,550 nanometers carries analog information such as video and 1,490 nanometers carries data such as Internet and voice). Meanwhile, one type of electrical component, small detectors, collects the photons coming into the home, while the another, lasers, produce light (at 1,310 nanometers) that sends information away from the home (say, an e-mail or phone call).
Today’s triplexers are made in two separate steps: optical waveguides are deposited on a chip, and then separately housed lasers and detectors must be carefully aligned and attached to the waveguides. Since much of the alignment must be done manually, manufacturing is costly and time-consuming, says Mario Dagenais, professor of electrical and computer engineering at the University of Maryland. The new triplexer PLC technology is able to integrate optical and electrical components onto a single chip, Dagenais says, by borrowing well-honed processes from semiconductor chip manufacturing.
Although it’s still in the testing phase, this kind of device could ultimately drive down the price of producing fiber-optic connections to homes and buildings, says Ferris Lipscomb, vice president of marketing at NeoPhotonics, a San Jose-based optical components manufacturer.
NeoPhotonics has developed one PLC triplexer. In their process, glass waveguides and filters are deposited onto a six-inch silicon wafer, and then semiconductor lasers and detectors are bonded onto the substrate in an automated process. Currently, PLC triplexers from NeoPhotonics are being field-tested by large telecommunication companies. NeoPhotonics expects them to be deployed in FTTH networks within a year.
Despite its promise, though, PLC triplexers are not yet the most cost-effective solution to getting fiber optics into the home, says Fred Leonberger, senior advisor at MIT’s Center for Integrated Photonic Systems, simply because the market isn’t big enough yet to justify the cost of developing the technology. Instead, the current solution of separately assembling triplexers is economical for the number of current consumers. “For that volume, it’s the cheapest solution,” he says.
As of February 2006, 3.6 million homes in the United States had the capability for a direct fiber connection, yet there were only about 548,000 subscribers, according to the Fiber-to-the-Home Council and Telecommunications Industry Association.
Still, points out Dagenais, Verizon began rolling out its FTTH program in the United States a couple of years ago (see “To Fight, Verizon Switches”), and has continued its commitment to bringing fiber to homes. The demand, he says, will drive the need for more FTTH devices such as triplexers, and this is where PLC technology will thrive. “Fiber to the home has been talked about for years,” says Dagenais, “But I think it’s finally coming.”
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