New option on the networking menu: Optical CDMA gives carriers something else to think about

Supercomm '98 featured one of the most interesting developments in optical networking in some time. Commercial Technologies Corp., Richardson, Texas, will deliver an optical networking system based on code division multiple access in early 1999.

Applying CDMA to an optical network is more difficult than applying it to wireless.

Keeping the photons in one channel from interfering with another was the primary challenge for CTC, said Bill Johnson, CTC's chief operating officer.

"The challenge is to put a whole lot of channels [on the fiber] without one interfering with another," Johnson said. "If you take the phase of a signal, if it's 180degree out of phase with another, they cancel each other."

To correct that problem, CTC developed "photon phasing." But because the patent is pending, CTC won't explain how it works. Still, Johnson hopes the company's presence at Supercomm will generate interest.

"My goal is to say, 'Here's something very new that you've never heard of, and we want a place in your budget,' " Johnson said.

Scott Clavenna, senior analyst for Pioneer Consulting, recently completed a study projecting optical networking deployment through 2007. The study ended up focusing on wavelength division multiplexing (WDM) deployment although the initial plan called for including optical CDMA.

"It seems that development is going on in laboratories, but we couldn't come up with a way of evaluating [optical CDMA's deployment prospects] to include it in our report," Clavenna said.

That's an indication of how little is known about optical CDMA as a commercially viable system. But Johnson claimed that CTC's CodeStream product will help advance the industry toward true all-optical networking.

CodeStream uses a single light source, which passes light through filters to create up to 128 channels by blocking certain portions of the light source and letting others through. A receiver has a filter that matches one of the bar codes generated by transmitters on the system and receives only those signals that match its filter (see figure).

The system is cheaper than a high-channel WDM system because the WDM system requires one laser per channel. The bar code system allows all channels to be transmitted to all points on a network served by the CodeStream system, allowing for optical-level cross-connecting and add/drop, Johnson said.

Although the system may compete with WDM in channelizing fiber, it may be used with WDM systems, Johnson said.

"Carriers could use WDM on express channels and CDMA on add/drop channels," he said. "We're creating an environment where everything's photonically switched."

The system is built from off-the-shelf components and doesn't require high-speed backplanes or multilayer circuit boards, Johnson said. The price will be $20,000 to $35,000 per channel, depending on quantity and functionality ordered.

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