Making no apologies for its bandwidth- and distance-expanding technology, an optical networking startup unveils its initial plans for DWDM, dispersion compensation, and fiber amplifier subsystems.
By: Erik Kreifeldt
Emerging from a year of venture funding with three optical subsystems in its initial product plans, Avanex Corp. (Fremont, CA) is combining diverse talent, new technology, and robust design capability to improve the cost, size, and efficiency of optical networking systems more quickly than the major equipment suppliers.
"We're a step up from a component supplier and a step down from a system supplier," says Avanex chief technology officer John Fee, who formerly spearheaded optical networking efforts at MCI and subsequently MCI WorldCom (Jackson, MS). "We understand what gives network operators heartburn," he continues. "Then, we can design something very quickly and assemble it."
To understand and solve optical network problems quicker than the telecommunications equipment giants, Avanex has armed itself with a formidable brain trust and design capability. Employees hail from MCI WorldCom, Pirelli Cables & Systems North America (Lexington, SC), and E-Tek Dynamics (San Jose, CA). The combined experience draws from the carrier, system integrator, and component supplier spaces, respectively.
In addition to talent, Avanex has cultivated optical network modeling capability that rivals that of major manufacturers and facilitates rapid product cycle times, according to Fee. Based on an outsourced software platform, Avanex has written in its own transfer functions, enabling designers to model performance among "pages" of variables.
Funding the Avanex operation are CrossPoint Venture Partners, JAFCO America, Sequoia Capital, and Mayfield Venture Partners. The startup is working on its third round of funding, $7.0 million in March, which follows $2.5 million in May 1998 and $1.0 million in February 1998.
Avanex is taking a four-dimensional approach to improving the performance of optical networking equipment: More wavelengths, higher bit rates, longer distance, and greater number of add/drop nodes, explains senior VP for technology development Simon Cao, former technical director for E-TEK. The first three products in the company's portfoliodubbed "photonic processors"are an adjustable dense wavelength division multiplexing (DWDM) subsystem, a tunable chromatic dispersion compensator, and a low-noise fiber amplifier.
Number of channels
Although he won't elaborate on the technique while Avanex secures its intellectual property, Cao characterizes the first product in Avanex's portfolio as a "fourth generation" DWDM subsystem that introduces a whole new way of multiplexingnot just another filter technology. "It's true optical signal processing," offers Fee.
The subsystem operates independent of channel spacing, bit rate, and power level, offering any number of channels that can fit into a given combination of amplifier bands, Cao continues. "The ultimate measure is how efficiently we use the bandwidth," he says. Defining efficiency as the ratio of signal bandwidth to channel spacing, he claims that the Avanex subsystem delivers 80% bandwidth efficiency, compared with the 20% put forth by state-of-the-art DWDM gear.
"My dream [while at MCI] was to drive multiplexing technology to be limited by information bandwidth," says Fee. His group initially sized channels with 24 nm spacing because the filter technology slope was too poor for tighter spacing. "Ideally, you'd put the signals right next to each other," he continues. Even with improved channel spacing, today's systems are filter-limited, not information bandwidth-limited, he adds.
Variable channel bandwidths
Today's filters are also limited to one type of signal, be it OC-48 (2.5 Gb/s) or OC-192 (10 Gb/s), Fee says. Although transponders enable network operators to mix and match transmission equipment on the same DWDM filter, the filter must accommodate the higher bit rate signal and space channels accordingly. Sending an OC-48 signal through a filter designed to accommodate higher-rate OC-192 signals with wider spacing is an inefficient use of the total information bandwidth, Fee notes.
"This technology allows you to mix and match the filter technology for the information bandwidth," Fee says of the Avanex subsystem, which adjusts channel spacing to accommodate different bit rates on each channel passing through the unit. Because the subsystem is a passive module, he asserts that the module does not propose major network element management system challenges. From a network operator perspective, Fee characterizes the subsystem as "a frequency-selectable patch panel."
The Avanex subsystem fills the gap of channel spacing presented by today's DWDM systems, Cao explains. A typical application would connect an Avanex subsystem to a channel port from a first-generation DWDM system, such as an 8-channel unit with 400 GHz spacing. "Carriers can still buy old, mature technology, then fill up the passband," he points out.
Avenex offers an example that uses its subsystem to multiplex 160 channels spaced at 50 Ghz. The subsystem demultiplexes eight bundles of 20 channels, which feed eight 20-channel demultiplexers with 400 GHz spacing. The end user saves money and space by using the 400 GHz units, but realizes a 160-channel throughput.
Avanex's second product, due to ship in beta units in the third quarter of 1999, is a tunable chromatic dispersion compensator. The electro-mechanical technique uses technology licensed from Fujitsu, Cao says. "It works exactly like a variable optical attenuator."
The device competes with modules offered by Lucent and Corning that use fiber coils to compensate for dispersion. One square-inch Avanex module placed on each end of a typical 400 km standard singlemode fiber link performs as well as five of the 23-in. fiber coil modules inserted at each amplifier site, Cao explains.
The compensator's tunability accommodates different bit rates and span lengthsparameters for which traditional compensators must be individually designed. Tunability also obviates problems with keeping many different kinds of compansators in stock for different applications. "We had many heated arguments with our dispersion compensation suppliers about inventory," Fee recalls of his MCI daysarguments that the Avanex approach would put to rest, he says.
Although today's dispersion compensation techniques enable OC-192 transmission on standard singlemode fiber, Fee says the OC-192 terminals do not operate at their optimal performance in this scenario. At 40 Gb/s, the range of dispersion tolerance2 kmbecomes too tight to operate within, he adds.
The third item in the Avanex arsenal is a line of low-loss bidirectional fiber amplifiers that enable transmission distance upwards of 5,000 km without electrical signal regeneration (now required at 600 km). "This amplifier is a brand new concept [based on] a new component that allows super-low noise," Cao says, adding that the amplifiers most important features are the way it handles dispersion mapping and optical nonlinearities.
Based on network designs that accept today's regenerator spans, the current generation of ultra-broadband cross connects maintain an electrical switch fabric to transport signals at STS-1 (52 Mb/s) and higher. It makes sense to groom traffic electronically where the signals are already broken down in the electrical domain for regeneration, and the spans match the distances between major cities and network hubs in the US, Cao observes. "But we believe that as soon as you solve the problem of transmission distance, optical cross-connects start to make sense."
An optical cross-connect based on the distances enabled by the low-noise amplifiers and dispersion compensators would enable the transparent pass-through of cross-country express traffic through network nodes without unnecessary electrical regeneration, Fee notes. "That's why you're starting to see some companies doing soliton work," he continues. "They're sending a clear message to systems providers: 'Do not try to come in here and sell us regenerators."
Bigger and longer pipes versus intelligence
In an industry fraught with activity related to turning DWDM wavelengths into networks with ultra-broadband cross-connects, optical add/drop multiplexers (OADMs), and software intelligence, Avanex executives make no apologies for focusing on transporting more bandwidth over longer distances. "OADMs and [ultra-broadband] cross-connects are more of an application," offers Cao.
"You've got to be able to put wavelengths on the fiber firstthen you worry about what you do with them," Fee says. "There is no reason we can not build different combinations of these optical processors to suit different applications in the future."
Push and pull
"We would like one day to be the Intel of this business," says Avanex president and CEO Walter Alessandrini, who held the same position recently at Pirelli Cables & Systems North America. Like the "Intel Inside" moniker on personal computers, carriers will end up with "Avanex Inside" network gear if the push-pull model pans out. Avanex refers to its product line as "photonic processors," which completes the analogy.
Using what Alessandrini calls a "push-pull" model, Avanex demonstrates its technology to network operators, convincing them to prod their vendors to integrate the Avanex product into the network equipment that the vendor supplies the carrier. "We market the systems to the end user, then we sell the product to the system provider," he explains, adding that Avanex is receiving orders for its DWDM subsystem from both carriers and system integrators.