EDWAs enable tomorrow's optical modules and subsystems

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The promise of erbium-doped waveguide arrays (EDWAs) as a lower-power alternative to erbium-doped fiber amplifiers (EDFAs) is resonating with many optical module and subsystem manufacturers. For the metro and enterprise spaces, in particular, EDWAs are smaller and more cost-effective—and new manufacturing techniques are adding even more functionality for system-on-a-chip (SoC) products.

Although the physical concept of an EDWA is the same as an EDFA, the medium is different. Instead of using a doped fiber, EDWAs are waveguides that have been embedded in an amorphous erbium-doped glass substrate—a process that is less costly than doping fiber (see Lightwave, February 2001, page 203). Erbium atoms provide the glass with gain in the 1550-nm fiber-optic window. The waveguide itself is a localized increase in the glass refractive index.

EDWAs, like EDFAs, are used as gain elements that compensate for optical losses between network elements. Unlike the typical EDFA, however, EDWAs can stand alone or be integrated with other components.

Several manufacturers are currently offering EDWAs commercially. Teem Photonics (Meylan, France), Molecular OptoElectronics (MOEC —Watervliet, NY), and Inplane Photonics (South Plainfield, NJ) have each announced EDWA products that offer a lower-cost alternative to traditional EDFAs. These and a handful of other manufacturers believe that waveguide technology has matured and is well positioned to respond to an ever-increasing demand for optical components.

Inplane Photonics claims the highest level of function integration—32 function—on a single EDWA chip. These functions include amplification, combining, splitting, and filtering. Inplane also recently demonstrated the function of "pump-sharing" at September's National Fiber Optic Engineers Conference in Dallas. The design enables several amplifiers to be driven by a single pump, such as the 980-nm pump laser. Since much of the optical-system costs stem from components, amplifier arrays are attractive because they drastically lower the cost per amplifier.

"The cost of an amplifier resides mostly in an individually packaged pump laser," says Tek-Ming Shen, vice president of product management at Inplane. "A lot of effort has been spent on reducing the cost of the pump through increasing the output power of the laser chip. This trend does not benefit amplifiers for sub-band and per-channel amplification, because each amplifier requires only modest power."

For instance, if a system design requires four amplifiers of 50 mW each, a single EDWA array using a 100-mW pump at an average cost per waveguide of $450 may be specified. Similarly, at higher powers, the pump-sharing function enables an EDWA array to use a single 200-mW pump at $1,000 shared by four amplifiers. The $250 per channel equates to an 80% cost advantage.

The applications for EDWA arrays include receivers, transmitters, and inline amplification. These applications can address several market segments, including the 10-Gbit/sec metro and metro core, 10-Gbit/sec long-haul, and 40-Gbit/sec metro and long-haul markets.

EDWA designs that support functional integration and cost-saving techniques like pump sharing will help spur continued growth in the optical IC market. In-Stat/MDR, a market research firm based in Newton, MA, projects that the optical IC market will reach $1.8 billion by 2006. Companies like Intel (San Jose, CA) are keenly interested in these SoC products.

"We look to integrate gain elements, both single and multiple channels, into our products to provide enhanced functionality to our customers," says Jerry Bautista, chief technologist at Intel Photonics Technology Operation. "This includes applications such as passive optical networking for access applications."Th 117746

This erbium-doped waveguide amplifier manufactured by Inplane Photonics demonstrates integrated pump-sharing waveguide structures on a chip level, with each individual channel controlled by a variable optical amplifier, a much-desired feature by cable television and passive-optical-network operators.

As EDWA arrays continue to develop with the integration of more functions, both active and passive, they promise to become key building blocks in optical networking. Channel counts in the arrays will increase, they will occupy less space, and less power will be consumed. "We see EDWA arrays being used

in channel balancing, multiplexing and demultiplexing, switching matrices, and many other applications," says John Kostibas, Inplane's vice president of marketing and sales. "Products like optical crossconnects and reconfigurable optical add/drop multiplexers will benefit greatly from the incorporation of low-cost, low-noise, wavelength-independent amplification via EDWA arrays."

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