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Dispersion compensator rides 10Gb transceivers

Posted: 16 Aug 2004 ?? ?Print Version ?Bookmark and Share

Keywords:optical? transceiver? multimode? fiber? dispersion?

Big Bear Networks Inc. is offering its electronic dispersion compensation (EDC) chips in a 10Gb optical transceiver Xenpak module designed for 80km links and in an upcoming multimode-fiber module designed for enterprise 10Gb LAN traffic.

Survival in the high-speed market has been touch-and-go for Big Bear, which started life with a systems-oriented view to handling chromatic dispersion and EDC problems in fiber networks. Its initial 40Gbps EDC products were aimed at automated test equipment and at long-haul telecom equipment designs. John Jaeger, vice president of product development, said that Big Bear's 40Gbps Kodiak product continues to be a revenue generator, despite the perceived moribund state for all 40Gb products.

In the meantime, Big Bear has looked for distance- and performance-limiting applications where adding EDC DSP circuits to a standard transceiver can improve noise margins and overall interoperability. The ITU G.959p1 standard for long-reach 10Gb transceivers seemed a natural place to start, Jaeger said. Several telecom OEMs tried to press the ITU to improve interoperability aspects of G.959 last year, but the organization thought the effort was too tough to define. Consequently, the Optical Internetworking Forum has been examining an interoperability implementation guideline for 80km optical links.

By embedding its EDC chip in a Xenpak 10GBase-ZR transceiver, Big Bear has improved the overall transmit margins to allow for greater interoperability, while improving receive equalization. The module integrates a 0dBm end-of-life transmitter optical subassembly for greater link margins. The current single-wavelength Tosa is designed to follow the ITU 100GHz grid for dense wavelength division multiplexing (D-WDM) applications.

The BBTR1024-Z1 transceiver operates at 10.3125Gbps. It is hot-pluggable and compatible with Xenpak, Xaui and MDIO standards. The 23.5dB link budget exceeds the industry minimum specification of 22dB, and the maximum reach of the transceiver is greater than 100km. Beta units of the device are shipped already, with production slated for the Q4.

Big Bear's next market for the EDC chip will be the emerging 802.3aq standard for serial 10Gb links inside the LAN, using multimode fiber. To date, the performance and cost point of the LX-4 standard has not met the expectations for LAN vendors using fiber-based vertical risers; hence the pressure for a true serial standard for Ethernet applications operating within the radius of a single building.

Jaeger said he expects some competition from the larger physical-layer IC specialists that want to integrate EDC with Serdes devices, but he said that a good 802.3aq solution will require a dual-stage equalizer with an advanced clock recovery circuit and a solution that costs no more than four times that of 1Gb Ethernet. Big Bear is designing an EDC that integrates with Serdes blocks easily, while having a power budget of less than 1W, Jaeger said.

In both metro and LAN applications, Big Bear will stick with its strategy of offering transceiver modules rather than standalone semiconductors.

- Loring Wirbel

EE Times

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