XENPAK-compatible, hot-pluggable EDFA eases terminal amplification

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Avanex (Fremont, CA), a provider of “intelligent” photonic products for optical networks, has released its PureGain 200, a hot-pluggable erbium-doped fiber amplifier (EDFA) initially targeted at 10-Gbit/sec applications that is fully compatible with the industry-standard XENPAK chassis normally associated with transceivers.

The company says the device significantly reduces the cost, development time, management, and complexity associated with adding 10 to 20 dB of amplification to terminal equipment.Th 208486

Avanex says its PureGain 200 hot-pluggable EDFA significantly reduces the cost and complexity of adding amplification to terminal equipment.

Peter Wigley, senior product line manager at Avanex, explains that a XENPAK form factor was chosen “because it’s pluggable [and] because, frankly, it’s out there already, and it’s adopted widely-particularly by companies like Cisco.

According to Avanex, up to eight PureGain 200 EDFAs can be integrated within a standard, high-port-density chassis, wherein EDFAs, transmitters, and receivers can be interchanged in the same XENPAK bay. In fact, while it looks like a transceiver, the PureGain 200 doesn’t include transceiver electronics; the signal to be amplified comes from a nieghboring port configured with a conventional transceiver. The EDFA integrates alarm monitor control and alarm set-point management with a standard command line interface compatible with the rest of the company’s PureGain product line. The device’s thermal and EMI performance is compatible with both XENPAK MSA and Telcordia qualification requirements.

Wigley admits that reducing the EDFA to fit in a XENPAK chassis was “not as much of a challenge as it would’ve been if we’d put it into a smaller package using available technology-and smaller packages are always preferable-which would’ve been SFP. [However], there are some design rules that one must-absolutely, explicitly must-respect with regard to erbium-doped amplifier design.”

Wigley explains that one such important rule revolves around the notion of minimum bend radius. “It’s well known in amplifier circles [that] the lifetime of a glass optical fiber is drastically reduced if you bend it very sharply,” he notes. Fiber bent in such a manner can develop fissures in its glass surface, whereby moisture can enter-a fatal scenario, in terms of system reliability. The company decided to design the amplifier in the XENPAK footprint so they wouldn’t have to break any design rules

Wigley maintains that, at least at the present time, there exist “some real challenges” associated with making an EDFA smaller than the XENPAK form factor. “There are fibers that you can wrap around a pencil and still see relatively good optical performance, but the lifetime of the fiber will be substantially reduced,” he notes. “It ultimately depends on the cost [of] squeezing the size down.”

Wigley says that reduced system downtime is an advantage with the EDFA. “I think the reason that the product has to be ‘hot pluggable’ is because when you have a rack full of XENPAK transceivers, you certainly don’t want to have to switch all of them off in order to replace one.” The device can be plugged in to “heal” an impaired channel withou affecting the other channels or traffic.

Also as a cost advantage, Avanex cites the device’s ability to eliminate all cards, controllers, and circuit packs dedicated to custom EDFAs, as well as its flexible shelf reconfiguration and “ad hoc” upgrade capabilities.

Wigley sums up, “In the XENPAK world, you buy a chassis-and you can buy a chassis from a number of vendors-and the chassis has slots in it. If you put one of those chassis into your network, you can talk to the chassis, you can power the chassis, you can handshake to the chassis-and if you plug one of our amps in instead of a transceiver, it will power up, it will go to 15-dBm output power, it will go to a gain set point, and it’ll sit there forever. That’s important.”

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