Letter to the Editor

March 1, 2005

Dear Editor,

A quick correction to Lightwave’s December 2004 issue [Analyst Corner, “10GBase-LRM and XFP win 10-GbE enterprise battles,” p. 33]. On page 38, there appears to be an error. In the well-written and thoughtful article, authors Daryl Inniss and Roy Rubenstein write, “LR is an elegant solution because it supports 10 km and 300 m” and “new passive alignment techniques will offer 10GBase-LR an opportunity to win significant 300-m multimode ports.”

This seems to be a misstatement. The LRM standard is attempting to add EDC circuits and additional testing to the base LR product to enable transmission of a serial 10-Gbit/sec 1310-nm source over 220 m of multimode fiber (MMF). If possible, the EDC circuit may enable 300 m, but that is uncertain. Without the EDC circuit, a 10GBase-LR will only be able to transmit up to 100 m over best-quality MMFs or less over most legacy MMF.

One of the key disadvantages of LRM, in my view, is that it will be more expensive than a 10GBase-LR. The LRM module will also require expanded final testing to confirm operation with dynamically changing signals as MMF vibrates, bends, or thermally cycles.

The 10GBase-LX4, on the other hand, can transmit over both 300-m MMF and 10 km of singlemode fiber (SMF).

Bryan R. Gregory, Vice president of marketing
Emcore, Downers Grove, IL

We would like to thank Bryan Gregory for pointing out that LR supports a minimum distance of 10 km on SMF and LR is not specified for MMF. After further review on this matter, we agree with his observation. We thank him for bringing this to our attention and further note that this correction does not change the conclusions of our analysis.

We would also like to point out that the draft of the LRM standard (IEEE 802.3aq Task Force) recently has been updated to support 300 m on legacy MMF.

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