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Category I and II are defined in the ANSI SMF-PMD for 20 and 60
kilometer distances, respectively.
Our SMF PMDs do not exactly match either Category I or Category II
specs of the ANSI FDDI SMF PMD document. Our product was developed
before the ANSI Document was finalized. We wanted to produce a SMF
FDDI link that would offer at least 40 kms distance capability, but we
also wanted to be certain that the product would be eye safe. To assure
that we needed to adhere to IEC/FDA Class 1 laser safety limits.
As we interpret the SMF PMD, the Category II laser would not be a Class
1 laser device. We designed our system to achieve 40 km link distances
(you can achieve 60 km if you use lower loss fibers), while also being
a laser safety Class 1 device. In order to do this, we lowered the
laser output power and the receiver sensitivity levels from the
Category II levels.
When it came to selecting laser and receiver products, we found that we
could achieve a power budget of 22 dB. While this does not match the
Category II power budget of 32 db, it is certainly sufficient for a
40 km link, and has been shown to be capable of running over 60 km,
with low loss SMF cables.
Please let me know if you need additional details.
Dick Kirk
Network Product Support
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