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RE: Question on Laser Safety Limits

Jonathan,
  I'm not privy to the latest changes in the laser safety classifications.  However, I can tell you that presently the IEC 825-1 is based on the following:
100 mm viewing distance
50 mm viewing aperture
 
With that combination, launch condition will have no effect on the laser safety calculation.  All of the light goes through the 50 mm aperture.
 
Now, the CDRH rules are based on:
20 cm viewing distance
7 mm aperture
 
For this case diffraction does matter.  Assuming gaussian propagation out of the fiber would be very bad for the CDRH calculation.  Fat gaussian beams have dramatically less divergence than multimode fiber.  I think your calculations are a not quite relevent, but you have identified an important issue.  We don't want to rely on fat (30um) gaussian beams for our calculations or CDRH will have to change more than exposure levels.  I bet one of the fiber people out there has a good answer for this.  (Hint, hint)
 
Hope that helps,
 
rob
 
-----Original Message-----
From: owner-stds-802-3-hssg@xxxxxxxx [mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Jonathan Thatcher
Sent: Friday, June 09, 2000 1:06 PM
To: HSSG_reflector (E-mail)
Subject: Question on Laser Safety Limits

Has anyone built a chart that shows what the new laser safety limits are in dBm for 850 nm lasers (min lambda = 840?) as a function of the restricted launch condition?
 
jonathan

Jonathan Thatcher,
Chair, IEEE 802.3ae (10 Gigabit Ethernet)
Principal Engineer, World Wide Packets
PO BOX 141719, Suite B; 12720 E. Nora, Spokane, WA 99214
509-242-9000 X228; Fax 509-242-9001; jonathan@xxxxxxxxxxxxxxxxxxxx