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RE: Question on Laser Safety Limits

Shelto (et al),
Yes, I saw the 2.46 dB increase over today's limit.
Now, if we restrict the launch by a factor of two (radius), a grossly simplified calculation would indicate that the power would be concentrated in an area of 1/4 the size and therefore have 4X the intensity. If we assume that this translates to a 6 dB increase into the laser safety aperture, and we similarly assume an increase in the safety limit of 2.46 dB, where did the other 3.54 dB go? Sounds like things got worse instead of better.
In Paul's presentation:
The maximum Tx launch is -1dBm (per charts 24 and 25) which is, I assume, kinda like the -1.24 number rounded a bit. In chart 26, there simply isn't enough unallocated budget to cover the missing 3.54 dB.
Now, this would not be anywhere near valid if the distribution of the launch were not gaussian in both cases. But, you will remember that Paul mentioned in a response that in fact the launch was Gaussian in defense of the 2r = D question.
So, knowing that the calculations are not as simple as I pretend above, I am simply asking the experts to build the chart that shows the effective power vs. launch conditions.
So far, no takers....
-----Original Message-----
From: []
Sent: Monday, June 12, 2000 12:22 PM
Subject: RE: Question on Laser Safety Limits

Hi Jonathan,

Paul Kolesar gave a very good presentation at the march plenary meeting on this issue. See:

In this presentation he expects the new levels for 850 nm to be -1.24 dBm. A 2.46 dB increase over today's limit .

Even more interesting, is the fact that they are anticipating a new category "Class 1M" with restrictions similar to Class 3A, that will allow levels up to +9.43 dBm.

But you bring up an interesting question in regards to the restricted launch conditions.

What will the test conditions be?

With the majority of the light going through the center of the exiting light cone, there could be a significant difference between a mathematical calculation assuming equal distribution over the cone and a practical measurement, measuring the maximum exposure through an aperture.

Have fun


Schelto van Doorn
Engineering Manager
Fiber Optics
Infineon Technologies
1730 North First St.
MS 22303
San Jose, CA 95112
Tel: 408.501.5665 Fax: 408.501.5670

-----Original Message-----
From: Jonathan Thatcher []
Sent: Friday, June 09, 2000 11:06 AM
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 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;