Thanks for the minutes. Reading
them reminded me of an issue that has been troubling me. I'm hoping
someone can clarify.
I have been wondering about the use
of a 7um FWHM singlemode beam in the simulations. From my calculations
I find this beam size to correspond to a fiber with an 8.4 um mode field
diameter, which is below the normal range of 8.8 to 9.5 um. This
can lead to differences between the simulated and measured DMD and other
mode-coupling dependent calculations. My calculations follow. I'd
appreciate a review and any comments regarding the effects of using a beam
that appears to be on the small side. For example, such a beam will
have a larger divergence angle and might couple into more mode groups than
an actual singlemode fiber used in DMD measurements or actual TOSA launch
The intensity profile of a step index
singlemode fiber is given by the following equation that describes the
shape of a Gaussian distribution:
I = Io e^(-2r^2/wo^2)
where Io is the intensity at the
r = radial position,
wo = mode field radius (the radius where the intensity drops to
1/e^2 = 0.135Io).
The electric field is the square root
of the intensity, and for Io
normalized to 1:
E = e^(-r^2/wo^2)
At the half max level
E = 0.5 = e^(-r^2/wo^2)
r = -(ln0.5)^1/2 wo = 0.833wo
Usual MFD = 2wo = 8.8 to 9.5 um
depending on fiber design, so
usual FWHM Efield= (0.833)(MFD)
= 7.3 to 7.9 um.
1300 East Lookout Drive
Richardson, TX 75082
yusun@IEEE.ORG Sent by: owner-stds-802-3-10gmmf@IEEE.ORG
10/06/2004 11:04 AM
Please respond to
"IEEE P802.3aq 10GBASE-LRM" <stds-802-3-10gmmf@IEEE.ORG>
[10GMMF] the minitues of task 4 Oct.
I attached the minutes of tele-conference
of task 4 group on Oct. 4th. I would appreciate your comments.
The proposed next task 4 meeting is
Oct 11th, 2004 (Monday), 11am
east coast, 8 am west coast and 4 pm UK.