Re: Interferometric noise, version 2
Peter,
I read your write-up with interest and I must say that the approach that
you take represents a shift in the right direction, getting closer to the
real numbers. I find your results to confirm my assertions (that I voiced
during the meeting in Irvine and later during our serial PMD
teleconference) that the IN penalty for the longest links is between 0.4
and 0.5 dB. I believe that your results are also implying that the penalty
for the shortest links is such that it does not cause negative margin (fig.
4, 5 and 6). They also confirm the numbers that are in the spreadheet that
I posted on the reflector (interferometric noise 3a.xls), which can be
found on the serial pmd site.
Having said that, I also have to express my surprise with your conclusions.
You continue to make the same conclusions, and propose the same remedy as
before, although your simulations now show reduced IN penalty, consistent
with my numbers. Your simulations confirm that the steps taken so far (3dB
ER limit for the transmitter, with 12 dB RL for both the TX and the RX) are
sufficient to guarantee the performance of the link with positive margin.
However, you do not comment on those things.
The only thing that we need to do is to add the 0.4-0.5 dB IN penalty to
the link budget (we already have 0.61 dB of margin, so people know that it
is not unallocated margin and can't be used for other things. As for the
argument that we need to accomodate air gaps, I think we should not
consider things that are outside of the standard, since that road is
slippery and can lead us to considering other conditions that are not part
of the standard.
Regards,
Peter
Petar Pepeljugoski
IBM Research
P.O.Box 218
Yorktown Heights, NY 10598
e-mail: petarp@xxxxxxxxxx
phone: (914)-945-3761
fax: (914)-945-4134
Peter Öhlén <Peter.Oehlen@xxxxxxxxxxxxx>@ieee.org on 01/29/2001 02:24:47 PM
Sent by: owner-stds-802-3-hssg-serialpmd@xxxxxxxx
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cc:
Subject: Interferometric noise, version 2
There have been some concerns about the validity of the worst-case
approach that was
taken in our previous document about interferometric noise. In this
document (see link below) we will extend the previous document in two
different ways. In both approaches worst-case polarization is assumed.
In real life the polarization state will vary slowly with time. However,
the polarization state will persist for a fairly long time and could
give random and unpredictable outages when the polarizations are
aligned.
In the first approach, instead of using the worst-case phase between the
main signal and the reflected signal, the BER is averaged over the phase
difference between the interfering signals. Chirp and other dynamic
effects are ignored in this approach. In the second approach a
rate-equation model for a single-mode laser is used, and the resulting
output signal is used to calculate the effect of the interferometric
noise. Here dynamic effects such as chirp and overshoots are taken into
account. Although the semi-analytical approach makes a number of
simplifications it compares fairly well to the more detailed simulated
approach.
The document was filtered by the exploder, please use this URL:
http://hem.passagen.se/peter.ohlen/interferometric2.pdf
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