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Re: [802.3_B400G] CWDM dispersion levels

Hi Scott,


This was the email I sent on 22 March.

Let me show specifically the fairly consistent curve of aggregated test results 100G PAM4 dispersion penalties shown in of CD penalty versus CD.

A lot of test results came from the 100G Lambda MSA work.

As you can see, for 30+ ps/nm the CD penalty goes above 4 dB and for 50 ps/nm it would go off the screen.

This is quite different from your claim of 0.5 dB for 50 ps/nm.

These results were used in the cu project to define the limits for 400GBASE-LR4-6.


Generally it’s my experience that simulations of dispersion penalty do not provide sufficiently reliable results to support choices for wavelengths.


Kind regards




From: Peter Stassar
Sent: Monday, March 22, 2021 4:43 PM
To: STDS-802-3-B400G@xxxxxxxxxxxxxxxxx
Subject: CWDM dispersion levels


Hi all,


I just pulled up my G.652 fiber dispersion Excel sheet to calculate the worst case dispersion numbers for the 8 CWDM channels mentioned by Scott in his presentation.


Conventional CWDM4 dispersion levels, taking into account conventional tolerance of +/- 6.5 nm:

1271 nm channel: -5.87 ps/

1331 nm channel: +3.3 ps/


Additional CWDM channels:

1351 nm channel: +4.96 ps/

1371 nm channel: +6.55 ps/

1391 nm channel: +8.07 ps/

1411 nm channel: +9.54 ps/


As one can see, from 1331 nm to 1411 nm the chromatic dispersion coefficient increases from 3.3 ps/ to 9.54 ps/ which is almost x3, which is quite significant.


The test results from the 802.3cu TF were contained in


As I clarified, I believe the group would be interested to see test data how tripling the amount of dispersion in a CWDM8 configuration could be established without a strong increase of dispersion penalty (TDECQ minus TECQ).


Kind regards,


Peter Stassar (Huawei)

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