On 27.11.2025 10:49, Mark Tinka wrote:
On 27/11/2025 11:32, Joel Busch wrote:
Oh that's actually the first I've heard of a manufacturer using
different grids for their ER4 lite vs their ER4! Now I get why you
were telling me not to combine ER4 lite and ER4, in your experience
they use nLWDM and LWDM respectively.
Not quite.
Both ER4 and ER4-Lite are nLWDM, because of the chromatic dispersion
sensitivity when using PAM4 modulation above 10km.
My impression was the opposite, that each seller sticks to one grid
for both. Examples below:
So Smartoptics use different wavelengths for ER4 and ER4-Lite:
https://smartoptics.com/product/tqd031-sn4c-so/
https://smartoptics.com/wp-content/uploads/2023/10/ds-tqd023-sl4c-so-
qsfpdd-400g-er4-lite-c4-r6.1.pdf
And they are using nLWDM for both.
The LWDM is primarily used for 100G-LR4, as there is no concern of
chromatic dispersion below 10km.
If I'm getting you right, you are saying there are three grids, two of
which are types of nLWDM? I think you're mixing something up. Especially
since 100G-LR4 already uses what Smartoptics uses for 400G-ER4-lite.
In my view we have the following three common grids in the O-band:
CWDM4: 1271 nm 1291 nm 1311 nm 1331 nm ( 20 nm spaced)
LWDM: 1295.56 nm 1300.05 nm 1304.58 nm 1309.14 nm (800 GHz spaced)
nLWDM: 1304.58 nm 1306.85 nm 1309.14 nm 1311.43 nm (400 GHz spaced)
100G-CWDM4 plugs existed but faded relatively soon in favour of 100G-LR4
plugs.
100G-LR4 plugs already use the LWDM wavelengths. See IEEE802.3 Table
88–7 "100GBASE-LR4 and 100GBASE-ER4 transmit characteristics" and
IEEE802.3 Table 88–5 "Wavelength-division-multiplexed lane assignments":
Center Range
1295.56 nm 1294.53 to 1296.59 nm
1300.05 nm 1299.02 to 1301.09 nm
1304.58 nm 1303.54 to 1305.63 nm
1309.14 nm 1308.09 to 1310.19 nm
This is also true of the 100G-LR4 from Smartoptics:
https://smartoptics.com/wp-content/uploads/2022/12/so-qsfp28-lr4-10l-r5.3.pdf
If you compare that to the 400G-ER4-Lite from Smartoptics you linked
you'll see the same wavelengths:
https://smartoptics.com/wp-content/uploads/2023/10/ds-tqd023-sl4c-so-qsfpdd-400g-er4-lite-c4-r6.1.pdf
Later the 400G-FR4 and 400G-LR4 went back to the CWDM4 wavelengths.
So 400G-LR4 ended up using wider spacing than 100G-LR4. A bit
counter-intuitive, but true:
https://smartoptics.com/wp-content/uploads/2022/12/so-qsfp-dd-4c-lr4-4-r5.6.pdf
My guess is it was hard enough to handle 10 km chromatic dispersion -
without FEC, remember - that people already moved to tighter spacings
for 100G-LR4. But then they could relax it in the 400G era because now
host KP4 FEC is mandatory.
I think the LWDM spacing of 100G-LR4 is also what makes the existence of
so called "LR4 ext" or "20km LR4" possible as a by-product.
So do they explain why they are using the same sets of wavelengths for
what they market as ER4 and ER4-Lite?
No, because I didn't ask, because I then thought it was normal :-)
And is there an appreciable difference in price between both types of
plugs?
Yeah around 30%, the lite makes do with an APD receiver and no SOA,
according to the spec sheet. Maybe that's where the savings come from.
But I didn't ask about that either.
This is very similar to the specified difference between their
100G-ER4-lite and 100G-ER4, so I didn't question it much.
Looking at Flex's web site, the ER4-Lite page says "not interoperable
with D.164HG.30", which is odd because D.164HG.30 is Flex's ER4-Lite:
https://www.flexoptix.net/en/d-164hg-30-e.html?option875=1
I think there is a documentation issue with Flex, but again, I could be
wrong :-).
Ah sorry I could have mentioned this ahead of time, since I ran into it
too. The D.164HG.30 is actually an older version of the ER4 lite.
They said it was cancelled, they can't sell it anymore. D.164HG.30.E and
D.164HG.40.E are the current ones I was referring to. That's also what
you and I both linked to. There is no shop page for the D.164HG.30 anymore.
Joel
--
Joel Busch,
Network Engineer
Switch, AS559
_______________________________________________
NANOG mailing list
https://lists.nanog.org/archives/list/[email protected]/message/FEKTSYWRBR55FQNX7NYVBKLMZUV2IFZB/
