Re: 400G ER4 wavelengths - two grids

[Joel Busch via NANOG <nanog () lists nanog org>]

On 28.11.2025 05:40, Mark Tinka wrote:
> On the single-lambda side, the 2km plug has been defined under 100G-FR1. 
> While I like those the most because data centre x-connects will 
> generally be under 2km long, experience is showing that operators are 
> carrying their "LR4" habit into 100G-LR1 world :-).

Yes we're seeing the same. And when I ask a customer if they would like 
their uplinks to be 100G-LR4 or 100G-LR they ask me what 100G-LR is :-)

> Yes, you are right. It can be quite cobbled up. But to summarize it, 
> there are 3 applications:
>
>   * 100G-LR4 (LWDM):
>       o 4×25G NRZ in O-band with the LAN-WDM 800GHz spacing, 10km class.
>       o Wavelengths: 1295.56/1300.05/1304.58/1309.14nm.
>
>   * 400G-LR4 (CWDM O-band):
>       o 4×100G PAM4 on CWDM4 wavelengths (wide 20nm spacing), 6km – 10km
>         class.
>       o Wavelengths: 1271/1291/1311/1331nm.
>
>   * 400G-ER4 (nLWDM):
>       o 4×100G PAM4 with tighter 400GHz spacing clustered near 1310nm to
>         keep dispersion low/flat, 30km - 40km class.
>       o Wavelengths: 1304.58/1306.85/1309.14/1311.43nm

Good summary.

Just don't forget to check if the 400G-ER4 you're buying really uses the 
400GHz spacing, everyone. Remember that FiberMall listing from my 
earlier email:

https://www.fibermall.com/sale-458209-qsfp-dd-400g-er4-lwdm4-40km.htm

And with ER4-lite all bets are off. It's anyone's guess which shop will 
sell which spacing, just make sure your inventory stays consistent for 
your own sanity.

Thanks for bouncing back and forth with me on this topic, Mark!

Good weekend to everyone, sooner or later, depending on timezone :-)

Joel


--
Joel Busch,
Network Engineer
Switch, AS559
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