On 27/11/2025 15:29, Joel Busch wrote:
100G-CWDM4 plugs existed but faded relatively soon in favour of 100G-LR4 plugs.
You can still buy 100G-CWDM4 today. It is the 2km option for 4-lane 100G. 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 :-). 100G-LR1 plugs are about 12% more expensive than 100G-FR1, on average, but it seems old habits die hard :-).
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.pd...
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-...
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....
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.
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
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.
That is correct. APD's are cheaper but are more susceptible to noise, especially at higher gains.
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.
Thank you :-). Mark.