This blog ETU-LINK will show you how to identify the wavelength of CWDM optical module through the color of the pull ring. We all know that CWDM has a total of 12 wavelengths, with a full band range of 1270-1610nm, with each wavelength interval of 20nm. The industry divides the entire band into front wave and back wave, with the front wave band of 1270-1450nm and the back wave band of 1470-1610nm. Generally, the back wave band is chosen for ultra long distance transmission.

For a conventional optical module, we can easily judge the wavelength of the optical module from the color of the latch ring. For example, the black pull ring represents 850nm, and the blue pull ring represents 1310nm. For SFP CWDM optical module, what wavelength does the color of its pull ring correspond to? Please take a look at the table below.

Ⅰ. CWDM SFP Latch‑Ring Color‑Code Reference Table

Front wave (SFP CWDM special wavelength):

Backwave (SFP CWDM conventional wavelength):

Ⅱ. Can Latch‑Ring Color Be Used As 100% Definitive Basis?

Important engineering reminder: Latch‑ring color is only a quick visual reference, NOT a mandatory MSA industry‑enforced standard.
1. Some third‑party or OEM private‑label CWDM modules may adopt custom non‑standard pull‑tab color schemes;
2. Same color may map to different wavelengths between ordinary single‑mode modules and CWDM modules. E.g. green pull‑tab means 1530 nm for CWDM, but stands for 80km ultra‑long‑reach for conventional ZR modules;
3. Grey‑colored pull‑tab covers multiple different CWDM wavelengths, visual check alone cannot distinguish them.
Recommended double‑check workflow: Visual latch‑ring color → check printed module label (model & wavelength) → verify real wavelength via SFF‑8472 DDM/DOM diagnostic function on the switch.

Ⅲ. Why Distinguish CWDM Wavelength Correctly In Real‑World Networking?

Through the above table, we believe that you can clearly identify the wavelength represented by the color of the latch ring of the SFP CWDM optical module. Understanding the wavelength represented by the color of the pull ring will help us identify the module with the corresponding wavelength.

Ⅳ.  ETU‑LINK CWDM SFP Product Reminder
ETU‑LINK provides complete SFP / SFP+ CWDM optical modules covering full 1270‑1610 nm ITU‑T CWDM channels, following above‑mentioned pull‑tab color‑coding standard. All modules support SFF‑8472 DDM real‑time wavelength monitoring, commercial and industrial temperature grades are available, fully compatible with mainstream brand switches and CWDM multiplexer equipment. Custom OEM private‑label pull‑ring color modification service is supported for large‑volume orders.

The above is the product knowledge related to the SFP CWDM optical module introduced by ETU-LINK. If you want to know more about the optical transceiver, you can read the previous articles.