2023 is close in the review mirror, and we went through many wavelengths in the optical transmission world. First, there were FWDM simple 1310/1550nm filters. Then, CWDM traversed almost the entire spectrum from 1270 to 1610nm. Next came the C-band DWDM, which we all thought was the end-all-be-all of fiber transmission. In addition, we threw in the L-band, which is a niche application. If those changes weren't enough, along comes 100G. How do we deal with 100G and its unique challenges? We used PAM4 modulation and tunable dispersion compensation for the C-band in an optical line system or CFP2 in a specialized DCO switch. The 100G Coherent QSFP28 is on the horizon, but it's not available yet. So why skip the 100G Coherent and go directly to 400G ZR+? Maybe your switch can't handle the power draw and heat dissipation, or your budget does not permit the price. What if you:

• Have a link 25km or under?
• Only need 1.6T and only have two fibers?
• Have a legacy FWDM, CWDM, or DWDM with a 1310 wideband port available where your legacy SONET gear resides?

The O-band could be the ideal option! You’re probably asking, “Why O-band?” I know that I did. O-band 100G PAM4 modulated optics have a place in the battle of the bands! Dispersion compensation modules (DCMs) or amplifiers are not required to reach 25km. Just a simple passive solution is needed, transceivers in the switch and passive MUX/DEMUX on the dark fiber or 1310 port if your loss budget is accommodating. Most 100G capable switches accommodate the QSFP28 form factor with a power draw of up to 5.5W. So, where does the O-band fit, and why should you consider it? It's a great option to consider if you have:

• A need for up to 16 100G services.
• Fiber distances under 25km.
• A switch with open QSFP ports that can handle 5.5W of power.
• Budget constraints that don't allow you to go to 400G.
• 1310 Wideband ports on your WDM passive filters.

In conclusion, there is a place for O-band DWDM solutions. It is a low-cost entry into 100G DWDM that meets your company's commitment to lower power consumption and stay "green" while maintaining a budget and scaling the network into the future.

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Larry Legg Senior Product Design Engineer Approved Networks Larry Legg is a well-recognized expert in the telecommunications field with 33 years of key decision-making responsibility. He stays on the cutting edge in the industry, continuously seeking knowledge to create innovative solutions. Click to explore Larry's ongoing informational series.