In PON access networks, the optical modules are key components. For years, Class B+ and Class C+ were the most common. Recently, Class D modules appeared, and many OLT vendors such as Huawei now support Class D. At the same time, Class B+ is being phased out.

Why? Because networks are developing rapidly, and so are the demands.

Taking the optical module of Huawei combo board CGHF for example, XG-PON&GPON Combo PON Optical Module (SFP+) specification:

Technical Advantages of Class D

Class D modules bring clear improvements over Class C+:

Higher optical Power – Stronger signals allow longer transmission under the same fiber loss.

Better Receiver Sensitivity – They work well even with weak signals, keeping performance stable.

Larger Link Budget – They cover more than 97% of fiber attenuation cases, giving planners more flexibility.

Why Class D module Emerged?

The rise of Class D modules shows two things:

• Optical module technology is advancing.
• Real network demand exists.

ODN networks today are huge but face many issues: mixed component quality, uneven supplier standards, complex environments, and non-standard construction. These lead to unstable links, frequent drops, and user complaints.

Many of these issues are linked to optical power. Raising transmit power is one of the most effective fixes. Class D modules were designed for this reason: to meet more scenarios and reduce risks.

Conclusion

The creation of Class D modules is no accident. They are a natural response to technology progress and market needs. With stronger power, better sensitivity, and greater flexibility, Class D is set to replace older classes and support the next stage of PON evolution.