Which wavelength does a passive optical network use

Passive optical networks use specific wavelength pairs for upstream and downstream traffic, typically ranging from 1260 nm to 1600 nm depending on the PON standard.

Standard Wavelength Allocations

PONs use wavelength-division multiplexing (WDM) to allow bidirectional communication over a single fiber. Each PON standard has defined wavelength ranges for upstream (US) and downstream (DS) traffic:

• GPON: Downstream 1480–1500 nm, Upstream 1290–1330 nm, with 1550 nm reserved for optional RF video overlay services .
• EPON: Downstream 1480–1500 nm, Upstream 1290–1330 nm, similar to GPON .
• XGS-PON: Downstream 1575–1580 nm, Upstream 1260–1280 nm, with 1550 nm reserved for optional services .
• TWDM-PON: Downstream 1596–1602 nm, Upstream 1524–1544 nm, supporting multiple wavelength channels for higher capacity .
• 25G/50G PON: Upstream 1260–1310 nm, Downstream 1340–1360 nm (25G) and 1340–1344 nm (50G) depending on the specific channel .

How Wavelengths Enable PON Functionality

• Downstream traffic (from OLT to ONT/ONU) uses a higher wavelength, while upstream traffic (from ONT/ONU to OLT) uses a lower wavelength. This separation prevents interference and allows simultaneous bidirectional communication on a single fiber .
• Optional overlay services, such as analog video, are typically assigned to the 1550 nm band to coexist with data traffic without interference .
• Guard bands and WDM filters are used to isolate signals and prevent crosstalk between different services and PON generations .

Summary

In essence, PONs rely on carefully allocated wavelength pairs to support efficient, bidirectional communication over a single optical fiber. The exact wavelengths vary by standard, but the general principle is lower wavelengths for upstream, higher wavelengths for downstream, and reserved bands for optional services. This design allows multiple PON technologies to coexist on the same fiber infrastructure and facilitates upgrades to higher-speed PONs without replacing the fiber plant .