In the WDM-PON network, wavelengths generated at the OLT can be used for multiple clients. Wavelengths can be shared between subscribers with the help of subcarrier multiplexing, or it can be used by single customer. ONUs/ONTs are responsible for correct forwarding of the intended signal to the intended user. Remote nodes provide signal multiplexing in the upstream direction and signal demultiplexing in the downstream. WDM source in the OLT can have following options:

 

• Multifrequency laser

• Gain-coupled DFB laser array

• Chirped-pulse WDM source

ONTs/ONUs are having colorless wavelength transmitter with the following options:

 

• Tunable laser

• Vertical-cavity surface-emitting laser diode

• Injection-locked laser

• RSOA (Reflective-type Semiconductor Optical Amplifier)

   

The WDM-PON can have injection-locked laser signal generator on both sides (OLT and ONT/ONU) which helps reduce overall cost of the network. In this system, multiple laser diodes are used, each having separate locked wavelength. These identical FP-LDs are used instead of wavelength-specific signal generators. During tests, these lasers showed good performance over 70 degree temperature range, with no failures.

 

Main obstacles in expansion and popularisation of the WDM-PON are high cost of the equipment and low performance of some components. As an example, the RSOA and FP lasers can be used, which are cheaper than tunable lasers but have worse performance. The RSOA gain for different fiber drop lengths can be also improved, which will affect network stability.