1. WDM

2. Types of transmission mode
Unidirectional WDM system
Bidirectional WDM system

3. Unidirectional WDM

4. Bidirectional WDM

5. Advantages
Because of lower bit rates, the distance limit due to chromatic dispersion is much larger.
The transmission capacity can be increased by adding additional wavelengths.
It can be a transparent system and allow different wavelengths at different bit rates.
WDM may be preferred to TDM in designing more complicated networks.

6. Disadvantages
WDM systems are generally not suitable for deployment over dispersion shifted fiber.
WDM systems require specially designed amplifiers that provide flat gain.
WDM systems require separate terminating equivalent for each channel.
Transparent WDM systems offer less monitoring and network management capability.