The WDM technologies allow multiple lasers carrying independent signals to be transmitted in the same fiber with appropriate spacings of wavelengths (frequencies) between laser carriers. Because of the broad bandwidths of lasers, the carried signals can be format-independent and be routed in networks independently.
Network Capacity/Flexibility/Security/Transparency
The lasers can carry digital or analog signals. The digital signals can be any speeds (155Mb/s OC-3, 625Mb/s OC-12, 2.5Gb/s OC-48 or 10Gb/s OC-192) or format (security-coding, compressed data and etc).The analog signals can be any formats or co-exist with digital signals. The analog signals can also be Frequency-Division-Multiplexed (FDM) in one laser because of the broad bandwidth of laser.

For digital signals, WDM systems increase network capacities. For example, the maximum network capacity for a eight-wavelength WDM system increases to 20Gb/s when each laser carries a 2.5Gb/s (SONET OC-48) signal. Furthermore, the broadband feature of optical communications allows transparent networks where the lasers can carry independent signal formats. For example, wavelength_1 can carry analog signals, wavelength_2 can carry a 2.5-Gb/s digital signal while wavelength_3 carries a 155-Mb/s digital signal. The transparent feature provides securities and flexibility to the networks. To achieve the transparency, the devices used in the networks have to be all optical.

Created by J.C. Chiao