Fig. 10.6. Concept of DWDM.

Features of DWDM :

1. DWDM carries different signals of different bit rate and different formats over a single fiber.

2. DWDM gives service providers the flexibility to expand capacity in any portion of their networks. This advantage is not offered by any other technologies.

3. The fiber optic amplifier component of the DWDM system enables a service provider to save costs by taking in and amplifying optical signals without converting them to electrical signals.

4. DWDM uses dercreased numer of amplifiers between source to destination. For example, DWDM system multiplexing upto 16 wavelength on a single fiber carriers can decrease the number of amplifiers by a factor of 16 at each regenerator site. Using fewer regenerators in long-distance networks results in fewer interruptions and improved efficiency.

5. Combined with optical wavelength add/drop (OWAD-wavelength or added or dropped to or from a fiber, without requiring a SONET terminal) and DWDM, the optical cross-connect (OXC) will offer service providers the ability to create a flexible, high capacity, efficient optical network with full optical bandwidth management.

6. Automatic adjustment of the optical amplifiers when channels are added or removed can be achieved with DWDM.

7. DWDM offers standards-compliant maintenance interface. Standard transaction language 1 interfaces are widely available for DWDM systems.

Limitations. The limitation in DWDM is due to the wavelength routing. The concept of wavelength routing is as follows. DWDM system uses optical cross connects (OXC). OXC's are switches with a certain number of input and output ports. The signals received at a input port are demultiplexed and switched to any one of its output part where they are remultiplexed. In this way, a virtual link created comprising a single wavelength routed through several OXC's. This is called wavelength routing.

By wavelength routing two limitation occurs. First, a signal with a wavelength is transmitted essentially unchanged after a power loss. The second one is that two signals modulating the same wavelength arriving on different ports cannot be transmitted on the same output port. The second limitations can be overcome by the wavelength converters that convert an input wavelength into a different wavelength while being transparent to the modulating data. The first limitations can be overcome by using powerloss compensation system.

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