Narrowband WDM vs Wideband WDM vs Coarse WDM vs Dense WDM
This page describes WDM types which include narrowband WDM,wideband WDM,coarse WDM and Dense WDM and provide difference between them.Following are evolutions of WDM used in fibre optical based communication system.
Early developments of WDM started in late 1980s. The system were using two widely spaced wavelengths of order 1310nm and 1550nm ( 850nm/1310nm) regions. This is referred as wideband WDM.
In the early 1990s , second generation of WDM have been developed referred as narrowband WDM. In this type 2 to 8 channels have been used. These channels are frequency spaced at interval of 400GHz in 1550nm window.
There are passive WDM systems which employs 2,4,8,12 and 16 channels. These techniques has distance coverage upto 100Km without any repeater module.
This type of coarse WDM used 20nm spacing for up to 18 channels. This can cover distance of about 50km on single mode fibres.
In the middle of 1990s, dense WDM (DWDM) has been developed which had 16-40 channels at frequency spacing of 100GHz to 200GHz .
Later in the late 1990s, DWDM systems were developed with 64-160 channel capacities. These systems were capable of packing at 50GHz or 25GHz spacing. These can transfer information at distance of several thousands kilometers with amplifiers and regenerators along the route.
Optical fibre based communication system uses wavelenths in near infrared region which is in non-visible spectrum. Following table mentions wavelengths at which fibre works best.
Optical Transmission Windows
|Optical Window||Operating Wavelength|
|800-900 nm||850 nm|
|1250-1350 nm||1310 nm|
|1500-1600 nm||1550 nm|