Fibre Channel SAN Extension over Optical Networks CWDM Concepts
Spectral Attenuation
Loss (dB)/km vs. Wavelength
Multimode
850nm
2.0 dB/Km
OH- Absorption Peaks in Fiber Attenuation Curve (Water Peaks)
Single mode
1310nm
CWDM/DWDM
1550nm
0.5 dB/Km 0.2 dB/Km
800
900 1000 1100 1200 1300 1400 1500
Wavelength in nanometers (nm)
1600
Spectral Attenuation
The diagram shows a spectral attenuation curve that demonstrates the wavelength-dependence of many of the signal attenuation factors. This diagram shows the span of wavelengths used in telecom fiber, from 600nm to 1600nm. The normal operating “bands” of wavelengths, centered around 850nm, 1310nm, and 1550nm, are highlighted and used for multimode, singlemode and CWDM/DWDM.
Factors such as Rayleigh Scattering and UV absorption decrease with longer wavelengths. UV absorption also decreases with wavelength. However, IR absorption picks up rapidly at the longer wavelengths and effectively limits the higher wavelength operations. DWDM uses wavelengths in the 1550nm range due to the low loss profile of that range.