Mumbai University > Electronics and telecommunication > Sem 7 > optical communication and networks

Marks: 05

Years: DEC 2014

• In case of optical transmission the loss is wavelength dependent. So, there is a specific band of wavelength where the signal attenuation is minimum which is known as optical or operating window. The wavelength of operation from the optical window is selected as they offer minimum attenuation.

• Figure below shows three optical windows which offer minimum signal attenuation and also relationship between attenuation and wavelength.

• The first optical window is defined from 800-900nm, where the minimum signal loss is 4dB/km. In early 1970’s this window was used for operation of optical sources and detectors.

• By reducing the concentration of hydroxyl ions and metallic impurities in the fiber material, in 1980’s manufacturers were able to fabricate optical fibers with very low loss in the 1100-1600nm region. This spectral band is called long wavelength region.

• The second optical window is centered at 1310nm also called O-band, which offers 0.5dB/km.

• The third optical window is centered at 1550nm also called C-band, which gives the loss of 0.2dB/km.

• Hence while designing optical systems for long distance applications the 1550nm wavelength is preferred because loss offered at this wavelength is minimum than any other wavelength.