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OPTICAL FIBRE COMMUNICATION SYSTEM

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The need for OFC

• More information carrying capacity
• Free from EMI, ESI
• Low attenuation : 0.25 db/km at 1550 nm
• Use of WDM
– Switching / routing at Optical signal level
• Self healing rings under NMS control

More information carrying capacity

According to Shannon’s information capacity
theorem :
C = BW. log2(1+SNR)
where
C = Information carrying capacity (bits/sec)
BW = Bandwidth of the link
SNR = Signal to noise power ratio

OFC Performance Windows

Signal Attenuation in Optical Fiber
• Attenuation has three components :
- Bending loss (Macro / Micro)
- Absorption loss
- Scattering loss
• In bending loss, there are 2 categories
- Macro bending loss (specified by manufacturer)
- Micro bending loss (not specified but included
in total attenuation accountal by manufacturer)

Macro-bending loss

• Macro-bending loss is caused by bending
of the entire fiber axis
• The bending radius shall not be sharper
than ‘30d’ where d is diameter of cable
• One single bend sharper than 30d can
cause loss of 0.5 dB
• If bending is even sharper, fiber may
break

Commercially Available Fibers

optical Fiber Sizes

• To ensure compatibility among splices/connectors, sizes of core & cladding have been standardized
• International standards for SM fiber
– Cladding diameter : 125 microns (micro meter)
– Cladding + coating : 245 microns (micro meter)
– Core diameter : 7 to 10 micro meter
• International standards for MM fibers
– Cladding diameter : 125 microns (micro meter)
– Cladding + coating : 245 microns (micro meter)
– Core diameter : 50 to 62.5 micro meter