FO Link Loss Calculating

1. Fiber Losses:
Fiber Losses and different Wavelengths
FiberType Wavelength FiberAttenuation ConnectorLoss Splice Loss
Single Mode 1310 nm 0.35 0.5 db 0.05 db
Single Mode 1550 nm 0.22 0.5 db 0.05 db
Attenuation:
The steady decrease or loss of signal power in an optical fiber, primarily due to absorption and scattering.
Attenuation is a wavelength dependent, measured in DB and can be converted to db/km.
Attenuation Formula:
Attenuation(db) = 10 * log2 (P1/P2)
In fiber optics attenuation can be measured as 10 times the log of ratio of input power (P1) to output
power (P2) in watts. Input power is always grater the output power, therefore the ratio will be greater
than 1 and attenuation will be a positive number.
Attenuation (db) = 10 * log2 (P1/P2)
Attenuation (db) = 10 * log2 (1000 uw/ 500 uw)
Attenuation (db) = 10 * log2 (2)
Attenuation (db) = 10 * 0.3
Attenuation (db) = 3 db
Attenuation per km = 3db/15km = 0.2 db/km

2. Link Loss
The total measured power loss of a fiber optic point to point span or link. The loss is a intrinsic
attenuation and extrinsic discontinuities in a fiber optic cable. Link Loss is wavelength dependent and
measured in decibels per kilometer or db/km.
Link loss is the total loss of power over one link when all factors including fiber attenuation and splices,
connectors, cable bends and other mechanical factors are measured.

3. Loss Budget :
Total calculated power loss in an optical link or span. Calculation is derived from the sum of all losses
including fiber attenuation splices, connectors and margin of error. Loss budget will be measured in in
db.
Calculate Loss by loss budget formula

4. Attenuation Test/Insertion loss (Measured by PM/LS)
Calculate Margin(= total loss budget – total measured insertion loss)

5. Attenuation Test Procedure