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Testing & Commissioning Optical Fiber Link -Part 2

1/6/2017

Testing & Commissioning Optical Fiber Link -Part 1 HERE

More Examples on Calculation of Optical Power Budget

Assuming our Multimode Fiber Optics cabling configuration as below :

As per Singlemode, there are 2 common operating wavelength namely 850nm and 1300nm.
The respective attenuation or loss as illustrated below :

Figure 2 : Operating Wavelength Attenuation

Please refer to the following link for calculation of optical fiber budget formula :-
Testing & Commissioning Optical Fiber Link -Part 1 HERE

Optical Power Budget Calculation
Using above Figure 1 fiber optics schematic diagram followings can be deduced :
a. Total length of fiber is 1km (please use OTDR to measure actual fiber length)
b. 2 nos of splicings
c. 2 nos of connectors
d. MM operating wavelength of 850 nm - 3dB/km, 1300nm - 1dB/km

Operating Wavelength at 850nm
Maximum Allowable Loss = Fiber Loss + Splicing Loss + Connector Loss
= (1 km x 3 dB/km) + ( 2 x 0.2dB) + ( 2 x 0.5dB)
= 4.4dB
Operating Wavelength at 1300nm
Maximum Allowable Loss = Fiber Loss + Splicing Loss + Connector Loss
= (1 km x 1 dB/km) + ( 2 x 0.2dB) + ( 2 x 0.5dB)
= 2.4dB

As such, when we do actual measurement using power meter & light source the measured loss must be less than the calculated allowable maximum loss.
If the actual measurement value is higher than calculated maximum loss then most likely there will no communication or transfer data between Station A and Station B.

On next articles we will emphasized on

Calculating budget loss if there are jointings or splicings between fiber optics cable
Calculating budget loss if few fiber optics cable are connected via connectors

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Testing & Commissioning Optical Fiber Link -Part 1

1/4/2017

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Calculation of Optical Power Budget

What is Optical Power Budget ?

The optical power budget identifies how much attenuation or loss is allowed across a fiber span while still maintaining sufficient output power for the receiver.

Assuming that we are in the planning of installing a singlemode fiber optics cable from point A to point B for our data communication project.
Prior to actual fiber implementation we need to calculate before hand the allowable maximum loss or optical power budget or optical power loss.

Figure 1 : Cabling Schematic Diagram

For Singlemode fiber optics the common operating wavelengths are both 1310nm and 1550nm.
For Multimode fiber optics the common operating wavelengths are both 850nm and 1300nm.
Based upon manufacturers fiber specification, the attenuation or fiber loss at both operating wave length are as follows :

Figure 2 : Fiber attenuation for both SM and MM

How To Calculate Optical Power Budget ?

The Optical Power Budget Loss is equivalent to the total loss of fiber loss + splicing loss + connector loss.
It is illustrated as below :

Figure 3 : Optical Power Budget

Fiber Loss = Length of fiber (km) x Attenuation (dB/km)
Length of fiber (km) - to get this value by using OTDR
Attenuation (dB/km) - SM 1310nm - 0.3dB/km & SM 1550nm - 0.2dB/km
MM 850nm - 3dB/km & MM 1300nm - 1 dB/km

Splicing Loss = No. of splicing x Max splicing loss (dB)
No. of splicing - total number of splicings done from Station A to Station B
Max splicing loss - as per TIA/EIA recommendation 0.2dB for each splicing

Connector Loss = No. of connector x Max connector loss (dB)
No. of connectors - total number of connectors from Station A to Station B
Max connector loss - as per TIA/EIA recommendation 0.75 dB for connectors
(but we take maximum connector loss at 0.5dB)

Optical Power Budget Calculation Example

Using above Figure 1 fiber optics schematic diagram followings can be deduced :
a. Total length of fiber is 1km
b. 2 nos of splicings
c. 2 nos of connectors
d. SM operating wavelength of 1310 nm - 0.3dB/km, 1550nm - 0.2dB/km

Operating Wavelength at 1310nm
Maximum Allowable Loss = Fiber Loss + Splicing Loss + Connector Loss
= (1 km x 0.3 dB/km) + ( 2 x 0.2dB) + ( 2 x 0.5dB)
= 1.7dB

Operating Wavelength at 1550nm
Maximum Allowable Loss = Fiber Loss + Splicing Loss + Connector Loss
= (1 km x 0.2 dB/km) + ( 2 x 0.2dB) + ( 2 x 0.5dB)
= 1.6dB

As such, when we do actual measurement using power meter & light source the measured loss must be less than the calculated allowable maximum loss.
If the actual measurement value is higher than calculated maximum loss then most likely there will no communication or transfer data between Station A and Station B.