NAME: TAKUDZWA S. T. MOYO
REG NUMBER : R189424U
Report Title : Loss and Power Budget In Fiber Optics
1 Objectives
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To investigate the effect of loss on optical system performance and characterize the
system with the power budget equation.
To use Optisystem software to optimize the fiber length of a communication system
2 Background
Light signals lose power as they travel from optical transmitter to optical receiver. Loss of power
is caused by many factors such as scattering, noise bending, dispersion and polarization in the
optic fiber. Link power budget analysis is done in order to measure the performance of an optic
fiber system.
If the signal power at the receiver is less than the receiver sensitivity then the signal will not be
received correctly. For a good signal at the receiver side the signal has to be greater than receiver
sensitivity. Power margin is the received signal and the power sensitivity of the receiver. Power
margin can be calculated by the following equation
𝑀 = 𝑃𝑡−𝑆𝑟 −𝐴𝐿𝑓−𝐿𝑐−𝐿𝑎,
Where
𝑃𝑡 is transmitter power
𝐴𝐿𝑓 is fiber loss
𝐿𝑎 is additional loss
𝑆r is receiver sensitivity
𝐿𝑐 is coupler loss
𝑀 is power margin
Power budget of an optical system can be done using software to design and virtually test an
optical link. Optisystem is a cost effective and efficient software that can be used to simulate a
fiber optic communication system.
Method and Materials
Materials
Optisystem software was used to design the fiber communication system shown below in Fig 1.
Figure 1: Fiber communication system
3 System Performance
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The power of the optical transmitter was correctly set to 2dBm and bit rate was set to 1
Gb/s
To simulate a receiver with a -30 dBm sensitivity the PIN photodiode’s Thermal power
density was set to 15e-24 W/Hz.
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The following components were placed:
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Optical Transmitter
Optical Fiber
Connector
Gaussian Optical Filter
Low Pass Gaussian Filter
PIN Photodiode
3R Regenerator
BER Analyzer
Transmitters Library/Optical Transmitters
Optical Fibers Library
Passives Library/Optical/Connectors
Filters Library/Optical
Filters Library/Electrical
Receivers Library/Photodetectors
Receivers Library/Regenerators
Visualizer Library/Electrical
The optical fiber length was set to 1.67km and the project was simulated and a BER of 4.02 ∗
10 was obtained as shown in graph below
Figure 2: Graph of log of BER against Time
3.1 Effect of loss on system performance

In the layout properties, the sequence length was changed from 128 to 1024 and a bit
error rate value of 1.06 ∗ 10 was obtained as shown in the graph below
Figure 3 : Graph of Q factor against time

A parameter sweep of the optical fiber length was created and varied from 18 km to 25
km with 10 total steps
Figure 4: Parameter sweeps from 18 to 25 km
3.2 Optisystem optimizations
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Starting from the same project file as used above, an optimization was run to determine
the optimal bandwidth of the Gaussian filter
First the parameter sweep was removed, by changing the fiber length parameter from
sweep to normal and it was assigned a value of 23 km and the total number of sweep
iterations to was set to 1.
The objective of this optimization was to determine the best cutoff frequency for the low
pass electrical filter. The optimizations window was opened by finding it in the Tools tab.
Figure 5: Opening the optimizations window
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The SPO Optimization (Single Parameter Single Result) was chosen and Inserted.
Figure 6 : Selecting the SPO Optimization from the Optimizations window.
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The properties were set. The goal for this optimization was to maximize the Q factor
result of the BER Analyzer within a 0.001 accuracy.
Figure 7: Setting up the optimization type.
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In the Parameter tab the cutoff frequency in the electrical Gaussian filter was located and
the range was set from 100 MHz to 1.5 GHz.
Figure 8: Selecting the parameter to optimize.
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The Max Q Factor result was located in the BER Analyzer and added to the optimization.
Figure 9: Choosing the result to maximize.
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At the calculation window all the optimizations were run. During the simulation the
student clicked on the optimizations tab to observe the optimization in progress.
Figure 10: Running the simulation and optimizations.
3.3 Optimize fiber length
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The cutoff frequency of the Gaussian low pass filter was set to 505 MHz and using the
above procedure, the longest fiber length that resulted in a Q factor of 2.37 was obtained
as shown in the figure below.
Figure 11: Diagram for a Max Q factor of 2.37
Questions
2.1.1 and 2.1.2
2.1.3
3.1.1 Graph for minium log of BER against fiber length
Figure 12: Graph for minium log of BER against fiber length
3.1.2 The minimum log of BER increases linearly as the length of the fiber increases. It then
reaches a point where it is constant and equal to 0 from 18.8km to 25km
3.1.3 Diagram showing the position were the optical power meter was strategically placed
Figure 13: Optical communication system with optical power meter
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The figure below shows the reading of -32.787dBm that was obtained from the optical
power meter
3.3.1 The fiber length that resulted in the highest Q factor of 2.37 was 25 km long
3.3.2 and 3.3.3
DISCUSSION
The Optisystem software helped to reduce the time required for the student to design and test the
optical communication system
The signal suffered losses as it travelled to the receiver . Some of the losses were due to
attenuation in the optical fiber and connector losses. Using 10 linear steps of length from 18 to
25 km resulted in an accurate graphical representation of the minimum log of BER against the
fiber length. The optical power meter obtained a receiver sensitivity reading of -32.787 dBm
which is close to the theoretical expected value of -30 dBm.
The value of the bit error rate was 4.02 ∗ 10 for a sequence length of 128 bits and it was of
1.06 ∗ 10 for a sequence length of 1024 bits, showing as the sequence length was increased a
more accurate value of the bit error rate was obtained.
CONCLUSION
Signals suffer loss as they travel through the optical fiber system. Minimum log of BER of a
optical communication system increases until it becomes constant. Software simulation helps
reduce the time required to test optical fiber communication systems. An optical power meter
can be used to measure the power at the receiver’s side.
REFERENCES
Slideplayer.com. 2022. CHAPTER 7 OPTICAL SYSTEM DESIGN. Transmission Types Two
types of transmissions: - Link (point to point) - Network -point to multipoint -Mesh -Ring. - ppt
download. [online] Available at: <https://slideplayer.com/slide/7995518/> [Accessed 14 May
2022].
Iopscience.iop.org. 2022. Link Power Budget and Traffict QoS Performance Analysis of Gygabit
Passive Optical Network. [online] Available at: <http://iopscience.iop.org/article/10.1088/17426596/953/1/012129/pdf> [Accessed 14 May 2022].
Fosco Connect. 2022. What is BER (Bit Error Ratio) and BERT (Bit Error Ratio Tester)?.
[online] Available at: <https://www.fiberoptics4sale.com/blogs/archive-posts/95047174-what-isber-bit-error-ratio-and-bert-bit-error-ratiotester#:~:text=A%20bit%20error%20ratio%20of,acceptable%20BER%20for%20telecommunica
tion%20applications.> [Accessed 14 May 2022].