The report covers these areas : Measures of optical powers, wave length and corresponding instruments Measure of optical spectrum and corresponding instruments Methods for high-resolution spectral characterization Experimental modeling of optical transmission systems and corresponding instrumentation Spectral measures of laser sources through the "optical power meter" and the "wavelength meter" Experimental procedure for the joint of optical fibers and corresponding measurement of the joint attenuation Experimental characterization of passive optical devices Realization of an optical amplifier and corresponding experimental characterization Spectral characterization of optical sources through optical spectrum analyzers and high resolution methods

1. Signal processing and transmission laboratory
Makan Mohammadi
S201977
Prof Valter Ferrero

2. Ivan Karamazov says that, more than anything else, the death of children makes
him want to give back his ticket to the universe. But he does not give it back. He
keeps on fighting and loving; he keeps on keeping on.
The experience of modernity
Marshall Berman

3. Laser Source Power
Meter
Lab 1
Power characterization of laser diode
Laser diode play a key role in high speed transmitter in optical networks. In this experiment to characterize
laser diode we measure the effect of current variation on output power (p-I). Output power theoretically
has a linear relation with current according to following formula:
𝑃𝑜𝑢𝑡 = 𝛽𝑠(𝐼 − 𝐼𝑡ℎ)
𝐼𝑡ℎ ∶ 𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝛽𝑠 ∶ 𝑆𝑙𝑜𝑝𝑒 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦
This laboratory consists of two parts; in first part the power is measured for a range set of current while
the temperature is fixed, in the second part power measurement is done for variable wavelength and
fixed temperature. Instruments exploited for the characterization of laser diode includes:
 Laser diode
 Laser diode controller
 Power head
 Power meter
According to the figure 1-1 instruments were connected together
figure 1-1
Configuration setting of first experiment is as below:
 Current variation from 0 mA to 57 mA
 Temperature steps are 20, 24, 32, 36, 40 degree
Result
First of all, we should consider that temperature can affect the power characterization, therefor the
temperature is fixed at above mentioned values while power is measured for different range of current.
As depicted in the graph1.1, the device produces small amount of incoherent light at the low currents. At
a threshold value where the emission gain can defeat the losses due to enough population inversion, the
output power starts rising linearly with the current. Moreover, it is observable for a specific current value,
by increasing the temperature, the output power is declining.
Temp & Current
Controller
Optical Head

4. Graph 1.1
For the second part similar graphs are plotted (Graph 2-1) for the same range of current and temperature
steps while we measure the laser wavelength. As expected for the different current values, the
wavelength variation is very small, considering the measurement points after the threshold. However,
obtained wavelength values increase by rising the temperature around 2 nm. Graph 3-1 is showing the
same result in 3 dimensional, which can help us to understand the relation between the current-
temperature for a determined power value.
10 20 30 40 50 60
Current
Graph 2-1
0 1 2 3 4 5 6
0
50
100
150
X
9Y:
26.37
Current
T=2
T=2
T=3
T=3
T=4
1556.8
1557
1557.2
1557.4
1557.6
1557.8
1558
1558.2
1558.4
T=20
T=24
T=32
T=36

5. Current – Temperature figure for fixed Wavelength

6. Current – Temperature figure for fixed Power

7. Lab 2
Characterization of the power loss of a splice
One of the most common methods to joint fiber optics is to use splicer. In this experiment fusion
core alignment splicer has been exploited. In this method the two cleaved fibers are automatically
aligned by the fusion splicer in the x, y, z plane, then are fused together. Our aim is to measure
the loss in terms of power that a permanent joint introduces to the system. In fact, part of the
beam photons propagates out of the medium which cause the power loss. Splicer device is also
able to estimate the loss base on physical characteristic of the joint.
The first step is to prepare the fiber by removing clad from its end using a fiber optic stripper then
high precision fiber cleaver is used to have a precise orthogonal cut. This device equipped with a
diamond blade. Eventually to remove any remaining dust we clean the fiber cut with alcohol
soaked cotton. Next step is to set up Laser diode as the optical source with the following values:
temperature 25 ˚C, wavelength 1550 nm, injection current 35 mA this setting provides a specific
power amount to obtain the output power directly from the laser naked fiber is connect to source
by means of an adapter and the other end connects to power meter to measure the power. Our
first power measured is 1.4205 dBm. Then we disconnect the fiber from adapter, joint another
fiber to it and reconnect it to source with the adapter we keep joining more fibers serially up to
30 junctions. Trivially loss can be measured by deducting the receiver power from the transmitter
power. The power measurement results are plotted in the following figure for all the 30
experiment iterations in red color. As mentioned before Splicer also has a power estimation which
is plotted in green color.
Distribution of the measured losses for red one is:
𝜇 = 0.2391 , 𝜎2
= 0.0223 𝜎 = 0.1495
Distribution of the measured losses for green one is:
𝜇 = 0.0466 , 𝜎2
= 2.5707𝑒 − 04 , 𝜎 = 0.0160
0 5 10 15 20 25 30
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Iteration
Loss(dB)
experimental loss
splicer loss result

8. 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Loss dB
0
1
2
3
4
5
6
7
8
9
10
11
12
Splicer
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0
2
4
6
8
10
12
14
Loss dB
Experimental Loss

9. Lab3
Characterization of optical isolator, WDM coupler and optical filter
In this section we characterize three optical components but firstly we have to characterize the
optical source. For this purpose, tunable laser power is measured for a range of different
wavelength from 1530 nm up to 1560 nm, it is lunched at 0 dBm and T= 20 ˚C. Below figures show
us input power in two scale. We use this input power in this experiment as input power for
isolator, coupler and optical filter.
1530 1535 1540 1545 1550 1555 1560
−0.08
−0.06
−0.04
−0.02
0
0.02
0.04
0.06
Wavelength (nm)
Input power
1530 1535 1540 1545 1550 1555 1560
−7
−6
−5
−4
−3
−2
−1
0
1
2
Wavelength (nm)
Input power

10. Optical Isolator
An optical isolator, is a two port optical component which allows the transmission of light in only
one direction. It is typically used to prevent unwanted feedback. Their typical specification is that
they are low loss in forward direction and high loss in backward direction. Our purpose is to
identify the input and output port of the isolator.
Then we connect the laser to Isolator port 1 and obtain the power measurements in port number2
using power meter for the whole wavelength range. In this way Isolator behavior in terms of
power is determined. We do the same experiment inverting the ports.
According to the result graphs port 1 is identified as input and port 2 as output because we
experiment low loss from port1 towards port2 and high loss vice versa.
Min Loss Port 1: :35.67 dB
Max Loss port 1: 48.09 dB
Min Loss Port 2: 0.94 dB
Max Loss port 2: 1.05 dB
1530 1535 1540 1545 1550 1555 1560
−50
−40
−30
−20
−10
0
10
Wavelength (nm)
Power of port1
Power of port2
Input power

11. Optical Filters
Optical filters are devices that selectively transmit light of different wavelengths. Our study case
is a triple port optic filter. To examine the ports, we pick one port as input and one port as output
and close the third with a plastic cap to ensure no loss occurring due to leakage from the third.
one is an input port and from the other two, one has a high loss at a certain wavelength while it
is low loss for the rest of wavelength range and the other port react exactly in opposite way. In
the following figures, power variation in each port in terms of different wavelength is observed.
For instance, port2 filters lambda=1553.5 from the rest of wavelengths. Here port 3 is Drop port.
𝑃𝑜𝑟𝑡 2 𝜆1, 𝜆2, 𝜆3
𝜆1, 𝜆2, 𝜆3, 𝜆4 𝑃𝑜𝑟𝑡 1
𝑃𝑜𝑟𝑡 3 𝜆4 = 1553.5 𝑛𝑚
1530 1535 1540 1545 1550 1555 1560
0
10
20
30
40
50
Wavelength (nm)
Loss port 1
Min :35.67
Max:48.09
Loss port 2
Min :0.94
Max:1.05
Filter

12. 1530 1535 1540 1545 1550 1555 1560
45
50
55
60
65
70
Wavelength (nm)
Loss port 3
Input port 2
Wavelength (nm)
1530 1535 1540 1545 1550 1555 1560
0
5
10
15
20
25
30
Loss
(dB)
Loss port 2
Input port 1
1530 1535 1540 1545 1550 1555 1560
0
10
20
30
40
50
loss port 3
Input port 1

13. Optical Coupler
Optical Coupler is a triple device with one input and two outputs.
A fiber optic coupler is a device with at least one input port and one or several output
ports. Light entering an input fiber can appear at one or more outputs and its power distribution
depending on α factor. Our study case has three ports; one input and two outputs which split the
input power according to this formulas:
𝑃2 = 𝛼.
1
𝜀
. 𝑃1 𝑃3 = (1 − 𝛼).
1
𝜀
. 𝑃1
𝛼 =
𝑃2
𝑃2 + 𝑃3
𝜀 = 𝛼.
𝑃1
𝑃2
𝑃2
𝑃1
𝑃3
We observer the figure of input power is as below figure.
Coupler
1530 1535 1540 1545 1550 1555 1560
−7
−6
−5
−4
−3
−2
−1
0
1
2
Wavelength (nm)
Input power

14. In our case , 𝑃1 is port 1 , 𝑃2 is port 2 and 𝑃3 is port 3 . As you can see between port 2 and 3 we
have high loss. For each measurement, first number is input port and second number is output
port and third port is closed. When we use this component as Splitter , 𝑃1 is input and 𝑃2 , 𝑃3 are
output . If we use component as Coupler, 𝑃2 , 𝑃3 are input and 𝑃1 is output.
Our mission is to calculate and plot α in terms of wavelength.
wavelength
Alfa Figure
1530 1535 1540 1545 1550 1555 1560
−10
0
10
20
30
40
50
60
Wavelength
Loss 1 − 2
Loss 1 − 3
Loss 2 −3
1535 1540 1545 1550 1555 1560
0.89
0.895
0.9
0.905
0.91
0.915
0.92
0.925
0.93
X: 1531
Y: 0.9138
X: 1540
Y: 0.9

15. As you can observe, α is around “0.9”; It means that we can use the coupler as tap.𝜀 excess loss is around
“1.2” .
As an agreement 3dB coupler/splitter of α = 0.5
Tap if of α = [0.9 – 0.95]
1530 1535 1540 1545 1550 1555 1560
1.1
1.12
1.14
1.16
1.18
1.2
1.22
1.24
1.26
1.28
1.3
Wavelength (nm)

16. Signal pump
Demux
Signal pump
Mux
Signal pump
Demux
Signal pump
Mux
Lab 4
Characterization of an Erbium Doped Fiber Amplifier (EDFA)
Erbium doped fiber amplifier (EDFA) is an optical repeater that is used to amplify the intensity of optical
signals being carried through a fiber optic system. An optical fiber is doped with the erbium so that the
fiber absorb light at one frequency and emit light at another frequency. An external semiconductor laser
couples light into the fiber at wavelengths of 980 nanometers. This action excites the erbium atoms.
Additional optical signals at wavelengths between 1530 and 1620 nanometers enter the fiber and
stimulate the excited erbium atoms to emit photons at the same wavelength as the incoming signal which
leads to amplify a weak optical signal to a higher power.
In this experiment two methods were used: Co-Propagation and counter Propagation pumping. In practice
both methods are exploited. Following figures show the two configuration schema:
Erbium Doped Fiber Pump monitor
port
Co Propagating
Pump monitor Erbium Doped Fiber
Counter propagating
As it is observed from the figure required components include:
980 or 1480 nm
Pump laser
980 or 1480 nm
Pump laser

17.  Erbium doped fiber amplifier (EDFA)
 Optical Isolator
 Pump laser
 Signal pump mux/Demux
 Optical Source Analyzer (OSA)
To begin, we must characterize the input power for different wavelength.
In fact, input power is set to “-20dbm” and temperature of 20˚C. Then the noise level and amplified signal
power are measured. Here are the results for amplified output power without considering noise in terms
of wavelength. Red line is input.
1530 1535 1540 1545 1550 1555 1560
−25
−20
−15
−10
−5
0
5
10
Wavelength (nm)
Power Input
Power Output CO −P ,100 mA
Power Output CO −P ,150 mA
Power Output COUNTER−P ,100 mA
Power Output COUNTER−P ,150 mA

18. Here are the results for amplified output power with considering noise ( 𝑃𝑜𝑢𝑡 − 𝑃𝐴𝑆𝐸 ) in terms of
wavelength.
1530 1535 1540 1545 1550 1555 1560
5
10
15
20
25
30
CO -P ,100 mA
CO-P ,150 mA
COUNTER-P ,100 mA
COUNTER-P, 150 mA
Wavelength (nm)

19. In theory the EDFA gain can be computed according to following formula:
𝐺 = 10𝑙𝑜𝑔10(
𝑃𝑜𝑢𝑡 − 𝑃𝐴𝑆𝐸
𝑃𝑖𝑛
)
for using this formula we must convert dBm to Watt for 𝑃𝑜𝑢𝑡 , 𝑃𝐴𝑆𝐸 𝑎𝑛𝑑 𝑃𝑖𝑛 and finally we have gain in
term of dB. For better understanding below graphs show the computed gain using method Counter-
Propagating 150 mA step by step , 𝑃𝑜𝑢𝑡 , 𝑃𝐴𝑆𝐸 ,𝑃𝑖𝑛 in watt dimension and finally Gain in dB dimension.
1530 1535 1540 1545 1550 1555 1560
0
0.5
1
1.5
2
2.5
X10^3
Wavelength (nm)
1530 1535 1540 1545 1550 1555 1560
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Wavelength (nm)
X10^5

20. 1530 1535 1540 1545 1550 1555 1560
17
18
19
20
21
22
23
24
25
26
Wavelength (nm)

21. Top graphs show the computed gain using both methods Co-Propagating and Counter-Propagating. In
both methods gain increases by current increment due to the fact that number of ions pumped raised
with current increment. However, Counter-Propagating method achieves higher gain in comparison with
Co-Propagating method in this experiment.
Eventually, the spontaneous emission factor 𝑛 𝑠𝑝 is computed from the following formula:
1535 1540 1545 1550 1555
16
17
18
19
20
21
22
23
24
25
Wavelength (nm)
Co-P 100mA
Co-P 150mA
1535 1540 1545 1550 1555 1560
16
17
18
19
20
21
22
23
24
25
Wavelength (nm)
Counter-P 100mA
Counter-P 150mA
1535 1540 1545 1550 1555
16
17
18
19
20
21
22
23
24
25
1535 1540 1545 1550 1555 1560
16
17
18
19
20
21
22
23
Co-P 150mA
Counter-P 150mA
Co-P 100mA
Counter-P 100mA

22. 𝑛 𝑠𝑝 =
𝑃𝐴𝑆𝐸
2ℎ𝑓(𝐺 − 1)𝐵
Here is the graph for factor in terms of wavelength, where this amount is between 3 and 4.
In this case we set resolution bandwidth ∆ 𝜆 =0.1 nm, 1530nm ≤ 𝜆 ≤1560nm , h is Planck
constant h=2.62607004x10^-34 [m^2Kg/s] , 𝑃𝐴𝑆𝐸 and G must be in linear format and
finally 𝑓[𝐻𝑧] = 𝑐/𝜆 and 𝐵 = 𝑐∆ 𝜆/𝜆2
Top graphs show, method “Counter-P 150mA” has better performance than other methods because it
has high gain and in comparison, amount of noise is less than Co-P 150 mA.
1530 1535 1540 1545 1550 1555 1560
3
3.2
3.4
3.6
3.8
4
Wavelength (nm)
Co-P 100mA
Co-P 150mA
Counter-P 100mA
Counter-P 150mA

23. Signal Laser
OSA
Power
Splitte
r ESA
Optical receiver
PC
Lab 5
Characterization of linewidth and spectral occupation of a laser
In this laboratory we are expected to characterize the laser optical source in terms of linewidth and
spectral occupation. 3 different methods are used for this purpose:
1. Measurement with an OSA
2. Heterodyne technique
3. Homodyne technique
Measurement with an OSA
Firstly, laser optical source is set once at 8 mA and then 40 mA injection current. Then power spectrum
linewidth is measured for two different Resolution bandwidth (𝑅 𝑏). According to the below figure we are
interested to measure the spectrum of laser source through Optical Spectrum Analyzer (OSA) screen. In
fact, we are interested in two values from the measured spectrum: the peak and the corresponding value
for 3db. We demonstrate that this method result goes wrong if the linewidth of the source is smaller than
internal tunable filter of the OSA. By using two different resolution bandwidth for a single signal we
achieve two different ∆𝜗 (Spectrum linewidth) which proves that we have measured the internal filter of
OSA instead of spectrum linewidth.
Heterodyne technique
In this method we used the following optical circuit including tunable laser that connects to polarization
controller (PC) which plays the Local Oscillator (LO) role here. A power splitter combines the LO signal
and signal laser which is connected to an optical receiver. This device transforms the optical signal into
Electric and forward it to Electrical Spectrum Analyzer (ESA). ESA has narrower resolution bandwidth
which enables us to measure the signal power spectrum linewidth. ESA works in microwave domain
(20GHz), therefore the output electrical signal should be in the same bandwidth domain, i.e. the signal
laser frequency and the LO frequency must be close to each other. To achieve this, we align the central
frequency signal by means of a device.
I T 𝑅 𝐵 Peak ∆𝜗(𝑛𝑚)
8 mA 20˚C 5 -39.92 53
8 mA 20˚C 10 -36.91 55
40 mA 20˚C 0.1 -4.65 0.092
40mA 20˚C 0.2 -3.47 0.176
Laser Source
Temp & Current
Controller
OSA
Tunable
Laser
LO

24. Linewidth = 24.33 MHz= ∆𝜗
𝑡 𝑐 =
1
𝜋∆𝜗
𝐿 𝑐 = 𝑡 𝑐. 𝑉𝑔
𝑉𝑔 = 𝑐/𝑛 𝑔
𝑛 𝑔 = 1.47 𝑖𝑛 𝑜𝑝𝑡𝑖𝑐𝑎𝑙 𝑓𝑖𝑏𝑒𝑟
𝐿 𝑐 = 2.6682 𝑚

25. Signal Laser
Power
Splitter
ESA
Optical receiver
PC
fiber spool
Homodyne technique
According to following schema, power splitter divides the input signal into 𝐸1 and 𝐸2 and fiber spool plays
the decorrelation role by applying delay on signal 𝐸1 then with the means of another power splitter these
two signals combines and are sent to optical receiver. The output electrical signal goes to ESA. In this
method against previous method, a separated local oscillator is not required and the signal is convoluted
to itself. In theory the curve maximum point we observe in ESA screen must happen at zero frequency,
but in practice we see an over shoulder shape at zero which is because of the internal local oscillator of
ESA. In case we turn off the optical source this shape still exists on the ESA screen.
I T Technique Peak ∆𝜗(MHz) 𝐿 𝑐
40 mA 20˚C Heterodyne -42.28 24.33 2.6682
40 mA 20˚C Homodyne -57.86 10.8 6.0108
Power
Splitter

26. Linewidth = 10.8 MHz= ∆𝜗
𝑡 𝑐 =
1
𝜋∆𝜗
𝐿 𝑐 = 𝑡 𝑐. 𝑉𝑔
𝑉𝑔 = 𝑐/𝑛 𝑔
𝑛 𝑔 = 1.47 𝑖𝑛 𝑜𝑝𝑡𝑖𝑐𝑎𝑙 𝑓𝑖𝑏𝑒𝑟
𝐿 𝑐 = 6.0108