A LAB REPORT ON
CHARACTERIZATION OF OPTICAL FIBER
&
DEMONSTRATION OF OPTICAL FIBER KIT “LIGHT RUNNER BASIC”
PSE605A: PHOTONICS LAB TECHNIQUES
Submitted by: BEYANT SINGH CHANDRAKAR
ROLL NO: 22116002
SEMESTER-II, MTech 2022
Submitted to
Prof. PRATIK SEN
SHIVAM SHUKLA (TA) DATE: 20/03/2023
CENTER FOR LASERS AND PHOTONICS
IIT KANPUR
1
INDEX
S.NO
CONTENTS
PAGE NO.
1
Objectives
3
2
Experimental Setup
3-8
3
Apparatus Required
3
4
Procedure
4-8
5
Observation Tables and Graphs
8-18
6
Calculations and Errors
19-20
7
Discussion and Conclusion
8
Sources of Error
20
20-21
2
Experiment No. 12, Part-I
Title: Characterization of Optical Fiber.
Objective:
The objectives of this experiment are as follows:
1.
2.
3.
4.
Optical Fiber Coupling Loss for single mode
Bending loss in single mode optical fiber
To determine NA of single mode optical fiber at two different positions
To determine misalignment loss for single mode optical fiber
▪ Longitudinal misalignment
▪ Transverse misalignment
▪ Angular misalignment
Equipment’s Required:
1. He-Ne Laser
2. Focusing objective (20X)
3. Optical fiber with alignment with (x, y, z & angular) mounts (quantity 2)
4. Translation stage
5. Photodetector with mount
6. Digital multi-meter
7. Mandrels
Experimental Setup & Procedure:
3
A.) To determine Optical Fiber Coupling Loss for single mode Fiber (SMF)
Figure-1: Optical Fiber Coupling Loss Measurement
Procedure:
1. First, we make the arrangement as show in the figure-1
2. Then the He-Ne laser source is turn on and wait for some 5 minutes to stabilize the
laser light.
3. Place an objective lens (20X) in front of the source. Align it in such that laser light is
passing through it and then adjust the focus of the lens and the horizontal and
vertical axis such that back reflection should fall at the center of the source in a
circular symmetry.
4. Now observe the power value on the photodetector.
5. Next place the fiber cable on a mount as shown in figure-1.
6. Adjust the height and position of the fiber with the help of alignment screws in the
mount so that maximum light propagates in the fiber (see in multi-meter).
7. Now measure the light intensity at the laser input right after the lens and also at the
output end of fiber.
8. Note down the readings and then calculate the coupling loss.
4
B.) To determine Bending loss in Single mode optical Fiber
Figure-2: Optical Fiber Bending Loss Measurement
Procedure:
9. Align all the components as shown in figure 2 as explained.
10. Bend the Fiber for different radius of curvatures using a mandrel.
11. Measure the variation of the output intensity falling at the photodiode for these
curvatures.
12. Calculate the loss for each reading.
13. Curve fit the loss with respect to the radius of curvature.
14. Calculate the value of critical radius.
C.) To measure Numerical Aperture of Single Mode Optical Fiber
Figure-3: Optical Fiber Numerical Aperture Measurement
5
Procedure:
15. Make the arrangement as shown in figure 3.
16. This time place the output end of Fiber over an angular stage.
17. Measure the output power of the Fiber with a photo-detector and read it on a multi-
meter.
18. Vary the angle of the stage to find the output power variation from minimum to
maximum then to minimum.
19. Plot these readings and find the data points at which the maximum power goes of its
value. These two angles would be ϕ and ϕ .
20. Calculate the acceptance angle with following formula
2ϕ
=ϕ
−ϕ
21. Calculate the numerical aperture by using measured acceptance angle as follows:
Numerical Aperture = n ∗ sin (ϕ )
D.) To determine Misalignment loss for Single Mode Optical Fiber
Figure-4: Optical Fiber Misalignment Loss Measurement full setup
6
Figure-5: Optical Fiber Misalignment Loss Measurement close setup
Figure-6: Optical Fiber Misalignment Loss Measurement schematic setup
Procedure:
22. Align the components as shown in figure 4.
23. Place another SMF near the end of the input SMF as shown in figure 4.
24. Couple the output intensity coming out from the Input SMF to the output SMF.
25. Align two of the Fiber edges until the maximum power starts coupling between
them.
26. Place a detector at the end of second SMF.
7
27. Measure the intensity with the help of a multi-meter.
28. Move output SMF with the help of an angular stage as used in figure 3 (Numerical
Aperture measurement) but mounting second SMF.
29. Take the readings for very small steps of angular movement. Curve fit the plot.
30. For the observation of transverse misalignment loss, we repeat 1 to 4 steps and then
mount the second SMF on a linear stage and then take the readings in a very small
steps in transverse direction until the two Fibers cross each other completely.
31. For observing the longitudinal misalignment loss after step 4 we mount the second
SMF on a linear stage and then move this Fiber in longitudinal direction. Start taking
the reading from where are getting maximum intensity up to the point where we get
minimum value of intensity.
Observations & Results:
A.) Coupling Loss in single mode fiber:
The coupling loss can be calculated using formula given below:
𝑉𝑜
𝑙𝑜𝑠𝑠 (𝑖𝑛 𝑑𝐵) = −10𝑙𝑜𝑔
𝑉𝑖
Vo = Power at the fiber output
Vi = Power emitted by He-Ne laser source.
The values are as follows Vo = 0.374 V, Vi = 0.470 V.
Hence the coupling loss for single mode fiber comes out to be 0.9923 dB.
B.) Bending Loss measurement:
The variation of output power with rest to mandrel diameter is provide in the table below.
The loss has been calculated according to the loss equation.
Sl
No.
1
2
3
4
5
6
Main Scale Reading
(mm)
15
14
13
12
11
9
Vernier Scale
count
5
6
9
9
31
37
Least Count
(mm)
0.02
0.02
0.02
0.02
0.02
0.02
diameter
(mm)
15.1
14.12
13.18
12.18
11.62
9.74
Output
Voltage (V)
349
346
346
346
346
342
Loss
(dB)
1.2927
1.3302
1.3302
1.3302
1.3302
1.3807
8
7
8
9
10
11
12
13
14
15
16
17
18
8
7
6
5
4
4
4
3
3
3
1
1
9
13
42
28
36
4
1
4
21
10
23
1
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
8.18
7.26
6.84
5.56
4.72
4.08
4.02
3.08
3.42
3.2
1.46
1.02
338
327
321
304
298
290
260
284
275
240
214
157
1.4318
1.5755
1.6559
1.8922
1.9788
2.0969
2.5712
2.1878
2.3276
2.9189
3.4168
4.7619
Fig 7: Bending loss plot with change in bend diameter of mandrel
9
Critical Diameter of Optical Fibre:
•
From the Graph-1, we see that from Mandrel diameter 3.55151 mm the loss is
rising sharply .
•
Hence, the Critical Radius = 3.55151 mm.
C.) Numerical aperture measurement:
S.No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Angle (in degrees)
0.083333333
0.166666667
0.25
0.333333333
0.416666667
0.5
0.583333333
0.666666667
0.75
0.833333333
0.916666667
1
1.083333333
1.166666667
1.25
1.333333333
1.416666667
1.5
1.583333333
1.666666667
1.75
1.833333333
1.916666667
2
2.083333333
2.166666667
2.25
2.333333333
2.416666667
2.5
2.583333333
2.666666667
2.75
Photo diode voltage(mV)
0
1
2
2
3
3
4
5
6
7
8
9
10
12
13
14
16
18
20
23
26
28
31
34
37
40
42
46
50
54
59
63
68
10
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
2.833333333
2.916666667
3
3.083333333
3.166666667
3.25
3.333333333
3.416666667
3.5
3.583333333
3.666666667
3.75
3.833333333
3.916666667
4
4.083333333
4.166666667
4.25
4.333333333
4.416666667
4.5
4.583333333
4.666666667
4.75
4.833333333
4.916666667
5
5.083333333
5.166666667
5.25
5.333333333
5.416666667
5.5
5.583333333
5.666666667
5.75
5.833333333
5.916666667
6
6.083333333
6.166666667
71
75
79
83
88
93
96
103
107
111
115
119
122
125
129
131
136
138
142
145
148
150
152
155
157
158
162
164
166
167
168
172
174
176
177
178
179
181
182
182
183
11
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
6.25
6.333333333
6.416666667
6.5
6.583333333
6.666666667
6.75
6.833333333
6.916666667
7
7.083333333
7.166666667
7.25
7.333333333
7.416666667
7.5
7.583333333
7.666666667
7.75
7.833333333
7.916666667
8
8.083333333
8.166666667
8.25
8.333333333
8.416666667
8.5
8.583333333
8.666666667
8.75
8.833333333
8.916666667
9
9.083333333
9.166666667
9.25
9.333333333
9.416666667
9.5
9.583333333
183
184
184
185
185
186
186
187
187
187
187
187
186
185
185
185
184
182
181
178
179
174
175
173
168
166
165
164
162
160
159
156
154
149
147
144
142
139
136
135
130
12
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
9.666666667
9.75
9.833333333
9.916666667
10
10.08333333
10.16666667
10.25
10.33333333
10.41666667
10.5
10.58333333
10.66666667
10.75
10.83333333
10.91666667
11
11.08333333
11.16666667
11.25
11.33333333
11.41666667
11.5
11.58333333
11.66666667
11.75
11.83333333
11.91666667
12
12.08333333
12.16666667
12.25
12.33333333
12.41666667
12.5
12.58333333
12.66666667
12.75
12.83333333
12.91666667
13
129
122
116
111
107
101
97
93
89
84
79
75
70
66
62
58
54
50
45
42
39
35
33
31
26
24
21
19
16
15
14
12
10
9
8
7
6
5
4
3
2
13
157
158
159
160
161
13.08333333
13.16666667
13.25
13.33333333
13.41666667
1
1
1
0
0
Fig 8: Voltage variation at the output end of the SMF with angular variation for NA
Measurement at 11.5 cm separation between detector and fiber tip
Numerical Aperture of Optical Fibre is calculated as:
For 11.5 cm Distance, we got 2θ = 9.789, from fig 8 we get difference in angle = 9.789
θ = 4.8945
14
Numerical Aperture = n∗ sin θ = 1 * sin (4.8945 ) = 0.0853
Here n= refractive index of air = 1
D.) Misalignment loss measurements:
1.) Transverse misalignment:
Sl.
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Distance in transverse direction (µm) Relative distance (µm) Voltage (mV) Loss (dB)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
157
158
158
160
165
172
185
198
202
204
194
184
174
166
159
159
157
4.761982055
4.73440771
4.73440771
4.679778753
4.546139137
4.36569411
4.049261295
3.754326677
3.667464885
3.624676905
3.84296128
4.072800349
4.315486097
4.519897699
4.707007336
4.707007336
4.761982055
15
Fig 9: Transverse Loss variation at the output end of the 2nd SMF with angular deviation
from zero position with respect to 1st SMF fiber input tip
2.) Longitudinal Misalignment Loss:
Sl. No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Distance (µm)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
Voltage (mV)
222
206
196
189
183
178
174
172
170
168
166
164
163
161
161
loss (dB)
3.257449
3.582306
3.798418
3.956361
4.096468
4.216779
4.315486
4.365694
4.416489
4.467886
4.519898
4.57254
4.599103
4.65272
4.65272
16
16
17
18
19
20
21
22
23
150
160
170
180
190
200
210
220
160
160
160
159
159
158
158
158
4.679779
4.679779
4.679779
4.707007
4.707007
4.734408
4.734408
4.734408
Fig 10: Longitudinal loss variation at the output end of the 2nd SMF with angular
deviation from zero position with respect to 1st SMF fiber input tip
3.) Angular misalignment:
Si. No.
1
2
3
4
5
6
Circular scale reading
-9
-8
-7
-6
-5
-4
Total angle in (degree)
-0.15
-0.13333
-0.11667
-0.1
-0.08333
-0.06667
Voltage (mV)
167
167
168
168
172
175
Loss (dB)
4.493813868
4.493813868
4.467885762
4.467885762
4.36569411
4.290598092
17
7
8
9
10
11
12
13
14
15
16
17
18
19
20
-3
-2
-1
0 (20th position)
1
2
3
4
5
6
7
8
9
10
-0.05
-0.03333
-0.01667
0
0.01667
0.03333
0.05
0.06667
0.08333
0.1
0.11667
0.13333
0.15
0.16667
185
194
200
202
198
192
183
176
172
170
168
168
167
167
4.049261295
3.84296128
3.710678623
3.667464885
3.754326677
3.887966292
4.096467682
4.265851901
4.36569411
4.416489366
4.467885762
4.467885762
4.493813868
4.493813868
Fig 11: Angular Loss variation at the output end of the 2nd SMF with angular
deviation from O0with respect to 1st SMF fiber input tip
18
Calculations:
1.) V number:
a = radius of core = 2.15𝜇m
𝜆 = 632.8 × 10−9 m
𝑉 = (𝟐𝚷/ 𝛌)× 𝑎 × 𝑁𝐴 =( 𝟐𝚷/632.8 × 10−9 )× 2.15 × 10−6 × 0.0853= 1.82096
2.) Mode Field Diameter:
w/a = 0.65 + 1.619/v^3/2 + 2.879/v^6
w/215*10^-6 = 0.65 + 1.619/1.82096^3/2+ 2.879/1.82096^6
w = 296.90*10^-6m
Mode field diameter = 2w= 593.80 × 10 − 6 m
3.) Longitudinal Misalignment Loss:
𝜆 = 632.8 × 10−9 m
say for D = 0.05 mm and n =1
D = (0.05*10^-3)(632.8*10^-9)/2*3.14*1*296.90*10^-6)2
D = 0.016
α1(dB) = 10 × log10(1 + 𝐷2 ) = 0.001112 dB
4.) Transverse Misalignment Loss:
Say u = 0.06 mm
𝛂t(𝐝𝐁) = 𝟒. 𝟑𝟒 (u/w)2= 4.34 ( 0.06*10-3/296.90*10-6)2= 0.1773 dB
Error Analysis:
1.) Numerical Aperture:
Theoretical Value = 0.12
Experimental Value = 0.0853
Relative Error =((0.12-0.0853)/0.12)*100 = 28.91%
19
2.) V Number:
Theoretical Value = 2.5617
Experimental Value = 1.82096
Relative Error = ((2.5617- 1.82096)/2.5617)*100 = 28.92%
3.) Longitudinal Misalignment Loss:
Theoretical Beam Waist = w = 2.2683 × 10 − 9 m
Theoretical Loss = 2.9178 dB
Experimental loss = 0.001112 dB
Relative Error = ((2.9178 – 0.001112)/2.9178)*100 = 99.962%
Discussion and Conclusion:
1. when we observe the Transverse Misalignment Loss than we see that it is high when the distance
between the fibre ends are high and significantly low when the distance is low. This change in
behaviour is due to small waist size of laser beam and the TEM 00 mode of the beam.
2. when we observe the Longitudinal Misalignment Loss, we see that it increases with relative distance
initially. After certain distance there is not much change in Loss with increase in Relative Distance.
3. Numerical Apertures at distance, 11.5cm distance between Aperture and Fibre
were calculated with the help of graphs. The value is 0.0853 nm.
4. we find Coupling loss, Bending Loss, Misalignment loss in Longitudinal and Transverse Alignments.
5. Relative Error in Misalignments is higher than Bending and Coupling Loss.
6. we observe that Bending Loss exponentially increases as Mandrel diameter reduces. For large diameters
of Mandrel, the loss is negligible.
Sources of Error & Precautions:
1. The optical components have very sensitive surfaces. These surfaces should not be touched with bare
hands under any circumstances.
2. Alignment is the most important part in any optical experiment. The optical components must be placed
properly otherwise the result will include significant error.
3. There should not be any dust on the surface of the optical components.
4. It should not be noted that the sensor must not be saturated because of the laser power. If necessary,
20
ND filters may be employed.
5. The errors also come from the least count of the translational and rotational stage.
6. Coupling between source and Fibre is very important and avoid touching the bare Fibre tip with hands
or with other objects because it may break the Fibre tip or change the output power and also, we
should be careful while fixing the Fibre in the Fibre mount.
7. Rough surface of Fibre will cause loss. Fibre must be cleaved as the broken tip can add significant error
in the data.
References:
1. Introduction to Optics 2nd ed - F. Pedrotti, L. Pedrotti (Prentice-Hall, 1993)
2. Optics by Hecht & Ganeshan
3. “Introduction to fiber optics” by A. Ghatak and K. Thyagarajan, Cambridge university press, 1st
edition (2000).
4. K P Zetie et al, 2000,Phys. Educ. 35,46
21
INDEX
S.NO
CONTENTS
PAGE NO.
1
Objectives
23
2
Apparatus Required
23
3
Procedure
23-28
4
Observation Tables and Graphs
28-34
6
Calculations and Errors
35
7
Discussion and Conclusion
35
22
Experiment No. 12, Part-II
Title: Demonstration of Optical Fibre kit ‘Light Runner Basic’
Objectives:
1. To measure the Attenuation, Dispersion, and Eye Pattern in an Optical Fibre
2. To determine the position of the fault in a fibre optic link using OTDR method
Apparatus Required:
1.
Optical Fibre Spool (1 km, 2 km, 3 km)
2.
Connectors
3.
BNC Connectors
4.
Fibre Connectors
5.
PC Link cable
6.
Fibre Optic Light runner Kit
7.
PC
Objective: To measure Attenuation Loss in an Optical Fibre
Figure-1: Measurement of Attenuation in Optical Fibre
Procedure:
1.
Switch ON the LIGHT RUNNER kit.
2.
3.
Connect 1550 laser source to the photodetector PD1 with the help of a patch
23
cord.
4.
Connect BNC connector adjacent to PD1 to any channel (CH1) of the digital
storage oscilloscope (DSO).
5.
Enable the 1550 laser and set the following parameters:
a.
frequency = continuous, 5 KHz
b.
duty cycle = 50%
c.
laser power= 50%
6.
Click on the START button, waveform will appear CH1 on the DSO screen.
7.
In case of detector saturation, reduce the laser power level below the
saturation level by using software control. First, we make the arrangement as
show in the figure-1.
8.
NOTE: While operating LIGHT RUNNER, if the detector is fed with high optical
power it will be saturated and will not give correct readings and waveforms
(on DSO). For reliable results, users are expected to keep optical power fed to
detector below the saturation limit by adjusting source power through
variable optical attenuator. One also carried out the absolute optical power
measurement using optical power meter.
9.
Note down the power level at PD1 as P1.
10.
Click on the STOP button.
11.
Disconnect the patch chord from PD1 and connect it to a fibre spool of known
length (L).
12.
Connect the other end to PD1.
13.
Click on the START button.
14.
Note down the power level at PD1 as P2.
15.
Calculate the attenuation loss using the equation:
𝛂 = (-10/Z(Km))log(p(z)/p0)
16. Repeat the experiments with various length of fibre by combining the individual
spools.
24
16.
17.
Each time a patch cord is connected to a spool, an extra connector loss (𝛂C)
would appear. So, the actual attenuation loss in all the configurations can be
computed by subtracting CL from 𝛂.
Repeat the procedure 3-16 for the other wavelength 850 nm. Here, the patch
cord needs to be connected to the other photodetector PD2 which would be
connected to the other channel (say CH2) via a BNC connector.
Objective: To measure Dispersion in an Optical Fibre
Figure-2: Measurement of Dispersion in Optical Fibre
Procedure:
1. Switch ON the LIGHT RUNNER kit.
2.
3. Connect the 850 nm laser to the appropriate port of the 3dB coupler which delivers
more power as compare to the other port.
4. NOTE: Connect the 850 nm to the both the ports of the 3 dB coupler and connect the
‘COM’port of the coupler to the power meter by using a patch cord.
5. Connect 1550 nm laser to the other port of the 3 dB coupler by using a patch cord.
25
6. Connect the ‘COM’port of the coupler to the ‘COM’of the WDM (wavelength division
multiplexor) coupler by using a patch cord.
7. Connect 15XX and 980 port of the WDM coupler to the photodetector PD1 and PD2
respectively.
8. Connect BNC connectors adjacent to PD1 and PD2 to the CH1 and CH2 of the DSO.
9. Enable 1550 nm laser by using stylus and set the following parameters:
a. frequency= 50 KHz
b. duty cycle= 50%
c. laser power= 60%
10. Click on the START button, waveform will appear at CH1 on the DSO screen.
11. Enable 850 nm laser by using stylus and set the following parameters:
a. frequency= 50 KHz
b. duty cycle= 50%
c. laser power= 60%
12. Click on the START button, waveform will appear at CH2 on the DSO screen. Help
Dispersion in optical fiber Enter 130
13. In case of detector saturation, reduce the laser power level below the saturation
level by using software control.
14. NOTE: while operating LIGHT RUNNER, if the detector is fed with high optical power
it will be saturated and will not give correct readings and waveforms (on DSO). For
reliable results, users are expected to keep optical power fed to detector below the
saturation limit by adjusting source power through variable optical attenuator.
15. By keeping the power level of both the lasers fixed, enable both the laser and run the
experiment.
16. Measure the time delay between the rising edges of both the pulses at CH1 and CH2.
17. Now connect a fibre spool of known length between the ‘COM’ of the coupler and
‘WDM’ coupler using patch cord and measure the time delay.
18. Repeat the experiment with various fibre length.
26
19. NOTE: Since, laser output at 850 nm is collected from the 980 port of WDM coupler,
there will be finite loss as the coupler response depends upon the wavelength.
20. NOTE: Due to finite response time of both the detector PD1 and PD2, the waveform
may get distorted for the high frequency of the input laser. So, a moderate frequency
in the range of 5-10 KHz is desirable.
21. NOTE: The power level of the 850 nm laser must be maintained at a higher power
value than the 1550 nm laser, as the former suffers larger attenuation loss.
Objective: To determine the position of the fault in a fibre optic link using OTDR
method
Figure-3: OTDR Setup
Procedure:
1.
Switch ON the LIGHT RUNNER kit.
2.
3.
Connect 1550 nm laser source to the port 1 of the optical circulator with the
help of a patch cord.
4.
Connect the port 2 of the circulator with a patch cord and keep the other end
of the patch cord free. (Assume that patch cord is having a break at the free
end).
27
Connect the port 3 of the circulator to the photodetector PD1 with a patch
5.
cord.
Connect the BNC connector adjacent to the PD1 to CH2 of the DSO with a
6.
BNC cable.
Now set the pulse width at 1 s (i.e. corresponding to minimum fibre
7.
detection length of ~ 206 m as vg~ 2.06*108 m/s) with the help of stylus and
run the experiment by clicking START button.
Decrease the detection voltage of DSO CH2 to display the low power
8.
reflected signal on DSO.
Connect a BNC cable OTDR clock to CH1/TRG of the DSO for the input
9.
reference clock.
NOTE: Keep the toggle switch under INT MOD to DIGITAL/OTDR clock. Help
10.
Optical Time Domain Reflectometer Enter 133
Measure the time delay between the rising edge of the reference clock pulse
11.
at CH1 and rising edge of the reflected pulse.
12.
Repeat the experiment with fibre spool having different lengths.
13.
NOTE: When more than one spools are connected by patch cords, one can
observe multiple reflected pulse by keeping the patch cord end a bit loose.
Table-1: Attenuation Loss in Optical Fibre
λ
L
(nm)
(km)
𝐏𝟏
𝐏𝟐
(W)
(W)
Attenuation(A)
in
Number of
Connector
Connectors
Loss (𝐜)
A’=
A-n𝐜
Attenuation
loss () in
dB/km = A’/L
(n)
dB=10log(P1/P2)
28
850
1550
1
173
94
2.6492
2
0.374
1.9012
1.9012
3
173
51
5.3047
2
0.374
4.5567
1.5189
4
173
14
10.9192
3
0.374
9.7972
2.4493
1
88
47
2.724
2
0.374
1.976
1.976
3
88
45
2.9127
2
0.374
2.1647
0.721567
4
88
3
14.674
3
0.374
13.552
3.388
The average loss of the fiber is ~0.367 dB/Km
Table-2: Dispersion in Optical Fibre
Fibre Length (km)
Rise Time of
Rise Time of
Delay between
Reference Pulses
in
850nm Pulses (in
n sec)
positions of
(n sec)
Dispersion
(p sec/ km-nm)
reference and
850nm
pulses (n sec)
1
36
2140
2104
0.001464
29
32
3
9950
9918
0.04901
Observation:
Rise time when no-fibre (only patch chords) was connected in between source and PDs
For 1550 nm = ~36 ns
For 850 nm = ~356 ns
The average value is about = ~0.00323 ps/Km-nm
Graphs:
Fig 4: Rise time for pulse when no fiber was connected
30
Fig 5: Rise time for pulse when 1 km fiber was connected
31
Fig 6: Rise time for pulse when 3 km fiber was connected
32
Table-3: Observation data for OTDR
Fibre Length (Km)
Approximate Time Delay
Between Pulses, t ( s)
1
Fibre Length, L=𝐯𝐠(t/2) (Km)
10.78
1.11034
2
22
2.266
3
30
3.09
4
34
3.502
Graphs:
33
Fig 7: Photograph of the OTDR experiment for 3 km fiber length where the reflected pulse
delayed by ~30 s
Fig 8: Photograph of the OTDR experiment for 1 km fiber length where the reflected pulse
delayed by ~10.78 s
34
Calculations:
1.
OTDR:
Fibre Length, L = vg(t/2) (Km)
t = Time gap between pulses ( s)
v = speed of the pulse = 2.06*105 km/s,
.
L = 2.06*105 (10.78/2)*10-6 = 1.11034 km.
Errors:
1. OTDR:
Fibre length theoretical: 1 km
Experimental length: 1.11034 km
.
Relative Error = ((1.11034-1)/1)*100
= 11.034%
Discussion and Conclusion:
1. we estimated the position of fault in the optical link used with the help of delay time
between given Input pulse and Reflected pulse.in OTDR experiment.
2. we observe that attenuation loss depends on optical power input and frequency of laser
beam, and the length of the fibre used.
3. We also observe that Dispersion increased with length of optical fibre, and the rise time
of 850nm pulses are greater than 1550nm pulses.
4. We find attenuation loss and Dispersion loss in optical fibre using light runner basic and
spool kit.
35
Concluding Remarks:
From the experiment the different length of the fiber (corresponding to fiber break point) has been
experimentally realized. The connector must be properly tightened so that connector reflection peaks
can be avoided.
36