1
FIBER OPTIC TEMPERATURE SENSOR
BASED ON IMAGE PROCESSING OF
INTERMODAL INTERFERENCE PATTERN
Prof. Patrice Megret, Prof.Marc Wuilpart, Ir Frédéric Musin
Starting point in Belgium : pipelines and
underground power cables
2
Pipeline blast
Wind farm power cable failures
Project architecture & milestones
3
Target

2010 :
Kick-off
2014 :
Proof of
concept
Local
prototyping
Patent
2016 :
Large scale
prototyping


Provide low-cost thermal
and vibration monitoring
solution for gas and electricity
power underground
distribution infrastructure
Range : 10 km
Alarming and if possible
monitoring and hot spot
localization
Schedule
4






Introduction
Interferometric intermodal technique
Numerical approach
Experimental approach
Extended scope
Conclusion
Low-cost approach
5

Fiber optic network
 New
and existing
fiber optic
telecommunication
network : G.652D
type
 Existing skills of
partners
Large
geographical
distribution
Vibration
and
temperature
Reuse of
existing
monitoring
network
Fiber
optic
Fiber Optic Distributed Temperature
Sensing (DTS) systems
6

Interferometric technique :



Cheap lasers and detectors
High sensitivity
Low-cost constraints :


High sensitivity sensor but low
sample rate (thermal domain)
Low coherence light source linked
to the range of detection


< 1 €/m
10 €/m
VCSEL for 100 m
DFB for several km
Interference concept (simplified)
7
One source
Two sources
Fiber optic Intermodal interference
principles
8



Fiber optic used at wavelength below cut-off : multimode
Responsible for modal noise
This pattern is sensitive to external constraints :



Temperature : thermal expansion and refractive index change
Mechanical : mode coupling, birefringence, torsion, …
Few mode pattern
[1] Spillman, W., Kline, B., Maurice, L., & Fuhr, P., “Statistical-mode
sensor for fiber optic vibration sensing uses” in Applied Optics, 28(15), pp.
3166–3176, 1989.
Schedule
9






Introduction
Interferometric intermodal technique
Numerical approach
Experimental approach
Extended scope
Conclusion
Modal equations
10
Temperature effect on propagation
11

Poynting vector
even and odd HE11 with same phase, TE01 an TM01 with a phase shift
of π/2, even and odd HE21 with a phase shift of π/2
[1]
Safaai-Jazi, A., & McKeeman, J. C., “Synthesis of intensity patterns in
few-Mode optical fibers” in Journal of Lightwave Technology, pp. 1047–
1052, 1991.

Temperature effect :

Propagation constant of
modes + mode coupling

Elongation
Interference pattern dynamics vs
temperature
12
Lobes power exchange
Lobes rotation
even and odd HE11 with same phase, TE01 an TM01 with a phase shift of π/2, even
and odd HE21 with a phase shift of π/2
[1]
Safaai-Jazi, A., & McKeeman, J. C., “Synthesis of intensity patterns in
few-Mode optical fibers” in Journal of Lightwave Technology, pp. 1047–
1052, 1991.
Image processing : need for one/two
spots interference pattern
13
Multiple modes :
Velocity field approach

Optical flow
 Horn
Schunck
Algorithm
Few mode :
Pattern recognition tracking

Block pattern matching
and tracking

Gravity center
tracking
Resulting pattern (gravity center tracking)
14
All modes and few modes : need for
spatial filtering to select modes
15
All modes (30)
Few modes (HE11, TE01 and TM01,
HE21, HE31, EH11, HE12)
Heating and cooling
16
Numerical approach : results (1)
17
Temperature(°C) or Calibrated total path length(pixels)
140
Calibrated total path length(pixels)
Temperature(°C)
120
100
80
60
40
20
0
0
5
10
15
Time(hours)
20
25
Numerical approach : results (2)
18
9
2500
Data
Equation :
y = 16.937*x + 33.699
8
2000
Total path length (pixels)
Path length(pixels)
7
6
5
4
3
2
1500
1000
500
1
0
0
0
2
4
6
8
10
12
Time (hours)
14
16
18
20
0
20
40
60
80
Temperature (°C)
100
120
140
Conclusion (part 1)
19
Linear
dependency
between
temperature
deviation and
total path
length of the
gravity center
of the fewmode and fewlobe
interference
pattern

Low-cost technique : < 1 €/m



Detector : Commercial CMOS camera sensor
(downto -60 dBm sensitivity threshold level)
Laser : VCSEL for 100 m, DFB for 10 km
Reuse of G.652 @ 850 nm :


Spatial filtering for mode selection and few spots
interference pattern
Image processing :

Pattern recognition / Gravity center
Schedule
20






Introduction
Interferometric intermodal technique
Numerical approach
Experimental approach
Extended scope
Conclusion
Experimental approach
21

Lab :
 water

On-site 1 :
7

tank
km underground cable between Leuze and Ligne
On-site 2 :
 Electrical
junctions
Experimental setup (1) : lab
22



VCSEL source @
850nm
200 m FUT
FUT from 12°C
upto 20 °C
Image processing : vectorization
23

Step 1 :

Neighborhood points selection :


45
Prevent from speckle
hopping/Vibration filtering
Step 2 :


41
39
37
Successive points processing :

43
Scan every following points
Compute distance to successive
segment


If close enough : don't take care
of the point
If far enough : insert point into
final traject
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33
31
29
27
25
60
65
70
75
80
85
HotnCool module
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Impact on interference pattern




Oscillation superimposed
Acceleration of the gravity center
when FUT & HnC both heating or
cooling
Deceleration when FUT heating and
HnC cooling
Deceleration when FUT cooling and
HnC heating
Enable heating/cooling discrimination
36
FUT & HnC
Heating
34
Total path length (pixels)

Heating/Cooling section
32
30
28
FUT heating & HnC
Cooling
26
24
0
50
100
150
200
Time (s)
250
300
350
400
Setup ORES 2012-2013
25

G.652 24 fibers cable laid between Leuze
and Ligne substations

850 nm and 1MHz laser source

Spatial mode filtering via connectors spacing
Functional blocks
26
Setup
27
Currents
28

10 days
I1, I2, I3 qh measurements
Currents (A)

Time (days)
Heating results
29

Heat index is computed :
 Sum
of the square of the current variation for all the
cables :
Failure scenario : soil drying
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
Soil drying :
Source : SOILVISION
Failure scenario
31

Soil drying :
Source : SOILVISION
Failure scenario : simulation
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
Simualted soil drying : 40 °C in 10 days over 250 m

Detected after 2 days
Experimental setup (3)
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


Electrical joints
95² cable @ (20V/0->600A)
5 m of G.652D wrapped around the joint
Thermal Study
34

IR camera:

For a defaulting junction: DJ
@ 200 [A]
@ 400 [A]
Optical Study
35

Functional block
Figure inspired by [2]
[2] Frédéric Musin, Fiber optic therm
sensor for linear
Infrastructures, 2013
Electrical joint study during 12 hours
36

Linearity
400 A
300 A
200 A
100 A
0A
Conclusion (part 2)
37


Good agreement between theory and practice
Sensitivity :


Linearity :




Harnessed on several days
Need for algorithm upgrade for months and years
Vibration filtering qualitative
Power black-out : need for recalibration


Confirmed in a specified image sampling rate range
Drift :


Between 2 and 3 pixel/K.m for G.652 and a 200*200 projection area of the speckle
UPS but very small consumption (10 mA)
Distance range :

Tested over 7 km return : 14 km
Schedule
38






Introduction
Interferometric intermodal technique
Numerical approach
Experimental approach
Extended scope
Conclusion
Pipeline monitoring
39
Source : OMNISENS
Scope extension to fire safety and leak
detection
40



Fire safety for ducts,
pipes and cables
Fire safety for
transformers and
electrical cabinet
Overheating
protection for IT
servers
Conclusions (part 2)
41
Target

2010 :
Kick-off
2014 :
Proof of
concept
Local
prototyping
Patent
2016 :
Large scale
prototyping


Provide low-cost thermal
and vibration monitoring
solution for gas and
electricity power
underground distribution
infrastructure in Belgium
as a start point
Range : 10 km
Localization !!!