OFDR for Single- and Multi-Mode Avionics Fiber Optics

OFDR for Single- and Multi-Mode
Avionics Fiber Optics Applications
Optopyrotechnics Workshop
Ian Shannan, Luna Technologies
17/11/2008
1
About Luna
• Luna Innovations commercializes
technology in advanced materials,
sensing, and instrumentation
• Founded 1992 with six VA
locations
• Luna Technologies, a division of
Luna Innovations
– Focused on measurement
instrumentation for fiber-optic
components and subsystems
• World headquarters in
Roanoke, VA
• World-wide sales offices and
representation
2
X-33 Launch Vehicle—circa 1996
“I want 10,000
strain sensors on
this vehicle.
…
The weight
budget is zero.”
3
600 Conventional gauges
4
Overview
• Overview of distributed reflectometry
methods for avionics
• Introduction to High Sensitivity Optical
Frequency Domain Reflectometry: OBR
• Measuring IL, RL and inspecting for
breaks in avionics circuits
• Application specific examples
• Distributed temperature and strain
mapping using OBR
• Conclusions
5
Reflectometry Techniques
Avionics applications:
- 200 m measurement window
- High sensitivity (backscatter-level)
- Large dynamic range (70 dB)
- High resolution a must (1 mm)
Length
10000m
OT
DR
1000m
C-OFDR/OBR
100m
10m
I-OFDR/OLCR
100 m
10-1 m
10-2 m
10-3 m
10-4 m
10-5 m
Resolution
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Rayleigh backscatter
Imperfections in fiber lead to Rayleigh backscatter
dx
Rayleigh scatter reflectivity ~ -70 dB/m
At 20 μm resolution, this becomes -120 dB
7
OBR vs. Conventional
Reflectometry
bad splice
~ 1.6 dB
fiber crack
8 cm
low bend-loss fiber
16 cm
8
OBR for Avionics Applications
• IL/RL verification – ensure network uptime
• High-resolution fault location
– Bend, break, bad splice, bad connector
• Failure mode analysis
– Fiber, connector, splice, Tx/Rx
• Fiber and component management
– Incoming inspection, manufacturing verification,
physical layer aging
• Distributed sensing
– Network integrity inspection, critical system health
monitoring, airframe health monitoring, 3-D wire
system positioning
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OBR Operational Principle
DUT/FUT
Tunable Laser
Source
combiner
splitter
Polarization
Diverse
Receiver
Fixed Path
High Speed
A/D
•Laser is continuously tunable (swept)
•Optical network is extremely simple (fiber, couplers)
•Receivers are off-the-shelf PIN PDs and TIAs
•Very sophisticated:
¾Laser phase-noise correction
¾Receiver/amplifier calibration (amplitude and phase)
¾Digital architecture
FPGA/DSP
Computer
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Optical Network for Rayleigh Scatter Measurement
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Polarization Diversity Detection
s-detector
r
Emeas
r
Eref
U s (t )
pol. cont.
r
r
Emeas + Eref = ( Es , E p )
U p (t )
p-detector
Interferometer fringes are measured and
recorded at the two data acquisition detectors,
“s” and “p”
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20 dB
125 dB
Example - Fiber and Connectors
FO Connectors
200 meters
13
Measure Return Loss
yellow readout
shows RL for
yellow section
ST adapter
MM FUT
OBR
P
J
launch
14
Measure Insertion Loss
This ‘drop’ is a loss event
Red = initial measurement
Blue = measurement at later time showing loss
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OBR – Loss Measurement
connector
bend
4 cm
16
PBS
APC
Bulkhead
FBG
APC
Bulkhead
detector
4m
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APC
ball lens
detector
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OBR Example Measurement
connectors
coiled sections
splice
Optical Backscatter Reflectometry gives the user
unprecedented visibility into optical components,
assemblies and short-haul networks
19
OBR – High Resolution
1 mm
Discriminate between
faults here…
…and here
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Event Signatures – Bend
21
Event Signatures – Bend
8 mm
Close-up on the first lossy bend
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Automated Analysis
connector
receivers
Define a mask
splitter
Automatic Pass/Fail
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Transceiver Mating Problems
1.5 mm
OBR can tell if a cable is securely installed
• Output power measurements CAN NOTdo this
• Getting cables attached correctly in LRUs can be difficult
• The Return Loss of a closed LC connection is - 27.056 dB
• The Return Loss of an open LC connection is - 22.352 dB
www.cotsworks.com
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Temperature Mapping
Distributed temperature in singlemode fiber run through hot and cold locations
40
30
ice water
spectral shift (GHz)
20
10
0
-10
-20
-30
45 C
-40
48 C
-50
52 C
51 C
54 C
-60
35.0
35.2
35.4
35.6
35.8
distance (m)
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Locate by Temperature
Distributed temperature
can be used as a
position locator in most
standard fiber types
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Strain Mapping
-6
Strain (x10 )
0
•62.5 μm core multimode fiber
•Four lead multimode cable
•79 mm radius mandrel
-500
-1000
-1500
-2000
5
6
7
Position (m)
8
9
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3D Wire Position Sensing
Real-time feedback of the dynamic
shape and position of structures
Š High-spatial resolution at
1 cm
Š Embedded or surface
attached
Š Independent of the
temperature or load
Š Sub-millimeter accuracy
Š Minimally intrusive
• Shape_46s.wmv
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Summary
• Reflectometry is a vital T&M element for all
99.999% uptime networks
• Key time-domain measurement metrics for
avionics applications
– Measurement Range
– Spatial Resolution
– Dynamic Range / Sensitivity
• High resolution in short-run networks is a must
• Temperature and Strain mapping a key value
added benefit of OBR
• Current platform: indoor environments
• Next generations: miniaturized and mobile
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Multi-Mode Loss
Offset cores
Bubble
Tapered Waist
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Multi-Mode Loss
Event
Insertion Loss (dB)
MM
meter
OFDR with mode
converter
1300 nm
1300 nm 1550 nm
A offset splice
0.36
0.42
0.34
B offset splice with
bubble
1.84
1.76
1.55
C offset splice
0.60
0.50
0.49
D offset splice
1.42
1.23
1.16
E bubble near
1.03
0.84
0.80
F tapered waist
0.62
0.48
0.39
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Thankyou
Any Questions?
Contact: [email protected]
+44 131 666 9044
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