Post on 13-Jan-2016
PL0471
KKrzysztofrzysztof M. Abramski M. Abramski
WDM WDM Fiber VibrometryFiber Vibrometry
PL0471
• IntroductionIntroduction
• The idea of multipoint fibre vibrometerThe idea of multipoint fibre vibrometer
• Heterodyne signalsHeterodyne signals
• DemodulatorsDemodulators
• Experiment and signal processingExperiment and signal processing
• ConclusionsConclusions
OutlineOutline
PL0471IntroductionIntroduction
PL0471Principles of operationPrinciples of operation
PL0471Principles of operationPrinciples of operation
PL0471
Homodyne Homodyne vvs. heterodyne detections. heterodyne detection
The low frequency noise spectrumThe low frequency noise spectrum Advantages of using heterodyne techniqueAdvantages of using heterodyne technique
PL0471FeaturesFeatures
Advantages:Advantages:
1.1. Visible radiation, aVisible radiation, an analyzedn analyzed point can be easy localized point can be easy localized
2.2. High resolution, it depends on a source wavelengthHigh resolution, it depends on a source wavelength
Disadvantages:Disadvantages:
1. Low output power, less than 1mW1. Low output power, less than 1mW
2. Multipoint measurement in the same time is impossible2. Multipoint measurement in the same time is impossible
PL0471Motivation for 1550 nmMotivation for 1550 nm
1.1. Relatively low prices of fibre elements, such like: optical Relatively low prices of fibre elements, such like: optical isolators, couplers, photodetectors, fibre Bragg gratings isolators, couplers, photodetectors, fibre Bragg gratings etc.etc.
2. Narrow linewidth laser diodes (DFB, DBR) are available2. Narrow linewidth laser diodes (DFB, DBR) are available
3. ”Eye safe” 1550 nm radiation3. ”Eye safe” 1550 nm radiation
4. Unique possibility of weak optical signals amplification by 4. Unique possibility of weak optical signals amplification by very useful device: Erbium Doped Fibre Amplifier (EDFA)very useful device: Erbium Doped Fibre Amplifier (EDFA)
5. WDM technique allows to make a multichannel vibrometer5. WDM technique allows to make a multichannel vibrometer
PL0471Idea of laser-fiber vibrometerIdea of laser-fiber vibrometer
PL0471
Multipoint vibrometerMultipoint vibrometer
PL0471
Experimental set-upExperimental set-up
PL0471
Fibre – free space out couplingFibre – free space out coupling
PL0471
EDFA - spectral gain characteristicEDFA - spectral gain characteristic
The best The best area for area for
multipoint multipoint vibrometervibrometer
The best The best wavelength wavelength for single for single
point point vibrometervibrometer
PL0471
WDM characteristicsWDM characteristics
PL0471
Optical spectraOptical spectra
PL0471
Detection of heterodyne signalsDetection of heterodyne signals
)(
)(
)cos()sin(
)sin()cos(
)(
)(
2
1
2
1
fE
fE
lli
lile
fE
fE
i
ili
o
o
Balanced photodetectorBalanced photodetector
PL0471
Demodulation of heterodyne signalsDemodulation of heterodyne signals
c
lV
f
c
f
lVc0
0001
1 1 – observed wavelength, – observed wavelength, 00 – source wavelength, c – light velocity, V – light source velocity, l – unit – source wavelength, c – light velocity, V – light source velocity, l – unit
vector in the direction of observation, fvector in the direction of observation, f00 – frequency of light source – frequency of light source
0101
ccfff
c
lVfcf 02
0
0lV
f
For 1550 nm we obtain carrier signal with frequency deviation:For 1550 nm we obtain carrier signal with frequency deviation:
sm
MHzlVD /
29,120
For For 632,8632,8 nm frequency deviation nm frequency deviation is is::
sm
MHzlVD /
16,320
PL0471ExperimentExperiment
drivingdrivingsignalsignal
vibration vibration at first at first pointpoint
vibration vibration at second at second
pointpoint
PL04714 - channel vibrometer4 - channel vibrometer
PL0471
ConclusionsConclusions
• WDM systems can be particularly useful for multichannel fibre vibrometry.WDM systems can be particularly useful for multichannel fibre vibrometry.
• We obtain heterodyne signals with SNR good enough for FM demodulation.We obtain heterodyne signals with SNR good enough for FM demodulation.
• Our experiment showed practical advantage of the system which can be Our experiment showed practical advantage of the system which can be adapted to many measurement application, particularly can be very flexible. adapted to many measurement application, particularly can be very flexible.
• The signal processing for speed – displacement – acceleration The signal processing for speed – displacement – acceleration measurement based on LabView environment is under development.measurement based on LabView environment is under development.
PL0471AcknowledgmentsAcknowledgments
This work has been carried out in the frame of This work has been carried out in the frame of „The EEA Financial Mechanism & Norwegian Financial „The EEA Financial Mechanism & Norwegian Financial
Mechanism” (PL0471) entitled: Mechanism” (PL0471) entitled:
„„Developing novel laser-fiber monitoring technologies to prevent Developing novel laser-fiber monitoring technologies to prevent environmental hazards from vibrating objectsenvironmental hazards from vibrating objects””
PL0471
Thank YouThank You