Post on 20-Jan-2016
transcript
Optical power variation only
Amplitude to phase conversion issue in telemetry
CONTEXT/OBJECTIVES: This work was realized within JRPs « SURVEYING »(SIB-60) and « LUMINAR » (IND-53). In both projects a compensation of air temperature and pressure variation is targeted using two different wavelengths (1550 nm and 780 nm) and air index dispersion. A first step is the realization of a robust and simple one wavelength telemeter at 1550 nm, with a resolution below 5 µm indoor. It turns out that the amplitude to phase conversion in photodetectors and electronic stage is a critical issue that has to be considered
PRINCIPLE OF THE TELEMETERINDOOR MEASUREMENTS
OUTDOOR MEASUREMENTS
0 100 200 300 400 500 600 700 800 900 1000
-27
-26.8
-26.6
-26.4
dis
tance (m
m)
0 100 200 300 400 500 600 700 800 900 1000-40
-30
-20
-10
0
am
plitude (dB
m)
measurement number
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-27
-26.8
-26.6
-26.4
dis
tance (m
m)
0 100 200 300 400 500 600 700 800 900 1000-40
-30
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-10
0
am
plitude (dB
m)
measurement number
in red = amplitudes equal to 7.9dB ± 2 dB
Std over 50 pointsbetween 11 & 24 µm
Standard deviation = 38 µm
Experimental setup at 1550nm
Optical switch: every second we compare the measured distance to a reference distance that do not vary during the measurement process. Thus, every variations observed on the reference path are interpreted as drifts from the system (for instance temperature evolution in amplifiers) and are so removed from the measured distance.
Joffray Guillory1, Jorge Garcia-Marquez1, Anne-Françoise Obaton1, Christophe Alexandre2, Daniel Truong1 and Jean-Pierre Wallerand1*.1 Laboratoire Commun de Métrologie LNE-CNAM (LCM), 1 rue Gaston Boissier, 75015 PARIS
2Centre d’études et de recherche en informatique et communications (CEDRIC), CNAM, 292 rue Saint-Martin, 75003 PARIS
* Corresponding author: jean-pierre.wallerand@cnam.fr
AMPLITUDE TO PHASE CONVERSION
RF
LO
S
S
mixer
Ph
ase
mete
r
IFamplifier
reference
single chip
DFB EAM
PD
AOM
powermeter
95% 5%
EDFA
biastee
bias voltage
AM generation
measure
Optical and RF power variation
RF
LO
S
S
mixer
Ph
ase
me
ter
IFamplifier
DFB EAM
PD
powermeter
95% 5%
EDFA
biastee
bias voltage
AOMDFB
50% 50%
laser 1
laser 2
AM generation
reference
measure
Metal semi conductor metal photdetector (Hamamatsu G7096-03)
InGaAs avalanche photodiode (Hamamatsu G8931-04)
Amplitude to phase variation conversion due to photodetector and electronic stage
Metal semi conductor metal photodetector InGaAs avalanche photodiode
sunny day, 35°C, along an asphalt road.
A selection of data within an amplitude interval of 4 dB greatly improves the robustness of the system.
Avalanche photodetector is less sensitive to amplitude to phase conversion. In that case the global amplitude to phase conversion is essentially due to electronic stage (mixer+amplifiers)
6 7 8 9 10 11 12 13 14 15-1000
-800
-600
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-200
0
200
400
Photodiode bias voltage (V)
d
ista
nce
/
opt
ical
pow
er (
µm
/dB
)
18.5 µW45.1 µW
93.3 µW
143.1 µW
196.1 µW251.2 µW
25 30 35 40-100
-50
0
50
100
150
200
250
300
350
400
450
Photodiode bias voltage (V)
d
ista
nce
/
opt
ical
pow
er (
µm
/dB
)
11.7 µW
28.9 µW
61.2 µW
6 7 8 9 10 11 12 13 14 15-1000
-500
0
500
Photodiode bias voltage (V)
d
ista
nce
/
opt
ical
pow
er (
µm
/dB
)
245.9 µW
25 30 35 40-50
0
50
100
150
200
250
Photodiode bias voltage (V)
d
ista
nce
/
opt
ical
pow
er (
µm
/dB
)
60.5 µW
CONCLUSION/PERSPECTIVES: A robust and compact telemeter was realized at 1550 nm using off-the-shelf components from telecommunication industry. A resolution of 3 µm was obtained indoor using a modulation frequency of 1,3 GHz. Amplitude to phase conversion was minimized by a selection of measurement data comprised in a given amplitude interval. A measurement of up to 600 m outdoor was realized (limited by available distance). Next steps will be to increase the modulation frequency and to add a second wavelength (773 nm) to the system in order to compensate air index fluctuation due to pressure and temperature variation.
lens
RF
LOS
S
mixer
Ph
ase
mete
r
10MHz.amplifier
Reference path
singlechip EAMDFB
PDbiastee
Biasvoltage
Att.
RF = radio frequency synthesizerLO = local oscillatorS = RF splitterDFB = distributed feedback laser diodeEAM = electro-absorption modulatorEDFA = erbium doped fiber amplifierSMF = single mode fiberAtt. = variable optical attenuatorPD = free-space photodiode
optical splitter(used as a circulator)
off-axisparabolic
mirror
distance D
Target
fiber connector(FC/APC)
cornercube
Measure path
optical switch
Φ
sine wave that hasbeen propagated
in free-space
electricalsine wave
10MHz
1310MHz
1300MHz
mirror
EDFA
SMFisolator
RFfn
ckD
2
2
ΦCnfRFk
the measured phase shiftthe speed of light in vacuumthe group refractive indexthe frequency modulation (1310MHz)an integer number of 2π modulowithin the distance to be measured.
RFfMeasurement during 90 mn over 2 m indoor. The modulation frequency was 1,3 GHz. The resolution (short term standard deviation) was approximately 3µm. Residual variations are due to uncompensated drifts in the optoelectronic system.
In black: electronic signals. In orange: fibered system. In red: free space light.
Over 400 m under favourable conditions:
Over 100 m under unfavourable conditions:
Selection of data
JRP IND 53
This project is performed within the joint research projects SIB60 “Surveying” and IND53 “Luminar” of the European Metrology Research Programme (EMRP). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.