Transcript Amplitude to phase conversion issue in telemetry

JRP IND 53
Amplitude to phase conversion issue in telemetry
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: [email protected]
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 TELEMETER
INDOOR MEASUREMENTS
Experimental setup at 1550nm
Bias
sine wave that has voltage
been propagated
in free-space
bias
Phasemeter
10MHz.
amplifier
PD
tee
lens
mixer
Φ
S
RF
LO
S
DFB
EAM
EDFA
SMF
Att.
PD
= radio frequency synthesizer
= local oscillator
= RF splitter
= distributed feedback laser diode
= electro-absorption modulator
= erbium doped fiber amplifier
= single mode fiber
= variable optical attenuator
= free-space photodiode
LO
1300MHz
10MHz
optical switch
electrical
sine wave
1310MHz
RF
f RF
Reference path
S
DFB
distance D
Att.
isolator
single
chip
Target
corner
cube
off-axis
parabolic
mirror
SMF
EAM
Φ
C
n
fRF
k
the measured phase shift
the speed of light in vacuum
the group refractive index
the frequency modulation (1310MHz)
an integer number of 2π modulo
within the distance to be measured.
Measurement 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.
mirror
optical splitter
(used as a circulator)
EDFA
 
 c
2 D  
k
 2
 n  f RF
fiber connector
Measure path
(FC/APC)
In black: electronic signals. In orange: fibered system. In red: free space light.
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.
OUTDOOR MEASUREMENTS
Over 400 m under favourable conditions:
AMPLITUDE TO PHASE CONVERSION
Optical and RF power variation
Amplitude to phase variation conversion due to photodetector and electronic stage
450
-400
-800
-1000
6
7
8
9
10
11
12
Photodiode bias voltage (V)
13
14
power
meter
LO
95%
5%
AOM
AM generation
reference
18.5 µW
45.1 µW
93.3 µW
143.1 µW
196.1 µW
251.2 µW
-600
PD
mixer
Phasemeter
-200
bias
tee
RF
EDFA
S
DFB
EAM
Selection of data
350
300
250
200
Over 100 m under unfavourable conditions:
150
100
sunny day, 35°C, along an asphalt road.
50
0
-50
single chip
-100
25
15
Metal semi conductor metal photdetector
(Hamamatsu G7096-03)
30
35
Photodiode bias voltage (V)
40
InGaAs avalanche photodiode (Hamamatsu G8931-04)
Optical power variation only
250
60.5 µW
500
bias voltage
measure
Phasemeter
0
bias
tee
power
meter
LO
reference
RF
-500
PD
mixer
S
 distance /  optical power (µm/dB)
IF
amplifier
200
95%
5%
50%
50%
S
laser 1
DFB
laser 2
EAM
DFB
EDFA
AOM
 distance /  optical power (µm/dB)
245.9 µW
6
7
8
9
10
11
12
Photodiode bias voltage (V)
13
14
Metal semi conductor metal photodetector
-26.8
-26.6
-27
-26.8
0
-27
00
100
100
Std over 50 points
between
24 µm 500
200
30011 &400
600
700
800
900
1000
Standard deviation = 38 µm
100
200
300
400
500
600
700
800
900
1000
50
0
15
-26.6
-26.4
150
AM generation
-1000
A selection
of data within an amplitude interval of 4 dB greatly
-26.4
improves the robustness of the system.
-50
25
30
35
Photodiode bias voltage (V)
40
InGaAs avalanche photodiode
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)
amplitudeamplitude
(dBm) (dBm)
amplifier
0
S
 distance /  optical power (µm/dB)
measure
IF
 distance /  optical power (µm/dB)
bias voltage
200
11.7 µW
28.9 µW
61.2 µW
400
(mm)
distance distance
(mm)
400
-10
0
-20
-10
in red = amplitudes equal to 7.9dB ± 2 dB
-30
-20
-40
-300
-40
0
100
100
200
200
300
300
400
500
600
measurement number
400
500
600
measurement number
700
700
CONCLUSION/PERSPECTIVES:
800
800
900
900
1000
1000
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.
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.