M.Lintz, ICSO 2008 2 mode laser telemetry 1 "T2M": two-mode telemetry for high accuracy absolute...
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Transcript of M.Lintz, ICSO 2008 2 mode laser telemetry 1 "T2M": two-mode telemetry for high accuracy absolute...
M.Lintz, ICSO 20082 mode laser telemetry
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"T2M": two-mode telemetry for high accuracy absolute distance measurement
M. Lintz, C. Courde, A. Brillet, C. N. Man
ARTEMIS, Observatoire de la Côte d'Azur
06300 NICE
Funded by CNES
PhD grant: Thales Alenia space and Région Provence-Alpes- Côte d'Azur
Towards nanometric accuracy without interferometry
M.Lintz, ICSO 20082 mode laser telemetry
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formation flights:
need for high accuracy distance measurementsover hundreds of meters
1µm as a first step
...device small enough to get onboard a SC
M.Lintz, ICSO 20082 mode laser telemetry
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- tune the frequency to get zero phase and measure F
- then Lmeas-Lref = K = K c/F (K integer)
- tune to next zero
Lmeas-Lref = (K+1) c/F' K= F / (F'-F)
HIGH ACCURACY
The modulated laser beam technique:
THE BASIC PRINCIPLE
!!drifts
=c/F
high frequency F
phase difference
LmeasLref
...is not the best one!
(with cyclic errors)
M.Lintz, ICSO 20082 mode laser telemetry
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Polarisation controller
polarisation analysis
PBS (x,y)
phase signal
synth=c/F
F ~13,01GHz
45°
13GHz
phasemeter
(meas)
(ref)
polarisationswitching
~ kHz
measrefmeas
ref
unchanged when polarisation switching high accuracy phase zero
tuned
(ref)- (meas) +offset
(meas)- (ref) +offset
improvedversion
M.Lintz, ICSO 20082 mode laser telemetry
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telemeter
signal
T2M (Two-mode telemeter) set-up
Phase lock
RF 10MHz
slave laser +F,F=13GHz+10MHz
master
laser
pol. contr.
pol. analysis
LIlock
2 kHz
AD
9901
lock
10MHz
ref
meas
red: laser beams
green: optical fibres
black: HF (13GHz)
blue: RF (10MHz)
purple: DC-100kHz
~13GHz VCO
13,01GHz
lock
freq.meas
telemeter
PBS (x,y)
M.Lintz, ICSO 20082 mode laser telemetry
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The XOR phase-metre
In 1 In 2
OUTOUT
phase-to-amplitude coupling
2 10-3 for a 20% imbalance. in1/in2
- no polarisation switch
- Lmeas scanned over 25mm
25
mm
vs LVM
phase signal
M.Lintz, ICSO 20082 mode laser telemetry
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20µm
1mn
Signal zeroes: the good ones, the bad ones...
BAD!
GOOD! noise subtraction!- "integer zero": LM -LR= Kc/F
- "1/2-integer zero": LM -LR=(K+1/2)c/F
1/2integer zero integer zero
M.Lintz, ICSO 20082 mode laser telemetry
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noise / systematics ?
Polarisation change in the corner cubes?
PBS Extinction defect?
HF/RF crosstalk?
Photodiode response?
Optical return from photodiodes?
Amplitude to phase coupling?
Defect of the polarisation switch?
Lock en phase
RF 10MHz
fixed frequency
laser
slave laser +F,F=13GHz+10MHz
pol. control
pol. analysis
DS
lock
qq kHz
AD
9901
lock
10MHz
ref
meas.
VCO 13GHz
13,01GHz
NO
NO
NO
YES
YES, 1µm
NO, not on "good" zeroes
PBScube
YES ~5µm
M.Lintz, ICSO 20082 mode laser telemetry
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The polarisation routing defect
- defect: 1% in intensity
- 10% in AMPLITUDE
the "noise" is due to the change of the
interference order (Lmeas-Lref)/opt with time
admixture (interference):
meas + ref, ref - meas
and reverses with the polarisation switch!
and amplitude-to-phase coupling
RMS amplitude of the 10 MHz signal
of Phd 1
Telemeter signal
pol. control
pol. analysis
M.Lintz, ICSO 20082 mode laser telemetry
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(corrected) telemeter signal: long term stability
"ref"
VM"meas"
"zero distance" stability test
RMS
Telemeter (raw)
Telemeter (corrected)
M.Lintz, ICSO 20082 mode laser telemetry
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Telemeter data: coherency(8m path)
2) Kc/F should be equal to (K+1)c/F' ...=(K+N)c/F(N) etc...
1) K F/(F'-F) has to be an integer
écart à l'entier K-F/(F'-F) ML 24/04/08
-1
-0,8
-0,6
-0,4
-0,2
0
0,2
0,4
0,6
0,8
1
0 1 2 3 4 5 6 7 8 9 10 11
indice = K-348
K-F/(F'-F)
distance to the next integer
L(mm) avec barres d'erreur statistique
7654,835
7654,840
7654,845
7654,850
7654,855
7654,860
7654,865
7654,870
0 5 10 15 20 25
série temporelle
L(mm)
L+barre
L-barre
5µm L(mm) with stat. error bars
time series
L(mm), avec barre d'erreur statistique(sélection des bonnes mesures)
ML 24/04/08
7654,844
7654,846
7654,848
7654,850
7654,852
7654,854
7654,856
0 2 4 6 8 10
série temporelle
L(mm)
L+barre
L-barre351
353
353
351
350
349
349 351
352
2µm
L(mm), selected data with low stat dispersion
time series
M.Lintz, ICSO 20082 mode laser telemetry
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Telemeter data: stability (8m path)
Long term (in)stability in the 10µm range probably thermal expansion of the opt. breadboard
To be checked in the future with separatetelemeter (heretodyne interferometry)
what about "nanometric" ??
10µm
"sub-micron"
M.Lintz, ICSO 20082 mode laser telemetry
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T2M: how to get "nanometric" ? Signal amplitude problem:
- improve polarisation controller (large drifts in the piezo squeezers)
- reduce the residual amplitude effect (intensity control loop)
- improve the phase-meter
Optical return from the photodiodes:
- switch to FC/APC, with -35dB return (instead of FC/PC, with -15dB return)
- insert optical isolators
- good AR coating for the collimator
Goal: 10nm accuracy
- without interferometry!- simple setup!
Closed loop noise on the telemeter signal (µm)
1,E-05
1,E-04
1,E-03
1,E-02
1,E-01
1,E+00
0,01 0,1 1 10 100
Offset freq (Hz)
closed loop noise on the telemeter signal (µm/Hz)
1nm/Hz
M.Lintz, ICSO 20082 mode laser telemetry
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