m.lintz, icso 2008 2 mode laser telemetry 1 "t2m": two-mode telemetry for high accuracy...

M.Lintz, ICSO 20082 mode laser telemetry

1

"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


2

formation flights:

need for high accuracy distance measurementsover hundreds of meters

1µm as a first step

...device small enough to get onboard a SC


3

- 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)


4

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


5

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)


6

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


7

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


8

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


9

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


10

(corrected) telemeter signal: long term stability

"ref"

VM"meas"

"zero distance" stability test

RMS

Telemeter (raw)

Telemeter (corrected)


11

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


12

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"


13

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


14

m.lintz, icso 2008 2 mode laser telemetry 1 "t2m": two-mode telemetry for high accuracy...

Documents