19 February 2009 Cophasing sensor for synthetic aperture optics applications First steps of the...
Transcript of 19 February 2009 Cophasing sensor for synthetic aperture optics applications First steps of the...
19 February 2009 Cophasing sensor for synthetic aperture optics applications
First steps of the development First steps of the development of a cophasing sensor for of a cophasing sensor for synthetic aperture optics synthetic aperture optics
applicationsapplications
Géraldine GUERRIGéraldine GUERRI
Post-Doc ARC @ CSL
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Framework : Extremely Large Telescopes (ELT)
• Ground-Based Large telescopes projects :
• Space telescopes projects :– JWST : 18 segments 6.5m aperture, 25 kg/m² density– Increasing demand for larger apertures : 20m
diameter, 6 kg/m² density
E-ELT(Europe)
GMT(USA)
TMT(Europe)
42 m diameter1000 segments
25 m diameter7 segments
30 m diameter492 segments
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Large lightweight telescope in
space • Technological need :
space mirrors
large diameter deployable lightweight cheap
• My work and CSL concern : development a demonstrator breadboard of a cophasing sensor for space segmented mirrors made with 3 or 7 segments
• Critical questions :
• How manufacturing this kind of mirror ?
• How controling the mirror wavefront error ?
• How aligning coherently the sub-apertures between each other?
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Cophasing sensor
• Measurement the relative positioning of each subaperture : determination of piston and tip-tilt errors
Piston : Translation along the optical axis (λ or nm)
Tip/ Tilt : Rotation of the sub-pupil perpendicular to the optical axis (rad or arsec)
• 2 phasing regimes to consider :
– Coarse phasing in open loop – Fine phasing in closed loop : error < λ/2
Increase sensor complexity
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Sensor requirements
• Cophasing of 3 to 7 sub-apertures• Separate measurement of piston and tip/tilt• Low weight and Compacity• Real-time correction • Reduced hardware complexity• Linearity, High range and accuracy
• At longer term use of integrated optical components
Piston measurement
Range: ± 1 mm
Accuracy: 50 nm
Tip/tilt measurement
Range: 100 µrad
Accuracy: 0.5 µrad
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Work plan
Survey of state of the art of cophasing sensor
Sensor techniques selection
Validation by numerical simulations
Experimental validation
Study and Design of a space-compatible breadboard
Feasibility demonstrator of the cophasing of 3 sub-apertures with standard optical
components
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Review of the state of art of cophasing sensor
Pupil plane detection sensor
Slope measurement :
Shack-Hartmann sensor,
Pyramidal sensor
Curvature sensor
Focal plane detection sensor
Dispersed fringe sensor,
Phase shifting interferometer
Phase retrieval/Phase diversity algorithm
• Trade-off criteria :Trade-off criteria :
• best compliance with the requirements
• sensor maturity
• breadboard feasibility within a short term
• Survey of 15 different principles :Survey of 15 different principles :
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Cophasing sensor : methods selection
PISTON TIP-TILT
Coarse phasingDispersed fringe sensing (CSL : Roose et al, 2006)
Shack-Hartmann Sensor(Shack & Platt, 1971)
Fine cophasing
Error < λ/2
Phase retrieval real-timealgorithm
(Baron et al., 2008)
Shack-Hartmann Sensor
or
Phase diversity real-time algorithm
(Mocoeur et al., 2008)
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
• Phase errors extracted from one simple focal image• The problem to solve is highly non linear• Classical Phase retrieval algorithm are iterative and time
consuming (~ 60 FFT computations)
• (Baron et al., 2008) : For fine cophasing (Piston < λ/2),
analytical and real-time solutions exists (only one FFT computation)
• Based on Optical Transfert Function (OTF) Computation
Phase retrieval algorithm
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Numerical validation of the phase retrieval
algorithm for piston estimation
3 sub-aperture pupil
PSFOTF
Modulus OTF
Phase
Without Piston error
With Piston error
Differential Piston errors can be determined from the intensity of peaks of the phase of the OTF
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
-400 -300 -200 -100 0 100 200 300 400-300
-200
-100
0
100
200
300
Valeur de piston introduite (nm)
Val
eur d
e pi
ston
obt
enue
(nm
)
• Algorithm validation
Phase retrieval algorithm numerical validation
• Algorithm Computation time (MATLAB) : 0.4s
• Test of the sensor linearity
Valeurs des pistons introduits (nm)-----------------------------------------------p1 : -50p2 : 0p3 :100
Différence de piston calculées (nm)------------------------------------------------p1-p2 : -50
p1-p3 : -150
p2-p3 : -100
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Phase retrieval demonstrator set-up
Laser diode
λ=633nm
Focusing Lens
f=300mm
Pupil mask
CCD Camera
Beam expander
Pinhole
Collimating Lens
f=50mm
Implementation in laboratory in progress ….
Window of known thickness
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Future prospects
• Experimental feasibility tests of the PR method
• Optimisation of the PR algorithm• Study and design of a system to introduce
various and precise piston values• Implementation of the coarse piston
sensor• Design and implementation of the tip-tiltmeasurement
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Outlook
• Tests of the preliminary sensor performances in open & closed loop
• Study and design of a compact and space-compatible sensor with fibered and integrated optics
• Implementation, validation and performance assessment of this cophasing sensor
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Thanks for your attention
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Différence de piston calculées (nm)------------------------------------------------p1-p2 : -50
p1-p3 : -150
p2-p3 : -100
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Phase retrieval demonstrator breadboard
PHOTO
CCD Camera Atmel :
• 2048x2048 pixels
• 7.4 µm x 7.4 µm pixels
• 10 bits dynamics
Shack Hartmann Sensor :
• 101 x 101 MicroLens
• λ/10 resolution
Implementation in progress ….
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Camera + source
Microlenses
S/W
Shack-Hartman system
Piston Sensor
DSP controller
Tip tilt controller
Tip Tilt actuator
AMOS
CSL
ULB
Thales
ULB
CSL
ULB
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Measuring steps
• Piston measurement : – Phase retrieval (PR) setup– Large amplitude piston : central fringe
identification from visibility estimation – Small amplitude piston : accurate phase
measurement by PR
• Tip-tilt measurement :– Shack-Hartmann Wavefront Sensor
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Valeurs des pistons introduits (nm)-----------------------------------------------p1 : -50p2 : 0p3 :100
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Framework
• Today’ s astronomy needs extremely large telescope (High FOV, high resolution) with huge diameter >30m
• Technological solutions– Large segmented telecopes– Multiple aperture telescopes
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Project presentation
- How to build : large diameter deployable mirrors lightweight cheap– Collaboration between CSL, SCMERO Laboratory
(Brussels University), AMOS & Thales
– The goal of the project is to develop a demonstrator with 3 (7 design goal) segments λ/10 mirror
– One of the critical issues is the control of the WFE of the system
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Numerical simulations
• Validation of two algorithms :– Dispersed speckle piston sensor .. in progress
Problems with sensor linearity
– Real-time phase retrieval algorithms
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Deformable mirror
preliminary design
WP 1000
ULB
Deformable mirror
Breadboard detailled design
WP 2000CSL
Procurement and bread
board manufacturing
WP 3000AMOS
Review the state-of-the-art of cophasing methods and
selectionWP 1100
CSL
Review the state-of-the-art in
piezo actuator control methods
and selectionWP 1200
Thales
Detailled design of the
cophasing and WFS sub systems
WP 2100CSL
Detailled design of the piezo control sub systems
WP 2200Thales
ThalesManagement and Reporting
WP 0300Thales
Overal Project
Management and reporting
WP 0100CSL
ULB Management and Reporting
WP 0200ULB
Management, reporting and
support WP 0000
CSL
AMOS Management and Reporting
WP 0400AMOS
Wafer technology review and preliminary
conceptWP 1300
ULB
Preliminary opto
mechanical concept WP 1400
AMOS
Wafer detailled design
WP 2300ULB
Opto mechanical
detailled design
WP 2400AMOS
Manufacturing of the piezo control sub
systems WP 3200Thales
Manufacturing of Wafer
subsystem WP 3300ULB
Manufacturing of Opto
mechanical subsystemWP 3400AMOS
Manufacturing of the
cophasing and WFS sub systems
WP 3100CSL
Rigid mode control and
control strategies overviewWP 1500ULB
Rigid mode control and
control strategies
detailled designWP 2500ULB
Control algorithm
developmentWP 3500
ULB
AIV and testing
WP 4000CSL
Test Results and Synthesis
Report WP 4300ULB
Establish Guidelines WP 5100XXX
Functional and
performance testing
WP 4200CSL
Guidelines and
Recommendations for
Future WorkWP 5000 ULB
AIVWP 4100AMOS
Lightweight space deformable mirror : project work plan
Critical issue : the manufacturing of the sub-system dedicated to cophasing and the wavefront sensor of the mirror
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Cophasing sensor selection
Complexity is transferred from hardware to software
• Focal-Plane WFS are very appealing:– Single/multi- aperture, simple hardware– Real-time algorithms exists (Baron et al., 2008
Mocoeur et al., 2008)– Performance experimentaly demonstrated at ONERA
Piston measurement
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
• Shack-Hartmann Wavefront sensor available at CSL
• Analytical and real time Phase retrieval algorithm
Tip-Tilt measurement
Cophasing sensor selection
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Piston – Tip/Tilt definition
X
Y
Z
Piston : Change of poistion along the Z axis (λ or nm)
Tip : Rotation of the surface around the Y axis (rad or arsec)
Tilt : Rotation of the surface around the X axis (rad or arsec)
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Review of the state of art of cophasing sensor
Pupil plane detection sensors Focal plane detection sensors
Parameter/ Method
Shack-Hartmann Sensor Curvature Sensor Pyramid Sensor
Dispersed fringe sensing
Dual Wavelength instantaneous Phase-shifting interferometer for close-loop control
"Classical" phase retrieval
"Real-time" phase retrieval
"Classical" phase diversity
Piston measurement ? NO (except for E-ELT) NO (except for E-ELT) YES YES YES YES YES YES
Tip-tilt measurement ? YES YES YES NO YES YES
YES but with restrictions with combined piston YES
#DOF MULTI3DOF for each segment
3 DOF for each 61 segments : 183 >11 >11 High
Algorithm N/A N/A N/A
Keck narrowband Algorithm (Chanan et al., 2000) N/A
Gradient-based iterative method
Analytic Least-Square approach
Gradient-based iterative method
Data processing Slope integration Poisson's equation Slope integration FFT 2D FFT 2D FFT 2D
Speed
Fast : up to 950 Hz (depends on configuration) Slow : up to 5 Hz Fast : 400 Hz Low 4.44 Hz
Time to compute between 20 and 60 FFT 2D on the zone of interest
Time to compute 1 FFT 2D on the zone of interest
Time to compute 100N FFT 2D on the zone of interest for N diversity focal images
#Apertures High High High 12 High High TBC already ? 12 High
H/W sourceMonochromatic or Polychromatic
Monochromatic or Polychromatic Visible or NIR Polychromatic
2 superluminescent diodes at 834.6 nm & 859.6 nm High flux needed
White light source + 1 narrow band filter (λc = 650 nm, Δλ = 40 nm) High flux needed
H/W detector CCD
Avalanche photodiode (bulky & expensive) or CCD CCD 1024x1024 CCD 4 CCD
Standard CCD Flux of
105 e-/frame
Standard CCD ; Flux
of 105 e-/frameDefocus generator + Standard CCD
Optical complexity Medium Medium Medium Medium High Simple Simple
Simple if only 2 phase diversity images are needed
Range up to 1500λ|Piston| < λ/2 ; High for tilt
|Piston| < λ/2 ; High for tilt 1 µm to 16 µm
Piston: ± 7.2 µm ; Tip-tilt: ± 250 µrad
[-λ/2 ; λ/2] for piston and tilt
λ/2 < Piston < λ/2 ; |Tilt| < 0.3λ
[-λ/2 ; λ/2] for piston and tilt
Linearity Close to 1 TBD TBD 0.98 TBD0,99 for Piston ; 0.93 for Tilt
0,96 for piston ; 1,15 for Tilt 0.99 for piston and tilt
Measurement accuracy From λ/100 to λ/1000 less than 15 nm rms λ/30 rms 90 nm better than λ/13 rms TBD TBD TBD
Repeatability < λ/200 rms TBD TBD TBDPiston: 0.48 nm rms ; Tip-tilt: 74 nrad rms
Piston : 0.75 nm for
5.105 photoe- ; Tilt :
1.21 nm for 3.3 104
photoe-
Piston : 0.75 nm for
5.105 photoe- ; Tilt :
1.21 nm for 1.6 105
photoe-
Piston : 0.75 nm for
2.105 photoe- ; Tilt :
1.21 nm for 1.1 104
photoe-
Particularities
Cylindrincal microlenses on the E-ELT sensor to measure piston steps
Restricted to spherical shapes that allow operation without gigantic beam expander
Excellent for phase reconstruction but time consuming
Need for diluted noncentrosymmetric pupil ; Small phase aberrations assumption (<2π rad)
Excellent for phase reconstruction but time consuming
Type of achievable phasing : Cophasing (fine) or coherencing coarse Both Both Both Coarse Phasing Fine Phasing Both Fine Phasing BothType of telescopes that can be controlled All Segmented Segmented Segmented Segmented Multi-aperture ; SegmentedMulti-aperture
Multi- Aperture ; Segmented
Maturity
Well know and manufactured in mass ; The most used sensor
Preliminary laboratory results and upcoming on-sky tests on the VLT
Preliminary laboratory results and upcoming on-sky tests on the VLT & LBT
Testbed results ; On sky test on Keck
Preliminary laboratory results and upcoming on-sky tests on the VLT
Laboratory tests in progress
Laboratory tests in progress
Laboratory tests in progress
Instrument controlled by this method or envisaged to be
Keck, VLT/NACO, Gemini North and South, MMT, Palomar, Lick, E-ELT, Grantecan
Subaru, VLT/MACAO, Gemini South/NICI, Grantecan, E-ELT ? LBT, WHT ?, E-ELT ? JWST ; Keck E-ELT
JWST ; Point-source and extended scenes observations
Darwin, SOTTISE (Earth Observation)
JWST ; Earth observation
Main references Platt & Shack, 1971 Roddier, 1988 Ragazzoni, 1996
Shi et al., Applied Optics 2004
Fogale Nanotech: Wilhem et al., Applied Optics 2008
F. Baron Thesis, ONERA, 2005 ; Baron et al., JOSA 2008
F. Baron Thesis, ONERA 2005 ; Baron et al., JOSA 2008
F. Baron Thesis, ONERA, 2005 ; Delavacquerie et al., 2008
Sensor type
Trade-off criteria
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Plan
• Framework and project presentation• State of the art of the cophasing sensors• Sensor selection• Numerical simulations of the selected sensors• Sensor Feasibility demonstration breadboard• Future propects
19 February 2009Géraldine GUERRICophasing sensor for synthetic aperture optics applications
Cophasing sensor selection
Complexity is transferred from hardware to software
• Focal-Plane WFS are very appealing:– Single/multi- aperture, simple hardware– Real-time algorithms exists (Baron et al., 2008
Mocoeur et al., 2008)– Performance experimentaly demonstrated at ONERA
– Multiple aperture piston/tip/tilt/more (DWARF)– Multiple aperture piston with extended scenes
Piston measurement