Prospects with the Crossed Cube Nuller
Prospects with the Crossed Cube Nuller François Hénault Institut de Planétologie et d’Astrophysique de Grenoble Université Grenoble-Alpes, Centre National de la Recherche Scientifique BP 53, 38041 Grenoble – France
Alain Spang Laboratoire Lagrange, Université Côte d’Azur Observatoire de la Côte d’Azur, CNRS, Parc Valrose, Bât. H. FIZEAU, 06108 Nice – France
Hi-5 Kickoff meeting
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Plan of presentation • • • • • • • •
General view of the Crossed-Cubes Nuller Design Cubes polarization model Use as a nulling combiner Preliminary manufacturing requirements Experiment and test results Discussion / Main advantages Integration into a Fully achromatic nulling interferometer (FANI) – Principle – Simulated fringe patterns – Potential SNR gain
• Conclusion Hi-5 Kickoff meeting
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
General view of the Crossed-Cubes Nuller (CCN) • •
Two “crossed” beamsplitter cubes generate four parallel beams, recombined axially. Only two of them are used to create a “null” at the focal plane centre It is independent of wavelength, chromatic flux unbalance and polarization orientation Input beam
Cube 1
Cube 2
Focusing optics Y Y’
Y-polarized
X
X-polarized
X’ Z O’
Cube 1
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Cube 2
Focusing optics
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Principle • Both cubes have their semi-reflective (SR) planes perpendicular one to the other • The input beams propagates parallel to both cubes SR layers • It is spitted into four parallel beams, being recombined axially • A null is created at the focal plane centre between the two diagonal, intensity symmetric outputs • It is independent wavelength, chromatic flux unbalance and polarization orientation • When used in reverse sense, this is actually an Achromatic phase shifter (APS) • “Cheapest nuller in the world: Crossed beamsplitter cubes,” Proceedings of the SPIE vol. 9146, n°914604 (2014) • “Experimental demonstration of a crossed cubes nuller for coronagraphy and interferometry,” Proceedings of the SPIE vol. 9907, n°99072H (2016) Hi-5 Kickoff meeting
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Cubes polarization model • Shown in coronagraph mode (interferometric mode is in reverse sense) • Only the two diagonal symmetric ports are usable for nulling
eiπ/2
eiπ AT AT
eiπ/2
eiπ/2
AT
Telescope
eiπ
Cube 2
Cube 1
eiπ/2 AR AT
eiπ/2
1
eiπ/2
AT AR
Focal plane side
AR AR AR
X-polarized
Y-polarized
AR AT
eiπ/2
π/2
eiπ/2 eiπ/2 eiπ/2 AT AR
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-π/2 -π/2
π/2
Modified Mach-Zehnder (MMZ) :
N = TC1 (λ )TC 2 (λ ) − RC1 (λ )RC 2 (λ )
CCN :
N = RC1 (λ )TC 2 (λ ) − TC1 (λ )RC 2 (λ )
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Use as a nulling combiner From collecting telescopes B
B
O
(P)
Telescope 1
Telescope 2
Relay optics 1
Crossedcubes nuller
Relay optics 2
Metrology beam 1
Metrology beam 2
Metrology beam 1
Crossedcubes nuller
Metrology beam 2
B’ Fringe tracker
(P’) O’
Other option
(P’) F’
F’
O”
Focal plane
Focal plane
Z
Z Hi-5 Kickoff meeting
O’
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Use as a nulling combiner – polarization model Cube 2
Cube 1
eiπ t2 eiπ/2
1
r
3
r2 3
1
eiπ/2
rt 3
eiπ t2
eiπ/2
3
eiπ/2
tr eiπ/2
eiπ/2
1
1
eiπ/2 iπ/2 t e
eiπ/2
rt
3
eiπ
t
tr eiπ/2
eiπ/2 eiπ
eiπ/2
1
1
r3
1
3
r2
Y
Y Y
2
1
X
3
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Output ports
Z X
Entrance telescopes
Liège, 03/10/17
1 X
3
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Prospects with the Crossed Cube Nuller
Use as a nulling combiner – polarization model Cube 2
Cube 1
eiπ/2
eiπ/2 eiπ/2
tr eiπ t2 2
2
t
4
rt eiπ/2
eiπ/2 eiπ
4
r2
eiπ
r2
t2 4
eiπ/2
eiπ/2
4
2
eiπ
r4
eiπ/2
2
4
r2 eiπ/2
tr
t
2
4
eiπ/2
2
rt
eiπ/2
eiπ/2
Y
2
1
X
3
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Y
Y
4
Output ports
Z X
Entrance telescopes
Liège, 03/10/17
2 X
4
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Prospects with the Crossed Cube Nuller
Preliminary manufacturing requirements • If OPDs are compensated for by optical delay lines, there remains one tight specification: Flux balance < 0.1 % PARAMETER Operating wavelength Spectral range Semi-reflective layer (SR) Transmission factor Reflection factor Flux mismatch Anti-reflective coating (AR) Geometrical parameters Cube hypotenuse Transmitted pathlength in glass Reflected pathlength in glass Pathlength difference in glass Angular errors Wavefront error
REQUIRED VALUE
REMARKS
λ = 10 µm 8-12 µm
Depending on science requirements Depending on science requirements
50 ± 0.1 % 50 ± 0.1 % < 0.1 % Standard
On full spectral band On full spectral band On full spectral band λ/4 AR coating
75.5 ± 0.1 mm 21.4 ± 0.1 mm 21.4 ± 0.1 mm < 0.005 µm < 3 arcmin < λ/4 PTV Total Null (RMS sum)
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EQUIVALENT NULLING RATE
1.0E-06
9.8E-06 7.6E-07 0.0E+00
Case of ZnSe material Case of ZnSe material Case of ZnSe material Only applicable to coronagraph For both SR/AR faces, including pyramid For both transmitted and reflected beams, on each sub-pupil
4.6E-06
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Experiment and test results • At Institut de Planétologie et d’Astrophysique de Grenoble (June 2016) Interference fringes
Two beams (ATAR–ARAT)
Focusing lens
Cube 2
Cube 2
Spectral power density
256 pixels of 5.2 µm
Cube 1
• At Laboratoire Lagrange (Observatoire de la Côte d’Azur): New tests in preparation
First fringes
N ≈ 1.8 10-3 Hi-5 Kickoff meeting
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Experiment and test results Two beams (ATAT–ARAR)
Four beams
Interference fringes
Two beams (ATAR–ARAT)
Spectral power density
256 pixels of 5.2 µm
Destructive and symmetric (balanced) N ≈ 1.8 10-3 Hi-5 Kickoff meeting
Constructive and not symmetric N ≈ 2.2 10-3 Liège, 03/10/17
Unlike Mach-Zehnder interferometer ! 11
Prospects with the Crossed Cube Nuller
Discussion / Main advantages • • • • •
Simple, compact, low mass and volume Reasonable manufacturing tolerances Potentially not expensive High throughput, close to maximum Good candidate for future space missions characterizing extra-solar planets atmospheres – Can also be implemented into a nulling coronagraph telescope
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Prospects with the Crossed Cube Nuller
The Crossed Cube Nuller could also be integrated into a
Fully achromatic nulling interferometer (FANI) for high SNR exoplanet characterization
Proceedings of the SPIE vol. 9605, n°960512 (2015)
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Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Classical interferometer Beam relaying optics
Telescope 1
L1
Multi-axial combining stage
L2
Beam collimatng optics
M1
F
X” L’1
L4
L5
L3
F’ M2
Entrance O baseline B B
Telescope 2
B’0
FD
FC Hi-5 Kickoff meeting
O”
O’
Multi-axial combining optics
FD
Z
Focal plane
Exit pupil plane Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Fully achromatic nulling interferometer Beam relaying optics
Telescope 1
L1
L2
Beam dispersing optics
M1
F
X” Grism lens
L3
L4
L5
F’ M2
B’0
Telescope 2
Entrance O baseline B B
Grism lens Hi-5 Kickoff meeting
FD
Grism mirrors FC
O”
O’
Multi-axial combining optics
FD
Z
Focal plane
Exit pupil plane Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Fully achromatic nulling interferometer Dispersed exit pupil
Entrance pupil
Y
O
Y’
O’
X
B’(λ0)
B Hi-5 Kickoff meeting
X’
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Simulated fringe patterns (Fizeau interferometer)
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4 telescopes
Spectral range 7-14 µm Entrance baseline B = 20 m Telescope diameter D=5m Compression factor m = 1/500 Dispersive material ZnSe Fizeau interferometer at λ = 10.5 µm
8 telescopes
Specifications
2 telescopes
Monochromatic PSF
π
Wideband PSF
Corrected PSF at centre
0
π
0 1”
π
0 0
π
π 0
0 π
π
0 Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Also covered in the original paper • • • •
Mathematical analysis Dimensioning the dispersive element Preliminary optical design Preliminary tolerancing (no critical alignment) Geometrical parameter Grism mirror translation along Z-axis Grism mirror decenter (along X’ and Y’ axes) Grism mirror tilt around X’-axis Grism mirror tilt around Y’-axis Grism mirror roll angle(around Z-axis) Grism thickness at centre Grism angle α
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Tolerance ≤ 0.1 mm ≤ 1 mm ≤ 5 degs. ≤ 1 deg. ≤ 5 degs. ≤ 0.1 mm ≤ 1 deg. 18
Prospects with the Crossed Cube Nuller
Potential SNR gain • • •
Planet detection possible on all bright fringes Higher Signal If used as a imaging stellar interferometer, SNR gain ≈ n for read noise But: – No quantitative study has been done so far – May not be useful for all types of spectrographs (IFS ?) Low dispersion spectrograph
Slit or multi-object spectrograph
Single mode fiber
T(u,v)
Detector array
Star
Single mode fibers
Detector array
Planet
u Broadband interferogram Hi-5 Kickoff meeting
FANI interferogram Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Where should we put the CCN ? Beam relaying optics
Telescope 1
L1
L2
Beam dispersing optics
M1
F
X” Grism lens
L3
L4
L5
F ’ M2
O
O ”
O’
Telescope 2
B
Probably here
FD
Focal plane
Exit pupil plane
FC
Hi-5 Kickoff meeting
FD
Multi-axial combining optics
Z
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Conclusion • •
CCN could have been used to build “PERSEE interferometer in a nutshell” Quick and dirty experiment in coronagraph configuration shows extinction below 1/256 bits – Next step: Measurements with higher dynamic range (Lagrange) – Demonstration in interferometer configuration (reverse) remains to be done Star and Planet Simulator
Axial combination (modified Mach-Zehnder interferometer)
Entrance sub-pupils OPD and tip-tilt injection errors
Spatial filtering (mono-mode optical fibers)
Periscope achromatic π-phase-shifter Fringe sensor
Delay lines
Hi-5 Kickoff meeting
Tip-tilt sensor
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Conclusion • •
CCN could have been used to build “PERSEE interferometer in a nutshell” Quick and dirty experiment in coronagraph configuration shows extinction below 1/256 bits – Next step: Measurements with higher dynamic range (Lagrange) – Demonstration in interferometer configuration (reverse) remains to be done Star and Planet Simulator
Axial combination (modified Mach-Zehnder interferometer)
Entrance sub-pupils OPD and tip-tilt injection errors
Spatial filtering (mono-mode optical fibers)
Periscope achromatic π-phase-shifter Fringe sensor
Delay lines
Hi-5 Kickoff meeting
Tip-tilt sensor
Liège, 03/10/17
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Prospects with the Crossed Cube Nuller
Questions ?
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