Transcript Zack - Center for Adaptive Optics

Characterization of a
Bimorph Deformable Mirror
in a Closed Loop Adaptive
Optics System for Vision
Science Purposes
Zachary Graham1
Sophie Laut2, David Horsley3, John Werner2
1
Hartnell Community College, Salinas, CA
of Ophthalmology and Psychophysics, UC Davis
3 Department of Mechanical and Aeronautical Engineering, UC Davis
2 Department
1
AO in vision science
 Removes aberrations in the eye
 Increases resolving power
 Allows for more thorough and advanced
study of the eye and brain (psychophysics)
2
My Project
 To help characterize a mirror for use in a
next generation Adaptive Optics imaging
system
 Helped with the setup of the system
 Wrote a program in MATLAB to generate
Zernike mode aberrations
 Took data on the mirror
3
Next Gen. AO System
 Will operate in 2 modes
 Scanning Laser Ophthalmoscope (SLO)
 Optical Coherence Tomography (OCT)
 2 Deformable Mirrors
 MEMS and Bimorph will be cascaded in one system
 Bimorph will replacethe role trial lenses
 Will remove more aberrations
 Computer automated
 Much more flexible
4
The Boston Micromachines MEMS mirror
Specification :
• Active area : 4 mm x 4 mm
• No of actuators : 100
• Continuous surface
• Stroke (wavefront) : +/- 2 m
• Response speed : ~3.5 kHz
• Operative voltage : 200 V
• Cost : ~ $25,000
Relatively small Stroke !
for high-order aberration correction
Slide Courtesy of Sophie Laut,
UC Davis Medical Center
5
The AOptix Bimorph deformable mirror
Specification :
• Active area : 12 mm, round
• No of actuators : 35
• Continuous surface
• Stroke (wavefront) : +/- 40 m
• Maximum deflection : +/- 20 m
• Response speed : ~4 kHz
• Operative voltage : 15-30 V
Actuator geometry
Usual applications : Optical telecommunication system
High Stroke !
for low-order aberration correction
Slide Courtesy of Sophie Laut,
UC Davis Medical Center
6
Imaging Setup
System Information
total g = 1.00
flatness = l/13
Hartmann – Shack
Wave front sensor
Laser
Diode
Telescope 2
g=1
Pupil
Plane
Telescope 1
g=1
Bimorph
DM 7
Characterization Process
Place aberration
into system
Control Loop closes and
mirror corrects wave front
Before/After data
analyzed
8
Characterization Process
Place aberration
into system
Control Loop closes and
mirror corrects wave front
Before/After data
analyzed
9
Aberrations
 Lower order aberrations
 were introduced using trial lenses.
 Cylinder and Sphere
 Higher ordered aberrations
 Trial lenses cannot be used
 Generated in MATLAB
10
Centroid Displacement Algorithm
 a1 
 
S
x
1
..
S
xn
,
S
y
1
..
S
yn

A



 
  ( x, y )  2  an 
ij  
xij

 x

lf
  ( x, y )  2
 

yij

y  l f

Matrix of partial
Solution
Vector
(Slope) ij 
derivatives for all used
zernike modes
•Starts with a file of reference
positions
•Reads the value of each
reference Centro id from a matrix
of partial derivatives for the
particular Fernike mode. and
calculates the slope in x and y
•The slope is direcly proportional
to the displacement
•The displacement is added to the
reference position and logged
Vector of
normalized zernike
coefficients
11
Preparing Simulated Aberrations
1.
2.
3.
4.
A specific Zernike mode is picked
Maximum detectable amplitude is determined
Aberrations are generated
Aberrations introduced to the system
12
Characterization Process
Place aberration
into system
Control Loop closes and
mirror corrects wave front
Before/After data
analyzed
13
AO in Action
14
Problems with trial lenses
The lenslet array could not resolve more
than 1.8 diopters of error (defocus)



If aberration too strong the WFS spots will be
displaced outside their sub-aperture
Occurs on physically introduced aberrations only
Limits testing to resolution of lenslet and not stroke of
mirror.
15
Dealing With Loss of WFS Spots
Some aberrations are so strong
that the computer cannot find
all of the WFS spots
Using MATLAB we can
correct for this by using an
extrapolation algorithm
16
Characterization Process
Place aberration
into system
Control Loop closes and
mirror corrects wave front
Before/After data
analyzed
17
Results
 The group are continuing to work on data
analysis algorithms and are implementing
them in MATLAB
 Will be presented at Optics East 2005
SPIE Conference in Boston1
 The OCT / SLO set-up is under
construction
1 Bimorph
deformable mirror; an appropriate wavefront
corrector for retinal imaging? –Sophie Laut, Steve Jones,
Hyunkyu Park, David Horsley, Scot Olivier, John Werner
18
OCT / SLO Schematic
MEMS DM
Talk about the SLO system
Bimorph DM
Slide Courtesy of Sophie Laut,
UC Davis Medical Center
19
Acknowledgements
 This project is supported by the National Science Foundation Science and




Technology Center for Adaptive Optics, managed by the University of
California at Santa Cruz under cooperative agreement No. AST - 9876783.
Dr. Scot Olivier and Dr. Steven Jones at LLNL
Dr. Sophie Laut and Prof. John Werner at UCDMC
Prof. David Horsley at UCD
Everyone at the CfAO, LLNL, and UCD for a great internship experience
20