Characterization of a Bimorph Deformable Mirror in a Closed by plj11999

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									   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
     2 Department of Ophthalmology and Psychophysics, UC Davis
  3 Department of Mechanical and Aeronautical Engineering, UC Davis   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
                                                                                5
Slide Courtesy of Sophie Laut,
  UC Davis Medical Center
           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
                                                                                   6
Slide Courtesy of Sophie Laut,
  UC Davis Medical Center
                          Imaging Setup
System Information
total g = 1.00
flatness = l/13           Hartmann – Shack                   Telescope 2
                          Wave front sensor
                                                               g=1




                                       Pupil
                  Laser                Plane                           Bimorph
                  Diode
                                               Telescope 1               DM 7
                                                  g=1
Characterization Process


   Place aberration         Control Loop closes and
      into system           mirror corrects wave front




                 Before/After data
                     analyzed


                                                         8
Characterization Process


   Place aberration         Control Loop closes and
      into system           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 
         Sx1..Sxn, Sy1..Syn  A   
                                             •Starts with a file of reference
                                           positions

             ( x, y )  2  an  
                                xij 
                                             •Reads the value of each
     ij                                 reference Centro id from a matrix
                x                lf       of partial derivatives for the
                                             particular Fernike mode. and
Solution
              ( x, y )  2                calculates the slope in x and y
      
 Vector
(Slope) ij                l f yij        •The slope is direcly proportional
                 
             partialy                      to the displacement
      Matrix of
    derivatives for all used
        zernike modes                        •The displacement is added to the
                                             reference position and logged
                            Vector of
                        normalized zernike
                           coefficients

                                                                                  11
     Preparing Simulated Aberrations

1.    A specific Zernike mode is picked
2.    Maximum detectable amplitude is determined
3.    Aberrations are generated
4.    Aberrations introduced to the system




                                                   12
Characterization Process


   Place aberration         Control Loop closes and
      into system           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.

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   Dealing With Loss of WFS Spots
Some aberrations are so strong      Using MATLAB we can
that the computer cannot find    correct for this by using an
all of the WFS spots                 extrapolation algorithm




                                                           16
Characterization Process


   Place aberration         Control Loop closes and
      into system           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     18
corrector for retinal imaging? –Sophie Laut, Steve Jones,
Hyunkyu Park, David Horsley, Scot Olivier, John Werner
OCT / SLO Schematic


              Talk about the SLO systemDM
                                     MEMS




  Bimorph DM



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  Slide Courtesy of Sophie Laut,
    UC Davis Medical Center
               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




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