1. FIBER-OPTIC LASERFIBER-OPTIC LASER
INTERFEROMETERINTERFEROMETER
FOR VISION RESEARCHFOR VISION RESEARCH
Timne Bilton
PI & Supervisor: Dr. David Williams
Collaborators: Julianna Lin, Silvestre Manzanera &
Sapna Shroff
University of Rochester
Center for Visual Science & Dept of Electrical and Computer Engineering

2. OBJECTIVEOBJECTIVE
To design and calibrate a fiber coupled laser
interferometer to be used in conjunction with the
University of Rochester’s adaptive optics
ophthalmoscope.
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3. Laser interferometry avoids blur
from diffraction and aberrations
WHAT IS INTERFEROMETRYWHAT IS INTERFEROMETRY
APPLIED TO THE EYE?APPLIED TO THE EYE?
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4. WHY USEFUL IN VISION?WHY USEFUL IN VISION?
Eye’s optical aberrations
primarily limit vision and
retinal imaging.
Adaptive optics reduces
these aberrations, but image
quality is still diffraction-
limited by the pupil.
Laser interferometry can
image fringes on that retina
that are immune to blur
from diffraction as well as
aberrations
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0.01
0.1
1
0 50 100 150 200 250
ModulationTransfer
Spatial Frequency (c/deg)
Eye's MTFs
in incoherent light
2 3 4 5 6 7.3 mm

5. APPLICATIONSAPPLICATIONS
Measuring neural visual performance (CSF)
Retinal image resolution exceeding the
diffraction limit using structured illumination
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6. STRUCTURED ILLUMINATIONSTRUCTURED ILLUMINATION
Simulation of imaging interference fringes onto the cone mosaic
Retinal images taken with AO should contain moire patterns such as
simulated below when the fringe frequency is 130 cycles/deg
Such moire patterns may contain valuable information about the cone
mosaic as well as other retinal structures.
50 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
Sampling Frequency

7. DESIGNDESIGN
690 nm fiber coupled laser is connected to a fiber splitter
The splitter feeds directly to two acousto-optic modulators
The altered beams are reflected off a right angle prismatic mirror through a
series of relay mirrors and a galvanometer
Light is sent to the pupil plane via the AO system
Fiber
modulator
Fiber-coupled
laser
Fiber
splitter
(1x2)
Fiber
modulator
Lens
Lens
Mirror on
galvanometer
Lens
Focusing
Lens
Mirror
Movable
platform
Right Angle Mirror
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8. CONTRAST CONTROL WITHCONTRAST CONTROL WITH
ACOUSTO-OPTIC MODULATORSACOUSTO-OPTIC MODULATORS
•AOMs will pulse the light beams
delivered to the retina 500 times a
second.
•Pulses arriving simultaneously
generate fringe contrast is 100%.
Phase delays bring contrast down
towards zero
•Digital control of pulse overlap
alters fringe contrast easily
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http://en.wikipedia.org/wiki/Acousto-opticc_modulator

9. BUILDINGBUILDING
Clockwise from the left:
• Construction and
alignment process.
• Bite bar for head
stabilization
• Assembled (inset)
prismatic mirror and U-
bench holding fiber
cable
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10. ZEMAX SIMULATIONZEMAX SIMULATION
•An approximate fringe image was
generated by generating a lens modeling
system.
•Resolution of this image was limited to
the ability of the computer’s memory
•EFL, FFD and BFD determined by
designer calculations
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TOP: Fringe Diagram at retinal plane
LEFT: Unfolded Layout of system (after
prismatic mirror)

11. SPATIAL FREQUENCYSPATIAL FREQUENCY
CALIBRATIONCALIBRATION
Ronchi rulings (transparent plate ruled with black
lines and clear spaces of equal width) of known
frequency placed in a conjugate retinal plane
Frequency match will be made by adjusting the
fringe frequency until the Moiré pattern formed
with the Ronchi ruling was zero spatial frequency.
U bench position will be recorded when
interference fringe has identical frequency.
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12. RESULTSRESULTS
Low contrast fringes were observed  able to
see magnified fringes on a piece of paper, but
disappear later in the system
Unexpected vibrations made fringe imaging
inconsistent
Laser issue: temporal coherence required for
contrast  current of the laser was below the
threshold current for lasing
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13. ACKNOWLEDGEMENTSACKNOWLEDGEMENTS
David R. Williams, PhD
Center for Visual Science, University of Rochester
Center for Adaptive Optics, University of California at Santa Cruz
College of Optical Sciences, University of Arizona
This project is supported by a Research Experiences for
Undergraduates (REU) supplement to the National Science
Foundation and Technology Center for Adaptive Optics,
managed by the University of California at Santa Cruz under
A cooperative agreement No. AST-9876783.
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14. REFERENCESREFERENCES
Publications:
•Miller, D., Williams, D.R., Morris, G.M., and Liang, J. (1996) Images of cone photoreceptors in the living human
eye. Vision Res., 36, 1067-1079 DOI link: doi:10.1016/0042-6989(95)00225-1
•Liang, J., Williams, D.R., and Miller, D.T. (1997) Supernormal vision and high resolution retinal imaging through
adaptive optics. J. Opt. Soc. Am. A., 14, 2884-2892.
•H. Hofer, L. Chen, G. Y. Yoon, B. Singer, Y. Yamauchi, and D. R. Williams, (2001) Improvement in retinal image
quality with dynamic correction of the eye's aberrations. Optics Express 8, 631-643.
•MacRae, S., Williams, D.R., (2001) Wavefront Guided Ablation. American Journal of Ophthalmology, 132:6, 915-
919
Wikipedia-The Free Encyclopedia (www.wikipedia.org/wiki/main_page)
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