Diffractive Lenses for Extended Depth
Of Focus and Presbyopic Correction
G. Michael Morris and Dale Buralli
Apollo Optical Systems, Inc.
330 Clay Road
Rochester, NY 14623
E-mail: [email protected]
Web: http://www.apollooptical.com
February 15, 2008
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Focus of the Presentation:
1. Use of longitudinal chromatic aberration
to extend the depth of focus
2. Use of wavefront-splitting methods to
create simultaneous-vision bifocal lenses
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Achromatic Doublets Bring Two Wavelengths
To A Common Focus
Lens Powers
Abbe Numbers
; Φ = Total Power
20 < νglass < 90
νdiff = −3.45
Hybrid Doublet
Conventional Doublet
Crown Glass
νa = 60
φa = 2.5 Φ
Crown Glass
νa = 60
φa = 0.95 Φ
Flint Glass
νb = 36
φb = −1.5 Φ
Diffractive Lens
νb = −3.45
φb = 0.05 Φ
Crown
Flint
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Extending the Depth of Focus
• Instead of correcting the chromatic aberration, a hybrid
(contact or intraocular) lens may introduce a desired
amount of longitudinal chromatic aberration in order to
extend the depth of focus.
• Two approaches:
– Hyperchromatic lens
All-Refractive (Whitefoot & Charman)
Refractive/diffractive (Freeman)
– Multi-order diffractive (MOD) lens (Faklis & Morris)
Purely diffractive (no refractive power)
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Previous Work with Refractive Lenses
Doubled LCA → 0.5 D
increase in DOF
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Conventional Diffractive vs. MOD Lens Concepts
(a)
Conventional
Diffractive Lens
F
(b)
Multi-Order
Diffractive (MOD) Lens
F
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Cross Sectional View of
Polychromatic (MOD) Diffractive Lens
D. Faklis and G. M. Morris, “Polychromatic diffractive lenses,”
U. S. Patent No. 5,589,982, December 31, 1996.
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Transmission Properties of a MOD Lens
Transmission Function
Phase Step = 2πp
m = Diffraction Order
Focal Length:
Note:
Wavelengths λ m,p that satisfy the following equation all focus at a
distance F from the lens.
Diffraction Efficiency
; ηm ~ 100% when
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Diffraction Efficiency of a MOD Lens
Design parameters: λ0 = 555 nm, p = 10
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MOD “Extended Focus Depth” Lens
A MOD lens possesses a range of powers or focal lengths,
which can be thought of as a type of “natural accommodation”.
Δφ
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Optical Performance
On-axis through-focus MTF; 10 cycles/degree
Photopic spectrum
Entrance pupil diameter = 4 mm
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Refractive Lens & MOD Lens
Performance Comparison
2.5 mm pupil diameter
Asphere
-2D
MOD 20
-2D
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5.0 mm pupil diameter
Simultaneous Vision Approaches
• Aperture segmentation
F2
F1
F2
F1
• Wavefront splitting (diffractive optics)
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primary diffraction orders
Evaluated Bifocal Designs
Theoretical & laboratory investigation of 17 different
bifocal designs, including:
• Aperture segmented
– Five-zone design
– Two-zone design, center near
• Wavefront splitting (diffractive)
– Blazed diffractive (Freeman)
– Apodized diffractive (Lee-Simpson)
– “Harmony” (Apollo)
– MOD lens with diffractive bifocal (Apollo)
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Diffractive “Harmony” Surface
(U.S. Patent No. 7,156,516 B2)
• Diffractive surface
formed by
superposition of
sinusoidal functions.
• Unlike blazed structure,
surface is smooth (no
sharp-edged
transitions).
• Reduced glare & image
artifacts
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Bi-Focal Lens Performance –
Laboratory Prototypes
2.5-mm Pupil
Distance
Near
2-zone Bifocal
5-zone Bifocal
Apollo Bifocal
[Insensitive to
pupil size]
60:40 split
(Distance: Near)
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5.0-mm Pupil
Distance
Near
Vision MembraneTM Lens in Anterior Chamber
Membrane Thickness
~ 500 - 600 µm
Curved Vision Membrane Lens
bridging over the pupil
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MULTI-FOCAL VISION MEMBRANE
VM = Green arrow
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Conclusions
• With simultaneous vision, wavefront splitting results in higher quality
images than aperture segmentation, and minimizes image quality
variations at different aperture sizes.
• A controlled (or desired) amount of longitudinal chromatic aberration
may be used to extend the depth of focus.
– Hyperchromatic correction using a refractive-diffractive hybrid lens
– MOD (purely diffractive) lens
• MOD lenses with a diffractive “Harmony” bi-focal design provide an
effective (low glare & low halo) simultaneous bifocal design with
extended depth of focus for both distance and near vision.
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