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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: morris@apollooptical.com 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

Conventional Doublet Hybrid Doublet Crown Glass

νa = 60 φa = 2.5 Φ

Flint Glass νb = 36

φb = −1.5 Φ

Crown Glass νa = 60

φa = 0.95 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

F

Conventional Diffractive Lens

F

Multi-Order Diffractive (MOD) Lens

(a)

(b)

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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

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

Phase Step = 2πp m = Diffraction Order

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Diffraction Efficiency of a MOD Lens Design parameters: λ0 = 555 nm, p = 10

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A MOD lens possesses a range of powers or focal lengths, which can be thought of as a type of “natural accommodation”.

Δφ

MOD “Extended Focus Depth” Lens

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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

Asphere -2D

MOD 20 -2D

2.5 mm pupil diameter 5.0 mm pupil diameter

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Simultaneous Vision Approaches •  Aperture segmentation

•  Wavefront splitting (diffractive optics)

F1 F2

F1 F2

primary diffraction orders

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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-zone Bifocal

5-zone Bifocal

Apollo Bifocal [Insensitive to pupil size] 60:40 split (Distance: Near)

2.5-mm Pupil 5.0-mm Pupil Distance Near Distance Near

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Vision MembraneTM Lens in Anterior Chamber

Curved Vision Membrane Lens bridging over the pupil

Membrane Thickness ~ 500 - 600 µm

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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.