Post on 18-Aug-2020
1
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
2
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
3
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
4
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)
5
Previous Work with Refractive Lenses
Doubled LCA → 0.5 D increase in DOF
6
Conventional Diffractive vs. MOD Lens Concepts
F
Conventional Diffractive Lens
F
Multi-Order Diffractive (MOD) Lens
(a)
(b)
7
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.
8
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
9
Diffraction Efficiency of a MOD Lens Design parameters: λ0 = 555 nm, p = 10
10
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
11
Optical Performance On-axis through-focus MTF; 10 cycles/degree Photopic spectrum Entrance pupil diameter = 4 mm
12
Refractive Lens & MOD Lens Performance Comparison
Asphere -2D
MOD 20 -2D
2.5 mm pupil diameter 5.0 mm pupil diameter
13
Simultaneous Vision Approaches • Aperture segmentation
• Wavefront splitting (diffractive optics)
F1 F2
F1 F2
primary diffraction orders
14
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)
15
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
16
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
17
Vision MembraneTM Lens in Anterior Chamber
Curved Vision Membrane Lens bridging over the pupil
Membrane Thickness ~ 500 - 600 µm
18
19
MULTI-FOCAL VISION MEMBRANE
VM = Green arrow
20
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.