Off-axis variable focus and aberration control mirrors and method

• US 20060232846A1
• Filed: 01/26/2004
• Published: 10/19/2006
• Est. Priority Date: 01/24/2003
• Status: Active Grant

• Current Assignee: Montana State University
• Original Assignee: Montana State University
• Inventors: Himmer, Phillip A., Dickensheets, David L.
• Granted Patent: US 7,494,233 B2
• Time in Patent Office: Days
• US Class Current: 359/224.100
• CPC Class Codes: G02B 26/06 for controlling the phase of light G02B26/08 takes precedence , measuring optical phase difference G01J9/00
• CPC Class Codes: G02B 26/0825 the reflecting element being a flexible sheet or membrane, e.g. for varying the focus flexible mirrors for cosmetic use A45D42/24

Abstract

An optical element with multi-layer composites that deforms to reduce optical aberrations in off-axis optic. Methods are also described in relation to the optical element.

Claims

1. A deformable optical element comprising:

a reflective surface that is operable to receive a light beam defining an incident beam axis, the reflective surface including a deformable member having a surface defining at least one zone movable relative to the incident beam axis; and

at least one actuator coupled to the at least one zone of the reflective surface, the reflective surface operable to be oriented oblique to the incident beam axis and the at least one actuator operable to be actuated such that upon actuation of the at least one actuator, the at least one zone is operable to deform to approximate a paraboloid section and reflect the light toward a focusing plane spaced from the reflective surface.

2. The deformable optical element of claim 1, wherein the paraboloid section comprises a section of the reflective surface having the shape defmed by z=a(x²+y²), where z defines an axis extending through the center of the at least one paraboloid reflector zone x, and y define orthogonal axes with respect to each other and the z axis, and a is the quadratic coefficient for the paraboloid section.

3. The deformable optical element of claim 2, wherein the paraboloid section comprises a section defined by a point on the parabolic reflector having the axis x rotated at an angle θ

about an axis parallel to the y axis so that the point is located on a new coordinate axes z′

, x′ and

y′

.

4. The deformable optical element of claim 3, wherein the angle θ

comprises at least one angle where a wavefront aberration is less than about 0.13 microns proximate the focusing plane over a focal length of at least 36 millimeters.

5. The deformable optical element of claim 4, wherein the angle comprises an angle of approximately 45 degrees such that the paraboloid section is defmed by (a/2)z′

²+ay′

²+a/2 x′

²−

ax′

z′

−

(√

2)z′

=0.

6. The deformable optical element of claim 3, wherein the optical element comprises a plurality of layers, and one of the layers includes a metal layer on at least one of the plurality of layers.

7. The deformable optical element of claim 6, wherein the metal layer comprises at least one reflective layer comprising at least one of:

gold, palladium, platinum, chromium, aluminum, tantalum, titanium, and combinations thereof.

8. The deformable optical element of claim 7, wherein the metal layer is operable to conducts electrons from an electromotive source.

9. The deformable optical element of claim 8, wherein the metal layer comprises a first surface exposed to the light beam and a second surface coupled to a nitride layer, the nitride layer couples to a thermal oxide of silicon, and wherein the plurality of layers further comprises a silicon substrate, and wherein an air gap is formed between the nitride layer and the silicon substrate.

10. The deformable optical element of claim 9, wherein the metal layer comprises a chromium layer bonded to a gold layer with the chromium layer having a thickness less than the gold layer.

11. The deformable optical element of claim 8, wherein the plurality of layers comprises the metal layer with a first surface exposed to the light beam and a second surface coupled to a nitride layer that couples to a substrate of at least one of polysilica, polyimide, and polyester or combinations thereof.

12. The deformable optical element of claim 1, wherein the at least one actuator comprises a first actuator surrounding a second actuator on the deformable member, and one of the first and second actuators is operable to move the deformable member over a distance.

18. The deformable optical element of claim 1, wherein the at least one zone is operable to deform such that a magnitude of wavefront aberrations of the light beam is reduced to a percentage of the wavelength of the light beam.

19. The deformable optical element of claim 18, wherein the magnitude of wavefront aberrations of the light beam is reduced to about 20 percent of the wavelength of the light beam.

20. The deformable optical element of claim 12, wherein the deformable member is operable to move over a distance of about 1.25 microns (1.25 μ

m).

13. A method comprising:

displacing a reflective surface along an axis generally orthogonal to the reflective surface so that the reflective surface deforms into an approximation of a sectioned surface of a paraboloid;

providing a light beam along an incident axis oblique to the reflective surface such that optical aberrations in the reflected light beam are reduced.

14. The method of claim 13, wherein the providing comprises transmitting the light beam without a beam splitter.

21. The method of claim 13, further comprising forming an image with the reflected light beam.

22. The method of claim 13, further comprising capturing an image with the reflected light beam.

15. A method of fabricating a deformable optical element on a substrate, the method comprising:

forming on a substrate a di-electric composite member that is operable to form a parabolic surface of curvature formed by a sectioned portion of a parabolic reflector when the composite member is energized by at least one electrically conductive material.

16. The method of claim 15, wherein the forming comprises providing an oval boundary that connects to the parabolic surface of curvature.

17. The method of claim 15, wherein the forming comprises:

coupling a phosphosilicate glass layer to the silicon substrate between the silicon substrate and a nitride layer;

adhering a metallic layer on the nitride layer; and

removing the phosphosilicate glass layer to provide the air gap.