LOW THERMAL STRESS CATADIOPTRIC IMAGING OPTICS

• US 20130107360A1
• Filed: 10/27/2011
• Published: 05/02/2013
• Est. Priority Date: 10/27/2011
• Status: Active Grant

• Current Assignee: IMAX Theatres International Limited (IMAX Corporation)
• Original Assignee: Eastman Kodak Company
• Inventors: Kurtz, Andrew F., Bietry, Joseph Raymond
• Granted Patent: US 8,830,580 B2
• Time in Patent Office: Days
• US Class Current: 359/434
• CPC Class Codes: G02B 1/00 Optical elements characterised by the material of which they are made; Optical coatings for optical elements
• CPC Class Codes: G02B 23/06 having a focussing action, e.g. parabolic mirror
• CPC Class Codes: G02B 27/149 using crossed beamsplitting surfaces, e.g. cross-dichroic cubes or X-cubes
• CPC Class Codes: G02B 27/283 used for beam splitting or combining
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02B 7/008 with means for compensating for changes in temperature or for controlling the temperature; thermal stabilisation
• CPC Class Codes: G03B 21/2013 Plural light sources
• CPC Class Codes: G03B 21/2066 Reflectors in illumination beam in projection beam G03B21/28
• CPC Class Codes: G03B 21/2073 Polarisers in the lamp house peculiar to electronic spatial light modulators H04N9/3197
• CPC Class Codes: G03B 21/208 Homogenising, shaping of the illumination light
• CPC Class Codes: G03B 33/12 using beam-splitting or beam-combining systems, e.g. dichroic mirrors
• CPC Class Codes: H04N 9/3105 for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10
• CPC Class Codes: H04N 9/3144 Cooling systems cooling of liquid crystal cells in general G02F1/133382; cooling of projectors not peculiar to the presence of an electronic spatial light modulator G03B21/16
• CPC Class Codes: H04N 9/3152 for shaping the light beam beam shaping per se G02B27/09

Abstract

Imaging optics having reduced susceptibility to thermally-induced stress birefringence for imaging an object plane to an image plane; comprising an aperture stop positioned between the object plane and the image plane; a first group of optical elements located on the object plane side of the aperture stop; and a second group of optical elements located on the image plane side of the aperture stop. The optical elements in the first and second groups that are immediately adjacent to the aperture stop are refractive lens elements fabricated using optical materials having a negligible susceptibility to thermal stress birefringence, and the other optical elements are a combination of reflective optical elements and refractive lens elements fabricated using optical materials having at most a moderate susceptibility to thermal stress birefringence.

Claims

1. Imaging optics having reduced susceptibility to thermally-induced stress birefringence for imaging an object plane to an image plane;

comprising;

an aperture stop positioned between the object plane and the image plane;

a first group of optical elements located on the object plane side of the aperture stop; and

a second group of optical elements located on the image plane side of the aperture stop;

wherein the optical elements in the first and second groups of optical elements that are immediately adjacent to the aperture stop are refractive lens elements fabricated using optical materials having a negligible susceptibility to thermal stress birefringence as characterized by a thermal stress birefringence metric; and

wherein the other optical elements in the first and second groups of optical elements, that are not the refractive lens elements immediately adjacent to the aperture stop, are a combination of reflective optical elements and refractive lens elements fabricated using optical materials having at most a moderate susceptibility to thermal stress birefringence as characterized by the thermal stress birefringence metric.

2. The imaging optics of claim 1 wherein the thermal stress birefringence metric includes factors relating to a coefficient of thermal expansion of the optical material, a stress optical coefficient of the optical material and a light absorption coefficient of the optical material.

3. The imaging optics of claim 2 wherein the thermal stress birefringence metric further includes at least one additional factor relating to a modulus of elasticity of the optical material, a thermal conductivity of the optical material, a Poisson'"'"'s ratio of the optical material, an optical power density in the optical material, a thickness of the refractive lens element or a clear aperture size of the refractive lens element.

4. The imaging optics of claim 2 wherein the thermal stress birefringence metric is given by:

M₁′

=ρ

κ

α

.

where ρ

is the coefficient of thermal expansion, κ

is the stress optical coefficient, and α

is the light absorption coefficient.

5. The imaging optics of claim 2 wherein the thermal stress birefringence metric is given by:

M₁=ρ

κ

α

E/(K·

(1<

μ

)).

where ρ

is the coefficient of thermal expansion, κ

is the stress optical coefficient, α

is the light absorption coefficient, E is the modulus of elasticity, K is the thermal conductivity, and μ

Poisson'"'"'s ratio.

6. The imaging optics of claim 5 wherein the optical materials having a negligible susceptibility to thermal stress birefringence satisfy the condition that M₁≦

0.1×

10<sup>−

6</sup> W<sup>−

1</sup> and the optical materials having at most a moderate susceptibility to thermal stress birefringence satisfy the condition that M₁<

1.60×

10<sup>−

6</sup> W<sup>−

1</sup>.

7. The imaging optics of claim 6 where all of the refractive lens elements satisfy the condition that M₁≦

0.80×

10<sup>−

6</sup> W<sup>−

1</sup>.

8. The imaging optics of claim 6 where at least one of the refractive lens elements is fabricated using an optical material where 0.8×

10<sup>−

6</sup> W<sup>−

1</sup>≦

M₁≦

1.60×

10<sup>−

6</sup> W<sup>−

1</sup>.

9. The imaging optics of claim 2 wherein the thermal stress birefringence metric is given by:

M₂=I₀Lρ

κ

α

E/(K·

(1−

μ

).

where I₀ is the optical power density in the optical material, L is the thickness of the refractive lens element, ρ

is the coefficient of thermal expansion, κ

is the stress optical coefficient, α

is the light absorption coefficient, E is the modulus of elasticity, K is the thermal conductivity, and μ

is Poisson'"'"'s ratio.

10. The imaging optics of claim 1 where the optical materials used to fabricate the refractive lens elements are also selected for properties that relate to achieving adequate image quality performance, including refractive index and chromatic dispersion properties.

11. The imaging optics of claim 1 wherein at least one surface of one or more of the refractive lens elements have an aspheric surface profile.

12. The imaging optics of claim 11 wherein at least one of the aspheric surface profile is an elliptical surface profile, a hyperbolic surface profile, a parabolic surface profile or a free-form surface profile.

13. The imaging optics of claim 1 wherein the optical elements include at least two concentric reflective optical elements arranged in an Offner configuration.

14. The imaging optics of claim 1 wherein the optical elements include at least two reflective optical elements arranged in a telescopic imaging configuration.

15. The imaging system of claim 1 wherein at least one of the reflective optical elements is an off-axis reflective optical element.

16. The imaging optics of claim 1 wherein the imaging optics perform the function of relay optics in a projection system which image a spatial light modulator onto an intermediate image plane, and wherein the projection system further includes projection optics which image the intermediate image plane onto a display surface.

17. The imaging optics of claim 1 wherein the imaging optics perform the function of projection optics in a projection system which image an intermediate image plane onto a display surface, and wherein the projection system further includes relay optics which image a spatial light modulator onto the intermediate image plane.

18. The imaging optics of claim 1 wherein the at least some of the optical materials used to fabricate the refractive lens elements are glasses or polymers.

19. Imaging optics having reduced susceptibility to thermally-induced stress birefringence for imaging an object plane to an image plane;

comprising;

an aperture stop positioned between the object plane and the image plane;

a first group of optical elements located on the object plane side of the aperture stop; and

a second group of optical elements located on the image plane side of the aperture stop;

wherein the optical elements in the first and second groups of optical elements that are immediately adjacent to the aperture stop are reflective optical elements or refractive lens elements fabricated using optical materials having a negligible susceptibility to thermal stress birefringence as characterized by a thermal stress birefringence metric;

wherein the other optical elements in the first and second groups of optical elements, that are not the optical elements immediately adjacent to the aperture stop, are reflective optical elements or refractive lens elements fabricated using optical materials having at most a moderate susceptibility to thermal stress birefringence as characterized by the thermal stress birefringence metric, or a combination thereof; and

wherein the optical elements in the first and second groups taken together include both reflective optical elements and refractive lens elements.

20. The imaging optics of claim 19 wherein the thermal stress birefringence metric includes factors relating to a coefficient of thermal expansion of the optical material, a stress optical coefficient of the optical material and a light absorption coefficient of the optical material.

21. The imaging optics of claim 20 wherein the thermal stress birefringence metric further includes at least one additional factor relating to a modulus of elasticity of the optical material, a thermal conductivity of the optical material, a Poisson'"'"'s ratio of the optical material, an optical power density in the optical material, a thickness of the refractive lens element or a clear aperture size of the refractive lens element.

22. The imaging optics of claim 20 wherein the thermal stress birefringence metric is given by:

M₁′

=ρ

κ

α

.

where ρ

is the coefficient of thermal expansion, κ

is the stress optical coefficient, and α

is the light absorption coefficient.

23. The imaging optics of claim 20 wherein the thermal stress birefringence metric is given by:

M₁=ρ

κ

α

E/(K·

(1−

μ

).

where ρ

is the coefficient of thermal expansion, κ

is the stress optical coefficient, α

is the light absorption coefficient, E is the modulus of elasticity, K is the thermal conductivity, and μ

is Poisson'"'"'s ratio.

24. The imaging optics of claim 23 wherein the optical materials having a negligible susceptibility to thermal stress birefringence satisfy the condition that M₁≦

0.1×

10<sup>−

6</sup> W<sup>−

1</sup> and the optical materials having at most a moderate susceptibility to thermal stress birefringence satisfy the condition that M₁<

1.60×

10<sup>−

6</sup> W<sup>−

1</sup>.