Method of manufacturing an optical element

1. An interferometer system comprising:

an optical delay apparatus including at least one beam splitter and at least one reflector for providing first and second optical paths having first and second optical path lengths, respectively, for a beam of light traversing the optical delay apparatus, wherein a distance between the at least one beam splitter and the at least one reflector is adjustable to adjust an optical path length difference between the first and second optical path lengths;

a light source for generating light of a coherence length; and

a Fizeau interferometer including an interferometer optics and a first Fizeau reference surface for directing measuring light towards an optical surface to be tested and disposed at a distance greater than half of the coherence length from the first Fizeau reference surface;

a position sensitive detector including a light detecting surface;

wherein the light source, the optical delay apparatus, the Fizeau interferometer and the detector are arranged such that measuring light generated by the light source may traverse the optical delay apparatus and the Fizeau interferometer to be incident on the detector,

such that a portion of the measuring light traversing the Fizeau interferometer is reflected from the first Fizeau reference surface,

such that a portion of the measuring light traversing the Fizeau interferometer is reflected from the optical surface to be tested, and

such that at least portions of the Fizeau surface and of the optical surface to be tested are imaged through the interferometer optics onto at least a portion of the light detecting surface of the detector;

wherein the interferometer system further comprises an aberration reducing transfer optics to supply the measuring light having traversed the optical delay apparatus to the Fizeau interferometer, wherein the aberration reducing transfer optics comprises an optical fiber.

2. The interferometer system according to claim 1 , wherein the optical fiber is a mono mode fiber.

3. The interferometer system according to claim 1 , wherein the optical delay apparatus comprises an adjustable light attenuator disposed in at least one of the first and second beam paths.

4. A method of manufacturing an optical element having opposite first and second surfaces using an interferometer system, the interferometer system comprising:

an optical delay apparatus including at least one beam splitter and at least one reflector for providing first and second optical paths having first and second optical path lengths, respectively, for a beam of light traversing the optical delay apparatus, wherein a distance between the at least one beam splitter and the at least one reflector is adjustable to adjust an optical path length difference between the first and second optical path lengths;

an interferometer apparatus including an interferometer optics, a first reference surface, and a second reference surface disposed at a distance from the first reference surface to form a cavity there between;

a light source for generating light of a coherence length; and

a position sensitive detector including a light detecting surface;

wherein the light source, the optical delay apparatus, the interferometer apparatus and the detector are arranged such that measuring light generated by the light source may traverse the optical delay apparatus and the interferometer apparatus to be incident on the detector,

such that at least a portion of the first reference surface is imaged onto at least a portion of the light detecting surface of the detector with measuring light reflected from the first reference surface,

such that at least a portion of the second reference surface is imaged onto the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface,

wherein the method comprises:

disposing the optical element within the cavity such that the first surface of the optical element is oriented towards the first reference surface and the second surface of the optical element is oriented towards the second reference surface,

such that at least portions of the first and second surfaces of the optical element are each imaged onto the portion of the light detecting surface of the detector with measuring light, and

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first reference surface and the first surface of the optical element, and

detecting at least one first interference pattern generated by measuring light reflected from the first reference surface which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the first surface of the optical element;

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the second surface of the optical element and the second reference surface, and

detecting at least one second interference pattern generated by measuring light reflected from the second surface of the optical element which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface;

processing at least one of the first and second surfaces of the optical element based on the at least one first and the at least one second interference pattern.

5. The method according to claim 4 , further comprising:

not disposing the optical element within the cavity; and

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first reference surface and the second reference surface, and

detecting, while the optical element is not disposed in the cavity, at least one third interference pattern generated by measuring light reflected from the first reference surface which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface;

wherein the processing of the optical element is further performed based on the at least one third interference pattern.

6. The method according to claim 5 , further comprising determining a distance between the first and second surfaces of the optical element substantially according to the following formula:

d

=

1

2

⁢

(

O

⁢

⁢

P

⁢

⁢

D

4

⁢

a

-

O

⁢

⁢

P

⁢

⁢

D

1

-

O

⁢

⁢

P

⁢

⁢

D

3

)

wherein

d represents the distance between the first and second surfaces of the optical element,

OPD 4a represents an optical path difference determined from the third interference pattern;

OPD 1 represents an optical path difference determined from the first interference pattern;

OPD 3 represents an optical path difference determined from the second interference pattern.

7. The method according to claim 4 , wherein the processing of the optical surface of the optical element comprises at least one of milling, grinding, loose abrasive grinding, polishing, ion beam figuring, magneto-rheological figuring, and finishing the optical surface of the optical element.

8. The method according to claim 7 , wherein the finishing comprises applying a coating to the optical surface.

9. The method according to claim 8 , wherein the coating comprises at least one of a reflective coating, an anti-reflective coating and a protective coating.

10. The method according to claim 4 , wherein the first and second surfaces of optical element are substantially flat surfaces oriented parallel to each other.

11. The method according to claim 4 , wherein the first and second surfaces of optical element are substantially spherical surfaces having substantially coinciding centers of curvature.

12. A method of manufacturing an optical element having opposite first and second surfaces using an interferometer system, the interferometer system comprising:

an optical delay apparatus including at least one beam splitter and at least one reflector for providing first and second optical paths having first and second optical path lengths, respectively, for a beam of light traversing the optical delay apparatus, wherein a distance between the at least one beam splitter and the at least one reflector is adjustable to adjust an optical path length difference between the first and second optical path lengths;

an interferometer apparatus including an interferometer optics, a first reference surface, and a second reference surface disposed at a distance from the first reference surface to form a cavity there between;

a light source for generating light of a coherence length; and

a position sensitive detector including a light detecting surface;

wherein the light source, the optical delay apparatus, the interferometer apparatus and the detector are arranged such that measuring light generated by the light source may traverse the optical delay apparatus and the interferometer apparatus to be incident on the detector,

such that at least a portion of the first reference surface is imaged onto at least a portion of the light detecting surface of the detector with measuring light reflected from the first reference surface,

such that at least a portion of the second reference surface is imaged onto the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface,

wherein the method comprises:

disposing the optical element within the cavity such that the first surface of the optical element is oriented towards the first reference surface and the second surface of the optical element is oriented towards the second reference surface,

such that at least portions of the first and second surfaces of the optical element are each imaged onto the portion of the light detecting surface of the detector with measuring light, and

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first reference surface and the second reference surface while the optical element is disposed in the cavity, and

detecting, while the optical element is disposed in the cavity, at least one fourth interference pattern generated by measuring light reflected from the first reference surface which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface;

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first and second surface of the optical element, and

detecting, while the optical element is disposed in the cavity, at least one fifth interference pattern generated by measuring light reflected from the first surface of the optical element which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the second surface of the optical element;

not disposing the optical element within the cavity; and

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first reference surface and the second reference surface, and

detecting, while the optical element is not disposed in the cavity, at least one third interference pattern generated by measuring light reflected from the first reference surface which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface;

processing at least one of the first and second surfaces of the optical element based on the at least one third, the at least one fourth and the at least one fifth interference pattern.

13. The method according to claim 12 , wherein a distance between the first and second surfaces of the optical element is determined substantially according to the following formula:

d

=

-

1

2

⁢

(

O

⁢

⁢

P

⁢

⁢

D

4

⁢

b

-

O

⁢

⁢

P

⁢

⁢

D

4

⁢

a

-

O

⁢

⁢

P

⁢

⁢

D

HV

)

wherein

d represents the distance between the first and second surfaces of the optical element,

OPD 4b represents an optical path difference determined from the fourth interference pattern;

OPD 4a represents an optical path difference determined from the third interference pattern;

OPD HV represents an optical path difference determined from the fifth interference pattern.

14. A method of manufacturing an optical element having opposite first and second surfaces using an interferometer system, the interferometer system comprising:

an optical delay apparatus including at least one beam splitter and at least one reflector for providing first and second optical paths having first and second optical path lengths, respectively, for a beam of light traversing the optical delay apparatus, wherein a distance between the at least one beam splitter and the at least one reflector is adjustable to adjust an optical path length difference between the first and second optical path lengths;

an interferometer apparatus including an interferometer optics, a first reference surface, and a second reference surface disposed at a distance from the first reference surface to form a cavity there between;

a light source for generating light of a coherence length; and

a position sensitive detector including a light detecting surface;

wherein the light source, the optical delay apparatus, the interferometer apparatus and the detector are arranged such that measuring light generated by the light source may traverse the optical delay apparatus and the interferometer apparatus to be incident on the detector,

such that at least a portion of the first reference surface is imaged onto at least a portion of the light detecting surface of the detector with measuring light reflected from the first reference surface,

such that at least a portion of the second reference surface is imaged onto the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface,

wherein the method comprises:

disposing the optical element within the cavity such that the first surface of the optical element is oriented towards the first reference surface and the second surface of the optical element is oriented towards the second reference surface,

such that at least portions of the first and second surfaces of the optical element are each imaged onto the portion of the light detecting surface of the detector with measuring light, and

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first reference surface and the second reference surface while the optical element is disposed in the cavity, and

detecting, while the optical element is disposed in the cavity, at least one fourth interference pattern generated by measuring light reflected from the first reference surface which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface;

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first reference surface and the second surface of the optical element, and

detecting, while the optical element is disposed in the cavity, at least one sixth interference pattern generated by measuring light reflected from the first reference surface which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the second surface of the optical element;

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first surface of the optical element and the second reference surface, and

detecting, while the optical element is disposed in the cavity, at least one seventh interference pattern generated by measuring light reflected from the first surface of the optical element which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface;

not disposing the optical element within the cavity; and

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first-reference surface and the second reference surface, and

detecting, while the optical element is not disposed in the cavity, at least one third interference pattern generated by measuring light reflected from the first reference surface which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface;

processing at least one of the first and second surfaces of the optical element based on the at least one third, the at least one fourth, the at least one sixth, and the at least one seventh interference pattern.

15. The method according to claim 14 , wherein a distance between the first and second surfaces of the optical element is determined substantially according to the following formula:

d

=

-

1

2

⁢

(

2

⁢

⁢

O

⁢

⁢

P

⁢

⁢

D

4

⁢

b

-

O

⁢

⁢

P

⁢

⁢

D

4

⁢

a

-

O

⁢

⁢

P

⁢

⁢

D

2

-

O

⁢

⁢

P

⁢

⁢

D

5

)

wherein

d represents the distance between the first and second surfaces of the optical element,

OPD 4b represents an optical path difference determined from the fourth interference pattern;

OPD 4a represents an optical path difference determined from the third interference pattern;

OPD 2 represents an optical path difference determined from the sixth interference pattern; and

OPD 5 represents an optical path difference determined from the seventh interference pattern.

16. A method of manufacturing an optical element having opposite first and second surfaces using an interferometer system, the interferometer system comprising:

an optical delay apparatus including at least one beam splitter and at least one reflector for providing first and second optical paths having first and second optical path lengths, respectively, for a beam of light traversing the optical delay apparatus, wherein a distance between the at least one beam splitter and the at least one reflector is adjustable to adjust an optical path length difference between the first and second optical path lengths;

an interferometer apparatus including an interferometer optics, a first reference surface, and a second reference surface disposed at a distance from the first reference surface to form a cavity there between;

a light source for generating light of a coherence length; and

a position sensitive detector including a light detecting surface;

wherein the light source, the optical delay apparatus, the interferometer apparatus and the detector are arranged such that measuring light generated by the light source may traverse the optical delay apparatus and the interferometer apparatus to be incident on the detector,

such that at least a portion of the first reference surface is imaged onto at least a portion of the light detecting surface of the detector with measuring light reflected from the first reference surface,

such that at least a portion of the second reference surface is imaged onto the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface,

wherein the method comprises:

disposing the optical element within the cavity such that the first surface of the optical element is oriented towards the first reference surface and the second surface of the optical element is oriented towards the second reference surface,

such that at least portions of the first and second surfaces of the optical element are each imaged onto the portion of the light detecting surface of the detector with measuring light, and

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first reference surface and the first surface of the optical element, and

detecting at least one first interference pattern generated by measuring light reflected from the first reference surface which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the first surface of the optical element;

not disposing the optical element within the cavity; and

adjusting the optical path length difference of the optical delay apparatus to be substantially equal to an optical path difference between the first reference surface and the second reference surface, and

detecting, while the optical element is not disposed in the cavity, at least one third interference pattern generated by measuring light reflected from the first reference surface which is superimposed on the portion of the light detecting surface of the detector with measuring light reflected from the second reference surface;

processing the first surface of the optical element based on the at least one first and the at least one third interference pattern.

17. The method according to claim 16 , wherein a surface height of the first surface of the optical element is determined substantially according to the following formula:

l

2

=

1

2

⁢

(

O

⁢

⁢

P

⁢

⁢

D

1

-

O

⁢

⁢

P

⁢

⁢

D

4

⁢

a

)

-

l

4

+

const

wherein

1 1 represents the surface height of the first surface of the optical element;

OPD 1 represents an optical path difference determined from the first interference pattern;

OPD 4a represents an optical path difference determined from the third interference pattern;

1 4 represents a surface height of the first surface of the second reference surface; and

const represents a constant.