Beam splitter assembly and interferometer having a beam splitter assembly

• US 6,369,951 B1
• Filed: 02/24/2000
• Issued: 04/09/2002
• Est. Priority Date: 02/26/1999
• Status: Expired due to Fees

• Current Assignee: Dr. Johannes Heidenhain GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Spanner, Erwin
• Primary Examiner(s): Mack, Ricky
• Assistant Examiner(s): O'NEILL, GARY WILLIAM
• Application Number:
  US09/511,757
• Time in Patent Office: 775 Days
• Field of Search: 359/618, 359/629, 356/451, 356/493, 356/498, 356/508
• US Class Current: 359/629
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02058 by particular optical compensation or alignment elements, e.g. dispersion compensation
• CPC Class Codes: G01B 9/02061 Reduction or prevention of effects of tilts or misalignment
• CPC Class Codes: G02B 27/106 for splitting or combining a plurality of identical beams or images, e.g. image replication
• CPC Class Codes: G02B 27/144 using partially transparent surfaces without spectral selectivity G02B27/147 takes precedence
• CPC Class Codes: G02B 27/145 having sequential partially reflecting surfaces

Abstract

A beam splitter assembly and an interferometer using the beam splitter assembly are described. The beam splitter assembly splits an incoming beam of rays that impinges thereon into at least one first outgoing beam and at least one second outgoing beam parallel thereto. To accomplish this, the beam splitter assembly includes a beam splitter element and a compensating element. The beam splitter element includes a transparent plate having two parallel boundary surfaces. The compensating element is arranged with respect to the beam splitter element so that the two outgoing beams propagate parallel to one another, and have essentially traveled the same optical path lengths in the beam splitter element as in the compensating element.

Claims

1. A beam splitter assembly for an interferometer adapted to split an incoming beam into at least one first outgoing beam and at least one second outgoing beam parallel to the at least one first beam, comprising:

at least one beam splitter element, each of the at least one beam splitter elements further comprising a transparent plate having two parallel boundary surfaces, a first of the two boundary surfaces having a portion functioning as an at least partially reflective reflector surface, and a second of the two boundary surfaces having a portion functioning as a beam splitter surface;

at least one compensating element disposed relative to the at least one beam splitter element so that the at least one first and second outgoing beams propagate parallel to one another, the at least one compensating element having dimensions adapted to provide a substantially identical optical path length in the at least one beam splitter element as in the at least one compensating element to the at least one first and second outgoing beams.

2. The beam splitter assembly according to claim 1, wherein the beam splitter surface is adapted to split the incoming beam that impinges thereon into two partial beams that are polarized perpendicularly relative to one another.

3. The beam splitter assembly according to claim 1, wherein the beam splitter surface is adapted to split the incoming beam that impinges thereon into two partial beams having the same polarization.

4. The beam splitter assembly according to claim 1, wherein the reflector surface is a highly reflective dielectric layer packet.

5. The beam splitter assembly according to claim 1, wherein the at least one compensating element is disposed a certain distance from the at least one beam splitter element.

6. The beam splitter assembly according to claim 1, wherein the at least one compensating element is a plane-parallel plate passing through the two parallel boundary surfaces through which the incoming and the at least first and second outgoing beams enter and exit.

7. The beam splitter assembly according to claim 1, wherein the at least one beam splitter element and the at least one compensating element are disposed such that the incoming beam enters the at least one beam splitter element at a specified angle of incidence relative to a perpendicular to the first boundary surface, and thereafter impinges on the beam splitter surface which splits the incoming beam into

a first partial beam reflected towards the first boundary surface, to the reflector surface which is adapted to further reflect said first partial beam towards a transparent portion of the second boundary surface forming a first exit of the beam splitter assembly for the at least one first outgoing beam, and into

a second partial beam transmitted towards a first boundary surface of the at least one compensating element, said first boundary surface of the at least one compensating element being adapted to direct the second partial beam to a second boundary surface of the at least one compensating element forming a second exit of the beam splitter assembly for the at least one second outgoing beam.

8. The beam splitter assembly according to claim 7, wherein the angle of incidence is substantially equal to a Brewster angle.

9. The beam splitter assembly according to claim 7, wherein a thickness of the compensating element is about twice a thickness of the beam splitter element.

10. The beam splitter assembly according to claim 1, wherein the at least one beam splitter element and the at least one compensating element are disposed so that the incoming beam impinges thereon at a specified angle of incidence relative to a perpendicular of the second boundary surface, and wherein the beam splitter surface splits said incoming beam into

a first partial beam transmitted through the beam splitter surface towards the first boundary surface of the beam splitter element, wherein the reflector surface reflects said first partial beam to a transparent portion of the second boundary surface of the beam splitter element forming a first exit of the beam splitter assembly for the at least one first outgoing beam, and into

a second partial beam reflected by the beam splitter surface towards a first boundary surface of the compensating element, and passing there through towards a second exit of the beam splitter assembly for the at least one second outgoing beam.

11. The beam splitter assembly according to claim 1, further comprising a second and a third beam splitter surface of the beam splitter element, and first and second compensating elements, wherein the at least one beam splitter element and the first and second compensating elements are disposed so that the incoming beam impinges thereon at a specified angle of incidence relative to a perpendicular of the first boundary surface, and wherein the beam splitter surface splits said incoming beam into

a first partial beam reflected by the beam splitter surface towards a first boundary surface of the first compensating element, the first partial beam thereafter exiting at a second boundary surface of the first compensating element forming a first exit of the beam splitter assembly for a first outgoing beam, into

a second partial beam transmitted through the beam splitter surface towards the second beam splitter surface of the beam splitter element, wherein the second partial beam is further split into

a third partial beam that is reflected back towards a partial area of the first boundary surface, wherein the third beam splitter surface further splits said third partial beam into

a fifth partial beam passing through the third beam splitter surface to a second exit of the beam splitter assembly for a second outgoing beam, parallel to the first outgoing beam, and into

a fourth partial beam transmitted through the second beam splitter surface towards a first boundary surface of the second compensating element, passing through the second compensating element towards a second boundary surface forming a third exit of the beam splitter assembly for a third outgoing beam, and

a sixth partial beam reflected by the third beam splitter surface towards a transparent portion of the second boundary surface of the at least one beam splitter, forming a fourth exit of the beam splitter assembly for a fourth outgoing beam, which is parallel to the third outgoing beam.

12. The beam splitter assembly according to claim 11, wherein the first and second outgoing beams are perpendicular to the third and fourth outgoing beams.

13. The beam splitter assembly according to claim 1, further comprising first and second compensating elements, forming exits from the beam splitter assembly for first and second outgoing beams parallel to one another, and the at least one beam splitter element having a portion forming an exit from the at least one beam splitter element for a third outgoing beam which is also parallel to the first and second outgoing beams.

14. The beam splitter assembly according to claim 1, further comprising a retro-reflective reflector element arranged separately from the at least one beam splitter element and the at least one compensating element, said retro-reflective reflector element being adapted to reflect a beam that propagates from a beam splitter surface of the at least one beam splitter element back onto the beam splitter surface.

15. An interferometer having at least one measuring arm and a reference arm, comprising:

a light source;

at least one stationary reference reflector in the reference arm;

at least one measuring reflector movable in a measuring direction in the measuring arm;

a detector unit for detecting a position-dependent interference signal;

an evaluation unit for processing the interference signal detected by the detector unit, and

at least one beam splitter assembly for splitting an incoming beam emitted by the light source into at least one first outgoing beam and at least one second outgoing beam parallel thereto, said at least one beam splitter assembly further comprising;

at least one beam splitter element comprising a transparent plate having two parallel boundary surfaces, one of these boundary surfaces having a portion functioning as a beam splitter surface, and a further boundary surface parallel to the aforementioned boundary surface having a portion functioning as an at least partially reflective reflector surface; and

at least one compensating element arranged with respect to the at least one beam splitter element so that at least two outgoing beams propagate parallel to one another, and so that the at least two outgoing beams travel along optical paths having substantially the same length in the interferometer before reaching the detector unit.

16. The interferometer according to claim 15, further comprising an optical element arranged in a beam path of the at least one first and second outgoing beam, said optical element being dimensioned for use in predefined optical path lengths for outgoing beams exiting the beam splitter assembly.

17. The interferometer according to claim 16, wherein the optical element is a plane-parallel plate.

18. The interferometer according to claim 15, wherein the at least one beam splitter assembly further comprises:

first and second compensating elements, forming exits from the beam splitter assembly for first and second outgoing beams parallel to one another, and the at least one beam splitter element having a portion forming an exit from the at least one beam splitter element for a third outgoing beam parallel to the first and second outgoing beams, wherein the first and second outgoing beams impinge on two measuring reflectors disposed together in a modular unit movable linearly in a measuring direction, and rotatable about an axis perpendicular to the measuring direction.

19. The interferometer according to claim 15 wherein the at least partially reflective reflector surface are planar mirrors.

20. A beam splitter assembly for an interferometer adapted to split an incoming beam into at least one first outgoing beam and at least one second outgoing beam parallel to the at least one first beam, comprising:

at least one beam splitter element, each of the at least one beam splitter elements further comprising a transparent plate having two parallel boundary surfaces, a first of the two boundary surfaces having a portion that is a highly reflective dielectric layer packet functioning as a reflector surface, and a second of the two boundary surfaces having a portion functioning as a beam splitter surface;

at least one compensating element disposed relative to the at least one beam splitter element so that the at least one first and second outgoing beams propagate parallel to one another, the at least one compensating element having dimensions adapted to provide a substantially identical optical path length in the at least one beam splitter element as in the at least one compensating element to the at least one first and second outgoing beams.

21. A beam splitter assembly for an interferometer adapted to split an incoming beam into at least one first outgoing beam and at least one second outgoing beam parallel to the at least one first beam, comprising:

at least one beam splitter element, each of the at least one beam splitter elements further comprising a transparent plate having two parallel boundary surfaces, a first of the two boundary surfaces having a portion functioning as an at least partially reflective reflector surface, and a second of the two boundary surfaces having a portion functioning as a beam splitter surface;

at least one compensating element disposed relative to the at least one beam splitter element so that the at least one first and second outgoing beams propagate parallel to one another, the at least one compensating element having dimensions adapted to provide a substantially identical optical path length in the at least one beam splitter element as in the at least one compensating element to the at least one first and second outgoing beams, wherein the at least one compensating element is a plane-parallel plate passing through the two parallel boundary surfaces through which the incoming and the at least first and second outgoing beams enter and exit.

22. The beam splitter assembly according to claim 21, wherein the at least one beam splitter element and the at least one compensating element are disposed such that the incoming beam enters the at least one beam splitter element at a specified angle of incidence relative to a perpendicular to the first boundary surface, and thereafter impinges on the beam splitter surface which splits the incoming beam into

a first partial beam reflected towards the first boundary surface, to the reflector surface which is adapted to further reflect said first partial beam towards a transparent portion of the second boundary surface forming a first exit of the beam splitter assembly for the at least one first outgoing beam, and into

a second partial beam transmitted towards a first boundary surface of the at least one compensating element, said first boundary surface of the at least one compensating element being adapted to direct the second partial beam to a second boundary surface of the at least one compensating element forming a second exit of the beam splitter assembly for the at least one second outgoing beam.

23. The beam splitter assembly according to claim 21, wherein the at least one beam splitter element and the at least one compensating element are disposed so that the incoming beam impinges thereon at a specified angle of incidence relative to a perpendicular of the second boundary surface, and wherein the beam splitter surface splits said incoming beam into

a first partial beam transmitted through the beam splitter surface towards the first boundary surface of the beam splitter element, wherein the reflector surface reflects said first partial beam to a transparent portion of the second boundary surface of the beam splitter element forming a first exit of the beam splitter assembly for the at least one first outgoing beam, and into

a second partial beam reflected by the beam splitter surface towards a first boundary surface of the compensating element, and passing there through towards a second exit of the beam splitter assembly for the at least one second outgoing beam.

24. The beam splitter assembly according to claim 21, further comprising a second and a third beam splitter surface of the beam splitter element, and first and second compensating elements, wherein the at least one beam splitter element and the first and second compensating elements are disposed so that the incoming beam impinges thereon at a specified angle of incidence relative to a perpendicular of the first boundary surface, and wherein the beam splitter surface splits said incoming beam into

a first partial beam reflected by the beam splitter surface towards a first boundary surface of the first compensating element, the first partial beam thereafter exiting at a second boundary surface of the first compensating element forming a first exit of the beam splitter assembly for a first outgoing beam, into

a second partial beam transmitted through the beam splitter surface towards the second beam splitter surface of the beam splitter element wherein the second partial beam is further split into

a third partial beam that is reflected back towards a partial area of the first boundary surface, wherein the third beam splitter surface further splits said third partial beam into

a fifth partial beam passing through the third beam splitter surface to a second exit of the beam splitter assembly for a second outgoing beam, parallel to the first outgoing beam, and into

a fourth partial beam transmitted through the second beam splitter surface towards a first boundary surface of the second compensating element, passing through the second compensating element towards a second boundary surface forming a third exit of the beam splitter assembly for a third outgoing beam, and

a sixth partial beam reflected by the third beam splitter surface towards a transparent portion of the second boundary surface of the at least one beam splitter, forming a fourth exit of the beam splitter assembly for a fourth outgoing beam, which is parallel to the third outgoing beam.

25. The beam splitter assembly according to claim 21, further comprising first and second compensating elements, forming exits from the beam splitter assembly for first and second outgoing beams parallel to one another, and the at least one beam splitter element having a portion forming an exit from the at least one beam splitter element for a third outgoing beam which is also parallel to the first and second outgoing beams.

26. The beam splitter assembly according to claim 21, further comprising a retro-reflective reflector element arranged separately from the at least one beam splitter element and the at least one compensating element, said retro-reflective reflector element being adapted to reflect a beam that propagates from a beam splitter surface of the at least one beam splitter element back onto the beam splitter surface.

27. A beam splitter assembly for an interferometer adapted to split an incoming beam into at least one first outgoing beam and at least one second outgoing beam parallel to the at least one first beam, comprising:

at least one beam splitter element, each of the at least one beam splitter elements further comprising a transparent plate having two parallel boundary surfaces, a first of the two boundary surfaces having a portion functioning as an at least partially reflective reflector surface, and a second of the two boundary surfaces having a portion functioning as a beam splitter surface;

at least one compensating element disposed relative to the at least one beam splitter element so that the at least one first and second outgoing beams propagate parallel to one another, the at least one compensating element having dimensions adapted to provide a substantially identical optical path length in the at least one beam splitter element as in the at least one compensating element to the at least one first and second outgoing beams,

wherein the at least one beam splitter element and the at least one compensating element are disposed such that the incoming beam enters the at least one beam splitter element at a angle of incidence substantially equal to a Brewster angle, the angle relative to a perpendicular to the first boundary surface, and thereafter impinges on the beam splitter surface which splits the incoming beam into

a first partial beam reflected towards the first boundary surface, to the reflector surface which is adapted to further reflect said first partial beam towards a transparent portion of the second boundary surface forming a first exit of the beam splitter assembly for the at least one first outgoing beam, and into

a second partial beam transmitted towards a first boundary surface of the at least one compensating element, said first boundary surface of the at least one compensating element being adapted to direct the second partial beam to a second boundary surface of the at least one compensating element forming a second exit of the beam splitter assembly for the at least one second outgoing beam.

28. The beam splitter assembly according to claim 27, wherein a thickness of the compensating element is about twice a thickness of the beam splitter element.

29. A beam splitter assembly for an interferometer adapted to split an incoming beam into at least one first outgoing beam and at least one second outgoing beam parallel to the at least one first beam, comprising:

at least one beam splitter element, each of the at least one beam splitter elements further comprising a transparent plate having two parallel boundary surfaces, a first of the two boundary surfaces having a portion functioning as an at least partially reflective reflector surface, and a second of the two boundary surfaces having a portion functioning as a beam splitter surface;

at least one compensating element disposed relative to the at least one beam splitter element so that the at least one first and second outgoing beams propagate parallel to one another, the at least one compensating element having dimensions adapted to provide a substantially identical optical path length in the at least one beam splitter element as in the at least one compensating element to the at least one first and second outgoing beams; and

a second and a third beam splitter surface of the beam splitter element, and first and second compensating elements, wherein the at least one beam splitter element and the first and second compensating elements are disposed so that the incoming beam impinges thereon at a specified angle of incidence relative to a perpendicular of the first boundary surface, and wherein the beam splitter surface splits said incoming beam into

a first partial beam reflected by the beam splitter surface towards a first boundary surface of the first compensating element, the first partial beam thereafter exiting at a second boundary surface of the first compensating element forming a first exit of the beam splitter assembly for a first outgoing beam, into

a second partial beam transmitted through the beam splitter surface towards the second beam splitter surface of the beam splitter element, wherein the second partial beam is further split into

a third partial beam that is reflected back towards a partial area of the first boundary surface, wherein the third beam splitter surface further splits said third partial beam into

a fifth partial beam passing through the third beam splitter surface to a second exit of the beam splitter assembly for a second outgoing beam, parallel to the first outgoing beam, and into

a fourth partial beam transmitted through the second beam splitter surface towards a first boundary surface of the second compensating element, passing through the second compensating element towards a second boundary surface forming a third exit of the beam splitter assembly for a third outgoing beam, and

a sixth partial beam reflected by the third beam splitter surface towards a transparent portion of the second boundary surface of the at least one beam splitter, forming a fourth exit of the beam splitter assembly for a fourth outgoing beam, which is parallel to the third outgoing beam.

30. The beam splitter assembly according to claim 29, wherein the first and second outgoing beams are perpendicular to the third and fourth outgoing beams.

31. A beam splitter assembly for an interferometer adapted to split an incoming beam into at least one first outgoing beam and at least one second outgoing beam parallel to the at least one first beam, comprising:

at least one beam splitter element, each of the at least one beam splitter elements further comprising a transparent plate having two parallel boundary surfaces, a first of the two boundary surfaces having a portion functioning as an at least partially reflective reflector surface, and a second of the two boundary surfaces having a portion functioning as a beam splitter surface;

at least one compensating element disposed relative to the at least one beam splitter element so that the at least one first and second outgoing beams propagate parallel to one another, the at least one compensating element having dimensions adapted to provide a substantially identical optical path length in the at least one beam splitter element as in the at least one compensating element to the at least one first and second outgoing beams; and

first and second compensating elements, forming exits from the beam splitter assembly for first and second outgoing beams parallel to one another, and the at least one beam splitter element having a portion forming an exit from the at least one beam splitter element for a third outgoing beam which is also parallel to the first and second outgoing beams.