Optical interferometer

• US 4,027,976 A
• Filed: 04/21/1975
• Issued: 06/07/1977
• Est. Priority Date: 05/13/1974
• Status: Expired due to Term

• Current Assignee: Jenoptik JENA GmbH (Jenoptik AG)
• Original Assignee: Jenoptik JENA GmbH (Jenoptik AG)
• Inventors: Amon, Georg
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Clark, Conrad
• Application Number:
  US05/570,048
• Time in Patent Office: 778 Days
• Field of Search: 356/106, 356/107, 356/108, 356/109, 356/110, 356/111, 356/112, 356/113
• US Class Current: 356/4.09
• CPC Class Codes: G01B 9/02081 simultaneous quadrature detection, e.g. by spatial phase shifting

Abstract

An optical interferometer, particularly for use in measurements of length, employs a light transmissive splitting cube which is provided with three beam splitting faces in parallel to each other. A light bundle entering the splitting cube is split into two partial light bundles.

After passage of an optical path within the splitting cube both partial light bundles interfere with each other and produce an interference pattern. Light portions of said interference pattern interfere with each other after having passed separate light paths. Both interference patterns so produced are 90° phase-shifted relative to each other. This phase shift permits a unique determination of direction in variations of length.

Claims

1. An optical interferometer for producing two interference patterns 90°

phase-shifted relative to each other, particular for use in length measurements, comprising

a light source emitting a light bundle,

a collimator for spreading said light bundle,

a partially transmissive optical body arranged in the path of said light bundle,

said partially transmissive optical body having a first beam splitting partially silvered face, inclinedly arranged relative to the incident light bundle,

a second and a third beam splitting and partially silvered face, substantially in parallel with and equally spaced relative to said first beam-splitting partialy silvered face,

said first beam splitting partially silvered face splitting up said light bundle into a first passed-on partial light bundle and into a first reflected partial light bundle,

a measuring reflector located in the path of said first passed-on partial light bundle,

said measuring reflector back-reflecting the incident first passed-on partial light bundle to said partially transmissive optical body parallel, however, in lateral displacement to said first passed-on partial light bundle,

said measuring reflector being displaceable along the path of said first passed-on partial light bundle,

a reference reflector located in the path of said first reflected partial light bundle,

said reference reflector reflecting the incident first reflected partial light bundle back to said partially transmissive optical body in parallel, however, laterally displaced to said first reflected partial light bundle,

said first passed-on partial light bundle and said first reflected partial light bundle, after reflection, being fused at said first beam splitting partially silvered face of said partially transmissive optical body and producing a first interference pattern,

said first beam splitting partially silvered face splitting up the impinging fused partial light bundles into a second passed-on partial light bundle passed through said face, and into a second reflected partial light bundle reflected thereupon,

the second, reflected partial light bundle being deviated at said second beam splitting partially silvered face, and fusing with the passed through second passed-on partial light bundle, being deviated at said third beam splitting partially silvered face, thereby producing a second interference pattern at said first beam-splitting partially silvered face,

said first interference pattern and said second interference pattern being 90°

phase-shifted relative to each other,

and means for evaluation of said interference patterns, phase-shifted relative to each other.

2. An optical interferometer as claimed in claim 1, wherein said partially transmissive optical body is a splitting cube constituted of two equilateral right angle prisms cemented with each other at their bases, which are parallel to each other, and one of which being provided with a partically transmissive layer, and wherein each of said right angle prisms is separated by a partially transmissive separating layer in parallel to said base faces, into two light-transmissive bodies.

3. An optical interferometer as claimed in claim 2, wherein said partially transmissive optical body is a splitting cube constituted of two right angle prisms which are cemented to each other at their base faces, being substantially parallel to each other, and wherein a partially transmissive layer is applied to each of said base faces in such a manner that a transmissive half of the one base face is opposed by a non-transmissive half of the other base face.

4. An optical interferometer as claimed in claim 1, wherein said first, second and third beam splitting face is embodied as a semi-silvered layer.

5. An optical interferometer as claimed in claim 1, wherein said first, second and third beam splitting face are inclined by 45°

with respect to the angle of incidence of said light bundle.

6. Optical interferometer as claimed in claim 1, wherein said measuring reflector and said reference reflector are right angle roof-edge prisms selected from light transmissive material, the base faces of which are at right angles to the direction of the incident light, wherein said measuring reflector is displaceable in the direction of the incident said first passed-on partial light bundle.

7. An optical interferometer as claimed in claim 1, wherein said means for evaluating the two interference patterns which are 90°

phase-shifted relative to each other, comprise

a photo electric detector for receiving the light from said first interference pattern,

a further photo electric detector for receiving the light from said second interference pattern and a phase sensitive counter for evaluating the electrical output signals from the photo electric detectors.