Phased array of computer generated holograms for waveform or surface measurement

Patent metadata

Field	Value
Publication number	US-8941837-B1
Application number	US-201313799748-A
Country	US
Kind code	B1
Filing date	Mar 13, 2013
Priority date	Mar 13, 2013
Publication date	Jan 27, 2015
Grant date	Jan 27, 2015

Abstract

An apparatus for testing an optical surface comprising an array of holograms. The array includes a plurality of individual holograms arranged in an M×N format, in which M is the number of rows and N is the number of columns in the array. The array of holograms is positioned between the optical surface and a wavefront sensor. The array of holograms reflects a reference beam back to the wavefront sensor, and transmits a test beam to the optical surface. The array of holograms also receives the test beam reflected from the optical surface and transfers the test beam back to the wavefront sensor.

First claim

What is claimed:

1. An apparatus for testing an optical surface comprising:
an array of holograms, the array including a plurality of individual holograms arranged in an M×N format, in which M is the number of rows and N is the number of columns in the array, and
the array of holograms positioned between the optical surface and a wavefront sensor,
wherein the array of holograms reflects a reference beam back to the wavefront sensor, and transmits a test beam to the optical surface, and
the array of holograms receives the test beam reflected from the optical surface and transfers the test beam back to the wavefront sensor.

2. The apparatus of claim 1 wherein
the array of holograms includes length and width dimensions, and
the length dimension includes M holograms of sufficient number to extend a radial dimension of the optical surface, and
the width dimension includes N holograms, wherein N is at least two rows.

3. The apparatus of claim 1 wherein
each row is staggered with respect to each adjacent row, and
a hologram in a first row is positioned between two holograms in an adjacent second row, forming the stagger between the first and second row.

4. The apparatus of claim 1 wherein
each hologram includes a layer having a pattern of arcs of a circle, and
a pattern of arcs in one hologram is phased with a pattern of arcs in an adjacent hologram.

5. The apparatus of claim 1 further including:
a collimating lens for receiving a beam of light emitted from the wavefront sensor, and collimating the beam toward the array of holograms.

6. The apparatus of claim 5 further including:
a diverger for diverging the beam of light emitted from the wavefront sensor, and
transmitting the diverged beam of light toward the collimating lens.

7. The apparatus of claim 1 wherein
the wavefront sensor emits a beam of light of a predetermined field-of-view (FOV), and
the FOV has a footprint area sized smaller than, or similar to an area formed by the array of holograms.

8. The apparatus of claim 7 further including:
a linear translational device for moving the FOV of the beam across a radial extent of the optical surface, and
a rotational device for rotating the optical surface,
wherein the translational device and the rotational device are configured to position the FOV of the beam across an entire area of the optical surface.

9. The apparatus of claim 1 wherein
each hologram includes opposing surfaces, and
a layer on one surface includes a pattern of arcs of a circle, and
a layer on the opposing surface includes a wedge for reducing ghosting effect.

10. The apparatus of claim 1 wherein one of the following is true:
the array of holograms is shaped to form a convex surface to match a convex surface of the optical surface, and
the array of holograms is shaped to form a concave surface to match a concave surface of the optical surface.

11. The apparatus of claim 1 further including:
a rigid frame having two ends,
wherein one end includes an M×N array of openings, in which each opening is configured to receive an individual hologram in the array of holograms, and
another end includes at least one opening configured to receive a hologram having a pattern configured for alignment of the rigid frame to the optical surface.

12. The apparatus of claim 1 wherein
the wavefront sensor includes a Fizeau interferometer and a Twyman-Greene interferometer.

13. The apparatus of claim 1 wherein
the wavefront sensor includes a camera for imaging an interference pattern formed by the reference beam and the test beam.

14. An apparatus for testing an optical surface comprising:
an array of holograms, the array including a plurality of individual holograms arranged in a two-dimensional matrix format; and
at least a portion of the array of holograms is illuminated by an incident beam from a wavefront sensor positioned above the array; wherein
the array of holograms modifies the incident beam to a reference beam and reflects back the reference beam to the wavefront sensor; and further modifies the incident beam to a test beam impinging on the optical surface positioned below the array of holograms.

15. The apparatus in claim 14 wherein
the array of holograms is calibrated for a plurality of diffractions orders using at least one of a Fizeau interferometry or a Twyman-Greene interferometry.

16. The apparatus of claim 14 wherein
each hologram includes at least one surface consisting of a plurality of auxiliary patterns for aligning the optical surface with the array, in addition to a pattern of arcs.

17. The apparatus of claim 14 wherein
at least two individual holograms have at least two different sized wedges with predetermined angles for bending the incident beam toward the optical surface.

18. The apparatus of claim 14 wherein
a row of holograms with respect to an adjacent row of holograms in the two-dimensional matrix is at least aligned or staggered.

19. The apparatus of claim 14 is further configured to test an optical system including an optical assembly.

20. The apparatus of claim 14 wherein
the portion of the array being illuminated corresponds to a predetermined field of view (FOV) set by the wavefront sensor.

21. A method for testing an optical surface comprising the steps of:
directing an incident beam from a wavefront sensor toward an array of holograms, the array including a plurality of individual holograms arranged in a two-dimensional matrix format;
illuminating at least a portion of the array of holograms;
modifying the incident beam by the array of holograms to produce a reference beam and a test beam;
reflecting the reference beam from the array of holograms to the wavefront sensor; and
impinging the test beam on the optical surface and reflecting the test beam back to the wavefront sensor.

22. The method of claim 21 further includes a step of mapping the optical surface using interferences between the reference and the test beams.

23. The method of claim 21 further includes a step of calibrating the array of holograms for a plurality of diffraction orders.

Assignees

• Exelis Inc

Inventors

• Olczak Eugene
• Merle Cormic
• Burdick Greg

Classifications

• G01B9/021 Primary

  using holographic techniques · CPC title

• G02B5/32

  Holograms used as optical elements · CPC title

• G01M11/0271

  by using interferometric methods · CPC title

• G01B9/02039

  by matching the wavefront with a particular object surface shape · CPC title

• G01M11/005

  Testing of reflective surfaces, e.g. mirrors · CPC title