Optics: measuring and testing – By light interference – Holography
Reexamination Certificate
2000-07-17
2002-10-22
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Holography
C356S515000
Reexamination Certificate
active
06469791
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical systems. More specifically, the present invention relates to systems and methods testing for optical systems.
2. Description of the Related Art
End-to-end interferometric testing of optical systems is problematic relative to the problem of testing the surface of an optical element. Interferometric testing can be performed from the object side of the optical system to the image side. To achieve end-to-end testing, a retro-reflective ball is typically placed in the image plane so that light traversing the optical system under test is reflected from the ball and returns to the interferometer. This test can be performed from the image side to the object side by focusing the interferometer at the image point and returning the beam with a plane mirror.
In many cases, it would be desirable to test the optical system from the image side rather than the object side.
In addition, current optical system testing does not generally rely on the results of a single test performed with respect to a single point source. On the contrary, it is currently common in the art to test optical systems with respect to a number of point sources.
There are generally two techniques for generating these point sources. The first is to physically lock the interferometer and a reference sphere, which generates the point source, with respect to one another. The interferometer-reference sphere combination is then moved to a series of predetermined locations relative to the optical system under test.
Alternatively, the reference sphere can be made to move to all the required “image points” to be tested. Yet another alternative involves the use of an array of lenses to generate a plurality of point sources.
One major problem with the latter technique is that the plurality of lenses needed to generate the multiple point sources physically interfere with one another, e.g., overlap, in fast systems.
What is needed is a system that facilitates testing of an optical system from the image side. More specifically, what is needed is a mechanism for generating multiple point sources of light to facilitate multipath testing of an optical system using an interferometer disposed in image space. Most specifically, what is needed is a mechanism for generating multiple point sources for testing of the optical system using an interferometer located in image space wherein each point source is generated without overlap in the optical elements of the mechanism. Ideally, the mechanism would permit optimization of the aperture generating each point source.
SUMMARY OF THE INVENTION
The need in the art is addressed by the system and method of the present invention. The inventive system is an interferometric testing system employing a multiple-aperture hologram. In an illustrative embodiment, the inventive optical testing system includes an interferometer which outputs a planar light beam and analyzes a reflected selected light beam. A multiple-aperture hologram generates N image points in an image plane of the optical system responsive to the planar light beam. A retro-reflector reflects a selected one of N light beams corresponding to the N image points transmitted by the optical system back through the optical system to generate the selected light beam.
According to one aspect of the present invention, the multiple-aperture hologram includes N apertures generating the N image points and one of the N apertures overlaps at least one other of the N apertures. According to another aspect of the invention, the multiple-aperture hologram intersects a plane perpendicular to an axis defined by the centers of the interferometer and the retro-reflector.
From an alternative perspective, the present invention provides an optical testing system that permits testing from the image side of the optical system under test. The inventive system includes a first device for generating a planar light beam and analyzing a selected light beam with respect to a reference light beam. A second device is included for generating the reference light beam. A third device is included for generating N image points in an image plane of an optical system responsive to the planar light beam. A fourth device is provided for reflecting a selected one of N light beams corresponding to the N image points transmitted by the optical system back through the optical system and thereby generate the selected light beam.
The optical testing system of the present invention advantageously provides an interferometric testing system which minimizes the need for system realignment between testing events with respect to individual point sources generated by the multiple-aperture hologram.
REFERENCES:
patent: 5815268 (1998-09-01), LaFleur
Connolly Patrick
Lanzen, Jr. Glenn H.
Raytheon Company
Schubert William C.
Turner Samuel A.
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