Modified compact 2f optical correlator

• US 5,016,976 A
• Filed: 03/30/1990
• Issued: 05/21/1991
• Est. Priority Date: 03/30/1990
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Makekau, Charles K., Fielding, Kenneth H., Horner, Joseph L.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/502,486
• Time in Patent Office: 417 Days
• Field of Search: 350/162.12, 350/162.13, 350/162.15, 364/822, 364/825
• US Class Current: 359/561
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: G06E 3/003 forming integrals of products, e.g. Fourier integrals, Laplace integrals, correlation integrals; for analysis or synthesis of functions using orthogonal functions

Abstract

A modified 2f Fourier transform optical correlator combines a collimation and first Fourier Transform lens into one thin lens. The resulting correlator thus utilizes one less lens relative to the unmodified 2f optical correlator.

Claims

1. In an optical correlation system comprising:

(a) first Fourier transform lens means for taking the Fourier transform of a first signal representing an input image and forming said Fourier transform at a first position along an optical axis;

(b) a filter located at said first position providing information obtained from a second signal which is to be correlated with said first signal;

(c) second Fourier transform lens means in optical alignment with said filter for taking the inverse Fourier transform of the product of the Fourier transform of said first signal, and said information of said second signal, and for forming said inverse Fourier transform at a second position along said optical axis, said inverse Fourier transform being substantially equivalent to the mathematical correlation function between said first signal and said second signal;

(d) input signal producing means for producing said first input signal behind said first Fourier transform lens to introduce a wavefront distortion quadratic phase term; and

(e) means for positioning said second Fourier transform lens means behind said filter, said second Fourier transform lens means having a focal length which removes said quadratic phase term from said wavefront while concurrently inverse Fourier transforming the disturbance behind the filter to produce a correlation signal at said second position;

(f) a collimating lens positioned in front of said first Fourier transform lens means for directing collimated coherent light thereat;

(g) the improvement comprising combining said collimating lens means with said Fourier transform lens means to produce a single Fourier transform lens means having a focal length about equal to f₅ where f₅ is determined by solving the equation 1/f₅ =1/f_c =1/f₁ ;

Where f_c equals the focal length of said collimating lens means and f₁ equals the focal length of said first Fourier transform lens means.

2. The improvement set forth in claim 1 wherein said single Fourier transform lens means consists essentially of a single simple thin lens.

3. The correlation system of claim 2 wherein said filter is a binary phase only filter.

4. The system of claim 2 wherein said second Fourier transform lens means is equivalent to a second and third thin lens in contact with one another and wherein the combined focal length of said second and third thin lenses is equal to the distance between said filter and said input signal producing means.

5. The correlation system of claim 4 wherein said filter is a binary phase only filter.

6. The system of claim 1 wherein said first and second Fourier transform lens means each consists essentially of a simple single element optical lens.

7. The correlation system of claim 6 wherein said filter is a binary phase only filter.

8. The system of claim 1 wherein said second Fourier transform lens means is equivalent to a second and third thin lens in contact with one another and wherein the combined focal length of said second and third thin lenses is equal to the distance between said filter and said input signal producing means.

9. The correlation system of claim 8 wherein said filter is a binary phase only filter.

10. The correlation system of claim 1 wherein said filter is a binary phase only filter.