Time delay beam formation

• US 5,202,776 A
• Filed: 12/12/1991
• Issued: 04/13/1993
• Est. Priority Date: 12/12/1991
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Essex Corporation (Northrop Grumman Corporation)
• Inventors: Lafuse, James L., Gesell, Leslie H.
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): Lester, Evelyn A.
• Application Number:
  US07/806,697
• Time in Patent Office: 488 Days
• Field of Search: 359/17, 359/20, 359/561, 359/305, 359/306, 359/310, 359/287, 359/578, 359/577, 356/345
• US Class Current: 359/17
• CPC Class Codes: G02F 1/212 Mach-Zehnder type
• CPC Class Codes: G02F 2/002 using optical mixing
• CPC Class Codes: G02F 2201/20 delay line
• CPC Class Codes: G06E 3/005 using electro-optical or opto-electronic means
• CPC Class Codes: H01Q 3/2676 Optically controlled phased array

Abstract

Optical systems are disclosed which are capable of generating and rapidly changing time delays of electrical signals for true time delay beam formation and beam steering. The systems utilize an interferometer configuration. A first optical modulator and a Fourier transform lens define a Fourier transform plane in a first leg of the interferometer. In a second leg of the interferometer, a second optical modulator provides beam steering to a prism stack, which produces a set of plane reference waves having a range of orientations required to generate a desired range of time delays. Preferably the optical modulators are acousto optic Bragg cells. Alternatively, a holographic optic element could be used in place of the prism stack.

Claims

1. A system for generating at least one time delay signal from an input signal, comprising:

a source of coherent light,

beam splitter means for splitting the coherent light into a first leg and a second leg,

first modulation means associated with the first leg for modulating the coherent light with a modulation signal and for s the modulated coherent light into a spectrum, wherein the first modulation means defining a Fourier transform plane,

second modulation means associated with the second leg for modulating the coherent light with a steering signal,

optical element means associated with the second leg for receiving an input beam from the second modulation means at an incidence angle and for producing a plurality of reference waves having a plurality of orientations that are a function of the incidence angle,

an array of photodiodes arranged substantially in the Fourier transform plane of the first modulation means for detecting interference between the spectrum associated with the first leg and the reference waves associated with the second leg and for producing an output signal corresponding to the detected interference,

whereby each photodiode produces an output signal corresponding to the modulation signal delayed by a time factor that is a function of the angle of incidence of the reference wave on the photodiode.

2. The system as in claim 1 wherein each of the photodiodes in the array of photodiodes is oriented and proportioned for capturing the full spectrum of the modulated light signal illuminating the photodiode.

3. The system as in claim 1 wherein the optical element means comprises a plurality of prisms.

4. The system as in claim 1 wherein at least one of the first modulation means and the second modulation means comprises a Bragg cell.

5. The system as in claim 1 wherein the first modulation means comprises a Fourier transform lens.

6. The system as in claim 1 wherein the optical element means comprises a holographic optic element.

7. The system as in claim 3 wherein each one of the plurality of prisms is associated with a corresponding one of the plurality of photodiodes, and wherein each one of the plurality of photodiodes is illuminated by a reference wave output of a corresponding one of the plurality of prisms.

8. A system for generating at least one time delay signal from an input signal, comprising:

a source of coherent light,

first modulation means for modulating the coherent light with a modulation signal and for producing a plane wave output having an angular orientation, the first modulation means having a plurality of points and defining an image plane and a Fourier transform plane, the angular orientation of the plane wave output corresponding to the position of points in the first modulation means,

an array of photodiodes arranged substantially in the image plane of the first modulation means,

optical mapping means for optically mapping points in the first modulation means onto the array of photodiodes, the optical mapping means comprising;

second modulation means for controlling the angular orientation of the plane wave output of the first modulation means with respect to a first axis,

third modulation means for controlling the angular orientation of the plane wave output of the first modulation means with respect to a second axis, the first axis and the second axis being substantially perpendicular and the second modulation means and the third modulation means each defining an image plane,

a optical element, arranged substantially in the Fourier transform plane of the first modulation means and substantially in the image plane of the second modulation means and the third modulation means, for mapping plane waves at the optical element into points on the photodiode array,

whereby the mapping of plane waves at the optical element into points on the photodiode array is determined by the angular orientation of the plane waves at the optical element, and

whereby each photodiode produces an output signal corresponding to the modulation signal delayed by a time factor.

9. The system as in claim 8 comprising:

beam splitter means for splitting the coherent light into a first leg and a second leg, the second leg providing a reference signal at the photodiode array for heterodyne detection, whereby the output signals of the photodiode array are a function of the modulation signal.

10. The system as in claim 8 wherein at least one of the first modulation means, the second modulation means and the third modulation means comprises a Bragg cell.

11. The system as in claim 8 wherein the optical element comprises a volume hologram.

12. A system for time delaying a plurality of signals and for summing the plurality of delayed signals, comprising:

a source of coherent light,

beam splitter means for splitting the coherent light into a first leg and a second leg,

first multi-channel modulation means associated with the first leg for modulating the coherent light with a plurality of modulation signals and for separating the modulated coherent light into a spectrum, the first multi-channel modulation means defining a Fourier transform plane,

second modulation means associated with the second leg for modulating the coherent light with a steering signal,

optical element means associated with the second leg for receiving an input beam from the second modulation means at an incidence angle and for producing a plurality of reference waves having a plurality of orientations that are a function of the incidence angle,

an array of photodiodes arranged substantially in the Fourier transform plane of the first multi-channel modulation means for detecting interference between the spectrum associated with the first leg and the reference waves associated with the second leg and for producing an output signal corresponding to the detected interference,

whereby each photodiode produces an output signal corresponding to the modulation signal delayed by a time factor that is a function of the angle of incidence of the reference wave on the photodiode.

13. The system as in claim 12 wherein the optical element means comprises a plurality of prisms.

14. The system as in claim 12 wherein at least one of the first modulation means and the second modulation means comprises a Bragg cell.

15. The system as in claim 12 wherein the first modulation means comprises a Fourier transform lens.