Time delay beam formation

• US 5,623,360 A
• Filed: 02/13/1995
• Issued: 04/22/1997
• 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: Gesell, Leslie H., Turpin, Terry M.
• Primary Examiner(s): Epps, Georgia Y.
• Assistant Examiner(s): Robbins, Thomas
• Application Number:
  US08/387,414
• Time in Patent Office: 799 Days
• Field of Search: 359/17, 359/20, 359/561, 359/305, 359/306, 359/310, 359/287, 359/578, 359/577, 356/345, 250/550, 250/227.12
• US Class Current: 359/287
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02F 1/212 Mach-Zehnder type
• CPC Class Codes: G02F 1/33 Acousto-optical deflection devices circuit or control arrangements therefor G02F1/113
• 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 and for signal processing applications. The systems utilize an interferometer configuration. A first optical modulator in a first leg of the interferometer is used to modulate coherent light with the signal to be delayed. 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 stack of lens pairs or diffractive optical elements or a holographic optic element may be used in place of the prism stack. The modulated optical signal from the first leg interferes on an array of photodiodes with the reference waves from the second leg. The resulting electrical signals out of the photodiodes are delayed replicas of the signals driving the optical modulator in the first leg.

Claims

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

A) a source of coherent light,

B) divider means for dividing the light into at least a first leg and a second leg,

C) modulation means for modulating light in the first leg by a signal,

D) optical isolator means for preventing light in the first leg from being reflected back towards the source of coherent light,

E) signal channelizer means for dividing modulated light in the first leg into a plurality of spectral components,

F) signal control means for dividing light in the second leg into a plurality of paths and for shifting the phase of light in each of the plurality of paths to thereby generate a plurality of phase-shifted optical reference signals, each one of the plurality of phase-shifted optical reference signals corresponding to one of the plurality of spectral components,

G) detection means for detecting each one of the plurality of phase-shifted optical reference signals together with a corresponding one of the spectral components and for generating an output signal, and

H) summation means for summing output signals generated by the detection means.

2. The system of claim 1, comprising at least one single mode optical fiber for guiding light between at least two of the elements A-H.

3. The system of claim 1, wherein at least one of the divider means, the signal channelizer means, and the signal control means comprises an optical coupler.

4. The system of claim 1, wherein the modulation means comprises an electro-optic phase modulator.

5. The system of claim 1, wherein the modulation means comprises an electro-optic Mach-Zender interferometer modulator.

6. The system of claim 1, wherein the signal channelizer means comprises a plurality of optical resonant cavities.

7. The system of claim 6, wherein at least one of the optical resonant cavities defines a first end and a second end and wherein a mirror is positioned substantially at at least one of the first end and the second end.

8. The system of claim 7, wherein the mirror comprises a Bragg reflection grating.

9. The system of claim 6, wherein at least one of the plurality of optical resonant cavities defines an optical path length and further comprising adjustment means for adjusting the optical path length of the optical resonant cavity.

10. The system of claim 9, wherein the cavity includes electro-optic material and defines an index of refraction, and wherein the adjustment means comprises means for applying an electrical voltage across the electro-optic material in the cavity to modify the index of refraction of the cavity.

11. The system of claim 10, wherein the adjustment means comprises means for controlling optical amplification in the cavity.

12. The system of claim 6 wherein at least one of the plurality of optical resonant cavities defines an input end and wherein the system further comprises means for reusing light reflected from the input end of the optical cavity.

13. The system of claim 12, wherein the means for reusing light reflected from the input end of the optical cavity comprises at least one multiple-port optical circulator.

14. The system of claim 1, wherein the detection means comprises an array of photodiodes.

15. The system of claim 1, wherein the means for shifting the phase of light in each of the plurality of paths comprises an electro-optic phase modulator.

16. The system of claim 15, wherein the phase modulator comprises means for generating one signal which provides a different phase shift to light in each of the plurality of paths.

17. The system of claim 15, wherein the phase modulator comprises means for independently controlling the phase of light in each of the plurality of paths.