Magneto-optical input system for infrared detectors

• US 5,491,334 A
• Filed: 08/22/1994
• Issued: 02/13/1996
• Est. Priority Date: 08/22/1994
• Status: Expired due to Term

• Current Assignee: Grumman Aerospace Corporation (Northrop Grumman Corporation)
• Original Assignee: Grumman Aerospace Corporation (Northrop Grumman Corporation)
• Inventors: Gartenberg, Alvin, Durst, David I.
• Primary Examiner(s): Allen, Stephone B.
• Application Number:
  US08/294,724
• Time in Patent Office: 540 Days
• Field of Search: 250/225, 250/227.21, 250/227.23, 250/352, 250/338.1, 250/338.2, 359/280, 365/122
• US Class Current: 250/227.21
• CPC Class Codes: G01J 5/061 by controlling the temperature of the apparatus or parts thereof, e.g. using cooling means or thermostats

Abstract

A detector interface system communicates signals between an infrared detector element maintained in a cryogenic environment and associated signal processing circuitry maintained in a non-cryogenic environment. An optical modulator disposed within the cryogenic environment in electrical communication with the infrared detector element converts the electrical output of the infrared detector element into an optical output signal representative thereof. An optical demodulator disposed in the non-cryogenic environment converts the optical output signal of the optical modulator into an electrical signal. The optical demodulator is an electrical communication with the signal processing circuitry. An optical path from the optical modulator to the optical demodulator provides thermal isolation between the infrared detector element and its associated signal processing circuitry and minimizes detector bias so as to mitigate 1/f noise.

Claims

1. An input circuit for receiving an output of an infrared detector element maintained in a comparatively lower temperature environment and communicating that output to associated signal processing circuitry maintained in a comparatively higher temperature environment, the infrared detector element having an electrical output thereof, the input circuit comprising:

a) a magneto-optical modulator disposed in the comparatively lower temperature environment and in direct electrical communication with the infrared detector element, said magneto-optical modulator providing an optical output to communicate a signal representative of the electrical output of said infrared detector element to the signal processing circuitry in a noise-resistant manner; and

b) wherein placing said magneto-optical modulator in direct electrical communication with the infrared detector element minimizes heat generation in the comparatively lower temperature environment so as to mitigate 1/f noise.

2. The input circuit as recited in claim 1 wherein said magneto-optical modulator modulates polarization of the optical output signal thereof.

3. The input circuit as recited in claim 1 wherein said magneto-optical modulator comprises a multi-turn helical coil of wire wound around a ferromagnetic magneto-optical rod.

4. The input circuit as recited in claim 3 wherein said ferromagnetic magneto-optical rod comprises gallium doped YAG.

5. A detector interface system for communicating signals between an infrared detector element maintained in a comparatively lower temperature environment and associated signal processing circuitry maintained in a comparatively higher temperature environment, the infrared detector element having an electrical output thereof, the detector interface system comprising:

a) an optical modulator disposed in the comparatively lower temperature environment in electrical communication with the infrared detector element for converting the electrical output of the infrared detector element into an optical output signal representative thereof;

b) an optical demodulator disposed in the comparatively higher temperature environment for converting the optical output signal of the optical modulator into an electrical signal representative thereof, said optical demodulator being in electrical communication with the signal processing circuitry; and

c) an optical path from said optical modulator to said optical demodulator for facilitating optical communication therebetween;

d) wherein said optical path provides thermal isolation between the infrared detector element and signal processing circuitry and direct connection of the infrared detector element to the optical modulator mitigates 1/f noise.

6. The detector interface system as recited in claim 5 wherein:

a) said optical modulator comprises a first magneto-optical modulator; and

b) said optical demodulator comprises a second magneto-optical modulator.

7. The detector interface system as recited in claim 6 wherein at least one of said first and second magneto-optical modulators comprise a multi-turn helical coil of wire wound around a ferromagnetic magneto-optical rod.

8. The detector interface system as recited in claim 6 wherein said optical demodulator further comprises:

a) a current source in electrical communication with said second magneto-optical modulator so as to effect modulation of an optical signal communicated from said first magneto-optical modulator thereto; and

b) an optical sensor for determining a given state of modulation of the optical signal;

c) wherein the optical signal is demodulated by determining the amount of current required to change the modulation of the optical signal to the given state of modulation,

9. The detector interface system as recited in claim 8 wherein said optical sensor comprises a polarization filter and a photoelectric detector.

10. The detector interface system as recited in claim 9 wherein said optical demodulator further comprises a feedback servo loop configured to rotate the optical output signal of said optical modulator to a cross-polarized null of said optical sensor.

11. The detector interface system as recited in claim 7 wherein said ferromagnetic magneto-optical rod(s) comprise gallium doped YAG.

12. The detector interface system as recited in claim 5 wherein:

a) said optical modulator modulates polarization of the optical output signal thereof; and

b) said optical demodulator senses polarization of the optical output signal of said optical modulator.

13. The detector interface system as recited in claim 5 wherein said optical path comprises at least one optical fiber.

14. The detector interface system as recited in claim 5 further comprising a laser disposed in the comparatively lower temperature environment, said laser providing plane polarized light to said optical modulator.

15. A method for communicating signals between an infrared detector element maintained in a comparatively lower temperature environment and associated signal processing circuitry maintained in a comparatively higher temperature environment, the infrared detector element having an electrical output, the method comprising the steps of:

a) converting the electrical output of the infrared detector element into an optical output signal representative thereof via a magneto-optical modulator, said converting being performed within the comparatively lower temperature environment;

b) transmitting the optical output signal from the comparatively lower temperature environment to the comparatively higher temperature environment; and

c) converting the optical output signal into an electrical signal representative thereof, said converting being performed within the comparatively higher temperature environment.

16. The method as recited in claim 15 wherein the step of converting the electrical output of the infrared detector element into an optical output signal representative thereof comprises converting the electrical output of the infrared detector element into an optical output signal via a magneto-optical modulator comprising a ferromagnetic magneto-optical rod.

17. A method for facilitating the maintenance of a desired low temperature of an infrared detector element, the infrared detector element having an output, said method comprising the steps of:

a) electrically communicating the output of the infrared detector element directly from the infrared detector element to a magneto-optical modulator;

b) modulating the output of the magneto-optical modulator to provide an optical output representative of the electrical output of the infrared detector element; and

c) communicating the optical output of the magneto-optical modulator to signal processing circuitry disposed remotely from the infrared detector element;

d) wherein electrically communicating the output of the infrared detector element directly from the infrared detector element to the magneto-optical modulator minimizes heat generation proximate the infrared detector element.

18. The method recited in claim 17 wherein the step of modulating the output of the magneto-optical modulator comprises modulating the polarization of the optical output of the magneto-optical modulator.

19. The method as recited in claim 17 wherein the step of electrically communicating the output of the infrared detector element directly from the infrared detector element to the magnetic-optical modulator comprises communicating the output of the infrared detector element directly from the infrared detector element to a multi-turn helical coil of wire wound around a ferromagnetic magneto-optical rod.

20. The method as recited in claim 17 wherein the step of electrically communicating the output of the infrared detector element directly from the infrared detector element to a magneto-optical modulator comprises communicating the output of the infrared detector element directly from the infrared detector element to a ferromagnetic magneto-optical rod comprised of gallium doped YAG.