Intrusion detector

• US 5,712,622 A
• Filed: 01/18/1996
• Issued: 01/27/1998
• Est. Priority Date: 01/19/1995
• Status: Expired due to Term

• Current Assignee: Holo Ltd.
• Original Assignee: Holo Ltd.
• Inventors: Kosoburd, Tatiana, Blit, Shmuel, Kotlicki, Yaacov, Grossinger, Israel
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): Huang, Sihong
• Application Number:
  US08/588,380
• Time in Patent Office: 740 Days
• Field of Search: 340/555, 340/556, 250/353, 250/DIG. 1, 250/216, 250/226, 250/237 G, 359/566, 359/568, 359/569
• US Class Current: 340/555
• CPC Class Codes: G08B 13/193 using focusing means

Abstract

An infrared detector including a sensor which provides an output signal responsive to infrared radiation incident on a face thereof, and a diffractive optical element which directs a substantial portion of incident visible radiation away from the sensor and which has substantially no diffractive effect on incident infrared radiation.

Claims

1. An infrared detector comprising:

a sensor which provides an output signal responsive to infrared radiation incident on a face thereof; and

a diffractive optical element which diffractively directs a substantial portion of incident visible radiation away from the sensor and which has substantially no diffractive effect on incident infrared radiation.

2. A detector according to claim 1 and also comprising a lens which focuses infrared radiation on the sensor.

3. A detector according to claim 2 wherein the lens comprises a multi-radii Fresnel lens comprising a plurality of sets of spherical surfaces, each set of spherical surfaces having a different radius of curvature.

4. A detector according to claim 3 wherein the multi-radii Fresnel lens comprises a segmented Fresnel lens which provides the sensor with a segmented field of view, the segmented Fresnel lens including a grooved surface comprising:

a first plurality of spherical surfaces, closer to the center of the Fresnel lens, having a first radius of curvature; and

a second plurality of spherical surfaces, closer to the edge of the Fresnel lens, having a second radius of curvature different from the first radius of curvature.

5. A detector according to claim 2 wherein the diffractive optical element comprises a diffraction grating formed on a surface of the lens which receives the incident radiation.

6. A detector according to claim 2 wherein the diffractive optical element comprises a diffraction grating formed on a surface of the lens facing the sensor.

7. A detector according to claim 2 wherein the diffractive optical element comprises a diffraction grating formed on a substrate situated between the lens and the sensor.

8. A detector according to claim 2 wherein the diffractive optical element comprises a diffraction grating formed on a substrate and wherein the lens is situated between the substrate and the sensor.

9. A detector according to claim 1 and comprising a mirror.

10. A detector according to claim 9 wherein the mirror focuses infrared radiation on the sensor.

11. A detector according to claim 9 wherein the diffractive optical element comprises a diffraction grating formed on a surface of the mirror.

12. A detector according to claim 9 wherein the diffractive optical element comprises a diffraction grating formed on a separate substrate detached from said mirror.

13. A detector according to claim 1 wherein the diffractive optical element comprises a diffraction grating formed with a spacing of between approximately 1 micrometer and approximately 17 micrometers.

14. A detector according to claim 13 wherein the spacing is substantially constant.

15. A detector according to claim 13 wherein the spacing is varied in accordance with a predetermined design.

16. A detector according to claim 13 wherein the spacing is varied randomly.

17. A detector according to claim 1 wherein the diffractive optical element comprises a diffraction grating formed with an optical depth of between approximately 0.4 micrometers and approximately 1.0 micrometers.

18. A detector according to claim 17 wherein the optical depth is substantially constant.

19. A detector according to claim 17 wherein the optical depth is varied in accordance with a predetermined design.

20. A detector according to claim 17 wherein the optical depth is varied randomly.

21. A detector according to claim 1 wherein the diffractive optical element comprises a multi-directional diffraction grating.

22. A detector according to claim 1 wherein the diffractive optical element diffracts a substantial portion of incident visible radiation and is substantially transparent to incident infrared radiation.