Projectile guidance system including a compact semi-active laser seeker with immersed filter stack and field lens

• US 8,188,411 B2
• Filed: 10/21/2009
• Issued: 05/29/2012
• Est. Priority Date: 10/21/2009
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: McCarthy, Patrick L.
• Primary Examiner(s): GREGORY, BERNARR E
• Application Number:
  US12/582,915
• Publication Number:
  US 20110089286A1
• Time in Patent Office: 951 Days
• Field of Search: 244 31- 319, 244 32- 33, 89/11.1, 342 52- 56, 342 61- 66, 343/700.R, 343/725, 250/200, 250/201.1, 250/203.1, 250/203.2, 250/203.3, 250/203.6, 250/336.1, 250/338.1, 250/353
• US Class Current: 244/3.16
• CPC Class Codes: F41G 7/008 Combinations of different guidance systems
• CPC Class Codes: F41G 7/2246 Active homing systems, i.e. comprising both a transmitter and a receiver
• CPC Class Codes: F41G 7/2253 Passive homing systems, i.e. comprising a receiver and do not requiring an active illumination of the target
• CPC Class Codes: F41G 7/226 Semi-active homing systems, i.e. comprising a receiver and involving auxiliary illuminating means, e.g. using auxiliary guiding missiles
• CPC Class Codes: F41G 7/2286 using radio waves
• CPC Class Codes: F41G 7/2293 using electromagnetic waves other than radio waves
• CPC Class Codes: F42B 15/01 Arrangements thereon for guidance or control steering arrangements F42B10/60; aircraft flight control B64C; guidance systems other than those installed aboard F41G7/00, F41G9/00; locating by use of radio or other waves G01S; flight control in general G05D1/00; computer aspects G06]
• CPC Class Codes: G01S 3/784 using a mosaic of detectors
• CPC Class Codes: G02B 3/0068 arranged in a single integral body or plate, e.g. laminates or hybrid structures with other optical elements G02B5/1885, G02B17/002, G02B30/27 take precedence

Abstract

A compact SAL seeker for a projectile guidance system comprises an optical sub-assembly to focus incident electro-magnetic radiation (EMR) such that target bearing in object space is mapped to a spatial irradiance in image space and a detector sub-assembly to generate at least one guidance signal in response to the position of the centroid of the focused EMR. The optical sub-assembly includes an integrated filter stack of a primary optical element, a spreader, a filter and secondary optical element in which at least one and typically both of the spreader and filter are immersed within the optical media of the stack. The detector sub-assembly may include a field lens in which the detector is immersed. Immersion reduces the number of “air-to-glass” interfaces, hence improves optical throughput. The detector sub-assembly may be integrally formed with a mounting bracket adapted to mate with mounting features on the optical sub-assembly to provide a self-aligned seeker.

Claims

1. A guidance system, comprising:

a non-imaging optical system to focus incident electro-magnetic radiation (EMR) in a detection band including at least one wavelength in a range of 0.35 microns to 15 microns, comprising;

a first optical element having a first side and a second side, wherein the first side is a first lens element configured to focus incident EMR;

a spreader configured to spatially homogenize EMR transmitted through the optical system;

a filter configured to reject EMR including wavelengths outside the detection band; and

a second optical element having a first side and a second side, wherein the second side is a second lens element configured to control the aberration characteristics of the EMR transmitted through the optical system;

said first optical element, spreader, filter and second optical element optically bonded together in an integrated filter stack having only a first air-to-glass interface at the first side of the first optical element and a second air-to-glass interface at the second side of the second optical element, and

an irradiance detector coupled to the optical system and configured to generate at least one guidance signal in response to the spatial displacement of the centroid of the focused incident EMR in the detection band.

2. The guidance system of claim 1, wherein the first lens element comprises one of a positively powered lens, an aspheric positively powered lens, a Fresnel lens formed on a positively powered surface and a Fresnel lens formed on a generally planar surface.

3. The guidance system of claim 1, wherein the second lens element comprises an aspheric lens.

4. The guidance system of claim 3, wherein the second lens comprises the aspheric lens formed on a positively powered surface.

5. The guidance system of claim 1, wherein the spreader comprises a diffuser.

6. The guidance system of claim 1, wherein the spreader comprises an array of lenslets.

7. The guidance system of claim 6, wherein each said lenslet has a rectangular shape.

8. The guidance system of claim 1, wherein the second side of the first optical element and the first side of the second optical element are generally planar, further comprising a generally planar optical substrate having a first side that supports the spreader and a second side that supports the filter.

9. The guidance system of claim 8, wherein the spreader faces the second side of the first optical element.

10. The guidance system of claim 8, wherein the spreader comprises a diffuser coating on the first side of the optical substrate and the filter comprises a filter coating on the second side of the optical substrate.

11. The guidance system of claim 1, wherein the second side of the first optical element and the first side of the second optical element are generally planar and bonded together, said spreader and filter on opposite sides of the second optical element.

12. The guidance system of claim 11, wherein the spreader faces the second side of the first optical element and the filter is at the second air-to-glass interface.

13. The guidance system of claim 1, wherein the spreader comprises an array of rectangularly-shaped lenslets positioned at the second side of the first optical element.

14. The guidance system of claim 1, further comprising:

a detector assembly, comprising;

a third optical element having a first side and a second side, wherein the first side is a field lens element and the second side is generally planar, and

said detector, said detector mounted on the generally planar second side of said third optical element facing the optical system.

15. The guidance system of claim 14, further comprising:

a mounting bracket that mounts the integrated filter stack to the detector assembly, said third optical element integrally formed with said mounting bracket and said second optical element comprising mounting features to mate with said mounting bracket.

16. A guidance system, comprising:

a non-imaging optical system to focus incident electro-magnetic radiation (EMR) in a detection band including at least one wavelength in a range of 0.35 microns to 15 microns, comprising;

a first optical element having a first side and a second side, wherein the first side is a first lens element configured to focus incident EMR and the second side is generally planar;

a filter including a generally planar substrate having a first side that comprises a diffuser coating to spatially homogenize EMR transmitted through the optical system and a second side that comprises a filter coating to reject EMR including wavelengths outside the detection band; and

a second optical element having a first side and a second side, wherein the first side is generally planar and second side is a second lens element configured to control the aberration characteristics of the EMR transmitted through the optical system, said first optical element, filter and second optical element optically bonded together in an integrated filter stack having only a first air-to-glass interface at the first side of the first optical element and a second air-to-glass interface at the second side of the second optical element; and

a detector assembly, comprising;

a third optical element having a first side and a second side, wherein the first side is a field lens element and the second side is generally planar; and

an irradiance detector mounted on the generally planar second side of said third optical element facing the integrated filter stack and configured to generate at least one guidance signal in response to the spatial displacement of the centroid of the focused incident EMR in the detection band.

17. A guidance system, comprising:

a non-imaging optical system to focus incident electro-magnetic radiation (EMR) in a detection band including at least one wavelength in a range of 0.35 microns to 15 microns, comprising;

a first optical element having a first side and a second side, wherein the first side is a first lens element configured to focus incident EMR and the second side is generally planar;

an array of rectangular-shaped lenslets to spatially homogenize EMR transmitted through the optical system;

a filter to reject EMR including wavelengths outside the detection band; and

a second optical element having a first side and a second side, wherein second side is a second lens element configured to control the aberration characteristics of the EMR transmitted through the optical system, said first optical element, array of rectangularly-shaped lenslets, filter and second optical element optically bonded together in an integrated filter stack having only a first air-to-glass interface at the first side of the first optical element and a second air-to-glass interface at the second side of the second optical element; and

a detector assembly, comprising;

a third optical element having a first side and a second side, wherein the first side is a field lens element and the second side is generally planar; and

a irradiance detector mounted on the generally planar second side of said third optical element facing the integrated filter stack and configured to generate at least one guidance signal in response to the spatial displacement of the rectangularly-shaped centroid of the focused incident EMR in the detection band.

18. The guidance system of claim 17, wherein the array of rectangularly-shaped lenslets are bonded to the second side of the first optical element, said filter positioned at between the second side of the first optical element and the first side of the second optical element.

19. A guidance system, comprising:

an optical sub-assembly to focus incident electro-magnetic radiation (EMR) in a detection band including at least one wavelength in a range of 0.35 microns to 15 microns, comprising;

a first optical element having a first side and a second side, wherein the first side is a first lens element configured to focus incident EMR;

a spreader configured to spatially homogenize EMR transmitted through the optical system;

a filter configured to reject EMR including wavelengths outside the detection band; and

a second optical element having a first side and a second side, wherein the second side is a second lens element configured to control the aberration characteristics of the EMR transmitted through the optical system, said second lens element formed with mounting features;

said first optical element, spreader, filter and second optical element optically bonded together in an integrated filter stack having only a first air-to-glass interface at the first side of the first optical element and a second air-to-glass interface at the second side of the second optical element; and

a detector sub-assembly comprising;

a third optical element having a first side and a second side, wherein the first side is a field lens element;

a mounting bracket integrally formed with said third optical element and mated with the mounting features formed in said second lens element; and

an irradiance detector coupled to the optical system and configured to generate at least one guidance signal in response to the spatial displacement of the centroid of the focused incident EMR in the detection band.

20. The guidance system of claim 19, wherein said first, second and third optical element and said mounting bracket all comprise the same plastic material.

21. The guidance system of claim 19, wherein the second side of the third optical element is generally planar, said detector mounted on said generally planar second side.

22. The guidance system of claim 19, wherein the spreader comprises an array of rectangularly-shaped lenslets that spatially homogenize the EMR and produce a rectangularly-shaped centroid of focused EMR on the detector.

23. The guidance system of claim 19, wherein the second side of the first optical element and the first side of the second optical element are generally planar, further comprising a generally planar optical substrate having a first side that supports the spreader and a second side that supports the filter.