Ladar Transmitter with Optical Field Splitter/Inverter

• US 20170307876A1
• Filed: 07/07/2017
• Published: 10/26/2017
• Est. Priority Date: 02/18/2016
• Status: Active Grant

• Current Assignee: AEye, Inc.
• Original Assignee: AEye, Inc.
• Inventors: Dussan, Luis Carlos, Demmer, David R., Stockton, John, Steinhardt, Allan, Cook, David
• Granted Patent: US 10,042,159 B2
• Time in Patent Office: Days
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 7/4814 of transmitters alone
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G02B 27/126 The splitting element being a prism or prismatic array, including systems based on total internal reflection
• CPC Class Codes: G02B 27/14 operating by reflection only
• CPC Class Codes: G02B 27/141 using dichroic mirrors

Abstract

Disclosed herein is a scanning ladar transmitter that employs an optical field splitter/inverter to improve the gaze characteristics of the ladar transmitter on desirable portions of a scan area. Also disclosed is the use of scan patterns such as Lissajous scan patterns for a scanning ladar transmitter where a phase drift is induced into the scanning to improve the gaze characteristics of the ladar transmitter on desirable portions of the scan area. Also disclosed is a compact beam scanner assembly that includes an ellipsoidal reimaging mirror.

Claims

1. A method comprising:

scanning a first mirror to a plurality of first mirror scan positions;

scanning a second mirror to a plurality of second mirror scan positions;

while the first and second mirrors are scanning, transmitting a ladar pulse, via the first and second mirrors, toward an optical field splitter/inverter;

splitting and inverting, via the field splitter/inverter, a scan area defined by the scanning of the first and second mirrors, wherein the splitting and inverting directs the transmitted ladar pulse toward a range point within the split and inverted scan area.

2. The method of claim 1 wherein the first mirror scanning step comprises scanning the first mirror at a sinusoidal frequency to define a periodic scan pattern along a first axis within the scan area;

wherein the second mirror scanning step comprises scanning the second mirror to define another scan pattern along a second axis within the scan area, wherein the scanning of the first and second mirrors defines the scan area.

3. The method of claim 2 wherein the scanning of the first and second mirrors defines a target scan area within the split and inverted scan area for a ladar transmitter that transmits the light pulses, the method further comprising:

positioning the field splitter/inverter such that the target scan area of the ladar transmitter moves relatively slower in a middle section of the split and inverted scan area than it does at outer sections of the split and inverted scan area.

4. The method of claim 1 wherein the field splitter/inverter comprises a triangular prism shape.

5. The method of claim 1 wherein the first mirror scanning step comprises scanning the first mirror at a resonant frequency.

6. The method of claim 5 wherein the resonant frequency is a first resonant frequency, and wherein the second mirror scanning step comprises scanning the second mirror at a second resonant frequency to define a Lissajous scan pattern for the scanning first and second mirrors.

7. A beam scanner apparatus for a ladar transmitter, the apparatus comprising:

a first scanable mirror configured to scan to a plurality of scan positions;

a second scanable mirror positioned optically downstream from the first scanable mirror, the second scanable mirror configured to scan to a plurality of scan positions, wherein the scan positions of the first and second scanable mirrors define where the ladar transmitter is targeted within a scan area; and

an optical field splitter/inverter positioned to split and invert the scan area defined by the first and second scanable mirrors.

8. The apparatus of claim 7 wherein the optical field splitter/inverter is positioned optically downstream from the first and second scanable mirrors.

9. The apparatus of claim 8 wherein the first scanable mirror is further configured to scan to a plurality of scan positions with respect to a first axis of the scan area;

wherein the second scanable mirror is further configured to scan to a plurality of scan positions with respect to a second axis of the scan area;

wherein the apparatus further comprises;

a beam scanner controller configured to drive the first and second scanable mirrors to scan along the first and second axes to define a scan pattern for targeting by the ladar transmitter within the scan area, wherein the beam scanner controller is further configured to drive the first and second scanable mirrors such that at least one of the first scanable mirror and the second scanable mirror scans at a sinusoidal frequency.

10. The apparatus of claim 9 wherein the field splitter/inverter is positioned such that the targeting of the ladar transmitter moves relatively slower in a middle section of the split and inverted scan area than it does at outer sections of the split and inverted scan area.

11. The apparatus of claim 8 wherein the field splitter/inverter comprises a triangular prism shape.

12. The apparatus of claim 11 wherein the triangular prism shape includes a first triangular face and a second triangular face at opposite ends of the triangular prism shape, wherein the triangular prism shape further includes a first side, a second side, and a third side, wherein the first, second, and third sides connect to the first and second triangular faces;

wherein at least a portion of an interior of the first, second, and third sides comprise mirrors; and

wherein the triangular prism shape is arranged and positioned to receive light pulses from the first and second scanable mirrors and reflect the received light pulses off the interior mirrors to achieve the split and inverted scan area.

13. The apparatus of claim 7 further comprising:

an ellipsoidal reflector positioned optically between the first scanable mirror and the second scanable mirror.

14. The apparatus of claim 7 wherein the optical field splitter/inverter comprises a beam splitter in combination with a positioning of resonant mirrors as the first and second scanable mirrors such that (1) the beam splitter is positioned to receive incident ladar pulses from a source and split the received ladar pulses to the resonant mirrors, and (2) the resonant mirrors are configured to scan a left and right angular interval.

15. A scanner apparatus comprising:

a first scanable mirror;

a second scanable mirror;

a lens that is positioned optically upstream from the first scanable mirror; and

an ellipsoidal mirror that is positioned optically between the first scanable mirror and the second scanable mirror.

16. The apparatus of claim 15 wherein the first scanable mirror, the second scanable mirror, and the ellipsoidal mirror are positioned such that, with respect to an ellipsoid, (1) the first scanable mirror has a central region that is positioned at a first focus of the ellipsoid, (2) the second scanable mirror has a central region that is positioned at a second focus of the ellipsoid, and (3) the ellipsoidal mirror lies along the ellipsoid at a position that is optically between the first scanable mirror and the second scanable mirror.

17. The apparatus of claim 16 wherein the ellipsoid has a major axis and an axis of symmetry along the major axis, and wherein the ellipsoidal mirror position is off the axis of symmetry.

18. The apparatus of claim 16 wherein the ellipsoidal mirror position is such that a ray fan from the first scanable mirror is reflected by the ellipsoidal mirror such that an intersection of all rays in a ray fan reflected by the ellipsoidal mirror lie on a plane which contains the central region of the second scanable mirror.

19. The apparatus of claim 15 wherein the first scanable mirror and the second scanable mirror comprise MEMS mirrors.

20. The apparatus of claim 15 wherein the first scanable mirror and the second scanable mirror are of equal size.

21. The apparatus of claim 15 wherein the apparatus includes a single reimaging mirror that is optically between the first scanable mirror and the second scanable mirror, wherein the ellipsoidal mirror serves as the single reimaging mirror.

22. The apparatus of claim 15 wherein the lens is adapted and positioned to provide a focal point for incident light, wherein the focal point lies between the first scanable mirror and the ellipsoidal mirror.

23. The apparatus of claim 15 wherein the ellipsoidal mirror and the lens are adapted and positioned to serve in aggregate as an afocal lensing system.

24. The apparatus of claim 15 wherein the second scanable mirror has a central tilt axis, wherein the 3D ellipsoid exhibits a horizontal width, wherein a distance A corresponds to half of the horizontal width, and wherein a distance C corresponds to a distance from a center of the ellipsoid to the central tilt axis of the second scanable mirror;

wherein a coplanar angle (CPA) for the first scanable mirror is defined such that

25. The apparatus of claim 15 wherein the first scanable mirror has a title angle α

, wherein the second scanable mirror has a central tilt axis, wherein the 3D ellipsoid exhibits a horizontal width, wherein a distance A corresponds to half of the horizontal width, and wherein a distance C corresponds to a distance from a center of the ellipsoid to the central tilt axis of the second scanable mirror;

wherein a coplanar angle (CPA) for the first scanable mirror is defined such that

26. The apparatus of claim 15 further comprising:

a beam scanner controller configured to drive (1) the first scanable mirror along a first axis, and (2) scan the second scanable mirror along a second axis to define a scan pattern within a scan area, wherein the beam scanner controller is further configured to drive the first and second scanable mirrors such that at least one of the first scanable mirror and the second scanable mirror scans at a sinusoidal frequency.

27. The apparatus of claim 15 further comprising:

an optical field splitter/inverter positioned optically downstream from the first and second scanable mirrors to split and invert a scan area defined by the first and second scanable mirrors.

28. The apparatus of claim 15 further comprising:

a light source positioned optically upstream from the lens, wherein the light source is configured to transmit light through the lens onto the first scanable mirror, whereupon the first scanable mirror reflects the light toward the ellipsoidal mirror, and whereupon the ellipsoidal mirror reflects the light toward the second scanable mirror.

29. The apparatus of claim 15 wherein the first and second scanable mirrors are positioned in a side-by-side arrangement.

30. A light steering method comprising:

transmitting light toward a lens;

the lens passing the transmitted light to a first scanning mirror;

the first scanning mirror reflecting the transmitted light toward an ellipsoidal mirror;

the ellipsoidal mirror reflecting the transmitted light toward a second scanning mirror; and

the second scanning mirror reflecting the transmitted light.