Compact economical lidar system

• US 20040119838A1
• Filed: 04/29/2003
• Published: 06/24/2004
• Est. Priority Date: 04/30/2002
• Status: Active Grant

• Current Assignee: Arete Associates
• Original Assignee: Arete Associates
• Inventors: Redman, Brian, Fetzer, Gregory, Griffis, Andrew, Gelbart, Asher, Sitter, David
• Granted Patent: US 7,830,442 B2
• Time in Patent Office: Days
• US Class Current: 348/215.1
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/486 Receivers
• CPC Class Codes: G01S 7/4861 Circuits for detection, sampling, integration or read-out
• CPC Class Codes: G01S 7/4865 Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487

Abstract

A lidar pulse is time resolved in ways that avoid costly, fragile, bulky, high-voltage vacuum devices—and also costly, awkward optical remappers or pushbroom layouts—to provide preferably 3D volumetric imaging from a single pulse, or full-3D volumetric movies. Delay lines or programmed circuits generate time-resolution sweep signals, ideally digital. Preferably, discrete 2D photodiode and transimpedance-amplifier arrays replace a continuous 1D streak-tube cathode. For each pixel a memory-element array forms range bins. An intermediate optical buffer with low, well-controlled capacitance avoids corruption of input signal by these memories.

Claims

1. A lidar system comprising:

means for generating a measurement signal that is at least one-dimensional, corresponding to a received at-least-one-dimensional lidar-beam pulse;

means for time-resolving the measurement signal, said resolving means comprising;

multiple memory elements for receiving and holding successive portions of the measurement signal respectively,

digital means for forming a digital sweep signal defining multiple digital states corresponding to the respective memory elements, and

means for applying the digital sweep signal to control distribution of the successive measurement-signal portions into the respective memory elements; and

means for reading the measurement-signal portions from the memory elements.

2. The system of claim 1, wherein:

the forming means comprise a logic circuit generating a series of digital pointers addressing the memory elements respectively.

3. The system of claim 2, wherein:

the memory elements comprise a dynamic RAM or other capacitive array receiving the measurement signal-portions substantially directly from the distribution controlled by the digital pointers.

4. The system of claim 2, further comprising:

multiple buffer switches transferring the successive measurement-signal portions to the multiple memory elements respectively;

each buffer switch having a respective enable terminal actuated by a respective one of the digital pointers.

5. The system of claim 4, further comprising:

multiple electrooptical converters respectively receiving the successive measurement-signal portions from the buffer switches, respectively, and in response generating corresponding optical signals; and

multiple optoelectronic converters receiving the corresponding optical signals and in response generating new corresponding measurement-signal portions for application to the multiple memory elements.

6. The system of claim 5, wherein:

the electrooptical converters are selected from the group consisting of VCSELs, LEDs, and organic LEDs.

7. The system of claim 5, wherein:

the optoelectronic converters are selected from the group consisting of CMOS elements, organic phase-shift molecular devices, and a printed-circuit stack of thin-film devices.

8. The system of claim 1, wherein:

the forming means comprise a tapped delay line having multiple taps addressing the multiple memory elements respectively.

9. The system of claim 8, wherein:

the memory elements comprise a dynamic RAM or other capacitive array receiving the measurement signal-portions substantially directly from the distribution controlled by the delay-line taps.

10. The system of claim 8, further comprising:

multiple buffer switches transferring the successive measurement-signal portions to the multiple memory elements respectively;

each buffer switch having a respective enable terminal actuated by a respective one of the delay-line taps.

11. The system of claim 10, further comprising:

multiple electrooptical converters respectively receiving the successive measurement-signal portions from the buffer switches, respectively, and in response generating corresponding optical signals; and

multiple optoelectronic converters receiving the corresponding optical signals and in response generating new corresponding measurement-signal portions for application to the multiple memory elements.

12. The system of claim 11, wherein:

the electrooptical converters are selected from the group consisting of VCSELs, LEDs, and organic LEDs.

13. The system of claim 11, wherein:

the optoelectronic converters are selected from the group consisting of CMOS elements, organic phase-shift molecular devices, and a printed-circuit stack of thin-film devices.

14. The system of claim 1, wherein:

the forming means comprise a delay line that comprises the memory elements;

the delay line itself has clock signals serving as the digital sweep signal; and

the delay line responds to the clock signals by successively advancing the received successive measurement-signal portions into the delay line.

15. The system of claim 14, wherein:

the memory elements comprise a dynamic RAM or other capacitive array receiving the measurement signal-portions substantially directly from the distribution controlled by the clock signals.

16. The system of claim 14, wherein:

the delay line is a shift register;

the memory elements are successive positions in the shift register itself; and

the reading means comprise parallel circuits for reading plural measurement-signal portions substantially simultaneously from the shift register.

17. The system of claim 14, further comprising:

an analog-to-digital converter, digitizing the successive measurement-signal portions for application to the delay line.

18. The system of claim 1, for detecting and ranging objects;

said system further comprising;

means for projecting an at-least-one-dimensional light pulse toward such objects; and

means for receiving an at-least-one-dimensional reflected light pulse from such objects;

wherein the generating means comprise means for generating said measurement signal in response to the received light pulse.

19. A lidar system comprising:

means for generating a measurement signal corresponding to a received lidar-beam pulse;

means for time-resolving the measurement signal;

multiple electrooptical converters respectively receiving time-resolved measurement-signal portions from the resolving means, and in response forming new corresponding optical signals; and

means for reading the measurement-signal portions as the new corresponding optical signals from the electrooptical converters.

20. The system of claim 19, wherein:

the electrooptical converters are LEDs.

21. The system of claim 19, wherein:

the electrooptical converters are organic LEDs.

22. The system of claim 19, wherein:

the electrooptical converters are VCSELs.

23. The system of claim 22, further comprising:

multiple optoelectronic converters receiving the corresponding new optical signals from the VCSELs and in response forming new corresponding measurement-signal portions for readout by the reading means.

24. The system of claim 23, wherein:

the optoelectronic converters are CMOS elements.

25. The system of claim 23, wherein:

the optoelectronic converters are optical phase-shift molecules.

26. The system of claim 23, wherein:

the optoelectronic converters are printed-circuit stacks of thin-film devices.

27. The system of claim 19, further comprising:

multiple optoelectronic converters receiving the new corresponding optical signals and in response forming new corresponding measurement-signal portions for readout by the reading means.

28. The system of claim 27, wherein:

the optoelectronic converters are CMOS elements.

29. The system of claim 19, wherein:

the resolving means comprise multiple buffer switches directing the time-resolved measurement-signal portions to the multiple electrooptical converters, respectively;

the multiple buffer switches comprise respective enable terminals actuated by a synchronous enable signal.

30. The system of claim 29, wherein:

the synchronous enable signal is substantially in controlled-delay synchronism with the lidar-beam pulse.

31. The system of claim 29, wherein:

before said synchronous enable signal, each enable terminal is connected to receive a bias input that holds the respective electrooptical converter just within a quiescent state.

32. The system of claim 31, wherein:

readout from the respective electrooptical converter is terminated by another synchronous signal after a time interval allowing for collection of the time-resolved measurement-signal portion from that respective electrooptical converter.

33. The system of claim 19, for detecting and ranging objects;

said system further comprising;

means for projecting an at-least-one-dimensional light pulse toward such objects; and

means for receiving an at-least-one-dimensional reflected light pulse from such objects;

wherein the generating means comprise means for generating said measurement signal in response to the received light pulse.

34. A lidar system comprising:

means for generating an at-least-one-dimensional measurement signal corresponding to an at-least-one-dimensional received lidar-beam pulse;

means for time-resolving the measurement signal;

multiple memory elements, comprising a dynamic RAM or other capacitive array, respectively receiving and holding time-resolved measurement-signal portions substantially directly from the resolving means; and

means for reading the held measurement-signal portions from the memory elements.

35. The system of claim 34, further comprising:

multiple buffer switches transferring the time-resolved measurement-signal portions from the resolving means substantially directly to the multiple memory elements respectively;

each buffer switch having a respective enable terminal actuated by the resolving means.

36. The system of claim 35, for detecting and ranging objects;

said system further comprising;

means for projecting an at-least-one-dimensional light pulse toward such objects; and

means for receiving an at-least-one-dimensional reflected light pulse from such objects;

wherein the generating means comprise means for generating said measurement signal in response to the received light pulse.

37. A lidar system comprising:

means for generating a measurement signal corresponding to a received lidar-beam pulse;

a delay line that accepts successive portions of the measurement signal;

means, within the delay line, for advancing successively accepted signal portions farther into the delay line; and

means for reading multiple measurement-signal portions substantially simultaneously from multiple positions along the delay line.

38. The system of claim 37, further comprising:

multiple memory elements receiving the measurement-signal portions substantially directly from the multiple positions along the delay line.

39. The system of claim 38, wherein:

the multiple memory elements take the form of a dynamic RAM or other capacitive array.

40. The system of claim 37, wherein:

the delay line is a shift register;

the memory elements receive the successive measurement-signal portions from successive stages of the shift register; and

the reading means comprise parallel circuits for reading plural measurement-signal portions substantially simultaneously from the shift register to the memory elements.

41. The system of claim 40, further comprising:

an analog-to-digital converter, digitizing the successive measurement-signal portions for application to the shift register.

42. The system of claim 40, wherein:

the analog-to-digital converter is a plural-bit device; and

the shift register is a plural-bit device.

43. The system of claim 40, wherein:

the shift register is a CMOS device.

44. The system of claim 37, wherein:

the delay line is a sample-and-hold delay line.

45. The system of claim 37, further comprising:

multiple buffer switches transferring the measurement-signal portions from the delay line substantially directly to the multiple memory elements respectively;

each buffer switch having a respective enable terminal actuated by a read signal after generation of the measurement signal is substantially complete.

46. The system of claim 37, for detecting and ranging objects;

said system further comprising;

means for projecting a light pulse toward such objects; and

means for receiving a reflected light pulse from such objects;

wherein the generating means comprise means for generating said measurement signal in response to the received light pulse.

47. A method for making three-dimensional images of a volume and features therein, using a two-dimensional array of multiple discrete photosensitive detectors and electronic circuitry connected with said detectors;

said method comprising the steps of;

directing a two-dimensional lidar pulse, reflected from the volume and features, to the array of multiple discrete photosensitive detectors;

generation of a corresponding two-dimensional array of multiple discrete electronic signals by the detectors;

passing the entire resulting array of signals from the photosensitive detectors to the electronic circuitry; and

operating the electronic circuitry to time-resolve the entire array of signals, generating a three-dimensional electronic image of the features.

48. The method of claim 47, wherein:

the operating step comprises generating the entire three-dimensional electronic image of the features from substantially a single lidar pulse.

49. The method of claim 47, further comprising the step of:

before the directing step, projecting a two-dimensional lidar pulse toward the volume and features, to create said reflected two-dimensional lidar pulse.

50. The method of claim 47, further comprising the step of:

after the operating step, using the three-dimensional image as a three-dimensional representation of the features in the volume.

51. The method of claim 50, wherein the using step comprises:

first storing the three-dimensional electronic image; and

later recovering the stored image for later use as said three-dimensional representation of the features.

52. A system for forming a three-dimensional image of a volume and features therein;

said system comprising;

a two-dimensional array of multiple discrete photodetectors receiving a two-dimensional lidar pulse reflected from such volume and features, and in response generating a two-dimensional array of corresponding discrete electronic signals; and

a two-dimensional array of multiple discrete electronic circuits connected to receive the array of signals from the detector array;

wherein the circuits comprise means for time-resolving the entire array of signals, to generate from said pulse a three-dimensional electronic image of the features.

54. The system of claim 52, further comprising:

the photodetectors comprise avalanche photodiodes (APDs).

55. The system of claim 52, wherein:

the photodetectors comprise positive intrinsic negative (PIN) photodiodes.

56. The system of claim 52, wherein:

the photodetectors comprise indium gallium arsenide detectors.

57. The system of claim 52, wherein:

the photodetectors comprise a charge-coupled device (CCD) array.

58. The system of claim 52, wherein:

the electronic circuits comprise a two-dimensional array of transimpedance amplifiers (TIAs) connected to receive the signal array from the detectors and to drive the time-resolving means.

59. The system of claim 52, wherein:

the electronic circuits comprise a two-dimensional array of operational amplifiers configured for low-noise transimpedance signal gain, and connected to receive the signal array from the detectors and drive the time-resolving means.

60. The system of claim 52, wherein the electronic circuits comprise:

a two-dimensional array of transmission lines connected to receive the signal array from the detectors, respectively; and

a two-dimensional array of microwave amplifiers fed by the transmission lines, respectively;

said transmission lines being connected to drive the time-resolving means.

61. The system of claim 52, wherein the time-resolving means comprise, for handling successive segments of the electronic signal from each detector:

a respective array of buffer amplifiers;

a respective array of time-controlled switches connected to actuate the buffer amplifiers.

62. The system of claim 61, further comprising:

a respective array of programmable logic circuits generating time-base control signals to operate the switches.

63. The system of claim 61, further comprising:

a respective array of delay lines generating time-base control signals to operate the switches.

64. The system of claim 52, wherein the time-resolving means comprise, for handling the electronic signal from each detector:

a respective array of vertical-cavity surface-emitting lasers (VCSELs) sampling successive segments of the electronic signal from each detector; and

a respective array of range-bin memory elements connected to receive and integrate signal samples from the VCSELs.

65. The system of claim 52, further comprising:

a handheld portable case enclosing and carrying substantially the entire photodetector array and the electronic circuits.

53. The system of claim 53, further comprising:

an optical source projecting a two-dimensional lidar pulse toward the volume and features, to create said reflected two-dimensional lidar pulse.