Ladar system for detecting objects

• US 6,844,924 B2
• Filed: 06/28/2002
• Issued: 01/18/2005
• Est. Priority Date: 06/29/2001
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Ruff, William C., Shen, Paul H., Stann, Barry L.
• Primary Examiner(s): Gregory, Bernarr E.
• Assistant Examiner(s): Andrea, Brian K
• Application Number:
  US10/183,536
• Publication Number:
  US 20030076485A1
• Time in Patent Office: 935 Days
• Field of Search: 356 501- 515, 356/28.5
• US Class Current: 356/5.09
• CPC Class Codes: G01S 17/34 using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/491 Details of non-pulse systems

Abstract

A high range resolution ladar includes a chirp generator for producing a chirp signal waveform that is used by a laser diode to propagate a divergent laser light waveform. The reflected light signals from the target are directed to a self mixing detector that is coupled to the chirp generator where the responsivity of the detector varies in accordance with the chirp waveform for converting reflected light signals from the target to electrical signals and for mixing the converted electrical signal with the chirp waveform to produce an output electrical signal whose frequency is proportional to the range to the target. The self-mixing detector includes at least one detector having a semiconductor substrate and first and second electrodes deposited on the substrate and spaced from each other, wherein the first set of electrodes is connected to the chirp generator and the second set of electrodes is connected to a memory for storing a plurality of frames of image data.

Claims

1. A high range-resolution ladar, comprising:

a chirp generator for generating a chirp waveform;

a bias tee coupled to the chirp generator, a DC current source, and a semiconductor laser diode, the bias tee summing the chirp waveform with the DC current source to provide a current drive for the semiconductor laser diode with a bandwidth at least equal to the chirp waveform;

the semiconductor laser diode coupled to the bias tee, for receiving the current drive and for outputting a light signal toward a target; and

a self-mixing detector coupled to and driven by the chirp generator, where the responsivity of the detector is varied in accordance with the chirp waveform for converting the reflected light signal received from the target to an electrical signal and for mixing the converted electrical signal with the chirp waveform to produce an output electrical signal whose frequency is proportional to the range to the target.

2. The high range resolution ladar of claim 1, wherein the self-mixing detector comprises at least one detector having a substrate, a first set of electrodes deposited on the substrate, and a second set of electrodes deposited on the substrate and spaced from the first set of electrodes, wherein the first set of electrodes is connected to the chirp generator and the second set of electrodes is connected to the a memory for storing a plurality of frames of image data.

3. The high range resolution ladar of claim 2, wherein the self-mixing detector comprises a plurality of detectors arranged in a two dimensional array.

4. A high range-resolution ladar comprising:

a chirp generator for generating a chirp waveform;

a bias tee coupled to the chirp generator, a DC current source, and a semiconductor laser diode, the bias tee summing the chirp waveform with the DC current source to generate a current drive for the semiconductor laser diode;

the semiconductor laser diode coupled to the bias tee for receiving the current drive and for producing an output light signal toward a target; and

a self-mixing detector coupled to and driven by the chirp generator, where the responsivity of the detector varies in accordance with the chirp waveform for receiving and mixing a reflected signal from the target with the chirp waveform to output an electrical signal whose frequency is proportional to the range to the target.

5. The high range-resolution ladar of claim 4, wherein the modulated electrical signal comprises a product of the reflected light signal from the target and the chirp waveform, the modulated electrical signal having a difference frequency signal whose frequency is proportional to range to the target.

6. The high range-resolution ladar of claim 5, further comprising:

a wideband RF power amplifier, coupled to the chirp generator, for receiving and modulating the chirp waveform and outputting an amplified chirp waveform for summing in the bias tee.

7. The high range-resolution ladar of claim 6, further comprising:

an impedance matching circuit, coupled to the wideband RF amplifier, for matching the driving impedance of the wideband RF power amplifier to the semiconductor laser diode over a range of the amplified chirp signal frequency such that light beam intensity from the semiconductor laser diode is highly amplitude modulated (AM) and the peak intensity of the light signal is constant as a function of chirp frequency.

8. The high range-resolution ladar of claim 4, wherein the self-mixing detector comprises a plurality of detectors arranged in an array.

9. The high range ladar of claim 8, wherein each detector comprises a substrate, a first set of electrodes deposited on the substrate, and a second set of electrodes deposited on the substrate and spaced from the first set of electrodes.

10. The high range ladar of claim 9, wherein the substrate is formed of a semiconductor material and the first and second sets of electrodes are metal.

11. The high range ladar of claim 10, wherein the semiconductor substrate material includes gallium arsenide.

12. The high range-resolution ladar of claim 4, wherein the self-mixing detector comprises at least one detector, wherein each detector comprises a substrate, a first set of electrodes deposited on the substrate, and a second set of electrodes deposited on the substrate and spaced from the first set of electrodes, and wherein the substrate is formed of a semiconductor material and the first and second sets of electrodes are metal.

13. The high range-resolution ladar of claim 4, further comprising:

a trigger circuit for generating a trigger signal that triggers and synchronizes the chirp generator and the self-mixing detector.

14. The high range-resolution ladar of claim 4, further comprising:

a memory, coupled to the self-mixing detector, for storing a plurality of frames of image data.

15. The high range-resolution ladar of claim 14, further comprising:

computing means, coupled to the memory, for performing a discrete fourier transform on the plurality of frames of image data and outputting results of the discrete fourier transform as a 3-D image file.

16. The high range resolution ladar of claim 4, wherein the self-mixing detector comprises a substrate, a first set of electrodes deposited on the substrate, and a second set of electrodes deposited on the substrate and spaced from the first set of electrodes, wherein the first set of electrodes is connected to the chirp generator and the second set of electrodes is connected to the a memory for storing a plurality of frames of image data.

17. A self mixing detector for use with a ladar system including a chirp generator for generating a chirp waveform, a DC current source, a semiconductor laser diode, and means coupled to the chirp generator and the DC current source and the laser diode to provide a current drive for the laser diode to produce an output light signal directed toward a target, comprising:

a detector coupled to and driven by the chirp generator, where the responsivity of the detector is varied in accordance with the chirp waveform for converting reflected light signals received from the target to an electrical signal and for mixing the converted electrical signal with the chirp waveform to produce an output electrical signal whose frequency is proportional to the range to the target.

18. The self mixing detector of claim 17, wherein the light signal is one of the group of ultraviolet, visible, near infrared, and infrared light.