Ladar systems with dynamic receiver filters

Patent metadata

Field	Value
Publication number	US-2018081045-A1
Application number	US-201514656533-A
Country	US
Kind code	A1
Filing date	Mar 12, 2015
Priority date	Mar 12, 2015
Publication date	Mar 22, 2018
Grant date	—

Abstract

LADAR systems and methods are disclosed. LADAR systems include a LADAR transmitter configured to emit a laser signal from a platform and a LADAR receiver configured to detect the laser signal returning from a target moving relative to the platform. The LADAR receiver includes a dynamic receiver filter with a receiver bandwidth (which may be about equal to the linewidth of the laser signal) and a tunable receiver center wavelength. The LADAR receiver is configured to adjust the receiver center wavelength to a wavelength that is Doppler-shifted due to the target velocity. Methods include transmitting a laser signal from a platform, returning the laser signal from a moving target, adjusting a dynamic receiver filter to a receiver center wavelength that is based upon the center wavelength of the returned laser signal (that includes a Doppler offset due to the relative velocity of the target), and receiving the returned laser signal.

First claim

1 . A method of detecting a LADAR signal, the method comprising:
transmitting a laser signal from a platform, wherein the laser signal has a transmitter center wavelength and a transmitter linewidth; returning the laser signal from a target that is moving relative to the platform with a target velocity by directing the laser signal toward the target, wherein the target velocity is a relative velocity of the target relative to the platform in a direction between the platform and the target, and wherein the laser signal returned from the target has a return center wavelength that is offset relative to the transmitter center wavelength by a Doppler offset due to the target velocity; adjusting a dynamic receiver filter to a receiver center wavelength that is based upon the return center wavelength; subsequent to the adjusting the dynamic receiver filter, filtering the laser signal returned from the target with the dynamic receiver filter to reject ambient light mingled with the laser signal returned from the target and to produce a filtered laser signal; and detecting the filtered laser signal to determine a distance between the platform and the target.

2 . The method of claim 1 , wherein the adjusting includes at least one of measuring, estimating, or determining the target velocity based upon at least one of measuring, estimating, or determining a velocity of the platform.

3 . The method of claim 1 , wherein the adjusting includes adjusting based on at least one of measuring, estimating, or determining the Doppler offset due to the target velocity.

4 . The method of claim 1 , wherein the adjusting includes adjusting the receiver center wavelength to about equal to the return center wavelength.

5 . The method of claim 1 , wherein the adjusting includes adjusting the receiver center wavelength to about equal to a sum of the transmitter center wavelength and the Doppler offset.

6 . The method of claim 1 , wherein the adjusting includes serially changing a center wavelength of the dynamic receiver filter to two or more values, measuring an intensity of the laser signal returned from the target through the dynamic receiver filter at each of the values of the center wavelength, and adjusting the receiver center wavelength to the center wavelength corresponding to a maximum of the intensities.

7 . The method of claim 6 , wherein the serially changing includes dithering the center wavelength within a range of values between a maximum Doppler-shifted wavelength and a minimum Doppler-shifted wavelength.

8 . The method of claim 1 , wherein the dynamic receiver filter has a receiver bandwidth that is less than the transmitter linewidth plus twice a magnitude of the Doppler offset.

9 . The method of claim 8 , wherein the receiver bandwidth is about equal to the transmitter linewidth.

10 . The method of claim 8 , wherein the receiver bandwidth is less than the transmitter linewidth plus 30 pm.

11 . The method of claim 1 , wherein a magnitude of the target velocity is at least 100 m/s.

12 . The method of claim 1 , further comprising determining the distance between the platform and the target based at least in part on the laser signal transmitted to the target and the laser signal returned from the target.

13 . A LADAR system comprising:
a LADAR transmitter configured to emit a laser signal from a platform, wherein the laser signal has a transmitter center wavelength and a transmitter linewidth, wherein the transmitter linewidth is less than 30 pm, and wherein the LADAR system is configured to cause the laser signal to return from a target that is moving relative to the platform with a target velocity of at least 100 m/s, wherein the target velocity is a relative velocity of the target relative to the platform in a direction between the platform and the target; and a LADAR receiver configured to detect the laser signal returning from the target to determine a distance between the platform and the target, wherein the LADAR receiver includes a dynamic receiver filter with a receiver center wavelength and a receiver bandwidth, wherein the receiver bandwidth is less than the transmitter linewidth plus 30 pm, wherein the LADAR receiver is configured to adjust the receiver center wavelength to a sum of the transmitter center wavelength and a Doppler offset due to the target velocity.

14 . The LADAR system of claim 13 , wherein the receiver bandwidth is about equal to the transmitter linewidth.

15 . The LADAR system of claim 13 , wherein a magnitude of the Doppler offset is at least 1 pm.

16 . The LADAR system of claim 13 , wherein the receiver center wavelength is tunable at least between the transmitter center wavelength minus an offset and the transmitter center wavelength plus the offset, and wherein the offset is at least 1 pm.

17 . The LADAR system of claim 13 , wherein the dynamic receiver filter includes at least one of an optical resonator, an etalon, an air-spaced etalon, a solid etalon, an angle-tuned etalon, a temperature-tuned etalon, a pressure-tuned etalon, a whispering gallery mode resonator, a distributed Bragg grating, a fiber Bragg grating, an absorptive filter, a colored glass filter, or an interference filter.

18 . The LADAR system of claim 13 , wherein the dynamic receiver filter includes a first dynamic receiver filter element and a second dynamic receiver filter element, and wherein a FWHM (full width at half maximum) of the first dynamic receiver filter element is greater than a FWHM of the second dynamic receiver filter element.

19 . The LADAR system of claim 18 , wherein the first dynamic receiver filter element has a static center wavelength and the second dynamic receiver filter element has a tunable center wavelength.

20 . The LADAR system of claim 18 , wherein the dynamic receiver filter includes a third dynamic receiver filter element, wherein a FWHM of the third dynamic receiver filter element is less than the FWHM of the second dynamic receiver filter element, and wherein the third dynamic receiver filter element has a tunable center wavelength.

Assignees

• Boeing Co

Inventors

• Gylys Vytas Thomas
• Cates Michael C
• Niksch Richard A
• Rodney Paul J
• Durkin Peter

Classifications

• G01S7/4912 Primary

  Receivers · CPC title

• G01S17/32

  using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated · CPC title

• G01S17/58

  Velocity or trajectory determination systems; Sense-of-movement determination systems · CPC title

• G01S7/497

  Means for monitoring or calibrating · CPC title

• G01S7/4816

  of receivers alone · CPC title