Low power laser sensing

Patent metadata

Field	Value
Publication number	US-9869756-B2
Application number	US-201414898446-A
Country	US
Kind code	B2
Filing date	Jun 19, 2014
Priority date	Jun 19, 2013
Publication date	Jan 16, 2018
Grant date	Jan 16, 2018

Abstract

The presently disclosed subject matter includes a laser system and a respective method of detecting a signal reflected from a target illuminated by a modulated CW light source configured to generate a modulated laser signal at a predefined modulation frequency. A signal comprising true laser signal portions reflected from said target, and noise is received; the signal is filtered for selecting laser signal portions at a modulation frequency band; and the true signal portions in the signal are detected, if the energy at the modulation frequency band is greater than a given threshold.

First claim

The invention claimed is:

1. A method of detecting a signal reflected from a target, the method comprising:
receiving light signals by sampling continuous wave (CW) input signals at a sampling rate selected to be greater than a frequency corresponding to predefined frequency bands used for signal modulation, and generating a plurality of samples; and
processing said plurality of samples, said processing including:
applying filtering to said plurality of samples for dividing said plurality of samples into different frequency bands during a given time window; and
analyzing the divided samples and determining the energy integrated at frequency bands including the energy integrated at a modulation frequency and the energy integrated at frequencies different from the modulation frequency;
determining a threshold as a function between the energy integrated at frequencies different from the modulation frequency and the energy integrated at the modulation frequency; and
applying said threshold to the divided samples, thereby detecting true signal portions reflected from said target corresponding to the modulation frequency band greater than said determined threshold.

2. The method according to claim 1 wherein said filtering applied to the plurality of samples is performed with the help of a digital filter.

3. The method according to claim 2 wherein the digital filter is a Fast Fourier filter.

4. The method according claim 1 wherein the signal is received by a 4 quarters laser sensor, each quarter is associated with a respective processing channel, wherein said filtering is performed in each of the processing channels for signals received at the respective quarter, the method further comprising:
determining a direction to a spot illuminated by the laser signal based on the distribution of the energy at the modulation frequency band across the 4 quarters of the sensor.

5. The method according claim 1 , wherein said filtering applied to the plurality of samples is performed with an anti-aliasing filter; the sampling rate being greater than a band-limit of the anti-aliasing filter.

6. The method according to claim 1 , further comprising:
upon receiving a laser signal with a given intensity,
detecting true signal portions based on signal intensity if the given intensity of the signal is greater than a predefined threshold; otherwise
detecting the true signal portions based the energy at the modulation frequency band.

7. The method according to claim 1 , further comprising:
summing energy of signals received in at least each pair of adjacent quarters, thereby generating 4 intermediate processing channels; and
performing said filtering on in each of the intermediate processing channels.

8. The method according to claim 1 , further comprising:
summing energy of signals received in all quarters, thereby generating a fifth intermediate processing channel; and
performing said filtering on the fifth processing channel.

9. A laser sensor unit operable for detecting a signal reflected from a target illuminated by a modulated CW light source configured to generate a laser signal modulated at a predefined modulation frequency, the laser sensor unit comprising:
a sensor head associated with at least one processing channel, the sensor head being operable to receive light input comprising true signal portions reflected from said target, and noise; said at least one processing channel including:
a sampler configured to sample the light input being received with a sampling rate which is greater than a frequency corresponding to predefined frequency bands used for signal modulation, and thereby generating a plurality of samples;
an energy integration module configured to process the plurality of samples and divide the samples into different frequency bands and integrate energy of the divided samples at said different frequency bands during a given time window, said energy integrated at different frequency bands including energy integrated at the modulation frequency and energy integrated at frequencies different from the modulation frequency; and
an energy threshold detector configured for processing said energy integrated at said different frequency bands for determining a threshold as a function between the energy integrated at frequencies different from the modulation frequency and the energy integrated at the modulation frequency, and applying the determined threshold to thereby detect the true signal portions in the signal, corresponding to the modulation frequency band greater than said threshold.

10. The laser sensor unit according to claim 9 is a 4 quarters laser sensor, each quarter being connected to a respective processing channel, wherein said integration is performed in each of the processing channels for signals received at the respective quarter, the laser sensor further comprising a target detection unit configured to determine a direction to a spot illuminated by the laser signal based on the distribution of the integrated energy at the modulation frequency band across the 4 quarters of the sensor.

11. The laser sensor unit according to claim 10 wherein each processing channel comprises an anti-aliasing filter configured to filter the received signal at the respective quarter in order to avoid folding; wherein the sampling rate is greater than the band-limit of the anti-aliasing filter.

12. The laser sensor unit according to claim 9 wherein the energy integrating module includes a digital filter configured to divide the received signal into different frequency bands and to enable to integrate the energy at different frequency bands.

13. The laser sensor unit according to according to claim 9 wherein each processing channel includes a respective frequency F cell selection module configured for selecting the integrated energy at the frequency band of the modulation frequency received at the respective quarter.

14. The laser sensor unit according to according to claim 9 wherein each processing channel includes a respective energy threshold detector configured to determine whether the integrated energy at the modulation frequency band is greater than a predefined threshold.

15. The laser sensor unit according to according to claim 9 is a dual purpose laser sensor configured to detect both high power laser signal and low power laser signal generated by the modulated CW light source; wherein each processing channel further includes a respective high power processing pathway for processing high power laser signals;
said laser sensor is configured, upon receiving a signal with intensity greater than a given threshold, to process the signal via the high power processing pathway and detect the true signal portions based on signal intensity.

16. The laser sensor unit according to according to claim 9 is further configured to sum energy of signals received in at least each pair of adjacent quarters, thereby generating 4 intermediate processing channels; and integrate energy in each of the intermediate processing channels.

17. The laser sensor unit according to according to claim 9 is further configured to sum energy of signals received in all quarters, thereby generating a fifth intermediate processing channel; and integrate energy in the fifth processing channel.

18. The laser sensor unit according to claim 9 being integrated in a laser system, the laser system further comprising the modulated CW light source.

19. The laser sensor unit according to claim 9 being integrated in a laser system, the laser system further comprising a

Assignees

• Israel Aerospace Ind Ltd

Inventors

• Levy Benjamin
• Heymann Valery
• Greenberg Igal
• Karazi Uri
• Ychye Amnon

Classifications

• F41G7/2293

  using electromagnetic waves other than radio waves · CPC title

• G01S3/784

  using a mosaic of detectors · CPC title

• F41G7/226

  Semi-active homing systems, i.e. comprising a receiver and involving auxiliary illuminating means, e.g. using auxiliary guiding missiles · CPC title

• G01S7/4913 Primary

  Circuits for detection, sampling, integration or read-out · CPC title

• G01S7/493

  Extracting wanted echo signals · CPC title