Method and system for using square wave digital chirp signal for optical chirped range detection

Patent metadata

Field	Value
Publication number	US-10534084-B2
Application number	US-201715661377-A
Country	US
Kind code	B2
Filing date	Jul 27, 2017
Priority date	Jul 27, 2017
Publication date	Jan 14, 2020
Grant date	Jan 14, 2020

Abstract

An apparatus is provided for using a square wave digital chirp signal for optical chirp range detection. A laser source emits an optical signal and a RF waveform generator generates an input digital chirp signal based on the square wave digital chirp signal. A frequency of the optical signal is modulated based on the input digital chirp signal. A splitter divides the optical signal into a transmit optical signal and a reference optical signal. A detector combines the reference optical signal and a return optical signal from an object. The detector generates an electrical output signal based on the combined reference optical signal and the return optical signal. A processor determines a range to the object based on a characteristic of a Fourier transform the electrical output signal. A method is also provided for using the square wave digital chirp signal for optical chirp range detection.

First claim

What is claimed is:

1. An apparatus comprising:
a laser source for emitting an optical signal;
a radio frequency (RF) waveform generator for generating an input digital chirp signal, said input digital chirp signal based on a square wave digital chirp signal;
a modulator for modulating a frequency of the optical signal based on the input digital chirp signal;
a splitter to divide the optical signal into a transmit optical signal and a reference optical signal;
a detector to combine the reference optical signal and a return optical signal based on the transmit optical signal backscattered off an object, wherein the detector is configured to generate an electrical output signal based on the combined reference optical signal and the return optical signal; and
a processor to determine a range to the object based on a characteristic of a Fourier transform the electrical output signal.

2. The apparatus as recited in claim 1 , wherein the input digital chirp signal has a bandwidth from a first frequency to a second frequency and wherein the RF waveform generator comprises:
a Field Programmable Gate Array (FPGA) including a transceiver configured to generate the square wave digital chirp signal; and
a filter configured to remove a range of frequencies from a frequency spectrum of the square wave digital chirp signal outside the bandwidth.

3. The apparatus as recited in claim 2 , wherein the RF waveform generator further comprises an equalizer configured to flatten an amplitude of the frequency spectrum over the bandwidth.

4. The apparatus as recited in claim 1 , wherein the RF waveform generator is further configured to generate a second input digital chirp signal based on a second square wave digital signal and wherein the apparatus further comprises a phase modulator for modulating a phase of the reference optical signal based on the second input digital chirp signal.

5. The apparatus as recited in claim 4 , wherein the RF waveform generator comprises a Field Programmable Gate Array (FPGA) with a transceiver having a first channel and a second channel, wherein the first channel is configured to transmit the input digital chirp signal to the modulator and wherein the second channel is configured to transmit the second input digital chirp signal to the phase modulator.

6. A method comprising:
emitting an optical signal from a laser source;
modulating a frequency of the optical signal with a modulator based on an input digital chirp signal from a radio frequency (RF) waveform generator, said input digital chirp signal based on a square wave digital chirp signal;
dividing the optical signal with a splitter into a transmit optical signal and a reference optical signal;
combining the reference optical signal and a return optical signal at a detector, wherein the return optical signal is based on the transmit optical signal backscattered off an object;
generating, with the detector, an electrical output signal based on the combining step;
determining, with a processor, a range to the object based on a characteristic of a Fourier transform the electrical output signal.

7. A method as recited in claim 6 , wherein the input digital chirp signal is the square wave digital chirp signal.

8. A method as recited in claim 6 , wherein the RF waveform generator comprises a Field Programmable Gate Array (FPGA).

9. A method as recited in claim 6 , wherein the input digital chirp signal has a bandwidth from a first frequency to a second frequency and wherein the method comprises forming, with the RF waveform generator, the input digital chirp signal including;
generating, with a transceiver of the RF waveform generator, the square wave digital chirp signal;
determining a frequency spectrum of the square wave digital chirp signal; and
removing, with a filter of the RF waveform generator, a range of frequencies from the frequency spectrum outside the bandwidth.

10. The method as recited in claim 9 , wherein the frequency spectrum is a frequency power spectrum and wherein the removing the range of frequencies comprises establishing a minimum dynamic range between an amplitude of the frequency power spectrum within the bandwidth and an amplitude of the frequency power spectrum outside the bandwidth.

11. The method as recited in claim 10 , wherein the minimum dynamic range is at least 20 dB.

12. The method as recited in claim 9 , wherein the forming the input digital chirp signal further comprises flattening, with an equalizer of the RF waveform generator, an amplitude of the frequency spectrum across the bandwidth from the first frequency to the second frequency.

13. The method as recited in claim 9 , wherein the transceiver is a transceiver of a Field Programmable Gate Array (FPGA).

14. The method as recited in claim 9 , wherein the bandwidth is in a range from about 10 GHz to about 30 GHz.

15. A method as recited in claim 6 , wherein the input digital chirp signal has a bandwidth from a first frequency to a second frequency and wherein the method comprises forming, with the RF waveform generator, the input digital chirp signal including;
determining a frequency spectrum of the square wave digital chirp signal; and
flattening, with an equalizer of the RF waveform generator, an amplitude of the frequency spectrum across the bandwidth from the first frequency to the second frequency.

16. The method as recited in claim 9 , wherein the generating the square wave digital chirp signal comprises:
outputting, with the transceiver of the RF waveform generator, a fixed amplitude signal over a first number of clock cycles to output a first frequency over the first number of clock cycles of the square wave digital chirp; and
outputting, with the transceiver of the RF waveform generator, the fixed amplitude signal over a second number of clock cycles different than the first number of clock cycles to output a second frequency different than the first frequency over the second number of clock cycles of the square wave digital chirp.

17. The method as recited in claim 16 , further comprising uploading a plurality of instructions into a memory of the transceiver, wherein the plurality of instructions includes data that indicates the fixed amplitude signal to be output over the first number of clock cycles and the fixed amplitude signal to be output over the second number of clock cycles.

18. The method as recited in claim 6 , further comprising modulating a phase of the reference optical signal with a phase modulator based a second input digital chirp signal from the RF waveform generator, said second input digital chirp signal based on a second square wave digital chirp signal.

19. The method as recited in claim 18 , wherein the frequency of the transmit optical signal is modulated based on the input digital chirp signal from a first channel of the RF waveform generator and wherein the phase of the reference optical signal is modulated based on the second input digital chirp signal from a second channel of the RF waveform generator.

20. The method as recited in claim 19 , wherein the second input digital chirp signal from the second channel is the input digital chirp signal from the first channel.

21. The method as recited in claim 9 , wherein the transceiver is a transceiver of a Digital Signal Processor (DSP).

Assignees

• Blackmore Sensors And Analytics Llc
• Blackmore Sensors & Analytics Llc

Inventors

• Crouch Stephen C
• Curry James
• Berg Trenton
• Funk Richard
• Oliver Kyle
• Ferguson Daniel

Classifications

• H04B10/5561

  Digital phase modulation · CPC title

• G01S7/484 Primary

  Transmitters · CPC title

• H04B10/505

  using external modulation · CPC title

• G01S7/4861

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

• G01S17/26 Primary

  wherein the transmitted pulses use a frequency-modulated or phase-modulated carrier wave, e.g. for pulse compression of received signals · CPC title