OPTICAL FREQUENCY COMB-BASED COHERENT LIDAR
First Claim
1. A method of comb-based coherent Light Detection and Ranging (LIDAR) comprising:
- generating a signal comb that transmits a signal pulse train reflected from a reference and a target to generate a target signal from the target and a reference signal from the reference;
generating a local oscillator (LO) comb that transmits a LO pulse train at a slightly different repetition rate than the signal pulse train with a coherent optical carrier;
detecting the reflected signal pulse train through linear optical sampling against the LO pulse train in which consecutive samples of an overlap between a signal pulse from the target signal and the references signal, and a LO pulse from the LO pulse train yields a high-resolution measurement of the target signal and reference signal;
Fourier transforming the target signal to extract the optical phase vs. frequency of the target signal;
Fourier transforming the reference signal to extract the optical phase vs. frequency of the reference signal;
determining a frequency dependant optical phase difference between the optical phase of the target signal and the optical phase of the reference signal;
fitting the optical phase difference to a straight line;
obtaining a time-of-flight distance measurement from a slope of the straight light and the known group velocity of light at the frequency of the coherent optical carrier;
obtaining an interferometric distance measurement between the target and the reference from the intercept of the straight line and the wavelength of the coherent optical carrier.
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Accused Products
Abstract
A coherent laser radar that uses two coherent femtosecond fiber lasers to perform absolute ranging at long distance. One coherent femtosecond fiber lasers acts as a source and the other as a local oscillator for heterodyne detection of the return signal from a cooperative target. The system simultaneously returns a time-of-flight range measurement for coarse ranging and an interferometric range measurement for fine ranging which is insensitive to spurious reflections that can cause systematic errors. The range is measured with at least 3 μm precision in 200 μs and 5 nm precision in 60 ms over a 1.5 m ambiguity range. This ambiguity range can be extended to 30 km through reversal of signal and LO source roles.
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Citations
9 Claims
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1. A method of comb-based coherent Light Detection and Ranging (LIDAR) comprising:
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generating a signal comb that transmits a signal pulse train reflected from a reference and a target to generate a target signal from the target and a reference signal from the reference; generating a local oscillator (LO) comb that transmits a LO pulse train at a slightly different repetition rate than the signal pulse train with a coherent optical carrier; detecting the reflected signal pulse train through linear optical sampling against the LO pulse train in which consecutive samples of an overlap between a signal pulse from the target signal and the references signal, and a LO pulse from the LO pulse train yields a high-resolution measurement of the target signal and reference signal; Fourier transforming the target signal to extract the optical phase vs. frequency of the target signal; Fourier transforming the reference signal to extract the optical phase vs. frequency of the reference signal; determining a frequency dependant optical phase difference between the optical phase of the target signal and the optical phase of the reference signal; fitting the optical phase difference to a straight line; obtaining a time-of-flight distance measurement from a slope of the straight light and the known group velocity of light at the frequency of the coherent optical carrier; obtaining an interferometric distance measurement between the target and the reference from the intercept of the straight line and the wavelength of the coherent optical carrier. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A Light Detection and Ranging (LIDAR) comprising:
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a first mode locked laser which generates a signal comb that transmits a signal pulse train reflected from a reference and a target; a second mode locked laser that generates a local oscillator (LO) comb; and a first continuous wave laser and a second continuous wave laser stabilized to an optical reference cavity, said first continuous wave laser phase locked at a first tooth of the signal comb and the LO comb, said second continuous wave laser phase locked at a second tooth of the signal comb and the LO comb different than the first tooth to relate a distance between the reference and the target to a known distance of said optical reference cavity. - View Dependent Claims (9)
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Specification