# US 10,871,554 B1 · Multispectral LADAR using wavelength shaping

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- Number: US 10,871,554 B1
- Document ID: US10871554B1
- Status: Granted
- Kind: B1
- Application number: 15/915,573
- Filed: 2018-03-08
- Granted: 2020-12-22
- Earliest claimed: 2018-03-08
- Applicants: Government of the United States, as represented by the Secretary of the Air Force
- Inventors: Christian K. Keyser; Luke A. Ausley; Chad M. Welsh
- Web page: https://patentgrep.com/patent/US10871554B1

## CPC

- G01S 7/4802: {using analysis of echo signal for target characterisation; Target signature; Target cross-section}
- G01S 7/4814: {of transmitters alone}
- G01S 7/4816: {of receivers alone}
- G01S 7/4818: {using optical fibres}
- G01S 17/06: Systems determining position data of a target
- G01S 17/10: using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32)
- G02F 1/365: in an optical waveguide structure (G02F1/377, {G02F1/395} take precedence)
- G02F 2202/32: Photonic crystals
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS

## Abstract

A LADAR having a transmitter and a receiver. The transmitter includes a laser for delivering an original beam pulse having a time duration. A nonlinear element receives the original beam pulse and outputs a multispectral incident beam pulse. For each wavelength component of the incident beam pulse, a unique wavelength-dependent variation of intensity is imparted over the time duration of the incident beam pulse. This creates a unique waveform shape for each component. Output optics direct the incident beam pulse onto a target, which reflects from the target as a scattered beam pulse. The receiver includes a single-pixel sensor for receiving the scattered beam pulse and measuring and outputting an intensity of the scattered beam pulse over time, which creates a scattered beam pulse envelope. A processor receives the scattered beam pulse envelope, applies factors to fit the waveform shapes to the scattered beam pulse envelope, and derives a reflectivity of the target for each of the wavelength components from the factors.

## Claims

### Claim 1

A LADAR, comprising:
a transmitter, comprising:
a laser for delivering an original beam pulse having a time duration,
a nonlinear element for receiving the original beam pulse and outputting a multispectral incident beam pulse, and for each wavelength component of the incident beam pulse, imparting a unique wavelength-dependent variation of intensity over the time duration of the incident beam pulse, thereby creating a unique waveform shape for each component, and
output optics for directing the incident beam pulse onto a target, the incident beam pulse thereby reflecting from the target as a scattered beam pulse,
a receiver, comprising:
a single-pixel sensor for receiving the scattered beam pulse and measuring and outputting an intensity of a combination of reflected wavelength components of the scattered beam pulse over time, thereby creating a scattered beam pulse envelope, and
a processor communicatively coupled to the transmitter and the receiver and which:
receives the scattered beam pulse envelope,
accesses factors of a respective waveform shape of each wavelength component of the incident beam pulse;
applies the factors to fit the waveform shapes to the scattered beam pulse envelope, and
derives a reflectivity of the target for each of the wavelength components from the factors.

### Claim 2 (depends on 1)

The LADAR of claim 1, wherein the laser is a supercontinuum laser having an output that is filtered to produce the original beam pulse comprised of discrete wavelengths.

### Claim 3 (depends on 1)

The LADAR of claim 1, wherein:
the laser is a monochromatic laser; and
the nonlinear element is a Raman fiber having a hollow-core photonic crystal fiber that is filled with a Raman-active gas, the Raman fiber generating the waveform components having different waveform shapes.

### Claim 4 (depends on 1)

The LADAR of claim 1, wherein:
the laser is a multispectral laser having an output of discrete wavelengths; and
the nonlinear element outputs different waveform shapes within the single beam pulse with the waveform components being identical pulse to pulse.

### Claim 5 (depends on 1)

The LADAR of claim 1, wherein:
the laser is one of: (i) a multispectral laser; and (ii) a supercontinuum laser; and
the nonlinear element is a Pockels cell comprising a pair of orthogonal polarizers respectively on an input end and an output end of the Pockels cell, a voltage ramp is applied to the Pockels cell that is synchronized with the original beam pulse traveling through the Pockels cell.

### Claim 6 (depends on 1)

The LADAR of claim 1, wherein the processor applies the factors is accomplished by performing a least squares regression.

### Claim 7 (depends on 1)

The LADAR of claim 1, wherein the processor applies the factors by:
iteratively,
selectively adjusting reflectivity factors, where there is one reflectivity factor for each wavelength in the scattered beam pulse,
applying the reflectivity factors to the waveform shapes to create computed waveform shapes,
adding the computed waveform shapes together to form a computed beam pulse envelope, and
comparing the computed beam pulse envelope to the scattered beam pulse envelope, and
when the computed beam pulse envelope fits the scattered beam pulse envelope to a desired degree of accuracy, outputting the reflectivity factors as the reflectivity of the target at each of the discrete wavelengths.

### Claim 8 (depends on 1)

The LADAR of claim 1, wherein the transmitter and the receiver are contained within a common housing.

### Claim 9 (depends on 1)

The LADAR of claim 1, wherein the processor further uses the reflectivity of the target at each of the wavelengths to determine target composition.

### Claim 10 (depends on 1)

The LADAR of claim 1, wherein the factors of the respective waveform shape of each wavelength component of the incident beam pulse is known from a design of the laser and a design of the nonlinear components.

### Claim 11 (depends on 1)

The LADAR of claim 1, wherein the factors of the respective waveform shape of each wavelength component of the incident beam pulse is known from direct measurement of at least one of the original beam pulse from the laser and the incident beam pulse from the nonlinear element.

### Claim 12 (depends on 1)

The LADAR of claim 1, wherein the factors of the respective waveform shape of each wavelength component of the incident beam pulse is known from an average of measurements of previous incident beam pulses from the nonlinear element.

### Claim 13 (depends on 5)

The LADAR of claim 5, wherein the Pockels cell functions as a voltage-controlled waveplate having the voltage ramp comprising one or more half-wave voltages that modulate the incident beam pulse into a wavelength-specific shape, wherein each wavelength component has a different waveform shape.

### Claim 14

A method, comprising:
delivering, by a laser, an original beam pulse having a time duration from a laser to a nonlinear element,
imparting, by the nonlinear element, a unique wavelength-dependent variation of intensity over the time duration of the original beam pulse to output a multispectral incident beam pulse to output optics;
directing, by the output optics the incident beam pulse onto a target, the incident beam pulse thereby reflecting from the target as a scattered beam pulse;
receiving the scattered beam pulse by a single-pixel sensor of a receiver;
measuring an intensity of a combination of reflected wavelength components of the scattered beam pulse over time, thereby creating a scattered beam pulse envelope;
accessing factors of a respective waveform shape of each wavelength component of the incident beam pulse by a processor of the receiver;
applying the factors to fit the waveform shapes to the scattered beam pulse envelope; and
deriving a reflectivity of the target for each of the wavelength components from the factors.

### Claim 15 (depends on 14)

The method of claim 14, wherein delivering the original beam pulse comprises:
generating an output by the laser comprising a supercontinuum laser; and
filtering the output to produce the original beam pulse comprised of discrete wavelengths.

### Claim 16 (depends on 14)

The method of claim 14, wherein:
the laser is a monochromatic laser; and
the nonlinear element is a Raman fiber having a hollow-core photonic crystal fiber that is filled with a Raman-active gas, the Raman fiber generating the waveform components having different waveform shapes.

### Claim 17 (depends on 14)

The method of claim 14, wherein:
the laser is a multispectral laser having an output of discrete wavelengths; and
the multispectral incident beam pulse is comprised of the waveform components having different waveform shapes within the single beam pulse with the waveform components being identical pulse to pulse.

### Claim 18 (depends on 14)

The method of claim 14, wherein:
the laser is one of: (i) a multispectral laser; and (ii) a supercontinuum laser; and
the nonlinear element is a Pockels cell comprising a pair of orthogonal polarizers respectively on an input end and an output end of the Pockels cell;
the method further comprising applying a voltage ramp to the Pockels cell that is synchronized with the original beam pulse traveling through the Pockels cell.

### Claim 19 (depends on 18)

The method of claim 18, wherein applying the voltage ramp comprises operating the Pockels cell as a voltage-controlled waveplate using the voltage ramp comprising one or more half-wave voltages that modulate the incident beam pulse into a wavelength-specific shape, wherein each wavelength component has a different waveform shape.

### Claim 20 (depends on 14)

The method of claim 14, wherein applying the factors comprises performing a least squares regression.

### Claim 21 (depends on 14)

The method of claim 14, wherein applying the factors further comprises:
iteratively,
selectively adjusting reflectivity factors, where there is one reflectivity factor for each wavelength in the scattered beam pulse,
applying the reflectivity factors to the waveform shapes to create computed waveform shapes,
adding the computed waveform shapes together to form a computed beam pulse envelope, and
comparing the computed beam pulse envelope to the scattered beam pulse envelope, and
when the computed beam pulse envelope fits the scattered beam pulse envelope to a desired degree of accuracy, outputting the reflectivity factors as the reflectivity of the target at each of the discrete wavelengths.

### Claim 22 (depends on 14)

The method of claim 14, further comprising using the reflectivity of the target at each of the wavelengths to determine target composition.

### Claim 23 (depends on 14)

The method of claim 14, wherein accessing the factors of the respective waveform shape of each wavelength component of the incident beam pulse comprises accessing data known from a design of the laser and a design of the nonlinear components.

### Claim 24 (depends on 14)

The method of claim 14, wherein accessing the factors of the respective waveform shape of each wavelength component of the incident beam pulse comprises directly measuring of at least one of the original beam pulse from the laser and the incident beam pulse from the nonlinear element.

### Claim 25 (depends on 14)

The method of claim 14, wherein accessing the factors of the respective waveform shape of each wavelength component of the incident beam pulse comprises averaging measurements of previous incident beam pulses from the nonlinear element.