US-12625235-B2 - Multispectral LiDAR comprising a spectral delay unit

Abstract

A multispectral laser detection and ranging device including a spectral delay unit configured for delaying the broadband laser beam pulse depending on the wavelength, to give a wavelength comb selected in the spectral range, such that the broadband laser beam pulse is transformed into a pulse-train wherein each pulse in the train is at a different wavelength of the wavelength comb.

Inventors

• Priit JAANSON
• Albert MANNINEN

Assignees

• IRIDESENSE

Dates

Publication Date

20260512

Application Date

20210125

Claims (20)

1. 1 . A multispectral laser detection and ranging device, the device comprising, an optical input for receiving a broadband laser beam pulse having a spectral range, an optical transmitter configured for outputting the broadband laser beam pulse along a direction, the optical input and the optical transmitter being optically connected, and an optical receiver configured to receive a reflection of the broadband laser beam pulse from said direction, and an optical detector configured to detect a time-of-flight and an optical power of at least part of the reflection of the broadband laser beam pulse, wherein the optical detector is optically connected to the optical receiver, wherein the device further comprises: -a spectral delay unit configured for delaying the broadband laser beam pulse depending on the wavelength, to give a wavelength comb selected in the spectral range, such that the broadband laser beam pulse is transformed into a pulse-train wherein each pulse in the train is at a different wavelength of the wavelength comb, wherein the spectral delay unit comprises an optical fiber, wherein the spectral delay unit comprises a delay input configured to receive the broadband laser beam pulse, and further comprises a delay output configured to transmit the pulse-train, wherein the delay input and the delay output are both a same end of said optical fiber of the spectral delay unit, wherein the device further comprises an optical circulator, wherein said optical circulator comprises a first port, a second port and a third port, and is configured such that light inputted in the first port is outputted from the second port, and light inputted in the second port is outputted from the third port, wherein said same end of the optical fiber is optically connected to the second port of the optical circulator, wherein the first port is fiber-coupled with the optical input, and the third port is fiber-coupled with a scanning module, wherein the scanning module comprises the optical transmitter, wherein the scanning module further comprises the optical receiver, and wherein the optical circulator further comprises a fourth port, configured such that light inputted in the third port is outputted from the fourth port, wherein the fourth port is fiber-coupled with the optical detector.
2. 2 . The device according to claim 1 , wherein the optical detector is a broadband unique detector.
3. 3 . The device according to claim 1 , wherein a pulse within the pulse train has a filtered bandwidth which is the bandwidth of the spectral range of the broadband laser beam pulse divided by 4 or 5.
4. 4 . The device according to claim 1 , wherein the optical detector is an avalanche photodiode electrically connected to a digitizer having a sample rate of 3 GS/s, and to Field Programmable Gate Arrays.
5. 5 . The device according to claim 1 , wherein the optical fiber is grated with a fiber Bragg grating.
6. 6 . The device according to claim 5 , wherein the optical fiber Bragg grating is a superstructured Fiber Bragg Grating comprising a plurality of successive fiber Bragg gratings, wherein the gratings are configured to reflect the wavelength comb part of the broadband laser beam pulse, wherein the length between two adjacent fiber Bragg gratings is selected as a function of a time interval between two adjacent pulses in the train pulses.
7. 7 . The device according to claim 1 , further comprising a broadband laser source connected to the optical input and configured to send the broadband laser beam pulses to the optical input.
8. 8 . The device according to claim 7 , wherein the laser source is a supercontinuum laser source.
9. 9 . The device according to claim 8 , wherein the broadband laser beam pulse has a spectral range comprised between 1000 nm and 1700 nm.
10. 10 . The device according to claim 8 , wherein each of the broadband laser beam pulse has a pulse duration comprised between 0.5 ns and 5 ns.
11. 11 . The device according to claim 10 , wherein the pulse duration is about 1 ns.
12. 12 . The device according to claim 8 , wherein each of the broadband laser beam pulse exhibits a bandwidth comprised between 200 nm and 300 nm.
13. 13 . The device according to claim 8 , wherein each of the laser beam pulse exhibits a bandwidth of 300 nm and the broadband laser beam pulse has a spectral range comprised between 1400-1700 nm, which is an optimum configuration for eye-safety and low-cost detection.
14. 14 . A vehicle comprising a device according to claim 1 .
15. 15 . A multispectral laser detection and ranging device, the device comprising, an optical input for receiving a broadband laser beam pulse having a spectral range, an optical transmitter configured for outputting the broadband laser beam pulse along a direction, the optical input and the optical transmitter being optically connected, and an optical receiver configured to receive a reflection of the broadband laser beam pulse from said direction, and an optical detector configured to detect a time-of-flight and an optical power of at least part of the reflection of the broadband laser beam pulse, wherein the optical detector is optically connected to the optical receiver, wherein the device further comprises: a spectral delay unit configured for delaying the broadband laser beam pulse depending on the wavelength, to give a wavelength comb selected in the spectral range, such that the broadband laser beam pulse is transformed into a pulse-train wherein each pulse in the train is at a different wavelength of the wavelength comb, wherein the spectral delay unit comprises an optical fiber, wherein the spectral delay unit comprises a delay input configured to receive the broadband laser beam pulse, and further comprises a delay output configured to transmit the pulse-train, wherein the delay input and the delay output are both a same end of said optical fiber of the spectral delay unit, wherein the device further comprises an optical circulator, wherein said optical circulator comprises a first port, a second port, a third port and a fourth port, and is configured such that light inputted in the first port is outputted from the second port, and light inputted in the second port is outputted from the third port, and configured such that light inputted in the third port is outputted from the fourth port, wherein said same end of the optical fiber is optically connected to the third port of the optical circulator, wherein the first port is fiber-coupled with the optical input, and the third port is fiber-coupled with a scanning module, wherein the scanning module comprises the optical transmitter, wherein the scanning module further comprises the optical receiver, and wherein the fourth port is fiber-coupled with the optical detector.
16. 16 . The device according to claim 15 , wherein the optical detector is a broadband unique detector.
17. 17 . The device according to claim 15 , wherein a pulse within the pulse train has a filtered bandwidth which is the bandwidth of the spectral range of the broadband laser beam pulse divided by 4 or 5.
18. 18 . The device according to claim 15 , further comprising a broadband laser source connected to the optical input and configured to send the broadband laser beam pulses to the optical input.
19. 19 . The device according to claim 18 , wherein the laser source is a supercontinuum laser source.
20. 20 . The device according to claim 15 , wherein each of the broadband laser beam pulse exhibits a bandwidth comprised between 200 nm and 300 nm.

Description

This application is the U.S. national phase of International Application No. PCT/EP2021/051639 filed Jan. 25, 2021, which designated the U.S. and claims priority to US 62/965,751 filed Jan. 24, 2020, the entire contents of each of which are hereby incorporated by reference. BACKGROUND OF THE INVENTION Field of the Invention The invention relates to multispectral LiDAR devices, and more particularly, to multispectral LiDAR devices acquiring data at different wavelengths to allow a recording of a diversity of spectral reflectance from objects. Description of the Related Art Light detection and ranging (LiDAR) systems are used to detect and/or measure distances of remote objects. A LiDAR includes a light source, such as a laser, and an optical sensor or a plurality of optical sensors. The light source emits light pulses in a portion or portions of the electromagnetic spectrum: in the infrared, visible, or ultraviolet portions for instance. When a light pulse is reflected by an object, the LiDAR can determine the distance based on the time of flight of a returned light pulse received by the optical sensor. LiDAR systems usually operate at a monochromatic wavelength measuring the range and the strength of the reflected energy (intensity) from objects. Recently, multispectral LiDAR sensors, which acquire data at different wavelengths, have emerged. This allows for recording of a diversity of spectral reflectance from objects. A multispectral LiDAR emits multiple light pulses with different electromagnetic characteristics, allowing a determination of the material composition of objects. A problem in multispectral LiDAR is to discriminate spectral information. When a multispectral LiDAR is sending pulses with different electromagnetic signatures, it is important to identify which spectral pulse (e.g. ultraviolet vs. infrared) is returned by an object and detected by the sensor. A multispectral LiDAR can use spectral filtering of the pulse. This allows to use a single detector, resulting in best available sensitivity. However, filtering reduces the spectral information per pulse by number of wavelength channels. Alternatively, a multispectral LiDAR can use a dispersive element and a detector array. This requires a complex detection system with reduced sensitivity and increased price compared to single detector. SUMMARY OF THE INVENTION Compared to the state of the art, it is proposed a multispectral LiDAR device which may combine the sensitivity and cost efficiency of a single detector multispectral LiDAR without losing spectral information to filtering. Determining the distance reliably from the time of flight from a single pulse measurement requires relatively high signal to noise ratios (for instance a signal to noise ratio higher than 8). Reducing this requirement by a factor of 4 would result in 100% higher measurement distance with same pulse energy. An objective of specific embodiments of the invention is to determine the distance of objects returning the pulse even in low signal to noise value situations. The invention provides a multispectral laser detection and ranging (LiDAR) device, the device comprising, an optical input for receiving a broadband laser beam pulse having a spectral range,an optical transmitter configured for outputting the broadband laser beam pulse along a direction, the optical input and the optical transmitter being optically connected, andan optical receiver configured to receive a reflection of the broadband laser beam pulse from said direction, andan optical detector configured to detect a time-of-flight and an optical power of at least part of the reflection of the broadband laser beam pulse, wherein the optical detector is optically connected to the optical receiver, wherein the device further comprises:a spectral delay unit configured for delaying the broadband laser beam pulse depending on the wavelength, to give a wavelength comb selected in the spectral range, such that the broadband laser beam pulse is transformed into a pulse-train wherein each pulse in the train is at a different wavelength of the wavelength comb. In other words, the LiDAR device transforms the outgoing single pulse into a pulse-train, where each pulse in the train is at different wavelength. Thanks to these features, the returning light, or reflected light, can be detected and spectrally discriminated using a single detector and fast digitizer. In addition, detecting the distance using a pulse train will be more robust than with a single pulse using frequency domain-based methods. Indeed, using a pulse train improves the accuracy of distance measurement compared to single pulse when using frequency domain based methods. One would understand that a reflection of the laser beam refers to either backscattered or specular reflection or combination thereof. One would understand that the wording “optically connected” between two optical modules (input, output, receivers, transmitters, units etc) either means co