CN118209958A - Laser radar apparatus - Google Patents
Laser radar apparatus Download PDFInfo
- Publication number
- CN118209958A CN118209958A CN202211581053.8A CN202211581053A CN118209958A CN 118209958 A CN118209958 A CN 118209958A CN 202211581053 A CN202211581053 A CN 202211581053A CN 118209958 A CN118209958 A CN 118209958A
- Authority
- CN
- China
- Prior art keywords
- optical
- continuous wave
- wave laser
- lidar device
- laser beam
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 230000003287 optical effect Effects 0.000 claims abstract description 307
- 239000000463 material Substances 0.000 claims description 23
- 238000001514 detection method Methods 0.000 claims description 21
- 230000010354 integration Effects 0.000 description 18
- 238000001914 filtration Methods 0.000 description 17
- 238000005259 measurement Methods 0.000 description 17
- 238000010586 diagram Methods 0.000 description 16
- 238000000034 method Methods 0.000 description 14
- 238000012545 processing Methods 0.000 description 11
- 230000008859 change Effects 0.000 description 10
- 238000012805 post-processing Methods 0.000 description 10
- 230000008569 process Effects 0.000 description 10
- 238000010168 coupling process Methods 0.000 description 7
- 238000005859 coupling reaction Methods 0.000 description 7
- 230000008901 benefit Effects 0.000 description 6
- 230000008878 coupling Effects 0.000 description 6
- 230000004044 response Effects 0.000 description 6
- 230000010287 polarization Effects 0.000 description 5
- 239000002178 crystalline material Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 230000006870 function Effects 0.000 description 4
- 238000002310 reflectometry Methods 0.000 description 4
- 239000007787 solid Substances 0.000 description 4
- 230000001629 suppression Effects 0.000 description 4
- 229910013641 LiNbO 3 Inorganic materials 0.000 description 3
- 238000003491 array Methods 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 230000001427 coherent effect Effects 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000004065 semiconductor Substances 0.000 description 3
- 229910052581 Si3N4 Inorganic materials 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 230000035559 beat frequency Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 230000009977 dual effect Effects 0.000 description 2
- 238000002592 echocardiography Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 2
- 238000013507 mapping Methods 0.000 description 2
- 239000004005 microsphere Substances 0.000 description 2
- 229920000620 organic polymer Polymers 0.000 description 2
- 239000002861 polymer material Substances 0.000 description 2
- 239000000523 sample Substances 0.000 description 2
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 2
- 238000005549 size reduction Methods 0.000 description 2
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 description 1
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 1
- GPXJNWSHGFTCBW-UHFFFAOYSA-N Indium phosphide Chemical compound [In]#P GPXJNWSHGFTCBW-UHFFFAOYSA-N 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000002457 bidirectional effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 239000002210 silicon-based material Substances 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
Landscapes
- Optical Radar Systems And Details Thereof (AREA)
Abstract
The present disclosure relates to a lidar device comprising a continuous wave laser, a wavelength sensing module, an optical filter, an electro-optic modulator, and a transmitting optical module. The continuous wave laser is configured to output a continuous wave laser beam. The wavelength sensing module is optically coupled to the continuous wave laser and is configured to receive a portion of the continuous wave laser beam and output a sensing electrical signal indicative of a center wavelength of the continuous wave laser beam. The optical filter is optically coupled to the continuous wave laser, and its passband has a center wavelength set based on the sensed electrical signal that matches the center wavelength of the continuous wave laser beam. The optical filter is configured to optically filter another portion of the continuous wave laser beam to output a filtered laser beam. The electro-optic modulator is configured to modulate the filtered laser beam with a frequency modulated electrical signal to output a modulated optical signal. The emission optical module is configured to direct an exit direction of the modulated optical signal to output a scanning beam for scanning an emission field of view.
Description
Technical Field
The present disclosure relates to the field of lasers, and more particularly to lidar devices, particularly frequency modulated continuous wave lidars.
Background
LiDAR (LiDAR) detects information such as distance, speed, surface reflectivity, and/or orientation of a target by emitting a laser beam toward the target object and receiving the beam reflected from the target. Depending on the type of emitted laser beam, lidars can be classified into Pulse (Pulse) lidars and Continuous Wave (CW) lidars, which in turn can be classified into non-modulated single-frequency or multi-frequency continuous wave lidars, amplitude modulated continuous wave lidars, and Frequency Modulated Continuous Wave (FMCW) lidars. Compared with pulse laser radar, the frequency modulation continuous wave laser radar has the advantages of low peak light power, large range, high range resolution, capability of realizing Doppler speed measurement, high speed resolution and the like.
One of the key technologies of the frequency modulated continuous wave lidar is the generation of frequency modulated optical signals. Most of the current frequency modulation continuous wave laser radar products obtain frequency modulation optical signals through a direct modulation laser. However, it is generally difficult to obtain high-quality frequency-modulated optical signals by using such a method of directly modulating a laser, for example, high linearity and low phase noise cannot be achieved, so that the ranging range and the measuring accuracy of the laser radar are affected. In this regard, existing solutions mostly require complex system control (e.g., adding structures such as optical phase locked loops) to improve the quality of the modulated optical signal.
Disclosure of Invention
The present disclosure provides a lidar apparatus. The lidar apparatus includes a continuous wave laser, a wavelength sensing module, an optical filter, an electro-optic modulator, and a transmitting optical module. The continuous wave laser is configured to output a continuous wave laser beam. The wavelength sensing module is optically coupled to the continuous wave laser. The wavelength sensing module is configured to receive a portion of the continuous wave laser beam and output a sensing electrical signal indicative of a center wavelength of the continuous wave laser beam. The optical filter is optically coupled to the continuous wave laser. The passband of the optical filter has a center wavelength set based on the sensed electrical signal that matches a center wavelength of the continuous wave laser beam, the optical filter being configured to optically filter another portion of the continuous wave laser beam to output a filtered laser beam. The electro-optic modulator is configured to modulate the filtered laser beam with a frequency modulated electrical signal to output a modulated optical signal. The emission optical module is configured to direct an exit direction of the modulated optical signal to output a scanning beam for scanning an emission field of view.
In some embodiments, the wavelength sensing module comprises a first optical add-drop ring resonator and the sensed electrical signal comprises a root mean square of the optical power ratio of the pass-through port and the drop port of the optical add-drop ring resonator.
In some embodiments, the first optical add-drop ring resonator comprises a whispering gallery mode microcavity.
In some embodiments, the optical filter has a passband bandwidth capable of suppressing one or more side lobes in the continuous wave laser beam.
In some embodiments, the optical filter includes a second optical add-drop ring resonator.
In some embodiments, the second optical add-drop ring resonator comprises a whispering gallery mode microcavity.
In some embodiments, the optical filtering apparatus further comprises a filter setting module. The filter setting module is configured to: receiving a sensing electrical signal; converting the sensed electrical signal into a physical quantity capable of setting a center wavelength of a passband of the optical filter; and supplying the physical quantity to the optical filter. The center wavelength of the passband of the optical filter is set based on the physical quantity.
In some embodiments, the physical quantity includes at least one of heat, sound waves, deformation, pressure, material refractive index, and vibration.
In some embodiments, the continuous wave laser is a tunable laser and the optical filter is a tunable optical filter.
In some embodiments, the emission optical module is configured to direct modulated optical signals generated based on continuous wave laser beams with different center wavelengths output by the tunable laser to respective different locations in the emission field of view.
In some embodiments, the transmitting optical module comprises an optical phased array.
In some embodiments, the transmitting optical module includes: a dispersive optical element configured to direct modulated optical signals generated based on continuous wave laser beams with different center wavelengths output by the tunable laser to different positions in a first direction in the emission field of view.
In some embodiments, the dispersive optical element comprises any one or more of an arrayed waveguide grating, a diffraction grating, and a sub-wavelength grating.
In some embodiments, the transmitting optical module further comprises: a deflectable mirror configured to direct the same light beam from the dispersive optical element to a different location in a second direction in the emission field of view by a different deflection, wherein the first direction is perpendicular to the second direction.
In some embodiments, the lidar device further comprises: a receiving optical module configured to receive an echo beam from a receiving field of view; an optical coupler configured to couple the modulated optical signal with the echo beam received by the receiving optical module to output a coupled optical signal; and a photodetector configured to detect the coupled optical signal to output a detection electrical signal.
In some embodiments, the photodetectors are balanced detectors.
In some embodiments, the lidar device includes a transceive coaxial optical system.
In some embodiments, the transmitting optical module includes: a dispersive optical element configured to direct modulated optical signals generated based on continuous wave laser beams with different center wavelengths output by the tunable laser to different positions in a first direction in the emission field of view; and a deflectable mirror configured to direct the same light beam from the dispersive optical element to a different location in a second direction in the emission field of view by a different deflection, wherein the first direction is perpendicular to the second direction, the receiving optical module comprising: the deflectable mirror is configured to direct echo beams from different locations in a second direction in the receive field of view to the transflector assembly by different deflections; and a transreflective assembly configured to direct the echo beam from the deflectable mirror to the optical coupler.
In some embodiments, a transflective assembly is disposed in the optical path between the dispersive optical element and the deflectable mirror.
In some embodiments, the transflector assembly comprises at least one of: a mirror having an opening in the center; a half-mirror; or a polarizing beam splitter.
Drawings
The foregoing and other objects and advantages of the disclosure are further described below in connection with the following detailed description of the embodiments, with reference to the accompanying drawings. In the drawings, the same or corresponding technical features or components will be denoted by the same or corresponding reference numerals.
Fig. 1 shows a schematic composition diagram of a lidar device according to an embodiment of the disclosure;
fig. 2 shows a schematic composition diagram of a receiving end of a lidar device according to an embodiment of the disclosure;
FIG. 3 shows a schematic structural diagram of a wavelength sensing module according to an embodiment of the present disclosure;
FIG. 4 shows a schematic diagram of the structure of an optical filter according to an embodiment of the disclosure;
FIG. 5 shows a schematic diagram of a structure integrating a wavelength sensing module and an optical filter of a lidar device according to an embodiment of the disclosure;
FIG. 6 illustrates a schematic diagram of the working principle of an optical filtering device for filtering a laser beam with a dynamically changing center wavelength according to an embodiment of the present disclosure;
Fig. 7 shows a schematic structural view of a transmitting optical module of a lidar device according to an embodiment of the present disclosure;
fig. 8 illustrates a schematic diagram of the working principle of scanning by a transmitting optical module of a lidar device according to an embodiment of the present disclosure; and
Fig. 9 illustrates a structural schematic diagram of a lidar device including a coaxial transceiving optical system according to an embodiment of the present disclosure.
Detailed Description
Embodiments of the technical scheme of the present invention will be described in detail below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present invention, and thus are merely examples, and are not intended to limit the scope of the present invention. The words and phrases used in the following description are only intended to provide a clear and consistent understanding of the present disclosure. In addition, descriptions of well-known structures, functions and configurations may be omitted for clarity and conciseness.
As mentioned above, in order to generate a frequency modulated optical signal for a lidar, a direct modulation laser scheme is currently generally used, for example, to achieve the purpose of laser frequency modulation by changing the driving current of the laser or adjusting the cavity of the laser. However, the carrier concentration of the direct-tuning laser is different at different frequencies along with the current change, so that frequency modulation nonlinearity occurs, and distortion is generated.
To overcome the drawbacks of the existing lidar systems, embodiments of the present disclosure propose a frequency modulated continuous wave lidar apparatus capable of providing high quality frequency modulated optical signals for measurement. It adopts an external modulation scheme combining a continuous wave laser with an electro-optic modulator. Compared with the direct modulation laser scheme, the external modulation scheme is easier to realize and control, not only can reduce nonlinearity introduced in the modulation process to improve the accuracy of laser radar measurement, but also is more convenient to improve the bandwidth of the frequency modulation electric signal to realize higher distance resolution. The quality of a light source from a continuous wave laser is improved by utilizing the laser wavelength measurement and wavelength tracking filtering technology, so that the signal-to-noise ratio of a continuous wave laser beam is improved on one hand, and the measurement precision of a laser radar is improved; on the other hand, the sidelobe suppression ratio of the continuous wave laser beam is improved, so that more nonlinear components can be prevented from being induced in subsequent electro-optic modulation from the source, and the accuracy of laser radar measurement is further improved.
Fig. 1 shows a schematic configuration diagram of a lidar device 100 according to an embodiment of the present disclosure. More specifically, fig. 1 shows the arrangement of the lidar device 100 at the transmitting end. The transmitting end arrangement and the receiving end arrangement of the lidar device may be separate or packaged together, even in some embodiments some lidar devices may include only the transmitting end and other lidar devices may include only the receiving end. Some aspects of the present disclosure are primarily directed to the design of a transmitting end of a lidar device, although improvements in the adaptation of the lidar device to a receiving end will also be described below. Solid arrows in fig. 1 represent optical signal paths, and broken arrows represent electrical signal paths.
As shown in fig. 1, lidar device 100 may include a continuous wave laser 102, a wavelength sensing module 104, and an optical filter 106. Together, these three modules can provide a high quality continuous wave laser beam.
The continuous wave laser 102 outputs a continuous wave laser beam 101. The laser beam will be used to detect or scan the target object. The continuous wave laser 102 may be, for example, a solid state laser such as a Vertical Cavity Surface Emitting Laser (VCSEL), an Edge Emitting Laser (EEL), or an external cavity semiconductor laser (ECDL), a laser diode, a fiber laser. The operating wavelength of the continuous wave laser 102 may be 650nm to 1150nm, 800nm to 1000nm, 850nm to 950nm, or 1300nm to 1600nm. The operating wavelength of the continuous wave laser 102 may be fixed or tunable. In one or more embodiments, the continuous wave laser 102 may further include an optical component optically coupled to the continuous wave laser 102 for collimating or focusing the beam of light emitted by the continuous wave laser 102.
The wavelength sensing module 104 is optically coupled to the continuous wave laser 102. The wavelength sensing module 104 is configured to receive a portion 101-1 of the continuous wave laser beam 101 output by the continuous wave laser 102 and output a sensing electrical signal 103 indicative of a center wavelength of the continuous wave laser beam 101. That is, the wavelength sensing module 104 may enable measurement of the center wavelength of the continuous wave laser beam 101, including photoelectric conversion from the optical signal 101-1 to the electrical signal 103. The sensing electrical signal 103 is indicative of the center wavelength of the continuous wave laser beam 101, which means that the center wavelength of the continuous wave laser beam 101 can be uniquely determined from the magnitude of the sensing electrical signal 103. The magnitude of the sensed electrical signal 103 may be linear or non-linear with the center wavelength of the continuous wave laser beam 101. The linear relationship means that if the center wavelength of the continuous wave laser beam 101 is changed, the magnitude of the sensing electric signal 103 is also changed accordingly, and the slope of the magnitude change amount of the sensing electric signal 103 with respect to the center wavelength change amount is constant for different center wavelengths. The nonlinear relationship means that if the center wavelength of the continuous wave laser beam 101 is changed, the magnitude of the sensing electric signal 103 is also changed accordingly, and the slope of the magnitude change amount of the sensing electric signal 103 with respect to the center wavelength change amount is not constant for different center wavelengths. The wavelength sensing module 104 may include, but is not limited to, various known wavelength measurement techniques based on interferometers, gratings, prisms, and the like.
In some embodiments, the magnitude of the sensing electrical signal 103 may be linear with the center wavelength of the continuous wave laser beam 101. The linear relationship is much simpler in terms of operation than the non-linear relationship. In this way, the mapping relationship between the center wavelength and the magnitude of the electrical signal is relatively simple, so that the calculation cost required for subsequent signal processing on the sensing electrical signal 103 to determine the center wavelength of the continuous wave laser beam 101 can be reduced.
In some embodiments, in addition to achieving a linear relationship between the sensed electrical signal 103 and the center wavelength of the continuous wave laser beam 101, it is desirable that the wavelength sensing module 104 have the advantage of a fast response and easy integration. In this regard, as will be described in greater detail below in connection with FIG. 3, the wavelength sensing module 104 may be implemented based on an optical add-drop (add-drop) ring cavity.
The optical filter 106 is also optically coupled to the continuous wave laser 102. The passband of the optical filter 106 has a center wavelength set according to the sensed electrical signal 103 output by the wavelength sensing module 104, which is set to match the center wavelength of the continuous wave laser beam 101. The optical filter 106 may be a passband filter whose center wavelength is configurable. In some embodiments, the optical filter 106 may receive the sensing electrical signal 103 from the wavelength sensing module 104 and determine the center wavelength of the continuous wave laser beam 101 from the sensing electrical signal 103 and be configured such that the center wavelength of its own passband matches, i.e., is substantially equal to, the center wavelength of the continuous wave laser beam 101. In some embodiments, the measurement of the center wavelength of the continuous wave laser beam 101 by the wavelength sensing module 104 may be done in real time (including near real time), i.e., the wavelength sensing module 104 has a higher response speed. This may be accomplished using, for example, the wavelength sensing module 300 described below in connection with fig. 3. Further, in some embodiments, setting the center wavelength of the passband of the optical filter 106 based on the sensed electrical signal 103 may also be done in real time (including near real time). This means that the setting of the passband center wavelength of the optical filter 106 can be done faster (including for example in the order of femtoseconds, nanoseconds, milliseconds) without a large delay, starting from the receipt of a portion 101-1 of the continuous wave laser beam.
In some embodiments, to achieve setting the center wavelength of the passband of the optical filter 106 based on the sensed electrical signal 103, the lidar device 100 may further include a filter setting module (not shown in the figures). The filter setting module may be included inside or outside the optical filter 106. The filter setting module is configured to receive the sensing electric signal 103, convert the sensing electric signal 103 into a physical quantity capable of setting the center wavelength of the passband of the optical filter 106, and then supply the physical quantity to the optical filter 106. Thus, the optical filter 106 can set the center wavelength of its passband based on the physical quantity. The optical filter 106 may be implemented using a variety of existing filtering structures (e.g., gratings, resonators, etc.), and the corresponding physical quantities that change the center wavelength of its passband may be different for different filtering structures. In some embodiments, the physical quantity includes a filter structure size parameter related to a passband center wavelength. In other embodiments, the physical quantity may include at least one of heat, sound waves, deformation, pressure, material refractive index, and vibration, as non-limiting examples. Such physical quantities can set the filter passband center wavelength by changing the effective refractive index of the optical transmission medium in the optical filter. Compared with structural size parameters, the physical quantity of the latter type has the advantages of high response speed and convenient adjustment.
In some embodiments, the optical filter 106 comprises a tunable optical filter, i.e., the passband center wavelength of the optical filter 106 may vary within a certain range. Thus, when the center wavelength of the continuous wave laser beam 101 varies with time, the sensing electrical signal 103 may comprise a one-dimensional matrix over time, each value in the matrix representing the center wavelength of the continuous wave laser beam 101 at a respective point in time, and accordingly, the center wavelength of the passband of the optical filter 106 is set to also vary based on the sensing electrical signal. That is, when the continuous wave laser 102 is a tunable laser, the optical filter 106 may be a tunable optical filter. As previously described, if the wavelength sensing module 104 and the optical filter 106 both have a fast response speed, the passband center wavelength of the optical filter 106 may change in real time as the center wavelength of the continuous wave laser beam 101 changes. This means that the tuning speed of the tunable optical filter can be of the same order as the tuning speed of the tunable laser.
After setting the passband center wavelength, or at about the same time, the optical filter 106 receives another portion 101-2 of the continuous wave laser beam 101, optically filters it, and outputs a filtered laser beam 105. Point a in fig. 1 may represent a beam splitter for splitting a continuous wave laser beam 101 into a beam 101-1 and a beam 101-2. Since beam 101-1 is used only for wavelength measurement, beam 101-1 may occupy only a small fraction (e.g., 1%, 2%, 5%, 10%, or other value meeting measurement accuracy requirements) of the energy of continuous wave laser beam 101, while the vast majority of the remainder of continuous wave laser beam 101 can be input as beam 101-2 to optical filter 106.
In some embodiments, the optical filter 106 may be a high Q filter for better beam quality improvement (e.g., better sidelobe suppression ratio). The higher the Q value, the smaller the filter passband bandwidth compared to its center frequency, i.e., the better the filter selectivity. In some embodiments, the optical filter 106 has a high Q value such that its passband width is capable of suppressing one or more side lobes in the input laser beam. In a further embodiment, the optical filter 106 has a Q value that is high enough to cause the side lobe of the input laser beam closest to the main lobe (often the side lobe with the highest intensity) to be outside the passband of the optical filter 106. For example, in the case where the center wavelength of the optical filter 106 is aligned with the center wavelength of the input laser beam, the passband width (e.g., full width at half maximum) of the optical filter 106 may be larger than the linewidth of the main lobe due to the high Q value of the micro-ring resonator, so as to ensure that the main lobe is not suppressed, but that the side lobe is suppressed.
The electro-optic modulator 108 receives the filtered laser beam 105 and modulates the frequency modulated electrical signal 107 onto the laser beam 105 to output a modulated optical signal 109. The electro-optic modulator 108 is a modulator based on the electro-optic effect of an electro-optic crystalline material. When a varying voltage carrying an electrical signal is applied to the electro-optic crystalline material, the refractive index of the electro-optic crystalline material changes, causing a corresponding change in the phase, amplitude, intensity and/or polarization state of the light waves passing through the crystalline material, whereby the electrical signal is loaded onto the light to form an optical signal. Electro-optic crystal materials include, but are not limited to, lithium niobate (LiNbO 3), gallium arsenide (GaAs), lithium tantalate (LiTaO 3), or the like. The electro-optic modulator 108 may be an intensity modulator, a phase modulator, or an I/Q (in-phase/quadrature-phase) modulator by employing different configurations. Taking the intensity modulator as an example, the electro-optic modulator 108 may be a Mach-Zehnder modulator (MZM) based on a Mach-Zehnder interferometer structure. The MZM includes a Radio Frequency (RF) input port and a bias input port. The RF input port is for receiving an electrical signal, such as a frequency modulated electrical signal 107; the bias input port is for receiving a bias voltage. In order to maintain linearity between the modulated optical signal and the frequency modulated electrical signal, the bias voltage may be set at a quadrature bias point (also known as a half-wave voltage), where the applied voltage results in a 50% transmission.
The frequency modulated electrical signal 107 is an electrical signal whose frequency varies with time, also called a chirp signal. In some embodiments, the frequency modulated electrical signal 107 may be generated by directly or indirectly frequency or phase modulating an electrical carrier signal. In another embodiment, the frequency modulated electrical signal 107 may be generated by an arbitrary waveform generator. The frequency modulated electrical signal 107 may include a chirp signal and a non-chirp signal. In lidar applications, the use of chirp signals may simplify the processing of electrical signals after photodetection of echo optical signals. As the chirp signal, the frequency-modulated electric signal 107 may include a saw-tooth wave signal, a triangular wave signal, a piecewise chirp signal, and the like from a curve of a frequency varying with time.
The emission optical module 110 is used for guiding the outgoing direction of the modulated optical signal 109 or a part thereof to output a scanning beam for scanning an emission field of view. The emission optics module 110 may enable one-or two-dimensional scanning of the emission field of view. In some embodiments, the emissive optical module 110 may include any number of optical mirrors driven by any number of drivers. For example, the transmit optical module 110 may include any one or more combinations of planar mirrors, prisms, mechanical galvanometers/turning mirrors, polarization gratings, optical Phased Arrays (OPAs), micro-electromechanical systems (MEMS) galvanometers, and the like. For MEMS galvanometers, the mirror surface is rotated or translated in one or two dimensions under electrostatic/piezoelectric/electromagnetic actuation. The emission optical module 110 directs the modulated optical signals to various locations within the field of view under the drive of the driver to effect scanning of the field of view.
The modulated optical signal 109 produced by modulation carries the frequency modulated electrical signal 107 in its intensity or phase. The modulated optical signal 109, or a portion thereof, is illuminated through the transmit optical module 110 to the transmit field of view and reflected upon encountering the target object. The reflection of the target object causes the frequency modulation electric signal carried on the modulated optical signal to change to a certain extent relative to the initial value, and the measurement of the target object is realized by detecting the change. For example, the distance of the target object is such that the frequency of the frequency modulated electrical signal carried by the echo beam varies with time with a certain delay with respect to the frequency of the frequency modulated electrical signal carried by the transmit beam, i.e. there is a frequency difference (beat frequency) from the same instant. The distance of the target object can be calculated by detecting the beat frequency. For another example, the velocity of the target object is such that the frequency modulated electrical signal carried by the echo beam is doppler shifted relative to the frequency modulated electrical signal carried by the transmit beam. The movement speed of the target object can be calculated by detecting the doppler shift.
From the principle of distance/speed measurement by using a laser radar based on frequency modulated continuous waves, it can be seen that the laser radar has high requirements on the stability and purity of the frequency of the light beam. The high stability means that the laser line width of the modulated optical signal is small and the phase noise is low. High purity means that the signal-to-noise ratio of the modulated optical signal is high, and clutter and interference components are few (i.e. linearity is high, and harmonics of each order, mixing components are few). According to the laser radar device disclosed by the embodiment of the invention, the continuous wave laser output by the continuous wave laser is precisely filtered by utilizing the wavelength sensing module and the optical filter, so that the signal-to-noise ratio of a light source beam per se can be improved, the phase noise is reduced, and side lobes are reduced; and the modulation optical signal is generated by combining an external modulation mode, so that better modulation linearity can be provided. The laser radar device according to the embodiment of the disclosure can improve the accuracy of measurement or detection based on the frequency modulation continuous wave principle. In addition, compared with a laser direct modulation scheme, the external modulation scheme allows more degrees of freedom on the frequency-modulated electric signal, more complex coding and modulation can be performed on the basis of frequency modulation, and more functions are realized.
In some embodiments, lidar device 100 may further comprise a receiving-end arrangement. Fig. 2 shows a schematic diagram of a structure of a lidar device at a receiving end according to an embodiment of the present disclosure. The receiving end arrangement of fig. 2 may be incorporated into the lidar device 100 of fig. 1, for example as a separate module from the transmitting end arrangement of fig. 1, or packaged together with the transmitting end of fig. 1. Solid arrows in fig. 2 represent optical signal paths, and broken arrows represent electrical signal paths.
After the beam is reflected from the target object, a portion of the reflected light, i.e., the echo beam 113, is returned to the laser radar device and received by the receiving optical module 112. The receiving optical module 112 sends the received echo beam 115 to the optical coupler 114. The receiving optics module 112 may enable the reception of light from different directions in the field of view. Similar to the transmit optics module 110, the receive optics module 112 may implement one-or two-dimensional scanning of the receive field of view. In some embodiments, the receiving optical module 112 may include any number of optical mirrors driven by any number of drivers. For example, the receiving optical module 112 may include any one or more combinations of planar mirrors, prisms, mechanical galvanometers/turning mirrors, polarization gratings, optical Phased Arrays (OPAs), microelectromechanical system (MEMS) galvanometers, and the like.
The optical coupler 114 couples the echo beam 115 received from the receiving optical module 112 with a portion of the modulated optical signal 109. The modulated optical signal 109 may be a modulated optical signal output from the electro-optic modulator 108. The portion of the modulated optical signal 109 may be a small portion of the modulated optical signal 109. For example, a small portion (e.g., 1%, 10%, 20%, etc.) of the modulated optical signal 109 output by the electro-optic modulator 108 may be split as reference light by an optical splitter or coupler (not shown) and input to the optical coupler 114, while the other large portion is emitted as a probe laser beam to the target, reflected as an echo beam 115. The echo beam 115 is signal light, as opposed to reference light. The coupled optical signal 117 output from the optical coupler 114 is supplied to the photodetector 116 to be photoelectrically converted, and a detection electric signal 119 is output. The optical coupler 114 may include a beam splitter/combiner. The signal light and the reference light are mixed for photoelectric detection, namely coherent detection. The use of coherent detection by a frequency modulated continuous wave lidar can combat interference from other lidar devices and stronger ambient light (e.g., sunlight) because only echoes at the same frequency as the emitted reference light can be detected. In addition, the signal to noise ratio of the system can also be improved by using coherent detection.
The photodetector 116 may include a detection unit and associated receive circuitry. Each receiving circuit may be adapted to process the output electrical signal of the corresponding detection unit. The detection unit comprises various forms of photo detection units or one-or two-dimensional arrays of photo detection units, and accordingly the receiving circuit may be a circuit or an array of circuits. The photodetector measures the power, phase or time characteristic of the coupled optical signal 117 and produces a corresponding current output. The photo detection unit may include an avalanche diode (APD), a Single Photon Avalanche Diode (SPAD), a PN photodiode, a PIN photodiode, or the like. In some embodiments, the photodetector 116 may also include a dual Photodiode (PD) structure, such as a balanced detector (BPD). When a balanced detector is employed, the optical coupler 114 may be integrated with the dual PD structure of the photodetector 116 as a balanced detector. Compared with a single PD structure, the balanced detector with the double PD structure can further reduce noise, improve signal to noise ratio and further improve measurement accuracy of the laser radar.
The detected electrical signal 119 carries beat information associated with the frequency modulated electrical signal 107. The beat information may be converted to a distance of the target object by subsequent circuit processing (e.g., frequency discrimination) and computation. In some embodiments, the detected electrical signal 119 also carries Doppler shift information associated with the frequency modulated electrical signal 107. The Doppler shift information can be converted into the velocity of the target object, also by subsequent circuit processing and computation. Thus, a frequency modulated continuous wave based lidar device allows each transmitted beam to measure distance and velocity information simultaneously. In contrast, most of the existing time-of-arrival (TOF) based lidar devices can only measure distance information, or cannot measure distance and velocity information simultaneously on each pulse, but instead require dense point cloud measurements to estimate velocity by post-computation.
In some embodiments, lidar device 100 may also include a controller 118. The controller 118 may be communicatively coupled to one or more of the continuous wave laser 102, the electro-optic modulator 108, the transmit optical module 110, the receive optical module 112, and the photodetector 116. The controller 118 may exist as a separate processing circuit or may be dispersed in one or more of the continuous wave laser 102, the electro-optic modulator 108, the transmit optical module 110, the receive optical module 112, and the photodetector 116. The controller 118 may control whether and when the continuous wave laser 102 emits a beam and further control the center wavelength of the emitted beam in the case where the laser 102 is a tunable laser. The controller 118 may control when the frequency modulated electrical signal 107 is loaded into the electro-optic modulator 108. The controller 118 may control the emission optics module 110 to scan the light beam to a specific angle/position. The controller 118 may control from which particular angle/position in the field of view the receiving optics module 112 receives reflected light. The controller 118 may process and analyze the electrical signals output by the photodetectors 116 to ultimately determine the position, velocity, etc. characteristics of the target object. The controller 118 may include an Integrated Circuit (IC), an Application Specific Integrated Circuit (ASIC), a microchip, a microcontroller, a central processing unit (cpu), a Graphics Processing Unit (GPU), a Digital Signal Processor (DSP), a Field Programmable Gate Array (FPGA), or other suitable circuitry for executing instructions or performing logic operations. The instructions executed by the controller 118 may be preloaded into an integrated or separate memory (not shown). The memory may store configuration data or commands for use in the continuous wave laser 102, the electro-optic modulator 108, the transmit optical module 110, the receive optical module 112, or the photodetector 116. The memory may also store the electrical signal output from the photodetector 116 or an analysis result based on the output electrical signal. The memory may include Random Access Memory (RAM), read Only Memory (ROM), hard disk, optical disk, magnetic disk, flash memory or other volatile or non-volatile memory, and the like. The controller 118 may include a single or multiple processing circuits. In the case of multiple processing circuits, the processing circuits may have the same or different configurations and may interact or cooperate with each other electrically, magnetically, optically, acoustically, mechanically, etc.
Fig. 3 shows a schematic structural diagram of one specific example of a wavelength sensing module 300 of a lidar device according to an embodiment of the present disclosure. As just one non-limiting example, the wavelength sensing module 300 may be used to implement the wavelength sensing module 104 of fig. 1. The wavelength sensing module 300 primarily includes an optical add-drop ring resonator 302. The optical add-drop ring resonator 302 may include a ring waveguide 307 and straight waveguides 306 and 308 coupled to the ring waveguide 307 on opposite sides thereof, respectively. The number of annular waveguides 307 in between the two straight waveguides 306 and 308 may be one or more. Annular waveguide 307 may include, but is not limited to, one or more of microspheres, micro-rings, micro-discs, micro-pillars, and micro-ring cores. The optical add-drop ring resonator 302 may include four ports: an input port 309, a through port 310 directly connected to the input port 309 by a straight waveguide, a drop port 311 on the other straight waveguide on the same side as the input port 309, and an insert port 312 on the other straight waveguide on the opposite side as the input port 309. The optical add-drop ring resonator 302 may have symmetry. This means that the input port 309 of the optical add-drop ring resonator 302 may not be limited to the specific location shown in fig. 3, but may be any one of four ports, and the locations of the corresponding other ports may also be changed.
An input laser beam 301 enters from an input port 309 of the ring resonator 302. Note that the root mean square of the ratio of the optical powers of the through port 310 and the drop port 311 of the ring resonator 302 is an Amplitude Comparison Function (ACF), the ACF can be expressed approximately as:
Where Δλ represents the shift of the center wavelength of the input laser beam 301 relative to the resonant wavelength of the ring resonator 302, r and t are the self-coupling coefficient and the mutual coupling coefficient of the ring resonator 302, respectively, k is the ratio of the coupling losses of the through port 310 and the drop port 311, and FSR is the free spectral range. After the ring cavity 302 is fabricated, r, t, k, and FSR are all values related to the micro-ring cavity geometry, i.e., are constants, and therefore the ACF exhibits a linear relationship with respect to Δλ.
In some embodiments, the linearity of the ACF with respect to Δλ is associated with the loss experienced by the laser in the annular waveguide 307 of the annular resonator 302. Specifically, the smaller the loss experienced by the laser traveling one turn in the annular waveguide 307 of the annular resonator 302, the closer the relationship of ACF to Δλ approximates the linear relationship in equation (1). The loss experienced by a laser traveling one turn in the annular waveguide 307 may be determined by the power loss coefficient γ (in 1/cm) of the annular waveguide material and the optical path length L of the annular waveguide 307 (i.e., the circumference of the annular waveguide 307). In the case where the annular waveguide material is constant, that is, the power loss coefficient γ is constant, the smaller the optical path length L is, the smaller the loss experienced by the laser light in the annular waveguide 307 is. As non-limiting examples, the optical path length L may be on the order of tens of microns, hundreds of microns, millimeters. At this time, if the annular waveguide 307 is considered to be made of a typical silicon material (as just one non-limiting example), the loss experienced by the laser light at the annular waveguide 307 can be extremely small, thereby effectively ensuring that ACF and Δλ obey the linear relationship in equation (1). In other embodiments, the optical path length L may be other lengths.
In some embodiments, to further increase the Q-value, operational stability, and size reduction of the ring resonator 302, the ring resonator 302 may be designed as a microcavity that operates in whispering gallery mode. This can be achieved by selecting the refractive index of the material on both sides of the dielectric boundary of the annular waveguide 307 of the ring resonator 302. In some embodiments, the ring resonator 302 may be implemented on a silicon-on-insulator (SOI) wafer. At this point, standard Complementary Metal Oxide Semiconductor (CMOS) fabrication processes may be used to facilitate integration with other optical circuits and circuitry. In other embodiments, the ring resonator 302 may be formed on other optical waveguide materials, including optical chip integration platforms such as silicon dioxide (SiO 2) materials, organic polymer materials, silicon nitride (SiN) materials, indium phosphide (InP) materials, and lithium niobate (LiNbO 3) materials. Since ring cavity 302 can be implemented on a variety of different material integration platforms, ring cavity 302 can sometimes be integrated simultaneously with at least a portion of the laser that produces the laser beam, increasing overall integration.
To calculate ACF, the wavelength sensing module 300 may include a power detection and post-processing circuit 313. The circuit 313 may include optical power measurement circuits 314 and 315 connected to the through port 310 and the drop port 311, respectively, and a post-processing circuit 316. The optical power measuring circuits 314 and 315 measure the optical power values of the two ports, respectively, and the post-processing circuit 316 calculates the ratio of the two optical power values and takes the square root. By way of example, post-processing circuitry 316 may include analog-to-digital converters (ADCs) and digital signal processing circuitry to enable the ratio and square root of power to be found in the digital domain. Based on digital circuit integration techniques, the post-processing circuitry 316 may be better integrated with the optical power measurement circuitry 314 and 315 (e.g., based on III-V semiconductor material process integration) and the ring resonator 302 (applicable to a variety of material integration platforms), reducing device size. Thus, the sensing electrical signal 303 output by the wavelength sensing module 300 is or indicates the root mean square of the ratio of the optical powers of the through port 310 and the drop port 311 of the ring resonator 302, i.e., ACF. It is to be appreciated that the structural composition of the power detection and post-processing circuit 313 shown in fig. 3 is merely exemplary, and that in other embodiments, the power detection and post-processing circuit 313 may employ other circuit configurations. For example, in some embodiments, the power detection and post-processing circuit 313 may further include a digital-to-analog converter (DAC) in the post-processing circuit 316 to convert the derived digital value into an analog current/voltage signal capable of indicating the magnitude of the center wavelength of the input laser beam 301 and output as the sensing electrical signal 303. As will be described later, the analog electrical signal may be provided to an optical filter 106 to control the center wavelength of its passband.
Fig. 4 shows a schematic structural diagram of one specific example of an optical filter 400 of a lidar device according to an embodiment of the disclosure. Optical filter 400 is merely an example, and not a limitation, of optical filter 106 in fig. 1. The optical filter 400 generally includes an optically add-split ring resonator 402, similar to the optically add-split ring resonator 302 of fig. 3. The optical add-drop ring resonator 402 may include a ring waveguide 407 and straight waveguides 406 and 408 coupled to the ring waveguide 407 on opposite sides thereof, respectively. The number of annular waveguides 407 intermediate the two straight waveguides 406 and 408 may be one or more. The annular waveguide 407 may include, but is not limited to, one or more of microspheres, micro-rings, micro-discs, micro-pillars, and micro-ring cores. The optical add-drop ring cavity 402 may include four ports: an input port 409, a through port 410 directly connected to the input port 409 through a straight waveguide, a drop port 411 on the other straight waveguide on the same side as the input port 409, and an insert port 412 on the other straight waveguide on the opposite side of the input port 409. The optical add-drop ring cavity 402 may have symmetry. For example, the optical add-drop ring cavity 402 may be centrally symmetric. This means that the input port 409 of the optical add/drop ring cavity 402 may not be limited to the specific position shown in fig. 4, but may be any one of four ports, and the positions of the respective other ports may be changed.
A laser beam 401 requiring optical filtering (e.g., continuous wave laser beam 101-2 of fig. 1) enters from an input port 409 of the ring cavity 402 and a filtered laser beam 405 exits from a drop port 411 of the ring cavity 402. The ring resonators 402 thus connected constitute a pass band filter.
The ring resonator 402 may set its passband center wavelength based on the sensed electrical signal 403. The passband center wavelength of the ring resonator 400 may be set based on the sensed electrical signal 403, for example, by the filter setting module 413. In some embodiments, the filter setting module 413 may convert the sensed electrical signal 403 (e.g., in the form of a voltage or current) into a physical quantity such as one or more of heat, sound waves, deformation, pressure, material refractive index, and vibration. The physical quantity is then provided to the ring cavity 402 to set or adjust the filter passband center wavelength of the ring cavity 402. For example, the physical quantity may be provided to the optical coupling region of the ring cavity 402 to set or adjust the filter passband center wavelength of the ring cavity 402 by changing the effective refractive index of the optical coupling region medium. Other features of the filter setting module are described above in connection with fig. 1, and are not described here again.
The optical filter 400 is used to realize the optical filter 106 of fig. 1, which not only can realize accurate filtering, but also has the advantages of high response speed, high Q value, small size and easy integration.
In some embodiments, to further increase the Q-value, operational stability, and size reduction of the ring cavity 402, the ring cavity 402 may be designed as a microcavity that operates in whispering gallery mode. This may be achieved by selecting the refractive index of the material on both sides of the dielectric boundary of the annular waveguide 407 of the annular resonator 402. In some embodiments, the ring resonator 402 may be implemented on an SOI wafer. At this point, standard CMOS fabrication processes may be used to facilitate integration with other optical circuits and circuitry. In other embodiments, the ring resonator 402 may be formed on other optical waveguide materials, including optical chip integration platforms such as SiO 2 materials, organic polymer materials, siN materials, inP materials, and LiNbO 3 materials. Because ring cavity 402 can be implemented on a variety of different material integration platforms, ring cavity 402 can sometimes be integrated simultaneously with at least a portion of the laser that produces the laser beam, increasing overall integration.
In some embodiments, for ease of fabrication, ring cavity 402 may be fabricated using the same integration process and the same dimensional parameters as ring cavity 302 of FIG. 3; or in a further step, ring cavity 402 may be fabricated using the same integrated process as ring cavity 302 but with different dimensional parameters.
Fig. 5 shows a schematic diagram of one example of integrating the wavelength sensing module of fig. 3 with the optical filter of fig. 4. The input light is split into two parts via an optical coupler 502, a small part of which is fed to the ring cavity 504 of the wavelength sensing module for wavelength sensing and a large part of which is fed to the ring cavity 510 of the optical filter for optical filtering. The through port and the drop port of the ring resonator 504 are connected to the photodetector PD, respectively, and each is subjected to analog-to-digital conversion (ADC) and then enters a post-processing circuit to obtain ACF. The digital values are converted into voltage/current signals by digital-to-analog conversion (DAC). The voltage/current signal is provided to the micro-heater 510 disposed in the optical coupling region of the ring resonator 510 to generate a certain amount of heat, and the refractive index of the optical coupling region is changed, so that the center wavelength of the passband of the ring resonator 510 is matched with the center wavelength of the input light sensed by the ring resonator 504, thereby achieving the purpose of accurate filtering.
Fig. 6 illustrates a schematic diagram of the working principle of dynamic filtering with a wavelength sensing module and an optical filter according to an embodiment of the present disclosure. The input laser beam 601 may have different center wavelengths lambda 1、λ2…λn at different times t 1、t2…tn, respectively. Taking time t n as an example, the spectrum of input laser beam 601 has side lobe 612 in its vicinity in addition to main lobe 611 at λ n. Curve 602 represents the ability of the wavelength sensing module in the optical filtering device to convert the center wavelength of the input laser beam 601 into a sensed electrical signal P output indicative of the center wavelength. In addition to the linear relationship shown in the figure, the wavelength λ and the signal P may have a nonlinear relationship. On the time series t 1、t2…tn, the sensed electrical signals P correspondingly constitute a one-dimensional matrix [ P 1,P2…Pn ]. Sub-graph 604 shows that at time t n, the optical filter has a filter curve 604-1 with a center wavelength of 604-1 that matches the center wavelength λ n at which main lobe 611 is located, allowing main lobe 611 to pass, while side lobe 612 is filtered out. Output 605 represents the filtered laser beam.
According to the wavelength sensing module and the optical filter, the central wavelength of the input laser beam is measured, and targeted filtering is performed, so that side lobes of the laser beam can be effectively restrained, and the beam quality is improved. By incorporating such a filter device into a frequency modulated continuous wave based lidar apparatus, the signal to noise ratio from the laser source itself can be improved and nonlinearity reduced. Furthermore, such a filtering device can operate in cases where the center wavelength of the input laser beam is unknown or varies, and is therefore particularly suitable for optimizing the laser beam from a tunable laser. This makes it possible for the lidar device to use a wavelength tunable laser in combination with an optical dispersive element (e.g. grating, OPA, etc.) for beam scanning. If the structures in fig. 3 and fig. 4 are further adopted to realize the wavelength sensing module and the optical filter respectively, the filtering device has the advantages of quick response, high Q value, small size, high integration level and the like, and the requirements of the laser radar device on high scanning speed, small size and convenience in integration are more satisfied.
An exemplary implementation of a scanning system of a lidar device at a transmitting end and a receiving end according to an embodiment of the present disclosure is described below. The scanning system at the transmitting end is mainly implemented by a transmitting optical module (e.g., transmitting optical module 110 of fig. 1). The scanning system at the receiving end is mainly implemented by a receiving optical module (e.g., receiving optical module 112 of fig. 2).
As previously described, since the wavelength sensing module and the optical filter according to the present disclosure have a dynamic filtering function, they are particularly suitable for filtering and optimizing the laser beam of a tunable laser. The lidar device according to embodiments of the present disclosure may thus use a tunable laser in combination with an Optical Phased Array (OPA) or dispersive optical element for beam scanning. The principle is that OPA or dispersive optical elements are capable of emitting light of different wavelengths to different locations in space. By changing the center wavelength of the continuous wave laser beam output by the tunable laser, scanning of a certain space can be realized. Compared with traditional mechanical scanning, the tunable laser is combined with the OPA or the dispersive optical element to perform beam scanning, so that the use of movable devices can be reduced, and the system is enabled to realize higher solid state, so that the stability and reliability are higher, and the integration is also facilitated.
However, without employing a wavelength sensing module and an optical filter according to the present disclosure, a lidar device using a tunable laser in combination with an OPA or a dispersive optical element for beam scanning may be susceptible to severe side lobes of the laser beam of the laser light source. This is because: on the one hand, the tunable laser which can be directly used is generally from the field of optical communication, such as Wavelength Division Multiplexing (WDM) application, and the requirement on the sidelobe suppression ratio in the field of optical communication is more than two orders of magnitude lower than that of laser radar application, so that the sidelobe suppression ratio of the output light beam of the tunable laser is not very high; on the other hand, main and side lobes in the laser beam may be directed in different directions in the field of view due to wavelength differences and dispersion effects. It is possible that there are no high reflectivity objects in the scan direction of the main lobe, whereas high reflectivity objects are present in the scan direction of the side lobe. The high reflectivity object has a large return gain. These two factors result in the possibility that the intensity of the light reflected back from the side lobe is greater than that reflected back from the main lobe, so that false detection, i.e. a "ghost" phenomenon, occurs in the laser radar.
Advantageously, the wavelength sensing module and optical filter according to the present disclosure also have the effect of suppressing side lobes, improving the quality of the laser beam, and reducing or eliminating "ghosting" due to side lobes when used in a laser radar apparatus that uses a tunable laser in combination with an OPA or dispersive optical element for beam scanning, reducing false detection.
For ease of description, referring again to fig. 1, in some embodiments, the continuous wave laser 102 of the lidar device is a tunable laser, and accordingly, the transmit optical module 110 may be configured to direct the modulated optical signal 109, or a portion thereof, generated based on the continuous wave laser beam 101 with a different center wavelength output by the tunable laser, to respective different locations in the transmit field of view. The center wavelength of the continuous wave laser beam 101 determines the beam scanning position/angle corresponding to the emission optical module 110. The range of wavelength tuning determines the maximum angular range of the beam sweep and the accuracy of wavelength tuning determines the beam sweep accuracy in space. For example, as the output center wavelength of the tunable laser varies between a minimum wavelength and a maximum wavelength, the beam emitted outward by the emission optical module 110 correspondingly varies between two extreme positions/angles corresponding to the minimum wavelength and the maximum wavelength, respectively.
In some embodiments, the emission optics module 110 may include an OPA. The OPA may comprise a one-or two-dimensional array to enable scanning in one or two dimensions.
In some embodiments, the transmitting optical module 110 may include a dispersive optical element. The dispersive optical element can realize the mapping of different light wavelengths to different positions in a one-dimensional space. For example, the dispersive optical element may direct modulated optical signals 109, or portions thereof, generated based on continuous wave laser beams 101 with different center wavelengths output by the tunable laser, to different locations in the first direction in the emission field of view. The first direction may be vertical, horizontal or any other direction depending on the configuration of the dispersive optical element. In some embodiments, the dispersive optical element may comprise a prism. In other embodiments, to facilitate integration and solidifiability, the dispersive optical element may comprise a grating structure, such as any one or more of an arrayed waveguide grating, a diffraction grating, and a sub-wavelength grating.
In addition to the dispersive optical element, the transmitting optical module 110 may also comprise a deflectable mirror in order to achieve scanning of another dimension of the two-dimensional space. The deflectable mirror may be a mechanical scanning galvanometer, turning mirror, or other mirror that mechanically moves under drive. The deflectable mirror directs the light output from the dispersive optical element through different deflections to different positions in a second direction in the emission field of view, which may be perpendicular to the first direction, thereby enabling scanning in two dimensions.
Fig. 7 shows a schematic diagram of a lidar device using a dispersive optical element in combination with a deflectable mirror as the transmitting optical module according to an embodiment of the present disclosure. The transmitting optical module 700 includes a dispersive optical element 702 and a deflectable mirror 704. For combination with a frequency modulated continuous wave lidar, the input beam of dispersive optical element 702 may be a laser beam modulated with a frequency modulated electrical signal, such as modulated optical signal 109 or a portion thereof in fig. 1. The dispersive optical element 702 may emit light beams of different center wavelengths lambda 1,λ2,…,λn incident at the same location at different locations, e.g., in the vertical direction. Light exiting at different locations is collimated by the emission lens group 706 and reflected via the deflectable mirror 704 to different locations in a first direction (e.g., also in a vertical direction) in the emission field of view, thereby effecting a first dimension scan. Fig. 8 provides a schematic diagram of a first dimension scan using dispersive optical elements. The light beams with different center wavelengths lambda 1,λ2,…,λn, which are output from the dispersive optical element 802 and are arranged in the vertical direction, are collimated by the emission lens group 806 and then mapped to different scanning areas in the vertical direction of the emission field of view. That is, each wavelength corresponds to one scanning area arranged in the vertical direction. For ease of description, FIG. 8 omits a deflectable mirror for the second dimension scan.
Returning to fig. 7, to achieve the second dimension scan, the deflectable mirror 704 may also deflect such that, for a beam of one of the wavelengths, exiting a particular location of the dispersive optical element 702, may reflect to a different location in the second direction (e.g., the horizontal direction) in the emission field of view via a different deflection of the deflectable mirror 704.
Note that in some embodiments, the emission lens groups 706 and 806 in fig. 7 and 8 may be omitted.
According to the embodiment of the disclosure, if the tunable laser is adopted to combine with the OPA or the dispersive optical element to perform beam scanning at the transmitting end, at least part of scanning devices can be multiplexed at the receiving end due to the good optical path bidirectional symmetry of the OPA and the dispersive optical element, so that a transceiver coaxial optical system is realized. Compared with a receiving and transmitting non-coaxial optical system, the receiving and transmitting coaxial optical system has no offset between a transmitting field of view and a receiving field of view, does not need to be registered, and has higher signal to noise ratio.
Fig. 9 shows an exemplary structure for further implementing a transceiving coaxial optical system on the transmit optical module of fig. 7. Wherein the dispersive optical element 902, the deflectable mirror 904, and the emission lens group 906 are the same as the dispersive optical element 702, the deflectable mirror 704, and the emission lens group 706 in fig. 7, respectively, and are not described herein. Unlike fig. 7, in fig. 9, the echo beam reflected from the target object is received via the deflectable mirror 904 and reflected to the transflector 908. Since the receive optical path partially coincides with the transmit optical path, the transflective assembly 908 may be disposed on the optical path (including an extension of the optical path) between the dispersive optical element 902 (the transmit lens group 906 if the transmit lens group 906 is present) and the deflectable mirror 904. The transflective assembly 908 directs the echo beam to an optical coupler 914 where it is mixed with reference light (e.g., a portion of the modulated optical signal 109) and then focused by a receive lens assembly 918 before being incident on a photodetector 916. Note that the receiving lens group 918 in fig. 9 is used for beam focusing, and may be omitted in some embodiments. The receiving lens group 908 may be composed of two or more lenses having different focal lengths. Each lens of the receiving lens group 908 may be double coated.
The transflective assembly 908 allows light from the transmit light path to pass through and reflects light from the reflected light path to the photodetector 916. In some embodiments, the transflective assembly 908 may include a mirror with an aperture in the center. The light beam of the transmit path may thus be transmitted through the aperture, while the light of the receive path may be reflected via the non-aperture region. The aperture may be located at the focal point of the emission lens group 904 to reduce obstruction of the probe beam on the emission path. The focal point of the emission lens group is often close to the emission lens group (e.g., several millimeters or tens of millimeters), and thus a mirror with an aperture is also disposed close to the emission lens group. The mirrors with openings may include dielectric film mirrors or metal mirrors. In other embodiments, the mirror 908 can be a half mirror. The transmittance of the half mirror may be 50%, 60% or 70% or other values. In other embodiments, mirror 908 can be a polarizing beam splitter. The light of the emission light path and the light of the reflection light path can have different polarization states, and then the polarization beam splitter is utilized to enable one path of light of the emission light path and the reflection light path to be transmitted and the other path of light to be reflected, so that the light paths are separated.
As can be seen from fig. 9, the transmitting optical module and the receiving optical module share a deflectable mirror 904, realizing a transceiving coaxial optical system. This allows the receive field of view to be consistent with the transmit field of view once the deflection angle of the deflection mirror 904 is determined at the time of the transmit scan, avoiding interference of echoes reflected in other areas outside the field of view, thereby improving the accuracy and sensitivity of detection.
Although fig. 9 shows a transceiving coaxial optical system, the lidar device according to the present disclosure is not limited thereto, and a transceiving non-coaxial optical system may also be employed. For example, the receiving optical module may be completely separate from the transmitting optical module without multiplexing any scanning devices.
The terms "upper," "lower," "inner," "outer," and the like in this disclosure indicate an orientation or positional relationship based on that shown in the drawings, merely for convenience in describing embodiments of the present invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the embodiments of the present invention.
The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Furthermore, the technical terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. References to a "first" component do not necessarily require the provision of a "second" component. Furthermore, unless explicitly indicated otherwise, reference to "a first" or "a second" component does not mean that the referenced component is limited to a particular order.
In the description of the present disclosure, the meaning of "a plurality" is two or more, unless explicitly defined otherwise. The term "or" means an inclusive "or" rather than an exclusive "or". The term "based on" means "based at least in part on.
In the description of the present disclosure, unless explicitly defined otherwise, the technical term "connected" should be interpreted broadly, for example, as being either fixedly connected, detachably connected, or integrally formed; or may be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the embodiments of the present invention will be understood by those of ordinary skill in the art according to specific circumstances.
In the description of the present disclosure, unless expressly stated and limited otherwise, a first feature "up" or "down" a second feature may be that the first and second features are in direct contact, or that the first and second features are in indirect contact via an intermediary.
Finally, it should be noted that: although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention, and are intended to be included within the scope of the appended claims and description. In particular, the technical features mentioned in the respective embodiments may be combined in any manner as long as there is no structural conflict. The present invention is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions falling within the scope of the claims.
Claims (21)
1. A lidar device, comprising:
a continuous wave laser configured to output a continuous wave laser beam;
a wavelength sensing module optically coupled to the continuous wave laser configured to receive a portion of the continuous wave laser beam and output a sensing electrical signal indicative of a center wavelength of the continuous wave laser beam;
An optical filter optically coupled to the continuous wave laser, a passband of the optical filter having a center wavelength set based on the sensed electrical signal that matches a center wavelength of the continuous wave laser beam, the optical filter configured to optically filter another portion of the continuous wave laser beam to output a filtered laser beam;
an electro-optic modulator configured to modulate the filtered laser beam with a frequency modulated electrical signal to output a modulated optical signal; and
And an emission optical module configured to guide an outgoing direction of the modulated optical signal to output a scanning beam for scanning the emission field of view.
2. The lidar device of claim 1, wherein the wavelength sensing module comprises a first optically-inserted split ring resonator, and the sensed electrical signal comprises a root mean square of an optical power ratio of a pass-through port and a drop-out port of the optically-inserted split ring resonator.
3. The lidar device of claim 2, wherein the first optical add-drop ring resonator comprises a whispering gallery mode microcavity.
4. The lidar device of claim 1, wherein the optical filter has a passband width capable of suppressing one or more side lobes in the continuous wave laser beam.
5. The lidar device of claim 1, wherein the optical filter comprises a second optically-inserted split ring resonator.
6. The lidar device of claim 5, wherein the second optical add-drop ring resonator comprises a whispering gallery mode microcavity.
7. The lidar device of claim 1, further comprising: a filter setting module configured to:
receiving the sensing electrical signal;
converting the sensed electrical signal into a physical quantity capable of setting a center wavelength of a passband of the optical filter; and
The physical quantity is supplied to the optical filter,
Wherein a center wavelength of a passband of the optical filter is set based on the physical quantity.
8. The lidar device of claim 7, wherein the physical quantity comprises at least one of heat, sound waves, deformation, pressure, material refractive index, and vibration.
9. The lidar device according to claim 1, wherein the frequency-modulated electrical signal is a chirp signal.
10. The lidar apparatus of claim 1, wherein the continuous wave laser is a tunable laser and the optical filter is a tunable optical filter.
11. The lidar device according to claim 10, wherein the transmit optical module is configured to direct the modulated optical signals generated based on continuous wave laser beams with different center wavelengths output by the tunable laser to respective different locations in a transmit field of view.
12. The lidar device of claim 11, wherein the transmit optical module comprises an optical phased array.
13. The lidar device of claim 11, wherein the transmit optical module comprises:
A dispersive optical element configured to direct the modulated optical signal generated based on continuous wave laser beams with different center wavelengths output by the tunable laser to different locations in a first direction in an emission field of view.
14. The lidar device according to claim 13, wherein the dispersive optical element comprises any one or more of an arrayed waveguide grating, a diffraction grating and a sub-wavelength grating.
15. The lidar device of claim 13, wherein the transmit optical module further comprises:
A deflectable mirror configured to direct the same light beam from the dispersive optical element to a different location in a second direction in the emission field of view by a different deflection, wherein the first direction is perpendicular to the second direction.
16. The lidar device of claim 1, further comprising:
a receiving optical module configured to receive an echo beam from a receiving field of view;
An optical coupler configured to couple the modulated optical signal with an echo beam received by a receiving optical module to output a coupled optical signal; and
A photodetector configured to detect the coupled optical signal to output a detection electrical signal.
17. The lidar device according to claim 16, wherein the photodetector is a balanced detector.
18. The lidar device according to claim 16, wherein the lidar device comprises a transceiving coaxial optical system.
19. The lidar device of claim 18,
Wherein the emission optical module comprises:
A dispersive optical element configured to direct the modulated optical signal generated based on a continuous wave laser beam having a different center wavelength output by the tunable laser to a different location in a first direction in an emission field of view; and
A deflectable mirror configured to direct the same light beam from the dispersive optical element through different deflections to different positions in a second direction in the emission field of view, wherein the first direction is perpendicular to the second direction,
Wherein the receiving optical module comprises:
the deflectable mirror is configured to direct echo beams from different positions in a second direction in the receive field of view to the transflector assembly by different deflections; and
The transflective assembly is configured to direct an echo beam from a deflectable mirror to the optical coupler.
20. The lidar device according to claim 19, wherein the transflector assembly is disposed in an optical path between the dispersive optical element and the deflectable mirror.
21. The lidar apparatus of claim 19, wherein the transflective assembly comprises at least one of:
a mirror having an opening in the center;
A half-mirror; or (b)
A polarizing beam splitter.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CN202211581053.8A CN118209958A (en) | 2022-12-09 | 2022-12-09 | Laser radar apparatus |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CN202211581053.8A CN118209958A (en) | 2022-12-09 | 2022-12-09 | Laser radar apparatus |
Publications (1)
Publication Number | Publication Date |
---|---|
CN118209958A true CN118209958A (en) | 2024-06-18 |
Family
ID=91456351
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CN202211581053.8A Pending CN118209958A (en) | 2022-12-09 | 2022-12-09 | Laser radar apparatus |
Country Status (1)
Country | Link |
---|---|
CN (1) | CN118209958A (en) |
-
2022
- 2022-12-09 CN CN202211581053.8A patent/CN118209958A/en active Pending
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US10578740B2 (en) | Coherent optical distance measurement apparatus and method | |
WO2022062105A1 (en) | Array coherent ranging chip and system thereof | |
WO2021012132A1 (en) | Lidar system | |
CA3141211C (en) | Frequency modulated scanning lidar with 360 degrees field of view | |
US11531111B2 (en) | 360 degrees field of view scanning lidar with no movable parts | |
US20200072979A1 (en) | Reduction of ADC Sampling Rates in LIDAR Systems | |
US11579294B2 (en) | Lidar system with integrated frequency shifter for true doppler detection | |
US11892565B2 (en) | Controlling direction of LIDAR output signals | |
CN212515027U (en) | Array type coherent ranging chip and system thereof | |
US11906665B2 (en) | Method for scanning a transmitted beam through a 360° field-of-view (FOV) | |
EP4246835A1 (en) | Coherent receiving device and anemometry lidar system | |
CN111880190A (en) | Coherent laser ranging chip and system thereof | |
US11624810B2 (en) | LIDAR system with reduced speckle sensitivity | |
CN111007533B (en) | Laser radar spectrum analyzer | |
US11536837B2 (en) | Generation of LIDAR data | |
JP7315154B2 (en) | Distance and speed measuring device | |
CN116626696A (en) | Frequency modulation continuous wave laser range unit | |
CN118209958A (en) | Laser radar apparatus | |
CN118259257A (en) | Lidar device and vehicle | |
CN116710740A (en) | Photonic integrated circuit | |
KR20220004432A (en) | LiDAR apparatus having improvded signal-to-noise ratio | |
CN118017340A (en) | Optical filter device, laser radar apparatus, and laser beam quality improvement method | |
CN118294926A (en) | Optical filter device, laser radar apparatus and vehicle | |
CN116577804B (en) | FMCW laser radar based on chip integration | |
US20240027582A1 (en) | Array coherent ranging chip and system thereof |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
PB01 | Publication | ||
PB01 | Publication | ||
SE01 | Entry into force of request for substantive examination |