CN113608228A - Two-dimensional multi-beam laser radar quick scanning device and method based on Blass matrix - Google Patents

Two-dimensional multi-beam laser radar quick scanning device and method based on Blass matrix Download PDF

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CN113608228A
CN113608228A CN202110880229.9A CN202110880229A CN113608228A CN 113608228 A CN113608228 A CN 113608228A CN 202110880229 A CN202110880229 A CN 202110880229A CN 113608228 A CN113608228 A CN 113608228A
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phase
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CN113608228B (en
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李王哲
王瑞璇
马尉超
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Aerospace Information Research Institute of CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/481—Constructional features, e.g. arrangements of optical elements
    • G01S7/4817—Constructional features, e.g. arrangements of optical elements relating to scanning
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G01S7/4911—Transmitters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G01S7/4912—Receivers
    • G01S7/4915—Time delay measurement, e.g. operational details for pixel components; Phase measurement
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Electromagnetism (AREA)
  • Variable-Direction Aerials And Aerial Arrays (AREA)

Abstract

The invention discloses a two-dimensional multi-beam laser radar quick scanning device and method based on a Blass matrix. The tunable laser source array is used for generating multiple paths of incoherent optical signals, the phases of the multiple paths of incoherent optical signals are adjusted according to the preset beam direction by controlling a phase shifter in the Blass matrix, so that each path of optical signal reaches each antenna unit with a specific phase difference, an optical phase control array is formed, and scanning in a dimension parallel to the plane of the antenna array is realized. Because the diffraction grating is etched on the end face of the waveguide of the antenna unit, the diffraction angle of the diffraction grating is related to the wavelength of an optical signal, the scanning on the dimension vertical to the plane of the antenna array can be realized by adjusting the central wavelength of the laser, and the rapid scanning on two dimensions is realized. In addition, the invention has the advantages of compact structure, easy integration, flexible expansion of the number of wave beams and the like, and can meet various application requirements.

Description

Two-dimensional multi-beam laser radar quick scanning device and method based on Blass matrix
Technical Field
The invention relates to the field of radar detection and imaging, and provides a two-dimensional multi-beam laser radar quick scanning device and method based on a Blass matrix, which are oriented to the requirement of quick scene scanning laser radar.
Background
With the rapid development of technologies such as automatic driving, bridge collision avoidance and space intersection butt joint, it is an important trend to further improve the ranging capability, imaging accuracy and imaging speed of the radar. The traditional microwave imaging radar has the problems of large system volume, wide antenna beam angle, long imaging time and the like, and is more limited in increasingly complex application environments in the future. The laser radar with fast ranging and high resolution imaging capability becomes an excellent choice for this application scenario.
The existing laser radar ranging technology mainly adopts single-beam scanning ranging, and realizes two-dimensional scanning by respectively adjusting the phase and the wavelength of light waves. Although fast scan imaging can be realized by controlling through an external circuit, new requirements are put on the radar ranging and the speed of scan imaging along with the complex change of the environment. In this regard, the multi-beam simultaneous scanning lidar is becoming the latest trend. Recently, a Butler matrix-based laser radar multi-beam fast scanning method is proposed, but in the scheme, because the Butler matrix can only meet the limitation of a fixed scanning angle, the system has to add a phase shifter behind the Butler matrix to realize angle scanning within a certain range, which undoubtedly increases the complexity of the system.
In conclusion, the existing laser radar has the problems of low distance measurement and imaging scanning speed, limited scanning angle and the like.
Disclosure of Invention
In order to overcome the defects of the conventional laser radar ranging and imaging method, the invention discloses a two-dimensional multi-beam laser radar quick scanning device and method based on a Blass matrix.
The technical scheme of the invention is as follows: a two-dimensional multi-beam laser radar fast scanning device based on a Blass matrix comprises the following components: the device comprises a tunable laser source array unit, a multi-beam forming unit, an optical phased array antenna unit, a signal receiving and processing unit and a laser control unit; wherein the content of the first and second substances,
the tunable laser source array unit comprises a plurality of tunable lasers for generating a plurality of continuous optical wave signals OS with the same wavelength, simultaneous tuning and mutually irrelevant phases1，OS2，...，OSMThe number of the tunable lasers is equal to the number M of the preset laser beam directions scanned simultaneously;
the multi-beam forming unit: the device is used for respectively shaping the amplitude and the phase of M paths of incoherent optical signals generated by a laser source array, adjusting the signal power transmitted to N antenna subunits in an optical antenna array and the phase difference value between adjacent antenna subunits according to the preset laser beam direction corresponding to each path of optical signal, and finally respectively splitting and shaping the M paths of incoherent optical signals and transmitting the M paths of incoherent optical signals to an optical phased array antenna unit;
the optical phased array antenna unit: a plurality of optical signals with fixed phase difference output by the multi-beam forming unit are emitted to form beams in the direction corresponding to the fixed phase difference, and the optical wave signals reflected by the target are received and then sent to a subsequent signal processing unit; in addition, a diffraction grating is added to each transmitting port of the optical antenna unit, so that the output laser beam is scanned in the other dimension;
a signal reception processing unit: the system is used for receiving the light signals reflected by the target in the direction of the split beams, combining the light signals with the light source signals corresponding to the direction, sending the light signals to a photoelectric detector for photoelectric conversion, and then converting the light signals into a digital domain for subsequent signal processing through low-speed sampling;
a laser control unit: the device is used for controlling the pumping current of the laser so as to adjust the wavelength of the output light of the laser according to the scanning angle requirement; and is also used for controlling the power and phase of each output optical signal in the multi-beam forming unit so as to realize the power required by the corresponding beam pointing and the phase difference between adjacent antenna sub-units, thereby realizing the simultaneous scanning of a plurality of different beam pointing.
Further, the tunable laser source array unit includes M tunable lasers for generating M incoherent optical signals with the same wavelength.
Further, the multi-beam forming unit comprises M × N MZI structures, each MZI structure is configured to control power of each signal transmitted to the optical antenna; each MZI structure comprises two 3-dB couplers and 1 phase shifter, wherein one end output of the first 3-dB coupler is connected with one input end of the second 3-dB coupler through the phase shifter; the other end output of the first 3-dB coupler is directly connected to the other input of the second 3-dB coupler.
Further, the multi-beam forming unit includes 2 × M × N phase shifters, including M × N phase shifters on the trunk and phase shifters in the upper branches of the M × N MZI structures, where the phase shifters on the trunk are used to control phase differences required by different light beams to point to corresponding optical signals, and the phase shifters on the upper branches of the MZI structures are used to control power of signals transmitted to the optical antennas on each path;
further, the optical phased array antenna unit includes: n optical waveguides with diffraction grating on the front end for transmitting and receiving light wave signals in specific beam direction as optical antenna;
further, the signal receiving and processing unit includes: the M circulators are used for outputting the received optical signals to subsequent processing equipment along 3 ports of the circulators so as to avoid aliasing with the transmitted optical signals;
the optical coupler comprises 2 multiplied by M optical couplers, wherein M optical couplers are used for splitting a light source signal, and the other M optical couplers are used for combining the light source signal and a received target reflected light signal;
m Photodetectors (PDs) for beat-frequency the light source signal and the received target reflected light signal.
Further, the digital sampling and processing module is configured to perform digital sampling on the beat signal output by the photodetector, and perform subsequent algorithm processing on the sampled signal to obtain required target information;
further, the control unit includes: the laser temperature control module is used for controlling the temperature of the laser so that the laser can stably work for a long time;
the laser pumping current control module is used for controlling the laser to generate a frequency sweeping signal and adjusting the optical wavelength by adjusting the pumping current of the laser;
the phase shifter phase shift control module is used for controlling the power and the phase difference of different optical antenna subunits and realizing the functions of different directions and scanning of light beams;
according to another aspect of the present invention, there is also provided a method for fast scanning a two-dimensional multibeam lidar based on a Blass matrix, comprising the following steps:
in the tunable laser source array unit, M laser sources simultaneously generate M paths of sweep-frequency light with the same center wavelength, sweep-frequency bandwidth and sweep-frequency period but different from each other by using a laser control unit, and the sweep-frequency light is sent to the multi-beam forming unit through ports 1 to 2 of the circulator;
in the multi-beam forming unit, for the i-th optical signal, the i-th optical signal is subjected to the combined action of the i-layer MZI structure and the phase shifter, so when calculating the phase shift value of the phase shifter corresponding to the preset beam direction, calculation is performed from the first layer, after the phase shifter of the first layer can meet the phase shift value required by the first beam direction, the phase shift value of the phase shifter of the first layer is kept unchanged, and then the phase shift value of the phase shifter of the second layer is adjusted, and when calculating, the multi-path effect introduced by the multi-layer MZI structure is additionally considered, for example, the light emitted from the laser 2 reaches the second optical antenna unit, two paths can be traveled, and one path is MZI2，1→MZI1，1→MZI1，2The other path is MZI2，1→MZI2，2→MZI1，2. Thus, the optical signals on the two paths may undergo different phase shifts at the MZI1，2Coherent superposition is realized, and finally, one path of optical signal is combined and radiated at the optical antenna unit 2, and so on. Therefore, when calculating the phase shift values of the phase shifters corresponding to the orientations of the plurality of light beams, the multipath effect inevitably exists. Based on the consideration of multipath effectAfter phase shift values corresponding to the phase shifters from the first layer to the Mth layer are calculated, the phase shift values are reversely pushed to current values required to be provided for the phase shifters according to the determined carrier control scheme, so that the control unit can control the phase shifters, and finally preset beam pointing scanning is realized;
in the optical phased array antenna unit, N optical waveguides with the same diffraction grating at the front end adjust the beam direction of M paths of optical signals after power and phase adjustment in the dimension perpendicular to the plane of the optical antenna array, and as for a specific diffraction grating, the angle of a beam diffracted by the optical wave after passing through the grating changes along with the change of the wavelength of the optical wave, the pumping current of M lasers can be adjusted simultaneously through the control unit, so that the central wavelength of the M paths of optical signals can be changed simultaneously, and the scanning of the beam in the dimension perpendicular to the plane of the optical antenna array can be realized;
in the signal receiving and processing unit, after optical signals received by the optical phased array antenna array pass through the multi-beam forming unit, target reflection signals from different beam directions are separated into M paths, the M paths are respectively coupled with corresponding initial light source signals after being output through ports 2 to 3 of the circulator, the signals are sent to the photoelectric detector for photoelectric conversion, and because the frequency of beat frequency generation signals is related to the target distance in the direction of the corresponding beam directions, the beat frequency signals can be sampled and processed to obtain related information about a target.
Has the advantages that:
(1) by utilizing the structural advantages of the Blass matrix, the invention provides an adaptive optical topological structure based on the Blass matrix architecture, and realizes the rapid two-dimensional scanning of laser beams. The Blass matrix is originally mainly applied to an electrical phased array, and one-dimensional scanning of microwave beams is realized. The invention focuses on the two-dimensional scanning of the laser beam, can realize the simultaneous emission or the reception of signals of the laser beam in a plurality of directions, can randomly expand the number of beams and the number of antennas, and can realize the scanning of any beam angle in a large angle range, thereby greatly improving the scanning speed of the laser radar and being beneficial to the rapid distance measurement and scanning imaging of a specific target.
(2) The scheme can be combined with compressed sensing, if the scene is in a sparse state, the direction of each beam can be selected according to specific scene requirements, so that the scanning time can be greatly reduced on the premise of ensuring that important information is not lost, and the performance of the system is improved.
(3) The device has a more compact structure, is favorable for realizing the integration of a system on a chip, and is also favorable for large-scale expansion.
Drawings
FIG. 1 is a schematic structural diagram of a two-dimensional multi-beam lidar fast scanning device based on a Blass matrix according to the present invention;
fig. 2 is a detailed structure of MZI in the multi-beam forming unit.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to fig. 1 and the following embodiments.
The invention provides a two-dimensional multi-beam laser radar quick scanning device based on a Blass matrix, which comprises: the device comprises a tunable laser source array unit, a multi-beam forming unit, an optical phased array antenna unit, a signal receiving and processing unit and a laser control unit;
as shown in fig. 1, the tunable optical fiber comprises M tunable lasers with tunable wavelengths, a laser control unit, M circulators, M × N MZI structures, 2 × M × N phase shifters, N optical antenna units with the same diffraction grating, M photodetectors, and M analog-to-digital conversion modules.
Referring to fig. 1, tunable laser source array unit (part I in fig. 1): for generating a plurality of simultaneously tunable, mutually phase-independent continuous light-wave signals OS of the same wavelength1，OS2，...，OSM. The number of the light sources is equal to the number M of the preset laser beam directions scanned simultaneously.
Multi-beam forming unit (part II in fig. 1): the laser source array is used for respectively shaping the amplitude and the phase of M paths of incoherent optical signals generated by the laser source array, adjusting the signal power transmitted to N antenna subunits in the optical antenna array and the phase difference value between adjacent antenna subunits according to the preset laser beam direction corresponding to each path of optical signal, and finally realizing the respective beam splitting and shaping of the M paths of incoherent optical signals and transmitting the M paths of incoherent optical signals to the optical phased array antenna unit.
Optical phased array antenna unit (part III in fig. 1): a plurality of optical signals with fixed phase difference output by the multi-beam forming unit are emitted to form beams in the direction corresponding to the fixed phase difference, and the optical wave signals reflected by the target are received and then sent to a subsequent signal processing unit; in addition, by adding a diffraction grating to each optical antenna unit emission port, the output laser beam can be scanned in another dimension.
Signal reception processing unit (IV part in fig. 1): the device is used for receiving the light signals reflected by the target in the direction of the split beams, sending the light signals to the photoelectric detector for photoelectric conversion after the light signals are combined with the light source signals corresponding to the direction, and then converting the light signals into a digital domain for subsequent signal processing through low-speed sampling.
Laser control unit (V portion in fig. 1): the device is used for controlling the pumping current of the laser so as to adjust the wavelength of the output light of the laser according to the scanning angle requirement; and is also used for controlling the power and phase of each output optical signal in the multi-beam forming unit so as to realize the power required by the corresponding beam pointing and the phase difference between adjacent antenna sub-units, thereby realizing the simultaneous scanning of a plurality of different beam pointing.
The tunable laser source array unit comprises:
m tunable lasers for generating M incoherent optical signals having the same wavelength;
the multi-beam forming unit comprising:
m x N MZI structures, each as shown in FIG. 2, for controlling the power of each signal delivered to the optical antenna;
2 × M × N phase shifters, including M × N phase shifters on the trunk in fig. 1 and phase shifters in upper branches of M × N MZI structures, where the phase shifters on the trunk are used to control phase differences required by different light beams to point to corresponding optical signals, and the phase shifters on the upper branches of the MZI structures are used to control power of signals transmitted to the optical antennas in each branch;
the optical phased array antenna unit includes:
n optical waveguides with diffraction grating on the front end for transmitting and receiving light wave signals in specific beam direction as optical antenna;
the signal receiving and processing unit comprises:
the M circulators are used for outputting the received optical signals to subsequent processing equipment along the 3 ports of the circulators so as to avoid aliasing with the transmitted optical signals;
the optical coupler comprises 2 multiplied by M optical couplers, wherein M optical couplers are used for splitting a light source signal, and the other M optical couplers are used for combining the light source signal and a received target reflected light signal;
m Photodetectors (PDs) for performing beat frequencies on the light source signal and the received target reflected light signal;
the digital sampling and processing module is used for carrying out digital sampling on the beat frequency signal output by the photoelectric detector and carrying out subsequent algorithm processing on the sampled signal to obtain required target information;
the control unit includes:
the laser temperature control module is used for controlling the temperature of the laser so that the laser can stably work for a long time;
the laser pumping current control module is used for controlling the laser to generate a frequency sweeping signal and adjusting the optical wavelength by adjusting the pumping current of the laser;
the phase shifter phase shift control module is used for controlling the power and the phase difference of different optical antenna subunits and realizing the functions of different directions and scanning of light beams;
preferably, the phase shift amount control of the phase shifter is selected carrier control. The phase shift control scheme of the phase shifter can be divided into three types, namely temperature control, current control and stress control, the tuning speed of the temperature control is low, thermal crosstalk is easy to cause, and additional heat insulation treatment is needed; the stress control needs to use a piezoelectric ceramic material, although the tuning speed of the scheme is high, the piezoelectric ceramic material is higher in price and is easier to damage in an actual working environment; in comparison, both the tuning speed and the cost of the carrier control are more suitable.
In the laser array module, a current signal after predistortion is input into the laser control module, so that each laser outputs a current signal with a central wavelength of lambda, and the central wavelength of lambda is used as the central wavelength of each laser0Frequency-modulated gamma sweep optical signal O1The procedure of multi-beam forming will be described next, in which the input circulator enters from the 1 port and the output enters the multi-beam forming unit from the 2 port:
the MZI structure in fig. 2 is explained first: each MZI structure comprises two 3-dB couplers and 1 phase shifter, wherein one end output of the first 3-dB coupler is connected with one input end of the second 3-dB coupler through the phase shifter; the output of the other end of the first 3-dB coupler is directly connected to the other input end of the second 3-dB coupler; e _ in1 and E _ in2 are two input signals, E _ out1 and E _ out2 are two output signals, the phase shift value of the phase shifter is set to phi, and then the input and output signals of the MZI structure can be represented by the following formula:
Figure BDA0003191757070000061
wherein j is a plurality of units. For simplicity, let:
Figure BDA0003191757070000062
then (1) can be simplified to:
Figure BDA0003191757070000071
during the following derivation, Einm，nAnd Eoutm，nSeparate table MZIm，nInput and output signals of, and rm，nAnd km，nThen it represents MZIm，nOf the coupling coefficient ofm，nRepresentation and MZIm，nThe phase shift value of the phase shifter at the corresponding position.
The relationship between the phase difference between adjacent antenna sub-elements and the beam pointing direction is as follows:
Figure BDA0003191757070000072
where d is the distance between adjacent antenna subunits, θ is the beam pointing angle, and λ is the center wavelength of the optical signal.
First, for the first optical signal, i.e. the first beam θ1Since the first layer has no multipath effect, the phase required by each antenna unit can be directly estimated according to the formula (4), so that the phase shifter (psi) of the first layer is utilized1，1，ψ1，2，...，Ψ1，N) Directly adjusting the phase difference of optical signals on the N paths of antenna units;
second, calculating and adjusting a second beam θ2The phase of each corresponding antenna subunit. The signal arriving at the antenna unit 1 is free from multipath effects and therefore the signal there can be expressed as:
Figure BDA0003191757070000073
E2refers to the beam from the second laser; while there are two paths to the antenna element 2, e.g. there may be two paths for the light from the laser 2 to reach the second optical antenna element, one being the MZI2，1→MZI1，1→MZI1，2The other path is MZI2，1→MZI2，2→MZI1，2. The signal can therefore be expressed as:
Figure BDA0003191757070000074
there are 3 paths to the antenna element 3, so the signal there can be expressed as:
Figure BDA0003191757070000075
by analogy, a signal expression corresponding to the light directed by each beam to each antenna subunit can be obtained, so that the phase shifter can be controlled to change the amplitude and the phase of the MZI output to realize the preset phase difference between adjacent antenna subunits and the beam direction corresponding to the phase difference, and the direction of each beam can be changed by continuously changing the phase shift value of the phase shifter, thereby realizing the scanning in the direction parallel to the plane of the antenna subunits. Because the optical signals output by each laser are incoherent, the optical signals directed by different beams are incoherent when reaching the antenna subunit, and the aliasing condition between the signals directed by different beams can not occur.
For the beam scanning in the direction perpendicular to the plane of the antenna unit, the beam scanning is realized by diffracting the optical signals with different wavelengths at different angles after passing through the diffraction grating at the waveguide port of the optical antenna. The diffraction angle σ of the light wave from the diffraction grating can be expressed by the following formula:
Figure BDA0003191757070000081
wherein λ is the central wavelength of the optical signal, Λ is the grating constant, neffIs the effective refractive index of the optical waveguide. As can be seen from the above formula, the central wavelength of the optical signal can be shifted by changing the pumping currents of the M lasers, so as to realize scanning in the dimension perpendicular to the plane of the optical antenna unit.
Because the optical path is reversible, the receiving process of the optical signal can be similar to the above-mentioned signal transmitting process, under the same condition, the beam direction of the transmitted optical signal is identical to the gain direction of the received optical signal, so that the optical signals reflected back by different beam directions to the target are identicalThe multi-beam forming unit of the parameters is redistributed, and the signals with the same beam direction are distributed to the initial preset transmitting end channel, namely the corresponding beam direction is thetaiThe reflected optical signal of (a) is returned to the optical path of the i-th layer after passing through the multi-beam forming unit.
Next, a subsequent signal processing procedure will be exemplified, and since optical signals between the light sources are incoherent and do not alias with each other, an optical signal directed from a single beam will be described. The light signal emitted by the light source can be expressed as:
Ei＝cos(2πft+πγt2+ψ0) (8)
wherein f is the center frequency, gamma is the modulation frequency of the sweep frequency, psi0Is the initial phase, t is a time variable.
The received signal after the target reflection is recombined and distributed by the multi-beam forming unit can be represented as:
Ei＝cos[2πf(t-τ0-τ)+πγ(t-τ0-τ)2+ψr] (9)
wherein, tau0For the time delay from the tunable laser source unit to the optical antenna array unit, which is a fixed value, it can be predetermined that τ is the time delay from the antenna to the target, reflecting the relevant position information of the target, ψrFor receiving the phase of the signal, typically with0Different.
The initial optical signal and the optical signal reflected by the target are combined by the coupler and sent to the photodetector for beat frequency, and the generated beat frequency signal can be expressed as:
EPD＝D.C.+H.F.+cos[2πγ(τ0+τ)t+2πf(τ0+τ)-πγ(τ0+τ)2+ψ0-ψr] (10)
d.c. is a direct current component, h.f. is a high frequency component, which can be subsequently filtered by a band pass filter, and the frequency of the beat signal is a function of the delay amount related to the target distance, and the distance s of the target can be inversely deduced from the frequency of the signal:
Figure BDA0003191757070000082
wherein f isPDThe frequency of the beat signal and c the propagation speed of the electromagnetic wave.
Therefore, the distance information of the target in the corresponding beam direction can be extracted from the frequency information of the beat frequency signal, and the whole information of the target can be acquired by performing beam scanning in two dimensions.
In summary, the invention utilizes the structural advantage of the Blass matrix, can realize the simultaneous transmission or reception of signals of laser beams in multiple directions, can arbitrarily expand the number of beams and the number of antennas, and can realize the scanning of any beam angle in a large angle range, thereby greatly improving the scanning speed of the laser radar and being beneficial to the rapid distance measurement and scanning imaging of specific targets.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but various changes may be apparent to those skilled in the art, and it is intended that all inventive concepts utilizing the inventive concepts set forth herein be protected without departing from the spirit and scope of the present invention as defined and limited by the appended claims.

Claims (10)

1. A two-dimensional multi-beam laser radar fast scanning device based on a Blass matrix is characterized by comprising the following components: the device comprises a tunable laser source array unit, a multi-beam forming unit, an optical phased array antenna unit, a signal receiving and processing unit and a laser control unit; wherein the content of the first and second substances,
the tunable laser source array unit comprises a plurality of tunable lasers for generating a plurality of continuous optical wave signals OS with the same wavelength, simultaneous tuning and mutually irrelevant phases1,OS2,…,OSMThe number of the tunable lasers is equal to the number M of the preset laser beam directions scanned simultaneously;
the multi-beam forming unit: the device is used for respectively shaping the amplitude and the phase of M paths of incoherent optical signals generated by a laser source array, adjusting the signal power transmitted to N antenna subunits in an optical antenna array and the phase difference value between adjacent antenna subunits according to the preset laser beam direction corresponding to each path of optical signal, and finally respectively splitting and shaping the M paths of incoherent optical signals and transmitting the M paths of incoherent optical signals to an optical phased array antenna unit;
the optical phased array antenna unit: a plurality of optical signals with fixed phase difference output by the multi-beam forming unit are emitted to form beams in the direction corresponding to the fixed phase difference, and the optical wave signals reflected by the target are received and then sent to a subsequent signal processing unit; in addition, a diffraction grating is added to each transmitting port of the optical antenna unit, so that the output laser beam is scanned in the other dimension;
a signal reception processing unit: the system is used for receiving the light signals reflected by the target in the direction of the split beams, combining the light signals with the light source signals corresponding to the direction, sending the light signals to a photoelectric detector for photoelectric conversion, and then converting the light signals into a digital domain for subsequent signal processing through low-speed sampling;
a laser control unit: the device is used for controlling the pumping current of the laser so as to adjust the wavelength of the output light of the laser according to the scanning angle requirement; and is also used for controlling the power and phase of each output optical signal in the multi-beam forming unit so as to realize the power required by the corresponding beam pointing and the phase difference between adjacent antenna sub-units, thereby realizing the simultaneous scanning of a plurality of different beam pointing.
2. The device according to claim 1, wherein the device comprises:
the tunable laser source array unit comprises M tunable lasers for generating M incoherent optical signals with the same wavelength.
3. The device according to claim 1, wherein the device comprises:
the multi-beam forming unit comprises M multiplied by N Mach-Zehnder interference (MZI) structures, each MZI structure being configured to control the power of each signal delivered to the optical antenna; each MZI structure comprises two 3-dB couplers and 1 phase shifter, wherein one end output of the first 3-dB coupler is connected with one input end of the second 3-dB coupler through the phase shifter; the other end output of the first 3-dB coupler is directly connected to the other input of the second 3-dB coupler.
4. The device according to claim 1, wherein the device comprises:
the multi-beam forming unit comprises 2 XMXN phase shifters, and the M XN phase shifters on a trunk line and the phase shifters in the upper branches of the MXN MZI structures, wherein the phase shifters on the trunk line are used for controlling phase differences required by different light beams to point to corresponding optical signals, and the phase shifters on the upper branches of the MZI structures are used for controlling the power of signals transmitted to the optical antennas in each path.
5. The device according to claim 1, wherein the device comprises:
the optical phased array antenna unit includes: n optical waveguides with diffraction grating on the front end are used as optical antenna to realize the transmission and reception of light wave signal with specific beam pointing direction.
6. The device according to claim 1, wherein the device comprises:
the signal receiving and processing unit comprises: the M circulators are used for outputting the received optical signals to subsequent processing equipment along 3 ports of the circulators so as to avoid aliasing with the transmitted optical signals;
the optical coupler comprises 2 multiplied by M optical couplers, wherein M optical couplers are used for splitting a light source signal, and the other M optical couplers are used for combining the light source signal and a received target reflected light signal;
m Photodetectors (PDs) for beat-frequency the light source signal and the received target reflected light signal.
7. The device according to claim 1, wherein the device comprises:
and the digital sampling and processing module is used for digitally sampling beat frequency signals output by the photoelectric detector and carrying out subsequent algorithm processing on the sampled signals to obtain required target information.
8. The device according to claim 1, wherein the device comprises:
the control unit includes: the laser temperature control module is used for controlling the temperature of the laser so that the laser can stably work for a long time;
the laser pumping current control module is used for controlling the laser to generate a frequency sweeping signal and adjusting the optical wavelength by adjusting the pumping current of the laser;
and the phase shifter phase shift control module is used for controlling the power and the phase difference of different optical antenna subunits and realizing the functions of different directions and scanning of light beams.
9. A two-dimensional multi-beam laser radar quick scanning method based on a Blass matrix is characterized by comprising the following steps:
in the tunable laser source array unit, M laser sources simultaneously generate M paths of sweep-frequency light with the same center wavelength, sweep-frequency bandwidth and sweep-frequency period but different from each other by using a laser control unit, and the sweep-frequency light is sent to the multi-beam forming unit through ports 1 to 2 of the circulator;
in the multi-beam forming unit, for the optical signal of the ith path, the phase shift value of the phase shifter corresponding to the preset beam direction is calculated through the combined action of the i-layer MZI structure and the phase shifterWhen calculating, the multi-path effect introduced by the multi-layer MZI structure is additionally considered, so that optical signals on two paths may pass through different phase shifts and then pass through the MZI structure1,2Coherent superposition is realized, and finally, a path of optical signal is combined and radiated at the optical antenna unit, and the rest can be done;
on the basis of considering the multipath effect, after phase shift values corresponding to the phase shifters from the first layer to the Mth layer are calculated, the phase shift values are reversely pushed to current values required to be provided for the phase shifters according to the determined carrier control scheme, so that the control unit can control the phase shifters, and finally preset beam pointing scanning is realized.
10. The method according to claim 9, further comprising the following steps:
in the optical phased array antenna unit, N optical waveguides with the same diffraction grating at the front end perform adjustment of beam pointing on a dimension perpendicular to the plane of an optical antenna array on M paths of optical signals after power and phase adjustment, and a control unit simultaneously adjusts pumping currents of M lasers, so that the central wavelength of the M paths of optical signals is changed simultaneously, and the beams are scanned on the dimension perpendicular to the plane of the optical antenna array;
in the signal receiving and processing unit, after optical signals received by the optical phased array antenna array pass through the multi-beam forming unit, target reflection signals from different beam directions are separated into M paths, the M paths are respectively coupled with corresponding initial light source signals after being output through ports 2 to 3 of the circulator, the signals are sent to the photoelectric detector for photoelectric conversion, the frequency of beat frequency generation signals is related to the target distance in the direction of the corresponding beam directions, and related information about a target can be obtained by sampling and processing the beat frequency signals.
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