CN113885042B - 1.55 mu m single photon coherent laser radar detection method and device - Google Patents
1.55 mu m single photon coherent laser radar detection method and device Download PDFInfo
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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
- G01S17/88—Lidar systems specially adapted for specific applications
- G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
- G01S17/894—3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
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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
- G01S17/50—Systems of measurement based on relative movement of target
- G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
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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
- 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
- G01S7/483—Details of pulse systems
- G01S7/484—Transmitters
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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
- 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
- G01S7/483—Details of pulse systems
- G01S7/486—Receivers
- G01S7/4861—Circuits for detection, sampling, integration or read-out
- G01S7/4863—Detector arrays, e.g. charge-transfer gates
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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
- 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
- G01S7/483—Details of pulse systems
- G01S7/486—Receivers
- G01S7/4865—Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak
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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
- 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
- G01S7/495—Counter-measures or counter-counter-measures using electronic or electro-optical means
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- 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
Abstract
A1.55 mu m single photon coherent laser radar system device relates to the application field of laser technology. For the existing laser radar, the detection mode needs to improve the detection sensitivity, improve the detection distance capability of a seeker, improve the capability of acquiring multi-dimensional information of a target, and improve the anti-interference and target identification capabilities. The invention applies GM-APD focal plane detection to a laser pulse coherence technology, adopts a Gm-APD heterodyne coherence scheme, selects a short-wave infrared wavelength, has higher detection sensitivity than a coherent detection system, can simultaneously acquire a three-dimensional distance value, a plane profile intensity value and a Doppler target velocity value of a remote target, obtains more accurate target information difference under a spatial stereo angle, provides reliable three-dimensional space data for target identification, tracking and the like, improves the detection sensitivity to a single photon level on the basis of strong anti-interference capability of heterodyne detection, and is suitable for the field of remote non-cooperative target weak light detection.
Description
Technical Field
Relates to the field of laser technology application, in particular to a 1.55 mu m single photon coherent laser radar detection method and a device.
Background
Since birth, the laser radar is widely applied to military applications all the time, wherein the laser active imaging guidance technology is the application direction with the most key technology and the greatest difficulty. In the beginning of the 20 th century and the 80 th era, the U.S. MIT Lincoln laboratory demonstrated successful two-dimensional unit scanning laser pulse coherent radar anti-tank guidance technology for the first time, and subsequently, DARPA and the U.S. air force supported Cruise Missile Advanced Guidance (CMAG) plans. In the early 90 s of the 20 th century, the technology is successfully assembled to the AGM-129A cruise missile, is the first model application in the world, solves the problem of terrain matching by Doppler velocity measurement, improves the guidance precision from 40m to 3m, and improves one order of magnitude.
For the existing laser radar, the detection mode puts higher requirements: (1) the detection sensitivity is improved, the bottleneck problem of limiting the single photon detection probability is broken through, and the detection distance capability of the seeker is improved; (2) the method improves the capability of acquiring multi-dimensional information of the target, comprehensively represents the target, breaks through the bottleneck problem of aliasing of interference sources and target information, and improves the anti-interference and target identification capabilities.
Disclosure of Invention
In order to solve the technical problem that the existing laser radar cannot meet the detection requirement in the active laser imaging guidance technology, the scheme adopted by the application is as follows:
a 1.55 single photon coherent lidar method of detecting μm, the method comprising:
dividing the continuous light into two beams by an optical fiber beam splitter, wherein one beam is local oscillation light LO, and the other beam is seed light MO;
chopping the seed light into pulse laser with the pulse width of 200ns, and simultaneously shifting the frequency of the seed light by 80MHZ to form frequency-shifted modulated light;
emitting the frequency shift modulated light to a target surface through a circulator collimator and a beam expander;
the echo signal reflected by the target surface is input to the coupler through the circulator;
splitting local oscillation light by a beam splitter to obtain 1% of attenuation light, and attenuating the attenuation light by a 0.6-50dB attenuator to obtain attenuation light;
transmitting the attenuated light through an electro-optical modulator to a coupler;
coupling the echo light and the attenuated light to form coupled light;
the coupled light is emitted to the detection device as a detection result;
and the seed light forms frequency shift modulation light and simultaneously activates a trigger APD (avalanche photo diode), and the trigger APD transmits a trigger signal to the Gm-APD single photon detector.
A 1.55 μm single photon coherent lidar system apparatus, comprising: the device comprises a 1550nm tunable laser, an acousto-optic modulator, a trigger APD, a circulator, a collimator, a beam expanding lens, an attenuator, an electro-optic modulator, a coupler, a Gm-APD single photon detector and an area array receiving module;
all parts of the device are connected by adopting optical fibers, and continuous light output by the tunable laser is divided into two beams of light, namely local oscillation light LO and seed light MO, by an optical fiber beam splitter;
transmitting a chopping signal to the acousto-optic modulator through a signal generator, performing frequency shift and chopping processing on the seed light through the acousto-optic modulator to form frequency shift modulated light, transmitting the frequency shift modulated light to a circulator, transmitting light output by the circulator to the surface of a target to be detected through a collimator and a beam expander in sequence, and inputting an echo signal reflected by the surface of the target to a coupler after passing through the circulator;
the signal generator also outputs a trigger APD, and the trigger APD outputs a trigger signal to the Gm-APD single photon detector as a trigger signal;
the local oscillator light is split by the beam splitter to obtain split light, and one of the split light is attenuated by the attenuator and then output to the coupler;
further, the device further comprises: a power meter; the power meter is used for detecting the power of the other beam of light output by the coupler.
Further, the continuous light is divided into two beams of light in a ratio of 1:9, wherein 10% of the light is local oscillation light, and 90% of the light is seed light.
Further, the acousto-optic modulator can shift the frequency of input light by 80MHz and modulate the pulse width to 200 ns.
Further, the attenuation capability of the attenuator energy is in the range of 0.6-55 dB.
Further, the local oscillator light is divided into two beams of light, the ratio of the two beams of light is 1:99, wherein 1% of the light is used as one beam of light entering the coupler.
Further, the apparatus further comprises: a three-pull three-top structure; the three-pull three-top structure is used for fixing the collimator and the beam expander, so that light output by the circulator passes through the central positions of the collimator and the beam expander.
Further, the device further comprises: mechanically tensioning the support; the mechanical tensioning support is used for fixing the collimator and the beam expander, so that light output by the circulator passes through the collimator and the beam expander and then is emitted to the middle position of a target.
Furthermore, the single photon detector adopts a 64 x 64 area array for detection.
The application has the advantages that:
the GM-APD focal plane detection is applied to a laser pulse coherence technology, can simultaneously obtain a three-dimensional distance value, a plane profile intensity value and a Doppler velocity value of a target, can examine the difference between interference source and target information from multiple dimensions, and is a technical direction for solving the bottleneck problem of the current optical imaging.
2. The method applies the prior art of GM-APD focal plane detection to the prior art of laser pulse coherence; the Gm-APD single photon detector has the characteristics that each pixel of the detector can be triggered into avalanche by single photoelectron, and the dark noise is much lower than that of the traditional linear detector, so that the triggering sensitivity of pulse coherent detection echo signals under the single photon detector is higher. However, the research on the detection mode in the prior art is theoretical analysis and is not proved by experiments. The method is combined through experiments, and the detection sensitivity can be improved to a single photon magnitude by the detection method.
3. The invention improves the detection sensitivity to the single photon magnitude on the basis of strong anti-interference capability of heterodyne detection, and is more suitable for the field of remote non-cooperative target weak light detection. For a detector with 4096 pixels, the advantage of the signal-to-noise ratio of the system is more obvious when the single-pulse peak power with the pulse width of 200ns is within 0.7 μ w, and the lower the power is, the more obvious the advantage of the system is compared with the direct detection.
Drawings
FIG. 1 is a block diagram of a 1.55 μm single photon coherent laser radar system.
Fig. 2 is a schematic diagram of the experimental platform constructed according to fig. 1.
Fig. 3 is a graph of the position of a window versus the spectral peak for the no-target experiment in the tenth embodiment.
Fig. 4 is a single-frame area array time domain statistical data result of the no-target experiment in the tenth embodiment.
Fig. 5 is a target scene diagram in the eleventh embodiment.
Fig. 6 is a power spectrum curve at the echo position obtained by the prior art detection in the eleventh embodiment.
Fig. 7 is a power spectrum curve at the echo position obtained by detection with the device provided by the invention in the eleventh embodiment.
Detailed Description
The first embodiment provides a 1.55 μm single photon coherent laser radar detection method, which includes:
dividing the continuous light into two beams by an optical fiber beam splitter, wherein one beam is local oscillation light LO, and the other beam is seed light MO;
chopping the seed light into pulse laser with the pulse width of 200ns, and simultaneously shifting the frequency of the seed light to 80MHZ to form frequency-shifted modulated light;
emitting the frequency shift modulated light to the target surface through a circulator collimator and a beam expander;
the echo signal reflected by the target surface is input to the coupler through the circulator;
splitting local oscillation light by a beam splitter to obtain 1% of attenuation light, and attenuating the attenuation light by a 0.6-50dB attenuator to obtain attenuation light;
transmitting the attenuated light through an electro-optical modulator to a coupler;
coupling said echo light with said chopper attenuated light to form coupled light;
the coupled light is emitted to the detection device as a detection result;
and the seed light forms frequency shift modulation light and simultaneously activates a trigger APD (avalanche photo diode), and the trigger APD transmits a trigger signal to the Gm-APD single photon detector.
Second embodiment, the present embodiment is described with reference to fig. 1, and the present embodiment provides a 1.55 μm single photon coherent laser radar system apparatus, including: the device comprises a 1550nm tunable laser, an acousto-optic modulator, a trigger APD, a circulator, a collimator, a beam expander, an attenuator, an electro-optic modulator, a coupler, a Gm-APD single photon detector and an area array receiving module;
all parts of the device are connected by optical fibers, and continuous light output by the tunable laser is divided into two beams of light, namely local oscillator Light (LO) and seed light (MO), by an optical fiber beam splitter;
transmitting a chopping signal to the acousto-optic modulator through a signal generator, performing frequency shift and chopping processing on the seed light through the acousto-optic modulator to form frequency shift modulated light, transmitting the frequency shift modulated light to a circulator, transmitting light output by the circulator to the surface of a target to be detected through a collimator and a beam expander in sequence, and inputting an echo signal reflected by the surface of the target to a coupler after passing through the circulator;
the signal generator also outputs a trigger APD, and the trigger APD outputs a trigger signal to the Gm-APD single photon detector as a trigger signal;
the local oscillator light is split by the beam splitter to obtain split light, and one of the split light is attenuated by the attenuator and then output to the coupler;
and the coupler couples the input echo signal and the split local oscillator light to output two beams of light, wherein one beam of light is emitted to a focal plane of the Gm-APD single photon detector.
The beneficial effects of the embodiment are as follows: the Gm-APD laser radar based on the single photon detection capability of the Gm-APD has the characteristics of high detection sensitivity, high response speed and capability of inspecting differences of interference source and target information from multiple dimensions. The laser pulse coherent detection technology can acquire multi-dimensional information such as target speed, intensity, distance and the like, and has remarkable advantages in the aspect of solving the problem of target identification. And the heterodyne detection system is utilized to inhibit background light noise, and meanwhile, the coherent detection sensitivity can be improved in a photon counting detection mode, so that the purpose of remote detection is achieved.
In a third embodiment, the present embodiment is described with reference to fig. 1, and the present embodiment is further limited to the 1.55 μm single photon coherent laser radar system apparatus according to the second embodiment, further including: a power meter; the power meter is used for detecting the power of the output light of the coupler.
In a fourth embodiment, the present embodiment is described with reference to fig. 1, and the present embodiment is further limited to the 1.55 μm single photon coherent laser radar system apparatus according to the second embodiment, wherein the continuous beam is divided into two beams of 1:9, 10% of the beams are local oscillation beams, and 90% of the beams are seed beams.
Fifth embodiment mode, the present embodiment mode is described with reference to fig. 1, and the present embodiment mode is a further limitation of the 1.55 μm single photon coherent laser radar system apparatus according to the second embodiment mode, wherein the acousto-optic modulator is capable of shifting an input light frequency by 80MHz and modulating a pulse width to 200 ns.
Sixth embodiment, the present embodiment is described with reference to fig. 1, and the present embodiment is further limited to the 1.55 μm single photon coherent lidar system according to the second embodiment, wherein the attenuation capability of the attenuator is in the range of 0.6 to 55 dB.
The beneficial effects of the embodiment are that: the size of the local oscillation light is adjusted according to the energy of the echo signal, so that the single photon heterodyne detection reaches the maximum signal-to-noise ratio, and the target information is more effectively extracted.
Seventh embodiment, the present embodiment is described with reference to fig. 1, and further limited to the 1.55 μm single photon coherent laser radar system apparatus according to the second embodiment, wherein the local oscillator light is divided into two beams, the ratio of the two beams is 1:99, and 1% of the beams enter the coupler as one beam.
An eighth embodiment is directed to the 1.55 μm single-photon coherent lidar system apparatus according to the second embodiment, further including: a three-pull three-top structure; the three-pull-three-top structure is used for fixing the collimator and the beam expander, so that light output by the circulator passes through the central positions of the collimator and the beam expander.
The beneficial effects of the embodiment are as follows: the three-pull three-top structure is added, so that the optical effective calibration is ensured, the optical and mechanical stability is kept, the coherent detection system becomes efficient, and the detection stability is improved.
Ninth embodiment is the 1.55 μm single photon coherent lidar system of the first embodiment, further including: mechanically tensioning the support; the mechanical tensioning support is used for fixing the collimator and the beam expander and ensuring that laser passes through the collimator and the beam expander and then strikes the middle position of a target.
The beneficial effects of the embodiment are as follows: the mechanical tensioning support is added, so that the optical effective calibration is ensured, the optical and mechanical stability is kept, the coherent detection system becomes efficient, and the detection stability is improved.
In the tenth embodiment, the present embodiment is described with reference to fig. 1, and the present embodiment is further limited to the 1.55 μm single photon coherent laser radar system apparatus according to the second embodiment, wherein the single photon detector detects with a 64 x 64 area array.
The beneficial effects of the embodiment are as follows: the Gm-APD adopts 64 x 64 area array detection, so that the information at the target position can be effectively obtained, and the data volume is enough for subsequent signal processing.
In the eleventh embodiment, the present embodiment is described with reference to fig. 1, and provides a specific embodiment of a 1.55 μm single photon coherent laser radar system apparatus according to the second embodiment, where the specific embodiment is: the system adopts an all-fiber receiving and transmitting system, continuous light emitted by a 1550nm tunable laser is divided into two beams through a 1:9 fiber beam splitter, one beam of light is used as local oscillation Light (LO), the other beam of light is used as main oscillation seed light (MO), the seed light is chopped into pulse light through an acousto-optic modulator (AOM) to be output, the frequency of the seed light is shifted by 80MHz at the same time, and the applicability of Gm-APD single photon heterodyne detection is verified with and without targets in the experimental process.
(1) When a target is detected, the signal light after frequency shift needs to be emitted out through a circulator, and then is emitted to the surface of the target through a collimator and a beam expander, and an echo signal passes through the circulator and then is emitted to a focal plane of a Gm-APD area array detector after being combined with a local oscillator light through a coupler.
(2) When no target exists, the seed light after frequency shift directly passes through the coupler and the local oscillator beam to be combined and then is irradiated onto a focal plane of the Gm-APD area array detector.
The split local oscillation light is split into two beams by using a 1:99 optical fiber beam splitter, 1% of the local oscillation light needs to be subjected to signal attenuation through a 0.6-50dB attenuator, and due to the Gm-APD detection principle, when a detector is opened, an impulse response exists, so that the attenuated local oscillation light needs to be subjected to chopping through EMO, and the impulse response of the detector is not influenced. After the modulated local oscillator light and the modulated signal light are coupled by the coupler, a beam of light is focused on a focal plane of the Gm-APD area array detector, a difference frequency signal single photon received on the Gm-APD is converted into photoelectrons, the Gm-APD area array detector is started to work, simultaneously, the counting work of the TDC counter is started, the work of the detector is stopped through avalanche amplification, a receiving record is stored, the work of a TDC timing circuit is stopped at the same time, a counting value is recorded, and round-trip time information of laser pulses is obtained through the counting value. The other beam of light is used as monitoring light to monitor the APD surface light power. A64 x 64 array of silicon Gm-APD array detectors in Geiger mode were used in the experiment.
In the embodiment, a statistical histogram is made of the arrival time of the pulse sequence acquired in the single photon counting system, and the distance value, the intensity value and the speed information of a target are calculated through subsequent signal processing.
The twelfth embodiment is described with reference to fig. 2 to 4, and the second embodiment provides an experimental platform built by the 1.55 μm single photon coherent laser radar system device, and the feasibility of the system is verified by adopting non-target detection in the experiment, that is, signal light modulated by AOM is directly accessed into the coupler, the average number of signal photons in a single pixel pulse width is set to 0.1, the signal light is modulated by the acousto-optic modulator and then shifted by 80MHz, the pulse width is modulated to 200ns, the 2pift local oscillator light is attenuated and then the average number of photons in a single pixel pulse width is set to 0.55, the acquisition range gate is set to 2us, and the start time of pulse distance APD acquisition is set to 100ns by adjusting the signal generator. The APD signal acquisition frequency is 250Mhz, namely the acquisition time interval is 4 ns.
In the embodiment, the relation between the position of the window and the spectrum peak curve obtained by performing windowed fourier transform (FFT) and spectrum accumulation on 20000 frames of experimental data is shown in fig. 3, the position of the echo signal is obtained according to fig. 3, the single-frame area array time domain statistical result on the position is shown in fig. 4, and the ordinate in fig. 4 represents the number of trigger detectors.
It can be seen from fig. 3 that the window where the fitted spectral peak is located is 25, i.e. 100ns, in agreement with reality. After single-frame time domain statistics is carried out on the position, the position can be seen in the time tau, due to the existence of local oscillation light and noise photons, the triggering probability in the time is high, and the position of 100 ns-300 ns is subjected to Fourier transform, so that a difference frequency signal of 80MHz can be seen, and the difference frequency signal is consistent with the actual difference frequency signal.
In a thirteenth embodiment, the present embodiment is described with reference to fig. 5 to 7, where in the present embodiment, a 1.55 μm single photon coherent laser radar system apparatus provided in the second embodiment is used for an indoor 45-meter target distance detection experiment, referring to fig. 5, a target to be detected is shown, a modulated laser pulse width is 200ns, a laser emission power is 20mw, an echo power is calculated to be 0.36nw, a total number of echo photons in an average pulse width of a single pixel is 0.014, a time difference between an APD acquisition start and a target echo signal is 100ns, direct detection is performed when there is no local oscillator light in the system, photonic heterodyne detection is performed when the local oscillator light is attenuated and the number of photons in the pulse width is 0.55, and echo signal light in direct detection shows a direct current component in a frequency spectrum, that is, i.e., an impulse function located at zero frequency according to an energy conservation law. The heterodyne term in the single photon heterodyne detection is represented as a signal amplitude of 100MHz in a power spectrum, so that after fourier transform is performed at the echo position in the two detection modes, and then the square is divided by the number of samples, the power spectrums at the 0 frequency and the difference frequency are summed respectively to obtain the energy of the signals in the two detection modes, fig. 6 is a power spectrum curve at the echo position obtained by detection in the prior art, and fig. 7 is a power spectrum curve at the echo position obtained by detection by using the device provided by the present invention.
From FIG. 6, it can be seen that the signal energy is 3.2 · 10 in the case of direct detection-6From FIG. 7, it can be seen that the system heterodyne term signal energy is 4.9 · 10-6The person skilled in the art can clearly know that the advantage of photonic heterodyne detection is obvious after the average number of photons of a single pixel element echo of the Gm-APD is less than 0.014.
The invention has the advantages that:
(1) the attenuation of the energy of the local oscillator light is adjustable within the range of 0.6-55dB, and the magnitude of the local oscillator light is adjusted according to the energy of the echo signal, so that the single photon heterodyne detection reaches the maximum signal-to-noise ratio, and the target information is extracted more effectively.
(2) The repetition frequency of laser pulses is 10kHz, the pulse width of the main oscillation light is adjustable, and the magnitude of the local oscillation light is adjusted according to the magnitude of the pulse width, so that the heterodyne item of single-photon heterodyne detection is maximized in the pulse width, and the signal-to-noise ratio of a system is improved.
(3) The Gm-APD adopts 64 x 64 area array detection, so that the information at the target position can be effectively obtained, and the data volume is enough for subsequent signal processing.
(4) The effective optical calibration and the optical and mechanical stability maintenance are the precondition of high efficiency and stable detection of the coherent detection system, and the optical calibration and the structural stability are realized by the cooperation of a three-pull three-top structure and a mechanical tensioning bracket.
According to the invention, a heterodyne coherence scheme based on Gm-APD is adopted, and short wave infrared wavelength is selected, so that the all-weather adaptability of the system is improved; compared with a coherent detection system, the detection scheme has higher imaging detection sensitivity and is more suitable for extracting the infinitesimal signals of a long-distance target; the method can simultaneously obtain the three-dimensional distance value, the plane contour intensity value and the Doppler target velocity value of the remote target, obtain more accurate target information difference under a space solid angle, provide reliable three-dimensional space data for target identification, tracking and the like, and is a technical direction for solving the bottleneck problem of the current optical imaging.
Claims (10)
1. A1.55 μm single photon coherent laser radar detection method is characterized by comprising the following steps:
dividing the continuous light into two beams by an optical fiber beam splitter, wherein one beam is local oscillation light LO, and the other beam is seed light MO;
chopping the seed light into pulse laser with the pulse width of 200ns, and simultaneously shifting the frequency of the seed light by 80MHZ to form frequency-shifted modulated light;
emitting the frequency shift modulated light to a target surface through a circulator collimator and a beam expander;
the echo signal reflected by the target surface is input to the coupler through the circulator;
splitting local oscillation light by a beam splitter to obtain 1% of attenuation light, and attenuating the attenuation light by a 0.6-50dB attenuator to obtain attenuation light;
transmitting the attenuated light through an electro-optical modulator to a coupler;
coupling the echo light and the attenuated light to form coupled light;
the coupled light is emitted to the detection device as a detection result;
and the seed light forms frequency shift modulation light and simultaneously activates a trigger APD (avalanche photo diode), and the trigger APD transmits a trigger signal to the Gm-APD single photon detector.
2. A1.55 mu m single photon coherent laser radar system device is characterized in that: the device comprises: the device comprises a 1550nm tunable laser, an acousto-optic modulator, a trigger APD, a circulator, a collimator, a beam expander, an attenuator, an electro-optic modulator, a coupler, a Gm-APD single photon detector and an area array receiving module;
all parts of the device are connected by adopting optical fibers, and continuous light output by the tunable laser is divided into two beams of light, namely local oscillation light LO and seed light MO, by an optical fiber beam splitter;
transmitting a chopping signal to the acousto-optic modulator through a signal generator, performing frequency shift and chopping processing on the seed light through the acousto-optic modulator to form frequency shift modulated light, transmitting the frequency shift modulated light to a circulator, transmitting light output by the circulator to the surface of a target to be detected through a collimator and a beam expander in sequence, and inputting an echo signal reflected by the surface of the target to a coupler after passing through the circulator;
the signal generator also outputs a trigger APD, and the trigger APD outputs a trigger signal to the Gm-APD single photon detector as a trigger signal;
the local oscillator light is split by the beam splitter to obtain split light, and one of the split light is attenuated by the attenuator and then output to the coupler;
the coupler couples the input echo signal and the split local oscillator light to output two beams of light, wherein one beam of light is emitted to a focal plane of the Gm-APD single photon detector, and the single photon detector outputs a signal to the area array receiving module.
3. A 1.55 μm single photon coherent lidar system apparatus of claim 2, wherein: the device further comprises: a power meter; the power meter is used for detecting the power of the other beam of light output by the coupler.
4. A 1.55 μm single photon coherent lidar system apparatus of claim 2, wherein: the continuous light is divided into two beams of light in a ratio of 1:9, wherein 10% of the light is local oscillation light, and 90% of the light is seed light.
5. A 1.55 μm single photon coherent lidar system apparatus of claim 2, wherein: the acousto-optic modulator can shift the frequency of input light by 80MHz and modulate the pulse width to 200 ns.
6. A 1.55 μm single photon coherent lidar system apparatus of claim 2, wherein: the attenuation capacity of the attenuator energy is in the range of 0.6-55 dB.
7. A 1.55 μm single photon coherent lidar system apparatus of claim 2, wherein: the local oscillator light is divided into two beams of light, the ratio of the two beams of light is 1:99, wherein 1% of light is used as one beam of light entering the coupler.
8. A 1.55 μm single photon coherent lidar system apparatus of claim 2, wherein: the device further comprises: a three-pull three-top structure; the three-pull three-top structure is used for fixing the collimator and the beam expander, so that light output by the circulator passes through the centers of the collimator and the beam expander.
9. A 1.55 μm single photon coherent lidar system apparatus of claim 2, wherein: the device further comprises: mechanically tensioning the support; the mechanical tensioning support is used for fixing the collimator and the beam expander, so that light output by the circulator passes through the collimator and the beam expander and then is emitted to the middle position of a target.
10. A 1.55 μm single photon coherent lidar system apparatus of claim 2, wherein: the single photon detector adopts a 64 x 64 area array for detection.
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