CN110161519B

CN110161519B - Macro-pulse photon counting laser radar

Info

Publication number: CN110161519B
Application number: CN201910500898.1A
Authority: CN
Inventors: 于洋; 刘博�; 陈臻; 王华闯
Original assignee: Institute of Optics and Electronics of CAS
Current assignee: Institute of Optics and Electronics of CAS
Priority date: 2019-06-11
Filing date: 2019-06-11
Publication date: 2022-09-20
Anticipated expiration: 2039-06-11
Also published as: CN110161519A

Abstract

The invention discloses a macropulse photon counting laser radar, which belongs to the technical field of laser radars and comprises a laser, a proportional beam splitter, an emission and reception optical system, a single photon detection (Gm-APD), a photodiode, a photon counting module and a signal processing module. The method can effectively overcome range ambiguity and realize rapid detection by periodically emitting pulse trains with unequal intervals, and has obvious advantages in measuring long-distance and high-speed moving targets compared with the traditional multi-pulse accumulated photon counting laser radar. Under the premise of not increasing the complexity of a traditional pulse accumulation photon counting laser radar system, the macropulse photon counting laser radar greatly improves the traditional capability of measuring a high-speed moving target, improves the practical value of the system, is widely applied to the fields of target ranging and imaging, and is particularly applied to the field of measuring the high-speed moving target.

Description

Macro-pulse photon counting laser radar

Technical Field

The invention relates to the technical field of laser radars, in particular to a macropulse photon counting laser radar.

Background

In the field of photon counting laser radar detection, researchers propose to improve the detection probability of a long-distance target by adopting a pulse accumulation technology. However, as the number of accumulated pulses increases, the imaging speed gradually slows, making photon counting lidar systems unsuitable for high-speed moving object detection and fast imaging. Although a high pulse repetition frequency laser source (tens of MHz) is used to reduce the data acquisition time, this also greatly reduces the unambiguous range of the system. Therefore, the pulse accumulation method is difficult to be used for the detection of a long-distance, high-speed moving object. In order to shorten the measurement time, researchers have proposed methods that employ pseudo-randomly encoded photon counts. However, pseudo-randomly coded photon-counting lidar typically requires an expensive signal generator, which makes the lidar system costly. In addition, when a single photon detector responds to one photon, it enters a dead zone and cannot respond to any other arriving photon. The pulse spacing of any two "1" bits in the pseudorandom sequence is random. When the pulse interval is less than the dead time of the detector, the leading "1" bit will cause the single photon detector to enter the dead zone, while the trailing "1" bit will not respond even if a signal photon arrives. Thereby reducing the ranging performance of the pseudorandom coded photon counting lidar. To solve these problems, we propose a macropulse photon counting lidar. On the premise of keeping the original ranging system simple and convenient, the method can simultaneously realize the detection of the long-distance and fast moving target and has great application value.

Disclosure of Invention

The invention aims to solve the problem that the traditional multi-pulse accumulation and pseudorandom coding photon counting laser radar is difficult to realize the detection of long-distance and high-speed moving targets.

The technical scheme adopted by the invention is as follows: the laser periodically emits a pulse train, the pulse train consists of a plurality of sub-pulses with unequal intervals, and the pulse train is called as a macro-pulse, and the characteristic of unequal intervals among the sub-pulses can effectively overcome the distance ambiguity of the system; the macro pulse output by the laser is divided into two parts by a proportional beam splitter; wherein, the part with smaller energy is detected by the photodiode and recorded by the photon counting module as a timing starting signal; a part of the remaining energy is irradiated to the target through an optical system, and an echo signal scattered by the target is collected; detecting target echoes collected by the optical system by single photon detection (GM-APD); recording the response output of the single photon detection (GM-APD) by the photon counting module as a timing stop signal; and finally, the signal processing module processes the timing start and stop information recorded by the photon counting module so as to obtain the distance information of the target.

The laser periodically emits macro-pulses, and sub-pulses in the macro-pulses have unequal pulse intervals, so that distance ambiguity can be effectively overcome, the unambiguous distance of a system is determined by the period of the macro-pulses, and the unambiguous distance of the system cannot be influenced by the number of the sub-pulses and the total interval of the sub-pulses.

The sub-pulses have known and fixed pulse intervals, when echo signal demodulation is performed, an echo sequence needs to be shifted according to the known pulse intervals, the delayed emission time of each pulse is compensated, and then the sub-pulses are accumulated in a traditional pulse accumulation mode to improve the signal-to-noise ratio of a system, so that the distance of a target is obtained.

The period of the macro pulse is far larger than the total interval of the sub pulses, so that the problem of distance ambiguity does not exist when a long-distance target is measured; the total interval of the sub-pulses is short, generally tens of microseconds, even hundreds of nanoseconds, so that the moving target can be approximate to a static target in a short time interval, and the influence of the target movement on the ranging precision and the detection probability of the system is effectively avoided.

The principle of the invention is as follows: a macro-pulse photon counting laser radar is characterized in that a laser adopts internal modulation or external modulation to obtain periodic macro-pulses, the period of the macro-pulses is generally longer, the long pulses are used to ensure that a system has a longer non-fuzzy distance, and the intervals of sub-pulses with unequal intervals in the macro-pulses are shorter, so that the system can obtain the capability of rapid detection.

The beam splitter is a proportional beam splitter, divides laser pulses into two beams of laser with different energy, wherein one part of the laser has smaller energy and is used for recording the intervals of the transmitted sub-pulses and the initial time of the transmitted pulses, and the other part of the main energy is used for realizing the detection of the target.

The optical system comprises a transmitting optical system and a receiving optical system, and is used for collimating and expanding the laser pulse and transmitting and receiving the laser pulse.

The photodiode is a linear detector, records the time of the transmitted sub-pulse, obtains the real pulse interval of the sub-pulse, and can also obtain the timing starting point of the pulse train.

The single photon detector (GM-APD) has single photon detection capability and extremely high detection sensitivity, and is widely applied to the detection of long-distance and weak echo signals. The single photon detector has unavoidable dead time, and in a macro-pulse photon counting laser radar system, in order to avoid the influence of the dead time of the detector on the ranging performance, the interval of sub-pulses in a transmitted ground pulse train is larger than the dead time of the detector.

And two channels of the photon counting module respectively record the electric pulse output of the photodiode and the single photon detector to obtain the timing starting time and the timing stopping time. The time resolution of the photon counting module causes a factor affecting the ranging accuracy, and the timing resolution of a common photon counting module generally reaches dozens or even several picoseconds.

And the signal processing module processes the timing start time and the timing stop time obtained by the photon counting module to obtain the distance information of the target.

The invention has the advantages that:

(1) the distance information of the target can be obtained by the macro-pulse photon counting laser radar in one period, and multi-pulse accumulation is not needed. The period of the macro-pulse is long, the unambiguous distance of a system can be effectively increased, the total interval of the continuously transmitted sub-pulse trains is generally tens of microseconds or even hundreds of nanoseconds, and the movement of the target in the extremely short interval can be ignored, so that the method has obvious advantages in measuring the high-speed moving target.

(2) The macro-pulse with fixed interval is periodically transmitted, and the number of the pulses is small, so that the electric pulse sequence is easy to realize on hardware; compared with the traditional pseudo-random encoding method, the hardware requirement on the system is greatly reduced.

(3) The interval of the transmitted sub-pulses can be adjusted randomly, and the interval of the sub-pulses can be ensured to be larger than the dead time of the detector, so that the influence of the dead time of the detector on the ranging performance is effectively avoided, and the ranging performance of the system can be effectively improved compared with the traditional pseudo-random encoding method.

Drawings

FIG. 1 is a schematic diagram of a macropulse photon counting lidar in accordance with the present invention;

fig. 2 is a schematic diagram of a method for extracting a return signal of a macropulse photon counting lidar according to the present invention.

Detailed Description

In order to make the objects of the invention, the macropulse photon counting lidar scheme, and its advantages clearer, the invention is explained in further detail with reference to the following detailed description and the attached drawings.

As shown in fig. 1, the present invention provides a macropulse photon counting lidar, which comprises a laser 1, a proportional beam splitter 2, an emission-reception optical system 3, a photodiode 7, a single photon detection (GM-APD)4, a photon counting module 5, and a signal processing module 6. Compared with the traditional pulse accumulation method, the method has the advantages that the periodically transmitted macro pulse is utilized to obtain the distance information of a target in one period on the premise of keeping the system to be long and not to obscure the distance, so that the detection speed of the system is greatly improved, and the method is very suitable for detecting the target moving at a long distance and at a high speed. Compared with the traditional pseudo-random coding method, the method effectively overcomes the influence of the dead time of the detector on the ranging performance, reduces the requirement of the system on hardware, and greatly improves the practical value of the system.

The specific implementation mode of the invention is as follows: the laser 1 periodically emits a macropulse which is composed of a plurality of unequally spaced subpulses. The unambiguous distance of the system is determined by the period of the macropulse, regardless of the number of subpulses and the total spacing of the subpulses. The total pulse interval of the sub-pulses is short, generally dozens of microseconds or even hundreds of nanoseconds, so that a moving target can be approximate to a static target in a short time interval, and the influence of the target motion on the ranging precision and the detection probability of the system is effectively avoided. One target distance can be obtained in one period without multiple accumulation, and the detection speed of the system is greatly improved.

The periodically emitted macro-pulses are transmitted to a proportional beam splitter 2; dividing an incident macro pulse into two parts with different proportions by a proportional beam splitter 2; wherein a part of the smaller energy is incident to the photodiode 7, and the sub-pulse is detected by the photodiode 7; in addition, a part with larger energy is irradiated to the target moving at high speed through the receiving optical system 3; the receiving optical system 3 collects laser signals scattered by a target and transmits the laser signals to a single photon detector (GM-APD) 4; a single photon detector (GM-APD)4 detects a target echo signal; the output response is recorded by the photon counting module 5; the signal processing module 6 processes the recorded laser emission time and the target echo time by the photon counting module, so as to obtain the distance information of the target.

The specific echo signal processing algorithm is explained in detail with reference to fig. 2: the time intervals of the sub-pulses are accurately detected by the photodiode 7 and recorded as known parameters. The pulse interval of any two sub-pulses of the macro-pulse is not equal in one period. As shown in FIG. 2, the echo signals detected by the single photon detector (GM-APD)4 are sequentially shifted by the pulse interval of the transmitted sub-pulses within one cycle. The shifted echo signals are stored and accumulated. The peak position corresponds to the time of flight of the macropulse. In other words, since the delay time of each sub-pulse with respect to the first sub-pulse is known, the flight time of the macro-pulse is equal to the flight time of the sub-pulse after the compensation delay time. By sequentially compensating the delay of the sub-pulses and then integrating the sub-pulses, the signal to noise ratio of the system can be effectively improved, and thus the distance information of the target can be obtained.

Claims

1. A macropulse photon counting laser radar is characterized by comprising a laser (1), a proportional beam splitter (2), an emitting and receiving optical system (3), a photodiode (7), a single photon detection (GM-APD) (4), a photon counting module (5) and a signal processing module (6), wherein the laser (1) periodically emits a pulse train, the pulse train is composed of a plurality of sub-pulses with unequal intervals and is called macropulse, and the characteristic of unequal intervals among the sub-pulses can effectively overcome the distance ambiguity of the system; the macro pulse output by the laser (1) is divided into two parts by a proportional beam splitter (2); wherein, the part with smaller energy is detected by the photodiode (7), and is recorded by the photon counting module (5) as a timing starting signal; a part of the remaining more energy is irradiated to the target through the transmitting and receiving optical system (3) and the echo signal scattered by the target is collected; detecting target echoes collected by the transmitting and receiving optical system (3) by single photon detection (GM-APD) (5); the response output of the single photon detection (GM-APD) (4) is recorded by the photon counting module (5) and is used as a timing stop signal; finally, the signal processing module (6) processes the timing start and stop information recorded by the photon counting module so as to obtain the distance information of the target;

the period of the macro pulse is far larger than the total interval of the sub pulses, so that the problem of distance ambiguity does not exist when a long-distance target is measured; and the total interval of the sub-pulses is shorter, so that the moving target can be approximate to a static target in a shorter time interval, and the influence of the target movement on the system ranging precision and the detection probability is effectively avoided.

2. The macropulse photon counting lidar according to claim 1, wherein the laser (1) periodically emits macropulses, and wherein the subpulses in the macropulses have unequal pulse intervals, thereby effectively overcoming range ambiguity such that the unambiguous range of the system is determined by the period of the macropulses, and wherein the number of subpulses and the total separation of the subpulses do not affect the unambiguous range of the system.

3. The macropulse photon counting lidar of claim 1, wherein the subpulses have known and fixed pulse intervals, and when demodulating the echo signal, the echo sequence is shifted according to the known pulse intervals, the delay time of each pulse is compensated, and then the subpulses are accumulated by using a traditional pulse accumulation method to improve the signal-to-noise ratio of the system, thereby obtaining the distance of the target.