CN110161522A - A kind of Gao Zhongying single-photon laser radar for eliminating range ambiguity - Google Patents

Abstract

The invention discloses a high-repetition-frequency single-photon laser radar capable of eliminating distance ambiguity, comprising a control module, a laser, a beam splitter, an emission optical system, a photodiode, an event timer, a receiving optical system, a single-photon detector, a signal processing module. The control module is used to generate a pulse signal with adjustable repetition frequency, which is used as the main control signal of the laser to control the emission time of the laser pulse. The event timer is used to record the reference light pulse and echo light pulse time respectively, and the signal processing module performs time-correlated single-photon counting processing. Due to the constant change of the laser pulse frequency, only the echo light pulse at this trigger time can be accumulated during the accumulation process. Finally, the echo light pulses not at the current trigger time are discretized, which finally enables the single-photon lidar to eliminate the distance ambiguity problem under the condition of high repetition frequency.

Description

A high-repetition single-photon lidar that eliminates range ambiguity

technical field

The invention belongs to the technical field of laser radar, and in particular relates to a high-repetition-frequency single-photon laser radar capable of eliminating distance ambiguity.

Background technique

Single-photon LiDAR uses a single-photon detector to receive photon-level echo signals, and uses Time-Correlated Single Photon Counting (TCSPC) technology to improve the optical signal detection sensitivity of time-of-flight ranging to the quantum limit. Greatly improves the range of lidar. Although the single-photon lidar has high detection sensitivity, the TCSPC technology it adopts requires multiple accumulations to extract the distance information of the target. Under the condition of a certain repetition frequency, increasing the accumulation times will cause the ranging time to be too long, and it cannot be applied to the laser ranging of moving targets. Therefore, increasing the repetition frequency of laser pulses is an effective way to improve the data update rate of single-photon lidar.

However, the increase of repetition rate will shorten the maximum unambiguous distance, which limits the application of single-photon lidar in long-distance target ranging. In order to solve the contradiction between the laser pulse repetition frequency and the maximum unambiguous distance, there are generally the following methods: one of them is the pseudo-random coding technology based on correlation operation, which encodes the long pulse emitted by the laser, The received echo pulse is correlated with the transmitted pulse to extract the target signal in the echo pulse, so as to realize long-distance moving target detection. At the same time, by applying different coding methods to each pulse, it can effectively solve the problem of high repetition frequency distance blur problem. However, the problem with this method is that the dead time of the single-photon detector reduces the correlation between the transmitted pulse and the echo pulse, which in turn reduces the sensitivity of echo detection. Another method is dual-frequency or multi-frequency modulation technology, that is, using two or fixed frequencies (corresponding periods are T ₁ , T ₂ , ..., T _n ) to modulate the laser pulse, the maximum detectable frequency is The fuzzy distance is d _max =c[T ₁ , T ₂ ,..., T _n ]/2, where [T ₁ , T ₂ ,..., T _n ] is the least common multiple of T ₁ , T ₂ ,..., T _n . However, when the time interval between two adjacent echo signals is very short (less than the dead time of the single photon detector), the dead time of the single photon detector will affect the detection probability of the echo signals.

SUMMARY OF THE INVENTION

In order to overcome the shortcomings and deficiencies of the prior art, the present invention proposes a high-repetition-frequency single-photon laser radar capable of eliminating distance ambiguity, which can realize long-distance moving target detection with a high repetition frequency.

In order to achieve the above purpose, the technical solution adopted in the present invention is: a high-repetition-frequency single-photon laser radar that can eliminate distance ambiguity, the laser radar includes a control module, a laser, a beam splitter, an emission optical system, a photodiode, a first An event timer, a receiving optical system, a single photon detector, a second event timer, and a signal processing module, wherein:

The control module is used to generate a trigger pulse signal with adjustable repetition frequency, which is used as the main control signal of the laser to control the emission time of the laser pulse;

The laser is used to generate laser pulse signals, and the pulse frequency is controlled by the control module;

The beam splitter divides the laser signal emitted by the laser into two parts, most of the laser light is transmitted to the emission optical system as signal light, and a small part of the laser light is transmitted to the photodiode as reference light;

The transmitting optical system is used for collimating and beam expanding the signal light and transmitting it to the measured target;

The photodiode is used to detect the reference light separated by the beam splitter, and use it as a timing reference signal;

The first event timer is used to accurately record the time of the reference light pulse, which is used as the starting point for measuring the time of flight of the pulse;

The receiving optical system is used for receiving the laser echo signal reflected/scattered by the measured target;

The single-photon detector is used to respond to a weak echo light pulse signal of the photon level;

The second event timer is used to accurately record the time of the echo light pulse as the end point of the pulse flight time measurement;

The signal processing module is used for time-correlated single-photon counting processing, so as to obtain a histogram, calculate the pulse flight time, and finally realize the measurement of the target distance.

Among them, the control module is used to generate a trigger pulse signal with adjustable repetition frequency as the main control signal of the laser, which is used to control the emission timing of the laser pulse, so that the time interval between two adjacent pulses output by the laser is different.

Among them, the event timer is used to accurately record the pulse timing of the reference light and the echo light, which can not only realize the time resolution of picosecond level, but also realize the time measurement range of a large range, which overcomes the time resolution and time measurement. inconsistencies between ranges.

Among them, the time interval between two adjacent laser pulses is different, so that in the accumulation process, only the echo light pulses corresponding to the current trigger time can be accumulated, and the echo light pulses not at the current trigger time will be discretized and processed. It cannot be accumulated, so that the emitted high repetition frequency laser pulse will not have multiple echoes under the condition of a large range of time measurement range.

Among them, the pulse frequency modulation form of high repetition frequency is adopted. The high repetition frequency not only solves the multiple accumulation problem of the photon counting system, but also adapts to the occasion of ranging under motion conditions. ranging from the target.

Compared with the prior art, the advantages of the high-repetition-frequency single-photon laser radar that can eliminate the distance ambiguity according to the present invention are:

(1) This high-repetition single-photon lidar uses both the reference light and the echo light to accurately record the pulse time using an event timer, which can not only achieve a time resolution of the order of picoseconds, but also a large-scale time measurement range .

(2) The high repetition frequency single-photon lidar uses different time intervals between two adjacent laser pulses, so that only the echo light pulses corresponding to the current trigger moment can be accumulated during the accumulation process, not the current time. The echo light pulse at the trigger time will be discretized and cannot be accumulated, so that the emitted high repetition frequency laser pulse will not have multiple echoes under the condition of a large time measurement range.

(3) The high repetition frequency single-photon lidar adopts high repetition frequency frequency modulated laser pulses, which not only solves the multiple accumulation problem of the photon counting system, but also adapts to ranging occasions under motion conditions, and can also eliminate the distance Fuzzy to achieve long-distance target ranging.

Description of drawings

FIG. 1 is a schematic structural diagram of a high-repetition-frequency single-photon laser radar capable of eliminating distance ambiguity according to the present invention.

FIG. 2 is a pulse frequency modulation waveform diagram of the present invention.

FIG. 3 is a schematic diagram of the echo signal extraction of the present invention.

Detailed ways

In order to make the objects, solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

The present invention is a high repetition frequency single photon laser radar capable of eliminating distance ambiguity. The high repetition frequency single photon laser radar comprises a control module 1, a laser 2, a beam splitter 3, an emission optical system 4, a photodiode 5, a first event A timer 6, a receiving optical system 7, a single-photon detector 8, a second event timer 9 and a signal processing module 10, the control module 1 is used to generate a trigger pulse signal with adjustable repetition frequency, which is used as a laser pulse signal. The main control signal is used to control the emission time of the laser pulse; the laser 2 is used to generate the laser pulse signal, and the pulse frequency is controlled by the control module 1; the beam splitter 3 divides the laser signal emitted by the laser into two , most of the laser light is transmitted to the emission optical system 4 as the signal light, and a small part of the laser light is transmitted to the photodiode 5 as the reference light; the emission optical system 4 is used to collimate and expand the signal light and emit it to on the measured target; the photodiode 5 is used to detect the reference light separated by the beam splitter 3 as a timing reference signal; the first event timer 6 is used to accurately record the time of the reference light pulse, Take this as the starting point of pulse time-of-flight measurement; the receiving optical system 7 is used to receive the laser echo signal reflected/scattered by the measured target; the single-photon detector 8 is used to respond to the weak echo light of the photon level Pulse signal; the second event timer 9 is used to accurately record the time of the echo light pulse as the end point of the pulse flight time measurement; the signal processing module 10 is used to perform time-correlated single-photon counting processing, thereby Obtain the histogram, calculate the pulse flight time, and finally realize the measurement of the target distance.

As shown in FIG. 1 , the high-repetition single-photon lidar proposed by the present invention that can eliminate distance ambiguity includes a control module 1, a laser 2, a beam splitter 3, an emission optical system 4, a photodiode 5, and a first event timer 6. A receiving optical system 7 , a single photon detector 8 , a second event timer 9 , and a signal processing module 10 . The trigger pulse signal with adjustable repetition frequency is generated by the control module 1, which is used as the main control signal of the laser 2 to control the emission time of the laser pulse. The first and second event timers are used to record the time of the reference light pulse and the echo light pulse respectively, and the signal processing module 10 performs time-correlated single-photon counting processing. Since the frequency of the laser pulse changes continuously, only this trigger time is in the accumulation process. The echo light pulses can be accumulated, and the echo light pulses not at the current trigger time are discretized, which finally enables the single-photon lidar to measure the distance of long-distance targets under the condition of high repetition frequency.

The pulse signal with a modulated repetition frequency generated by the control module 1 is used as the main control signal of the laser 2 to control the emission timing of the laser pulse. The pulse frequency modulation waveform diagram is shown in FIG. 2 . As long as the variation of the repetition frequency of the laser pulse is reasonably controlled, it can be ensured that only the echo light pulse corresponding to the current trigger moment falls within the same distance gate under the specified relative motion speed of the target during the pulse trigger timing process, so it can accumulate The echo light pulses not at this trigger time will be discretized and cannot be accumulated, so that the emitted high repetition frequency laser pulse will not have multiple echoes under the condition of a large timing range. In this way, the single-photon lidar does not have the problem of distance ambiguity, and can emit laser pulses at a high repetition frequency to achieve laser ranging of moving targets.

In order to explain in more detail the basic principle of the high-repetition-frequency single-photon lidar that can eliminate distance ambiguity, the method for extracting echo signals is described here, as shown in Figure 3. In a time measurement cycle, only _ri is the echo generated by the laser pulse emitted at the time t _i of the pulses collected after the timing is triggered, and the time interval between _ri and _ti represents the real round-trip flight of the laser pulse time, which can be used to calculate the target distance; and r _j (i≠j) is the echo generated by the laser pulses emitted at other times. The time interval between r _j and t _i is not the real round-trip flight time of the laser pulse, which cannot be Used to calculate the target distance.

In addition, in order to prevent the r _j (i≠j) pulses collected after the trigger timing at time t _i from being superimposed during multiple accumulation processes, these pulses must be discretely distributed and not appear in the same distance gate . In order to achieve this effect, the time t _i that triggers the timing must satisfy the following relationship:

Here T _bin is the distance gate time, V is the relative motion speed of the target, and c is the speed of light. That is to say, in the process of multiple accumulation, the time interval between two laser pulses should satisfy the following conditions:

As long as the period of the laser pulses is different by a distance gate time T _bin , the r _j (i≠j) pulses collected after the trigger timing at time t _i will not appear in the same distance gate in the multiple accumulation process, So they don't stack up.

The present invention is a high repetition frequency laser ranging method based on pulse frequency modulation, which can not only eliminate distance ambiguity to achieve long-distance target ranging, but also solve the multiple accumulation problem of the photon counting system, and is suitable for ranging occasions under motion conditions. At the same time, an event timer is used to accurately record the pulse timing of the reference light and the echo light, which can not only achieve a time resolution of the order of picoseconds, but also a large range of time measurement, which overcomes the need for time resolution and time measurement. inconsistencies between ranges.

Claims (5)

1. the Gao Zhongying single-photon laser radar that one kind can eliminate range ambiguity, it is characterised in that: the Gao Zhongying single-photon laser Radar includes control module (1), laser (2), beam splitter (3), optical transmitting system (4), photodiode (5), the first thing Part timer (6), receiving optics (7), single-photon detector (8), second event timer (9) and signal processing module (10), the control module (1) is for generating the adjustable start pulse signal of repetition rate, as the master control of laser Signal, for controlling the emission time of laser pulse；The laser (2) is for generating laser pulse signal, pulse frequency It is controlled by control module (1)；The laser signal that laser emits is divided into two by the beam splitter (3), major part therein Laser is transmitted to optical transmitting system (4) as signal light, and fraction laser is transmitted to photodiode (5) as reference Light；The optical transmitting system (4) is concurrently incident upon measured target for being collimated and being expanded to signal light；The light Electric diode (5) is for detecting the reference light that beam splitter (3) separates, in this, as time base signal；The first event At the time of timer (6) is for accurately recording reference light pulse, in this, as the starting point of pulse time-of-flight measurement；Described connects Optical system (7) are received for receiving measured target reflection/scattering laser echo signal；The single-photon detector (8) is used In the faint echo light pulse signal of response photon magnitude；The second event timer (9) is for accurately recording echo light At the time of pulse, in this, as the terminal of pulse time-of-flight measurement；The signal processing module (10) is for carrying out the time Correlated single photon counting processing calculates pulse time-of-flight, the final measurement for realizing target range to obtain histogram.

2. the Gao Zhongying single-photon laser radar according to claim 1 for eliminating range ambiguity, it is characterised in that: use Control module (1) generates master signal of the adjustable start pulse signal of repetition rate as laser, for controlling laser arteries and veins The emission time of punching, so that the time interval between the two neighboring pulse of laser output is different.

3. the Gao Zhongying single-photon laser radar according to claim 1 for eliminating range ambiguity, it is characterised in that: use Event timer accurately records the pulse time of reference light and echo light, has both been able to achieve the time resolution of picosecond magnitude Rate, and range when being able to achieve the survey of wide range, contradiction when overcoming temporal resolution and surveying between range.

4. the Gao Zhongying single-photon laser radar according to claim 1 for eliminating range ambiguity, it is characterised in that: adjacent Time interval between two laser pulses is different, so that there was only the corresponding echo light of this triggering moment in accumulation Pulse could be accumulated, and the echo light pulse of this non-triggering moment will be discretized processing and can not accumulate, so that The Gao Zhongying laser pulse of transmitting multiple echoes will not occur under range of condition in the survey of wide range.

5. the Gao Zhongying single-photon laser radar according to claim 1 for eliminating range ambiguity, it is characterised in that: use The pulse frequency modulated form of Gao Zhongying, high repetition rate had not only solved the problems, such as the multiple accumulation of photon counting system, but also The ranging occasion under moving condition is adapted to, and pulse frequency modulated can eliminate range ambiguity and realize distant object ranging.