CN110161522B - High-repetition-frequency single-photon laser radar capable of eliminating range ambiguity - Google Patents

Abstract

The invention discloses a high repetition frequency single photon laser radar capable of eliminating range ambiguity. The control module is used for generating a pulse signal with adjustable repetition frequency, and the pulse signal is used as a main control signal of the laser and is used for controlling the emission time of the laser pulse. The event timer is utilized to record the reference light pulse time and the echo light pulse time respectively, the signal processing module is used for carrying out time-related single photon counting processing, the laser pulse frequency is changed constantly, only the echo light pulse at the triggering time can be accumulated in the accumulation process, the echo light pulse at the non-triggering time is discretized, and finally the single photon laser radar can eliminate the distance ambiguity problem under the high repetition frequency condition.

Description

A High Repetition Rate Single-Photon LiDAR with Range Blur Removal

technical field

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

Background technique

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

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 a pseudo-random coding technology based on correlation operations, which encodes the long pulses emitted by the laser, and passes the detector The received echo pulse is correlated with the transmitted pulse to extract the target signal in the echo pulse, so as to realize the long-distance moving target detection. At the same time, by applying different encoding methods to each pulse, it can effectively solve the problem of high repetition frequency. distance ambiguity problem. However, the problem with this approach is that the dead time of the single-photon detector reduces the correlation between the transmitted pulse and the echo pulse, thereby reducing the sensitivity of echo detection. Another method is dual-frequency or multi-frequency modulation technology, that is, using two or fixed frequencies (the corresponding periods are T ₁ , T ₂ , ..., T _n ) to modulate the laser pulse, then the maximum non-detectable 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 signal.

Contents 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 range ambiguity, which can realize long-distance moving target detection with a relatively high repetition rate.

In order to achieve the above object, the technical solution adopted by the present invention is: a high repetition rate single-photon laser radar that can eliminate distance ambiguity, the laser radar includes a control module, a laser, a beam splitter, a transmitting 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 an adjustable repetition rate, 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 splits the laser signal emitted by the laser into two, most of the laser light is transmitted to the transmitting 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 to collimate and expand the signal light and transmit it to the measured target;

The photodiode is used to detect the reference light split by the beam splitter as a timing reference signal;

The first event timer is used to accurately record the moment of the reference light pulse as the starting point of pulse time-of-flight measurement;

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

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

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

The signal processing module is used for time-correlated single photon counting processing, thereby obtaining a histogram, calculating the pulse flight time, and finally realizing 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 time 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 time of the reference light and the echo light, which can not only realize the time resolution of picosecond level, but also realize the large-scale time measurement range, and overcome the time resolution and time measurement. Inconsistency between ranges.

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

Among them, the pulse frequency modulation form with 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 ranging occasion under the condition of motion. Distance target ranging.

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

(1) The high-repetition-frequency single-photon lidar uses both the reference light and the echo light to accurately record the pulse time with an event timer, which can not only achieve picosecond-level time resolution, but also achieve a large-scale time measurement range .

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

(3) The high-repetition-frequency single-photon lidar uses a high-repetition-frequency frequency-modulated laser pulse, which not only solves the problem of multiple accumulations in the photon counting system, but also adapts to ranging occasions under moving conditions, and can also eliminate distance Blur realizes distance measurement of distant objects.

Description of drawings

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

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

Fig. 3 is a principle diagram of echo signal extraction in the present invention.

Detailed ways

In order to make the purpose, solution and advantages of the present invention more clear, 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 that can eliminate distance ambiguity. The high-repetition-frequency single-photon laser radar includes a control module 1, a laser 2, a beam splitter 3, a transmitting optical system 4, a photodiode 5, and a first event Timer 6, receiving optical system 7, single photon detector 8, second event timer 9 and signal processing module 10, described control module 1 is used for generating the trigger pulse signal with adjustable repetition frequency, it is used as laser 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 signal light, and a small part of the laser light is transmitted to the photodiode 5 as a 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 split by the beam splitter 3 as a timing reference signal; the first event timer 6 is used to accurately record the moment 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 photon level pulse signal; the second event timer 9 is used to accurately record the moment of the echo light pulse as the end point of the pulse time-of-flight 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 Figure 1, the high repetition rate single-photon laser radar proposed by the present invention that can eliminate distance ambiguity includes a control module 1, a laser 2, a beam splitter 3, a transmitting 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 control module 1 is used to generate a trigger pulse signal with adjustable repetition frequency, 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 is constantly changing, only this trigger time is in the accumulation process The echo light pulses can be accumulated, and the echo light pulses at the non-triggering time are discretized, which finally enables the single-photon lidar to measure the distance of the long-distance target under the condition of high repetition frequency.

The pulse signal with a repeatable frequency modulation generated by the control module 1 is used as the main control signal of the laser 2 to control the emission time of the laser pulse. The pulse frequency modulation waveform diagram is shown in FIG. 2 . As long as the variation of the laser pulse repetition frequency is reasonably controlled, it can be ensured that only the echo light pulses corresponding to this triggering time fall within the same range gate under the specified relative moving speed of the target during the pulse triggering timing process, and thus can accumulate The echo light pulses at other than this triggering time will be discretized and cannot be accumulated, so that the emitted high repetition frequency laser pulses will not appear multiple echoes under the condition of a large time measurement range. In this way, the single-photon lidar will not have the problem of distance ambiguity, and can emit laser pulses at a higher repetition rate 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 range ambiguity, the echo signal extraction method is described here, as shown in Figure 3. In a time measurement period, only r _i is the echo generated by the laser pulse emitted at the time t _i is triggered after the timing is triggered, and the time interval between r _i and t _i represents the real round-trip flight of the laser pulse Time can be used to calculate the target distance; while r _j (i≠j) is the echo generated by the laser pulse 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, and cannot Used to calculate target distance.

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

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

As long as it is ensured that the period of the laser pulse differs by a range gate time T _bin , the r _j (i≠j) pulses collected after trigger timing at time t _i will not appear in the same range gate during multiple accumulation processes, So they don't add up.

The invention provides a high-repetition frequency laser ranging method based on pulse frequency modulation, which can not only eliminate distance ambiguity to realize long-distance target ranging, but also solve the multiple accumulation problem of the photon counting system, and is suitable for ranging occasions under moving conditions. At the same time, the event timer is used to accurately record the pulse time of the reference light and the echo light, which can not only realize the time resolution of picosecond level, but also realize the large-scale time measurement range, and overcome the time resolution and time measurement. Inconsistency between ranges.

Claims (1)

1. A high repetition frequency single photon laser radar capable of eliminating range ambiguity is characterized in that: 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 timer (6), a receiving optical system (7), a single-photon detector (8), a second event timer (9) and a signal processing module (10), wherein the control module (1) is used for generating a trigger pulse signal with adjustable repetition frequency, and the trigger pulse signal is used as a main control signal of the laser and is used for controlling the emission time of laser pulses; the laser (2) is used for generating a laser pulse signal, and the pulse frequency is controlled by the control module (1); the beam splitter (3) divides a laser signal emitted by the laser into two parts, wherein most of the laser is transmitted to the emission optical system (4) to be used as signal light, and the small part of the laser is transmitted to the photodiode (5) to be used as reference light; the emission optical system (4) is used for collimating and expanding signal light and emitting the signal light to a measured target; the photodiode (5) is used for detecting the reference light split by the beam splitter (3) and taking the reference light as a timing reference signal; the first event timer (6) is used for accurately recording the time of the reference light pulse and taking the time as the starting point of the measurement of the flight time of the pulse; the receiving optical system (7) is used for receiving a laser echo signal reflected/scattered by a measured target; the single photon detector (8) is used for responding to a weak echo light pulse signal of a photon magnitude; the second event timer (9) is used for accurately recording the time of the echo light pulse, and the time is used as an end point of the pulse flight time measurement; the signal processing module (10) is used for carrying out time correlation single photon counting processing so as to obtain a histogram, calculating the flight time of pulses and finally realizing the measurement of a target distance;

a control module (1) is adopted to generate a trigger pulse signal with adjustable repetition frequency as a main control signal of the laser, and the trigger pulse signal is used for controlling the emission time of laser pulses so that the time intervals between two adjacent pulses output by the laser are different;

the event timer is adopted to accurately record the pulse time of the reference light and the echo light, so that the time resolution of picosecond magnitude can be realized, the time measuring range of large measuring range can be realized, and the contradiction between the time resolution and the time measuring range is overcome;

the time intervals between two adjacent laser pulses are different, so that only the echo light pulse corresponding to the triggering time of this time can be accumulated in the accumulation process, the echo light pulse at the triggering time of non-this time cannot be accumulated due to discretization processing, and a plurality of echoes cannot appear in the emitted high-repetition-frequency laser pulse under the condition of a large-range time measurement range;

the pulse frequency modulation mode with high repetition frequency is adopted, the high repetition frequency not only solves the problem of multiple accumulation of a photon counting system, but also can adapt to the ranging occasion under the motion condition, and the pulse frequency modulation can eliminate the range ambiguity and realize the ranging of a long-distance target;

wherein, in a time measurement period, t _i The pulse collected after the time trigger timing is only r _i Is the echo, r, produced by the laser pulse emitted at that moment _i And t _i The time interval between the two represents the real round-trip flight time of the laser pulse, and is used for calculating the target distance; and r _j I ≠ j, is the echo generated by the laser pulse emitted at other times, r _j And t _i The time interval between is not the true round-trip time of laser pulse and cannot be used to calculate the target distance;

to make t _i R collected after time trigger timing _j I ≠ j, the pulses cannot be superposed in the process of multiple accumulation, the pulses must be distributed discretely and do not appear in the same range gate, and the timing time t is triggered _i The following relationship must be satisfied:

here T _bin For the range gate time, V is the target relative motion velocity and c is the speed of light, i.e. the time interval between two laser pulses during multiple accumulation should satisfy the following condition:

as long asEnsuring that the periods of the laser pulses differ by a time T from the gate _bin Can make t be _i R collected after time triggering and timing _j (i ≠ j) pulses do not occur within the same range gate during multiple accumulations and thus do not overlap.

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