KR101272908B1 - Lidar system and signal processing method using spectral time-of flight(tof) - Google Patents

Abstract

PURPOSE: A LIDAR system is provided to reduce measurement errors by measuring the absolute distance of a target using the arrival time difference between chirped microwave pulses with different wavelengths. CONSTITUTION: A LIDAR system using a spectral time of flight method includes a transmission unit(31) which separates a microwave pulse outputted from a laser into two and transmits the separated pulses, a receiving unit(32) which gets a measuring pulse and a reference pulse which are the reflection of the transmitted pulses off a target object and a fixed reference object respectively, a dispersion unit(33) which disperses the received measuring pulse and the received reference pulse, generates a chirped measuring pulse and a chirped reference pulse, and outputs the chirped pulses, a spectrum unit(34) which separates the chirped measuring pulse and the chirped reference pulse by wavelength, generates a spectral measuring pulse and a spectral reference pulse, and outputs the spectral pulses, a detection unit(35) which converts incident pulses, the spectral measuring pulse and the spectral reference pulse, according to a wavelength into electric signals sequentially and obtains a clock rate of each pulse, and an arrival time and a light intensity distribution of each wavelength, a control unit(36) which obtains the absolute distance of the target object(10) by getting the time difference of each wavelength between the measuring pulse and the reference pulse through the clock rate and the arrival time of each wavelength and gets the physical properties of the target object by getting the absorption spectrum of the target object through the light intensity distribution of each wavelength. [Reference numerals] (10) Target object; (20) Standard object; (31) Transmission unit; (32) Receiving unit; (33) Dispersion unit; (34) Spectrum unit; (35) Detection unit; (36) Control unit

Description

Lidar system and signal processing method using spectral time-of flight (TOF)}

The present invention relates to a rider (LIDAR) system and a rider signal processing method using the spectroscopic flight time method, and more specifically, it is possible to obtain the absolute distance and the property information of the measurement target by using the time difference of arrival of each ultrashort pulse. Rider (LIDAR) system and signal processing method.

Light detection and ranging (LIDAR) is a light-based telemetry technique that is similar in principle to the well-known radar (radio detection and ranging).

The radar reflects the electromagnetic wave of the microwave level to the object and receives the electromagnetic wave reflected from the object to find the distance, direction, and altitude of the object, while the rider (LIDAR) emits light in the visible or infrared region. It is used for more precise distance observation because it acquires distance information and physical property information of the material to be measured.

Conventionally, as a distance sensor of an unmanned vehicle, a terrestrial laser scanner (TLS) is used to detect a location of a measurement object using a pulse laser and a flight time method, and an absolute distance of the measurement object is obtained as shown in Equation 1 below. Can be. In this case, the flight time method measures the distance of the measurement object by multiplying the round trip time of the pulse laser returning by hitting the measurement object to the speed of light and uses the difference between the transmission time and the reception time of the pulse.

은 펄스의 왕복시간이고, N은 빛이 통과한 경로의 군굴절률이다.Where c is the speed of light

Is the round trip time of the pulse, and N is the group refractive index of the path through which light passes.

Therefore, according to Equation 1, if the round trip time of the pulse can be accurately measured through the detector, the absolute position of the measurement object can be measured without limiting the distance.

1 illustrates an absolute distance measuring principle using a conventional pulse laser.

Referring to FIG. 1, the distance may be calculated by measuring a difference between the rising edge values of the start pulse and the stop pulse using an external clock having a high bandwidth.

)는 아래의 수학식 2와 같다.In FIG. 1, when the phase difference between the rising edge and the start pulse and the stop pulse is ε and σ, respectively, the time difference between the actual start pulse and the stop pulse (

) Is shown in Equation 2 below.

과

사이에는 측정시간의 오차가 발생하며, 이로 인하여 거리 측정 오차가 발생한다.Therefore, as measured using a clock as shown in FIG.

and

An error in the measurement time occurs between, and thus a distance measurement error occurs.

이며, 최대 값은

가 된다.The distance measurement error is

, The maximum value is

.

Therefore, when the ultra-short pulse is applied to the conventional time-of-flight method, a measurement error occurs due to the detection bandwidth of the clock and the bandwidth of the photodetector as in the distance measurement using a conventional pulse laser.

In order to solve this problem, the papers proposed by Joohyung Lee, Young Jin Kim, Keunwoo Lee, Sanghyun Lee, and Seung Woo Kim "Time-of flight measurement with femtosecond light pulses (Nature photonics, 2010.10, vol. 4, pp. 716-720) discloses a distance resolution of several nm using a light source having a narrow pulse width of 150 fs for distance measurement.

However, according to the above method, there is a point that cannot be measured in the range of 200m or less, and in order to solve this problem, it is necessary to add a repetition rate multiplication method of the light source. There are problems such as the need for an additional process.

The problem to be solved by the present invention is to provide a system that can reduce the measurement error by measuring the absolute distance of the measurement object by using the time difference of arrival of each wavelength of the chirped ultrashort pulse.

The problem to be solved by the present invention is to provide a system that can obtain information on the physical properties of the measurement target by obtaining the absorption spectrum of the measurement target using the light intensity distribution for each wavelength obtained through the detector.

In order to solve the above problems, the present invention provides a transmitter for separating and transmitting two ultra-short pulses output from a laser, and the two ultra-short pulses are reflected on a measurement object and a reference object having a fixed position. A receiver for receiving a measurement pulse and a reference pulse, a dispersion unit for dispersing the received measurement pulse and the reference pulse to generate and output a chirped measurement pulse and a chirped reference pulse, and the chirped measurement pulse and the chirped reference A spectroscope which generates and outputs a spectroscopic measurement pulse and a spectroscopic reference pulse by separating the pulses by wavelength, and converts the incident spectroscopic measurement pulse and the spectroscopic reference pulse according to the wavelength into electrical signals in sequence, and then clocks and wavelengths of each pulse. A detection unit for acquiring the time of arrival for each star and the distribution of light intensity for each wavelength, and the measurement pulse and the unit based on the number of clocks and the time of arrival for each wavelength. And a control unit for acquiring a measurement time difference for each wavelength of a pulse to determine an absolute distance of the measurement target, and acquiring an absorption spectrum of the measurement target through the light intensity distribution for each wavelength to determine physical property information of the measurement target. A rider system using the spectroscopic time method is proposed as an example.

The dispersing unit generates a difference in the group velocity of each wavelength component with respect to the reference pulse and the measurement pulse composed of the ultrashort pulses and spreads a pulse so that the pulse for each wavelength passes a specific point at different times. You can chirp.

The spectroscope may separate the chirped reference pulse and the chirped measurement pulse by wavelength using a prism, a diffraction grating, a mirror, an optical fiber, and the like.

In order to solve the above problems, the present invention comprises the steps of separating and transmitting two ultra-short pulses output from the laser through the transmitter, and the two ultra-short pulses are separated from the measuring unit and the position is respectively fixed Receiving a measurement pulse and a reference pulse reflected back to a reference object, dispersing the received measurement pulse and the reference pulse through a dispersion unit to generate and output a chirped measurement pulse and a chirped reference pulse, and spectroscopy Generating a spectroscopic measurement pulse and a spectroscopic reference pulse by separating the chirped measurement pulses and the chirped reference pulses for each wavelength through a signal, and outputting the spectroscopic measurement pulses and the spectroscopic reference pulses incident to the wavelengths through a detector; Converting into a signal and acquiring the clock number of each pulse, the arrival time value for each wavelength, and the light intensity distribution for each wavelength; Using the clock number and the arrival time value for each wavelength, the measurement time difference between the measurement pulse and the reference pulse is acquired for each wavelength, and the absolute distance of the measurement target is determined. According to another embodiment, a rider signal processing method using a spectroscopic flight time method including a control unit for acquiring an absorption spectrum of the measurement target and grasping the physical property information of the measurement target is provided.

According to the present invention, the measurement error can be reduced by measuring the absolute distance of the measurement target by using the time difference of arrival of the chirped ultrashort pulses for each wavelength, and the detection resolution that was limited due to the detection limit of the conventional photodetector or the bandwidth of the clock. Can improve. In addition, the property information of the measurement target may be obtained through the light intensity distribution for each wavelength obtained by the light detector.

1 illustrates an absolute distance measuring principle using a conventional pulse laser.
Figure 2 schematically shows a distance measuring method using the spectroscopic flight time method according to an embodiment of the present invention.
Figure 3 shows the configuration of a rider system using the spectroscopic flight time method according to an embodiment of the present invention.
4 illustrates an electrical signal conversion of a pulse signal for each wavelength according to an embodiment of the present invention.
5 illustrates a time measurement method for each wavelength of a reference pulse according to an exemplary embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, parts irrelevant to the description are omitted to clearly describe the present invention, and the same reference numerals are used for the same parts throughout the specification.

Whenever a component is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements, not the exclusion of any other element, unless the context clearly dictates otherwise. In addition, the terms “… unit”, “module”, etc. described in the specification mean a unit that processes at least one function or operation, which may be implemented by hardware, software, or a combination of software.

Throughout the specification, "extreme pulse" means a very short pulse having a time width of femtosecond region, "reference object" means a target having a fixed position and knowing an absolute distance, and "measurement object" By a rider system of the present invention means a target (target) to obtain absolute distance or property information.

Figure 2 schematically shows a distance measuring method using the spectroscopic flight time method according to an embodiment of the present invention.

The pulse output from the ultra-short pulse laser is divided into two pulses, and one pulse is reflected on the fixed reference plane and then returned to the reference signal, and the other pulse is reflected on the measurement object and then measured pulse ( Return to Measurement signal.

The reference pulse and the measurement pulse maintain a short pulse width with respect to the time axis. When the reference pulse and the measurement pulse are passed through a medium having a large dispersion value, group velocity dispersion occurs and each wavelength component included in the pulse reaches one point. The time it takes to change.

Therefore, in the time axis, the chirp phenomenon occurs in the reference pulse and the measurement pulse.

The chirped reference pulses and the chirped measurement pulses pass through the optical spectrometer and then enter the multi-channel photodetector, and the pulse components for each wavelength incident from each channel of the photodetector are converted into electrical signals to measure the distance of the measurement target. do.

Hereinafter, a method of obtaining absolute distance and physical property information of a measurement target through a rider system using a spectroscopic flight time method according to an embodiment of the present invention will be described in detail.

Figure 3 shows the configuration of a rider system using the spectroscopic flight time method according to an embodiment of the present invention.

The rider system 30 of FIG. 3 may obtain absolute distance and physical property information of a measurement target using an ultrashort pulse, and may include a transmitter 31, a receiver 32, a dispersion unit 33, and a spectrometer 34. And a detector 35 and a controller 36.

The transmitter 31 includes a pulse laser for irradiating a beam in the visible or infrared region, and separates the ultra-short pulses output from the pulse laser into two and irradiates the measurement target 10 and the reference target 20, respectively. .

In addition, the transmission unit 31 may be connected to the control unit 36 to control the frequency or wavelength of the beam irradiated through the control unit 36 (not shown in FIG. 1).

The receiver 32 receives the measurement pulse and the reference pulse that are reflected by the two ultra-short pulses irradiated by the transmitter 31 to the measurement object 10 and the reference object 20, respectively.

The dispersion unit 33 distributes the measurement pulse and the reference pulse received by the receiver 32 to generate the chirped measurement pulses and the chirped reference pulses, and output them to the spectroscope 34.

At this time, the pulses for each wavelength pass through different points by spreading the pulse by generating a difference in the group velocity of each wavelength component with respect to the measurement pulse and the reference pulse composed of the ultra-short pulses.

As a result, the measurement pulse and the reference pulse have different wavelengths without changing the frequency of each wavelength, thereby causing a difference in speed for each wavelength.

일 경우, 클럭의 반 주기 즉,

가 되도록 매질의 길이를 결정해주는 것이 바람직하다.At this time, since the length of the measurement pulse and the reference pulse increases with the distance of the medium, the degree of dispersion of the measurement pulse and the reference pulse has a clock cycle.

, The half period of the clock,

It is desirable to determine the length of the medium so that

The spectrometer 34 separates the chirped measurement pulses and the chirped reference pulses by wavelength, generates spectroscopic measurement pulses and spectroscopic reference pulses, and outputs them to the detection unit 35.

In this case, the spectrometer 34 may be implemented as one of a prism, a diffraction grating, a mirror, and an optical fiber.

The detector 35 converts the spectroscopic measurement pulse and the spectral reference pulse incident on the wavelength by the spectroscope 34 into an electrical signal, and include a pn junction photodiode, a pin photodiode, a metal semiconductor metal diode, and a quantum well type multilevel diode. It may be implemented in a laser diode, a light emitting diode and a combination thereof.

4 illustrates an electrical signal conversion of a pulse signal for each wavelength according to an embodiment of the present invention.

As shown in FIG. 4, an electrical signal obtained for each wavelength is generated at predetermined time intervals according to the degree of chirping.

At this time, by measuring the time difference according to the wavelength can be improved the detection resolution that was limited by the detection limit of the conventional photodetector and the bandwidth of the clock.

In addition, the clock number of each pulse, the arrival time value for each wavelength, and the light intensity distribution for each wavelength are obtained through the electric signal.

5 illustrates a time measurement method for each wavelength of a reference pulse according to an exemplary embodiment of the present invention.

Referring to FIG. 5, the arrival time value of the wavelength and the number of clocks may be obtained from the rising edge value of the clock for each wavelength with respect to the reference pulse converted into the electrical signal through the detector 35.

In addition, the arrival time value and the number of clocks for each wavelength can also be obtained in a method similar to that of FIG. 5.

The controller 36 calculates the absolute distance and the physical property information of the measurement target 10 by using the number of clocks obtained by the detector 35, the arrival time value for each wavelength, and the light intensity distribution for each wavelength.

The controller 36 calculates the time difference of arrival of the measurement pulse and the reference pulse for each wavelength based on the number of clocks acquired by the detector 35 and the arrival time value for each wavelength, and obtains the absolute distance of the measurement target 10 by using the same.

At this time, the error of the measurement distance according to the arrival time measurement method for each wavelength of FIG. 5 is shown in Equation 3 below, and it can be seen that the measurement distance error is reduced by 2N times as compared to the conventional flight time method.

는 클럭의 주기이며,

는 펄스의 분산 정도이고, N은 검출부의 채널 개수이다.At this time,

Is the period of the clock,

Is the degree of dispersion of the pulse and N is the number of channels in the detector.

In addition, the control unit 36 calculates an absorption spectrum of the measurement target 10 through the light intensity distribution for each wavelength obtained by the detection unit 35 and uses information of the color or material of the measurement target 10 using the absorption spectrum. Obtain property information.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention as defined in the following claims are also the rights of the present invention. It belongs to the range.

10: measurement object 20: reference object
30: rider system 31: transmitter
32: receiving unit 33: distribution unit
34: spectrometer 35: detector
36: control unit

Claims (4)

A transmitter for separating and transmitting two ultra-short pulses output from a laser;
A receiver for receiving the measurement pulse and the reference pulse in which the two ultra-short pulses are reflected back to the measurement object and the reference object having a fixed position;
A dispersion unit configured to disperse the received measurement pulse and the reference pulse to generate and output a chirped measurement pulse and a chirped reference pulse;
A spectrometer configured to generate the spectroscopic measurement pulse and the spectroscopic reference pulse by separating the chirped measurement pulse and the chirped reference pulse for each wavelength;
A detector for converting the spectroscopic measurement pulses and the spectral reference pulses incident to the wavelengths into electrical signals sequentially, and obtaining a clock number of each pulse, a time value of arrival for each wavelength, and a light intensity distribution for each wavelength; And
The absolute distance of the measurement object is determined by obtaining the measurement time difference of the measurement pulse and the reference pulse by the wavelength using the clock number and the arrival time value by wavelength, and the absorption spectrum of the measurement object is determined through the light intensity distribution for each wavelength. A control unit which acquires and grasps physical property information of the measurement target;
Rider system using a spectroscopic flight time method comprising a. The method of claim 1, wherein the dispersion unit,
By diffusing a pulse by generating a difference in the group velocity of each wavelength component with respect to the reference pulse and the measurement pulse composed of ultra-short pulses, the pulse for each wavelength passes through a specific point at different times. Rider system using spectroscopic flight time method. The method of claim 1, wherein the spectroscopic portion,
And a spectral time-of-flight method for separating the chirped reference pulses and the chirped measurement pulses by wavelength using a prism, a diffraction grating, a mirror, and an optical fiber. Separating and transmitting two ultra-short pulses output from the laser through a transmitter;
Receiving a measurement pulse and a reference pulse, in which the two ultra-short pulses are reflected back to the measurement object and the reference object having a fixed position, respectively through a receiver;
Dispersing the received measurement pulse and the reference pulse through a dispersion unit to generate and output a chirped measurement pulse and a chirped reference pulse;
Generating a spectroscopic measurement pulse and a spectroscopic reference pulse by separating the chirped measurement pulse and the chirped reference pulse by wavelength through a spectroscope;
Converting the spectroscopic measurement pulse and the spectral reference pulse incident to the wavelength through the detection unit into an electric signal, and obtaining a clock number of each pulse, a time value of arrival for each wavelength, and a light intensity distribution for each wavelength;
Obtaining a measurement time difference for each wavelength of the measurement pulse and the reference pulse using the clock number and the arrival time value for each wavelength through a control unit, and determining an absolute distance of the measurement object; And
A control unit which acquires an absorption spectrum of the measurement target and obtains physical property information of the measurement target by using the light intensity distribution for each wavelength through a control unit;
Rider signal processing method using a spectroscopic flight time method comprising a.

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