JP6793033B2 - Distance measuring device - Google Patents

Description

The present invention relates to a ranging device.

Currently, after projecting measurement light such as laser light toward an object, the return light from the object is detected, and the time from the projection to the object to the detection of the return light is used to reach the object. Development of a TOF (Time of Flight) type distance measuring device for measuring a distance is underway. As a conventional distance measuring device, for example, there is a propagation measurement time device described in Patent Document 1. In this conventional ranging device, pulsed light having a wide wavelength band is separated for each wavelength as measurement light and irradiated to an object. In this case, it is possible to configure the device so that the return position of the return light from the object is different depending on the wavelength. Therefore, by detecting the return light at each position with a photodetector and calculating the time from the emission time of the measurement light to the detection time of the return light for each pixel of the photodetector, the distance to the object can be reduced to two. It can be measured dimensionally.

Japanese Patent No. 5230858

Since the conventional ranging device described above does not have a driving unit that drives at high speed like a scanning mirror, it has an advantage that it is not easily affected by vibration or the like. However, in the conventional ranging device described above, since the measurement light from the light source is separated for each wavelength, the return light for each wavelength from the object becomes weak, and the accuracy and sensitivity of the measurement cannot be sufficiently obtained. There is a risk. In this case, if the intensity of the measurement light is simply increased, there may be a problem that the optical elements constituting the optical system are damaged by the measurement light.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a distance measuring device capable of performing high-speed, high-precision and high-sensitivity measurement without requiring a high-speed driving unit.

The ranging device according to one aspect of the present invention is a ranging device that measures the distance to an object, and is a wavelength sweep light source that generates light whose wavelength changes with time as measurement light, and measurement toward the object. It includes a measurement light displacement element that shifts the optical axis of light according to a wavelength, and an optical detector that detects return light from an object at a different position for each wavelength.

This distance measuring device includes a wavelength sweep light source that generates light whose wavelength changes with time as measurement light. The optical axis of the measurement light generated by the wavelength sweep light source is displaced according to the wavelength by the measurement light displacement element. Since the measurement light from the wavelength sweep light source is monochromatic light at each moment, the light of the measurement light is measured by the measurement light displacement element, unlike the conventional case where the measurement light from the pulse light source is dispersed for each wavelength. There is no decrease in the amount of light when the shaft is displaced. Therefore, it is possible to detect the return light for each wavelength from the object with a sufficient amount of light. Therefore, this distance measuring device does not require a high-speed drive unit, can sufficiently secure the measurement sensitivity, and can sufficiently secure the measurement accuracy according to the amount of light. Further, in this distance measuring device, since the detection position of the return light can be associated with the wavelength, the next measurement light having a different wavelength between the generation of the measurement light and the detection of the return light can be obtained. Can be generated. Therefore, the measurement speed can be increased.

Further, the wavelength sweep light source may be configured to include an electro-optical element arranged in the resonator and a voltage sweep power source that applies a voltage that changes with time to the electro-optical element. In this case, it becomes possible to electrically perform wavelength sweeping of the measurement light. Therefore, it is possible to avoid increasing the number of mechanical drive units in the configuration of the distance measuring device.

Further, the distance measuring device may further include an optical fiber that outputs the measurement light generated by the wavelength sweep light source toward the object. In this case, the degree of freedom in arranging the wavelength sweep light source can be improved.

Further, the ranging device may further include a return light displacement element that displaces the optical axis of the return light toward the photodetector according to the wavelength. In this case, the photodetector can more reliably detect the return light at different positions for each wavelength.

In addition, the ranging device may further include an optical fiber that guides the return light toward the photodetector. In this case, the return light can be guided, and the measurement sensitivity and the measurement accuracy can be more sufficiently ensured. In addition, the degree of freedom in arranging the photodetector can be improved.

Further, the distance measuring device may further include an optical amplifier that amplifies the intensity of the return light. In this case, by amplifying the intensity of the return light, the measurement sensitivity and the measurement accuracy can be more sufficiently ensured.

Further, the distance measuring device may further include an optical scanning unit that scans the optical axis of the measurement light in a direction orthogonal to the displacement direction by the measurement light displacement element. In this case, the range in which the measurement light is irradiated on the object can be expanded. The scanning of the measurement light by the optical scanning unit may be performed based on the wavelength sweep cycle by the wavelength sweep light source, and high-speed driving is not required.

According to the present invention, high-speed, high-precision and high-sensitivity measurement can be performed without the need for a high-speed drive unit.

It is the schematic which shows the structure of the distance measuring apparatus which concerns on 1st Embodiment. It is a figure which shows the state of the measurement light output from the wavelength sweep light source. It is the schematic which shows an example of the structure of the wavelength sweep light source. It is the schematic which shows the structure of the distance measuring apparatus which concerns on 2nd Embodiment. It is the schematic which shows the structure of the distance measuring apparatus which concerns on 3rd Embodiment.

Hereinafter, a preferred embodiment of the distance measuring device according to one aspect of the present invention will be described in detail with reference to the drawings.
[First Embodiment]

FIG. 1 is a schematic view showing a configuration of a distance measuring device according to the first embodiment. The distance measuring device 1 shown in FIG. 1 is a TOF (Time of Flight) type distance measuring device. After irradiating the measurement light L1 which is a laser beam toward the object S, the distance measuring device 1 detects the return light L2 from the object S, and the time from the emission of the measurement light L1 to the detection of the return light L2. The distance to the object S is measured based on. The object S is an obstacle such as another vehicle, a wall, or a pedestrian if it is used for in-vehicle use, and is a structure such as a road, a bridge, or a building if it is used for surveying.

As shown in FIG. 1, the distance measuring device 1 includes a wavelength sweep light source 2 that generates the measurement light L1, a measurement light light guide unit 3 that guides the measurement light L1, and a measurement light that displaces the optical axis of the measurement light L1. The displacement element 4, the return light light guide unit 5 that guides the return light L2 from the object S, the return light displacement element 6 that displaces the optical axis of the return light L2, and the light detector 7 that detects the return light L2. And the analysis unit 8.

The wavelength sweep light source 2 is a light source that generates light whose wavelength changes with time as measurement light L1. The wavelength of the measurement light L1 generated by the wavelength sweep light source 2 changes in a sinusoidal manner at a constant period with time, for example, as shown in FIG. 2A. Therefore, paying attention to each wavelength component of the measurement light L1, short-time light emission occurs periodically. Further, the intensity of the measurement light L1 generated by the wavelength sweep light source 2 may fluctuate slightly periodically due to some wavelength dependence, as shown in FIG. 2B, for example, but is the same as the CW light. , Almost constant over time. Therefore, the average intensity of the measurement light L1 can be increased to a level limited mainly by thermal and electrical factors.

The wavelength band of the measurement light L1 is, for example, 1.0 μm to 1.1 μm or 1.27 μm to 1.37 μm. The wavelength band of 1.0 μm to 1.1 μm is suitable because it is not easily affected by humidity. Further, the infrared wavelength is suitable from the viewpoint of eye safety. For example, in the 1.3 μm band, about 10 times the light intensity is allowed as compared with the light in the 1 μm band. Also, the scattering probability due to Rayleigh scattering is inversely proportional to the fourth power of the wavelength. Therefore, the longer the wavelength of the measurement light L1, the more suitable for distance measurement in an environment where there is a lot of dust and the like. For example, in the 1.3 μm band, absorption into water is relatively small, and the scattering probability can be reduced to about 35% as compared with light in the 1 μm band. When sunlight affects as ambient light, it is preferable to use the measurement light L1 having a wavelength near 940 μm.

The wavelength sweep cycle of the measurement light L1 is from several tens of kHz to several hundreds of kHz. For example, assuming that the wavelength sweep period of the measurement light L1 is 200 kHz, the time interval between the generation of light having a certain wavelength and the generation of light having the same wavelength again is 5 μs. Since the measurement light L1 travels about 1.5 km during this period, the operating distance of the distance measuring device 1 (distance to the object S) is estimated to be about 750 m at the maximum, considering the round trip of the light. Further, when the wavelength sweep width of the measurement light L1 is 100 nm and the instantaneous wavelength purity (full width at half maximum) is 0.1 nm, 1000 points can be measured in 5 μs.

FIG. 3 is a diagram showing an example of the configuration of the wavelength sweep light source 2. As shown in the figure, in the present embodiment, the wavelength sweep light source 2 is composed of a semiconductor laser (ECLD: External Cavity Laser Diode) 11 provided with an external resonator. The semiconductor laser 11 includes, for example, a semiconductor optical amplifier 12 including an output coupler 13 and a mirror 15 forming a resonator 14 between the output coupler 13. Further, an electro-optical element 16, a λ / 2 wave plate 17, a transmission type diffraction grating 18, and a collimator lens 19 are arranged in the resonator 14. A voltage sweep power supply 20 that applies a voltage that changes with time to the electro-optical element 16 is electrically connected to the electro-optical element 16.

The electro-optical element 16 is, for example, a KTN (potassium niobate tantalate) crystal. The KTN crystal is a kind of nonlinear optical crystal, and changes the angle of the optical axis of the emitted light with respect to the optical axis of the incident light by the electro-optical effect according to the value of the voltage applied from the voltage sweep power supply 20. As a result, in the wavelength sweep light source 2, the resonance wavelength can be changed regardless of the mechanical drive unit, and light whose wavelength changes with time can be generated as the measurement light L1. Since the electro-optical element 16 acts like a convex lens with respect to passing light, it is preferable to arrange the concave lens 21 that cancels the action so as to sandwich the electro-optical element 16.

The measurement optical light guide unit 3 is an optical system that guides the measurement light L1 toward the object S, and is composed of an optical fiber 22 and a collimator lens 23. The optical fiber 22 is, for example, a polarization-holding fiber, and is connected to the output end of the wavelength sweep light source 2. The measurement light L1 propagating through the optical fiber 22 is emitted from the optical connector 24 and is collimated by the collimator lens 23. The parallel lighted measurement light L1 is guided toward the measurement light displacement element 4.

The measurement light displacement element 4 is an element that displaces the optical axis of the measurement light L1 toward the object S according to the wavelength. The optical axis of the measurement light L1 is displaced by the measurement light displacement element 4 according to the wavelength, so that the irradiation position of the measurement light L1 on the object S can be associated with the wavelength. Examples of the measurement optical displacement element 4 include a prism and a diffraction grating. When a prism is used, the angle range in which the optical axis of the measurement light L1 is displaced is narrower than that of the diffraction grating, but the loss of the measurement light L1 can be suppressed. When a diffraction grating is used, the angle range in which the optical axis of the measurement light L1 is displaced can be widened.

Further, an Echelle grating may be used as the measurement optical displacement element 4, and a two-dimensional displacement optical system using the Echelle diffraction photon may be configured. In this case, for example, the measurement light L1 that has passed through the slit is folded back by a concave mirror and incident on the Echelle diffraction grating. Then, the optical axis of the measurement light L1 is displaced in the uniaxial direction according to the wavelength by the Echelle diffracted photon, and the optical axis of the measured light L1 is displaced in the other uniaxial direction by the prism or the diffraction grating arranged after the Echelle diffracted photon. Let me. As a result, the optical axis of the measurement light L1 toward the object S can be two-dimensionally displaced according to the wavelength.

The return light light guide unit 5 is composed of, for example, a mirror 31, an optical fiber 32, and an optical amplifier 33. In the present embodiment, the return light L2 is focused so as to be substantially coaxial with the optical axis of the measurement light L1 toward the measurement light displacement element 4. However, since the return light L2 is composed of the reflected light or the scattered light from the object S, the beam diameter of the focused light is large. Therefore, while the mirror 31 is arranged so as not to obstruct the passage of the measurement light L1, it is necessary to reflect many components of the return light L2 from the object S at a right angle. As a configuration of such a mirror 31, for example, as shown in FIG. 1, when a perforated mirror having a hole in the passing region of the measurement light L1 is used with respect to a mirror having a diameter corresponding to the beam diameter of the return light L2. , It is possible to improve the light utilization efficiency of the device. The mirror 31 is not limited to the perforated mirror, and even if the mirror 31 is arranged by shifting the normal mirror with respect to the center of the optical axis of the measurement light L1 so that at least a part of the measurement light L1 passes by. Good. Further, the optical fiber 32 is, for example, a multimode fiber. The return light L2 reflected by the mirror 31 enters the optical fiber 32 from the optical connector 34 and is guided to the optical amplifier 33.

The optical amplifier 33 is a portion that amplifies the intensity of the return light L2. Since the return light L2 is composed of the reflected light or the scattered light of the measurement light L1 generated from the wavelength sweep light source 2, it has the same wavelength band as the measurement light L1. Therefore, it is preferable that the optical amplification band of the optical amplifier 33 covers the entire light generation band of the wavelength sweep light source 2. Therefore, for example, when the wavelength sweep light source 2 has a configuration as shown in FIG. 3, it is preferable to use an optical amplifier 33 having the same function as the semiconductor optical amplifier 12 inside.

If the wavelength band of the measurement light L1 generated from the wavelength sweep light source 2 can be covered even with other configurations, the optical amplifier 33 can be a glass to which a rare earth element such as Nd is added, or a rare earth element such as Nd. A solid-state amplifier having YAG to which an element is added as a gain medium can be used. The optical amplifier 33 may be configured to include a multi-stage solid-state amplifier, or may be a combination of a one-stage solid-state amplifier and a loop optical system for multiple amplification. Further, the optical amplifier 33 may be, for example, an optical fiber amplifier in which a rare earth element such as Yb (ytterbium) is added as a gain medium to at least a part of the core of the optical fiber. The return light L2 amplified by the optical amplifier 33 is incident on the return light displacement element 6.

The use of such an optical amplifier 33 is particularly effective when the measurement light L1 having a wavelength of 1.1 μm or more is used. This is because it is difficult for a compound semiconductor photodetector such as an InGaAs-based photodetector used for detecting light in this wavelength band to significantly amplify a signal in the detector as compared with the case where a silicon-based photodetector is used. .. Further, in this wavelength band, the sensitivity of a vacuum type photodetector such as a photomultiplier tube is not sufficient.

The return light displacement element 6 is an element that displaces the optical axis of the return light L2 toward the photodetector 7 according to the wavelength. The return light displacement element 6 displaces the optical axis of the return light L2 according to the wavelength, so that the incident position of the return light L2 on the detection surface of the photodetector 7 can be associated with the wavelength. Examples of the return light displacement element 6 include a prism and a diffraction grating. When a prism is used, the angle range in which the optical axis of the return light L2 is displaced is narrower than that of the diffraction grating, but the loss of the return light L2 can be suppressed. When a diffraction grating is used, the angle range in which the optical axis of the return light L2 is displaced can be widened.

The photodetector 7 is a portion that detects the return light L2 from the object S at a different position for each wavelength. As the photodetector 7, for example, an MPPC (Multi-Pixel Photon Counter), an avalanche photodiode array, or the like can be used. The MPPC is a silicon-based photodetector, and is used when the wavelength of the measurement light L1 is less than 1.1 μm. The MPPC is a semiconductor linear sensor having an amplification means, and is effective when the distance to the object S is long and the amount of return light is weak. When MPPC is used, the arrangement of the optical amplifier 33 may be omitted. Further, the avalanche photodiode array is used when the wavelength of the measurement light L1 is 1.1 μm or more. The photodetector 7 generates detection result information in which the intensity of the return light L2 on the detection surface is associated with the incident position and outputs the detection result information to the analysis unit 8.

The analysis unit 8 is a part that analyzes the distance to the object S based on the detection result information output from the photodetector 7. The analysis unit 8 analyzes the distance to the object S based on the TOF (Time of Flight) method. That is, in the analysis unit 8, the distance to the object S is based on the difference (delay time) between the time when the measurement light L1 is generated by the wavelength sweep light source 2 and the time when the return light L2 is detected by the photodetector 7. To analyze. The intensity-time waveform of each wavelength component of the return light L2 has a certain correlation with the intensity-time waveform of each wavelength component of the measurement light L1 generated by the wavelength sweep light source 2. Therefore, in the analysis unit 8, the delay time analysis can be performed more accurately by fitting the intensity time waveform of each wavelength component of the return light L2 to the intensity time waveform of each wavelength component of the measurement light L1. it can.

The analysis unit 8 is physically a computer configured to include a memory such as a RAM and a ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, a storage unit such as a hard disk, and a display unit such as a display. .. Examples of such computers include personal computers, cloud servers, smart devices (smartphones, tablet terminals, etc.) and the like. The computer executes a function of analyzing the distance to the object S by executing the program stored in the memory on the CPU.

As described above, the distance measuring device 1 includes a wavelength sweeping light source 2 that generates light whose wavelength changes with time as measurement light L1. The optical axis of the measurement light L1 generated by the wavelength sweep light source 2 is displaced by the measurement light displacement element 4 according to the wavelength. In this ranging device 1, since the measurement light from the wavelength sweep light source 2 is monochromatic light at each moment, the measurement light displacement is different from the conventional case where the measurement light from the pulse light source is dispersed for each wavelength. When the optical axis of the measurement light L1 is displaced by the element 4, the amount of light does not decrease. Therefore, it is possible to detect the return light L2 for each wavelength from the object S with a sufficient amount of light. Therefore, the distance measuring device 1 does not require a high-speed drive unit, can sufficiently secure the measurement sensitivity, and can sufficiently secure the measurement accuracy according to the amount of light. Further, in the distance measuring device 1, since the detection position of the return light L2 can be associated with the wavelength, the following having different wavelengths between the generation of the measurement light L1 and the detection of the return light L2. The measurement light L1 can be generated. Therefore, the measurement speed can be increased.

Further, in the present embodiment, the wavelength sweep light source 2 is configured to include an electro-optical element 16 arranged in the resonator 14 and a voltage sweep power source 20 that applies a voltage that changes with time to the electro-optical element 16. There is. With such a configuration, the wavelength sweep of the measurement light L1 can be electro-optically executed in the wavelength sweep light source 2. Therefore, it is possible to avoid increasing the number of mechanical drive units in the configuration of the distance measuring device 1.

Further, in the present embodiment, the distance measuring device 1 includes an optical fiber 22 that outputs the measurement light L1 generated by the wavelength sweep light source 2 toward the object S. This makes it possible to improve the degree of freedom in arranging the wavelength sweep light source 2.

Further, in the present embodiment, the distance measuring device 1 includes a return light displacement element 6 that displaces the optical axis of the return light L2 toward the photodetector 7 according to the wavelength. As a result, the photodetector 7 can more reliably detect the return light L2 at different positions for each wavelength.

Further, in the present embodiment, the distance measuring device 1 includes an optical fiber 32 that guides the return light L2 toward the photodetector 7. As a result, the return light L2 can be efficiently guided, and the measurement sensitivity and the measurement accuracy can be more sufficiently secured. In addition, the degree of freedom in arranging the photodetector 7 can be improved.

Further, in the present embodiment, the distance measuring device 1 includes an optical amplifier 33 that amplifies the intensity of the return light L2. In this case, by amplifying the intensity of the return light L2, the measurement sensitivity and the measurement accuracy can be more sufficiently secured. This configuration is particularly useful when a photodetector 7 without an amplification means inside is used.
[Second Embodiment]

FIG. 4 is a schematic view showing the configuration of the distance measuring device according to the second embodiment. As shown in the figure, the distance measuring device 41 according to the second embodiment is different from the first embodiment in that the optical scanning unit 42 is provided on the front stage side of the measurement optical displacement element 4.

The optical scanning unit 42 is a portion that scans the optical axis of the measurement light L1 at least in a direction orthogonal to the displacement direction (referred to as the X-axis direction here) by the measurement optical displacement element 4. The optical scanning unit 42 is composed of, for example, a MEMS mirror, a polygon mirror, or the like, and scans the measurement light L1 on one or two axes. When the optical scanning unit 42 is a uniaxial scanning unit, the optical scanning unit 42 is arranged so that the measurement light L1 is periodically scanned in the Y-axis direction. As a result, the measurement light L1 whose optical axis is displaced in the X direction by the measurement light displacement element 4 is scanned in the Y-axis direction by the optical scanning unit 42, and has a constant solid angle with respect to the object S. It is possible to measure the distance of the range at once.

When the optical scanning unit 42 is a biaxial scanning unit, the optical scanning unit 42 is arranged so that the measurement light L1 is periodically scanned in the X-axis direction and the Y-axis direction. That is, one scanning axis of the optical scanning unit 42 is in the same direction as the displacement direction of the optical axis of the light L1 measured by the measuring optical displacement element 4, and one scanning axis of the optical scanning unit 42 is displaced by the measuring optical displacement element 4. The direction is orthogonal to the displacement direction of the optical axis of the measurement light L1. One scan in the X-axis direction is set to be about the same as the displacement range of the optical axis of the measurement light L1 by the measurement light displacement element 4, for example, and the optical scanning unit 42 scans in the X-axis direction and the Y-axis direction. Scan to and perform discretely. In this case, for example, several cycles of the wavelength sweep of the measurement light L1 measured by the wavelength sweep light source 2 are synchronized with one cycle of scanning in the Y-axis direction, and several cycles of scanning in the Y-axis direction are set in the X-axis direction. It may be synchronized with one cycle of scanning. This makes it possible to perform distance measurement in a range having a wider solid angle.
[Modification example]

The present invention is not limited to the above embodiment. For example, in the above embodiment, the wavelength sweep light source 2 by the electro-optical means using the electro-optical element 16 is illustrated, but for example, the wavelength sweep light source in which the resonator length of the Fabry-Perot resonator is changed by mechanical means. May be used. Further, in the above embodiment, the return optical light guide unit 5 is configured by the mirror 31, the optical fiber 32, and the optical amplifier 33. Instead of such a configuration, for example, the ranging device 51 shown in FIG. As described above, a large-diameter lens 52 may be arranged on the front stage side of the return light displacement element 6, and the return light L2 focused by the lens 52 may be incident on the return light displacement element 6. In the configuration of the distance measuring device 51, since the return light L2 is focused at different positions for each wavelength by the large-diameter lens 52, the return light displacement element 6 can be omitted. As described above, in the distance measuring device 51 shown in FIG. 5, the device configuration can be further simplified.

1,41,51 ... ranging device, 2 ... wavelength sweep light source, 4 ... measurement light displacement element, 6 ... return light displacement element, 7 ... light detector, 14 ... resonator, 16 ... electro-optical element, 20 ... voltage Sweep power supply, 22 ... optical fiber, 32 ... optical fiber, 33 ... optical amplifier, 42 ... optical scanning unit, L1 ... measurement light, L2 ... return light, S ... object.

Claims (7)

A distance measuring device that measures the distance to an object.
A wavelength sweep light source that generates continuously oscillating light whose wavelength changes with time as measurement light,
A measurement light displacement element that displaces the optical axis of the measurement light toward the object according to the wavelength.
A photodetector that detects the return light from the object at a different position for each wavelength is provided .
The wavelength sweep light source is a distance measuring device including means for changing the resonance wavelength of the resonator . Said means, said electro-optical element disposed in the resonator, the distance measuring apparatus according to claim 1, wherein is configured to include a voltage sweep power supply for applying a voltage varying with time to the electro-optical element. The distance measuring device according to claim 1 or 2, further comprising an optical fiber that outputs the measurement light generated by the wavelength sweep light source toward the object. The distance measuring device according to any one of claims 1 to 3, further comprising a return light displacement element that displaces the optical axis of the return light toward the photodetector according to a wavelength. The distance measuring device according to any one of claims 1 to 4, further comprising an optical fiber that guides the return light toward the photodetector. The distance measuring device according to any one of claims 1 to 5, further comprising an optical amplifier for amplifying the intensity of the return light. The distance measuring device according to any one of claims 1 to 6, further comprising an optical scanning unit that scans the optical axis of the measurement light in a direction orthogonal to the displacement direction of the measurement light displacement element.

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