JP2019027783A - Photodetector - Google Patents

Abstract

To improve the signal to noise ratio (S/N ratio) and improve the distance measuring performance in the range finding device.SOLUTION: A range finding device 100 including a light source 10 and performing measurement using light emitted from the light source 10 includes; a light quantity measuring light receiving element 20 for measuring the light quantity of the light emitted from the light source 10 by separating and receiving a part of the light emitted from the light source 10; a light quantity comparator 22 which compares the measured light quantity output from the light quantity measuring light receiving element 20 with a reference light quantity, and outputs a control signal for changing the light emission characteristic of the light source 10 so as to make the difference between the compared quantities to be small; and a light source driving circuit 12 which drives the light source 10 and changes the light emission characteristic of the light source 10 based on the control signal from the light quantity comparator 22.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light detection device.

2. Description of the Related Art A distance measuring device that measures the distance to an object by irradiating pulsed light from a light source and receiving reflected light reflected by the object is known. In such a distance measuring device, the temperature detection unit measures the temperature of the semiconductor laser element (LD), estimates the current emission wavelength λ _LD based on the measured temperature, and band according to the estimated emission wavelength λ _LD. A configuration in which the central transmission wavelength λ _BPF is changed by tilting the pass filter (BPF) is disclosed (Patent Document 1). Thereby, even if the emission wavelength of the LD shifts with a temperature change, the transmission wavelength can be changed accordingly, and the light reflected by the object can be prevented from being attenuated by the BPF.

JP 2007-85832 A

  As described above, the emission wavelength changes as the temperature of the LD, which is the light source, changes. Therefore, a technique for stabilizing the emission wavelength is desired.

  Further, when using BPF, the light transmission wavelength band of BPF cannot be narrowed because the emission wavelength of the light source is not stable due to the above-mentioned temperature change. As a result, noise components such as external light that is transmitted (passed) through the BPF increase, and the signal noise ratio (S / N ratio) of the signal for object detection cannot be increased.

  Further, in order to control the angle of the BPF based on the temperature of the LD detected by the temperature detection unit, it is necessary to measure the relationship between wavelength fluctuations with respect to the LD temperature in advance and create a correspondence table or the like. Also, the wavelength dependence on the LD temperature varies from element to element and is not constant. Therefore, accurate temperature compensation cannot be performed unless a correspondence table is provided for each element. Furthermore, enormous costs are required to create a correspondence table for each element.

  Moreover, since the result obtained by the control cannot be confirmed, it is impossible to know whether or not the control result is appropriate.

  Furthermore, mechanically movable parts are necessary to tilt the BPF, and it is difficult to increase the reliability of the apparatus, which may increase the cost.

  One aspect of the present invention is a light detection device that includes a light source and performs measurement using light emitted from the light source, by separating and receiving a part of the light emitted from the light source. The light quantity measuring light receiving element for measuring the light quantity of light emitted from the light source is compared with the measured light quantity output from the light quantity measuring light receiving element and the reference light quantity, and the light source so that the difference is reduced A light amount comparator that outputs a control signal for changing the light emission characteristic of the light source, and a light source driving circuit that drives the light source and changes the light emission characteristic of the light source based on the control signal from the light amount comparator, It is provided with this.

  Here, the light source and the light receiving element for light quantity measurement are housed in the same casing, and include an internal reflector that reflects a part of light emitted from the light source inside the casing, and the light quantity measurement It is preferable that the light receiving element for light receives the reflected light reflected by the internal reflector.

  Moreover, it is preferable that the light emission characteristic of the light source is at least one of a light emission amount and a light emission wavelength.

  It is preferable that an optical bandpass filter that is disposed in front of the light receiving element for light quantity measurement and has a transmission wavelength that is a wavelength that can be emitted from the light source is preferable.

  Further, it is preferable that the light source driving circuit controls a voltage or a current for the light source based on the control signal from the light quantity comparator.

  Further, it is preferable that the light source driving circuit controls the temperature of the light source based on the control signal from the light quantity comparator.

  In addition, it is preferable that a light shielding member for shielding external light is provided in at least a part of an optical path between the light source and the light receiving element for light quantity measurement.

  A light amount measured by the light amount measuring light receiving element when light is not emitted from the light source, and a light amount measured by the light amount measuring light receiving element when light is emitted from the light source, It is preferable that the difference value is the measurement light quantity.

  According to the present invention, the emission wavelength of the light source can be stabilized. Further, it becomes possible to use a narrow band BPF in a distance measuring device or the like.

It is a figure which shows the structure of the distance measuring device of 1st Embodiment. It is a figure which shows the structure of the modification of the ranging device of 1st Embodiment. It is a figure which shows the structure of the distance measuring device of 2nd Embodiment. It is a figure which shows the example of a characteristic of a laser diode (LD). It is a figure explaining the control method of the distance measuring device of 3rd Embodiment. It is a figure which shows the structure of the distance measuring device of 4th Embodiment. It is a figure which shows the structure of the distance measuring device of 5th Embodiment.

[First Embodiment]
As shown in FIG. 1, the distance measuring device 100 according to the first embodiment includes a light source 10, a light source driving circuit 12, a distance measuring light receiving element 14, a distance calculating unit 16, an internal reflector 18, and a light amount measuring light reception. The device 20 is configured to include a light amount comparator 22 and a housing 24. In the present embodiment, the light source 10, the light source driving circuit 12, the ranging light receiving element 14, the ranging calculation unit 16, the internal reflector 18, the light quantity measuring light receiving element 20, and the light quantity comparator 22 are included in the same housing 24. It is stored in. The casing 24 is made of a material that shields outside light except for the window 24a.

The distance measuring device 100 outputs light having a predetermined wavelength λ _LD from the light source 10, and receives the reflected light reflected by the measurement object 200 by the light receiving element 14 for distance measurement, thereby the distance to the measurement object 200. Is used to measure

In the present embodiment, the distance measuring device 100 is described as an example, but the scope of application of the present invention is not limited to this. In other words, any photo detector that can compensate for the change in the emission wavelength λ _LD of the light source 10 due to temperature can be used.

The light source 10 emits light used for distance measurement in the distance measuring device 100. The light source 10 can be a laser diode (LD). As the light source 10, for example, an _LD whose center emission wavelength λ _LD is an infrared band (such as 870 nm) is generally used.

  The light source driving circuit 12 is an electric circuit for driving the light source 10 to emit light. The light source driving circuit 12 outputs light by supplying power to the light source 10. The light source driving circuit 12 includes temperature control means 12a for adjusting the temperature of the light source 10. The temperature control unit 12a can be configured to include a temperature adjustment unit and a distance measurement calculation unit. The temperature adjusting means is means for changing the temperature of the light source 10 such as a Peltier element, a fan, a heater, or the like. The light source drive circuit 12 receives a control signal output from a light amount comparator 22 described later, and adjusts the temperature of the light source 10 by controlling the temperature adjusting means according to the control signal.

In the present embodiment, pulsed light is output from the light source 10 under the control of the light source driving circuit 12. When pulsed light is emitted from the light source 10, the emission time t ₀ is input to the distance measurement calculation unit 16.

  The ranging light receiving element 14 includes a light receiving element. The distance measuring light receiving element 14 is configured, for example, by arranging a plurality of light receiving elements. For example, a configuration is shown in which a total of 16 light receiving elements of 4 vertical x 4 horizontal are arranged in an array. However, the arrangement of the light receiving elements in the distance measuring light receiving element 14 is not limited to this, and may be one-dimensionally or two-dimensionally arranged. Further, the ranging light receiving element 14 may be constituted by a single light receiving element.

  Each light receiving element can include a photodiode. For example, a single photon avalanche photodiode that can operate in Geiger mode may be used. This is called SPAD (Single-Photon Avalanche Diode). In this case, one light receiving element can be composed of a SPAD, a quenching resistor, and a pulse converter. SPAD is operated with a reverse bias voltage equal to or higher than a breakdown voltage, and causes an avalanche phenomenon even when a single photon is incident. Therefore, SPAD has high sensitivity to light such as laser light. In SPAD, it is preferable to make the area of the guard ring and the metal wiring as small as possible and increase the fill factor (aperture ratio), which is the ratio of the light receiving area to the element area. In particular, the fill factor can be increased by not forming quenching elements and recharge elements inside the SPAD arranged in a matrix. The quenching resistor is connected in series with SPAD. The quenching resistor can be composed of a transistor or a resistor. When an avalanche current is generated in SPAD, the bias voltage with respect to SPAD drops due to a voltage increase between the terminals of the quenching resistor, and when it becomes less than the breakdown voltage, the avalanche current stops. The quenching resistor is also used to generate a detection signal for the pulse converter. A pulse converter is provided for each pair of SPAD and quenching resistor. The pulse conversion unit compares the terminal voltage of the quenching resistor with a predetermined reference value, and generates a rectangular pulse according to the comparison result. The pulse conversion unit can be configured to include, for example, a comparator, an inverter, and the like. With such a configuration, when light enters each light receiving element of the distance measuring light receiving element 14, a pulse signal is output to the distance calculating unit 16.

When receiving a pulse signal from the light receiving element 14 for distance measurement, the distance measuring unit 16 receives a difference Δt (= t _{d )} between the reception time t _d when the pulse signal is received and the emission time t ₀ of the pulsed light from the light source 10. and it calculates the distance to the measurement object 200 based on -t _0). The distance measurement calculation unit 16 multiplies the difference Δt by the speed of light c and divides it by 2 to obtain the distance D to the measurement object 200.

The internal reflector 18 is a member that reflects part of the light emitted from the light source 10 and guides it to the light-receiving element 20 for light quantity measurement. The internal reflector 18 can be configured by a mirror that can reflect light of wavelength λ _LD emitted from the light source 10.

  The light quantity measuring light receiving element 20 receives the light from the light source 10 reflected by the internal reflector 18. The light quantity measuring light receiving element 20 includes a light receiving element. The light quantity measuring light receiving element 20 has, for example, a configuration in which a plurality of light receiving elements are arranged. For example, the configuration of four light receiving elements arranged side by side is shown. However, the arrangement of the light receiving elements in the light quantity measuring light receiving element 20 is not limited to this, and may be two-dimensionally arranged. Further, the light quantity measuring light receiving element 20 may be constituted by one light receiving element. The configuration of the light quantity measuring light receiving element 20 may include a photodiode. The light quantity measuring light receiving element 20 outputs a signal having an intensity corresponding to the light quantity of the light reflected by the internal reflector 18 to the light quantity comparator 22.

  The light amount comparator 22 compares the light amount measured by the light receiving element 20 for light amount measurement with the reference light amount, generates a control signal corresponding to the difference, and outputs the control signal to the light source driving circuit 12. That is, the light quantity comparator 22 detects whether the light quantity measured by the light quantity measuring light receiving element 20 is excessive or insufficient with respect to the reference light quantity, and outputs a control signal corresponding to the quantity.

When the wavelength λ _{LD of the} light emitted from the light source 10 changes, the amount of light measured changes depending on the wavelength dependency of the sensitivity of the light receiving element 20 for light amount measurement. That is, as the wavelength λ _LD of the light emitted from the light source 10 changes, the intensity of the signal output from the light quantity measuring light receiving element 20 changes. The light source driving circuit 12 adjusts the temperature so that the change in the wavelength λ _LD is reduced by heating or cooling the light source 10 according to the control signal from the light quantity comparator 22.

Thus, feedback control is performed so that the light emission wavelength λ _LD of the light source 10 becomes constant. Therefore, the emission wavelength λ _LD of the light source 10 can be stabilized. By stabilizing the light emission wavelength λ _LD of the light source 10, the amount of light received by the distance measuring light receiving element 14 in the distance measuring device 100 can be stabilized, and the accuracy of distance measurement can be increased.

  Further, as shown in FIG. 2, the internal reflector 18 may be configured by a part of the housing 24. For example, a part of the sand proof hood or the waterproof hood of the casing 24 has a characteristic of reflecting light emitted from the light source 10, and the light emitted from the light source 10 is reflected by the portion to receive a light amount measuring light receiving element. 20 may be incident.

[Second Embodiment]
As shown in FIG. 3, the distance measuring device 102 according to the second embodiment is incident on the light receiving element 14 for distance measurement and the light receiving element 20 for light amount measurement with respect to the distance measuring apparatus 100 according to the first embodiment. The difference is that a band pass filter (BPF) 30 is provided on the front surface.

The bandpass filter 30 is a filter that transmits light in a desired wavelength range and attenuates light outside the wavelength range. The bandpass filter 30 preferably has a center transmission wavelength λ _BPF that matches the emission wavelength λ _LD of the light source 10. That is, the band-pass filter 30 may be a filter that transmits light in a wavelength region (including the center wavelength and standard wavelength) that can be emitted from the light source 10 and attenuates light outside the other wavelength region. The band-pass filter 30 is disposed at an optical position through which light incident on the distance measuring light receiving element 14 and the light amount measuring light receiving element 20 passes. One band-pass filter 30 may be provided in common for the distance measuring light receiving element 14 and the light quantity measuring light receiving element 20, or the same characteristics as the distance measuring light receiving element 14 and the light quantity measuring light receiving element 20. May be provided separately.

Thus, by providing the band pass filter 30, light outside the transmission wavelength range can be attenuated, the influence of outside light outside the vicinity of the emission wavelength λ _LD of the light source 10 can be reduced, and the signal to noise ratio (S / N ratio) can be increased. In particular, according to the present embodiment, by controlling the temperature of the light source 10, the attenuation of the light amount due to the change in the light emission wavelength λ _LD of the light source 10 is detected, and the light emission wavelength λ _LD is maintained in a narrow range. Can do. Then, by stabilizing the emission wavelength λ _LD of the light source 10 near the central transmission wavelength of the bandpass filter 30, the transmission wavelength range of the bandpass filter 30 can be further narrowed, and the signal noise ratio (S / N ratio). ) Can be further increased.

Note that the distance measuring device 100 according to the first embodiment and the measurement target object 200 according to the second embodiment may be configured such that only the heater is provided as the temperature control means of the light source drive circuit 12. In this case, the state in which the light source 10 is heated to a temperature higher than the normal temperature is assumed to be normal, and the output of the light receiving element 20 for light quantity measurement at the emission wavelength λ _LD of the light source 10 at the normal time is used as a reference in the light quantity comparator 22. It is preferable to set the light amount. Thereby, the light source 10 can be cooled by turning off the heater, and both heating and cooling of the light source 10 can be realized only by the heater.

[Third Embodiment]
The distance measuring device in the third embodiment is provided with temperature adjusting means in the light source driving circuit 12 of the distance measuring device 100 in the first embodiment, whereas the temperature of the light source 10 is controlled by controlling the light source 10 itself. It is different in that the configuration is adjusted.

In the light source driving circuit 12 of the distance measuring device in the present embodiment, the emission wavelength λ _LD of the light source 10 is controlled by adjusting the temperature of the light source 10 using the leakage current of the laser diode (LD) that is the light source 10. To do.

As shown in FIG. 4, the laser diode (LD) does not emit light unless a voltage equal to or higher than the threshold voltage V _TH determined by the semiconductor characteristics of the element is applied. However, even if the voltage is _lower than the threshold voltage V _TH , a slight leak current flows, and the leak current increases as the applied voltage increases. The laser diode (LD) itself is heated by Joule heat due to this leakage current. Therefore, by controlling the leakage current, the temperature of the laser diode (LD) can be adjusted, and the emission wavelength λ _LD can be controlled.

Specifically, as shown in FIG. 5, the temperature of the laser diode (LD) is adjusted by controlling the offset voltage V _OS of the DC voltage superimposed on the applied voltage V _LD to the laser diode (LD), The emission wavelength λ _LD can be controlled.

According to the distance measuring apparatus of the present embodiment, the light emission wavelength λ _LD of the light source 10 can be controlled without the need for temperature control means such as a Peltier element, a heater, or a fan.

[Fourth Embodiment]
As shown in FIG. 6, the distance measuring device 104 according to the fourth embodiment is provided with a light shielding member 32 in the optical path between the internal reflector 18 and the light quantity measuring light receiving element 20 in order to block outside light. The configuration. The light shielding member 32 may be, for example, an opaque cylindrical member that covers the optical path between the internal reflector 18 and the light quantity measuring light receiving element 20.

Thereby, according to the distance measuring device 104, the external light can be blocked well and reliably, and the temperature of the light source 10 is determined based on the measurement result of the light quantity measuring light receiving element 20 obtained by removing the influence of the external light. Can be adjusted. Therefore, the emission wavelength λ _LD of the light source 10 can be controlled more accurately.

[Fifth Embodiment]
As shown in FIG. 7, the distance measuring device 106 according to the fifth embodiment includes a memory 34 that temporarily stores the amount of light measured by the light-receiving element 20 for light amount measurement. Memory 34 stores the intensity S ₁ of the signal corresponding to the amount measured by the light quantity measuring light receiving element 20 in a state which does not emit light source 10. Strength S ₁ of the signal is a noise component due to external light in the state that does not emit light source 10. The light quantity comparator 22 subtracts the intensity S ₁ of the signal stored in the memory 34 from the intensity S _{2 of} the signal corresponding to the light quantity measured by the light receiving element 20 for measuring the light quantity when the light source 10 is caused to emit light. Thus, the noise component due to the external light is removed, only the signal component due to the light from the light source 10 is extracted, and a control signal corresponding to the amount is output.

  As described above, according to the distance measuring apparatus 106 in the present embodiment, even when the light shielding by the housing 24 and the light shielding member 32 cannot be sufficiently performed, the signal component due to the reflected light of the light from the light source 10. The temperature of the light source 10 can be controlled based on the above.

  Note that the measurement by the light quantity measurement light-receiving element 20 in a state where the light source 10 is not emitted and the measurement by the light quantity measurement light-receiving element 20 in a state where the light source 10 is caused to emit light are performed at timings as close as possible. Is preferred.

  Moreover, in the said embodiment, although it was set as the structure which isolate | separates a part of light radiate | emitted from the light source 10 with the internal reflector 18, it is not limited to this. For example, an arrangement may be adopted in which a part of the light emitted from the light source 10 is directly incident on the light quantity measuring light receiving element 20. Moreover, it is good also as a structure which isolate | separates a part of light radiate | emitted from the light source 10 using optical elements, such as a diffraction grating, instead of the internal reflector 18. FIG.

  In the above embodiment, the distance measuring light receiving element 14 and the light quantity measuring light receiving element 20 are separated from each other. However, they may be integrated as one chip.

  Further, the light immediately reflected by the internal reflector 18 has a very large amount (strong). Therefore, if the light receiving element 20 for light quantity measurement and the light receiving element 14 for distance measurement have the same sensitivity, the light quantity measuring light receiving element 20 may cause signal saturation and the like, and there is a concern that the light quantity cannot be measured accurately. Therefore, it is preferable that the reflected light from the internal reflector 18 be attenuated. In addition, it is preferable that the sensitivity of the light quantity measuring light receiving element 20 is lower than the sensitivity of the distance measuring light receiving element 14. In order to reduce the sensitivity, a method of lowering the bias voltage applied to the light receiving element 20 for measuring the light amount or a device structure with originally low sensitivity can be mentioned.

DESCRIPTION OF SYMBOLS 10 Light source, 12 Light source drive circuit, 12a Temperature control means, 14 Distance measuring light receiving element, 16 Distance calculating part, 18 Internal reflector, 20 Light quantity measuring light receiving element, 22 Light quantity comparator, 24 Case, 24a Window, 30 band pass filter, 32 light shielding member, 34 memory, 100, 102, 104, 106 distance measuring device, 200 object to be measured.

Claims (8)

A light detection device that includes a light source and performs measurement using light emitted from the light source,
A light receiving element for measuring the amount of light that measures the amount of light emitted from the light source by separating and receiving a part of the light emitted from the light source;
A light amount comparator that compares a measured light amount output from the light receiving element for light amount measurement with a reference light amount, and outputs a control signal for changing the light emission characteristics of the light source so that the difference is reduced;
A light source driving circuit for driving the light source and changing a light emission characteristic of the light source based on the control signal from the light amount comparator;
An optical detection device comprising: The photodetection device according to claim 1,
The light source and the light receiving element for light quantity measurement are housed in the same housing,
An internal reflector that reflects a part of the light emitted from the light source inside the housing;
The light-detecting device, wherein the light-receiving element for light quantity measurement receives reflected light reflected by the internal reflector. The photodetecting device according to claim 1 or 2,
The light emission characteristic of the light source is at least one of a light emission amount and a light emission wavelength. The photodetection device according to any one of claims 1 to 3,
An optical detection device comprising: an optical bandpass filter that is disposed in front of the light receiving element for measuring light quantity and has a transmission wavelength that is a wavelength that can be emitted from the light source. The photodetection device according to any one of claims 1 to 4,
The light source driving circuit controls a voltage or a current for the light source based on the control signal from the light amount comparator. The photodetection device according to any one of claims 1 to 4,
The light source driving circuit controls the temperature of the light source based on the control signal from the light quantity comparator. The photodetection device according to any one of claims 1 to 6,
A light detection device, wherein a light shielding member for shielding external light is provided in at least a part of an optical path between the light source and the light receiving element for light quantity measurement. The photodetection device according to any one of claims 1 to 7,
The difference between the light quantity measured by the light quantity measuring light-receiving element when light is not emitted from the light source and the light quantity measured by the light quantity measurement light-receiving element when light is emitted from the light source A light detection apparatus characterized in that the value is the measured light quantity.

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