CN113835081A

CN113835081A - Transmitting terminal device for direct time-of-flight sensor and control method thereof

Info

Publication number: CN113835081A
Application number: CN202111250180.5A
Authority: CN
Inventors: 元军; 史斌; 王万胜
Original assignee: Shanghai Trance Microelectronics Technology Co ltd
Current assignee: Shanghai Trance Microelectronics Technology Co ltd
Priority date: 2021-10-26
Filing date: 2021-10-26
Publication date: 2021-12-24

Abstract

The invention provides a transmitting terminal device for a direct time-of-flight (DTOF) sensor and a control method thereof, wherein the transmitting terminal device comprises: an emission laser source configured to emit light; an emission end optical element configured such that a first portion of light emitted by an emission laser source is transmitted through the emission end optical element and such that a second portion of light emitted by the emission laser source is reflected by the emission end optical element; and at least one single photon avalanche diode SPAD light sensing unit, the at least one SPAD light sensing unit receiving the second part of the light reflected by the emission end optical element and outputting an optical signal related to the returned light, wherein the starting time of the emission laser source is determined according to the optical signal output by the at least one SPAD light sensing unit.

Description

Transmitting terminal device for direct time-of-flight sensor and control method thereof

Technical Field

The invention relates to the field of 3D depth sensing, in particular to a human eye safety protection and starting time metering method and system of a direct time of flight (DToF) sensor.

Background

With the technical development of laser radar, a direct time-of-flight ranging method has received increasing attention, and the DTOF principle is to obtain the distance of an object to be measured by continuously emitting light pulses to the object to be measured, then receiving light reflected from the object to be measured with a sensor, and by detecting the time of flight of the light pulses.

A direct time of flight (dtod) sensor is an active optical sensor that contains at least two main parts, a transmitting terminal Tx and a receiving terminal Rx. Tx emits short pulse laser, irradiates the object to be measured, and part of the laser is received by Rx after being reflected by the object to be measured.

In a direct time of flight (DToF) sensor, the distance of the object to be measured is calculated by recording the time difference of the received signals Tx and Rx. It is common to transmit a light-emitting signal to start recording the start time and Rx receives a measured light signal to record the end time by a control circuit signal. The time difference is the time t when the laser flies back and forth in the air, and the distance d of the object is 1/2C t by knowing the speed of light C.

However, since the VCSEL laser itself has an inductance effect, the light emitting time of the VCSEL laser is driven to have a certain jitter after the electrical signal is transmitted, and the system only records the start time of the signal driving, which leads to inaccurate recording of the light emitting time and further leads to inaccurate distance detection results.

A Vertical-cavity surface-emitting laser (VCSEL) at the emitting end Tx emits light through a Diffractive Optical Element (diffraction Optical Element) to form a discrete light spot in a far field. Because the light spot of the laser is diffused by the optical element, the laser beam can not cause damage to human eyes under normal work. However, if the optical element is broken, it cannot perform the splitting function, and the laser beam without splitting may cause irreversible damage when irradiated to the human eye. The solution is that a metal circuit can be made on the diffraction optical element, the system tests the resistance condition of the circuit in real time, if the diffraction optical element is broken, the circuit is disconnected or the resistance is greatly changed, the system closes the laser output of the Tx end after detecting, and the effect of protecting the safety of human eyes is achieved.

However, the improvement of the accuracy of the detection distance cannot be solved by adding a structure or a component to record the signal change after the optical element is broken to control whether Tx emits laser light to protect human eyes.

In view of the above technical problems, there is a need for a direct time of flight (DToF) sensor that improves accuracy of detection distance and controls whether a transmitting terminal Tx transmits laser light to protect human eyes.

Disclosure of Invention

One aspect of the present invention provides a transmitting end device for a direct time-of-flight DTOF sensor, comprising: an emission laser source configured to emit light; an emission end optical element configured such that a first portion of light emitted by an emission laser source is transmitted through the emission end optical element and such that a second portion of light emitted by the emission laser source is reflected by the emission end optical element; and at least one single photon avalanche diode SPAD light sensing unit, the at least one SPAD light sensing unit receiving the second part of the light reflected by the emission end optical element and outputting an optical signal related to the returned light, wherein the starting time of the emission laser source is determined according to the optical signal output by the at least one SPAD light sensing unit.

An aspect of the invention provides a transmitting end device for a direct time-of-flight DTOF sensor, wherein a starting time of light emission of the transmitting laser source is determined by determining a peak value of the optical signal.

An aspect of the invention provides a transmitting end device for a direct time-of-flight DTOF sensor, further comprising a transmitting laser source driving circuit configured to switch off the transmitting end device upon determining that a peak variation of a calibrated optical signal exceeds a first threshold.

An aspect of the present invention provides a transmitting end apparatus for a direct time-of-flight DTOF sensor, wherein the first threshold is ± 20%.

An aspect of the invention provides a transmitting end device for a direct time-of-flight, DTOF, sensor, wherein the transmitting end optical element comprises a collimating lens.

An aspect of the invention provides a transmitting end device for a direct time-of-flight, DTOF, sensor, wherein the transmitting end optical element comprises a diffractive optical element for generating an interference effect light spot.

One aspect of the present invention provides an emission end device for a direct time-of-flight DTOF sensor, wherein the diffractive optical element comprises an optical microstructure and an optical substrate, wherein the optical microstructure and the optical substrate are transparent materials in an operating wavelength band.

One aspect of the invention provides an emission end device for a direct time-of-flight DTOF sensor, wherein the emission end optical element comprises a light homogenizing sheet.

One aspect of the present invention provides an emission end device for a direct time-of-flight DTOF sensor, wherein the light uniformizing plate comprises an optical microlens array and an optical substrate, and the optical microlens array and the optical substrate are made of transparent materials in an operating waveband.

An aspect of the invention provides an emission end device for a direct time-of-flight DTOF sensor, wherein the emission end optical element further comprises a band pass filter configured to allow only light rays in the vicinity of the operating wavelength of the DTOF sensor to pass through.

An aspect of the invention provides a direct time-of-flight DTOF sensor device comprising a transmitting end device as described above, the DTOF sensor device comprising: a transmitting end device configured to emit short pulse laser light to irradiate an object to be measured and record a start time of the emission of the short pulse laser light; and a receiving end device configured to receive the partial laser light reflected by the measured object and record an end time of receiving the measured optical signal to acquire a distance of the measured object by a time difference between the start time and the end time.

An aspect of the invention provides a method of controlling an emitting end device for a direct time-of-flight, DTOF, sensor, the emitting end device comprising an emitting laser source, emitting end optics, at least one single photon avalanche diode, SPAD, photosite, and an emitting laser source drive circuit, the method comprising: emitting light by an emitting laser source; transmitting a first portion of light emitted by the emission laser source through the emission end optical element and reflecting a second portion of light emitted by the emission laser source through the emission end optical element; and receiving, by at least one SPAD light sensing unit, a second portion of the light reflected by the transmitting-side optical element and outputting an optical signal related to the returned light, wherein a start time of the emission laser source is determined according to the optical signal output by the at least one SPAD light sensing unit; and switching off the transmitting terminal device when the transmitting laser source driving circuit determines that the peak value change of the calibrated optical signal exceeds a first threshold value.

Advantageous effects

According to the direct time of flight (DToF) sensor device provided by the invention, the eye safety can be protected, the initial time recording accuracy is improved, and the system scheme of the detection distance result is improved.

Drawings

FIG. 1 is a schematic diagram of a transmitting end of a direct time-of-flight DToF sensor according to an embodiment of the invention;

FIG. 2a is a schematic diagram of Tx far field speckle distribution under normal operating conditions according to an embodiment of the present invention;

FIG. 2b is a schematic diagram of Tx far field speckle distribution in the event of a failure of a diffractive optical element according to an embodiment of the present invention;

FIG. 3a is a schematic diagram of the output of the SPAD histogram under normal operating conditions according to an embodiment of the present invention;

FIG. 3b is a schematic representation of the SPAD histogram output in the event of a failure of the diffractive optical element according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of the transmit end of a direct time-of-flight DToF sensor according to an embodiment of the present invention;

FIG. 5a is a schematic diagram of Tx far field spot distribution under normal operating conditions according to an embodiment of the present invention;

FIG. 5b is a schematic diagram of Tx far field spot distribution in the event of a dodging sheet failure, according to an embodiment of the present invention;

FIG. 6a is a schematic diagram of the output of the SPAD histogram under normal operating conditions according to an embodiment of the present invention;

FIG. 6b is a schematic diagram of the output of the SPAD histogram in the event of a dodging slice failure in accordance with an embodiment of the present invention;

FIG. 7 is a schematic diagram of the transmit end of a filtered direct time-of-flight DToF sensor according to an embodiment of the invention; and

fig. 8 is a schematic diagram of spectral transmittance of a filter according to an embodiment of the present invention.

Detailed Description

Before proceeding with the following detailed description, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms "couple," "connect," and derivatives thereof refer to any direct or indirect communication or connection between two or more elements, whether or not those elements are in physical contact with one another. The terms "transmit," "receive," and "communicate," as well as derivatives thereof, encompass both direct and indirect communication. The terms "include" and "comprise," as well as derivatives thereof, mean inclusion without limitation. The term "or" is inclusive, meaning and/or. The phrase "associated with … …" and derivatives thereof means including, included within … …, interconnected, contained within … …, connected or connected with … …, coupled or coupled with … …, in communication with … …, mated, interwoven, juxtaposed, proximate, bound or bound with … …, having an attribute, having a relationship or having a relationship with … …, and the like. The term "driver" refers to any device, system, or part thereof that controls at least one operation. Such a driver may be implemented in hardware, or a combination of hardware and software and/or firmware. The functionality associated with any particular drive may be centralized or distributed, whether locally or remotely. The phrase "at least one of, when used with a list of items, means that a different combination of one or more of the listed items can be used and only one item in the list may be required. For example, "at least one of A, B, C" includes any one of the following combinations: A. b, C, A and B, A and C, B and C, A and B and C.

Definitions for other specific words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.

In this patent document, the application combination of modules and the division of sub-modules are only used for illustration, and the application combination of modules and the division of sub-modules may have different ways without departing from the scope of the present disclosure.

Fig. 1 is a schematic diagram of a transmitting end of a direct time-of-flight DToF sensor according to an embodiment of the present invention.

The components of the transmitting end Tx 100 of the direct time of flight (dtod) sensor according to an embodiment of the present invention include: an emitting laser source VCSEL103, a VCSEL driving circuit 102, a collimating lens 105, a diffractive optical element 110, at least one Single Photon Avalanche Diode (SPAD) light sensing unit 104, and SPAD control circuitry and SPAD readout circuitry (not shown). Referring to fig. 1, a VCSEL light source 103 is disposed inside a cavity 101, a lower portion thereof is connected to an associated driving circuit 102, and at least one SPAD photosensitive unit 104 is disposed near the VCSEL light source 103. The light emitted from the VCSEL light source 103 passes through the collimating lens 105 and reaches the diffractive optical element 110, and the diffractive optical element 110 includes two parts, namely an optical microstructure 111 and an optical substrate 112, which are both made of transparent materials in the operating wavelength band. The optical microstructure 111 is a grating-like structure, and the overall structure thickness is usually within 100 μm. The surface of the optical microstructure 111 is composed of a series of step-like structures with fluctuant heights, the design of the specific structure is different according to different actually realized facula patterns, but the principle is that an incident beam of light is decomposed into a plurality of beams of light through interference, and the effect of increasing the number of final facula is achieved. The optical substrate 112 is typically flat glass, which serves as a substrate for the optical structure and provides support and protection.

After passing through the diffractive optical element 110, the light spot is replicated due to the interference effect, resulting in a light spot distribution in the far field as shown in fig. 2 a. The intensity of each spot is reduced as the spots are replicated. Meanwhile, since a part of the light is reflected on the surface of the diffractive optical element 110 and returns to the cavity 101, the SPAD sensing unit 104 receives the returned light signal, and the histogram result of one frame for ranging formed after the signal processing and passing through the readout circuit is shown in fig. 3a, and the position with the highest histogram can be considered as the starting time of light emission. Wherein, it should be apparent to those skilled in the art that one frame for ranging may be different according to a range in which ranging is required.

When the diffractive optical element 110 is damaged (e.g., the optical substrate 112 is broken, or the optical microstructure 111 is scratched or absorbs moisture), the optical function thereof fails to function as a copy of the light spot, and the light emitted from the light source VCSEL103 passes through the collimating lens 105 to form a light spot distribution in the far field as shown in fig. 2 b. Since the spots are not duplicated, the intensity of each spot becomes strong, and the laser intensity in this case may cause damage to the human eye. The histogram of the signal received by the SPAD sensing unit 104 after processing is shown in fig. 3 b. As the diffractive optical element 110 is damaged, the light intensity reflected back to the cavity 101 will be weakened, so that the number of photons received back by the SPAD photosensitive unit 104 is reduced, the number of triggering times is reduced, and the histogram result formed after the signal processing by the readout circuit is shown in fig. 3b, and it can be seen that the peak value of the histogram is obviously reduced. It should be clear to a person skilled in the art that the embodiments described above with reference to fig. 1-3 b merely serve to illustrate the concept of the present invention, and are not intended to limit the present invention to the embodiments shown in fig. 1-3 b, for example, when the diffractive optical element 110 is destroyed, the peak of the processed histogram of the signal received by the SPAD photosensitive unit 104 may also rise significantly (when the destroyed diffractive optical element 110 reflects most of the collimated light back to the SPAD photosensitive unit 104). Therefore, by determining that the peak value in one frame varies from the calibration value by more than a certain range (e.g., ± 20%) after calibration, the diffractive optical element is considered to be failed, and the driver is required to turn off the Tx module.

So far, the whole Tx module completes two functions of measuring signal transmission time and protecting human eyes.

Fig. 4 is a schematic diagram of the transmitting end of a direct time-of-flight DToF sensor according to an embodiment of the present invention.

A direct time of flight (DToF) sensor according to an embodiment of the present invention is an active optical sensor, and the transmitting end Tx thereof includes: the optical pickup comprises an emitting laser source VCSEL 403, a VCSEL driving circuit 402, a dod sheet 410, at least one SPAD light sensing unit 404, and SPAD control circuitry and SPAD readout circuitry (not shown). Referring to fig. 4, a VCSEL light source 403 is disposed inside a protective cavity 401, a lower portion of which is connected to an associated driving circuit 402, and at least one SPAD light sensing unit 404 is disposed around the VCSEL light source 403. The light emitted from the VCSEL light source 403 reaches the light uniformizing sheet 410, and the light uniformizing sheet 410 includes two portions, namely an optical microlens array 411 and an optical substrate 412, which are both made of transparent materials in the operating wavelength band. The optical microlens array 411 is composed of a series of sub-lenses arranged in a certain order on an optical substrate, and the diameter of the sub-lenses is from hundreds of nanometers to millimeters. The optical substrate 412 is typically flat glass, which serves as a substrate for the optical structure and provides support and protection.

After passing through the light homogenizing plate 410, the light source is diffused and shaped by the action of the micro-lens, and a light spot distribution as shown in fig. 5a is formed in a far field according to needs. Since the light spot is diffused, the light intensity per unit angle is reduced. Meanwhile, since a part of the light is reflected on the surface of the dodging sheet 410 and returns to the cavity 401, the SPAD sensing unit 401 receives the returned light signal, and the result of the histogram formed after the signal processing is performed by the readout circuit is shown in fig. 6a, and the position with the highest histogram can be considered as the starting time of light emission.

When the dodging sheet 410 is damaged (for example, the light substrate 412 is broken, or the optical microlens array 411 is peeled off or scratched), the optical function thereof is disabled and cannot function as a light spot diffusion, so that the light emitted from the light source VCSEL 403 passes through the damaged dodging sheet 410 to form a light spot distribution in the far field as shown in fig. 5b, that is, the original emitting light spot distribution of the VCSEL. Since the light spot is not diffused, the intensity of the light spot becomes strong, and the intensity of the laser light in this case may cause damage to the human eye. The processed histogram of the signal received by the SPAD sensing unit 404 at this time is shown in fig. 6 b. Since the dodging sheet 410 is damaged, the light intensity of the reflective cavity 101 is weakened, so that the number of photons received by the SPAD photosensitive unit 404 and returned is reduced, the number of triggering times is reduced, and a histogram result formed by the reading circuit and the signal processing is shown in fig. 6b, it can be seen that the peak value of the histogram is obviously reduced, after calibration, it is determined that the change of the peak value in one frame relative to the change of the calibration value exceeds a certain range (such as ± 20%), the dodging sheet is considered to be invalid, and the Tx module needs to be turned off by the driver.

Fig. 7 is a schematic diagram of the emitting end of a filtered direct time-of-flight DToF sensor according to yet another embodiment of the invention.

A direct time of flight (DToF) sensor according to an embodiment of the present invention is an active optical sensor, and the transmitting end Tx thereof includes: the emitting laser source VCSEL 703, the VCSEL driver circuit 702, the dod sheet 710, the at least one SPAD sensing unit 704, the SPAD control circuit and the SPAD readout circuit are not shown, and an optional bandpass filter 720. Referring to fig. 7, the VCSEL light source 703 is disposed inside the protective cavity 701, the lower portion thereof is connected to the associated driving circuit 702, and at least one SPAD light sensing unit 704 is disposed around the VCSEL light source 703. The light emitted from the VCSEL light source 703 reaches the light uniformizer 710. the light uniformizer 710 includes two parts, namely an optical microlens array 711 and an optical substrate 712, both of which are transparent materials in the operating band. Meanwhile, a band pass filter 720 is attached to the upper surface of the light unifying sheet 710, and the spectral transmittance curve thereof is shown in fig. 8 (here, the operating wavelength is selected to be 940 nm).

Since the band-pass filter 720 only allows light near the operating wavelength of the system to pass through, it does not affect the transmission of laser light emitted by the VCSEL light source 703, and limits the interference of the spectrum of external ambient light, such as the visible light band of the sun, on the SPAD photosensitive unit 704. The system has the advantages that the interference of ambient light on the SPAD photosensitive unit in different light and shade environments is greatly reduced, and the condition that the emission end Tx is switched off by the system due to false alarm is avoided. In this case, after calibration, the variation threshold range (e.g., ± 10%) of the output histogram can be reduced, and when the variation threshold range is exceeded, the optical element is considered to be failed, and the driver is required to turn off the Tx module.

The optional narrow-band-pass filter is added, so that the robustness of the system can be improved, the false alarm probability is reduced, and the eye safety protection function is better realized.

According to an embodiment of the present invention, there is provided a direct time-of-flight DTOF sensor device comprising a transmitting end device as described above, the DTOF sensor device comprising: a transmitting end device configured to emit short pulse laser light to irradiate an object to be measured and record a start time of the emission of the short pulse laser light; and a receiving end device configured to receive the partial laser light reflected by the measured object and record an end time of receiving the measured optical signal to acquire a distance of the measured object by a time difference between the start time and the end time.

According to an embodiment of the invention, there is provided a method of controlling an emitting end device for a direct time of flight, DTOF, sensor, the emitting end device comprising an emitting laser source, emitting end optics, at least one single photon avalanche diode, SPAD, photosensing unit, and an emitting laser source drive circuit, the method comprising: emitting light by an emitting laser source; transmitting a first portion of light emitted by the emission laser source through the emission end optical element and reflecting a second portion of light emitted by the emission laser source through the emission end optical element; and receiving, by at least one SPAD light sensing unit, a second portion of the light reflected by the transmitting-side optical element and outputting an optical signal related to the returned light, wherein a start time of the emission laser source is determined according to the optical signal output by the at least one SPAD light sensing unit; and switching off the transmitting terminal device when the transmitting laser source driving circuit determines that the peak value change of the calibrated optical signal exceeds a first threshold value.

Although the present disclosure has been described with exemplary embodiments, various changes and modifications may be suggested to one skilled in the art. The present disclosure is intended to embrace such alterations and modifications as fall within the scope of the appended claims.

None of the description in this specification should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope. The scope of patented subject matter is defined only by the claims.

Claims

1. A transmitting end device for a direct time-of-flight, DTOF, sensor, comprising:

an emission laser source configured to emit light;

an emission end optical element configured such that a first portion of light emitted by an emission laser source is transmitted through the emission end optical element and such that a second portion of light emitted by the emission laser source is reflected by the emission end optical element; and

at least one single photon avalanche diode, SPAD, light sensing unit that receives a second portion of light reflected by the transmit side optical element and outputs an optical signal related to the returned light,

wherein the start time of the emission of light by the emission laser source is determined according to the optical signal output by the at least one SPAD photosensing unit.

2. The transmitting end device according to claim 1, wherein the starting time of the transmitting laser source to emit light is determined by determining a peak value of an optical signal within one frame.

3. The transmitting end device according to, further comprising a transmitting laser source driving circuit configured to turn off the transmitting end device when it is determined that a peak value of the optical signal within one frame is changed from a calibration value by more than a first threshold value.

4. The transmitting end apparatus according to claim 3, wherein the first threshold is ± 20%.

5. The transmitting end device of claim 1, wherein the transmitting end optical element comprises a collimating lens.

6. The transmitting end device according to claim 1, wherein the transmitting end optical element comprises a diffractive optical element for generating an interference effect spot.

7. The transmitting end device of claim 6, wherein the diffractive optical element comprises an optical microstructure and an optical substrate, wherein the optical microstructure and the optical substrate are transparent materials in the operating wavelength band.

8. The transmitting end device of claim 1, wherein the transmitting end optical element comprises a light homogenizing sheet.

9. The transmitting end device of claim 8, wherein the light homogenizing plate comprises an optical micro-lens array and an optical substrate, wherein the optical micro-lens array and the optical substrate are made of transparent materials in the working wavelength band.

10. The transmitting end device of claim 8, wherein the light homogenizing plate comprises an optical micro-lens array and an optical substrate, wherein the optical micro-lens array and the optical substrate are made of transparent materials in the working wavelength band.

11. The transmitting end device of claim 8, wherein the transmitting end optical element further comprises a band pass filter configured to allow only light rays near the operating wavelength of the DTOF sensor to pass through.

12. A direct time-of-flight, DTOF, sensor device comprising a transmitting end device according to any of claims 1 to 11, the DTOF sensor device comprising:

a transmitting end device configured to emit short pulse laser light to irradiate an object to be measured and record a start time of the emission of the short pulse laser light; and

and the receiving end device is configured to receive the partial laser reflected by the measured object and record the end time of receiving the measured optical signal so as to obtain the distance of the measured object through the time difference between the starting time and the end time.

13. A method of controlling an emitting end device for a direct time-of-flight, DTOF, sensor, the emitting end device comprising an emitting laser source, emitting end optics, at least one single photon avalanche diode, SPAD, photosite, and an emitting laser source drive circuit, the method comprising:

emitting light by an emitting laser source;

transmitting a first portion of light emitted by the emission laser source through the emission end optical element and reflecting a second portion of light emitted by the emission laser source through the emission end optical element; and

receiving, by at least one SPAD light sensing unit, a second portion of the light reflected by the emission-side optical element and outputting an optical signal related to the returned light, wherein a start time of the emission laser source is determined according to the optical signal output by the at least one SPAD light sensing unit; and

and switching off the transmitting terminal device when the transmitting laser source driving circuit determines that the peak value of the optical signal in one frame changes relative to the calibration value and exceeds a first threshold value.