JP6899005B2 - Photodetection ranging sensor - Google Patents

Description

The present invention generally relates to optoelectronic devices, in particular to photodetector and distance measuring (rider) sensors.

There is an increasing need for real-time 3D imaging in existing and emerging consumer applications. These imaging devices, also commonly known as photodetector and distance measuring (rider) sensors, illuminate the target scene with a light beam and analyze the reflected optical signal to obtain the distance (distance) of each point on the target scene. In many cases, intensity) (so-called target scene depth) can be measured remotely. A commonly used technique for determining the distance to each point on a target scene is to send a beam of light toward the target scene, move from the source to the target scene, and return to the detector adjacent to the source. It involves measuring the round trip time required by the beam, i.e. the flight time (ToF).

A detector suitable for a ToF-based rider is provided by a single-photon avalanche diode (SPAD) array. SPAD, also known as a GAPD (Geiger-mode avalanche photodiode), is a detector capable of capturing individual photons with a very high arrival time resolution on the order of tens of picoseconds. These can be made by dedicated semiconductor processes or standard CMOS techniques. An array of SPAD sensors made on a single chip has been used experimentally in 3D imaging cameras. Carbon et al. Provides a useful commentary on the SPAD technology of the "SPAD sensor" published in TOF Range-Imaging Cameras (Springer-Verlag, 2013), which is incorporated herein by reference.

In SPAD, the pn junction is reverse biased at a level well above the yield voltage of the junction. With this bias, the electric field is so high that a single charge carrier injected into the depletion layer can trigger a self-sustaining avalanche with incident photons. The rising edge of the avalanche current pulse indicates the arrival time of the detected photon. By lowering the bias voltage below the yield voltage, the current continues until the avalanche disappears. This latter function is performed by a quench circuit, which may simply include a high resistance ballast load in series with the SPAD, or it may include an active circuit element.

Embodiments of the present invention described below describe improved rider sensors and how to use them.

Therefore, according to an embodiment of the present invention, a laser light source configured to emit at least one beam of light pulses and a beam steering device configured to transmit and scan at least one beam over a target scene. And an electro-optic device including an array of sensing elements. Each sensing element is configured to output a signal indicating the time of incidence of a single photon on the sensing element. The focused optical system is configured to image a target scene scanned by the transmitted beam onto an array. The circuitry is coupled to operate the sensing element only within a selected region of the array and to sweep the selected region above the array in synchronization with the scan of at least one beam.

In some embodiments, the circuit comprises a portion of an array in which the selected region images the area of the target scene where the focused optics are illuminated by at least one beam at any moment during scanning. It is configured to select the area. The selected region may include one sensing element or may include a plurality of sensing elements.

In the disclosed embodiments, the circuit is configured to process the signal output by the sensing element to determine each distance to a point in the target scene. Typically, the sensing element includes a single photon detector such as a single photon avalanche diode (SPAD).

In some embodiments, the laser light source radiates at least two beams along each different beam axis so that the focused optics are illuminated by at least two beams at any moment during scanning. Each area of the scene is configured to form an image on each of the different areas of the sensing element. In one of these embodiments, the beam steering device is configured to scan at least two beams over the target scene in a two-dimensional scan, and the circuit is arrayed in a two-dimensional pattern corresponding to the two-dimensional scan. It is configured to sweep over the selected area above. For example, two-dimensional scanning may form a raster pattern in which the beam axes of at least two beams are offset laterally from each other with respect to the scanning line direction of the raster pattern.

Alternatively, the beam steering device is configured to scan at least two beams in a linear scan in a first direction over the target scene, with at least two beams in a second direction perpendicular to the first direction. Includes multiple beams arranged along the column axis. In one embodiment, the beams are arranged in at least two rows, with each row axis orthogonal to the first direction of scanning and offset from each other.

According to an embodiment of the present invention, there is also provided a sensing method comprising emitting at least one beam of an optical pulse and transmitting and scanning this at least one beam over a target scene. An array of sensing elements is provided, and each sensing element is configured to output a signal indicating the time of incidence of a single photon on the sensing element. The target scene scanned by the transmitted beam is imaged on the array. The sensing element is operated only within a selected region of the array, and the selected region is swept across the array in synchronization with the scan of at least one beam.

The present invention will be more fully understood from the following detailed description of embodiments of the present invention, which will be construed in conjunction with the following drawings.

It is the schematic of the rider system which concerns on one Embodiment of this invention. It is a block diagram which shows typically the SPAD type sensing apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the component of the sensing element in a SPAD array which concerns on one Embodiment of this invention. FIG. 5 is a block diagram schematically showing a SPAD array having a sensitivity region to be scanned according to an embodiment of the present invention. It is the schematic of the detector array which has a circular illumination spot to be scanned which concerns on one Embodiment of this invention. FIG. 6 is a schematic diagram of a detector array having circular illuminated spots to be scanned according to another embodiment of the present invention. FIG. 5 is a schematic diagram of a detector array having elliptical illuminated spots to be scanned according to yet another embodiment of the present invention. FIG. 5 is a schematic diagram of a detector array having elliptical illuminated spots to be scanned according to yet another embodiment of the present invention. FIG. 5 is a schematic diagram of a detector array having elliptical illuminated spots to be scanned according to yet another embodiment of the present invention. FIG. 5 is a schematic diagram of a detector array having two circular illumination spots scanned by a two-dimensional raster scan according to an embodiment of the present invention. FIG. 5 is a schematic diagram of a detector array having a staggered array of illumination spots scanned by one-dimensional scanning according to an embodiment of the present invention. It is the schematic of the rider apparatus which carries out one-dimensional scanning which concerns on one Embodiment of this invention. It is the schematic of the rider apparatus which carries out one-dimensional scanning which concerns on another embodiment of this invention. It is the schematic of the rider apparatus using the laser light source which can adjust the light emitting power which concerns on embodiment of this invention. It is the schematic of the rider apparatus which used two laser light sources with different emission powers which concerns on embodiment of this invention.

Overview Distance measurements to points within a target scene (target scene depth) using a rider are often compromised in practical practice due to some environmental, basic, and manufacturing obstacles. .. An example of an environmental hazard is the presence of uncorrelated background light, such as ambient sunlight, for indoor and outdoor applications ^{, typically reaching an irradiance of 1000 W / m 2.} The underlying obstacles are particularly related to the loss caused by the optical signal during reflection from the surface of the target scene due to the low reflectance of the target scene and the limitation of the focused aperture, as well as the electron and photon emission noise. These limitations often result in inflexible trade-offs, generally in large optical apertures, high optical power, narrow field of view (FoV), bulky mechanical configurations, low frame rates, and controlled environments. Force designers to rely on solutions that involve the limitation of operating sensors.

Embodiments of the invention described herein provide accurate, high-resolution depth imaging that can operate in an uncontrolled environment with a compact, low-cost rider by resolving the above limitations. Allows you to. The disclosed embodiment uses one or more pulsed laser sources that emit a beam to generate a highly irradiant illumination spot at the intersection of the emitted beam axis and the target scene. The beam, and thus the illumination spot, is scanned across the target scene. The illumination reflected from the target scene is imaged by the focused optics on a flight time single photon detector array for a high signal-to-noise ratio, detected by the flight time single photon detector array, and the target scene. The distance to each point of is derived from this flight time data.

By imaging the target scene on the detector array, there is a one-to-one correspondence between the position in the target scene and the position on the detector array defined by geometric optics known in the art. Generated. In this way, the area of the target scene is imaged on the corresponding image area on the detector, and the linear length in the image is set to the corresponding length within the area of the target scene with an optical magnification of M (for the rider system). Is typically obtained by multiplying by M << 1. Similarly, since the sensing element of the detector array can be considered to be imaged on the target scene at a magnification of 1 / M, the position and area of the target scene "visible" by the sensing element is given.

In the disclosed embodiments, the detector array includes a two-dimensional array of single photon time-sensitive sensing elements such as a single photon avalanche diode (SPAD). By dealing with each SPAD individually via a dedicated control circuit, the sensitivity of each SPAD, including the on / off state, is controlled by that particular inverse pn junction high voltage. In some embodiments, the SPAD acts as an individual sensing element, but in other embodiments, some SPADs are grouped into superpixels. At any moment during the scan, only the sensing elements within the area (s) of the array configured to receive the illumination reflected from the beam being scanned are activated. Thus, the sensing elements are only activated if their signals provide useful information. This technique reduces the background signal, which reduces the signal-to-background ratio, and also reduces the power needs of the detector array.

The rider measures the distance to the target scene for a set of discrete points that associate a finite averaging area with each point. In the disclosed embodiments, the measurement parameters, as well as the operation of the sensing element, are affected by the following system parameters of the rider.
1) Lighting spot size,
2) Beam steering device resolution (step size or deviation of beam steering device between continuous distance measurements),
3) The size of the superpixels in the detector array, i.e., the number of sensing elements binned together in the ToF measurement (including when one sensing element is used as the superpixel).

The effects of rider system parameters can be classified into two cases.
a) When the illumination spot is a small spot smaller than the size of the super pixel.
b) When the illumination spot is a large spot larger than the size of the super pixel.

Size comparisons are made by looking at both illuminated spots and superpixels in the same optical plane (either in the scene of interest or on the detector array). These two cases can be summarized in the table below, which is further detailed in the context of the figure.

In some embodiments of the invention, the target scene is illuminated and scanned by either one laser beam or a plurality of beams. In some embodiments that utilize multiple beams, these beams are generated by splitting the laser beam using diffractive optics, prisms, beam splitters, or other optics known in the art. .. In other embodiments, multiple beams are generated using several separate laser sources. In some of these embodiments, multiple beams are generated using a monolithic laser array, such as an array of VCSELs or VCSELs.

In some embodiments, a beam steering device, such as a scanning mirror, operates to scan a target scene with a single light beam in two-dimensional raster scanning. (Raster scans generally include long, substantially linear back-and-forth scans, so-called scan lines, with short movements that shift the scan point from one scan line to the next). A raster pattern is described herein as an example, and alternative scanning patterns that implement the same principles are considered to be within the scope of the present invention. When using a single light beam, the scan resolution in the direction perpendicular to the scan lines of the raster scan is given by the distance between the sequential scan lines. You can increase the scan resolution by reducing the distance between the sequential scan lines, but this kind of resolution increase requires a larger number of scan lines to cover the scene, so the frame rate is increased. It comes at the cost of reducing it. Alternatively, if the number of scanning lines per frame is not changed, the resolution can be increased at the expense of reducing the field of view. Mechanical constraints limit the extent to which the scanning speed of the mirror can be increased to offset these effects.

In one embodiment, a plurality of light beams spread laterally with respect to the scanning line direction and in the scanning line direction are used to increase the scanning resolution in the direction perpendicular to the scanning line. The separation distance of the light beams along the scan line is configured such that each light beam illuminates a separate superpixel on the detector array to individually identify each light beam. Here, the scanning resolution is determined not by the scanning linear density but by the lateral separation distance of the light beam. The disclosed embodiments can alleviate the miniaturization requirement of the detector array by increasing the lateral resolution without reducing the size of the sensing element.

In another embodiment, the plurality of illumination spots are scanned over the target scene in a linear scan. (Linear scanning in this context includes scanning along a single direction in which the scanning line is distorted from the straight line due to optical or mechanical defects.) Using one-dimensional linear scanning is more than two-dimensional scanning. Although a simple and inexpensive beam steering device can be used, the number of optical beams covering the target scene with sufficiently high resolution is generally larger than the number of optical beams required for two-dimensional scanning. A single-row scan is composed of rows perpendicular to the scan line and can be performed with multiple light beams that generate a row of illumination spots. The highest scan resolution in the column axis direction is achieved when each illumination spot is imaged on a separate sensing element in the detector array.

In another embodiment utilizing linear scanning, the scanning resolution perpendicular to the scanning line is increased by generating multiple rows of illumination spots that are perpendicular to the scanning line and offset from each other in the column axis direction. Further, since the plurality of rows are offset from each other in the scanning line direction by at least one sensing element so that each illumination spot illuminates a separate sensing element, each illumination spot can be specified separately. In this embodiment, the requirement for miniaturization of the detector array can be relaxed by increasing the lateral resolution without reducing the size of the sensing element.

Some embodiments of the present invention provide a rider system that has a wide-angle field of view (FoV) and covers a wide depth range. Implementing highly efficient and wide FoV optics makes the components bulky and expensive, so in these embodiments, the scene depth is measured over a wide range of FoVs and distances while maintaining a simple optical design and configuration. For this purpose, special designs and usage patterns for laser light sources, detector arrays, optics and algorithms are applied.

What should be considered for the laser light source is the emission power. When using only a low emission power laser source for scanning the target scene, the signal received by the detector array from apogee of the target scene is too weak for robust and accurate measurements. On the other hand, when only a laser light source having a high emission power capable of measuring a distant target scene point is used, an unnecessarily high emission power is used by the rider with respect to a nearby target scene point. Increases power consumption. Therefore, in some embodiments of the present invention, the emission power of the laser light source is adjusted according to the measured distance.

Description of the System FIG. 1 schematically shows a rider system 18 according to an embodiment of the present invention. The beam (s) from the laser light source 20 containing one or more pulsed lasers is directed at the target scene 22 by the dual axis beam steering device 24, and the illumination spot 26 forms and scans over the target scene. (In the present specification, the term "light" is used to refer to any type of light radiation, including radiation in the visible, infrared and ultraviolet ranges.) Beam steering devices are used, for example, scanning mirrors. Alternatively, any other suitable type of light deflector or scanner known in the art can be provided. The illumination spot 26 is imaged by the condensing optical system 27 on a two-dimensional detector array 28 including a single photon such as a SPAD and a time-dependent sensing element.

Further, the target scene 22 is illuminated by an ambient light source 36 such as the sun in addition to the illumination spot 26. To achieve a high signal-to-background ratio, the irradiance of the illumination spot is chosen to be much higher than the ambient illumination, which can reach up ^{to 1000 W / m 2 due to, for example, the irradiance from the sun.} A bandpass filter 37 is used to further reduce ambient illumination to the detector array 28.

The control circuit 38 is connected to the laser light source 20 to control the timing of pulse emission, controls their emission power, and is connected to the dual-axis beam steering device 24 to scan the illumination spot 26. To control. Further, the control circuit 38 controls the operation and sensitivity of each SPAD by dynamically adjusting the reverse pn junction high voltage of each SPAD of the detector array 28. Utilizing the known timing of the pulse from the laser light source 20 and the known state of the dual-axis beam steering device 24 that determines the position of the illumination spot 26 on the target scene 22, the control circuit 38 is at any moment. Only those SPADs whose illumination spots are imaged by the focused optical system 27 are activated. Further utilizing the above knowledge of the laser light source 20 and the beam steering device 24, and the signal read from the detector array 28, the control circuit 38 uses the measured flight time from the laser light source to the detector array. , The distance to each scanning point in the target scene 22 is determined.

2 to 4 schematically illustrate the architecture and function of the detector array 28 according to the embodiment of the present invention. These drawings show one possible scheme that can be used to selectively operate SPAD-type sensing elements in an array, using a combination of global and local bias controls. Alternatively, other types of bias and actuation schemes, as well as other types of single photon sensing devices, may be used for these purposes.

FIG. 2 is a block diagram schematically showing a detector array 28 according to an embodiment of the present invention. The detector array 28 includes a sensing element 44, each of which includes a SPAD and associated bias and processing circuits, as described below. The global high voltage bias generator 46 applies a global bias voltage to all sensing elements 44 in the array 28. Further, the local bias circuit 48 in each sensing element 44 applies an excess bias to be added to the global bias of the sensing element. The sensing element bias control circuit 50 sets the excess bias voltage applied by the local bias circuit 48 to each value by different sensing elements. Both the global high voltage bias generator 46 and the sensing element bias control circuit 50 are connected to the control circuit 38 (FIG. 1).

FIG. 3 is a block diagram showing one component of the sensing element 44 in the array 28 according to the embodiment of the present invention. In the disclosed embodiment, the array 28 includes a two-dimensional matrix sensing element formed on the first semiconductor chip 52, and the second two-dimensional matrix bias control circuit and processing circuit are the second semiconductor chip. It is formed on 54. Chips 52 and 54 (indicating only each single element of the two matrices) are such that the two matrices are coupled to each other in a one-to-one correspondence so that each sensing element on the chip 52 is on the chip 54. Is in contact with the corresponding bias control element and processing element of.

Both chips 52, 54, together with the accompanying bias control and processing circuits described herein, are manufactured from silicon wafers using well-known CMOS fabrication processes based on SPAD sensor designs known in the art. Can be done. Alternatively, the detection designs and principles described herein may be implemented using other materials and processes with the necessary modifications. For example, all of the components shown in FIG. 3 may be formed on a single chip, or the distribution of the components among the chips may be different. All such alternative embodiments are considered to be within the scope of the present invention.

The sensing element 44 includes a SPAD 56, which includes a photosensitive pn junction, as is known in the art. Peripheral circuits, including the quench circuit 58 and the local bias circuit 48, are typically located on the chip 54. As described above, the actual bias applied to the SPAD 56 _{is the sum of the global bias voltage V bias} applied by the bias generator 46 (FIG. 2) and the excess bias applied by the bias circuit 48. The sensing element bias control circuit 50 (FIG. 2) sets the excess bias applied to each sensing element by setting the corresponding digital value in the bias memory 60 on the chip 54.

In response to each captured photon, the SPAD 56 outputs an avalanche pulse, which is received by a processing circuit on the chip 54 that includes a digital logic 62 and a memory configured as an output buffer 64. These processing elements can be configured to function, for example, as a time-to-digital converter (TDC), which measures the delay of each pulse output by the SPAD 56 with respect to the reference time and the digital data corresponding to that delay. It outputs a value. Alternatively, or in addition, the logic 62 and buffer 64 may measure and output other types of values, including (but not limited to) pulse delay time histograms, binary or multi-valued digital waveforms. Good. The output from the chip 54 is connected to the control circuit 38 (FIG. 1).

FIG. 4 is a block diagram schematically showing a SPAD array 28 having a sensitivity scanning region 70 according to an embodiment of the present invention. In this case, the bias control circuit 50 sets the bias voltage of the sensing element 72 in the region 70 to a value higher than that of the remaining sensing elements 76, and the bias voltage is set so that the sensing element 76 is turned off. There is. However, the bias control circuit 50 dynamically adjusts the bias voltage of the sensing element 48 to sweep the region 70 across the array, as shown by the arrows in the figure. The circuit 50 can sweep the region 70 with a raster scan, for example, in synchronization with the scan of the laser beam over the target scene imaged on the array 28 (as shown in the drawings below).

As described above, the present embodiment is useful in adapting the sensitive region of the array 28 to the shape of the illumination light beam or the shape of the area of interest in the imaged target scene, thereby not contributing to the signal. The sensitivity of the array 28 to power consumption can be maximized while reducing background noise from the sensing element.

In an alternative embodiment of the invention (eg, illustrated in FIG. 9), the bias control circuit 50 has a region 70 having a linear shape, the linear shape extending along one or more rows of the array 28. The local bias voltage is set to fit the linear illumination beam or array of beams. The circuit 50 may then sweep this linear region 70 across the array 28 in synchronization with the illumination beam. Alternatively, other scan patterns may be performed that include both regular and adaptive scan patterns.

Illustrated Scanning Patterns and Super Pixels FIG. 5 is a schematic diagram showing a detector array 28 in which images of scanned circular illumination spots 26 (FIG. 1) are superimposed on an array according to an embodiment of the present invention. Moving image of the illuminated spot 26 made on the detector array 28 by the condensing optical system 27, three successive time points observed _{t = t i-1, t} = t i, and t = t i _{+ 1} Observed at. The images of the scanned illumination spots 26 at three consecutive time points are represented by circles 84, 86 and 88, respectively, their diameters being twice the pitch of the sensing element 44 in this example. The arrow 90 indicates the scanning direction of the image of the scanned illumination spot 26, and the planned position of the image of the scanned illumination spot 26 is determined from the knowledge about the state of the beam steering device 24.

At each time point, the sensing element 44 within the region of the array 28 that best matches the position of the image of the illumination spot 26 at that time point is activated. These actuated sensing elements can be considered as "superpixels". In the embodiment shown in FIG. 5, each superpixel comprises an array of 2x2 sensing elements, but in some embodiments the size of the superpixel takes other values statically or dynamically.

At time t = ti _-1 , the superpixel 92 is activated (surrounding the circle 84), at time t = ti, the superpixel 94 is activated (circle 86), and at time t = ti _{+ 1} , the superpixel 92 is activated. Super pixel 96 is activated (yen 88). Thus, in the illustrated embodiment, each sensing element 44 is associated with two adjacent superpixels. Only these sensing elements within the active superpixel are activated at a given moment, and the remaining sensing elements are turned off by reducing the bias voltage to a level where the avalanche multiplication cannot be sustained. This operation maximizes the light signal from the scanned image of the illumination spot 26 while reducing the exposure of the target scene to the background illumination that does not correlate with the illumination spot, thereby reducing the signal-to-background ratio of the array 28. To increase. In some embodiments of the invention, the output of the sensing element not illuminated by the image of the scanning spot 26 is masked using standard logic gates.

The lateral resolution of the target scene 22 in the scanning direction is determined by the discrete step size of the scan (determined by the scanning speed and the laser pulse repetition rate), which is one pitch of the sensing element 44 in this embodiment. .. The area where the distances of the target scenes are averaged are (approximately) superpixel areas.

FIG. 6 is a schematic diagram showing a detector array 28 in which an image of a circular illumination spot 26 (FIG. 1) to be scanned is superimposed on an array according to another embodiment of the present invention. Three time points t the moving image of the illuminated spot is continuous _{= t 1-i, t =} t i, is observed in t = t i + _1. Both the diameter of the image of the illuminated spot being scanned and the scanning step between two consecutive time points are half the pitch of the sensing element 44. The images of the illuminated spots 26 scanned at three consecutive time points are represented by circles 100, 102, 104, respectively. The arrow 105 indicates the scanning direction, and the planned position of the image determined from the knowledge about the state of the beam steering device 24 is determined. In the present embodiment, by using the super-pixels of a single sensing element 44, superpixel 106 is operated at t = t _i-1, also superpixel 108, t = t _i and t = t 1 _{+ i} It is operated by both. The lateral resolution of the image of the target scene 22 in the scanning direction is half the pitch of the sensing element 44, and the area of the target scene where the distance is averaged is the area of the illumination spot 26.

7A-C are schematic views showing a detector array 28 in which images of scanned elliptical illumination spots 26 (FIG. 1) are superimposed on the array according to yet another embodiment of the present invention. The elliptical illumination spot is obtained, for example, from an end face emitting laser diode having a rectangular emission junction cross section with a high aspect ratio. In this embodiment, the elliptical illumination spot 26 having an aspect ratio of 3: 1 is shown, but in other embodiments, other aspect ratios can be used. The degree of the so-called fast axis (long dimension) of the elliptical image of the illumination spot 26 on the detector array 28 is approximately 6 times the pitch of the sensing element 44, and the degree of the slow axis (short dimension) is the pitch. It is double. FIG 7A~C, like FIGS. 5-6 schematically the moving image of the illuminated spot 26 at three successive times _{t = t i-1, t} = t i, t = t i + 1 Shown. Each scanning step on the detector array 28 is one pitch of the sensing element 44. In this embodiment, superpixels of 2x2 sensing elements are used.

FIG. 7A schematically shows the illumination spot 110, which is an image of the scanned illumination spot 26 at time t = ti _-1. The superpixels activated at this time are pixels 112, 114, 116 based on the planned position of the illumination spot 110 (the farthest top and bottom edges of the illumination spot contribute little to the signal and are therefore ignored). Arrow 118 indicates the scanning direction, and the planned position of the illumination spot 110 is determined from knowledge of the state of the beam steering device 24.

Figure 7B is an image of the illumination spot 26 is scanned at time t = t _i, and the illumination spot 120 is schematically shown. The superpixels activated at this time are 112, 114, 116, 122 based on the planned position of the illumination spot 120. Here, the four superpixels are activated because the significant part of the illumination spot 120 (the upper end of the ellipse) is still in pixel 112 and the other significant part (the lower end of the ellipse) is in pixel 122. Is. Superpixels 112, 114, 116 continuously collect signals to improve the signal-to-noise ratio. As shown in Figure 7A, arrows 118 indicate the scanning direction, predetermined position of the illumination spot 120 at t = t _i is determined from knowledge of the state of the beam steering device 24.

FIG. 7C schematically shows the illumination spot 124, which is an image of the scanned illumination spot 26 at time t = ti _{+ 1.} The activated superpixels at this time are here 114, 116, 122 based on the planned position of the illumination spot 124. Here, only three superpixels are activated and pixel 112 (FIG. 7B) is no longer illuminated by any significant portion of illumination spot 124. As shown in FIGS. 7A-B, the arrow 118 indicates the scanning direction, and _{the planned position of the illumination spot 124 at t = ti + 1} is determined from the knowledge about the state of the beam steering device 24. In the illustrated embodiment, each superpixel is exposed to an image of the illumination spot 26 during seven scanning steps, which improves the signal-to-noise ratio.

Since the length of the elliptical illumination spot is much longer than the superpixel, the resolution in the scanning direction is determined by the size of the superpixel. Since the size of the superpixel is 1/3 of the length along the speed (length) axis of the elliptical illumination spot, the resolution obtained in the scanning line direction is three times the resolution obtained only by the elliptical illumination spot (numerically). 1/3). The averaging area for distance measurement is the superpixel area.

In FIGS. 5-7, the ideal shape (circular or elliptical) is used as the shape of the image of the illumination spot 26 on the detector array 28. In one embodiment of the invention, the control circuit 38 calculates (or refers to) the actual shape of the illuminated spot image on the detector array, and the calculation result selects a sensor element that starts at each point in the scan. Used when doing. This calculation takes into account the design of the beam steering device 24, its scanning movement characteristics, the exact state of the beam steering device, and the angle between the beam from the laser light source 20 and the beam steering device. This is because it affects the shape, moving direction, and orientation of the image of the illumination spot 26. Further, the dependence of the image on the distance between the rider device and the target scene 22 is considered. This effect is particularly important for a target scene range that is shorter than the distance between the beam steering device 24 and the focusing optical system 27. The above calculation is performed to optimally overlay the activated sensing element 26 with the image of the illumination spot 28 on the detector array 44 while achieving the desired aspect resolution, thereby the signal vs. background index. And the signal vs. noise figure can be optimized.

FIG. 8 is a schematic view showing a technique for improving the resolution of the raster scanning rider according to the embodiment of the present invention. The beam steering device 24 scans the image of the illumination spot 26 (FIG. 1) on the detector array 28 with the raster scan pattern 130 down in one row of the detector array and up in the next row. If only one illumination spot was used, the lateral resolution perpendicular to the scan line of the raster scan would be the pitch of the sensing element 44. However, in this embodiment, the lateral resolution is doubled by using the two illuminated spots 26 to be scanned, and the image on the detector array 28 is equal to the pitch of the sensing elements 44 along the scanning lines. It is separated by the distance and by half of this pitch laterally with respect to the scanning line. The repetition rate of the beam steering device 24 and the laser light source 20 is configured such that continuous illumination spots are separated by half a step of the pitch of the sensing element 44 in the scanning line direction of raster scanning. Each superpixel contains one sensing element 44.

Figure 8 shows two images of the illumination spot 26 at two time points t = t _i and t = t i _{+ 1} consecutive schematically. At time t = t _i, the image of the illumination spot is the spot 132 and spot 134, spot 132 is in the super pixel 136, the spot 134 is in the super-pixel 138. All other superpixels are turned off. At time t = t _{i + 1} , both spots move to new positions 142, 144, half a superpixel down, as indicated by arrow 140. These spots are still _{within the same superpixels 136 and 138 as at t = t i} , but the positions of the illumination spots 142 and 144 are determined by the state of the beam steering device 24 at _{t = t i + 1.} .. By always assigning the two spots to separate superpixels, the spots can be identified individually, and the resolution of the rider laterally to the scan line is in that direction rather than the pitch of the sensing element 44. Determined by the distance between the images of the two illumination spots 26, which eases the miniaturization requirement for the detector array 28. The distance averaging area measured by each light spot 26 is the area of that light spot.

In another embodiment (not shown), the number of scanned illumination spots 26 is increased to more than two (compared to FIG. 8), and these illumination spots have different images of each illumination spot. They are separated along the raster scan pattern 130 so that they are located within the sensing element 44. In an embodiment where all the images of the N illumination spots 26 are in one row of the detector array 28, the lateral resolution with respect to the raster scan 130 is given by N-dividing the pitch of the sensing element 44. ..

Linear Scanning Patterns FIGS. 9 to 11 are schematic views showing a rider based on linear scanning according to an embodiment of the present invention. Linear (one-dimensional) scanning is advantageous because it uses a potentially smaller, cheaper, and more reliable beam steering device design than required for two-dimensional scanning. The resolution in the linear scanning direction is determined by the resolution of the beam steering device. Since scanning is not performed laterally with respect to the linear scanning direction, the resolution in the linear scanning direction is achieved using the plurality of illumination spots 26 arranged over the target scene 22.

FIG. 9 is a schematic view showing a one-dimensional scan imaged on the detector array 28 according to an embodiment of the present invention. The direction perpendicular to the linear scan by using the pattern 150 of the image of the illumination spot 26 including the two staggered rows 151, 152, where the circle 153 represents the planned position of the image of the individual illumination spots on the sensor array 28. The resolution of the rider is improved beyond the pitch of the sensing element 44. Arrow 154 indicates the scanning direction.

In the rows 151 and 152 of the pattern 150, as the circle 153 shows, the image spacing of the illumination spots 26 along each row axis is equal to the pitch of the sensing elements 44. The two rows 151 and 152 are offset from each other by half the pitch of the sensing element 44 in the row axis direction. The rows 151 and 152 are separated by one pitch in the scanning direction so that the two rows are assigned to separate sensing elements. In some embodiments (not shown), the lateral resolution for linear scanning is further improved by using more than two rows of illumination spots 26 with smaller offsets from each other in the column axis direction. Thereby, for example, by using four rows offset from each other by a pitch of 1/4 of the sensing element 44, a resolution of a pitch of 1/4 can be realized.

FIG. 10 is a schematic view showing a rider 159 based on a one-dimensional scan according to an embodiment of the present invention. The beam from a single pulsed laser light source 160 is split by diffractive optics (DOE) 162 into two staggered multiple beams. These beams are directed to and scanned over the target scene 22 by the single-axis beam steering device 166, forming two staggered illumination spots 168 on the target scene 22. The illumination spots are imaged on the detector array 28 by the condensing optics 27 to form two staggered rows 151, 152 with a pattern 150 as shown in FIG.

Only the sensing element 44 containing the image of the illumination spot 26 of the pattern 150 is activated at any moment during scanning and the remaining sensing elements are turned off to prevent unnecessary integration of the background light and result in a high signal pair. A background ratio can be achieved. Similar to FIG. 1, the control circuit 38 is connected to the laser light source 160, the beam steering device 166, and the detector array 28, controls their functions, and uses the flight time data to determine the distance to the target scene 22. Collect data to do so.

FIG. 11 is a schematic diagram showing a rider 170 based on a one-dimensional scanning and coaxial optical architecture according to another embodiment of the present invention. The beam from a single pulsed laser light source 160 is split by DOE162 into multiple beams in two staggered rows. These beams pass through the polarizing beam splitter 176, are directed to the target scene 22 by the uniaxial beam steering device 166, and are scanned over it to form two staggered illumination spots 168. The illumination spots reflected from the target scene 22 are imaged on the detector array 28 through the beam steering device 166, the polarization beam splitter 176, and the focusing optics 27, and are two staggered patterns 150 shown in FIG. Rows 151 and 152 are formed.

Due to the coaxial architecture of optical transmission and acquisition, the pattern 150 on the detector array 28 is (nearly) stationary with respect to scanning. Therefore, the number of columns of sensor elements 44 on the detector array along the axis perpendicular to the scanning direction may be significantly smaller than the number of rows of sensor elements along the scanning direction. Similar to FIG. 1, the control circuit 38 is connected to the laser light source 160, the beam steering device 166, and the detector array 28, controls their functions, and uses the flight time data to determine the distance to the target scene 22. Collect data to do so.

In both embodiments shown in FIGS. 10 and 11, the lateral resolution perpendicular to the scanning direction is half the pitch of the sensing element 44, and the resolution along the scanning is the scanning speed of the beam steering device 166 and the laser light source. It is determined by the pulse repetition rate of 160. Each of the illuminated spots 168 averages distance measurements over the area of the spot.

In the present specification, the vertical orientations of columns 151 and 152 in the pattern 150 are shown as an example, and alternative orientations for implementing the same principle are also considered to be within the scope of the present invention.

Multi-range sensing FIGS. 12 to 13 are schematic views showing a rider adapted to a long distance and a short distance of a target scene according to an embodiment of the present invention.

FIG. 12 is a schematic diagram showing a rider 199 suitable for measuring the distance to both near and far target scene points according to the embodiment of the present invention. The beam of the pulsed laser light source 200 is directed to the target scene 22 by the dual-axis beam steering device 24, forms an illumination spot 206 on the target scene, and scans the spot over the target scene. The illumination spot 206 is imaged on the detector array 28 by the condensing optical system 27. The control circuit 38 is connected to the laser light source 200, the beam steering device 24, and the detector array 28.

The laser light source 200 has the ability to emit light at two power levels, low emission power and high emission power, under signal control from the control circuit 38. Concomitantly, the sensing element 44 (see FIG. 2) of the detector array 28 has the ability to operate in two separate modes: short-range mode and long-range mode. For a given mode of operation of a particular sensing element, the control circuit 38 adjusts its timing and sensitivity, as well as the signal processing algorithm for optimal performance in that mode. Typically, in short range mode, the sensing element 44 is biased to a relatively low sensitivity (resulting in low noise) and gated to sense a short flight time. In long range mode, the sensing element 44 is biased to a relatively high sensitivity and gated to detect longer flight times, reducing the possibility of spurious detection of short range reflections.

In order to determine the operation mode required for each area of the target scene 22, the area is first scanned using the laser light source 200 at a low emission power level suitable for short-distance detection. The sensing element 44 in the detector array 28 that receives the light from the laser light source 200 is actuated by a related signal processing algorithm set for its timing, sensitivity, and short range measurements.

Following this short-range scan, the control circuit 38 controls the rider 199 only in areas where this short-range, low-power scan did not provide a sufficiently robust distance measurement, based on predetermined criteria. Perform a long-distance scan. In long-distance scanning, the timing, sensitivity, and algorithm of the sensing element 44, which is operated to receive the reflected light from these areas, is appropriately changed, and a light source 200 having a high emission power level is used in these areas. Repeat the measurement.

FIG. 13 is a schematic diagram showing a rider 210 suitable for measuring distances to both near and far target scene points according to another embodiment of the present invention. The beams of the two pulsed laser light sources 218 and 220 are directed toward the target scene 22 by the dual-axis beam steering device 24, form a lighting spot 226 on the target scene 22, and scan the lighting spot over the target scene 22. (In FIG. 13, the distance between the laser light source 218 and the laser light source 220 is exaggerated to show two separate light sources). As detailed below, only one of the laser sources emits light at a given time. The illumination spot 226 is imaged on the detector array 28 by the condensing optical system 27. The control circuit 38 is connected to the laser light sources 218 and 220, the beam steering device 24, and the detector array 28.

When activated, the laser light sources 218 and 220 emit light at a specific emission power level by using the laser light source 218 that emits light at a low emission power level and the laser light source 220 that emits light at a high emission power level. The control circuit 38 selects which laser light source should be actuated at each point in the scan based on the types of criteria described above with reference to FIG. Similarly, the sensing element 44 (see FIG. 2) of the detector array 28 has the ability to operate in two separate modes: short-range mode and long-range mode. For a given mode of operation of a particular sensing element 44, the control circuit 38 adjusts its timing and sensitivity, as well as the signal processing algorithm for optimal performance in that mode.

To determine the required mode of operation for a given area of target scene 22, the area is first scanned using a low emission power laser light source 218. These sensing elements 218 in the detector array 28 that receive light from the laser light source 44 are operated with timing, sensitivity, and associated signal processing algorithms set for short range measurements. As in the preceding embodiment, if the control circuit 38 determines that it is not possible to make a sufficiently robust distance measurement for a given area using the laser light source 218, then the laser light source 220 is used. The timing, sensitivity, and algorithm of the sensing element 44 that operates to receive light are appropriately changed, and the measurement for the area is repeated with a laser having a higher emission power using the laser light source 220.

The above embodiments are given as examples, and it will be understood that the present invention is not limited to those specifically illustrated and described above. Rather, the scope of the invention is both a combination and a partial combination of the various features described above, as well as those not disclosed in the prior art that would be conceived by one of ordinary skill in the art by reading the aforementioned description. Includes variants and modifications of.

Claims (11)

With a laser source configured to emit at least one beam of light,
A beam steering device configured to transmit and scan the at least one beam across a target scene.
An array of sensing elements configured so that each sensing element outputs a signal indicating the incident of a photon on the sensing element.
A focused optical system configured to image the target scene scanned by the transmitted beam onto the array.
The beam steering device includes a focused optical system that scans at least one beam across the target scene with a spot size and scanning resolution smaller than the pitch of the sensing element.
A circuit coupled to actuate the sensing element only within a selected region of the array and sweep the selected region above the array in synchronization with scanning of the at least one beam. With
The laser light source emits at least two beams along each different beam axis so that the focused optics are illuminated by the at least two beams at any moment during the scan of the subject scene. Each area is configured to form an image on each of the different sensing elements.
The beam steering device is configured to scan at least two beams over the target scene in a two-dimensional scan, the circuit being said on the array in a two-dimensional pattern corresponding to the two-dimensional scan. Configured to sweep selected areas,
The two-dimensional scan forms a raster pattern, and the beam axes of the at least two beams are offset laterally from each other with respect to the scan line direction of the raster pattern.
Electro-optic device. The circuit comprises a portion of the array in which, at any moment during the scan, the selected region forms an area of the target scene in which the condensing optics are illuminated by the at least one beam. The device of claim 1, wherein the region is configured to include. The device of claim 2, wherein the selected region comprises one sensing element. The device of claim 2, wherein the selected region comprises a plurality of sensing elements. The device according to claim 1, wherein the circuit is configured to process a signal output by the sensing element to determine a respective distance to each point in the target scene. The device according to any one of claims 1 to 5, wherein the sensing element includes a single photon detector. The device according to claim 6, wherein the single photon detector is a single photon avalanche diode (SPAD). To emit at least one beam of light and
To transmit and scan the at least one beam across the target scene,
To provide an array of the sensing elements configured such that each sensing element outputs a signal indicating the incident of a photon on the sensing element.
To image the target scene scanned by the transmitted beam on the array.
The at least one beam is scanned over the target scene with a spot size and scanning resolution smaller than the pitch of the sensing element.
Only in selected areas of the array to actuate the sensing element, in synchronization with the scanning of the at least one beam, seen including and a sweeping said selected areas on said array,
Emitting at least one beam means radiating at least two beams along each different beam axis so that the focused optics are illuminated by the at least two beams at any moment during the scan. Each area of the target scene is imaged on each of the different sensing elements.
Scanning the at least one beam includes scanning the at least two beams over the target scene in a two-dimensional scan, and activating the sensing element is a two-dimensional pattern corresponding to the two-dimensional scan. Sweep the selected area on the array with
The two-dimensional scan forms a raster pattern, and the beam axes of the at least two beams are offset from each other in the lateral direction with respect to the scan line direction of the raster pattern.
Sensing method. Activating the sensing element is the array in which the selected region images the area of the target scene in which the focused optics are illuminated by the at least one beam at any moment during the scanning. 8. The method of claim 8 , comprising selecting the area to include a portion of the above. 8. The method of claim 8 , comprising processing the signal output by the sensing element to determine the respective distance to each point in the target scene. The method of claim 8 , wherein the sensing element comprises a single photon detector.

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