CN108490725B

CN108490725B - VCSEL array light source, pattern projector and depth camera

Info

Publication number: CN108490725B
Application number: CN201810340167.0A
Authority: CN
Inventors: 许星; 王兆民
Original assignee: Shenzhen Orbbec Co Ltd
Current assignee: Shenzhen Orbbec Co Ltd
Priority date: 2018-04-16
Filing date: 2018-04-16
Publication date: 2020-06-12
Anticipated expiration: 2038-04-16
Also published as: CN108490725A

Abstract

The invention discloses a VCSEL array light source, a pattern projector and a depth camera, wherein the VCSEL array light source comprises: a substrate; and a plurality of VCSEL light sources arranged in an array on the substrate; the array arrangement of the plurality of VCSEL light sources includes a central region and a peripheral region having a density less than the central region. By using two regions of different density distributions: the light beams projected by the VCSEL array light source can provide a light source hardware basis for an overlapped pattern projector, and further can effectively solve the problem that the quality of a depth image is reduced due to gaps generated in a projection pattern caused by temperature change or manufacturing errors.

Description

VCSEL array light source, pattern projector and depth camera

Technical Field

The invention relates to the field of electronic and optical component manufacturing, in particular to a VCSEL array light source, a pattern projector and a depth camera.

Background

The depth camera can acquire depth information of a target, so that 3D scanning, scene modeling and gesture interaction are realized. For example, the depth camera is combined with a television, a computer and the like to realize the motion sensing game so as to achieve the effect of integrating game and fitness. In addition, the combination of the miniaturized depth camera and the mobile device can realize the functions of face recognition, unlocking, payment and the like, and brings brand-new biological recognition experience to the devices such as a tablet, a mobile phone and the like.

The core component in depth cameras is the laser pattern projector, which is continually evolving towards smaller and smaller volumes and higher performance with the continual pursuit of volume and power consumption. Generally, a laser pattern projector is composed of a light source, a Diffractive Optical Element (DOE), and the like, and a current wafer-level Vertical Cavity Surface Emitting Laser (VCSEL) array light source enables the volume of the projector to be reduced to be embedded in a miniature electronic device such as a mobile phone. The DOE may split the light emitted by the VCSEL array light source to form a pattern with more light beams, such as the scheme described in patent application CN 201711080702.5.

However, there are problems associated with having a projector project a desired patterned beam. The ideal pattern formed by projecting the patterned beam onto a plane should have high degree of irrelevance, uniformity and field angle, but the three are often difficult to combine, for example, when the degree of irrelevance is high and the field angle is large, the uniformity is often poor; more importantly, after the projector is miniaturized, the heat dissipation of the light source, the optical element and the like is relatively poor, and the pattern projected by the projector is unstable under the temperature change, so that the irrelevance, the uniformity, the angle of view and the like of the pattern are affected, and the calculation accuracy of the subsequent depth image is reduced.

Disclosure of Invention

To solve the above problems, the present invention provides a VCSEL array light source, a pattern projector, and a depth camera.

The present invention provides a VCSEL array light source, comprising: a substrate; and a plurality of VCSEL light sources arranged in an array on the substrate; the array arrangement of the plurality of VCSEL light sources includes a central region and a peripheral region having a density less than the central region.

In some embodiments, the peripheral region includes 4 corner regions and 4 side regions excluding the middle region and the corner regions. Wherein the density of the corner region is 1/4 of the density of the middle region, and the density of the side region is 1/2 of the density of the middle region.

In some embodiments, the arrangement of the light sources in the corner regions that are diagonal is complementary to each other, so that when overlapping, the light beams corresponding to the respective light sources do not overlap; the arrangement of the light sources at opposite sides in the side edge regions is complementary to each other, so that the light beams corresponding to the light sources are not overlapped when being overlapped.

The present invention also provides a pattern projector comprising: the VCSEL array light source as described above for emitting a plurality of light beams; the lens receives and converges the light beams to form sub-pattern light beams corresponding to the light source arrangement in the VCSEL array light source; a diffractive optical element for projecting the sub-pattern beam with a larger field angle after copying; the patterned beam is formed by combining a plurality of sub-pattern beams, and the sub-pattern beams are partially overlapped to form a partial overlapping area.

In some embodiments, the partial overlap region corresponds to the peripheral region. It is composed ofIn (3), an included angle Δ θ corresponding to the partial overlapping region satisfies the formula:

where m is the number of diffraction orders, Λ is the period of the DOE, θ_mRefers to the diffraction angle of the m-th order diffracted beam generated when a beam with the wavelength of lambda is incident on the DOE, and delta lambda refers to the wavelength variation of the VCSEL array light source caused by temperature variation or manufacturing error.

In some embodiments, the partial overlap area is no more than 50% of the patterned beam area. In other embodiments, the partial overlap region is no more than 10% of the patterned beam region.

The present invention also provides a depth camera comprising: a pattern projector as described above for projecting a structured-light patterned beam into space; the acquisition module is used for acquiring the structured light pattern; and the processor receives the structured light pattern and then calculates a depth image.

The invention has the beneficial effects that: the arrangement of the light sources on the VCSEL array light source uses two regions of different density distribution: the light beams projected by the VCSEL array light source can provide a light source hardware basis for an overlapped pattern projector, and further can effectively solve the problem that the quality of a depth image is reduced due to gaps generated in a projection pattern caused by temperature change or manufacturing errors.

Drawings

FIG. 1 is a side view of a structured light depth camera according to one embodiment of the present invention.

FIG. 2 is a schematic view of a laser projection module according to an embodiment of the invention.

FIG. 3 is a schematic diagram of a DOE splitting a single beam incident thereon, according to one embodiment of the present invention.

Figure 4 is a schematic diagram of a VCSEL array light source in accordance with one embodiment of the present invention.

FIG. 5 is a schematic diagram of a change in a projected pattern due to a change in temperature, according to one embodiment of the invention.

FIG. 6 is a schematic diagram of a projected pattern according to one embodiment of the present invention.

Fig. 7 is a schematic diagram of a VCSEL array light source distribution according to an embodiment of the present invention.

Detailed Description

The present invention is described in further detail below with reference to specific embodiments and with reference to the attached drawings, it should be emphasized that the following description is only exemplary and is not intended to limit the scope and application of the present invention.

FIG. 1 is a side schematic view of a structured light depth camera according to one embodiment of the present invention. The structured light depth camera 10 mainly comprises a pattern projector 103, an acquisition module 105, a main board 102, and a processor 101, and in some depth cameras, an RGB camera 104 is provided. The pattern projector 103, the acquisition module 105 and the RGB camera 104 are typically mounted in the same depth camera plane and on the same base line, one for each module or camera 106. Typically, the processor 101 is integrated on the motherboard 102, and the pattern projector 103 and the acquisition model 105 are connected to the motherboard 102 via an interface, which in one embodiment is an FPC interface. The pattern projector 103 is configured to project the coded structured light patterned beam into the target space, and the acquisition module 105 acquires the structured light pattern and then obtains a depth image of the target space through calculation by the processor 101.

The pattern projector 103 mainly includes a light source, which may include a light source such as an LED, a laser, or the like, for emitting visible light and invisible light such as infrared, ultraviolet, or the like, and an optical element. Optical elements such as lenses, diffractive optical elements, mirrors, etc. are used to modulate the light beam emitted by the light source to project the structured light pattern beam outward. By structured light pattern beam is meant herein that projection of the pattern beam onto a spatial plane will form the pattern. Collection module 105 and pattern projector 103 often one-to-one, the field of view of pattern projector 103 generally need cover the field of view of collection module 105 in measuring range, and on the other hand, collection module 105 often needs set up the corresponding light filter of the beam wavelength that emits with pattern projector 103 to let the light of more structured light pattern light beams pass through and reduce the image noise that other wavelength light beams brought simultaneously.

In one embodiment, the structured light pattern is an infrared speckle pattern (ir speckle pattern) having a relatively uniform distribution of particles but a high local irrelevancy, where local irrelevancy refers to a high uniqueness of each sub-region in the pattern when the acquisition module 105 is the corresponding ir camera. The structured light pattern may also be in the form of stripes, two-dimensional patterns, and the like.

The depth camera based on the time-of-flight (TOF) principle is mainly composed of a pattern projector and an acquisition module, the pattern projector is used for emitting time-recording light pulses, the acquisition module acquires the light pulses and then obtains the flight time of the light in the space, and the processor is used for calculating the distance of corresponding space points.

Fig. 2 is an embodiment of the pattern projector 103 of fig. 1. The pattern projector 103 includes a base (including a main base 201, a sub base 202, and a circuit board 203), a light source chip 204, a mirror base 206, a lens 207, and a Diffractive Optical Element (DOE) 208. The light beam emitted from the light source chip 204 is collimated or focused by the lens 207 and then emitted into the space by the DOE208, generally, the lens 207 is located between the light source chip 204 and the DOE208, and the distance between the lens 207 and the light source chip 204 is equal to or approximately equal to the focal length of the lens 207. In other embodiments, the lens 207 and the DOE208 may be integrated into one optical element, for example, formed on two surfaces of a transparent substrate. In some embodiments, a thermistor 205 may be further provided to measure the temperature around the light source chip 204, and any suitable thermistor may be applied in the module, such as NTC, PTC, etc.

The light source chip 204 may be a semiconductor LED, a semiconductor laser, etc., and preferably adopts a vertical cavity surface laser emitter (VCSEL) array as a light source, since the VCSEL has the characteristics of small volume, small light source emission angle, good stability, etc., and meanwhile hundreds of VCSEL light sources may be arranged on a semiconductor substrate with an area of 1mmx1mm, the VCSEL array light source chip thus formed is not only small in volume and low in power consumption, but also is more favorable for generating structured light spot patterned light beams.

Figure 4 shows a schematic diagram of a VCSEL array light source. The VCSEL array light source is composed of a substrate 401, a plurality of VCSEL light sources 402, and a control assembly (not shown in the figure). A plurality of VCSEL light sources 402 are arranged in an array on a substrate and emit light under the control of a control assembly. The VCSEL light sources can be controlled in different modes, for example, all VCSEL light sources can be controlled on and off synchronously, or the VCSELs on the chip can be controlled individually or in groups to produce different illumination densities. In some embodiments, the first mode is used, i.e. all VCSEL light sources on the chip are controlled on and off synchronously. In other embodiments, the second mode may be used, i.e., the VCSELs on the chip are controlled individually or in groups to produce different optical densities.

The VCSEL402 can be in a variety of forms and arrangements depending on the specific application, such as a uniform regular array arrangement or an irregular arrangement in a random, uncorrelated pattern. The shape, area, wavelength, etc. properties of the individual VCSELs may also be different. In some embodiments, the plurality of VCSELs 402 are uniformly regularly arranged on the semiconductor substrate 401 to form a regular array light source. In other embodiments, the plurality of VCSELs 402 are arranged irregularly in an uncorrelated pattern on the semiconductor substrate 401 to form an irregular array of light sources, as shown in fig. 4.

The VCSEL array light source 204 emits multiple beams with a certain divergence angle, the multiple beams enter the lens 207 to form sub-pattern beams corresponding to the arrangement pattern of the VCSEL array, and the sub-pattern beams are then incident on the DOE208 and expanded multiple times to form a patterned beam with a larger field angle. The lens 207 may be one or a combination of a lens group and a micro lens array, and focuses multiple light beams emitted from the VCSEL array light source 204 to emit outwards, and forms a sub pattern corresponding to the arrangement pattern of the VCSEL array in the far field, where the correspondence includes the same manner, a mirror image manner, a central symmetry manner, a rotation manner, and the like. DOE208 receives the array of beams from the lens and applies the same splitting pattern to each beam in the array of beams. Fig. 3 shows a schematic diagram of the splitting of a single beam incident on a DOE. The single beam 301 is split into one-dimensional 5-order diffracted beams (3, 1, 0, -1, -3) after entering the DOE302, which is only described with reference to 1-5 as an example, and may be split into other number of diffraction orders in practice, or the diffraction orders may be two-dimensionally distributed. If the period of the periodically arranged sub-elements in the DOE302 is Λ and the wavelength of the incident beam is λ, the diffraction angle of the m-th order diffracted beam is expressed as follows according to the grating equation:

when the incident beam is a sub-pattern beam, the DOE302 will replicate multiple sub-patterns to form the final patterned beam, and in one embodiment, the design of the DOE is such that the multiple sub-patterns are arranged adjacently to form the final patterned beam, as shown in the left diagram of fig. 5, the pattern 50 formed by the incident of the patterned beam on the plane is composed of 9 sub-patterns 51, and each sub-pattern 51 is composed of beams of the same diffraction order from different light sources. The image is shown in the form of a pattern 50 which takes into account distortion of the lens etc. DOE302 splits each single beam of light incident by a factor of 9.

In the actual use process, when the temperature changes, the wavelength of the VCSEL light source changes, and generally the wavelength is larger when the temperature is higher; in addition, the wavelength of the VCSEL light source produced in mass production is different due to the manufacturing uniformity problem, and the DOE is designed according to a certain wavelength. Therefore, if a DOE capable of projecting a pattern as shown in the left diagram of fig. 5 is designed according to a certain wavelength, the design may be different from the pattern in actual use.

From equation (1) we can obtain:

further, the method can be obtained as follows:

when the wavelength is from λWhen the diffraction angle becomes lambda', the diffraction angle of the m-th order diffraction beam is changed from theta_mBecomes θ'_mChanges in wavelength and diffraction angle are represented by Δ λ and Δ θ, respectively.

When the wavelength variation is small, i.e., Δ λ is small, d λ - Δ λ, d θ_m～Δθ_mThe formula (3) is transformed to obtain:

the diffraction angle change caused by the wavelength change is given in the above formula, as shown in fig. 3, when the temperature is increased or the manufacturing error causes the wavelength to be higher than the design wavelength, the wavelength of the light source is increased, which finally causes the angle of each diffraction order relative to the design to be shifted, and the shifted light beam is shown as the dotted line in fig. 3. For a VCSEL array light source, the resulting projected pattern of the patterned beam will be as shown in the right diagram of fig. 5. It can be seen that, since a plurality of gaps are generated in the pattern projected by the pattern projector due to temperature variation, when the depth image is calculated based on the pattern, holes may also appear at corresponding positions in the depth image, and the quality of the depth image is seriously reduced.

FIG. 6 is a schematic diagram of a projected pattern according to one embodiment of the present invention. The pattern 60 includes 9 sub-patterns 601 to 609, each sub-pattern corresponding to an arrangement pattern of VCSEL light sources in the VCSEL array light source. There is a partial overlap between two adjacent sub-patterns, for example, the overlap area between the sub-patterns 601 and 606 is 611, and the overlap area between the sub-patterns 601, 602, 605, and 606 is 610. The purpose of the partial overlap here is to avoid the situation where the wavelength variation results in an actual projected pattern as shown in the right diagram of fig. 5. The size of the overlapping region can be set according to the wavelength variation, for example, if the DOE is designed according to the wavelength λ, and the wavelength variation is assumed to be Δ λ at most, the included angle corresponding to the overlapping region is Δ θ shown in equation (4).

Generally, the overlap area is small relative to the area of the individual sub-patterns, such as not exceeding 1/10 of the sub-pattern areas, to avoid affecting the density distribution of the overall projected pattern when the overlap area is too large. Theoretically, the overlap area does not exceed 50% of the sub-pattern area.

It is understood that in the projection pattern shown in fig. 6, the pattern density distribution in the overlapped regions such as 610 and 611 is larger than that in the non-overlapped region, and if the density of the arrangement pattern of the VCSEL array light sources is uniformly distributed, the density of the overlapped

regions

610 and 611 is about 2 times and 4 times that of the non-overlapped region, respectively. When the area of the overlapping region is smaller than the area of the whole projection pattern region, the density of the overlapping region is increased without greatly affecting the density distribution of the whole projection pattern, however, in some embodiments, the area of the overlapping region is relatively larger, which results in the density distribution of the overlapping region being larger, and in addition, the overlapping region is also prone to have a situation that the light beams are overlapped to cause the light spot brightness to be too large.

Figure 7 is a schematic diagram of a VCSEL array light source in accordance with one embodiment of the present invention. The VCSEL array light source is composed of a substrate 701 and a plurality of VCSEL light sources 702. The density of the VCSEL light sources 702 is non-uniform, with peripheral regions having a lower density than the central regions, and the VCSEL array light sources are schematically shown as being divided into multiple regions by dashed lines. Preferably, where the density of the middle region 703 is highest, the peripheral regions are divided into two, one being four corner regions 705, whose density is 1/4 of the middle region 703; the other is four side regions 704 except for four corner regions and a middle region, whose density is 1/2 of the middle region 703.

When the VCSEL array light source shown in fig. 7 is used as the light source of the pattern projector, and the DOE of the pattern projector is designed to form the pattern shown in fig. 6, a patterned beam with a uniform density distribution can be generated when the peripheral region in the VCSEL array light source corresponds to the partially overlapped region of the sub-pattern in the pattern. Specifically, the VCSEL array light source shown in fig. 7 emits multiple beams, which are converged by the lens to generate sub-pattern beams corresponding to the arrangement of the VCSEL array in fig. 7, where the sub-pattern beams also have the characteristics of a wide middle region and a low density of peripheral regions, and the sub-pattern beams are diffracted and expanded by the DOE to form a patterned beam formed by combining multiple sub-patterns, where adjacent sub-patterns are partially overlapped, and the partially overlapped regions are just the peripheral regions with a low density. Thus, the overlapping region 611 in the pattern 60 is composed of exactly two side regions with density of the non-overlapping region 1/2, and the overlapping region 610 is composed of exactly 4 corner regions with density of the non-overlapping region 1/4, such that the density of the overlapping

regions

610 and 611 is the same as the density of the non-overlapping regions. Thus, partially overlapping patterned beams with uniform density distribution can be projected.

In one embodiment, in order to achieve that the size of the side and corner regions in the VCSEL array light source can exactly correspond to the overlapping region in the projection pattern, when the included angle Δ θ corresponding to the overlapping region is determined, if the focal length of the lens is f, the width d of the side region in the VCSEL array light source can be set as follows:

from another perspective, when the wavelength variation Δ λ, the focal length f of the lens, and the size of each region of the VCSEL array light source are known, a reasonable DOE can be designed based on the equations (1), (4), (5) to project partially overlapped patterned beams with uniform density distribution.

As can be seen from fig. 6 and 7, the overlapping region between adjacent sub-patterns in fig. 6 can be regarded as the overlapping between the peripheral regions of the VCSEL array light source, for example, the overlapping region 611 is formed by overlapping the sub-pattern regions corresponding to two opposite side regions (opposite up and down or opposite left and right) of the VCSEL array light source, and the overlapping region 610 is formed by overlapping the sub-pattern regions corresponding to four corner regions of the VCSEL array light source. In the overlapping region, it is necessary to avoid the phenomenon that the two light beams fall on the same point to cause over-high brightness, and the overlapping of the two light beams also affects the density distribution, so that the arrangement of the light sources in 4 opposite side regions and 4 corner regions in the VCSEL array light source can be set in a complementary form, that is, the upper side region and the lower side region are complementary, the left side region and the right side region are complementary, and the 4 corner regions are complementary, which means that when the complementary regions are overlapped, the light spots corresponding to the light sources can be mutually staggered so that overlapping does not occur.

The invention provides a pattern projector, which is used for projecting a patterned light beam consisting of a plurality of sub-patterns, and ensures that the projected patterned light beam can generate patterns with higher quality under different conditions by partially overlapping the sub-patterns so as to adapt the projector to temperature change and manufacturing errors. Also provided for this aspect is a VCSEL array light source in which the arrangement density of the intermediate light sources is greater than that of the peripheral light sources, thereby making it possible to make the density of the overlapped region nearly the same as that of the non-overlapped region even if the sub-patterns are partially overlapped.

The foregoing is a more detailed description of the invention in connection with specific/preferred embodiments and is not intended to limit the practice of the invention to those descriptions. It will be apparent to those skilled in the art that various substitutions and modifications can be made to the described embodiments without departing from the spirit of the invention, and these substitutions and modifications should be considered to fall within the scope of the invention.

Claims

1. A pattern projector, comprising:

a VCSEL array light source for emitting a plurality of light beams, the VCSEL array light source comprising a substrate and a plurality of VCSEL light sources arranged in an array on the substrate, the array arrangement of the plurality of VCSEL light sources comprising a central region and a peripheral region having a density less than the central region;

the lens receives and converges the light beams to form sub-pattern light beams corresponding to the light source arrangement in the VCSEL array light source;

a diffractive optical element for projecting the sub-pattern beam with a larger field angle after copying; the patterned beam is formed by combining a plurality of sub-pattern beams, and the sub-pattern beams are partially overlapped to form a partial overlapping area;

wherein the peripheral region in the VCSEL array light source corresponds exactly to a partial overlap region of the sub-pattern to produce a patterned beam with a uniform density distribution.

2. The pattern projector according to claim 1, wherein the peripheral region includes 4 corner regions and 4 side regions excluding the middle region and the corner regions.

3. The pattern projector as claimed in claim 2 wherein the density of the corner regions is 1/4 of the density of the middle region and the density of the side regions is 1/2 of the density of the middle region.

4. The pattern projector according to claim 2, wherein the arrangement of the light sources diagonally in the corner regions are complementary to each other so that the light beams corresponding to the respective light sources do not overlap when overlapped; the arrangement of the light sources at opposite sides in the side edge regions is complementary to each other, so that the light beams corresponding to the light sources are not overlapped when being overlapped.

5. The pattern projector according to claim 1, wherein the included angle Δ θ corresponding to the partial overlap region satisfies the formula:

where m is the number of diffraction orders, Λ is the period of the diffractive optical element, θ_mRefers to a diffraction angle of an m-th order diffracted beam generated when a beam having a wavelength λ is incident on the diffractive optical element, and Δ λ refers to a wavelength variation of the VCSEL array light source caused by a temperature variation or a manufacturing error.

6. The pattern projector according to claim 5, wherein the size of the partial overlap region matches the size of the peripheral region; the width d of the peripheral region satisfies the formula: d ≈ f Δ θ where f is the focal length of the lens.

7. The pattern projector according to claim 1, wherein the partial overlap area is no more than 50% of the patterned beam area.

8. The pattern projector of claim 1 wherein the partial overlap area is no more than 10% of the patterned beam area.

9. A depth camera, comprising:

the pattern projector of any of claims 1 to 8, for projecting a structured-light patterned beam into space;

the acquisition module is used for acquiring the structured light pattern;

and the processor receives the structured light pattern and then calculates a depth image.