A distortion-corrected dot matrix projection device

Abstract

The present application discloses a distortion elimination dot matrix projection device, which includes an array light source, an inverse scanning lens, and a diffractive optical element. A first light beam emitted by the array light source is emitted as a second light beam through the inverse scanning lens, and the second light beam is replicated by the diffractive optical element into an emitted third light beam. There is a constraint relationship between the field of view angle α of the second light beam 102 and the field of view angle γ of the third light beam 103: α > 0.8γ. The present application can eliminate the distortion of the dot matrix pattern projected by the projector, so as to be better applied in a D-TOF 3D imaging device.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D depth imaging, and in particular to a distortion-eliminating dot matrix projection device. Background Art

[0002] We call such imaging devices 3D imaging devices, which can obtain depth information, that is, the distance information between the object and the shooting device. 3D imaging devices have begun to be applied to some electronic consumer products in the market, such as motion recognition in somatosensory games, 3D applications of AR / VR to the physical world, 3D face recognition in the new generation of iPhones, and automotive laser radars. 3D imaging devices can greatly enrich the user experience and enhance product competitiveness.

[0003] TOF technology is a key mainstream technology for realizing 3D imaging. The full name of TOF is Time-Of-Flight, which is the time interval from the emission of the emitted light to the time when it is reflected by the object to the receiving end. According to the principle of the invariance of the speed of light, distance measurement can be achieved. TOF technology is divided into I-TOF and D-TOF. The mature and commonly used technology in the market is I-TOF technology, namely Indirect Time-Of-Flight. I-TOF uses a laser emitting device to emit a beam of periodically modulated laser light to the surface of the object. The return light produces a time delay relative to the incident light in the timing, which is specifically manifested as a phase delay. The magnitude of the phase delay has a corresponding calculation relationship with the flight time of the light, that is, the flight time of the light is "indirectly" obtained by measuring the phase delay, thereby realizing distance measurement. D-TOF (Direct Time-Of-Flight) technology directly measures the flight time of light, rather than indirectly obtaining it through other means. At present, this technology has some applications in scientific research and testing equipment, large-scale industrial measurement equipment, laser radar and other fields, and miniaturized applications in the field of consumer electronics are about to begin to rise.

[0004] Regardless of the type of active 3D imaging device, it consists of two parts: a light projector and a receiver. In D-TOF technology using a dot matrix solution, it is necessary to face the problem of distortion control of the dot matrix projector in order to accurately match the pixel position on the acquisition sensor (such as the SPAD array), otherwise it will cause large measurement errors.

[0005] In the prior art, the TOF-based calibration methods provided in the patent application documents with publication numbers CN 109946681A and CN 109754425A are both used to calibrate the internal and external parameters and radial distortion parameters of the TOF camera to eliminate distortion, and are not improvements to the components of the device itself. Summary of the invention

[0006] To solve the above technical problems, the present application proposes a dot matrix projection device for eliminating distortion, which eliminates the distortion of the dot matrix pattern projected by the projector, so as to be better applied in the D-TOF 3D imaging device.

[0007] To achieve the above invention purpose, the present application adopts the following technical solutions:

[0008] A dot matrix projection device for eliminating distortion, comprising an array light source, an inverse scanning lens and a diffractive optical element;

[0009] The first light beam emitted by the array light source is emitted as a second light beam through the inverse scanning lens, and the second light beam is replicated as an emitted third light beam through the diffractive optical element; there is a constraint relationship between the field of view angle α of the second light beam and the field of view angle γ of the third light beam: α > 0.8γ.

[0010] The following also provides several optional ways, but it is not an additional limitation to the above overall solution, but only a further supplement or preference. Without technical or logical contradictions, each preferred way can be combined with the above overall solution alone, or multiple preferred ways can be combined with each other.

[0011] Preferably, the array light source includes a plurality of sub-light sources, each sub-light source emits a sub-light beam, and all the emitted sub-light beams form the first light beam.

[0012] Preferably, the array light source is a vcsel array light source.

[0013] Preferably, the inverse scanning lens is a single lens or a lens group composed of multiple lenses.

[0014] Preferably, the field of view angle β of the diffractive optical element < 5°.

[0015] Preferably, the surface microstructure of the diffractive optical element is distributed according to a random phase, that is, a random phase DOE.

[0016] Preferably, the array light source is arranged by arranging multiple single laser emitters.

[0017] Preferably, the array light source is composed of multiple independently controlled sub-array light sources. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of a dot matrix projector in an embodiment of the present application;

[0019] Figure 2 It is an effect diagram of dot matrix projection distortion in an embodiment of the present application;

[0020] Figure 3It is the distortion-free dot projection pattern in the embodiment of the present application;

[0021] Figure 4 It is the vcsel array light source diagram in the embodiment of the present application. Diagram a shows regularly arranged light-emitting holes, and diagram b shows randomly arranged light-emitting holes;

[0022] Figure 5 It is the partially enlarged top view of the diffractive optical element in the embodiment of the present application;

[0023] Figure 6 It is the diffraction comparison diagram of a single-point laser collimated beam by a conventional diffraction DOE and a random phase DOE. Diagram a is the diffraction pattern of a single-point laser collimated beam by a conventional diffraction DOE, and diagram b is the diffraction pattern of a single-point laser collimated beam by the random phase DOE 30 in the embodiment of the present application. Detailed implementation manners

[0024] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention. However, the present invention may be implemented in other ways different from those described herein. Therefore, the present invention is not limited by the limitations of the specific embodiments disclosed below.

[0025] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0026] A conventional dot projector includes a vcsel array light source, a collimating lens, and a diffraction element DOE. The field of view angle of the collimating lens is small, and the diffraction element DOE adopts a strictly periodic phase design method, which is based on vector diffraction theory and has a large field of view angle. The dot projection effect of the entire projector is as Figure 2 shown. It can be seen that there is a large distortion in the entire projected dot pattern, and the distortion is more serious closer to the edge.

[0027] As Figure 1 shown is a dot projector according to an embodiment of the present invention, which includes a vcsel array light source 10, an inverse scanning lens 20, and a random phase DOE 30. After the first beam 101 emitted by the vcsel array light source 10 passes through the inverse scanning lens 20, it becomes a second beam 102 with a large field of view angle. The field of view angle α of the inverse scanning lens 20 is greater than 0.8 times the field of view angle γ of the entire dot projector. After the second beam 102 passes through the random phase DOE 30, under its distortion-free diffraction replication effect, it becomes a third beam 103 that emits more sub-beams. The third beam 103 forms a distortion-free dot projection pattern as Figure 3 shown on the front receiving screen 40.

[0028] The VCSEL array light source 10 includes a plurality of laser emission holes 1010, which can be regularly arranged, as shown in Figure 4 Figure a, or can be randomly arranged, as shown in Figure 4 Figure b. As shown in Figure 1 Figure, each laser emission hole 1010 emits a sub-beam 1011, and the emitted sub-beams of all holes together constitute the above-mentioned first beam 101. The emission wavelength of the VCSEL array light source can cover ultraviolet light, visible light, and infrared light, which is selected according to application requirements. At the same time, the laser emission holes 1010 in different regions can also be formed into sub-arrays to realize independent control of the light emission switch of the sub-arrays. In some embodiments, multiple individual laser emitters can be appropriately arranged and combined to achieve the same light emission effect as the VCSEL array light source 10.

[0029] The inverse scanning lens 20 can be in the form of a single lens or a lens group composed of multiple lenses. Its function is to collimate each sub-beam emitted by the VCSEL array light source 10 into a parallel beam and emit it at a large angle. Figure 1 After the sub-beam emitted by the laser emission hole 1010 at the outermost edge position in the VCSEL array light source 10 passes through the inverse scanning lens 20, it becomes a parallel beam 1021 and is emitted. The beam angle α represents the field of view angle of the inverse scanning lens 20, that is, the field of view angle of the second beam. This field of view angle is much larger than that of an ordinary collimating lens, that is, the inverse scanning lens 20 has an obvious beam expansion effect. The first beam 101 passes through the inverse scanning lens 20 and is emitted to form the second beam 102, which includes the parallel beam 1021 corresponding to each laser emission hole.

[0030] The random phase DOE 30 is a micro-nano optical element with a surface microstructure distributed according to a random phase. It is designed based on the scalar diffraction theory and can perform distortion-free diffraction replication, as shown in Figure 5 Figure is a partial enlarged top view of the random phase DOE 30. It can be seen that the microstructure pattern is random and irregular. The figure shown is only a schematic of one of the patterns. In actual applications, there will be various random and irregular microstructure patterns. The function of the random phase DOE 30 is to perform distortion-free diffraction replication on the incident beam with a very small field of view angle, that is, it has two characteristics: a very small field of view angle and distortion-free diffraction. The field of view angle of the random phase DOE 30 is usually less than 5°. The ordinary diffraction DOE uses a strictly periodic phase design method and is based on the vector diffraction theory, following the strict grating diffraction formula, and inevitably generates distortion, as shown in Figure 6 (a) The figure shows the diffraction pattern of the ordinary diffraction DOE for the collimated beam of a single-point laser, which has obvious distortion. Figure 6(b) is the diffraction pattern of the random phase DOE 30 of this embodiment for the single-point laser collimated beam, with the effect of eliminating distortion. As a preferred embodiment, after each parallel beam 1021 passes through the random phase DOE 30 in Figure 1 , it is replicated into 3 beams and exits respectively. The figure shows the replication effect in the yz plane. In fact, there is also the same 3-fold replication effect in the xz plane, that is, the total diffraction replication multiple is 3×3 = 9 times. The angle between the edge beam and the central beam of these 3 beams is β, and the angle β is the field of view angle of the random phase DOE 30. β < 5°. Due to the existence of this diffraction field of view angle, the field of view angle γ of the third beam 103 is slightly increased relative to the field of view angle α of the second beam 102, and it also has a certain beam expansion effect. The angle γ is also the field of view angle of the entire distortion-eliminating dot matrix projection device. The diffraction replication multiple of 9 in the figure is only for illustration, and the random phase DOE 30 can be designed with any diffraction replication multiple according to needs.

[0031] In this embodiment, there is a constraint relationship between the field of view angle α of the second beam 102 and the field of view angle γ of the third beam 103: α > 0.8γ, and γ is also the field of view angle of the entire distortion-eliminating dot matrix projection device, that is, the field of view angle of the entire distortion-eliminating dot matrix projection device is basically determined by the field of view angle of the inverse scanning lens 20.

[0032] As Figure 3 shown, in this embodiment, after passing through the entire distortion-eliminating dot matrix projection device, the beam emitted from the laser emission hole 1010 in the foregoing Figure 1 finally reaches the receiving screen 40 to form a spot area 1031. The spot 10101 is the spot formed by the central diffraction beam, that is, the zero order, and the surrounding adjacent 8 spots are all the spots replicated by its diffraction, jointly constituting a 3*3 = 9-fold replication relationship in the xy direction. From Figure 3 it can be seen that the diffraction replication spots generated by the random phase DOE 30 are all within a small range around the central spot, which is the effect brought by the small field of view angle diffraction of the DOE.

[0033] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A distortion-corrected dot matrix projection device, comprising an array light source, a reverse scanning lens, and a diffractive optical element, characterized in that: The dot matrix projection device is applied to a D-TOF 3D imaging system; The first light beam emitted by the array light source is emitted as a second light beam through the reverse scanning lens, and the second light beam is replicated by the diffractive optical element into an emitted third light beam; there is a constraint relationship between the field of view angle α of the second light beam and the field of view angle γ of the third light beam: α > 0.8γ; The surface microstructure of the diffractive optical element is distributed according to a random phase, and the field of view angle β of the diffractive optical element < 5°, and performs diffractive replication with extremely small field of view angle for distortion correction of the incident light beam; The spots around the central spot emitted by the array light source are all spots replicated by its diffraction, and the diffractive replication spots are all within a small range around the central spot.

2. The distortion-eliminating dot matrix projection device according to claim 1, characterized in that, The array light source includes a plurality of sub-light sources, each sub-light source emits a sub-light beam, and all the emitted sub-light beams form the first light beam.

3. The distortion-eliminating dot matrix projection device according to claim 1, characterized in that, The array light source is a vcsel array light source.

4. The distortion-eliminating dot matrix projection device according to claim 1, wherein, The reverse scanning lens is a single lens or a lens group composed of multiple lenses.

5. The distortion-eliminating dot matrix projection device according to claim 1, wherein The array light source is arranged by arranging a plurality of single-body laser emitters.

6. The distortion-eliminating dot matrix projection device according to claim 1, characterized in that, The array light source is composed of a plurality of independently controlled sub-array light sources.

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