A structured light projection module with controllable polarization state and a 3D imaging device

Abstract

The present invention discloses a structured light projection module with controllable polarization state and a 3D imaging device having the structured light projection module, wherein the structured light projection module comprises: a laser vcsel array light source, the light emitting surface of the laser vcsel array light source has a high-contrast grating layer, and the outgoing light of each light-emitting point has a consistent and controllable polarization state after passing through the high-contrast grating layer; a diffractive optical element, which matches the polarization state and is used to replicate the outgoing light and diffuse it. The present invention utilizes a high-contrast grating layer to make the outgoing light of the laser vcsel array light source have a consistent and controllable polarization state, effectively improving the light energy utilization rate of the entire 3D imaging device, the uniformity of the projection pattern, and effectively reducing the zero-order brightness of the projection pattern, thereby further improving the imaging accuracy of the device.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and in particular to a structured light projection module with controllable polarization state and a 3D imaging device. Background Art

[0002] Unlike traditional 2D imaging devices, such as cameras, which can only obtain the flat 2D information of objects, 3D imaging devices can also obtain the depth information of objects and construct a three-dimensional 3D model. Therefore, 3D imaging devices are widely used in industrial measurement, part modeling, medical diagnosis, security monitoring, machine vision, biometrics, augmented reality AR, virtual reality VR and other fields, and have great application value.

[0003] The 3D imaging device based on structured light technology is a new type of technical device with small size and high imaging accuracy. It has great commercial application potential and has been applied to a certain extent in the field of consumer mobile phones. For example, the patent application document with publication number CN206805630U provides a structured light projection module based on a VCSEL array light source, including: a VCSEL array light source, the VCSEL array light source includes: a semiconductor substrate, and at least two groups of VCSEL sub-arrays arranged on the semiconductor substrate, the VCSEL sub-array is composed of VCSEL light sources; a diffractive optical element, the diffractive optical element includes: at least two diffractive optical element sub-units; the diffractive optical element sub-units correspond to the VCSEL sub-arrays respectively, and are used to replicate the light beam emitted by the light source of the VCSEL sub-array at a certain multiple and then project it outward.

[0004] VCSEL (Vertical Cavity Surface Emitting Laser) array light source will become the preferred light source for structured light projection modules due to its advantages such as small size, high power, small beam divergence angle, stable operation, etc. VCSEL light source array can perform laser projection by arranging multiple VCSEL light sources on an extremely small substrate, such as arranging 100 or even more VCSEL light sources on a 2mm×2mm semiconductor substrate.

[0005] The core part of the structured light 3D imaging device is the structured light projection module. The output light of the projection module in the structured light 3D imaging devices currently on the market does not have the characteristic of controllable polarization state. Therefore, it has disadvantages such as low light energy utilization, poor uniformity of the projection pattern, and brighter zero order, which has a negative impact on the accuracy of the 3D imaging device. Summary of the invention

[0006] The present invention provides a structured light projection module with controllable polarization state, which can effectively improve the light energy utilization rate of the entire 3D imaging device, the uniformity of the projection pattern, and effectively reduce the zero-order brightness of the projection pattern, thereby further improving the imaging accuracy of the device.

[0007] The specific technical solution adopted by the present invention is as follows:

[0008] A structured light projection module with controllable polarization state, comprising:

[0009] A laser VCSEL array light source, wherein a high contrast grating (HCG) layer is provided above the light emitting surface of the laser VCSEL array light source, and the outgoing light of the light emitting point has a consistent and controllable polarization state after passing through the high contrast grating (HCG) layer;

[0010] The diffractive optical element matches the polarization state of the emergent light and is used for replicating the emergent light and diffusing it.

[0011] The light-emitting points of the above-mentioned laser vcsel array light source are distributed and arranged according to certain random pattern rules to form the entire light-emitting point array. The light-emitting surface can be understood as the light beam exit surface of the laser vcsel array light source. The sub-wavelength grating in the high contrast grating (HCG) layer covers the light-emitting point array. Each light-emitting point corresponds to a sub-wavelength grating microstructure, and each sub-wavelength grating microstructure is identical and consistent.

[0012] After the outgoing light of the laser VCSEL array light source passes through the high contrast grating (HCG) layer, its polarization state will become controllable and consistent. Since the high contrast grating layer has a sub-wavelength grating microstructure, including two types of sub-wavelength periodic and sub-wavelength non-periodic types, after the outgoing light of the light point passes through the sub-wavelength grating microstructure, the polarization direction of the light will become consistent with the grid direction of the sub-wavelength grating microstructure.

[0013] Preferably, the laser vcsel array light source comprises an N-electrode layer, a substrate layer, an N-type DBR layer, an active layer, a P-type DBR layer, a P-electrode layer and a high contrast grating (HCG) layer arranged in sequence, and the P-electrode layer is etched with light holes to form the light-emitting points.

[0014] The high contrast grating (HCG) layer is located on the surface of the P-type DBR layer.

[0015] Preferably, a collimating lens is further included to receive the light beam emitted by the laser vcsel array light source and collimate it into parallel light to be emitted into the diffractive optical element.

[0016] Preferably, the collimating lens is a single lens or a lens group including multiple lenses.

[0017] Preferably, the high contrast grating layer comprises a plurality of sub-wavelength gratings corresponding to the number of the light-emitting points, and after the outgoing light from the light-emitting points passes through the sub-wavelength gratings, the polarization direction of the light becomes consistent with the grating direction of the sub-wavelength gratings.

[0018] The shape of the sub-wavelength grating is consistent with the shape of the light-emitting hole. For example, if a circular light-emitting hole is used, the high-contrast grating layer also contains multiple separated circular sub-wavelength gratings (Note: not limited to circular, as long as they can cover the light-emitting hole). The number is the same as the number of light-emitting points, and the size is consistent with or slightly larger than the light-emitting hole of the light-emitting point, just covering the top of each light-emitting point.

[0019] The high contrast grating (HCG) is composed of a single layer of multiple separated circular sub-wavelength gratings. The refractive index ratio between the high refractive index area and the low refractive index area is very high, reaching more than 2. Preferably, the high refractive index is 3.59, the low refractive index is 1, and the ratio is 3.59. The period of the sub-wavelength grating is between 0 and λ, which varies with different system requirements, where λ is the emission wavelength of the laser VCSEL array light source. The number of circular sub-wavelength gratings is the same as the number of light-emitting points, and the size is the same as or slightly larger than the light-emitting hole of the light-emitting point, just covering the top of each light-emitting point.

[0020] Preferably, the diffractive optical element matches the polarization state of the output light of the laser vcsel array light source, that is, the polarization state of the output light of the laser vcsel array light source is used as a parameter for designing the diffractive optical element.

[0021] In the present invention, the diffractive optical element is designed so that the polarization state of the incident light is set to be consistent with the output light of the laser VCSEL array light source. Therefore, compared with the design in which the polarization state of the incident light is not set to be consistent with the output light of the VCSEL array light source, the uniformity of the diffractive optical element finally manufactured according to the design can be reduced by more than 9%, the brightness of the zero-order pattern can be reduced by more than 0.4%, and the light energy utilization rate can be increased by more than 10%.

[0022] The present invention also provides a 3D imaging device, comprising:

[0023] The above-mentioned structured light projection module with controllable polarization state is used to project a structured light pattern onto a target;

[0024] An image receiving module, used to obtain the structured light pattern;

[0025] The processing module calculates the depth information according to the structured light pattern.

[0026] Compared with the prior art, the present invention utilizes a high-contrast grating layer to ensure that the output light of the laser vcsel array light source has a consistent and controllable polarization state, and when the diffraction optical element DOE is designed, the polarization state used is set to be consistent with the polarization state of the output light of the laser vcsel array light source, thereby effectively improving the light energy utilization rate of the entire 3D imaging device, the uniformity of the projection pattern, and effectively reducing the zero-order brightness of the projection pattern, thereby further improving the imaging accuracy of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the principle diagram of a 3D imaging device based on structured light technology;

[0028] Figure 2 It is a schematic diagram of the optical principle of a structured light projection module with controllable polarization state;

[0029] Figure 3 It is a schematic diagram of the light-emitting point array of the laser vcsel array light source;

[0030] Figure 4 It is a schematic diagram of the longitudinal structure of a traditional laser VCSEL array light source;

[0031] Figure 5 It is a schematic diagram of the polarization state of the light-emitting point of a traditional laser vcsel array light source;

[0032] Figure 6 It is a longitudinal structural schematic diagram of a laser VCSEL array light source with controllable polarization state;

[0033] Figure 7 Schematic diagram of the microstructure of a high-contrast grating

[0034] Figure 8 It is a schematic diagram of the polarization state of the light-emitting point of a laser VCSEL array light source with controllable polarization state;

[0035] Fig. 9 It is a comparison table of design simulation results; DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to the embodiments and the accompanying drawings, but the present invention is not limited thereto.

[0037] like Figure 1The 3D imaging device shown includes a structured light projection module 100, an image receiving module 200, and a processing and operation module 300. The structured light projection module 100 is used to project a structured light pattern to a target, the image receiving module 200 (such as a camera) is used to obtain the projected structured light pattern, and the processing and operation module 300 calculates depth information based on the obtained structured light pattern. When an actual object, such as a human face, is within a range of 20cm-120cm in front of the device, the 3D imaging device starts to work and can eventually obtain the 3D depth information of the face in front. Among them, the structured light projection module 100 includes a laser vcsel array light source 10, a collimating lens 20 and a diffractive optical element DOE 30.

[0038] like Figure 2 The polarization-state controllable structured light projection module 100 shown mainly includes three parts: a laser VCSEL array light source 10b, a collimating lens 20, and a diffractive optical element DOE 30, which are arranged in order from left to right in space.

[0039] The light-emitting point array 1001 of the laser vcsel array light source 10b is distributed and arranged according to a certain random pattern rule, and the entire light-emitting point array 1001 is called a pattern. Figure 3 As shown in the top view. Figure 4 The longitudinal structure of the conventional laser vcsel array light source 10a is N-electrode layer 101, substrate layer 102, N-type DBR layer 103, active layer 104, P-type DBR layer 105 and P-electrode layer 106 from bottom to top, wherein the P-electrode layer 106 is etched with a plurality of separate holes using etching technology to form the above-mentioned light-emitting point array 1001. Figure 5 As shown, the light-emitting point array 1001 of this laser VCSEL array light source 10a has an uncontrollable polarization state of the emitted laser, that is, the polarization direction of the emitted light from each light-emitting point is inconsistent, and the arrows in the figure represent the polarization state. Figure 6 As shown, the laser VCSEL array light source 10b used in this embodiment has an additional layer in the longitudinal structure, called a high contrast grating (HCG) layer 107, which is located above the P electrode layer 106. The layer contains a plurality of separated circular sub-wavelength gratings 1071, as shown in FIG. Figure 7 As shown, the number is the same as the number of light-emitting points, and the size is the same as or slightly larger than the light-emitting hole of the light-emitting point, just covering the top of each light-emitting point. After the light emitted from each light-emitting point 1001 passes through the corresponding sub-wavelength grating microstructure 1071, the polarization direction of the light will become consistent with the grid direction of the sub-wavelength grating microstructure 1071, so the polarization state of all the emitted light will become consistent and can be controlled according to the different designs of the sub-wavelength grating microstructure 1071. Figure 8FIG. 1 is a schematic diagram of the polarization state of the output light that finally passes through the high contrast grating (HCG) layer 107 , where the arrows represent the polarization state.

[0040] The refractive index ratio between the high refractive index region and the low refractive index region of the sub-wavelength grating 1071 is very high, reaching more than 2. Preferably, the high refractive index is 3.59, the low refractive index is 1, and the ratio is 3.59. The period of the sub-wavelength grating is between 0 and λ, and varies with different system requirements, where λ is the emission wavelength of the laser VCSEL array light source. The emission wavelength of the laser VCSEL array light source 10b is in the infrared band, and the present invention preferably has a wavelength of 940nm, which is invisible infrared light. The sub-wavelength grating microstructure 1071 includes two types: sub-wavelength periodic type and sub-wavelength non-periodic type. The present invention preferably uses a sub-wavelength periodic type.

[0041] The emitted light of the laser vcsel array light source 10b is received by the subsequent collimating lens 20, which converges it and makes it emitted as parallel light, and this process does not change the polarization state of the light. The collimating lens 20 can be a single lens or a lens group including multiple lenses.

[0042] The outgoing light beam of the collimating lens 20 continues to propagate forward and passes through the diffractive optical element DOE 30. The diffractive optical element is designed so that the polarization state of the incident light is set to be consistent with the outgoing light of the laser vcsel array light source. Therefore, compared with the design in which the polarization state of the incident light is not consistent with the outgoing light of the vcsel array light source, the diffractive optical element finally manufactured according to the design can reduce its uniformity by more than 9%, the brightness of the zero-order pattern can be reduced by more than 0.4%, and the light energy utilization rate can be increased by more than 10%. The diffractive optical element DOE 30 copies the incident light beam into multiple pattern beams, and then diffuses them to form a multi-level pattern of spatial structured light. The beam pattern hits the object in front, forming a structured light spatial encoding effect on the object. The structured light projection module 100 in the ordinary structured light 3D imaging device has an unknown and inconsistent polarization state of the outgoing light from each light-emitting point of the laser vcsel array light source 10a. Therefore, when designing the diffraction optical element DOE30, the polarization state setting of the incident light cannot be consistent with the outgoing light of the vcsel array light source, that is, it cannot match the polarization state of the outgoing light from each light-emitting point of the laser vcsel array light source 10a, resulting in low light energy utilization, poor uniformity of the projected pattern light beam, and high brightness of the zero-order pattern light beam, which ultimately hinders the improvement of the 3D imaging performance of the entire device.

[0043] The design simulation comparison results based on this embodiment are as follows Fig. 9As shown, it can be seen that the performance of the design 2 based on this embodiment in terms of uniformity, zero-order brightness, and light energy utilization is significantly better than that of the design 1 of the traditional solution. The calculation formula for uniformity is as follows:

[0044]

[0045]

[0046]

[0047] Among them, MAX represents the highest light intensity among all the patterns, and MIN represents the lowest light intensity among all the patterns;

[0048] The above description is only an example of a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A structured light projection module with controllable polarization state, characterized in that: include: A laser VCSEL array light source, wherein a high-contrast grating layer is provided above the light-emitting surface of the laser VCSEL array light source, and the outgoing light of each light-emitting point has a consistent and controllable polarization state after passing through the high-contrast grating layer; A diffractive optical element, which matches the polarization state of the outgoing light and is used to replicate the outgoing light and diffuse it out; The high contrast grating layer comprises a plurality of sub-wavelength gratings corresponding to the number of the light-emitting points. After the light emitted from the light-emitting points passes through the sub-wavelength gratings, the polarization direction of the light becomes consistent with the grid direction of the sub-wavelength gratings.

2. The structured light projection module with controllable polarization state as claimed in claim 1, characterized in that: The laser vcsel array light source comprises an N-electrode layer, a substrate layer, an N-type DBR layer, an active layer, a P-type DBR layer, a P-electrode layer and a high-contrast grating layer arranged in sequence, and the P-electrode layer is etched with light holes to form the light-emitting points; The high contrast grating layer is located on the surface of the P-type DBR layer.

3. The structured light projection module with controllable polarization state as claimed in claim 1, characterized in that: It also includes a collimating lens, which receives the light beam emitted by the laser vcsel array light source and collimates it into parallel light to emit into the diffraction optical element.

4. The structured light projection module with controllable polarization state as claimed in claim 3, characterized in that: The collimating lens is a single lens or a lens group including multiple lenses.

5. The structured light projection module with controllable polarization state as claimed in claim 1, characterized in that: The matching refers to using the polarization state of the light emitted by the laser VCSEL array light source as a parameter for designing the diffractive optical element.

6. A 3D imaging device, characterized in that: include: The structured light projection module with controllable polarization state as described in any one of claims 1 to 5, used for projecting a structured light pattern onto a target; An image receiving module, used to obtain the structured light pattern; The processing module calculates the depth information according to the structured light pattern.

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