Coded projection device with integrated metasurface of monolithic light source

Abstract

The monolithic light source integrated metasurface projection device disclosed in the present invention belongs to the field of micro-nano optics, optical detection and machine vision application technology. The present invention integrates the optimized and coded metasurface into a monolithic light source to minimize the number of devices and achieve high integration; through the integrated production of the monolithic metasurface and the light source, the complexity of processing and assembly is reduced, and the anti-vibration performance is improved. The projection pattern is generated by phase modulation of the metasurface, which solves the problem that the amount of pattern information depends on the number and arrangement of light sources in traditional technology, thereby improving the projection density of the projection device. The flexible light field control capability of the metasurface device is utilized to realize local pseudo-random point cloud or global pseudo-random point cloud pattern mode, expanding the diversity of projection modes. The use of a metasurface device based on geometric phase has the characteristics of broadband response insensitivity, which can effectively suppress the temperature drift effect of the laser, so that the projection pattern is not offset, and the stability of the projection device is enhanced.

Description

Technical Field

[0001] The present invention relates to a coding projection device of a monolithic light source integrated metasurface, belonging to the technical fields of micro-nano optics, optical detection and machine vision applications. Background Art

[0002] Projection devices are commonly used in active optical information acquisition technologies such as structured light and lidar to obtain information such as the reflectivity, three-dimensional shape, and speed of objects. They are widely used in machine vision, industrial inspection, unmanned driving, and consumer electronics. With the development of the application of projection devices at different spatial scales, the market has increasingly higher requirements for their miniaturization and versatility. Traditional projection devices are composed of laser light sources, collimating lens groups, and diffractive optical elements. The hardware structure of multiple separate components makes the system face a series of problems such as complex installation and adjustment, vibration sensitivity, and complicated processing. In terms of performance, projection technology is mostly determined by the arrangement of the light source array and the beam replication function of the diffractive optical element. The projection pattern is a regularly distributed point cloud array. Not only is the resolution of the spatial encoding limited, but the high-order diffraction generated by the diffractive optical element is prone to stray interference, reducing the signal-to-noise ratio of the projection pattern, limiting the high-precision and versatility development space of the system.

[0003] With the development of micro-nano optics, metasurfaces, as sub-wavelength planar optical elements, provide very promising technical prospects for the integration of traditional optical systems. At the same time, the flexible light field control capability of metasurfaces opens up great freedom for the design of optical systems. Based on the powerful advantage of overcoming the high-order diffraction of diffractive optical elements, it is expected to change the traditional system paradigm and develop versatile devices and equipment with strong applicability. Summary of the Invention

[0004] In order to solve the technical problems of high system complexity, low integration and limited applicability of projection patterns in related technologies, the present invention provides a projection device and a manufacturing method of a single-chip light source integrated metasurface, which integrates the optimized coded metasurface into the single-chip light source, and has the following advantages: (1) The projection pattern generation does not need to depend on the number and arrangement of light sources; (2) The integrated manufacturing reduces the complexity of processing and assembly and improves the anti-vibration performance; (3) It has the advantage of flexible light field control of the metasurface and can generate multi-mode point cloud projection patterns; (4) Based on the subwavelength size characteristics of the metasurface, the generated projection pattern is not out of focus when working at a long distance; (5) By utilizing the characteristics of the metasurface that is insensitive to broadband response, the metasurface integrated in the single-chip light source is not affected by the temperature drift effect, thereby enhancing the stability of the projection device.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The coded projection device with a monolithic light source integrated metasurface disclosed in the present invention is composed of a monolithic metasurface integrated with a laser light source. The monolithic metasurface is optimized using metasurface phase design and a holographic algorithm. The optimized coded metasurface is integrated into the monolithic light source, so that the projection pattern generation does not need to rely on the number and arrangement of light sources. Based on the subwavelength size characteristics of the metasurface, the generated projection pattern is not out of focus at long distances. In addition, the metasurface is used to flexibly control the light field to generate multi-mode point cloud projection patterns. The metasurface has the characteristic of being insensitive to broadband response, so the metasurface integrated into the monolithic light source is not affected by temperature drift effects, thereby enhancing the stability of the projection device.

[0007] Preferably, the monolithic metasurface and light source are manufactured in an integrated manner to reduce the complexity of processing and assembly and improve vibration resistance.

[0008] Preferably, the light source in the monolithic light source integration is a vertical cavity surface emitting laser, and the number is one.

[0009] Furthermore, the wavelength band of the light source in the monolithic light source integration includes visible light and infrared light.

[0010] Furthermore, phase design is a key step in the design of the metasurface, and its implementation method is as follows: the target pattern is a projected pseudo-random coding pattern, and the parameters are initialized according to the target pattern; the initial parameters are the pseudo-random coding pattern and the randomly distributed phase, and the amplitude and phase distribution of the metasurface plane are obtained after inverse Fourier transform IFFT. By modifying the amplitude of the metasurface plane to a uniformly distributed target area and an edge area with zero light intensity distribution, the iterative optimization of the metasurface plane and the target plane is performed until the iteration converges to obtain the optimized metasurface phase distribution.

[0011] The monolithic metasurface adopts a two-dimensional subwavelength microstructure.

[0012] Furthermore, the two-dimensional sub-wavelength microstructure is a rotation angle modulated unit structure based on a geometric phase principle or a characteristic size modulated unit structure based on a propagation phase principle, or a combination of the above two structures.

[0013] Furthermore, the two-dimensional sub-wavelength microstructure is in the shape of a nano-cylinder, a nano-square column or a hollow nano-cylinder, or a combination of the above structures.

[0014] Furthermore, the shape and size of the two-dimensional subwavelength microstructure are determined by rigorous coupled wave analysis or finite difference time domain method.

[0015] Furthermore, the material of the two-dimensional sub-wavelength microstructure comprises one or more combinations of gallium nitride, silicon nitride, titanium dioxide, and amorphous silicon;

[0016] Furthermore, the phase design includes a de-distortion design so that the projection pattern does not deform due to the diffraction angle.

[0017] Furthermore, the reproduced projection pattern is a local pseudo-random point cloud pattern or a global pseudo-random point cloud pattern.

[0018] Beneficial effects:

[0019] 1. The monolithic light source integrated metasurface projection device disclosed in the present invention minimizes the number of components and achieves high integration by integrating an optimized and coded metasurface into a monolithic light source. By integrating the monolithic metasurface and the light source into one piece, the complexity of processing and assembly is reduced, and the vibration resistance performance is improved.

[0020] 2. The single-chip light source integrated metasurface projection device disclosed in the present invention uses phase modulation of the metasurface to generate projection patterns. The generation of the projection pattern does not need to depend on the number and arrangement of light sources. The amount of information in the projection pattern depends on the number of pixels of the metasurface, which solves the problem in traditional technologies that the amount of pattern information depends on the number and arrangement of light sources. Therefore, it can significantly improve the projection density of the projection device.

[0021] 3. The single-chip light source integrated metasurface projection device disclosed in the present invention utilizes the flexible light field control capability of the metasurface device to break the regularly distributed point cloud array pattern mode in traditional technology, realize local pseudo-random point cloud or global pseudo-random point cloud pattern mode, expand the diversity of projection modes, and enhance the versatility of the device.

[0022] 4. The single-chip light source integrated metasurface projection device disclosed in the present invention adopts a metasurface device based on geometric phase, which has the characteristics of broadband response insensitivity, can effectively suppress the temperature drift effect of the laser, and can ensure that the phase modulation of the metasurface device remains unchanged when the laser works for a long time, so that the projection pattern has no offset, thereby enhancing the stability of the projection device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the monolithic light source integrated metasurface projection device provided in this example;

[0024] Figure 2 This is a schematic diagram of the working principle of the coding projection device provided in this example;

[0025] Figure 3 Schematic diagram of a top view of an optional metasurface structure unit provided in this example;

[0026] Figure 4 Schematic diagram of a top view of another optional metasurface structure unit provided in this example;

[0027] Figure 5 This is the phase design algorithm process provided by this example;

[0028] Figure 6 Schematic diagram of a global pseudo-random projection pattern of Example 1;

[0029] Figure 7 This is a schematic diagram of a local pseudo-random projection pattern in Example 2.

[0030] Among them: 101—single-chip metasurface, 102—single laser light source, 1011—propagation phase metasurface, 1012—geometric phase metasurface, 201—global pseudo-random pattern, 202—local pseudo-random projection pattern. DETAILED DESCRIPTION

[0031] In order to more clearly illustrate the purpose, technical solutions and advantages of the present invention, the implementation method of the invention is further described in detail below with reference to the accompanying drawings and examples.

[0032] like Figure 1 As shown, the monolithic light source integrated metasurface projection device disclosed in this embodiment includes a single laser light source 102 and a monolithic metasurface 101. The single laser light source 102 is a vertical cavity surface emitting laser, and the monolithic metasurface 101 is directly processed on the beam exit surface of the laser light source 102 using a semiconductor processing technique. A specific implementation method using amorphous silicon as the metasurface material includes the following steps:

[0033] 1) A 600 nm thick amorphous silicon film was deposited by plasma-enhanced chemical vapor deposition (PECVD). A polymethyl methacrylate (PMMA) resist was then spin-coated on the amorphous silicon film and baked on a hotplate at 170°C for 2 minutes to remove the solvent.

[0034] 2) The desired structures were fabricated using standard electron beam lithography, followed by development of the sample in a 1:3 MIBK:IPA solution and subsequent coating with a 20 nm thick chromium layer by electron beam evaporation;

[0035] 3) Complete the stripping process in hot acetone;

[0036] 4) Inductively coupled plasma reactive ion etching (ICP-RIE) is used to convert the desired structure from chromium to silicon, and finally a standard wet etching process is used to remove the remaining chromium mask.

[0037] The working principle of the single-chip light source integrated metasurface projection device to realize pattern projection disclosed in this embodiment is as follows: Figure 2 As shown. Based on the principle of Fourier computational holography, the light emitted from the projection device satisfies the Fourier transform in the Fourier domain. Therefore, the light intensities I1 and I2 on projection plane 1 and projection plane 2 satisfy

[0038]

[0039] Among them (x0,y0,z0) and (x d ,y d ,z d ) are the spatial coordinates that satisfy the projection transformation on projection plane 1 and projection plane 2 respectively. In the Fourier diffraction space, the pattern projection satisfies the projection transformation. At the same time, due to the subwavelength size of the metasurface, the range greater than 10 mm from the projection device all belongs to the Fourier diffraction space, ensuring that the image is not out of focus and has a longer working distance, which is impossible for a refractive optical system.

[0040] The schematic top views of the two optional metasurface structural units disclosed in this embodiment are as follows: Figure 3 and Figure 4 As shown, they are propagation phase metasurface 1011 and geometric phase metasurface 1012. The propagation phase metasurface represents a metasurface structural unit composed of different cross-sectional areas, and the geometric phase metasurface represents another optional metasurface type with the same structure but the rotation angle needs to be designed separately. Figure 3 and Figure 4 The schematic diagram includes basic shapes such as cylinders and square prisms. The specific design steps are as follows: Through rigorous coupled wave analysis, the length and width of the amorphous silicon antenna are scanned in 5-nanometer steps from 60 μm to half the wavelength of the light source. The materials involved include but are not limited to amorphous silicon. Based on the transmission efficiency and phase distribution, suitable metasurface structural units are selected as the design units of the propagation phase metasurface 1011. Structural dimensions with high anti-circular polarization transmittance and low co-circular polarization transmittance are selected as the design units of the geometric phase metasurface 1012.

[0041] The phase design algorithm process disclosed in this embodiment is as follows: Figure 5 As shown in the figure, phase design is a key step in metasurface design. The selected metasurface unit structure is arranged through phase design engineering. The phase design algorithm is an optimization algorithm based on the Gerchberg-Saxton (GS) algorithm. The initial parameters are a pseudo-random coding pattern, i.e., a reconstructed image of the Fourier hologram, and a randomly distributed phase. After an inverse Fourier transform (IFFT), the amplitude and phase distribution of the metasurface plane are obtained. By modifying the amplitude to a uniform distribution in the target area and a zero-intensity distribution in the edge area, the GS iterative algorithm is entered to obtain the final metasurface phase distribution.

[0042] The projection pattern of Example 1 disclosed in this embodiment is a global pseudo-random projection pattern 201, such as Figure 6 As shown. Phase calculation needs to be calculated according to the corresponding coding pattern. Figure 6The figure shows an optional global pseudo-random coding pattern. The design steps are as follows: first, a pseudo-random sequence is generated based on the principal variable polynomial, then it is converted into a pseudo-random matrix based on the idea of ​​block matrix, and the global uniqueness of the point cloud distribution is constrained.

[0043] The projection pattern of Example 2 disclosed in this embodiment is a local pseudo-random projection pattern 202, such as Figure 7 As shown in Figure 2, the local pseudo-random projection pattern is composed of an array distribution of the global pseudo-random pattern 201 and is an optional projection pattern. The physical implementation mechanism is that the phase design of the metasurface exhibits the periodic characteristics of the grating distribution. Multi-level diffraction patterns of the metasurface hologram can be designed to increase the field of view of the projection pattern.

[0044] In summary, this embodiment discloses a monolithic light source integrated metasurface coding projection device. While miniaturizing and integrating the device, the flexibility of the metasurface light field control opens up the freedom of coding pattern design, and the design of related algorithms based on Fourier holographic theory realizes highly adaptable and universal coding pattern projection. This will greatly expand the development of active optical information technology and take a solid step towards the practical application of the micro-nano industry. In addition, based on the characteristics of the metasurface such as the subwavelength size, the high-order diffraction introduced by the diffraction optical element is avoided; the geometric metasurface has the characteristics of broadband response insensitivity, so that the metasurface integrated in the monolithic light source is not affected by the temperature drift effect, thereby enhancing the stability of the projection device; combined with the characteristics of Fourier space holographic reproduction, the device has a long working distance and high image quality.

[0045] The above specific description further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A coded projection device with a monolithic light source integrated metasurface, characterized by: The system is composed of a monolithic metasurface integrated with a laser light source; the monolithic metasurface is optimized using metasurface phase design and holographic algorithms. The optimized encoded metasurface is integrated into the monolithic light source, so that the projection pattern generation does not depend on the number and arrangement of light sources. The subwavelength size characteristics of the metasurface ensure that the generated projection pattern is not out of focus even at long distances. In addition, the metasurface is used to flexibly control the light field to generate multi-mode point cloud projection patterns. By utilizing the broadband response insensitivity of metasurfaces, metasurfaces integrated into a single-chip light source are not affected by temperature drift, thus enhancing the stability of the projection device. Phase design is a key step in the metasurface design, and its implementation method is as follows: the target pattern is a projected pseudo-random coding pattern, and the parameters are initialized according to the target pattern; the initial parameters are the pseudo-random coding pattern and the randomly distributed phase. After inverse Fourier transform (IFFT), the amplitude and phase distribution of the metasurface plane are obtained. By modifying the amplitude of the metasurface plane to a uniformly distributed target area and an edge area with zero light intensity distribution, the iterative optimization of the metasurface plane and the target plane is performed until the iteration converges to obtain the optimized metasurface phase distribution.

2. The coded projection device with a monolithic light source integrated metasurface according to claim 1, characterized in that: The monolithic metasurface and light source are integrated to reduce the complexity of processing and assembly, and improve vibration resistance. The light source in the monolithic light source integration is a vertical cavity surface emitting laser, and the number is one.

3. The coded projection device with a monolithic light source integrated metasurface according to claim 1 or 2, characterized in that: The wavelength band of the light source in the monolithic light source integration includes visible light and infrared light.

4. The coded projection device with a monolithic light source integrated metasurface according to claim 1, characterized in that: The monolithic metasurface adopts a two-dimensional subwavelength microstructure.

5. The coded projection device with a monolithic light source integrated metasurface according to claim 4, characterized in that: The two-dimensional subwavelength microstructure is a rotation angle modulated unit structure based on the geometric phase principle or a characteristic size modulated unit structure based on the propagation phase principle, or a combination of the above two structures; The two-dimensional sub-wavelength microstructure is in the shape of a nano-cylinder, a nano-square column or a hollow nano-cylinder, or a combination of the above structures; The shape and size of the two-dimensional subwavelength microstructure are determined by rigorous coupled wave analysis or finite-difference time-domain method; The material of the two-dimensional sub-wavelength microstructure includes one or more combinations of gallium nitride, silicon nitride, titanium dioxide, and amorphous silicon.

6. The coded projection device with a monolithic light source integrated metasurface according to claim 1, characterized in that: The phase design includes a de-distortion design so that the projection pattern does not deform due to the diffraction angle.

7. The coded projection device with a monolithic light source integrated metasurface according to claim 1, characterized in that: The reconstructed projection pattern is a local pseudo-random point cloud pattern or a global pseudo-random point cloud pattern.

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