Preparation method of two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity

Abstract

The present invention discloses a method for fabricating a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity. The method comprises optimizing the binary phase difference #imgabs0# and the spatial modulation coordinates of the phase change points based on a minimized cost function. Based on the optimized binary phase difference #imgabs1# and the spatial modulation coordinates of the phase change points, the diffraction grating structural parameters and etching depth are obtained, and a photolithography mask is generated. A substrate is micro-nano-machined based on the photolithography mask to obtain a two-dimensional beam-splitting diffraction grating element. By optimizing the binary phase difference and the spatial modulation coordinates of the phase change points, the present invention achieves control over the intensity of specific diffraction orders. Furthermore, by varying the machining etching depth, the intensity of the zero-order diffraction order is controlled, thereby varying the diffraction lattice pattern. This method overcomes the problem of excessive zero-order diffraction order intensity in practical applications of Dammann gratings. Furthermore, the method allows for the construction of a uniform lattice distribution with equal intensity as required, further expanding its application in multiple fields.

Description

Technical Field

[0001] The invention belongs to the technical field of two-dimensional beam-splitting diffraction grating preparation, and in particular relates to a method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity. Background Art

[0002] An optical array generator is a device that splits an incoming laser beam into an array of outgoing beams with a specific power distribution. Among various optical array generators, a Dammann grating achieves a laser far-field multi-level spectral array of equal intensity by modulating the spatial coordinates of binary optical phase change points.

[0003] As early as the 1970s, Dammann et al. proposed the concept of Dammann grating in the process of studying multiple image replication, and introduced large-scale integrated circuit technology into the field of optics for the first time, which laid the foundation for the development of micro-nano optics.

[0004] Dammann gratings efficiently convert incident monochromatic light into a lattice of uniform intensity distribution in the far field, exhibiting advantages such as simple design, mature manufacturing technology, and the absence of precise registration. In recent years, they have attracted widespread attention due to their enormous potential in applications such as facial recognition, 3D imaging, structured light projection, optical communications and computing, and VR (virtual reality) / AR (augmented reality).

[0005] The traditional Dammann grating is a binary phase (0, π) diffraction grating. During the actual processing, due to the unavoidable process errors introduced by micro-nano processing links such as etching and development, the intensity of the 0th diffraction order at the center of the lattice will be too high, and the uniformity of the diffraction spot will drop sharply, which greatly limits the application of Dammann grating in structured light, three-dimensional imaging, micro-nano optics and other fields. Summary of the Invention

[0006] In view of this, the main object of the present invention is to provide a method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity.

[0007] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] An embodiment of the present invention provides a method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity, the method comprising:

[0009] Optimize the binary phase difference value according to the minimized cost function and the spatial modulation coordinates of the phase change point;

[0010] The binary phase difference value obtained by the optimization As well as the spatial modulation coordinates of the phase change point, the diffraction grating structure parameters and etching depth are obtained, and a photolithography mask is generated;

[0011] The substrate is micro-nano processed according to the photolithography mask to obtain a two-dimensional beam splitting diffraction grating element.

[0012] In the above solution, the cost function is constructed based on the actual required diffraction order of the light spot array, combined with the diffraction efficiency and the diffraction order uniformity error.

[0013] In the above scheme, the actual required diffraction order of the spot array is constructed in combination with the diffraction efficiency and the diffraction order uniformity error. Specifically, taking the target minimized diffraction orders of ±p and ±q as an example, the cost function is expressed as: Among them I k′ To minimize the far-field light intensity distribution of the diffraction orders ±p and ±q, I k is the far-field intensity distribution of the kth diffraction order excluding the target minimized diffraction order, ranging from -n to n, excluding ±p and ±q, N is the sum of the diffraction orders excluding the target minimized diffraction order, and η is the target total diffraction efficiency.

[0014] In the above scheme, the binary phase difference value is optimized according to the minimized cost function And the spatial modulation coordinates of the phase change point, specifically: set the initial temperature T = TO, randomly generate the normalized phase change point spatial modulation coordinate initial solution x, O < x < 1 and the binary phase difference value initial solution Calculate the cost function Set the number of iterations L for each T value, let T = kT, O < k < 1, k represents the temperature drop rate; for the current solution x and Apply random perturbations to generate new solutions in its neighborhood: x_new=x+Δx, Calculate the cost function value of the new solution Calculate the increment of the objective function value If Δcost<0, accept x_new and As the new current solution, otherwise use the probability exp(-Δcost / kT) to determine whether to accept x_new and As the new current solution; at temperature T, repeat the perturbation and acceptance process L times; if the temperature T reaches the termination temperature level, terminate the algorithm and obtain the optimized binary phase difference value and the spatial modulation coordinates of the phase change point.

[0015] In the above scheme, the binary phase difference value obtained according to the optimization is And the spatial modulation coordinates of the phase change point, the diffraction grating structure parameters are obtained, specifically: the binary phase difference value obtained by optimization The spatial modulation coordinates of the phase change points determine a one-dimensional grating structure, and then the one-dimensional grating is expanded in an orthogonal direction to obtain a two-dimensional grating structure.

[0016] In the above scheme, the binary phase difference value obtained according to the optimization is And the spatial modulation coordinates of the phase change point, the etching depth is obtained, specifically: the etching depth s is expressed as: Where λ is the wavelength of the incident light and n1 is the refractive index of the substrate material.

[0017] In the above solution, after obtaining the diffraction grating structure parameters and etching depth, the method further includes changing the zero-order diffraction order intensity by adjusting the etching depth s, and determining the far-field spot array image according to the zero-order diffraction order intensity.

[0018] Compared with the existing technology, the present invention controls the intensity of specific diffraction orders by optimizing the binary phase difference and the spatial modulation coordinates of the phase change point, and controls the intensity of the zeroth diffraction order by changing the processing etching depth, thereby achieving a change in the diffraction lattice pattern. This overcomes the problem of excessive intensity of the zeroth diffraction order in the Dammann grating in practical applications, and can construct the required uniform lattice distribution of equal intensity according to actual needs, further expanding its application in multiple fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings described herein are used to further understand the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0020] Figure 1 A flow chart of a method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity is provided for an embodiment of the present invention;

[0021] Figure 2 A flow chart of a method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity is provided for Example 1 of the present invention;

[0022] Figure 3 A schematic structural diagram of a grating in a method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity is provided for embodiment 1 of the present invention;

[0023] Figure 4 A schematic structural diagram of a photolithography mask pattern in a method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity is provided for embodiment 1 of the present invention;

[0024] Figure 5 A schematic diagram of far-field spot array imaging in a method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity is provided for Example 1 of the present invention;

[0025] Figure 6 A graph showing the relationship between the zero-order diffraction efficiency of a diffraction grating and the etching depth in a method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity is provided for Example 1 of the present invention;

[0026] Figure 7 A schematic diagram of far-field spot array imaging with minimized diffraction efficiency of the zero-order diffraction grating in a method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity is provided for embodiment 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] The same or similar numbers in the drawings of this embodiment correspond to the same or similar parts; in the description of the present invention, it should be understood that the terms "upper", "lower", "left", "right", "inner", "outer", etc. indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0029] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, article, or device comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, article, or device comprising the element.

[0030] The embodiment of the present invention provides a method for preparing a two-dimensional beam splitting diffraction grating with adjustable zero-order light intensity, such as Figure 1 As shown, the method includes:

[0031] S11: Optimize the binary phase difference value according to the minimized cost function and the spatial modulation coordinates of the phase change point;

[0032] Specifically, a computer iterative optimization algorithm (including but not limited to iterative optimization algorithms such as simulated annealing and gradient descent) can be used to minimize the cost function.

[0033] The cost function is constructed based on the actual required diffraction order of the light spot array, combined with the diffraction efficiency and the diffraction order uniformity error.

[0034] Taking the target minimization of diffraction orders of ±p and ±q as an example, the cost function is expressed as: Among them I k′ To minimize the far-field light intensity distribution of the diffraction orders ±p and ±q, I k is the far-field intensity distribution of the kth diffraction order excluding the target minimized diffraction order, ranging from -n to n, excluding ±p and ±q, N is the sum of the diffraction orders excluding the target minimized diffraction order, and η is the target total diffraction efficiency.

[0035] The binary phase difference value is optimized according to the minimized cost function And the spatial modulation coordinates of the phase change point, specifically: set the initial temperature T = TO, randomly generate the normalized phase change point spatial modulation coordinate initial solution x, 0 < x < 1 and the binary phase difference value initial solution Calculate the cost function Set the number of iterations L for each T value, let T = kT, 0 < k < 1, k represents the temperature drop rate; for the current solution x and Apply random perturbations to generate new solutions in its neighborhood: x_new=x+Δx, Calculate the cost function value of the new solution Calculate the increment of the objective function value If Δcost<O, accept x_new and As the new current solution, otherwise use the probability exp(-Δcost / kT) to determine whether to accept x_new and As the new current solution; at temperature T, repeat the perturbation and acceptance process L times; if the temperature T reaches the termination temperature level, terminate the algorithm and obtain the optimized binary phase difference value and the spatial modulation coordinates of the phase change point.

[0036] S12: Binary phase difference value obtained according to the optimization As well as the spatial modulation coordinates of the phase change point, the diffraction grating structure parameters and etching depth are obtained, and a photolithography mask is generated;

[0037] Specifically, the binary phase difference value obtained by optimization is The spatial modulation coordinates of the phase change points determine a one-dimensional grating structure, and then the one-dimensional grating is expanded in an orthogonal direction to obtain a two-dimensional grating structure.

[0038] The etching depth s is expressed as: Where λ is the wavelength of the incident light and n1 is the refractive index of the substrate material.

[0039] S13: performing micro-nano processing on the substrate according to the photolithography mask to obtain a two-dimensional beam splitting diffraction grating element.

[0040] After obtaining the diffraction grating structure parameters and etching depth, the method further includes changing the zero-order diffraction order intensity by adjusting the etching depth s, and determining the far-field light spot array image according to the zero-order diffraction order intensity.

[0041] By adjusting the etching depth s, the intensity of the zero-order diffraction level can be controlled, and thus the far-field diffraction lattice pattern can be changed without remaking and replacing the mask.

[0042] According to the basic theory of Fourier optics, by performing Fourier transform on the transmission function of the periodic binary phase grating, the light intensity distribution of each diffraction order of the binary phase grating can be obtained, and its expression is:

[0043]

[0044]

[0045] Where I0 is the intensity of the zero-order diffraction level, I k is the kth diffraction order intensity, {x i} is the normalized phase change point spatial modulation coordinate, p is x i The total number of

[0046] Example 1

[0047] Embodiment 1 of the present invention provides a method for preparing a two-dimensional beam splitting diffraction grating with adjustable zero-order light intensity, such as Figure 2 As shown, the method includes:

[0048] S21: Construct a cost function based on the actual required diffraction order of the spot array, combined with the diffraction efficiency and the diffraction order uniformity error.

[0049] S22: Minimize the cost function and optimize the binary phase difference value and the spatial modulation coordinates of the phase change point;

[0050] Specifically, a computer iterative optimization algorithm (including but not limited to iterative optimization algorithms such as simulated annealing and gradient descent) can be used to minimize the cost function.

[0051] Taking the target minimization diffraction order as ±p and ±q as an example, the cost function is expressed as: Among them I k′ To minimize the far-field light intensity distribution of the diffraction orders ±p and ±q, I kis the far-field intensity distribution of the kth diffraction order excluding the target minimized diffraction order, ranging from -n to n, excluding ±p and ±q, N is the sum of the diffraction orders excluding the target minimized diffraction order, and η is the target total diffraction efficiency.

[0052] Taking the simulated annealing algorithm as an example, the binary phase difference value is specifically explained As well as the optimization process of the spatial modulation coordinates of the phase change point, the optimization process of other iterative optimization algorithms is similar to this;

[0053] Step (2201) sets the initial temperature T = TO, randomly generates the initial solution x (0 < x < 1) of the normalized phase change point spatial modulation coordinate and the initial solution of the binary phase difference value Calculate the cost function

[0054] Step (2202) sets the number of iterations L for each T value, and sets T = kT (0 < k < 1, indicating the temperature drop rate);

[0055] Step (2203) is to calculate the current solution x and Apply random perturbations to generate new solutions in its neighborhood: x_new=x+Δx,

[0056] Step (2204) calculates the cost function value of the new solution Calculate the increment of the objective function value

[0057] Step (2205) If Δcost < 0, accept x_new and As the new current solution, otherwise use the probability exp(-Δcost / kT) to determine whether to accept x_new and as the new current solution;

[0058] Step (2206) repeats the perturbation and acceptance process L times at temperature T, i.e., executing steps (2203)-(2205);

[0059] Step (2207) determines whether the temperature T reaches the termination temperature level. If so, the algorithm is terminated to obtain the optimized binary phase difference value. and the spatial modulation coordinates of the phase change point, otherwise return to step (2202) and repeat the iterative process.

[0060] Taking the goal of minimizing the far-field light intensity of ±3 diffraction orders as an example, the spatial modulation coordinates of the normalized phase change point and the binary phase difference of a two-dimensional beamsplitting diffraction grating with adjustable zero-order light intensity are given.

[0061] Table 1 shows the spatial modulation coordinates and binary phase difference values of a normalized phase change point of a diffraction grating provided by an embodiment of the present invention.

[0062] Spatial modulation coordinates of the normalized phase change point 0，0.3387，0.5837，0.6719，0.7884，0.8930 Binary phase difference 0.80π

[0063] S23: Binary phase difference value obtained according to the optimization As well as the spatial modulation coordinates of the phase change point, the diffraction grating structure parameters and etching depth are obtained, and a photolithography mask is generated;

[0064] Specifically, if Figure 3 As shown, the binary phase difference value obtained by optimization is The spatial modulation coordinates of the phase change points determine a one-dimensional grating structure, and then the one-dimensional grating is expanded in an orthogonal direction to obtain a two-dimensional grating structure.

[0065] The etching depth s is expressed as: Where λ is the wavelength of the incident light and n1 is the refractive index of the substrate material.

[0066] S24: performing micro-nano processing on the substrate according to the photolithography mask to obtain a two-dimensional beam splitting diffraction grating element.

[0067] like Figure 4 As shown, a pattern of a single-period photolithography mask of a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity provided by an embodiment of the present invention is provided, wherein black represents the etched area and white represents the non-etched area. The number of two-dimensional grating periods can be determined based on the actual minimum line width of the photolithography process and the required far-field field of view angle.

[0068] After obtaining the diffraction grating structure parameters and etching depth, the method further includes changing the zero-order diffraction order intensity by adjusting the etching depth s, and determining the far-field light spot array image according to the zero-order diffraction order intensity.

[0069] like Figure 5 As shown, a schematic diagram of diffraction grating far-field spot array imaging provided by an embodiment of the present invention is provided. In this example, the far-field light intensity of ±3 diffraction orders is minimized. In other embodiments, the same effect can be achieved by minimizing the far-field light intensity of one or more other diffraction orders.

[0070] like Figure 6 As shown in FIG. 1 , a curve showing the relationship between the diffraction efficiency of the 0th diffraction order and the etching depth of a diffraction grating provided in an embodiment of the present invention is shown. For a traditional (0, π) binary phase difference Dammann grating, an etching depth error, whether positive or negative, will lead to an increase in the diffraction efficiency of the 0th diffraction order, which in turn leads to excessive 0th diffraction order light intensity at the center of the lattice and a sharp decrease in the uniformity of the diffraction spot. However, for the (0, 0.80π) binary phase difference Dammann grating optimized by this embodiment, an etching depth error will cause the diffraction efficiency of the 0th diffraction order to show both increasing and decreasing trends. This can improve the problem of excessive 0th diffraction order light intensity of the Dammann grating in practical applications according to actual needs.

[0071] In this embodiment, when the etching depth error reaches +40nm, the diffraction efficiency of the 0th order diffraction can be minimized, and the far-field spot array imaging schematic diagram is shown as follows: Figure 7 As shown, this embodiment can control the 0th order diffraction intensity by adjusting the etching depth, and thus can change the far-field diffraction lattice pattern without remaking and replacing the mask.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention.

Claims

1. A method for preparing a two-dimensional beam splitting diffraction grating with adjustable zero-order light intensity, characterized in that: The method includes: Optimize the initial solution of binary phase difference according to the minimized cost function and the spatial modulation coordinates of the phase change point; The binary phase difference value obtained by the optimization As well as the spatial modulation coordinates of the phase change point, the diffraction grating structure parameters and etching depth are obtained, and a photolithography mask is generated; Performing micro-nano processing on the substrate according to the photolithography mask to obtain a two-dimensional beam splitting diffraction grating element; The initial solution of the binary phase difference is optimized according to the minimized cost function And the spatial modulation coordinates of the phase change point, specifically: set the initial temperature T = T0, randomly generate the normalized phase change point spatial modulation coordinate initial solution x, 0 < x < 1 and the binary phase difference value initial solution Calculate the cost function Set the number of iterations L for each T value, let T = kT, 0 < k < 1, k represents the temperature drop rate; for the current solution x and Apply random perturbations to generate new solutions in its neighborhood: x_new=x+Δx, Calculate the cost function value of the new solution Calculate the increment of the objective function value If Δcost < 0, accept x_new and As the new current solution, otherwise use the probability exp(-Δcost / kT) to determine whether to accept x_new and As the new current solution; at temperature T, repeat the perturbation and acceptance process L times; if the temperature T reaches the termination temperature level, terminate the algorithm and obtain the optimized binary phase difference value and the spatial modulation coordinates of the phase change point; The cost function is constructed based on the actual required diffraction order of the spot array, combined with the diffraction efficiency and the diffraction order uniformity error; Taking the target minimization diffraction order as ±p and ±q as an example, the cost function is expressed as: Among them I k′ To minimize the far-field light intensity distribution of the diffraction orders ±p and ±q, I k is the far-field intensity distribution of the kth diffraction order excluding the target minimized diffraction order, ranging from -n to n, excluding ±p and ±q, N is the sum of the diffraction orders excluding the target minimized diffraction order, and η is the target total diffraction efficiency.

2. The method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity according to claim 1, characterized in that: The binary phase difference value obtained according to the optimization And the spatial modulation coordinates of the phase change point, the diffraction grating structure parameters are obtained, specifically: the binary phase difference value obtained by optimization The spatial modulation coordinates of the phase change points determine a one-dimensional grating structure, and then the one-dimensional grating is expanded in an orthogonal direction to obtain a two-dimensional grating structure.

3. The method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity according to claim 2, characterized in that: The binary phase difference value obtained according to the optimization And the spatial modulation coordinates of the phase change point, the etching depth is obtained, specifically: the etching depth s is expressed as: Where λ is the wavelength of the incident light and n1 is the refractive index of the substrate material.

4. The method for preparing a two-dimensional beam-splitting diffraction grating with adjustable zero-order light intensity according to claim 3, characterized in that: After obtaining the diffraction grating structure parameters and the etching depth, the method further includes changing the zero-order diffraction order intensity by adjusting the etching depth s, and determining the far-field light spot array image according to the zero-order diffraction order intensity.

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