CN114217454B - Design and Implementation Method of Spatial Spectrum Modulation Device Based on Diffractive Optical Element - Google Patents

Abstract

The invention discloses a design and realization method of a space spectrum modulation device based on a diffractive optical element, and belongs to the field of optical devices. The method includes: processing a light suppression area on the base device of the diffractive optical element to obtain a spatial filter; determining the phase distribution of the diffractive optical element and converting it into structural parameters of each diffractive unit; The spatial filter is processed to obtain a spatial spectrum modulation device. In the present invention, a diffractive optical element with mature processing technology is used as the main light field modulation device; and before the diffractive optical element is processed, a piece of opaque or gradient transmission with specific design parameters is processed in the center of its base device through a coating process. The area of distribution characteristics enables the spatial spectrum modulation device proposed in the present invention to have the capability of complex modulation of the frequency-domain light field, and at the same time take into account the advantages of customizability and zero power consumption.

Description

Design and Implementation Method of Spatial Spectrum Modulation Device Based on Diffractive Optical Element

technical field

The invention belongs to the field of optical devices, and more particularly, relates to a design and implementation method of a spatial spectrum modulation device based on a diffractive optical element.

Background technique

Spatial spectrum modulation devices are used to modulate the spatial spectrum of light. By modulating the spatial spectrum, the properties of an optical system can be easily and accurately analyzed and modulated, and have been widely used in imaging and optical analog computing.

Existing spatial spectrum modulation devices mainly include spatial light modulators, traditional optical devices, and emerging integrated optical components such as metasurfaces.

The most common spatial light modulators are liquid crystal spatial light modulators and digital micromirror arrays. This type of device can usually control the distribution and properties of the modulation unit array on its device through a computer, so as to realize the phase of the frequency domain light field. or amplitude modulation, which can achieve a flexible modulation effect in a very convenient and efficient way, but the biggest problem is that the current type of devices are all electronically controlled active devices, and their energy consumption cannot be ignored. Limited to industrial processing capabilities, its pixel units tend to have larger sizes (for the visible light band, their pixel units can often reach the order of ten times the wavelength), which makes their modulation capabilities, device size, etc. subject to greater constraints. limit.

Traditional optical devices are mainly fixed devices. The main problem is that it is difficult to flexibly adjust and change according to the needs. At the same time, its structure and working characteristics make the volume of the system using such devices very large.

Metasurfaces are a new type of emerging planar optical devices with ultra-high integration in recent years. Compared with spatial light modulators and traditional optical devices, their design flexibility is extremely high and they have a higher degree of modulation freedom. It is difficult to design, and at the same time its processing technology is difficult, the cost is high, and it is difficult to achieve large-scale practical application.

At the same time, due to the amplitude and phase characteristics of the optical field, the existing spatial spectrum modulation devices often modulate a single amplitude or phase, and it is difficult to perform complex modulation of the optical field at the same time (modulate the amplitude and phase at the same time), although it can be Through optical design, various modulation devices are combined to realize the complex modulation function to a certain extent, but this will increase the complexity of the entire optical system and greatly reduce the final efficiency. The most important thing is that this method has a low degree of modulation freedom. It is difficult to achieve some more complex modulation requirements, which also limits the application of current spatial spectrum modulation devices in fields such as optical computing that require high modulation complexity and flexibility.

SUMMARY OF THE INVENTION

In view of the defects and improvement requirements of the prior art, the present invention provides a design and implementation method of a spatial spectrum modulation device based on diffractive optical elements, and takes the realization of optical edge detection as an implementation example, provides a spatial spectrum modulation device and The edge detection device aims to solve the problems of flexibility, high efficiency, low energy consumption or even zero energy consumption of existing spatial spectrum modulation devices, as well as the design difficulties and high processing costs of new optical components represented by metasurfaces.

In order to achieve the above object, in the first aspect, the present invention provides a design and implementation method of a spatial spectrum modulation device based on a diffractive optical element, comprising: processing a light suppression area on the base device of the diffractive optical element to obtain a spatial filter. determining the phase distribution of the diffractive optical element and converting it into the structural parameters of each diffractive unit; processing the spatial filter according to the structural parameters of each diffractive unit to obtain a spatial spectrum modulation device.

Further, the light suppression area is an opaque area or an area where the light transmittance gradually increases radially from the center to the periphery.

Further, the determining the phase distribution of the diffractive optical element includes: taking the phase distribution of the orbital angular momentum with a topological charge value of ±1 as the phase distribution of the diffractive optical element.

Further, the determining the phase distribution of the diffractive optical element includes: superimposing the phase distribution of the orbital angular momentum with a topological charge value of ±1 and the phase distribution having a focusing function, and using the superimposed phase distribution as the diffractive optical element. phase distribution.

In a second aspect, the present invention provides a spatial spectrum modulation device based on a diffractive optical element, obtained by using the method described in the first aspect.

In a third aspect, the present invention provides an edge detection device based on a diffractive optical element, comprising: a first lens, a spatial spectrum modulation device, and a second lens, wherein the spatial spectrum modulation device is located at the back focal plane of the first lens and the second lens. The front focal plane of two lenses; the first lens is used to transform the light field to be processed on the front focal plane of the first lens into the frequency domain space, and obtain the light field to be processed on the back focal plane of the first lens The spatial spectrum distribution of The light field distribution after edge detection is obtained.

In a fourth aspect, the present invention provides an edge detection device based on a diffractive optical element, comprising: a lens and a spatial spectrum modulation device, wherein the spatial spectrum modulation device is located on the back focal plane of the lens; the lens is used to The light field to be processed on the front focal plane of the lens is transformed into the frequency domain space, and the spatial spectrum distribution of the light field to be processed is obtained on the back focal plane of the lens; the spatial spectrum modulation device is used to modulate the spatial spectrum distribution, And the light field distribution after edge detection is obtained on the focal plane of the spatial spectrum modulation device.

In general, through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

(1) Compared with the existing spatial spectrum modulation device, the present invention uses a diffractive optical element with mature processing technology as the main light field modulation device; and before processing the diffractive optical element, it is processed on its base device by a coating process A region with a specific design distribution such as opaque or gradient light transmission, which works together with the phase distribution provided by the diffractive optical element, makes the final spatial spectrum modulation device capable of complex modulation of the light field. The spectral modulation device realized based on this scheme has a higher theoretical upper limit in terms of light field modulation;

(2) Compared with the traditional method of complex modulation of the light field, the present invention is less restricted in terms of specific design and implementation, and can theoretically achieve a variety of designed amplitude and phase distributions, while the final device integration is relatively low. High, to a certain extent, avoids the problems of bulky volume and low efficiency caused by cascading multiple optical elements for complex modulation;

(3) Compared with the existing spatial spectrum modulation device, the spatial spectrum modulation device proposed in the present invention takes into account the flexibility of electronically controlled active spatial light modulators such as liquid crystal spatial light modulators and the low cost of traditional optical components such as spiral phase plates. Features of power consumption or even zero power consumption;

(4) The device and system for optical edge detection proposed based on the present invention take advantage of the large phase degree of freedom of diffractive optical elements, and on the basis of modulation to generate a helical phase light field, superimpose an optical edge with a specific focal length. , Phase distribution with focusing ability. This focusing phase is equivalent to an ideal thin lens without any amplitude loss, which is completely equivalent in effect to the second Fourier lens of the optical 4f system, which performs the function of performing a two-dimensional Fourier transform on the light field. This makes the spatial spectrum modulation device of the present invention only need to work under the optical 3f system, which improves the disadvantage of poor integration of the optical 4f system to a certain extent;

(5) Based on the device and system for optical edge detection proposed by the present invention, compared with the solution of processing an opaque area in the center of the base device of the diffractive optical element, the present invention also proposes that the base of the diffractive optical element is The scheme of processing a region with radially increasing light transmittance from the center to the periphery of the device center, in this way, the amplitude distribution and phase distribution of the obtained spatial spectrum modulation device theoretically meet the requirements of the differential properties of the standard Fourier transform. The distribution of , is theoretically equivalent to the standard first-order optical differentiator, which makes the spatial spectrum modulation device capable of achieving the theoretical optimal effect obtained by differential calculation in edge detection;

(6) The edge detection device based on the diffractive optical element proposed in the present invention has much lower design difficulty and processing cost than the metasurface as a modulation device, and is more advantageous for practical applications. And the efficiency of edge detection devices based on diffractive optical elements can usually reach more than 90%, which is significantly higher than other optical edge detection schemes such as surface plasmon polaritons and spin Hall effect.

Description of drawings

FIG. 1 is a schematic flowchart of a method for designing and implementing a spatial spectrum modulation device based on a diffractive optical element according to Embodiment 1 of the present invention.

FIG. 2 is a schematic diagram of a helical phase field distribution with a topological charge value of 1 according to Embodiment 1 of the present invention.

FIG. 3 is a schematic flowchart of a method for designing and implementing a spatial spectrum modulation device based on a diffractive optical element according to Embodiment 2 of the present invention.

FIG. 4 is a schematic flowchart of a method for designing and implementing a spatial spectrum modulation device based on a diffractive optical element according to Embodiment 3 of the present invention.

5 is a schematic diagram of a phase field distribution after superimposing a focusing phase on a helical phase field with a topological charge value of 1 according to Embodiment 3 of the present invention.

FIG. 6 is a schematic diagram of the amplitude distribution of the high-pass helical phase device provided in Embodiment 3 of the present invention.

FIG. 7 is a schematic diagram of the phase distribution of the high-pass helical phase device provided in Embodiment 3 of the present invention.

8 is a schematic flowchart of a method for designing and implementing a spatial spectrum modulation device based on a diffractive optical element according to Embodiment 4 of the present invention.

FIG. 9 is a schematic diagram of the amplitude distribution of the first-order optical differentiator provided in Embodiment 4 of the present invention.

FIG. 10 is a schematic diagram of the phase distribution of the first-order optical differentiator provided in Embodiment 4 of the present invention.

11 is a schematic flowchart of a method for designing and implementing a spatial spectrum modulation device based on a diffractive optical element according to Embodiment 5 of the present invention.

FIG. 12 is a schematic structural diagram of an edge detection apparatus according to Embodiment 6 of the present invention.

FIG. 13 is a schematic structural diagram of an edge detection apparatus according to Embodiment 7 of the present invention.

FIG. 14 is an input image provided by Embodiment 8 of the present invention.

FIG. 15 is a schematic diagram of a simulation result provided by Embodiment 8 of the present invention.

FIG. 16 is an image to be detected provided by Embodiment 8 of the present invention.

FIG. 17 is a schematic diagram of an edge detection result according to Embodiment 8 of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, 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, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

In the present invention, the terms "first", "second" and the like (if any) in the present invention and the accompanying drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

Diffractive Optical Elements (DOE) are a class of ultra-light and ultra-thin optical devices designed based on optical diffraction effects, which can realize high-precision optical field modulation. Compared with helical phase plates and spatial light modulators, it has a high degree of design freedom, zero power consumption, and a small integration volume, which can be easily inserted into optical systems. Compared with metasurfaces, the design of diffractive optical elements and The processing difficulty is much lower than that of metasurfaces, and it has obvious advantages compared with metasurfaces in large-scale applications, and most devices based on diffractive optical elements are polarization-independent devices.

Example 1:

As shown in FIG. 1 , the present invention provides a method for designing and implementing a spatial spectrum modulation device based on a diffractive optical element, including:

S101, processing a light suppression area on the base device of the diffractive optical element to obtain a spatial filter;

In this embodiment, the substrate device may be a common silicon dioxide material substrate, an ITO conductive glass substrate and other conventional transparent substrates. The light suppression area can be an opaque area or a gradient light transmittance area. When an opaque or gradient light transmittance area is processed on the substrate through the coating process, due to the influence of the material, compared with the original transparent substrate, the light field is When passing through these areas, it will be limited to a certain extent, that is, the light transmittance of the processed part will be suppressed (the final suppression effect depends on the design goal), so it is called the suppression area, and the overall device will play a role in its effect. to the role of the spatial filter.

It should be noted that, according to the design goal, the light suppression area can be any shape, such as circle, square, hexagon, etc., among which, circle, as the most basic isotropic shape, can easily satisfy the modulation of isotropic devices requirements; it can also be processed anywhere on the device substrate. Preferably, in this embodiment, the circular opaque area is arranged at the center of the device substrate.

Exemplarily, when the spatial spectrum modulation device is used in the field of edge detection, its amplitude distribution requires that an opaque area or an area whose transmittance increases radially from the center to the periphery should be set in the center of the device substrate. This area is theoretically Any opaque material can be used for processing using a coating process. The size of this area depends on the actual size of the entire optical system in the application scenario. In principle, the larger the size of the dark area, the better the edge detection effect, but the device efficiency will be reduced. reduce.

After completing this step, the obtained device can be called a spatial filter according to its properties. Further, since its central light suppression region plays a role in suppressing low-frequency components in the frequency domain, high-frequency components can pass through normally. , so it can also be specifically called a high-pass filter.

S102, determine the phase distribution of the diffractive optical element, and convert it into the structural parameters of each diffractive unit;

In this embodiment, the phase distribution of the diffractive optical element is determined according to actual design requirements. For example, when the spatial spectrum modulation device is applied to the field of edge detection, taking this embodiment as an example, the diffractive element distribution of the diffractive optical element needs to be designed to generate Spiral phase light field; when the spatial spectrum modulation device is applied to off-axis imaging, the diffractive element distribution of the diffractive optical element needs to be designed to generate a phase light field with off-axis focusing ability; when the spatial spectrum modulation device is applied to multifocal imaging , it is necessary to design the diffractive element distribution of the diffractive optical element as a phase light field with multiple focus focusing capabilities; it should be noted that, according to the design features proposed by the present invention, the phase distribution of the diffractive optical element should be determined at this time. The transmittance distribution of the filter is combined, and the complex amplitude modulation capability brought by the combination is considered.

After the phase distribution of the diffractive optical element is determined, the phase distribution of the diffractive optical element is converted into the structural parameters of each diffractive element according to the actual processing requirements.

Illustratively, taking the diffractive element distribution of the diffractive optical element designed to generate a helical phase light field as an example, the phase distribution of the orbital angular momentum with a topological charge value of ±1 can be used as the phase distribution of the diffractive optical element.

的相位差（具有该性质的螺旋相 位分布恰好与拓扑荷值为±1的轨道角动量光束一致），该相位差会使得最终变换回空间域 的光场中，非边缘部分产生干涉相消，边缘部分由于存在振幅或相位梯度，频谱调制器所施 加的相位差不是严格的

，这导致了最终的干涉相消不完美，最终起到了强调边缘的效 果。拓扑荷值为±1的螺旋相位场分布图如图2所示。 Among them, the phase distribution form of the helical phase comes from the optical first-order radial Hilbert transform theory. When the frequency domain modulation function satisfies the distribution required by the theory, the phase distribution form of the spatial spectrum modulation device is exactly the topological charge value. is in the form of a helical phase of ±1. The diffractive optical element with helical phase further modulates the light field, so that any 2 points symmetrical about the radial in the frequency domain will have

(the helical phase distribution with this property is exactly the same as the orbital angular momentum beam with a topological charge value of ±1), the phase difference will make the light field finally transformed back into the spatial domain, the non-edge parts produce interference cancellation, The phase difference imposed by the spectral modulator is not strictly due to the presence of an amplitude or phase gradient at the edge

, which leads to imperfect interference cancellation, and finally has the effect of emphasizing the edges. Figure 2 shows the helical phase field distribution with a topological charge of ±1.

S103: Process the spatial filter according to the structural parameters of each diffraction unit to obtain a spatial spectrum modulation device.

In this embodiment, the diffractive optical element is directly processed by the grayscale exposure technique. This technology only needs a grayscale image of a specific distribution to process an array of diffractive cell structures. Compared with steps such as etching in a traditional lithography process, the grayscale exposure technology has higher flexibility and efficiency.

Embodiment 2:

As shown in FIG. 3 , the present invention provides a method for designing and implementing a spatial spectrum modulation device based on a diffractive optical element, including:

S201, processing an opaque area on the base device of the diffractive optical element to obtain a spatial filter;

S202, using the phase distribution of the orbital angular momentum with the topological charge value of ±1 as the phase distribution of the diffractive optical element; and converting the phase distribution of the diffractive optical element into the structural parameters of each diffractive unit;

S203: Process the spatial filter according to the structural parameters of each diffraction unit to obtain a spatial spectrum modulation device.

Based on this embodiment, the obtained spatial spectrum modulation device may be called a high-pass spiral spatial spectrum modulation device according to its structural characteristics and properties.

Embodiment three:

As shown in FIG. 4 , the present invention provides a method for designing and implementing a spatial spectrum modulation device based on a diffractive optical element, including:

S301, processing an opaque area on the base device of the diffractive optical element to obtain a spatial filter;

S302, superimpose the phase distribution of the orbital angular momentum with the topological charge value of ±1 and the phase distribution with the focusing function, and use the superimposed phase distribution as the phase distribution of the diffractive optical element; and convert the phase distribution of the diffractive optical element is the structural parameter of each diffraction unit;

S303: Process the spatial filter according to the structural parameters of each diffraction unit to obtain a spatial spectrum modulation device.

The difference between this embodiment and the second embodiment is that the device phase distribution of the diffractive optical element in this embodiment is based on modulation to generate a helical phase light field, and a phase distribution with a specific focal length and focusing ability is superimposed. This focusing phase is equivalent to an ideal thin lens without any amplitude loss, which is completely equivalent in effect to the second Fourier lens of the optical 4f system, which performs the function of performing a two-dimensional Fourier transform on the light field. Figure 5 shows the phase field distribution after superimposing the focusing phase on the helical phase field with a topological charge of ±1.

，则在透镜焦距面上，得到输出 场分布为

，其中x、y代表空间 位置坐标，R表示系统通光口径的半径值，

表示圆形函数，描述无穷大不透明屏上 半径为R的圆孔的透过率，此处取半径为R的圆孔的透过率为1，表示无任何光强损失，f表示 光波的频率，

表示光波的波长，i表示虚数单位，k表示空间波矢，

和v分别表示光场的 二维空间频率分量，x和y分别表示光场的二维空间位置坐标。标准光学4f系统在上述情况 下得到的输出场分布为

，可以 看到二者分布只有一个相位项的差别，因此这不会影响最终光场的强度分布特点。 The equivalence and effectiveness of the superimposed focusing phase are specifically described below in conjunction with the calculation formula. According to the ideal lens imaging formula, this design method is equivalent to placing an ideal thin lens close to the spatial spectrum modulation device, and the light field distribution just after being modulated by the spatial spectrum modulation device is written as

, then on the lens focal length plane, the output field distribution is obtained as

, where x and y represent the spatial position coordinates, R represents the radius value of the system's clear aperture,

Represents a circular function, describing the transmittance of a circular hole with a radius of R on an infinite opaque screen, where the transmittance of a circular hole with a radius of R is taken as 1, indicating that there is no loss of light intensity, f represents the frequency of the light wave,

represents the wavelength of the light wave, i represents the imaginary unit, k represents the space wave vector,

and v represent the two-dimensional spatial frequency components of the light field, respectively, and x and y represent the two-dimensional spatial position coordinates of the light field, respectively. The output field distribution obtained for the standard optical 4f system in the above case is

, it can be seen that the difference between the two distributions is only one phase term, so this will not affect the intensity distribution characteristics of the final light field.

Based on this embodiment, after completing this step, the final spatial spectrum modulation device obtained can be called a high-pass helical spatial spectrum modulation device with focusing ability according to its structural characteristics and properties, and the schematic diagram of its amplitude distribution and phase distribution is shown in the figure 6 and Figure 7. It should be noted that the scale data in FIG. 6 and FIG. 7 are only data set for example, and do not represent the actual size of the device proposed by the present invention in a real situation, and the actual size can be designed as required.

Embodiment four:

As shown in FIG. 8 , the present invention provides a method for designing and implementing a spatial spectrum modulation device based on a diffractive optical element, including:

S401, processing a gradient light transmission area on the base device of the diffractive optical element to obtain a spatial filter;

In this embodiment, the substrate device may be a common silicon dioxide material substrate, an ITO conductive glass substrate and other conventional transparent substrates. The gradient light transmittance area can be radial gradient (transmittance increases or decreases in the radial direction from the center to the periphery), linear gradient (linear gradient transmittance in any direction), and the specific distribution needs to be determined by the actual application target. In this embodiment, the goal is to realize a first-order optical differentiator for optical edge detection. Therefore, preferably, according to the device distribution characteristics required by the differential properties of the first-order Fourier transform, the transmittance from the center to the periphery is adopted. The distribution with the radial gradient increasing is used as the device base distribution (the center of the gradient region described in this embodiment is the center of the overall device).

，i表示虚 数单位，

表示频率。空间域函数

的微分的傅里叶变换就等价于

的傅里叶变换 在频域中与频域调制函数

相乘，频域调制函数即为本实施例中所需要构造的器 件能够提供的调制函数。由于计算目标是实现二维空间上，各向同性的微分计算，因此参考 光学径向希尔伯特变换的思想，沿着频谱面径向方向对每一条直径应用一阶微分调制函 数，这可以看作是无限个一阶微分调制函数的旋转、叠加，所得到的二维，最终得到的振幅 和相位分布分别为图9和图10所示。 In the following, the reasons for selecting the radial gradient of light transmittance to increase the distribution will be explained in combination with the specific calculation formula. From the differential properties of the first-order Fourier transform formula, it can be known that,

, i represents the imaginary unit,

Indicates frequency. space domain function

The Fourier transform of the differential is equivalent to

The Fourier transform in the frequency domain with the frequency domain modulation function

Multiplying, the frequency domain modulation function is the modulation function that can be provided by the device to be constructed in this embodiment. Since the calculation goal is to achieve isotropic differential calculation in two-dimensional space, referring to the idea of optical radial Hilbert transform, apply a first-order differential modulation function to each diameter along the radial direction of the spectrum surface, which can Considered as the rotation and superposition of infinite first-order differential modulation functions, the obtained two-dimensional, and finally obtained amplitude and phase distributions are shown in Figure 9 and Figure 10, respectively.

S402, use the phase distribution of the orbital angular momentum with a topological charge value of ±1 as the phase distribution of the diffractive optical element; and convert the phase distribution of the diffractive optical element into the structural parameters of each diffractive unit;

S403: Process the spatial filter according to the structural parameters of each diffraction unit to obtain a spatial spectrum modulation device.

The difference between this embodiment and the second embodiment is that in this embodiment, a region where the light transmittance gradually increases radially from the center to the periphery is processed in the center of the base device of the diffractive optical element. The device obtained in this embodiment is compared with In the second embodiment, the amplitude distribution required by the differential property of the standard Fourier transform is theoretically satisfied, and in the application of edge detection, the most ideal edge detection effect can theoretically be obtained.

Embodiment 5:

As shown in FIG. 11 , the present invention provides a method for designing and implementing a spatial spectrum modulation device based on a diffractive optical element, including:

S501, processing a gradient light transmission area on the base device of the diffractive optical element to obtain a spatial filter;

In this embodiment, the gradient light transmittance region is preferably a region in which the light transmittance radially increases gradually from the center to the periphery.

S502, superimpose the phase distribution of the orbital angular momentum with the topological charge value of ±1 and the phase distribution with the focusing function, and use the superimposed phase distribution as the phase distribution of the diffractive optical element; and convert the phase distribution of the diffractive optical element is the structural parameter of each diffraction unit;

S503, the spatial filter is processed according to the structural parameters of each diffraction unit to obtain a spatial spectrum modulation device.

The difference between this embodiment and the fourth embodiment is that the device phase distribution of the diffractive optical element in this embodiment is based on modulation to generate a helical phase light field, and a phase distribution with a specific focal length and focusing ability is superimposed. This focusing phase is equivalent to an ideal thin lens without any amplitude loss, which is completely equivalent in effect to the second Fourier lens of the optical 4f system, which performs the function of performing a two-dimensional Fourier transform on the light field.

Based on this embodiment, the obtained spatial spectrum modulation device is also called a first-order optical differentiator, and the schematic diagrams of its amplitude distribution and phase distribution are shown in FIG. 9 and FIG. 10 .

Embodiment 6:

As shown in FIG. 12 , the present invention provides an edge detection device based on a diffractive optical element, comprising: a first lens, a spatial spectrum modulation device and a second lens, the spatial spectrum modulation device is located at the back focal plane of the first lens and the front focal plane of the second lens; the first lens is used to transform the light field to be processed on the front focal plane of the first lens into the frequency domain space, and obtain the to-be-processed light field on the back focal plane of the first lens The spatial spectrum distribution of the light field; the spatial spectrum modulation device is used to modulate the spatial spectrum distribution; the second lens is used to convert the modulated spatial spectrum distribution to the spatial domain, and is used after the second lens. The light field distribution after edge detection is obtained on the focal plane.

In this embodiment, the light field with the target characteristic distribution enters from the input surface, then passes through the first lens, the spatial spectrum modulation device and the second lens in sequence, and finally presents the light field distribution after edge detection on the observation surface. The focusing phase of the spatial spectrum modulation device can be designed as different focal lengths according to actual needs, and the relationship between the focal length of the focusing phase and the focal length of the lens will affect the size of the final actual image.

It should be noted that the spatial spectrum modulation device in this embodiment is obtained by using the method of the second embodiment or the fourth embodiment.

Embodiment 7:

As shown in FIG. 13 , the present invention provides an edge detection device based on diffractive optical elements, comprising: a lens and a spatial spectrum modulation device, the spatial spectrum modulation device is located on the back focal plane of the lens; the lens is used to The light field to be processed located on the front focal plane of the lens is transformed into the frequency domain space, and the spatial spectrum distribution of the light field to be processed is obtained on the back focal plane of the lens; the spatial spectrum modulation device is used for performing the spatial spectrum distribution. modulation and obtain the light field distribution after edge detection at the focal plane of the spatial spectrum modulation device.

In this embodiment, the light field with the target characteristic distribution enters from the input surface, then passes through the lens and the spatial spectrum modulation device in sequence, and finally presents the light field distribution after edge detection on the observation surface. The focusing phase of the spatial spectrum modulation device can be designed as different focal lengths according to actual needs, and the relationship between the focal length of the focusing phase and the focal length of the lens will affect the size of the final actual image.

It should be noted that, the spatial spectrum modulation device in this embodiment is obtained by using the method of Embodiment 3 or Embodiment 5. The phase distribution of the optical filter in this embodiment is based on the modulation to generate a helical phase light field, and a phase distribution with a specific focal length and focusing ability is superimposed, which plays the role of performing a two-dimensional Fourier transform on the light field. function, therefore, the light field distribution after edge detection can be obtained directly at the focal plane of the spatial spectrum modulation device, without the need for a second lens.

Embodiment 8:

In this embodiment, a suitable size value of the central dark area of the high-pass helical phase device is selected based on the first-order optical differentiator through simulation. The simulation parameters are: the working wavelength is 532 nm, the size of the calculation matrix is 5000×5000, the size of a single square pixel is 2 microns, the focal length of the Fourier lens is 20000 microns, and the focal length provided by the focusing phase superimposed on the spatial spectrum modulation device is 40000 microns , the entire circular aperture of the system is 5000 microns, and the diffraction propagation algorithm is the angular spectrum method.

First, construct the high-pass helical spatial spectrum modulation device with the amplitude and phase distribution shown in Fig. 6 and Fig. 7 .

It should be noted that the device superimposes the phase with focusing ability on the basis of the modulation phase.

Then the first-order optical differentiator of the amplitude and phase distribution shown in Figure 9 and Figure 10 is constructed. The principle of the device comes from the differential properties of the Fourier transform and the idea of the radial Hilbert transform. The device is constructed on the amplitude In the form of radially increasing light transmittance from the center to the periphery, its phase is the same as the phase distribution of orbital angular momentum with a topological charge value of ±1 (only the distribution characteristics are the same).

It should be noted that the device superimposes the phase with focusing ability on the basis of the modulation phase.

It should be noted that the theory of Fourier transform requires a distribution on an infinite plane, but in the specific implementation process, limited by factors such as the device aperture, compared with the theoretical distribution, the specific distribution can only be an approximate distribution, However, this does not affect the essential characteristics and capabilities of the distribution, and the final modulation effect can still approach the theoretical optimal effect.

It should be noted that the phase distribution of these two types of devices is the modulation phase superimposed on the focusing phase. Compared with the standard optical 4f system, the final calculation result of this device has one more coefficient on the phase term, but this coefficient does not affect the final result. Light intensity distribution, it can still be considered that the final operation result is the result of the differential operation.

It should be noted that in the simulation, the geometric dimensions of the high-pass helical spatial spectrum modulation device and the first-order optical differentiator and the equivalent focal length of the focusing phase are exactly the same, and only the dark area size of the high-pass helical phase device is a variable value.

Then, using the image shown in FIG. 14 as the simulation input, the sharpness index is calculated for the simulation result. For the high-pass helical phase device, simulations were performed with different central dark area size values, and all simulation results were plotted on the curves shown in Figure 15. For the first-order optical differentiator, when the geometric size is fixed, all its parameters are fixed, so there is only one set of simulation parameters, which is drawn in the form of dotted lines in Figure 15. It can be seen that under the current simulation parameters, when the high-pass helical phase When the radius of the central dark area of the device is about 160um, its sharpness index is comparable to that of the first-order optical differentiator, but its realization difficulty is much lower than that of the first-order optical differentiator.

FIG. 16 is a picture with the word H, and the edge detection result obtained after modulation by the high-pass helical phase device proposed in the present invention is shown in FIG. 17 .

Since the invention has the characteristics of simplicity, high efficiency, few restrictions, mature processing technology and low cost, it can be used as a front-end processing component of a vision system for large-scale practical application.

It is easily understood by those skilled in the art that the above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (7)

1. a design and realization method based on the spatial spectrum modulation device of diffractive optical element, is characterized in that, comprises: A light suppression area is processed on the base device of the diffractive optical element to obtain a spatial filter with amplitude modulation capability; Determine the phase distribution of the diffractive optical element and convert it into the structural parameters of each diffractive element; The spatial filter is processed according to the structural parameters of each diffraction unit to obtain a spatial spectrum modulation device with complex modulation capability. 2. the design and realization method of the spatial spectrum modulation device based on diffractive optical element according to claim 1, it is characterized in that, described light suppression area is opaque area or from center to surrounding light transmittance radially gradually increasing. large area. 3. The design and implementation method of a diffractive optical element-based spatial spectrum modulation device according to claim 2, wherein the determining the phase distribution of the diffractive optical element comprises: The phase distribution of the orbital angular momentum with a topological charge value of ±1 was taken as the phase distribution of the diffractive optical element. 4. The design and implementation method of a diffractive optical element-based spatial spectrum modulation device according to claim 2, wherein the determining the phase distribution of the diffractive optical element comprises: The phase distribution of orbital angular momentum with a topological charge value of ±1 is superimposed with the phase distribution with focusing function, and the superimposed phase distribution is used as the phase distribution of the diffractive optical element. 5 . A spatial spectrum modulation device based on a diffractive optical element, characterized in that, it is obtained by the method according to any one of claims 1 to 4 . 6. An edge detection device based on a diffractive optical element, characterized in that it comprises: a first lens, a spatial spectrum modulation device and a second lens obtained by the method as claimed in claim 3, wherein the spatial spectrum modulation device is located in the the back focal plane of the first lens and the front focal plane of the second lens; The first lens is used to transform the light field to be processed on the front focal plane of the first lens into a frequency domain space, and obtain the spatial spectrum distribution of the light field to be processed on the back focal plane of the first lens; The spatial spectrum modulation device is used for modulating the spatial spectrum distribution; The second lens is used to convert the modulated spatial spectrum distribution to the spatial domain, and obtain the light field distribution after edge detection on the back focal plane of the second lens. 7. An edge detection device based on a diffractive optical element, comprising: a lens and a spatial spectrum modulation device obtained by the method as claimed in claim 4, the spatial spectrum modulation device being located on the back focal plane of the lens ; The lens is used to transform the light field to be processed on the front focal plane of the lens into a frequency domain space, and obtain the spatial spectrum distribution of the light field to be processed on the back focal plane of the lens; The spatial spectrum modulation device is used to modulate the spatial spectrum distribution, and obtain the light field distribution after edge detection on the focal plane of the spatial spectrum modulation device.

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