A two-phase constrained full-space light field modulation method and a diffractive optical imaging assembly

Abstract

The application relates to a dual-phase constrained full-space light field regulation method and a diffractive optical imaging assembly, and relates to the technical field of optical communication.The application comprises the following steps: constructing a light field propagation model, and obtaining an initial phase distribution of a diffractive optical element; based on the current phase distribution, calculating a one-time phase modulation light field of a transmission light path, obtaining a corresponding first reconstructed image, calculating a two-time phase modulation light field of a reflection light path, and obtaining a corresponding second reconstructed image; calculating a first light intensity error of the first reconstructed image and a first target image, and a second light intensity error of the second reconstructed image and a second target image; updating the phase distribution according to the first light intensity error and the second light intensity error, and repeatedly performing the steps of reconstructing an image, calculating a light intensity error and updating a phase distribution until a convergence condition is met, so as to obtain a target phase distribution of the diffractive optical element.The application realizes the joint optimization of transmission space and reflection space imaging functions, and can independently reconstruct different target images in the two spaces.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, specifically to a dual-phase-constrained full-space optical field modulation method and a diffractive optical imaging component. Background Technology

[0002] With the development of 5G / 6G communication technologies, free-space optical communication has become one of the key technologies for next-generation wireless communication due to its advantages such as high bandwidth, low latency, no interference, and high security. At the same time, the demand for full-space light field manipulation is increasing in fields such as augmented reality, structured light projection, optical anti-counterfeiting, and light field display. Existing diffractive optical elements can typically only achieve light field manipulation in a single space (transmission or reflection), making it difficult to simultaneously achieve independent imaging or pattern projection in both transmission and reflection spaces on the same element.

[0003] Previous studies have attempted to introduce phase modulation of different magnitudes in the transmission and reflection spaces by combining semi-transparent and semi-reflective films with diffractive optical elements, thereby enabling separate manipulation of the light fields in the two spaces. However, in existing methods, there is a strong phase coupling between the imaging functions of the transmission and reflection spaces, which is difficult to optimize independently, resulting in limited reconstructed image quality. Summary of the Invention

[0004] This application provides a dual-phase-constrained full-space light field manipulation method and a diffractive optical imaging component, which realizes the joint optimization of imaging functions in transmission space and reflection space, and can independently reconstruct images of different targets in the two spaces.

[0005] In a first aspect, embodiments of this application provide a method for controlling the entire optical field under dual-phase constraints, the method comprising: Construct a light field propagation model and obtain the initial phase distribution of the diffractive optical element; Based on the current phase distribution of the diffractive optical element, the one-time phase-modulated optical field of the transmitted optical path is calculated using the optical field propagation model, and the corresponding first reconstructed image is obtained; and the two-time phase-modulated optical field of the reflected optical path is calculated, and the corresponding second reconstructed image is obtained. Calculate the first light intensity error between the first reconstructed image and the first target image, and the second light intensity error between the second reconstructed image and the second target image; The phase distribution is updated based on the first light intensity error and the second light intensity error, and the process of reconstructing the image, calculating the light intensity error, and updating the phase distribution is repeated until the convergence condition is met to obtain the target phase distribution of the diffractive optical element.

[0006] In conjunction with the first aspect, in one embodiment, the phase-modulated optical field of the transmission optical path is the phase modulation amount generated by the incident light passing through the diffractive optical element in a single pass. The light field; The double-phase-modulated optical field of the reflected optical path is the phase modulation amount generated when the incident light passes through the diffractive optical element, is reflected by the reflecting surface, and then passes through the diffractive optical element again, with a phase modulation of 2. The light field; in, This represents the current phase distribution of the diffractive optical element.

[0007] In conjunction with the first aspect, in one implementation, constructing the light field propagation model includes: An angular spectrum propagation operator is constructed based on the operating wavelength, pixel size, resolution, and propagation distance.

[0008] In conjunction with the first aspect, in one embodiment, calculating the first light intensity error between the first reconstructed image and the first target image, and the second light intensity error between the second reconstructed image and the second target image, includes: Calculate the root mean square error of light intensity between the first reconstructed image and the first target image, and use it as the first light intensity error; The root mean square error of light intensity between the second reconstructed image and the second target image is calculated as the second light intensity error.

[0009] In conjunction with the first aspect, in one implementation, it further includes: Select the corresponding first signal window and second signal window in the central region of the first reconstructed image and the second reconstructed image, respectively. Only the root mean square error between the first reconstructed image and the first target image within the first signal window, and the root mean square error between the second reconstructed image and the first target image within the second signal window are calculated.

[0010] In conjunction with the first aspect, in one embodiment, updating the phase distribution based on the first light intensity error and the second light intensity error includes: The gradient of the phase distribution is calculated by backpropagation of the error based on the first light intensity error and the second light intensity error. The gradient descent optimization algorithm is used to adjust the update step size and direction of the gradient; The phase distribution is updated based on the adjusted gradient.

[0011] In conjunction with the first aspect, in one implementation, the gradient descent optimization algorithm is the Adam algorithm.

[0012] Secondly, embodiments of this application provide a diffractive optical imaging component, the diffractive optical imaging component comprising: Semi-permeable and semi-reflective membrane; A diffractive optical element is disposed on the semi-transparent and semi-reflective film, and the diffractive optical element has a target phase distribution as obtained by the above-described dual-phase constrained full-space optical field modulation method, so that the incident light is transmitted through the diffractive optical element and generates a one-time phase modulation to form a first reconstructed image, and the incident light is reflected by the semi-transparent and semi-reflective film and passes through the diffractive optical element again and generates a two-time phase modulation to form a second reconstructed image.

[0013] In conjunction with the second aspect, in one embodiment, the semi-transparent and semi-reflective film includes a beam-splitting film and an anti-reflection film.

[0014] In conjunction with the second aspect, in one embodiment, the diffractive optical element is fabricated using electron beam lithography, ultraviolet lithography, nanoimprinting, or two-photon polymerization 3D micro / nano printing, and integrated onto the beam-splitting film or antireflection film.

[0015] The beneficial effects of the technical solutions provided in this application include: The dual-phase-constrained full-space optical field manipulation method in this application constructs an optical field propagation model and obtains the initial phase distribution of the diffractive optical element. Based on the current phase distribution of the diffractive optical element, it uses the optical field propagation model to calculate the one-time phase modulation optical field of the transmitted optical path and obtains the corresponding first reconstructed image. It also calculates the two-time phase modulation optical field of the reflected optical path and obtains the corresponding second reconstructed image. It calculates the first light intensity error between the first reconstructed image and the first target image, and the second light intensity error between the second reconstructed image and the second target image. It updates the phase distribution according to the first light intensity error and the second light intensity error, and repeats the process of reconstructing the image, calculating the light intensity error, and updating the phase distribution until the convergence condition is met, so as to obtain the target phase distribution of the diffractive optical element.

[0016] Therefore, this application can achieve independent imaging effects that meet preset requirements in the transmission and reflection spaces using the same diffractive optical element, effectively solving the technical problem in traditional design methods where phase coupling causes crosstalk between transmission and reflection imaging and makes independent optimization impossible, and significantly improving the independence and image quality of dual-space imaging. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of an embodiment of the dual-phase-constrained full-space optical field manipulation method of this application; Figure 2This is a schematic diagram of the structure of an embodiment of the diffractive optical imaging component of this application; Figure 3 This is a flowchart illustrating the DOE phase distribution design for this application. Figure 4 Example 1 shows the full-space DOE imaging effect of this application, where (a) is a DOE phase distribution diagram, (b) is an incident space imaging effect diagram, and (c) is a reflected space imaging effect diagram. Figure 5 Example 2 shows the full-space DOE imaging effect of this application, where (a) is the DOE phase distribution diagram, (b) is the incident space imaging effect diagram, and (c) is the reflected space imaging effect diagram. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0021] In a first aspect, embodiments of this application provide a dual-phase constrained full-space optical field manipulation method.

[0022] In one embodiment, reference is made to Figure 1 , Figure 1 This is a flowchart of an embodiment of the dual-phase-constrained full-space optical field manipulation method of this application. Figure 1 As shown, the dual-phase constrained full-space optical field manipulation method includes: S1. Construct a light field propagation model and obtain the initial phase distribution of the diffractive optical element; In step S1, the optical field propagation model is mainly constructed based on the working wavelength, pixel size, resolution and propagation distance to build the angular spectrum propagation operator.

[0023] It should be noted that angular spectrum propagation refers to the physical laws (or mathematical models) describing the propagation of light waves in free space or a homogeneous medium. Its core idea is to decompose the complex wavefront (light field) into a superposition of a series of plane waves propagating in different directions (i.e., the "angular spectrum"), allowing each plane wave to propagate independently (multiplied by its own phase delay factor), and then superimposing the propagated plane waves to obtain the light field on a new plane. In this embodiment, it is used to simulate the forward and reverse propagation of light waves within a specified distance. The angular spectrum propagation operator is the specific algorithm, tool, or mathematical function that implements the aforementioned physical laws.

[0024] A diffractive optical element (DOE) is an optical element based on the principle of light diffraction. By etching patterns with specific microstructures (such as stepped or continuous relief patterns) on its surface (or interior), it modulates the phase, amplitude, or polarization of incident light waves, thereby achieving arbitrary shaping and control of the light field (beam). When light waves pass through (or are reflected) the surface of a DOE with micro / nano structures, the transmitted (or reflected) light waves at different locations will produce different phase delays (i.e., phase modulation). These light waves carrying different phase information interfere with each other during propagation, redistributing the light field and thus forming the desired pattern or light field distribution at specific locations.

[0025] In this embodiment, the relief height distribution of the DOE corresponds to the designed target phase distribution. By mapping the target phase distribution to the surface relief height, the DOE can be fabricated using photolithography or imprinting processes. It is understood that initially, it is uncertain what kind of surface structure can achieve the target; therefore, a completely random surface model (initial phase distribution) is first generated.

[0026] See Figure 2 As shown, DOE can be fabricated using electron beam lithography, ultraviolet lithography, nanoimprinting, or two-photon polymerization 3D micro-nano printing technology, and integrated into the beam-splitting or antireflective film surface of a semi-transparent and semi-reflective membrane. It is compatible with the physical structure of the semi-transparent and semi-reflective membrane and can be directly used in scenarios such as full-space optical imaging, optical anti-counterfeiting, and structured light projection.

[0027] S2. Based on the current phase distribution of the diffractive optical element, calculate the phase-modulated light field of the transmitted light path using the light field propagation model, and obtain the corresponding first reconstructed image; and calculate the phase-modulated light field of the reflected light path, and obtain the corresponding second reconstructed image. In step S2, the phase-modulated optical field of the transmission optical path is the phase modulation amount generated by the incident light passing through the diffractive optical element once. The light field; the double-phase-modulated light field of the reflected light path is the phase modulation amount generated by the incident light passing through the diffractive optical element, being reflected by the reflecting surface, and then passing through the diffractive optical element again, with a phase modulation amount of 2. The light field; among which, This represents the current phase distribution of the diffractive optical element.

[0028] It should be noted that phase distribution refers to the phase response corresponding to the spatial height profile of the DOE micro / nano surface, which is an inherent property of the device. Phase modulation refers to the actual phase value added to the light wave after passing through the device.

[0029] See Figure 2 As shown, this means that the phase distribution of this DOE simultaneously satisfies the following: in the transmission space, the incident light, after passing through the DOE, produces a one-time phase modulation. This forms the first reconstructed image A; in the reflection space, light is reflected by the semi-transparent and semi-reflective film and then passes through the DOE again, generating a double phase modulation 2. This forms the second reconstructed image B.

[0030] S3. Calculate the first light intensity error between the first reconstructed image and the first target image, and the second light intensity error between the second reconstructed image and the second target image; In step S3, the light intensity error between the reconstructed image and the target image is calculated, mainly by comparing the image similarity.

[0031] In specific implementation, the calculation of the first light intensity error between the first reconstructed image and the first target image, and the second light intensity error between the second reconstructed image and the second target image, includes: Calculating the first light intensity error between the first reconstructed image and the first target image, and the second light intensity error between the second reconstructed image and the second target image, includes: calculating the root mean square error of light intensity between the first reconstructed image and the first target image as the first light intensity error; and calculating the root mean square error of light intensity between the second reconstructed image and the second target image as the second light intensity error.

[0032] Typically, during the design phase, only the content at the center of the image is considered, ignoring the black background at the edges. Calculating only the error in the central region eliminates background noise interference, allowing the computation to focus more effectively and accelerating convergence. Therefore, to define the effective signal range, accelerate algorithm convergence, and improve optimization stability, the central region of the reconstructed image can be selected as the signal window.

[0033] That is, select the corresponding first signal window and second signal window in the central region of the first reconstructed image and the second reconstructed image respectively; then calculate only the root mean square error between the first reconstructed image and the first target image in the first signal window, and the root mean square error between the second reconstructed image and the first target image in the second signal window.

[0034] S4. Update the phase distribution based on the first light intensity error and the second light intensity error, and repeat the process of reconstructing the image, calculating the light intensity error and updating the phase distribution until the convergence condition is met, so as to obtain the target phase distribution of the diffractive optical element.

[0035] The essence of this embodiment is to adjust the phase of the DOE so that the final projected light spot brightness pattern (reconstructed image) overlaps as much as possible with the desired brightness pattern (target image). The standard for measuring the degree of overlap is the root mean square error of the light intensity data.

[0036] Specifically, in step S4, updating the phase distribution based on the first light intensity error and the second light intensity error includes: S41. Calculate the gradient of the phase distribution based on the first light intensity error and the second light intensity error through error backpropagation; S42. Adjust the update step size and direction of the gradient using the gradient descent optimization algorithm; In this embodiment, the gradient descent optimization algorithm used is the Adam optimization algorithm. The Adam optimization algorithm has the ability to adapt the learning rate and is suitable for optimization problems with high resolution and high-dimensional phase distribution. It can automatically adjust the magnitude of each correction according to the previous error changes, making the convergence faster and more stable, and can effectively avoid local optima.

[0037] S43. Update the phase distribution based on the adjusted gradient.

[0038] Understandably, the above steps (S2 to S4) are repeated until the error can no longer be minimized, at which point the result is obtained. It refers to the final target phase distribution.

[0039] To facilitate understanding, the above steps are summarized and outlined below: In this embodiment, the phase distribution of the DOE is designed jointly by an improved angular spectrum propagation model and the Adam optimization algorithm. The optimization objectives are: minimizing the root mean square error between the first reconstructed image and the first target image A under one-time phase modulation; and minimizing the root mean square error between the second reconstructed image and the second target image B under two-time phase modulation.

[0040] like Figure 3As shown, the design steps for the phase distribution of a DOE are as follows: First, initialize the random phase distribution. Then, an angular spectrum propagation operator is constructed to simulate the forward and backward propagation of light waves within a specified distance. In each iteration, the reconstructed light field is calculated at one-time phase and two-time phase, and the error between the reconstructed image and the target image is calculated. The phase gradient is calculated through backpropagation of the error. Simultaneously, the Adam optimization algorithm is used to update the phase distribution, constraining it to minimize the error within the signal window. This iteration is repeated until convergence, and the final target phase distribution is output.

[0041] like Figure 4 and Figure 5 As shown, the phase distribution maps and corresponding imaging in transmission and reflection spaces of two different designed DOEs are illustrated. In Example 1, the target image in transmission space is set as the uppercase letter "U", and the target image in reflection space is set as the uppercase letter "H", to verify the DOE's ability to independently image in all spaces under text-like patterns. In Example 2, the target image in transmission space is set as a checkerboard pattern, and the target image in reflection space is set as a vortex light field pattern, to verify the generalization ability and imaging quality of the proposed method under different types of structured light fields.

[0042] In summary, the dual-phase-constrained full-space optical field manipulation method in this application constructs an optical field propagation model and obtains the initial phase distribution of the diffractive optical element; based on the current phase distribution of the diffractive optical element, it uses the optical field propagation model to calculate the one-time phase modulation optical field of the transmission optical path and obtains the corresponding first reconstructed image, and calculates the two-time phase modulation optical field of the reflection optical path and obtains the corresponding second reconstructed image; it calculates the first light intensity error between the first reconstructed image and the first target image, and the second light intensity error between the second reconstructed image and the second target image; it updates the phase distribution according to the first light intensity error and the second light intensity error, and repeats the process of reconstructing the image, calculating the light intensity error, and updating the phase distribution until the convergence condition is met, so as to obtain the target phase distribution of the diffractive optical element.

[0043] Therefore, this application can achieve independent imaging effects that meet preset requirements in the transmission and reflection spaces using the same diffractive optical element, effectively solving the technical problem in traditional design methods where phase coupling causes crosstalk between transmission and reflection imaging and makes independent optimization impossible, and significantly improving the independence and image quality of dual-space imaging.

[0044] Secondly, embodiments of this application provide a diffractive optical imaging component.

[0045] In one embodiment, reference is made to Figure 2 , Figure 2 This is a schematic diagram of the structure of an embodiment of the diffractive optical imaging component of this application. Figure 2As shown, the diffractive optical imaging component includes: Semi-permeable and semi-reflective membrane; A diffractive optical element is disposed on the semi-transparent and semi-reflective film, and the diffractive optical element has a target phase distribution as obtained by the above-described dual-phase constrained full-space optical field modulation method, so that the incident light is transmitted through the diffractive optical element and generates a one-time phase modulation to form a first reconstructed image, and the incident light is reflected by the semi-transparent and semi-reflective film and passes through the diffractive optical element again and generates a two-time phase modulation to form a second reconstructed image.

[0046] Furthermore, in one embodiment, the semi-transparent and semi-reflective film includes a beam-splitting film and an anti-reflection film.

[0047] Furthermore, in one embodiment, the diffractive optical element is fabricated using electron beam lithography, ultraviolet lithography, nanoimprinting, or two-photon polymerization 3D micro / nano printing, and integrated onto the beam-splitting film or antireflection film.

[0048] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0049] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0050] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for controlling the entire optical field under dual-phase constraints, characterized in that, The dual-phase constrained full-space optical field manipulation method includes: Construct a light field propagation model and obtain the initial phase distribution of the diffractive optical element; Based on the current phase distribution of the diffractive optical element, the one-time phase-modulated optical field of the transmitted optical path is calculated using the optical field propagation model, and the corresponding first reconstructed image is obtained; and the two-time phase-modulated optical field of the reflected optical path is calculated, and the corresponding second reconstructed image is obtained. Calculate the first light intensity error between the first reconstructed image and the first target image, and the second light intensity error between the second reconstructed image and the second target image; The phase distribution is updated based on the first light intensity error and the second light intensity error, and the process of reconstructing the image, calculating the light intensity error, and updating the phase distribution is repeated until the convergence condition is met to obtain the target phase distribution of the diffractive optical element.

2. The dual-phase constrained full-space optical field manipulation method as described in claim 1, characterized in that: The phase-modulated optical field of the transmission optical path is the phase modulation amount generated by the incident light passing through the diffractive optical element once. The light field; The double-phase-modulated optical field of the reflected optical path is the phase modulation amount generated when the incident light passes through the diffractive optical element, is reflected by the reflecting surface, and then passes through the diffractive optical element again, with a phase modulation of 2. The light field; in, This represents the current phase distribution of the diffractive optical element.

3. The dual-phase-constrained full-space optical field manipulation method as described in claim 1, characterized in that, The construction of the light field propagation model includes: An angular spectrum propagation operator is constructed based on the operating wavelength, pixel size, resolution, and propagation distance.

4. The dual-phase-constrained full-space optical field manipulation method as described in claim 1, characterized in that, The calculation of the first light intensity error between the first reconstructed image and the first target image, and the second light intensity error between the second reconstructed image and the second target image, includes: Calculate the root mean square error of light intensity between the first reconstructed image and the first target image, and use it as the first light intensity error; The root mean square error of light intensity between the second reconstructed image and the second target image is calculated as the second light intensity error.

5. The dual-phase-constrained full-space optical field manipulation method as described in claim 4, characterized in that, Also includes: Select the corresponding first signal window and second signal window in the central region of the first reconstructed image and the second reconstructed image, respectively. Only the root mean square error between the first reconstructed image and the first target image within the first signal window, and the root mean square error between the second reconstructed image and the first target image within the second signal window are calculated.

6. The dual-phase-constrained full-space optical field manipulation method as described in claim 1, characterized in that, The step of updating the phase distribution based on the first light intensity error and the second light intensity error includes: The gradient of the phase distribution is calculated by backpropagation of the error based on the first light intensity error and the second light intensity error. The gradient descent optimization algorithm is used to adjust the update step size and direction of the gradient; The phase distribution is updated based on the adjusted gradient.

7. The dual-phase-constrained full-space optical field manipulation method as described in claim 6, characterized in that: The gradient descent optimization algorithm is the Adam algorithm.

8. A diffractive optical imaging component, characterized in that, The diffractive optical imaging component includes: Semi-permeable and semi-reflective membrane; A diffractive optical element is disposed on the semi-transparent and semi-reflective film, and the diffractive optical element has a target phase distribution obtained by the dual-phase constrained full-space optical field modulation method as described in any one of claims 1 to 7, such that the incident light is transmitted through the diffractive optical element and generates a one-time phase modulation to form a first reconstructed image, and the incident light is reflected by the semi-transparent and semi-reflective film and passes through the diffractive optical element again and generates a two-time phase modulation to form a second reconstructed image.

9. The diffractive optical imaging assembly as described in claim 8, characterized in that: The semi-transparent and semi-reflective film includes a beam-splitting film and an anti-reflection film.

10. The diffractive optical imaging assembly as described in claim 9, characterized in that: The diffractive optical element is fabricated using electron beam lithography, ultraviolet lithography, nanoimprinting, or two-photon polymerization 3D micro / nano printing, and integrated onto the beam-splitting film or antireflection film.

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