Vortex light interference device and method

Abstract

The invention provides a vortex light interference device and method, and relates to the technical field of optical systems.The device comprises a circular polarization generating unit, a first interference unit, a second interference unit, a vortex beam generating unit, a first Dove prism, a second Dove prism, a first CCD camera and a second CCD camera. The vortex beam generation unit is arranged at the two interference light paths of the first interference unit and converts the two interference light beams into vortex beams, the first Dove prism and the second Dove prism are arranged at the light paths of the first transmission light and the first reflection light respectively, and the first Dove prism and the second Dove prism relatively rotate by an angle of pi / 2, so that the vortex beams are generated. And the first CCD camera and the second CCD camera are respectively used for imaging the first emergent light and the second emergent light. According to the invention, visual demonstration of vortex light interference and multimode mixed vortex light orbital angular momentum separation can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of optical systems, and in particular to a vortex light interference device and method. Background Art

[0002] Vortex beams are known for their unique phase vortex characteristics. The wavefront of a vortex beam presents a spiral shape, and there is a phase singularity in the center, which results in zero light intensity at the center and a ring-shaped light intensity distribution. Vortex beams have gradually become a hot topic of research. Various vortex beams such as Laguerre-Gaussian beams, Bessel beams, Airy vortex beams, and perfect vortex beams have been gradually realized and widely used in various fields such as astronomy, microscopy, particle manipulation, optical communications, and quantum entanglement. Therefore, it is particularly important to understand the basic concepts and characteristics of vortex beams, understand how vortex beams are generated, and master the characteristics and principles of vortex beam interference with different lights.

[0003] Currently, there are devices that can generate vortex light and realize vortex light interference demonstration. However, problems existing in related technologies restrict the development of vortex light interference research. On the one hand, existing vortex light interference devices usually only focus on realizing interference demonstration between vortex lights of different modes, and cannot realize the separation demonstration of orbital angular momentum of multi-mode mixed vortex light.

[0004] On the other hand, there are many challenges in generating interference images with CCD cameras, which seriously affect the subsequent research of technicians in this field. Existing CCD cameras lack the processing of generated interference images. Even if some studies have performed image processing on interference images, it is difficult for existing image processing algorithms to fully and accurately extract multi-scale features and dynamic change information in vortex light interference images. And because the mode, orbital angular momentum and other characteristics of vortex light change continuously over time during the propagation and interference process, traditional methods are difficult to effectively capture these dynamic information and make accurate predictions. For example, in the real-time analysis scenario of multi-mode mixed vortex light, traditional technology cannot timely and accurately distinguish the evolution process of vortex light of different modes, which limits the research on the complex behavior of vortex light. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, an object of the present invention is to provide a vortex light interference device and method to solve the deficiencies in the prior art.

[0006] In order to achieve the above-mentioned object, a first aspect of the present invention provides a vortex light interference device, comprising: a circular polarization generating unit, a first interference unit, and a second interference unit; A circular polarization generating unit, used for generating circular polarized light; The first interference unit is configured to perform Mach-Zehnder interference based on the circularly polarized light generated by the circularly polarized light generating unit, and transmit the combined beam to the second interference unit; The second interference unit includes a first mirror, a first beam splitter prism, a second mirror, a third mirror, and a second beam splitter prism; the first mirror reflects the beam transmitted by the first interference unit to the first beam splitter prism, the first beam splitter prism divides the beam into a first transmitted light and a first reflected light, the first transmitted light is reflected by the second mirror and then enters the second beam splitter prism, and the first reflected light is reflected by the third mirror and then enters the second beam splitter prism; the second beam splitter prism generates a first output light and a second output light, the first output light includes the beam obtained by reflecting the first transmitted light by the second beam splitter prism and the beam obtained by transmitting the first reflected light by the second beam splitter prism, and the second output light includes the beam obtained by transmitting the first transmitted light by the second beam splitter prism and the beam obtained by reflecting the first reflected light by the second beam splitter prism; It further includes a vortex beam generating unit, a first Dove prism, a second Dove prism, a first CCD camera, and a second CCD camera. When demonstrating the separation of the orbital angular momentum of multimode hybrid vortex light, the vortex beam generating unit is arranged at the two interference optical paths of the first interference unit and is configured to convert both interference beams into vortex beams. The first Dove prism and the second Dove prism are respectively arranged on the optical paths of the first transmitted light and the first reflected light, and the first Dove prism and the second Dove prism are rotated relative to each other by an angle of π / 2. The first CCD camera and the second CCD camera are respectively used to image the first output light and the second output light to obtain interference images; wherein neural network chips are embedded in both the first CCD camera and the second CCD camera; The neural network chip integrates a convolutional neural network model, and the convolutional neural network model includes a multi-scale pyramid convolution module, a feature enhancement module, and a recurrent memory fusion module; the multi-scale pyramid convolution module is composed of multiple convolutional layers with different-sized convolutional kernels in parallel; the interference image passes through different convolutional layers to obtain feature maps of different scales, and the obtained feature maps of different scales are fused to obtain interference image features; in the feature enhancement module, first, global average pooling is performed on the interference image features to obtain the global feature vector of each channel; then, the attention weights are calculated through two fully connected layers; finally, the attention weights and the interference image features are multiplied to obtain an enhanced feature map; the recurrent memory fusion module is composed of multiple long short-term memory network units connected end to end, and the enhanced feature map is sequentially input into the long short-term memory network units in chronological order, where the long short-term memory network unit includes a forget gate, an input gate, an output gate, and a memory unit.

[0007] Preferably, the first interference unit includes a first polarization beam splitter prism, a fourth mirror, a fifth mirror, a second polarization beam splitter prism, a first quarter-wave plate, and a third polarization beam splitter prism; the first polarization beam splitter prism splits the circularly polarized light generated by the circularly polarized light generating unit into a second transmitted light and a second reflected light. The second transmitted light enters the second polarization beam splitter prism after being reflected by the fourth mirror, and the second reflected light enters the second polarization beam splitter prism after being reflected by the fifth mirror. After the second transmitted light and the second reflected light are combined at the second polarization beam splitter prism, they sequentially pass through the first quarter-wave plate and the third polarization beam splitter prism and are transmitted to the first mirror.

[0008] Preferably, the circularly polarized light generating unit includes a solid-state laser, an attenuation sheet, a half-wave plate, a beam expander unit, and a second quarter-wave plate. The laser generated by the solid-state laser is sequentially attenuated by the attenuation sheet, its polarization state is changed by the half-wave plate, and it is expanded by the beam expander unit to obtain linearly polarized light. The second quarter-wave plate converts the linearly polarized light into circularly polarized light and outputs it to the first interference unit; the beam expander unit includes a first plano-convex lens with a first focal length and a second plano-convex lens with a second focal length.

[0009] Preferably, the vortex beam generating unit includes a first vortex beam generating unit and a second vortex beam generating unit. The first vortex beam generating unit includes a first q-wave plate and a third quarter-wave plate, and the second vortex beam generating unit includes a second q-wave plate and a fourth quarter-wave plate. The orders of the first q-wave plate and the second q-wave plate are different; the order of the first q-wave plate is an even number, and the order of the second q-wave plate is an odd number.

[0010] Preferably, the long short-term memory network unit takes the enhanced feature map and the hidden state of the previous moment as inputs. In the long short-term memory network unit, first, a forget gate calculation is performed, then an input gate calculation is performed, and a candidate memory unit is generated. Then, the memory unit is updated according to the forget gate calculation result, the input gate calculation, and the candidate memory unit to determine the information at the current moment. Finally, the hidden state output at the current moment is determined through the output gate.

[0011] Preferably, in the cyclic memory fusion module, except for the last long short-term memory network unit, the hidden states output by other long short-term memory network units will be used as inputs for the long short-term memory network unit at the next moment.

[0012] In a second aspect of the present invention, based on the vortex light interference device provided in the first aspect, a vortex light interference method is further provided, including: Two vortex beam generating units with different orders are respectively arranged at the first transmission path and the first reflection path of the first interference unit, so that the first interference unit outputs a dual-mode hybrid vortex beam; The first Dove prism is arranged between the first beam-splitting prism and the second reflector, and the second Dove prism is arranged between the third reflector and the second beam-splitting prism, and the first Dove prism and the second Dove prism are relatively rotated by an angle of π / 2; The first CCD camera is arranged at the exit of the first outgoing light of the second beam-splitting prism to image the first outgoing light to obtain a first interference image; the second CCD camera is arranged at the exit of the second outgoing light of the second beam-splitting prism to image the second outgoing light to obtain a second interference image; An interference image is acquired, preprocessed and then input into a convolutional neural network model to output an analytical diagram of vortex light interference; when the interference image is input into the convolutional neural network model, first the features of the interference image are extracted by a multi-scale pyramid convolution module, then the features of the interference image are enhanced by a feature enhancement module to output an enhanced feature map, and then an analytical diagram of vortex light interference is output by a cyclic memory fusion module.

[0013] Compared with the prior art, the beneficial effects of the present invention are: The present invention can realize vortex light interference and intuitively demonstrate the separation of the orbital angular momentum of multimode hybrid vortex light. The circularly polarized light generation unit and the first interference unit can realize the interference of the vortex beam, and at the same time can generate a dual-mode hybrid vortex beam and input it into the second interference unit. The second interference unit, based on the Dove prism and the Mach-Zehnder interferometer, can separate the orbital angular momentum components of the dual-mode hybrid vortex beam, and image the outgoing light through a CCD camera to clearly show the fringes of the separated single-mode vortex beam.

[0014] Neural network chips are embedded in the CCD cameras of the present invention. The multi-scale pyramid convolution module in the convolutional neural network model uses convolution kernels of different sizes to work in parallel to comprehensively capture multi-scale features from image details to overall contours, making the model more accurate in identifying characteristics such as vortex light patterns and orbital angular momentum, and having significant advantages in the analysis of complex multimode hybrid vortex light interference images. At the same time, the cyclic memory fusion module learns the long-term dependence relationship of the image sequence through LSTM units, combines enhanced context awareness, adaptive memory update and dynamic adjustment output mechanism, effectively captures the dynamic changes of vortex light interference, and can accurately predict the movement of interference fringes, mode transformation, etc., providing a powerful tool for the study of dynamic processes.

[0015] Advantages of additional aspects of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic 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.

[0017] Figure 1 Schematic structural diagram of a vortex light interference device provided by the present invention; Figure 2 Theoretical simulation diagram of the interference between a plane wave and a vortex beam; Figure 3 Theoretical simulation diagram of the interference between a spherical wave and a vortex beam; Figure 4 For Theoretical simulation diagram of the interference of the vortex beam.

[0018] Figure 5 Flowchart of a vortex light interference method provided by the present invention; Wherein, 1. Solid laser; 2. Attenuator; 3. Half-wave plate; 4. First plano-convex lens with a focal length; 5. Second plano-convex lens with a focal length; 6. Second quarter-wave plate; 7. First polarization beam splitter prism; 8. Fourth mirror; 9. Fifth mirror; 10. Second polarization beam splitter prism; 11. First quarter-wave plate; 12. Third polarization beam splitter prism; 13. First mirror; 14. First beam splitter prism; 15. Second mirror; 16. Second beam splitter prism; 17. Third mirror; 18. Second CCD camera. Specific embodiments

[0019] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0020] In the embodiments of the present invention, as Figure 1 shown, first, a vortex light interference device is provided, including: a circularly polarized light generation unit, a first interference unit, and a second interference unit.

[0021] The circularly polarized light generation unit is used to generate circularly polarized light.

[0022] The first interference unit is used to implement Mach-Zehnder interference according to the circularly polarized light generated by the circularly polarized light generation unit and transmit the combined beam to the second interference unit.

[0023] The second interference unit includes a first reflector 13, a first beam splitter prism 14, a second reflector 15, a third reflector 17, and a second beam splitter prism 16. The first reflector 13 reflects the light beam transmitted by the first interference unit to the first beam splitter prism 14. The first beam splitter prism 14 divides the light beam into a first transmitted light and a first reflected light. The first transmitted light enters the second beam splitter prism 16 after being reflected by the second reflector 15, and the first reflected light enters the second beam splitter prism 16 after being reflected by the third reflector 17. The second beam splitter prism 16 generates a first output light and a second output light. The first output light includes the light beam obtained by reflecting the first transmitted light by the second beam splitter prism 16 and the light beam obtained by transmitting the first reflected light by the second beam splitter prism 16. The second output light includes the light beam obtained by transmitting the first transmitted light by the second beam splitter prism 16 and the light beam obtained by reflecting the first reflected light by the second beam splitter prism 16. For the convenience of description, hereinafter, the optical path where the first transmitted light is located is referred to as the first transmission path (t' path), and the optical path where the first reflected light is located is referred to as the first reflection path (r' path).

[0024] The device further includes a vortex beam generation unit, a first Dove prism, a second Dove prism, a first CCD camera, and a second CCD camera 18. When demonstrating the separation of the orbital angular momentum of a multimode hybrid vortex light, the vortex beam generation unit is arranged at the two interference optical paths of the first interference unit for converting both interference light beams into vortex beams. The first Dove prism and the second Dove prism are respectively arranged at the optical paths of the first transmitted light and the first reflected light, and the first Dove prism and the second Dove prism are rotated relative to each other by an angle of π / 2. The first CCD camera and the second CCD camera 18 are respectively used for imaging the first output light and the second output light.

[0025] The first interference unit includes a first polarization beam splitter prism 7, a fourth mirror 8, a fifth mirror 9, a second polarization beam splitter prism 10, a first quarter-wave plate 11, and a third polarization beam splitter prism 12. The first polarization beam splitter prism 7 splits the circularly polarized light generated by the circularly polarized light generating unit into a second transmitted light and a second reflected light. The second transmitted light enters the second polarization beam splitter prism 10 after being reflected by the fourth mirror 8, and the second reflected light enters the second polarization beam splitter prism 10 after being reflected by the fifth mirror 9. After the second transmitted light and the second reflected light are combined at the second polarization beam splitter prism 10, they sequentially pass through the first quarter-wave plate 11 and the third polarization beam splitter prism 12 and are transmitted to the first mirror 13. The first polarization beam splitter prism 7 and the second polarization beam splitter prism 10 are polarization beam splitter prisms for decomposing circularly polarized light into vertically polarized light and horizontally polarized light, where the transmission path is horizontally polarized light and the reflection path is vertically polarized light. For the convenience of description, hereinafter, the optical path where the second transmitted light is located is referred to as the second transmission path (t path), and the optical path where the second reflected light is located is referred to as the second reflection path (r path). The first quarter-wave plate 11 can convert the light beam decomposed into linearly polarized light by the second polarization beam splitter prism 10 into circularly polarized light, so that the two light beams interfere. The third polarization beam splitter prism 12 is used for polarization detection and only allows horizontally polarized light to pass through to achieve imaging on the CCD camera. By adjusting the first polarization beam splitter prism 7, the fourth mirror 8, the fifth mirror 9, and the second polarization beam splitter prism 10, Mach-Zehnder interference can be achieved.

[0026] The circularly polarized light generating unit includes a solid-state laser 1, an attenuation sheet 2, a half-wave plate 3, a beam expander unit, and a second quarter-wave plate 6. The solid-state laser 1 uses a 532-nm solid-state laser, and the emitted light is vertically polarized light. The attenuation sheet 2 is arranged behind the solid-state laser 1 and is used to reduce the light intensity incident on the CCD camera to prevent the lens from being burned out. The half-wave plate 3 is a half-wave plate with a working wavelength of 532 nm and is used to change the polarization state of the light emitted by the solid-state laser. The beam expander unit includes a first plano-convex lens 4 with a focal length and a second plano-convex lens 5 with a focal length. In this embodiment, the first plano-convex lens 4 is a plano-convex lens with a focal length of 25 mm, and the second plano-convex lens 5 is a plano-convex lens with a focal length of 250 mm. The combination of the first plano-convex lens 4 and the second plano-convex lens 5 can expand the light beam. The second quarter-wave plate 6 is used to convert linearly polarized light into circularly polarized light, thereby realizing the generation of circularly polarized light.

[0027] The vortex beam generating unit consists of a q-wave plate and a quarter-wave plate, which can be set in the optical path as needed to generate a vortex beam. In this embodiment, the vortex beam generating unit includes a first vortex beam generating unit and a second vortex beam generating unit. The first vortex beam generating unit includes a first q-wave plate and a third quarter-wave plate, and the second vortex beam generating unit includes a second q-wave plate and a fourth quarter-wave plate. For an intuitive demonstration of the orbital angular momentum separation of multimode hybrid vortex light, the orders m of the first q-wave plate and the second q-wave plate are different, and the order of the first q-wave plate is even (in this embodiment, the order m of the first q-wave plate is 2), and the order of the second q-wave plate is odd (in this embodiment, the order m of the second q-wave plate is 3).

[0028] The device also includes a plano-convex cylindrical lens, which is used to convert the first outgoing light and / or the second outgoing light into Hermite-Gaussian beams when demonstrating the orbital angular momentum separation of multimode hybrid vortex light, and is set in front of the first CCD camera and / or the second CCD camera. The plano-convex cylindrical lens selected in this embodiment is a plano-convex cylindrical lens with a focal length of 50 mm.

[0029] In addition to the demonstration of the orbital angular momentum separation of multimode hybrid vortex light, the device can also realize demonstrations such as the interference between a vortex beam and a plane wave, the interference between a vortex beam and a spherical wave, and the interference between different-mode vortex beams. At this time, the CCD camera can be set between the first interference unit and the second interference unit (i.e., between the third polarization beam splitter prism 12 and the first mirror 13), and the circularly polarized light generating unit and the first interference unit are used for experimental demonstrations. On the basis of setting the first CCD camera and the second CCD camera, a third CCD camera can be additionally added and detachably set between the first interference unit and the second interference unit. The first CCD camera can also be designed to be detachable. When demonstrating interference experiments such as the interference between a vortex beam and a plane wave, the interference between a vortex beam and a spherical wave, and the interference between different-mode vortex beams, the first CCD camera is set between the first interference unit and the second interference unit. When demonstrating the orbital angular momentum separation experiment of multimode hybrid vortex light, the first CCD camera is set in the optical path of the first outgoing light.

[0030] In some embodiments, for the convenience of understanding the basic concept and characteristics of the vortex beam, understanding the generation method of the vortex beam, and mastering the characteristics and principles of its interference with different lights, it is preferably to use the solid-state laser 1, the attenuation sheet 2, the half-wave plate 3, the first focal length plano-convex lens 4, the second focal length plano-convex lens 5, the second quarter-wave plate 6, the first polarization beam splitter prism 7, the fourth mirror 8, the fifth mirror 9, the second polarization beam splitter prism 10, the first quarter-wave plate 11, the third polarization beam splitter prism 12, the first mirror 13, the first beam splitter prism 14, the second mirror 15, the second beam splitter prism 16, the third mirror 17, the second CCD camera 18, that is Figure 1Each structure shown in the figure is designed as a fixed element fixed to the device base plate; the first q-wave plate, the second q-wave plate, the first quarter-wave plate, the second quarter-wave plate, the plano-convex cylindrical lens, the third focal length plano-convex lens (for the interference demonstration of the vortex beam and the spherical wave), and the first CCD camera are designed as magnetic attraction elements that can be flexibly changed in position, so as to meet the requirements of different experimental demonstrations.

[0031] The following will introduce different experimental demonstration methods respectively.

[0032] Generation of vortex beam: The q-wave plate (q-plate) is a polarization modulation device made of nematic liquid crystal that can realize the exchange of the spin angular momentum and orbital angular momentum of the light beam. By controlling the uneven distribution of the main axis of the liquid crystal molecules in the cross-section, a local half-wave plate is formed at each point in the cross-section, introducing a geometric spiral phase to the modulated light, so that the output light beam carries orbital angular momentum, that is, a vortex beam is generated. Therefore, by placing a q-wave plate at an appropriate position in the optical path (the placement positions are different for different types of interference), a vortex beam can be generated.

[0033] Interference between vortex beam and plane wave: The electric field expression of the vortex beam is , where is the amplitude. For simplicity, let it be a constant, is the angular quantum number of the vortex beam. The expression of the plane wave is , is a constant. Let , then the light intensity distribution I 1 after the interference between the vortex beam and the plane wave is: ; where, E P represents the electric field expression of the interference between the vortex beam and the plane wave, E P * represents E P the conjugate of, θ is the azimuth angle, x is the coordinate in the rectangular coordinate system, λ is the wavelength, and in the formula 2π / λ = k, k is the wave vector. According to the above formula, the interference pattern between the plane wave and the vortex beam can be simulated. When , the interference pattern is as shown in Figure 2 .

[0034] Based on Figure 1For the device shown, to achieve the interference between the vortex beam and the plane wave, a quarter-wave plate (the first quarter-wave plate) rotated to 45 degrees and the first q-wave plate with m = 2 need to be placed at the middle position between the first polarization beam splitter prism 7 and the fourth mirror 8, that is, in the second transmission path (t path). Among them, the first quarter-wave plate is used to convert linearly polarized light into circularly polarized light, and the first q-wave plate is used to convert circularly polarized light into a vortex beam. At this time, the beam in the t path is a vortex beam, and the beam in the r path is a plane wave. By adjusting the first polarization beam splitter prism 7, the fourth mirror 8, the fifth mirror 9, and the second polarization beam splitter prism 10, the plane wave and the vortex beam can interfere to form interference fringes. By placing the first CCD camera between the third polarization beam splitter prism 12 and the first mirror 13, the interference pattern can be observed in the CCD software connected to the first CCD. The theoretical diagram of the interference pattern is as shown in Figure 2 shown below.

[0035] Interference between the vortex beam and the spherical wave: The expression of the spherical wave is , where and are constants. The expression of the plane wave is . Let , then the light intensity distribution I 2 after the interference between the vortex beam and the spherical wave is: ; Among them, E s represents the electric field expression of the interference between the vortex beam and the spherical wave, E P * represents E P conjugate, θ is the azimuth angle, x and y are the coordinates in the rectangular coordinate system, λ is the wavelength, and in the formula 2π / λ = k, where k is the wave vector. According to the above formula, the interference pattern between the spherical wave and the vortex beam can be simulated. When , the interference pattern is as shown in Figure 3 shown below.

[0036] Based on Figure 1For the device shown, to achieve the interference between the vortex beam and the plane wave, a quarter-wave plate (the third quarter-wave plate) rotated to 45 degrees and the first q-wave plate with m = 2 need to be placed at the middle position between the first polarization beam splitter prism 7 and the fourth mirror 8, that is, in the second transmission path (t path); a third focal length plano-convex lens with a focal length of 50 mm needs to be placed at the middle position between the fifth mirror 9 and the second polarization beam splitter prism 10, that is, in the second reflection path (r path). The third focal length plano-convex lens is used to convert the plane wave into a spherical wave. At this time, the beam in the t path is a vortex beam, and the beam in the r path is a spherical wave. By adjusting the first polarization beam splitter prism 7, the fourth mirror 8, the fifth mirror 9, and the second polarization beam splitter prism 10, the spherical wave and the vortex beam can be made to interfere to form interference fringes. By placing the first CCD camera between the third polarization beam splitter prism 12 and the first mirror 13, the interference pattern can be observed. The theoretical diagram of the interference pattern is as shown in Figure 3 shown.

[0037] Interference between vortex beams of different modes: Consider the simplest case, that is, the coaxial combination of two vortex beams with equal intensity. Let their angular quantum numbers be and respectively. Then the complex amplitude E of the vortex beam after their coaxial combination is: ; It can be seen from this that the cross-sectional light intensity distribution satisfies the following formula: ; The above formula shows that for the vortex beam after the coaxial combination of two beams with equal intensity, its cross-sectional light intensity distribution is a function of the angular coordinate . At the same time, it is not difficult to understand that the light field after the coaxial combination of two vortex beams with equal intensity has a petal-like structure, and the number of petals is equal to . Moreover, for the vortex beam after the coaxial combination of two single-mode beams with equal intensity, its phase distribution is also different from that in the single-mode case, but the result of the interaction after the superposition of two spiral phases.

[0038] Based on the device shown in Figure 1 , to achieve the interference of two vortex beams, a quarter-wave plate (the third quarter-wave plate) rotated to 45 degrees and the first q-wave plate with m = 2 need to be placed at the middle position between the first polarization beam splitter prism 7 and the fourth mirror 8, that is, in the second transmission path (t path); a quarter-wave plate (the fourth quarter-wave plate) rotated to 45 degrees and the second q-wave plate with m = 3 need to be placed at the middle position between the fifth mirror 9 and the second polarization beam splitter prism 10, that is, in the second reflection path (r path). At this time, the beam in the t path is the vortex beam, and the beam in the r path is the For the vortex beam, by adjusting the first polarization beam splitter prism 7, the fourth mirror 8, the fifth mirror 9, and the second polarization beam splitter prism 10, the two-path equal-intensity vortex beams can be combined to form interference fringes. By placing the first CCD camera between the third polarization beam splitter prism 12 and the first mirror 13, the interference pattern can be observed. The theoretical diagram of the interference pattern is as shown in Figure 4 shown.

[0039] Separation of orbital angular momentum of multimode hybrid vortex light: Based on the above demonstration of interference between different-mode vortex beams, the separation of orbital angular momentum of multimode hybrid vortex light can be further demonstrated. Place two identical Dove prisms (i.e., the first Dove prism and the second Dove prism) on the t' path and the r' path respectively, and rotate the two Dove prisms relative to each other by an angle, which means that when the light beam passes through the first Dove prism, the light field distribution in the cross-section perpendicular to the z-axis will be flipped relative to the x-axis, and when the same light beam passes through the second Dove prism, the light field distribution in the cross-section perpendicular to the z-axis will be flipped relative to the x-axis and rotated by the angle.

[0040] Since the vortex beam with angular quantum number contains the phase factor , when this vortex beam passes through the second Dove prism, the helical phase factor becomes , and when it passes through the first Dove prism, the helical phase factor becomes . Obviously, when the vortex beams with the same angular quantum number pass through the first Dove prism and the second Dove prism respectively, a phase difference will be generated.

[0041] The first beam splitter prism 14, the second mirror 15, the second beam splitter prism 16, and the third mirror 17 form a Mach-Zehnder interferometer. The principle of separating the orbital angular momentum of the vortex beam by the Mach-Zehnder interferometer with Dove prisms on both arms can be understood through "destructive interference". Define two operators and , when they act on the vortex optical field , they satisfy the following formula: ; ; In the formula, is the expression in polar coordinates and can be expressed as: ; where r is the radial distance.

[0042] The above formula shows that acts on the optical field to make the optical field symmetric with respect to the straight line ; while When acting on the optical field, it will rotate the optical field by an angle. Therefore, the operator of the mirror can be expressed as , and the operator of the Dove prism on the optical field can be expressed as: .

[0043] For the outgoing light at point A, that is, the first outgoing light, it includes the light beam obtained by transmitting the first reflected light on the r' path through the second beam splitter prism 16, and the light beam obtained by reflecting the first transmitted light on the t' path through the second beam splitter prism 16. Among them, in the r' path, the incident light is reflected by the first beam splitter prism 14 to produce a phase change caused by the half-wave loss, and then is reflected by the third mirror 17 to produce a phase change. After passing through the second Dove prism, it produces a fixed phase change and a phase delay , and then passes through the second beam splitter prism 16 to produce a fixed phase change . In the t' path, the incident light is transmitted by the first beam splitter prism 14 to produce a fixed phase change , passes through the first Dove prism to produce a fixed phase change , and then is reflected by the second mirror to produce a phase change, and then is reflected by the second beam splitter prism 16 to produce a fixed phase change . Therefore, when the incident vortex beam has a helical phase term , the phase difference between the two light beams entering the CCD at point A in the r' path and the t' path is .

[0044] Similarly, when the incident vortex beam has a helical phase term , for the second outgoing light at point B, the phase difference between the two light beams in the r' path and the t' path is .

[0045] The above analysis shows that for a vortex beam with an even angular quantum number after passing through a Mach-Zehnder interferometer with Dove prisms installed on both arms, at point B, the phase difference between the two light beams is an odd multiple of , resulting in destructive interference, and the electric field vector at point B , so the optical field energy will only be output from point A. Similarly, for a vortex beam with an odd angular quantum number , at point A, the phase difference between the two light beams is an odd multiple of , resulting in destructive interference, and the electric field vector at point A , after passing through this Mach-Zehnder interferometer, the optical field energy is output from point B. It should also be noted here that during the transmission of the light beam emitted from point A, three reflections occur, resulting in the inversion of the order of the vortex beam or the sign of the orbital angular momentum carried; while for the light beam emitted from point B, two and four total reflections occur respectively during the transmission, and the order of the emitted light beam or the sign of the orbital angular momentum carried remains unchanged. Specifically, for the light beam emitted from point A, the light beam transmitted through path t', after passing through the first beam splitter prism 14, is reflected once by the first Dove prism, once by the second mirror 15, and once by the second beam splitter prism 16 and then exits from point A. The light beam transmitted through path r' is reflected once by the first beam splitter prism 14, once by the third mirror 17, and once by the second Dove prism, and then exits from point A after passing through the second beam splitter prism 16; for the light beam emitted from point B, the light beam transmitted through path t', after passing through the first beam splitter prism 14, is reflected once by the first Dove prism and once by the second mirror 15, and then exits from point B after passing through the second beam splitter prism 16. The light beam transmitted through path r' is reflected once by the first beam splitter prism 14, once by the third mirror 17, once by the second Dove prism, and once by the second beam splitter prism 16 and then exits from point B.

[0046] When the dual-mode hybrid vortex beam is incident, after passing through the Mach-Zehnder interferometer equipped with Dove prisms, single-mode vortex beams of +2 order and +3 order can be observed at points A and B respectively.

[0047] When demonstrating the separation of the orbital angular momentum of the multi-mode hybrid vortex beam, place the first CCD camera at point A where the first output light exits, and place the first Dove prism and the second Dove prism that are relatively rotated by an angle of π / 2 on paths t' and r' respectively. Then it can be observed that the interference pattern in the form of a 5-petal flower pattern that could originally be observed between the third polarization beam splitter prism 12 and the first mirror 13 "disappears". At this time, place a plano-convex cylindrical lens with a focal length of 50 mm in front of the first CCD camera and the second CCD camera respectively. At this time, the vortex beam is transformed into a Hermite-Gaussian beam, and the pattern will become a stripe pattern tilted upward to the upper right. The pattern of the first CCD camera is 2 stripes, and the pattern of the second CCD camera is 3 stripes. From this, it can be judged that the separation of the orbital angular momentum components of the multi-mode hybrid vortex beam has been successfully achieved.

[0048] In this embodiment, neural network chips are also embedded in both the first CCD camera and the second CCD camera. When the first CCD camera images the first outgoing light to obtain a first interference image, or the second CCD camera images the second outgoing light to obtain a second interference image. The interference image is acquired, preprocessed, and then input into a convolutional neural network model to output a vortex light interference analysis diagram. When the interference image is input into the convolutional neural network model, it first extracts the interference image features through a multi-scale pyramid convolution module, then enhances the interference image features through a feature enhancement module to output an enhanced feature map, and finally outputs a vortex light interference analysis diagram through a cyclic memory fusion module.

[0049] Specifically: the preprocessing of the interference image includes adaptive multi-scale image enhancement, feature normalization, and multi-scale sampling and stitching. For the input interference image , it is first decomposed into sub-images of different scales , s = 1, 2, …, n, where n represents the number of scales. The decomposition process can be achieved through the Gaussian pyramid algorithm, that is , where is the Gaussian kernel function at different scales s. Then, for each sub-image at scale s, its local contrast is calculated. The local contrast is obtained by calculating the ratio of the standard deviation σ of the pixel values within the local region centered on pixel i to the mean μ, and the formula is , ε is a very small constant used to avoid the denominator being zero.

[0050] According to the local contrast s, the pixel values of the sub-image are adaptively adjusted. The formula for the enhanced sub-image s' is , where αs is the enhancement coefficient corresponding to scale s, which is adaptively adjusted according to the importance of different scale features and the overall situation of the image. Finally, the enhanced sub-images are recombined into a complete enhanced image , and the enhanced image is the preprocessed interference image.

[0051] In the convolutional neural network model, the multi-scale pyramid convolution module is used to extract the interference image features. The multi-scale pyramid convolution module consists of multiple convolutional layers with different sizes of convolutional kernels in parallel. Taking 3 × 3, 5 × 5, 7 × 7 convolutional kernels as an example, for the input preprocessed interference image , through different convolutional kernels 、 、 convolve respectively to obtain feature maps of different scales 、 、 。

[0052] ; ; ;Among them, the pixel position on the feature map is the pixel position within the convolutional kernel. Then these feature maps of different scales are concatenated and fused by channels into interference image features, and the interference image features are , 。This multi-scale convolution method can capture image features of different scales more comprehensively.

[0053] In the feature enhancement module, first perform global average pooling on the interference image features to obtain the global feature vector of each channel , and the formula is , where and are the height and width of the feature map, represents the number of channels. Then calculate the attention weights and through two fully connected layers , first pass through for dimensionality reduction, and then pass through for dimensionality increase, and the formula is , , , where is the sigmoid function, which is used to map the weight value to the interval (0,1). Finally, multiply the attention weights by the interference image features to obtain the enhanced feature map , and the formula is . This can highlight the key feature channels related to the characteristics of vortex light.

[0054] In the cyclic memory fusion module, the cyclic memory fusion module is composed of multiple long short-term memory network units connected end to end. The long short-term memory network unit includes a forget gate 、an input gate 、an output gate and a memory unit . Each long short-term memory network unit receives the hidden state of the previous moment 、the enhanced feature map of the current moment as inputs.

[0055] In the long short-term memory network unit, first, the forget gate calculation is performed. The forget gate determines which information in the memory unit of the previous moment is retained. The formula is . Among them, is the weight matrix of the forget gate, represents concatenating the hidden state of the previous moment and the current enhanced feature map in a specific dimension, is the bias of the forget gate, is the sigmoid function, which maps the output value to the interval (0, 1). The closer the value is to 1, the higher the degree of retaining the corresponding information.

[0056] Then, the input gate calculation is performed, and a candidate memory unit is generated. The input gate controls the degree to which the input information at the current moment enters the memory unit and simultaneously generates a candidate memory unit . The calculation formula of the input gate is , and the calculation formula of the candidate memory unit is . Among them, , are the corresponding weight matrices, , are the biases, is the hyperbolic tangent function, which maps the output value to the interval (-1, 1).

[0057] The memory unit is updated according to the calculation results of the forget gate, the input gate calculation, and the candidate memory unit to determine the information at the current moment. The formula for updating the memory unit is ; among them, represents element-wise multiplication, that is, it determines which parts of the memory unit of the previous moment to retain according to the output of the forget gate, and then adds the new information at the current moment determined by the input gate and the candidate memory unit.

[0058] The output gate determines which information in the memory unit is used to generate the output at the current moment, and the hidden state at the current moment is also determined accordingly. The calculation formula of the output gate is , and the calculation formula of the hidden state is ; among them, is the weight matrix of the output gate, is the bias. The output of the memory unit information is controlled by the output gate, and after processing the memory unit with the hyperbolic tangent function, it is multiplied by the result of the output gate to obtain the hidden state. Except for the last long short-term memory network unit, the hidden states output by other long short-term memory network units will be used as the input of the long short-term memory network unit at the next moment.

[0059] The hidden state output by the last long short-term memory network unit Features containing time series information can record the changes in the interference characteristics of vortex light over time. To obtain the final analytical diagram of vortex light interference, the hidden state needs to be mapped to a specific dimension through a fully connected layer. After being converted into an image, the analytical diagram of vortex light interference can be obtained. The analytical diagram of vortex light interference includes features such as the vortex light mode and orbital angular momentum that change continuously over time.

[0060] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A vortex light interference device, characterized in that: include: A circular polarization generating unit, a first interference unit, and a second interference unit; A circular polarization generating unit, used for generating circular polarized light; A first interference unit is used to realize Mach-Zehnder interference according to the circularly polarized light generated by the circularly polarized light generating unit, and transmit the combined light beam to the second interference unit; The second interference unit comprises a first reflector, a first beam splitter prism, a second reflector, a third reflector and a second beam splitter prism; the first reflector reflects the light beam transmitted by the first interference unit to the first beam splitter prism, the first beam splitter prism splits the light beam into a first transmitted light and a first reflected light, the first transmitted light enters the second beam splitter prism after being reflected by the second reflector, and the first reflected light enters the second beam splitter prism after being reflected by the third reflector; the second beam splitter prism generates a first output light and a second output light, the first output light comprises a light beam obtained by reflecting the first transmitted light through the second beam splitter prism and a light beam obtained by transmitting the first reflected light through the second beam splitter prism, the second output light comprises a light beam obtained by transmitting the first transmitted light through the second beam splitter prism and a light beam obtained by reflecting the first reflected light through the second beam splitter prism; It also includes a vortex beam generating unit, a first dove prism, a second dove prism, a first CCD camera, and a second CCD camera. When the multi-mode hybrid vortex light orbital angular momentum separation is demonstrated, the vortex beam generating unit is arranged at the two interference light paths of the first interference unit, and is used to convert both interference light beams into vortex beams. The first dove prism and the second dove prism are respectively arranged at the light paths of the first transmitted light and the first reflected light, and the first dove prism and the second dove prism are relatively rotated by an angle of π / 2. The first CCD camera and the second CCD camera are respectively used to image the first outgoing light and the second outgoing light to obtain an interference image; wherein the first CCD camera and the second CCD camera are both embedded with a neural network chip; The neural network chip is integrated with a convolutional neural network model, which includes a multi-scale pyramid convolution module, a feature enhancement module and a recurrent memory fusion module; the multi-scale pyramid convolution module is composed of multiple groups of convolution layers with different sizes of convolution kernels in parallel; the interference image passes through different convolution layers to obtain feature maps of different scales, and the obtained feature maps of different scales are fused to obtain interference image features; in the feature enhancement module, the interference image features are firstly globally averaged pooled to obtain a global feature vector of each channel; then the attention weight is calculated through two fully connected layers; finally, the attention weight and the interference image feature are multiplied to obtain an enhanced feature map; the recurrent memory fusion module is composed of multiple long short-term memory network units connected end to end, and the enhanced feature map is sequentially input into the long short-term memory network unit in chronological order, wherein the long short-term memory network unit includes a forget gate, an input gate, an output gate and a memory unit.

2. A vortex light interference device as claimed in claim 1, characterized in that: The first interference unit includes a first polarization beam splitter prism, a fourth reflector, a fifth reflector, a second polarization beam splitter prism, a first quarter wave plate, and a third polarization beam splitter prism; the first polarization beam splitter prism splits the circularly polarized light generated by the circularly polarized light generating unit into a second transmitted light and a second reflected light, the second transmitted light enters the second polarization beam splitter prism after being reflected by the fourth reflector, the second reflected light enters the second polarization beam splitter prism after being reflected by the fifth reflector, the second transmitted light and the second reflected light are combined at the second polarization beam splitter prism, pass through the first quarter wave plate and the third polarization beam splitter prism in sequence, and are transmitted to the first reflector.

3. A vortex light interference device as claimed in claim 1, characterized in that: The circularly polarized light generating unit comprises a solid laser, an attenuation plate, a half-wave plate, a beam expansion unit and a second quarter-wave plate. The laser light generated by the solid laser is attenuated by the attenuation plate, the polarization state is changed by the half-wave plate, and the linearly polarized light is obtained after the beam expansion unit expands the laser light. The second quarter-wave plate converts the linearly polarized light into circularly polarized light and outputs the circularly polarized light to the first interference unit. The beam expansion unit comprises a first focal length plano-convex lens and a second focal length plano-convex lens.

4. A vortex light interference device as claimed in claim 1, characterized in that: The vortex beam generating unit includes a first vortex beam generating unit and a second vortex beam generating unit. The first vortex beam generating unit includes a first q-wave plate and a third quarter-wave plate. The second vortex beam generating unit includes a second q-wave plate and a fourth quarter-wave plate. The orders of the first q-wave plate and the second q-wave plate are different; the order of the first q-wave plate is an even number, and the order of the second q-wave plate is an odd number.

5. A vortex light interference device as claimed in claim 1, characterized in that: The long short-term memory network unit takes the enhanced feature map and the hidden state of the previous moment as input. In the long short-term memory network unit, the forget gate calculation is first performed, and then the input gate calculation is performed, and a candidate memory unit is generated. Then the memory unit is updated according to the forget gate calculation result, the input gate calculation and the candidate memory unit to determine the current moment information, and finally the hidden state of the output at the current moment is determined through the output gate.

6. A vortex light interference device as claimed in claim 1, characterized in that: In the recurrent memory fusion module, except for the last long short-term memory network unit, the hidden states output by other long short-term memory network units will be used as the input of the long short-term memory network unit at the next moment.

7. A vortex light interference method, characterized in that: A vortex light interference device according to any one of claims 1 to 4, comprising: Two vortex beam generating units with different orders are respectively arranged at the first transmission path and the first reflection path of the first interference unit, so that the first interference unit outputs a dual-mode mixed vortex beam; The first dove prism is arranged between the first beam splitter prism and the second reflector, the second dove prism is arranged between the third reflector and the second beam splitter prism, and the first dove prism and the second dove prism are relatively rotated by an angle of π / 2; The first CCD camera is arranged at the position where the first outgoing light of the second beam splitter prism emerges, and the first outgoing light is imaged to obtain a first interference image; the second CCD camera is arranged at the position where the second outgoing light of the second beam splitter prism emerges, and the second outgoing light is imaged to obtain a second interference image; An interference image is obtained, and the interference image is preprocessed and input into a convolutional neural network model to output a vortex light interference analysis map; wherein the interference image is input into the convolutional neural network model, and the interference image features are firstly extracted through a multi-scale pyramid convolution module, and then the interference image features are enhanced through a feature enhancement module, and an enhanced feature map is output, and then the vortex light interference analysis map is output through a recurrent memory fusion module.

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