Method for quickly acquiring hologram based on elastic membrane liquid lens

Abstract

The invention provides a hologram rapid acquisition method based on an elastic film liquid lens. The method comprises the following three steps: step 1, acquiring a focus stack of a real 3D scene in real time by using a liquid camera based on the elastic film liquid lens; 2, inputting the obtained focus stack into an angular spectrum diffraction propagation model so as to quickly calculate complex amplitude distribution of the focus stack on a hologram plane; and 3, quickly coding the complex amplitude distribution of the focus stack on the hologram plane into a pure phase hologram by using a double-phase coding method. The obtained pure phase hologram is loaded to a spatial light modulator, and a real 3D scene is reproduced after laser irradiation.

Description

1. Technical Field

[0001] The present invention relates to holographic display technology, and more specifically, to a method for quickly acquiring a hologram based on an elastic membrane liquid lens. 2. Background Technology

[0002] Holographic 3D display technology can provide the human eye with all the depth clues needed to perceive 3D objects, and is therefore regarded as one of the most promising naked-eye 3D display technologies. However, due to the large amount of data and complex expression of real 3D scenes, the acquisition process of real 3D scenes is time-consuming and the acquisition speed of holograms is slow. In order to speed up the acquisition speed of holograms of real 3D scenes, some researchers use electrowetting liquid lenses to quickly acquire real 3D scenes from the perspective of improving the acquisition speed of real 3D scenes. However, due to the limitation of the aperture of the electrowetting liquid lens, the response speed of the electrowetting liquid lens is usually slow. Other researchers have designed a polarization camera based on a metasurface, which can obtain the complex amplitude information of the real 3D scene with only a single exposure. However, the processing of the metasurface is expensive, and the assembly of the polarization camera is complex, which further increases the difficulty of acquiring the real 3D scene. In addition, in the calculation process of the hologram, it is usually necessary to pre-calculate the full focus map and depth map of the real 3D scene, and processing the acquired information of the real 3D scene into the full focus map and depth map often requires additional computing time. At present, how to quickly obtain a hologram of a real 3D scene is still an unresolved problem in the field of holographic 3D display. III. Summary of the invention

[0003] The present invention proposes a method for quickly acquiring a hologram based on an elastic membrane liquid lens. Figure 1 As shown in the figure, the method includes three steps: the first step is to use a liquid camera based on an elastic membrane liquid lens to obtain the focal stack of a real 3D scene in real time; the second step is to input the obtained focal stack into the angular spectrum diffraction propagation model to quickly calculate the complex amplitude distribution of the focal stack on the hologram plane; the third step is to use the dual-phase encoding method to quickly encode the complex amplitude distribution of the focal stack on the hologram plane into a pure phase hologram. The obtained pure phase hologram is loaded onto a spatial light modulator, and the real 3D scene is reproduced after laser irradiation.

[0004] In step 1, the liquid camera is composed of an elastic film liquid lens, a solid lens group and a CCD target surface, as shown in the attached Figure 2 As shown. Among them, the elastic membrane liquid lens is the key component to realize the real-time zoom function of the liquid camera, the solid lens group is used to provide the main optical focal length, and the CCD target surface is used to record the focal plane information captured. The optical focal length of the liquid camera Φ C It is expressed as:

[0005] Φ C=Φ L +Φ S -d LS ·Φ L ·Φ S (1)

[0006] Among them, Φ L and Φ S Respectively represent the optical power of the elastic membrane liquid lens and the solid lens group, d LS represents the distance between the optical principal planes of the elastic membrane liquid lens and the solid lens group. When the liquid camera is assembled, Φ S and d LS When a liquid camera is used to capture a focal stack of a real 3D scene, the focal power Φ of the elastic membrane liquid lens L Changes with the change of driving current. Therefore, the optical focal length Φ of the liquid camera can be realized by changing the driving current of the elastic membrane liquid lens. C changes.

[0007] As attached Figure 3 As shown in the figure, the elastic membrane liquid lens is prepared based on the voice coil motor driving principle. The elastic membrane liquid lens consists of a magnet, a glass window, an elastic membrane, an exhaust hole, a coil, a pressure plate, a filling liquid, a liquid pool and a shell. In the elastic membrane liquid lens, the coil is in a radial magnetic field formed by the magnet. The exhaust hole is used to ensure that the air pressure inside the lens is consistent with the outside. The pressure plate is tightly connected to the coil and the elastic membrane. The elastic membrane and the liquid pool form a closed space. The filling liquid is encapsulated in the liquid pool. When no power is applied, the elastic membrane forms a natural curved surface at the aperture of the lens. When a DC current is passed through the coil, the coil is acted upon by the Ampere force, thereby driving the pressure plate to move.

[0008] As attached Figure 4 As shown in (a), when the direction of the Ampere force is to the right, the pressure plate moves to the right. Since the filling liquid cannot be compressed, the filling liquid gathers in the central area of ​​the liquid pool sealed by the elastic membrane. At this time, the elastic membrane liquid lens forms a convex shape, achieving the effect of converging light. Figure 4 As shown in (b), when the direction of the Ampere force is to the left, the pressure plate moves to the left. At this time, the elastic membrane liquid lens forms a concave shape, achieving the effect of diverging light. The liquid material of the elastic membrane liquid lens has the characteristics of high refractive index. The elastic membrane liquid lens also uses an elastic membrane surface control component. The designed elastic membrane liquid lens has the characteristics of fast response speed and large zoom range, thereby ensuring that the liquid camera obtains the focus stack of the real 3D scene in real time.

[0009] In step 2, for the i-th (i=1, 2, ..., M) layer of focus stack collected by the liquid camera in step 1, the intensity distribution corresponding to the i-th layer of focus stack is recorded as O i(x0, y0), the complex amplitude distribution U(x, y) of the hologram is expressed as:

[0010]

[0011] Where M represents the number of focus stack layers, j represents an imaginary number, and represent Fourier transform and inverse Fourier transform respectively, λ represents wavelength, z i represents the recording distance of the i-th layer focal stack, f x and f y represent the frequencies in the x and y directions respectively.

[0012] In step 3, the complex amplitude distribution U(x, y) of the hologram is encoded using the dual-phase encoding method, and the complex amplitude distribution H(x, y) of the pure phase hologram is obtained as:

[0013]

[0014] Among them, angle[] represents the phase of the complex amplitude distribution, abs[] represents the amplitude of the complex amplitude distribution, cos -1 {} represents the arccosine trigonometric function, and % represents the remainder operation. IV. Description of the drawings

[0015] Attached Figure 1 It is a schematic diagram of a method for quickly acquiring a hologram based on an elastic membrane liquid lens according to the present invention.

[0016] Attached Figure 2 It is a schematic structural diagram of a liquid camera based on an elastic membrane liquid lens of the present invention.

[0017] Attached Figure 3 It is a schematic structural diagram of the elastic membrane liquid lens of the present invention.

[0018] Attached Figure 4 Schematic diagram of the surface shape change of the elastic membrane liquid lens of the present invention. Figure 4 (a) is a schematic diagram of the lens converging light when the surface of the elastic membrane liquid lens is convex. Figure 4 (b) is a schematic diagram of the divergent light rays emitted by the lens when the surface of the elastic membrane liquid lens is concave.

[0019] Attached Figure 5 Attached is an experimental result diagram of an embodiment of a method for quickly acquiring a hologram based on an elastic membrane liquid lens of the present invention. Figure 5 (a) and Figure 5 (b) is the focal stack captured by the liquid camera based on the elastic membrane liquid lens, with Figure 5 (c) is the pure phase hologram of the focal stack calculated using the angular spectrum diffraction model. Figure 5 (d) and Figure 5 (e) is the holographic reconstruction image of the "No Parking" sign and the "Traffic Light" sign when they are focused respectively.

[0020] The diagram numbers in the above-mentioned drawings are:

[0021] (1) Elastic membrane liquid lens, (2) solid lens group, (3) CCD target surface, (4) magnet, (5) glass window, (6) elastic membrane, (7) exhaust hole, (8) coil, (9) pressure plate, (10) filling liquid, (11) liquid pool, (12) shell, (13) glass window, (14) pressure plate, (15) filling liquid, (16) air, (17) elastic membrane.

[0022] It should be understood that the above drawings are only schematic and are not drawn to scale. V. Specific implementation methods

[0023] The following is a detailed description of an embodiment of a method for quickly acquiring a hologram based on an elastic membrane liquid lens proposed by the present invention, and further describes the present invention. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Personnel skilled in the art may make some non-essential improvements and adjustments to the present invention based on the above invention content, which still fall within the scope of protection of the present invention.

[0024] The embodiment of the present invention is as follows: In the experiment, the aperture number of the solid lens group in the liquid camera is 2.8, the focal length is 16mm, the pixel pitch of the CCD target surface is 2.4μm, and the area of ​​the CCD target surface is 1 / 1.8". The current control driver of the elastic membrane liquid lens is developed based on STM32G070, and the minimum adjustment step of the current is 1mA. The light aperture of the elastic membrane liquid lens is 10mm, and the thickness of the lens is 12mm. When the DC current is controlled to change from -40mA to 40mA in a step of 1mA, the optical focal length of the liquid camera changes from 30mA to 12mA. -1 Change to -10m -1 The recorded real 3D scene consists of a “No Parking” sign and a “Traffic Light” sign, and the actual depth interval between the two signs is 50 mm.

[0025] The focus stack of the "No Parking" sign and the "Traffic Light" sign captured by the liquid camera based on the elastic membrane liquid lens is shown in the attached figure. Figure 5As shown in (a) and 5(b), the zoom response time of the liquid camera is 15ms. The focal stack of the real 3D scene collected by the liquid camera in real time is input into the angular spectrum diffraction propagation model, and the complex amplitude distribution of the focal stack on the hologram plane is calculated. Then, the complex amplitude distribution of the focal stack on the hologram plane is quickly encoded into a pure phase hologram using the dual-phase encoding method. The resolution of the output pure phase hologram is 1920×1080, as shown in the attached figure. Figure 5 As shown in (c), the calculation time of the pure phase hologram is 20ms.

[0026] In the optical reconstruction experiment, the output pure phase hologram is loaded onto a spatial light modulator with a resolution of 1920×1080, a pixel pitch of 6.4μm, and a refresh rate of 60Hz. After irradiation with colored lasers, the reconstruction effect of the pure phase hologram is obtained. The holographic reconstruction images of the "No Parking" sign and the "Traffic Light" sign when they are focused are shown in the attached figure. Figure 5 (d) and 5(e). The hologram acquisition method based on elastic membrane liquid lens proposed in the present invention can achieve rapid acquisition of holograms of real 3D scenes within 35ms.

Claims

1. A method for quickly acquiring a hologram based on an elastic membrane liquid lens, characterized in that: The method includes three steps: the first step is to use a liquid camera based on an elastic membrane liquid lens to obtain a focal stack of a real 3D scene in real time; In the second step, the obtained focal stack is input into the angular spectrum diffraction propagation model to quickly calculate the complex amplitude distribution of the focal stack on the hologram plane; In the third step, the dual-phase encoding method is used to quickly encode the complex amplitude distribution of the focus stack on the hologram plane into a pure phase hologram, and the obtained pure phase hologram is loaded onto the spatial light modulator, and the real 3D scene is reproduced after laser irradiation.

2. The method for quickly acquiring a hologram based on an elastic membrane liquid lens according to claim 1, characterized in that: In step 1, the liquid camera is composed of an elastic membrane liquid lens, a solid lens group and a CCD target surface, wherein the elastic membrane liquid lens is a key component for realizing the real-time zoom function of the liquid camera, the solid lens group is used to provide the main optical focal length, and the CCD target surface is used to record the focal plane information captured. The optical focal length of the liquid camera is Φ C It is expressed as: F C =Φ L +F S -d LS ·F L ·F S Among them, Φ L and Φ S Respectively represent the optical power of the elastic membrane liquid lens and the solid lens group, d LS Represents the distance between the optical principal planes of the elastic membrane liquid lens and the solid lens group. When the liquid camera is assembled, Φ S and d LS When the focal stack of a real 3D scene is captured using a liquid camera, the focal power Φ of the elastic membrane liquid lens remains unchanged. L The optical power Φ of the liquid camera is realized by changing the driving current of the elastic membrane liquid lens. C changes; The elastic membrane liquid lens is prepared based on the voice coil motor driving principle. The elastic membrane liquid lens consists of a magnet, a glass window, an elastic membrane, an exhaust hole, a coil, a pressure plate, a filling liquid, a liquid pool and a shell. In the elastic membrane liquid lens, the coil is in a radial magnetic field formed by a magnet. The exhaust hole is used to ensure that the air pressure inside the lens is consistent with the outside world. The pressure plate is tightly connected to the coil and the elastic membrane. The elastic membrane and the liquid pool form an enclosed space. The filling liquid is encapsulated in the liquid pool. When no electricity is applied, the elastic membrane forms a natural curved surface at the aperture of the lens. When a DC current is passed through the coil, the coil will be affected by the Ampere force, thereby driving the pressure plate to move. When the direction of the Ampere force is to the right, the pressure plate moves to the right. Since the filling liquid cannot be compressed, the filling liquid gathers in the central area of ​​the liquid pool sealed by the elastic membrane. At this time, the elastic membrane liquid lens forms a convex shape, which realizes the effect of converging light. When the direction of the Ampere force is to the left, the pressure plate moves to the left. At this time, the elastic membrane liquid lens forms a concave shape, which realizes the effect of diverging light. The liquid material of the elastic membrane liquid lens has the characteristic of high refractive index. The elastic membrane surface control component is also used in the elastic membrane liquid lens. The designed elastic membrane liquid lens has the characteristics of fast response speed and large zoom range, thereby ensuring that the liquid camera can obtain the focal stack of the real 3D scene in real time.

3. The method for quickly acquiring a hologram based on an elastic membrane liquid lens according to claim 1, characterized in that: In step 2, for the i-th (i=1, 2, ..., M) layer of focus stack collected by the liquid camera, the intensity distribution corresponding to the i-th layer of focus stack is recorded as O i (x0, y0), the complex amplitude distribution U(x, y) of the hologram is expressed as: Where M represents the number of focus stack layers, j represents an imaginary number, and represent Fourier transform and inverse Fourier transform respectively, λ represents wavelength, z i represents the recording distance of the i-th layer focal stack, f x and f y represent the frequencies in the x and y directions respectively.

4. The method for quickly acquiring a hologram based on an elastic membrane liquid lens according to claim 1, characterized in that: In step 3, the complex amplitude distribution U(x, y) of the hologram is encoded using the dual-phase encoding method, and the complex amplitude distribution H(x, y) of the pure phase hologram is obtained as: Among them, angle[] represents the phase of the complex amplitude distribution, abs[] represents the amplitude of the complex amplitude distribution, cos -1 {} represents the arccosine trigonometric function, and % represents the remainder operation.

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