A multi-focal surface display optical system that eliminates vergence accommodation conflict

Abstract

The application provides a multi-focal surface display optical system for eliminating vergence accommodation conflict, and relates to the technical field of optical display, comprising an LCD display panel; a Mini-LED backlight plate is located on the light entrance side of the LCD display panel and comprises a plurality of independently controllable backlight subareas; a zoom module is located on the light exit side of the LCD display panel and comprises at least one transmissive geometric phase liquid crystal lens and at least one polarization switch, the polarization switch is located on the light entrance side of the geometric phase liquid crystal lens and is used for dynamically switching the polarization state of the light incident to the geometric phase liquid crystal lens to change the equivalent focal length of the zoom module; the Mini-LED backlight plate is configured to sequentially light different backlight subareas in time sequence, and the polarization switch is configured to switch synchronously with the lighting time sequence of the backlight subareas, so that when a target backlight subarea is lighted at any time sequence, the zoom module is switched to the focal length matched with the focal surface corresponding to the target backlight subarea, thereby avoiding the vergence accommodation conflict.

Description

Technical Field

[0001] This invention relates to the field of optical display technology, and in particular to a multifocal display optical system that eliminates convergence-adjustment conflict. Background Technology

[0002] In recent years, with the rapid maturation of virtual reality (VR) content ecosystems and hardware platforms, head-mounted displays (HWD / HMDs), as a core component of VR devices, have been widely used in scenarios such as gaming, smart classrooms, and virtual training. Currently, most commercial HWDs rely on binocular parallax to construct three-dimensional depth perception, that is, by presenting images with parallax to the left and right eyes respectively to induce binocular convergence. However, this traditional display method often leads to convergence-accommodation conflict (VAC): in the real world, the convergence and accommodation of the human eye usually point to the same target depth, but in traditional HWDs, the display system only images on a fixed two-dimensional image plane, causing the user's accommodation to be locked to this fixed focal plane, while the convergence cue changes with the depth of the virtual object. This mismatch between accommodation and convergence cues is one of the main reasons for nausea, dizziness, and visual fatigue when wearing VR devices for extended periods.

[0003] To address the VAC (Active Accommodation and Focusing) problem, researchers have proposed various technical solutions, including light field displays, holographic displays, and multifocal displays, aiming to introduce focusing cues that conform to the physiological laws of the human eye. While light field displays can reconstruct a four-dimensional light field to support natural accommodation response, they face a fundamental trade-off between viewing angle and resolution, and suffer from enormous computational load and a complex, large optical system, making lightweight design difficult. Holographic display technology can theoretically achieve perfect three-dimensional wavefront reconstruction, but its limitations are imposed by the number of pixels in the spatial light modulator, resulting in restrictions on exit pupil size and field of view. Furthermore, speckle noise introduced by coherent light sources severely impacts image quality, and real-time computation requirements are extremely high, currently making it difficult to meet the practical needs of VR.

[0004] In contrast, multifocal plane displays (VCAs) use spatial or temporal multiplexing to stack multiple focal planes to approximate the reconstruction of continuous 3D scenes, and are considered one of the most promising VAC solutions currently available. However, existing multifocal plane display solutions still face many challenges: the core component, the zoom lens (such as liquid lenses and mechanically moving lenses), is difficult to simultaneously meet the requirements of VR devices, such as a large aperture (approximately 40mm), fast response time (less than 15ms), and thin design; in addition, the dense stacking of focal planes often requires sacrificing system size or refresh rate. Although some research has used digital micromirror devices (DMDs) in conjunction with liquid crystal panels to achieve high-speed focal plane switching, DMD systems require additional projection or relay optical elements, resulting in complex optical paths and difficulty in compressing the size, which cannot meet the stringent requirements of VR systems for a compact form factor. Summary of the Invention

[0005] This invention provides a multi-focal plane display optical system that eliminates convergence-accommodation conflict, thereby solving the technical problem that existing technologies cannot effectively resolve convergence-accommodation conflict.

[0006] On one hand, the present invention provides a multifocal plane display optical system for eliminating convergence adjustment conflict, comprising: LCD display panel, used to display image information; The Mini-LED backlight panel is located on the light-incident side of the LCD display panel and includes multiple independently controllable backlight zones. A zoom module, located on the light-emitting side of the LCD display panel, includes at least one transmissive geometric phase liquid crystal lens and at least one polarization switch. The polarization switch is located on the light-incident side of the geometric phase liquid crystal lens and is used to dynamically switch the polarization state of the light incident on the geometric phase liquid crystal lens to change the equivalent focal length of the zoom module. The Mini-LED backlight panel is configured to sequentially illuminate different backlight zones according to a time sequence, and the polarization switch is configured to switch synchronously with the illumination time sequence of the backlight zones, so that when a target backlight zone is illuminated at any time sequence, the zoom module switches to a focal length that matches the focal plane corresponding to the target backlight zone, thereby realizing multi-focal plane display.

[0007] Optionally, the geometric phase liquid crystal lens achieves focal length switching based on geometric phase modulation, and the in-plane orientation angle distribution of its liquid crystal molecules satisfies: ; in, The focal length of the lens; Wavelength; For higher-order phase terms, Let x be the abscissa of a two-dimensional rectangular coordinate system established on the plane of the liquid crystal lens, with the center of the lens (usually the intersection of the optical axis and the lens surface) as the origin. The vertical axis is used as the coordinate. It is the in-plane orientation angle.

[0008] Optionally, the thickness of the geometric phase liquid crystal lens satisfies the half-wave condition, so that the polarization state of the incident circularly polarized light is reversed after passing through the lens, and it has different response states to circularly polarized light with different chiralities; by switching the polarization state of the incident light, the positive and negative focal lengths are converted, thereby achieving dynamic adjustment of the optical power without moving the lens. The Jones matrix of the geometric phase liquid crystal lens is represented as follows: ; in, The Jones matrix represents the liquid crystal lens; For incident circularly polarized light, the horizontal and vertical components of this vector have equal amplitudes.

[0009] Optionally, the resolution of the Mini-LED backlight is lower than that of the LCD display panel; The number of backlight zones of the Mini-LED backlight panel is equal to the number of focal planes that the zoom module can switch. The Mini-LED backlight is configured to operate at a refresh rate higher than the preset critical flicker frequency for the human eye, in order to cooperate with the zoom module to achieve multi-focal surface display.

[0010] Optionally, the zoom module includes N transmissive geometric phase liquid crystal lenses and N polarization switches; N is an integer greater than or equal to 2. Each of the polarization switches is configured to switch the polarization chirality of the incident light to control the switching of the focal length of the corresponding geometric phase liquid crystal lens; The N geometric phase liquid crystal lenses and N polarization switches are stacked and combined, and a 2D polarization encoding is achieved based on binary optical power coding. N Switching between equivalent focal lengths.

[0011] Optionally, when N=2, the ratio of the focal lengths of the two geometric phase liquid crystal lenses is 2:1, and the corresponding ratio of optical power is 1:2. By combining the states of the two polarization switches, the zoom module can switch to four discrete focal planes, with its optical power range covering the positive and negative symmetrical intervals.

[0012] Optionally, the focal lengths of the two geometric phase liquid crystal lenses are 0.9m and 1.8m, respectively, corresponding to optical powers of 1.1D and 0.55D. The zoom module switches between four discrete focal planes within the range of -1.65D to 1.65D by combining the states of the two polarization switches, with an optical power interval of 1.1D between adjacent focal planes.

[0013] Optional, also includes: A diffuser is disposed between the Mini-LED backlight panel and the LCD display panel to reduce the screen-door effect generated when the Mini-LED backlight panel is illuminated in sections.

[0014] Optionally, the geometric phase liquid crystal lens includes a light alignment layer and a multilayer liquid crystal layer stacked on top of the light alignment layer; The liquid crystal molecules at the bottom of the liquid crystal layer that are in contact with the light alignment layer are arranged according to the arrangement of light alignment molecules, and the molecules in contact between the liquid crystal layers are arranged in the same direction. Each liquid crystal layer has a spontaneous spiral structure in the direction perpendicular to the substrate, and the liquid crystal rotation angle and thickness of each liquid crystal layer are configured such that the diffraction efficiency of the liquid crystal lens in the visible light band is greater than a preset efficiency threshold.

[0015] Optionally, the polarization switch includes a TN-type liquid crystal cell and a polarization compensation film. The polarization compensation film is composed of multiple A-plates with different optical axis rotation angles, used to control the circular polarization chirality of the incident light.

[0016] This invention provides a multi-focal plane display optical system that eliminates convergence conflict. By employing a Mini-LED backlight panel with independently controllable zones in conjunction with a zoom module containing a geometric phase liquid crystal lens and a polarization switch, the system achieves rapid time-division multiplexing display of different focal planes through the sequential lighting of the backlight zones and the synchronous switching of the polarization switch. This structure not only effectively solves the convergence conflict problem and eliminates visual fatigue by utilizing the high response speed of the geometric phase liquid crystal lens, but also avoids the defects of complex optical paths and large size of zoom systems through the compact combination of the Mini-LED backlight panel and the geometric phase liquid crystal lens. It achieves lightweight and integrated optical system while ensuring a natural focusing experience at multiple depths. Attached Figure Description

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

[0018] Figure 1 This is a schematic diagram of the structure of a multifocal surface display optical system for eliminating convergence adjustment conflict provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the working process of the multi-focal surface display system provided in the embodiment of the present invention; Figure 3 This is a schematic diagram of the molecular arrangement of the alignment layer in a geometric phase liquid crystal lens provided in an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the convergence and divergence characteristics of a geometric phase liquid crystal lens for circularly polarized light, provided in an embodiment of the present invention. Figure 5 This is a schematic diagram of the quasi-continuous zoom lens provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the stacked structure of the geometric phase liquid crystal lens provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the polarization switch configuration provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the architecture of a multifocal display optical system for eliminating convergence adjustment conflicts provided in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] Figure 1 This is a schematic diagram of the structure of a multifocal display optical system for eliminating convergence adjustment conflict provided in an embodiment of the present invention.

[0021] See Figure 1 The multifocal surface display optical system 10, which eliminates convergence adjustment conflict, may include an LCD display panel 110, a Mini-LED backlight 120, and a zoom module 190.

[0022] The LCD display panel 110 is used to display image information.

[0023] Mini-LED backlight 120 is located on the light-incident side of LCD display panel 110 and includes multiple independently controllable backlight zones.

[0024] The zoom module 190 is located on the light-emitting side of the LCD display panel 110. It includes at least one transmissive geometric phase liquid crystal lens 130 and at least one polarization switch 140. The polarization switch 140 is located on the light-incident side of the geometric phase liquid crystal lens 130 and is used to dynamically switch the polarization state of the light incident on the geometric phase liquid crystal lens 130 to change the equivalent focal length of the zoom module 190.

[0025] The Mini-LED backlight panel 120 is configured to sequentially illuminate different backlight zones according to a timing sequence. The polarization switch is configured to switch synchronously with the lighting timing of the backlight zones, so that when the target backlight zone is illuminated at any timing, the zoom module 190 switches to a focal length that matches the focal plane corresponding to the target backlight zone, thereby realizing multi-focal plane display.

[0026] In this embodiment, the LCD display panel 110 is a high-resolution panel, and the Mini-LED backlight panel 120 is a low-resolution backlight panel. By employing the independently controllable Mini-LED backlight panel 120 in conjunction with the zoom module 190 containing the geometric phase liquid crystal lens 130 and polarization switch, the timing of the backlight partition lighting and the synchronous switching of the polarization switch are used to achieve fast time-division multiplexing display of different focal planes. This structure not only effectively solves the convergence conflict problem by utilizing the high response speed of the geometric phase liquid crystal lens 130 and eliminating visual fatigue, but also avoids the defects of complex optical path and large size of zoom system through the compact combination of Mini-LED backlight panel 120 and geometric phase liquid crystal lens 130, achieving lightweight and integrated optical system while ensuring a multi-depth natural focusing experience.

[0027] Figure 2 This is a schematic diagram illustrating the operation of the multi-focal surface display system provided in this embodiment of the invention. The schematic diagram includes an RGBD image, an LCD image, and an LED image. The RGBD image can include a color image and a depth image. The four regions A, B, C, and D within the RGBD image correspond to different depth positions arranged from near to far, as shown in the near and far sections of the depth image. The depth image records the relative distance information of each region. The LCD image displays the contents of the four regions A, B, C, and D simultaneously on the same screen. The LED image indicates that the four independent partitions of the Mini-LED backlight panel correspond to regions A, B, C, and D respectively. During operation, the system sequentially illuminates each backlight partition in the order of A, B, C, D or vice versa, and simultaneously controls the zoom module to switch to a focal length matching the depth of the currently illuminated area. Since the content displayed on the LCD remains constant and includes A, B, C, and D, the persistence of vision in the human eye can be utilized by switching the backlight zones in a timely manner and the focal length of the zoom module synchronously. This allows for a multi-focal display effect where all four different focal planes are clear within one display cycle, thus effectively eliminating convergence adjustment conflicts without sacrificing the LCD's own frame rate.

[0028] In one embodiment of this specification, the light is modulated by the geometric phase liquid crystal lens, and the molecules at the bottom of the liquid crystal layer in contact with the light alignment layer are arranged according to the light alignment molecular arrangement. The geometric phase liquid crystal lens achieves focal length switching based on geometric phase modulation, and the in-plane alignment angle distribution of its liquid crystal molecules satisfies the following formula (1): (1); in, The focal length of the lens; Wavelength; For higher-order phase terms, Let x be the abscissa of a two-dimensional rectangular coordinate system established on the plane of the liquid crystal lens, with the center of the lens (usually the intersection of the optical axis and the lens surface) as the origin. The vertical axis is used as the coordinate. It is the in-plane orientation angle.

[0029] In this embodiment, geometric phase modulation is used to achieve focal length switching, solving the problem that zoom lenses cannot simultaneously meet the requirements of large aperture, fast response time, and thinness. Conventional solutions typically rely on voltage-controlled tilt angle of liquid crystal molecules to change the effective refractive index for focusing; this embodiment, however, directly modulates the light wave phase by designing the planar rotational arrangement of liquid crystal molecules. This overcomes the strict limitations of traditional liquid crystal cell thickness and birefringence, allowing for more flexible introduction of higher-order phase terms to optimize image quality and breaking through the limitations of traditional refractive index modulation methods in phase distribution design.

[0030] In one embodiment of this specification, the thickness of the geometric phase liquid crystal lens satisfies the half-wave condition, so that the polarization state of the incident circularly polarized light is reversed after passing through the lens, and it has different response states to circularly polarized light with different chiralities. By switching the polarization state of the incident light, the positive and negative focal lengths can be switched, thereby achieving dynamic adjustment of the optical power without moving the lens. The Jones matrix of a geometric phase liquid crystal lens is expressed by the following formula (2): (2); in, The Jones matrix represents the liquid crystal lens; For incident circularly polarized light, the horizontal and vertical components of this vector have equal amplitudes; +i represents right-handed circularly polarized light; -i represents left-handed circularly polarized light.

[0031] In this embodiment, the in-plane orientation angle 201 can be referred to... Figure 3 Based on the aforementioned geometric phase modulation principle, once a liquid crystal zoom lens has a determined phase distribution, it can achieve both converging and transmitting effects depending on the polarization state, i.e., it possesses both positive and negative refractive powers and focal lengths. Furthermore, if the orientation of the liquid crystal lens is reversed, its positive and negative refractive power and focal length characteristics also reverse. Without loss of generality, assume the incident light is right-handed circularly polarized (RCP), which becomes left-handed and converges after passing through the geometric phase liquid crystal lens. When the incident light is left-handed circularly polarized (LCP), the left-handed light, after passing through the geometric phase liquid crystal lens, is converted into right-handed diverging light, such as... Figure 4 As shown, +f represents the positive focal length, and -f represents the negative focal length. This means that if the chirality of the input polarization state can be dynamically controlled by a polarization converter (first operating state 401, second operating state 403), a bifocal active lens 404 can be created, such as... Figure 5 As shown. Stacking N pairs of bifocal lens modules together yields a lens with a focal length of 2. N The geometric phase liquid crystal zoom lens can be regarded as a quasi-continuous zoom lens.

[0032] In this embodiment, the thickness of the geometric phase liquid crystal lens satisfies the half-wave condition and, in conjunction with a polarization switch, changes the circular polarization chirality of the incident light. Utilizing the spin-orbit coupling characteristics of the geometric phase, dynamic adjustment of optical power and conversion of positive and negative focal lengths are achieved without moving the physical position of the lens. This avoids the problems of large system size and slow response speed caused by mechanical displacement in zoom schemes. Conventional schemes typically rely on voltage to control the tilt angle of liquid crystal molecules to change the effective refractive index for focusing, and their focal length adjustment range is often limited by the birefringence of the material. This embodiment, however, directly changes the sign of the geometric phase by switching the polarization state, using the polarization conversion mechanism described by the Jones matrix to achieve discrete switching of the focal length. This eliminates the dependence on physical deformation or small changes in refractive index, enabling efficient and rapid wide-range zooming with a more compact planar optical structure.

[0033] In one embodiment of this specification, the resolution of the Mini-LED backlight panel is lower than that of the LCD display panel; The number of backlight zones on a Mini-LED backlight panel is equal to the number of focal planes that the zoom module can switch. The Mini-LED backlight is configured to operate at a refresh rate higher than the preset human eye's critical flicker frequency in order to work with the zoom module to achieve multi-focal surface display.

[0034] In this embodiment, the resolution of the Mini-LED backlight panel is lower than that of the LCD display panel, and the number of backlight zones is configured to be equal to the number of focal planes that the zoom module can switch. This avoids the problem of difficulty in accurately synchronizing images of different depths with backlight illumination and the tendency to cause screen flickering in multi-focal plane display systems. Conventional solutions typically use constant backlighting across the entire area or simple local dimming. Their backlight control mainly serves image brightness or contrast and does not involve timing coordination with focal plane switching. However, this embodiment uses backlight zones as the physical carriers of focal planes. Through high-frequency timing multiplexing, multiple images of different depths are projected within the persistence of vision of the human eye. This achieves flicker-free, highly synchronized multi-depth 3D display with a simple hardware architecture. The preset critical flicker frequency for the human eye can be set according to individual needs.

[0035] In one embodiment of this specification, the zoom module includes N transmissive geometric phase liquid crystal lenses and N polarization switches; N is an integer greater than or equal to 2. Each polarization switch is configured to switch the polarization chirality of the incident light to control the switching of the focal length of the corresponding geometric phase liquid crystal lens; Among them, N geometric phase liquid crystal lenses and N polarization switches are stacked and combined, and 2 is achieved based on binary optical power encoding. N Switching between equivalent focal lengths.

[0036] In this embodiment, a stacked structure of multiple geometric phase liquid crystal lenses is used, with each lens independently controlled by a polarization switch. By combining the positive and negative focal length states of each lens, an exponentially increasing number of focal planes is obtained with a smaller number of lenses. This significantly improves the depth resolution of multi-focal plane displays while maintaining the ultra-thin and compact optical system.

[0037] In one embodiment of this specification, when N=2, the ratio of the focal lengths of the two geometric phase liquid crystal lenses is 2:1, and the corresponding ratio of optical power is 1:2. By combining the states of the two polarization switches, the zoom module can switch to four discrete focal planes, with its optical power range covering the positive and negative symmetrical intervals.

[0038] In this embodiment, the effect of switching between four discrete focal planes can be achieved using only two lenses, avoiding the problems of excessive stacking of optical components and reduced system transmittance faced by multi-focal-plane display systems when increasing the number of depth layers.

[0039] In one embodiment of this specification, the focal lengths of the two geometric phase liquid crystal lenses are 0.9m and 1.8m, respectively, corresponding to optical powers of 1.1D and 0.55D. The zoom module switches between four discrete focal planes in the range of -1.65D to 1.65D by combining the states of two polarization switches, with an optical power interval of 1.1D between adjacent focal planes.

[0040] In one embodiment of this specification, the multifocal display optical system for eliminating convergence adjustment conflict further includes a diffuser. A diffuser is placed between the Mini-LED backlight panel and the LCD display panel to reduce the screen-door effect caused when the Mini-LED backlight panel is lit in sections.

[0041] In this embodiment, the backlight is processed by a diffuser to diffuse the point light source into a uniform surface light source, eliminating uneven brightness and dark areas. This improves the uniformity of the displayed image while maintaining the high refresh rate and high zone control precision of Mini-LED.

[0042] In one embodiment of this specification, the geometric phase liquid crystal lens includes a light alignment layer and a multilayer liquid crystal layer stacked on top of the light alignment layer; The liquid crystal molecules at the bottom of the liquid crystal layer that are in contact with the light alignment layer are arranged according to the arrangement of the light alignment molecules, and the molecules in contact between the liquid crystal layers are arranged in the same direction. Each liquid crystal layer has a spontaneous spiral structure in the direction perpendicular to the substrate, and the liquid crystal rotation angle and thickness of each liquid crystal layer are configured such that the diffraction efficiency of the liquid crystal lens in the visible light band is greater than a preset efficiency threshold.

[0043] In this embodiment, the preset efficiency threshold is generally 90%. In general, the fabrication of liquid crystal lenses often relies on traditional rubbing alignment techniques, which make it difficult to achieve complex and precise molecular arrangement patterns and maintain high diffraction efficiency over a wide wavelength range. This embodiment uses optical alignment technology to precisely control the initial arrangement direction of liquid crystal molecules, combined with the spontaneous helical structure and parameter optimization of multilayer liquid crystal layers, so that the lens has a diffraction efficiency of over 90% in the visible light band, while ensuring the accuracy and reproducibility of the liquid crystal molecule arrangement.

[0044] The configuration of the geometric phase liquid crystal lens is as follows Figure 6 As shown, the bottom layer 501 is a photoalignment layer, and above it are multiple liquid crystal layers, such as a first liquid crystal layer 502 and a second liquid crystal layer 503, for example, M liquid crystal layers, where M is an integer greater than 1. The molecules at the bottom of the liquid crystal layer in contact with the photoalignment layer are arranged according to the photoalignment molecules, and the molecules in contact between each layer of liquid crystal are arranged in the same direction. Each liquid crystal layer has a spontaneous helical structure 504 in the direction perpendicular to the substrate. In the first liquid crystal layer 502, the liquid crystal molecules rotate at a certain angle in the direction perpendicular to the substrate. It also has a thickness d1. The liquid crystal corners of each layer... (i=1~M) and thickness d i (i=1~M) should ensure that the liquid crystal lens has an efficiency greater than 90% in the visible light band. i represents the liquid crystal layer index.

[0045] In one embodiment of this specification, the polarization switch 140 includes a TN-type liquid crystal cell 603 and a polarization compensation film 601. The polarization compensation film 601 is composed of multiple A-plates 602 with different optical axis rotation angles, and is used to control the circular polarization chirality of the incident light.

[0046] In this embodiment, by combining a TN-type liquid crystal cell with a polarization compensation film composed of multiple A-layer plates, efficient and precise circular polarization chiral switching can be achieved in the visible light band. This ensures that the light incident on the geometric phase liquid crystal lens has the expected polarization state, thereby guaranteeing the focal length switching accuracy of the zoom module. The A-layer plate is an optical phase compensation film, specifically a uniaxial birefringent film whose optical axis is parallel to the plane of the film. In this embodiment, the configuration of the polarization switching device is as follows: Figure 7 As shown, the structure consists of a TN-type liquid crystal cell 603 and a polarization compensation film 601. The polarization compensation film 601 is composed of three A-plates 602 with different optical axis rotation angles. The optical axis rotation angle of each compensation film is configured such that the polarization conversion efficiency of the polarization switch in the visible light band is greater than a preset efficiency threshold. Both TN-type liquid crystal cells also have a spontaneous spiral structure in the direction perpendicular to the substrate, where the liquid crystal molecules rotate at a certain angle and have thickness.

[0047] The invention will now be illustrated by a specific example. The prototype of the multi-focal surface display system built by this invention can be divided into two parts: a zoom module and a display module, ultimately achieving a multi-focal surface display with four focal planes at a frame rate of 120Hz.

[0048] For the zoom module, a 1D zoom distance is considered to be the distance between two adjacent focal planes during natural accommodation. Therefore, in this example, geometric phase liquid crystal lenses with focal lengths of 0.9m and 1.8m were fabricated, corresponding to optical powers of 1.1D and 0.55D, respectively. By turning polarization switches on and off, the focal lengths of the two liquid crystal lenses can be dynamically switched within the ranges of ±0.55D and ±1.1D, respectively. The final zoom module can achieve rapid switching between four focal planes between -1.65D and 1.65D, with intervals of 1.1D, thus meeting the distance required by the eye during natural accommodation.

[0049] For the display module, a Sharp LS055R1SX04 LCD screen with the backlight removed was used. This 5.5-inch LCD has a resolution of 2560×1440 pixels and a pixel density of approximately 530 PPI, supporting high-resolution image display. Mini-LED, as the new backlight for the LCD, uses a 64×64 RGB LED matrix with 2mm pixel spacing, sourced from Adafruit, enabling a high refresh rate of 1000Hz, sufficient to support the high frame rate requirements of the system prototype. Additionally, a diffuser was added to the system to reduce the screen-door effect caused by the Mini-LED.

[0050] Synchronization between the geometric phase liquid crystal zoom lens and the Mini-LED zoned backlight is achieved using an STM control board (STM32H7R7) to operate the Mini-LED array and signal generator based on a series of digital signals using its internal clock and coded program. The signal generator then generates a square wave signal to control the polarization switch. A block diagram of the overall signal operation for the multifocal light field display is shown below. Figure 8As shown, the system may include a computer, an STM control board, a signal generator, an LED backlight array, an LCD, and a zoom module. The computer writes control programs to the STM control board and simultaneously outputs image signals to the LCD via an HDMI interface through the graphics card. Based on its internal clock and program, the STM control board controls each LED section (e.g., LED1 to LED64) in the LED backlight array through multiple digital ports (e.g., digital port 1 to digital port 14), enabling each backlight section to light up sequentially according to a set timing sequence. Simultaneously, after the signal generator is initialized, the STM control board sends a pulse signal to the signal generator, triggering the generator to produce a square wave signal, which is then sent to the zoom module to dynamically switch the polarization switch state, thereby changing the chirality of the circularly polarized light incident on the geometric phase liquid crystal lens (switching between RCP and LCP), and thus controlling the equivalent focal length of the zoom module to rapidly switch between positive and negative values. Through this synchronous control, while keeping the LCD display content unchanged, the timing of the backlight section lighting and the focal length switching of the zoom module are precisely matched, achieving high frame rate multi-focal plane display.

[0051] Through the above technical solution, this invention significantly improves the display frame rate of the system compared to the traditional time-division multiplexing method when realizing multiple focal planes, thereby achieving a high frame rate multi-focal plane display optical system. This technical solution fully leverages the advantages of liquid crystal holographic elements in phase modulation and unique polarization response, as well as the high frame rate of Mini-LEDs, effectively replacing traditional zoom lenses and synchronization schemes. It provides a feasible and significantly advantageous technical path for resolving convergence conflict in near-eye virtual reality display devices.

[0052] 1. Achieving high frame rate multi-focal plane display while maintaining the number of focal planes: This application uses localized backlighting based on Mini-LEDs to achieve multi-focal plane display, overcoming the constraints between multi-focal display and the number of focal planes. Because Mini-LEDs have a small number of pixels, their driving is simple, enabling a higher frame rate. In this case, multi-focal display does not sacrifice the LCD's frame rate. Assuming the LCD can support a maximum frame rate of 120Hz, displaying four focal planes simultaneously still results in a final image frame rate of 120Hz, thus meeting the system's frame rate requirements. Compared to traditional multi-focal displays based on time-domain multiplexing, with four focal planes, the corresponding final image display frame rate is 1 / 4 of the LCD frame rate, i.e., 30Hz.

[0053] 2. Zooming achieved using a geometric phase liquid crystal lens and a polarization switch, overcoming the limitations of traditional zoom lenses: This application employs a combination of a transmissive geometric phase liquid crystal lens and a polarization switch to achieve zooming, utilizing the unique polarization dependence of the geometric phase liquid crystal lens to adjust the focal length. Compared to traditional zooming schemes based on liquid lenses, this not only achieves a larger aperture (approximately 4 cm) but also boasts a higher switching speed (~1 kHz). Simultaneously, the synchronous control of the liquid crystal lens and the Mini-LED backlight makes focal plane switching smoother and more efficient, avoiding the aberration and response delay problems of traditional liquid lenses at large apertures.

[0054] 3. The optical system has a simple structure, is easy to integrate and manufacture, and can effectively eliminate convergence conflict: Compared with optical systems based on light field displays and holographic displays, which typically require more complex optical modulation equipment and laser light sources, or multi-focal plane displays based on DMD light modulation that require additional projection or relay optical components, the optical system of this application adopts a combination of geometric phase liquid crystal lenses and Mini-LED partitioned backlighting, which has high integration and low manufacturing complexity. The solution of this application can be implemented using commercially available LCD and Mini-LED arrays, making it easy to integrate and manufacture. At the same time, the system can effectively eliminate convergence conflict. Through the dynamic switching and precise adjustment of multiple focal planes, it reduces visual fatigue and discomfort caused by focal length mismatch, significantly improving the user's wearing comfort and visual experience.

[0055] Although only two geometric phase liquid crystal lenses are used in this invention, their number can actually be increased to achieve more focal planes. Furthermore, the liquid crystal lenses used in this example are fabricated from simple lens templates via holographic exposure, resulting in low degrees of freedom. This is mainly because it is easier to manufacture liquid crystal zoom lenses in actual production. In reality, high-degree-of-freedom holographic liquid crystal lenses can be fabricated using freeform surfaces, but this requires prior optimization and design of the wavefront of the geometric phase liquid crystal lenses.

[0056] In addition, the low-resolution Mini-LED backlight used in the example has a pixel pitch of 2mm. If a display system with better image quality and higher frame rate is achieved by using a Mini-LED backlight with a smaller pixel pitch, it also falls within the technical scope of this invention.

[0057] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units.

[0058] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as OM / AM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-focal plane display optical system for eliminating convergence accommodation conflict, characterized in that, include: LCD display panel, used to display image information; The Mini-LED backlight panel is located on the light-incident side of the LCD display panel and includes multiple independently controllable backlight zones. A zoom module, located on the light-emitting side of the LCD display panel, includes at least one transmissive geometric phase liquid crystal lens and at least one polarization switch. The polarization switch is located on the light-incident side of the geometric phase liquid crystal lens and is used to dynamically switch the polarization state of the light incident on the geometric phase liquid crystal lens to change the equivalent focal length of the zoom module. The Mini-LED backlight panel is configured to sequentially illuminate different backlight zones according to a time sequence, and the polarization switch is configured to switch synchronously with the illumination time sequence of the backlight zones, so that when a target backlight zone is illuminated at any time sequence, the zoom module switches to a focal length that matches the focal plane corresponding to the target backlight zone, thereby realizing multi-focal plane display.

2. The multi-focal plane display optical system for eliminating convergence accommodation conflict according to claim 1, characterized in that, The geometric phase liquid crystal lens achieves focal length switching based on geometric phase modulation, and the in-plane orientation angle distribution of its liquid crystal molecules satisfies: ； in, The focal length of the lens; Wavelength; For higher-order phase terms, Let x be the abscissa of a two-dimensional rectangular coordinate system established on the plane of the liquid crystal lens, with the center of the lens (usually the intersection of the optical axis and the lens surface) as the origin. The vertical axis is used as the coordinate. It is the in-plane orientation angle.

3. The multi-focal plane display optical system for eliminating convergence accommodation conflict according to claim 2, characterized in that, The thickness of the geometric phase liquid crystal lens satisfies the half-wave condition, so that the polarization state of the incident circularly polarized light is reversed after passing through the lens, and it has different response states to circularly polarized light with different chiralities; by switching the polarization state of the incident light, the positive and negative focal lengths can be converted, thereby achieving dynamic adjustment of the optical power without moving the lens. The Jones matrix of the geometric phase liquid crystal lens is represented as follows: ； in, The Jones matrix represents the liquid crystal lens; For incident circularly polarized light, the horizontal and vertical components of this vector have equal amplitudes.

4. The multi-focal plane display optical system for eliminating convergence accommodation conflict according to claim 1, characterized in that, The resolution of the Mini-LED backlight panel is lower than that of the LCD display panel; The number of backlight zones of the Mini-LED backlight panel is equal to the number of focal planes that the zoom module can switch. The Mini-LED backlight is configured to operate at a refresh rate higher than the preset critical flicker frequency for the human eye, in order to cooperate with the zoom module to achieve multi-focal surface display.

5. The multi-focal plane display optical system for eliminating convergence accommodation conflict according to claim 1, characterized in that, The zoom module includes N transmissive geometric phase liquid crystal lenses and N polarization switches; N is an integer greater than or equal to 2; Each of the polarization switches is configured to switch the polarization chirality of the incident light to control the switching of the focal length of the corresponding geometric phase liquid crystal lens; The N geometric phase liquid crystal lenses and N polarization switches are stacked and combined, and a 2D polarization encoding is achieved based on binary optical power coding. N Switching between equivalent focal lengths.

6. The multi-focal plane display optical system for eliminating convergence accommodation conflict according to claim 5, characterized in that, When N=2, the ratio of the focal lengths of the two geometric phase liquid crystal lenses is 2:1, and the corresponding ratio of optical power is 1:

2. By combining the states of the two polarization switches, the zoom module can switch to four discrete focal planes, with its optical power range covering the positive and negative symmetrical intervals.

7. The multi-focal plane display optical system for eliminating convergence accommodation conflict according to claim 6, characterized in that, The focal lengths of the two geometric phase liquid crystal lenses are 0.9m and 1.8m, respectively, corresponding to optical powers of 1.1D and 0.55D. The zoom module switches between four discrete focal planes within the range of -1.65D to 1.65D by combining the states of the two polarization switches, with an optical power interval of 1.1D between adjacent focal planes.

8. The multi-focal plane display optical system for eliminating convergence accommodation conflict according to claim 1, characterized in that, Also includes: A diffuser is disposed between the Mini-LED backlight panel and the LCD display panel to reduce the screen-door effect generated when the Mini-LED backlight panel is illuminated in sections.

9. The multi-focal plane display optical system for eliminating convergence accommodation conflict according to claim 1, characterized in that, The geometric phase liquid crystal lens includes a light alignment layer and multiple liquid crystal layers stacked on top of the light alignment layer; The liquid crystal molecules at the bottom of the liquid crystal layer in contact with the light alignment layer are arranged according to the arrangement of light alignment molecules, and the molecules in contact between the liquid crystal layers are arranged in the same direction.

10. The multi-focal plane display optical system for eliminating convergence accommodation conflict according to claim 1, characterized in that, The polarization switch includes a TN-type liquid crystal cell and a polarization compensation film. The polarization compensation film is composed of multiple A-plates with different optical axis rotation angles, which are used to control the circular polarization chirality of the incident light.

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