A high uniformity directional backlight module and a three-dimensional display system including the backlight module.

Abstract

This invention discloses a high-uniformity directional backlight module and a 3D display system including the backlight module, belonging to the field of free-form stereoscopic display. The backlight module includes a substrate, a light source array, an aperture array, a lens array, and a microprism homogenizing film. A set of light sources, apertures, and lenses with a one-to-one correspondence forms a directional homogenizing control unit, achieving beam homogenization and collimation. The microprism homogenizing film can improve illumination defects caused by manufacturing errors and splicing problems, as well as viewing problems caused by lens surface shape, without affecting the collimation of the emitted light. This backlight module can achieve continuous, large-area, high-uniformity, and high-collimation directional illumination that completely covers the emission surface of the backlight module. The 3D display system includes the aforementioned backlight module, liquid crystal display element, and light field control element, providing a high-performance, thin, and eye-friendly 3D display with a comfortable visual experience.

Description

Technical Field

[0001] This invention relates to the field of free-form stereoscopic display, and more particularly to a high-uniformity directional backlight module and a three-dimensional display system including the backlight module. Background Technology

[0002] 3D display, as an emerging technology in the display field, is gradually moving from concept to reality and slowly changing our lifestyles. A direct example is the 3D movies we watch in cinemas. The three-dimensional effect brings us a richer viewing experience, but we need to wear 3D glasses to watch them. This is because this type of 3D display transmits different images to the left and right eyes through methods such as polarization, requiring viewers to wear corresponding devices. To further enhance the visual experience of 3D displays, the concept of glasses-free 3D display has been proposed. A primary method for viewing 3D displays without wearing devices is viewpoint reconstruction, which involves directionally transmitting the corresponding images to the left and right eyes respectively. Combined with eye-tracking devices, dynamic glasses-free 3D display can be achieved within a certain viewing area.

[0003] Traditional backlight modules have a large emission divergence angle, with each point emitting a beam across a wide spatial range. This directly leads to crosstalk and a decrease in viewing quality, making directional beam control extremely difficult. Therefore, designing a directional backlight module with high collimation is crucial for achieving low crosstalk and high-quality naked-eye 3D displays. Currently, direct-lit directional backlights using lens array control face several challenges: first, achieving both high collimation and uniformity simultaneously is difficult; second, manufacturing errors and splicing issues in the lenses result in imperfections and dark seams in the illuminated area; and third, the curved surface of the lenses allows their shape to be observed through subsequent components, causing viewing problems for the observer. Solving these three key issues is a critical factor in the widespread application of directional backlights. Summary of the Invention

[0004] The purpose of this invention is to provide a high-uniformity directional backlight module and a 3D display system including the backlight module. The backlight module provides illumination with high collimation, high uniformity, and high directionality. This backlight module is thin and lightweight, and can smooth out lighting defects caused by manufacturing errors and splicing issues. It also prevents viewers from seeing the lens structure through subsequent components, making it well-suited for 3D display systems and enabling true 3D display.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] This invention provides a high-uniformity directional backlight module, comprising a substrate, a light source array, an aperture array, a lens array, and one or more microprism light-diffusing films.

[0007] The light source array includes a plurality of light sources arranged on a substrate;

[0008] The aperture array includes several apertures arranged on the substrate, each aperture corresponding to a light source. The apertures limit the transmission angle of the light beam emitted by the light source to avoid crosstalk between light sources.

[0009] The lens array includes several lenses that correspond one-to-one with the aperture stop, which homogenize and collimate the outgoing light beam after passing through the aperture stop.

[0010] The microprism light-diffusing film is an optical film. Both the upper and lower surfaces of the microprism light-diffusing film are covered with microprism structures. The microprism structures on the two surfaces are arranged in the same direction but the prisms face opposite directions. The refractive index, thickness, and prism apex angle of the microprism light-diffusing film are designed to improve the illumination defects caused by manufacturing errors and splicing problems, as well as the viewing problems caused by the lens surface shape, without affecting the collimation of the emitted beam.

[0011] When the microprism light-diffusing film is multilayered, each of the microprism light-diffusing films is parallel to the substrate, and the multilayered microprism light-diffusing films are placed one after the other in the optical path direction of the beam.

[0012] A set of light sources, apertures and lenses with one-to-one correspondence constitutes a directional uniform light control unit. The backlight module is composed of the directional uniform light control unit arranged in an array and a microprism uniform light film.

[0013] Furthermore, the design steps of the microprism homogenizing film are as follows:

[0014] 1) Lens splicing and manufacturing errors can cause dark seams and defects in the backlight module, resulting in decreased emission uniformity and deteriorated visual effect. The light beam after passing through the lens is injected into the microprism uniform light film, and the incident light beam is divided into two outgoing light beams of equal width, thereby achieving aliasing and broadening. A diffusion screen is set on one side of the outgoing surface of the microprism uniform light film to observe the outgoing light beam of the microprism uniform light film.

[0015] 2) Based on the law of refraction, the structure of the microprism, and the geometric relationship of the transmitted beam, the relative relationship between the refractive index of the microprism homogenizing film and the apex angle of the prism is calculated. A high-transmittance plastic or glass is selected as the material of the microprism homogenizing film. The high-transmittance plastic is an optical plastic with high transmittance such as PMMA (polymethyl methacrylate) and PC (polycarbonate). After selecting the refractive index of the microprism homogenizing film, the apex angle of the prism can be determined so that the transmission direction of the incident beam in the microprism homogenizing film is parallel to the side of the prism, thereby avoiding unexpected total internal reflection or stray light transmission and improving energy utilization.

[0016] 3) Based on the law of refraction and according to the determined refractive index and prism apex angle, the thickness of the microprism homogenizing film is designed. The incident beam illuminates the lens array to form an outgoing beam with a dark slit. The outgoing beam with the dark slit is split by the microprism homogenizing film to form two slits. When observed on the diffusion screen, if there is an overlapping area between the two slits after beam splitting, it indicates that the relative displacement between the outgoing beams of the microprism homogenizing film is too small, and the thickness of the microprism homogenizing film needs to be increased. If the relative displacement between the two slits after beam splitting exceeds the size of the directional homogenizing control unit, it indicates that the relative displacement between the outgoing beams of the microprism homogenizing film is too large, and the thickness of the microprism homogenizing film needs to be reduced. At the same time, the thickness of the microprism homogenizing film should not be too large to ensure the thinness of the backlight module. Finally, the thickness of the microprism homogenizing film is determined according to the uniformity of the illumination area on the diffusion screen and the visual effect.

[0017] Furthermore, when the microprism light-diffusing film is multilayered, the first layer of the microprism light-diffusing film is designed first according to the design method.

[0018] Furthermore, based on the determined upper-layer microprism homogenizing film, the thickness of the next layer of microprism homogenizing film is designed. Specifically, any slits present in the emitted beam of each upper-layer microprism homogenizing film are split into two secondary slits after passing through the current microprism homogenizing film. A diffusion screen is placed on one side of the emitted surface of the current microprism homogenizing film for observation. If the two secondary slits formed by splitting a single slit have an overlapping area, it indicates that the relative displacement between the emitted beams of the current microprism homogenizing film is too small, and the thickness of the microprism homogenizing film needs to be increased. If the relative displacement between the two secondary slits formed by splitting a single slit exceeds the size of the directional homogenizing control unit, it indicates that the relative displacement between the emitted beams of the current microprism homogenizing film is too large, and the thickness of the microprism homogenizing film needs to be decreased. Finally, based on the uniformity and visual effect of the illumination area on the diffusion screen, the thickness of the microprism homogenizing film to be designed is obtained, which can improve illumination defects and viewing problems.

[0019] Repeat the above steps until the design of all microprism homogenizing films is completed.

[0020] Furthermore, the full width at half maximum (FWHM) of the emitted beam intensity of the backlight module is less than 5°.

[0021] Furthermore, the prism apex angles of the microprism structures on the two surfaces of the microprism homogenizing film are the same;

[0022] The microprisms on the two surfaces of the microprism homogenizing film have different prism spacings, or the microprisms on either surface of the microprism homogenizing film have non-periodic prism spacings, in order to avoid the influence of moiré fringes.

[0023] The microprisms are arranged in a direction that avoids the direction of dark seams caused by lens splicing and manufacturing errors.

[0024] Furthermore, the emitted light direction of the backlight module is along the normal direction of the substrate or is inclined at a certain angle to the normal direction of the substrate.

[0025] The present invention also provides a three-dimensional display system, including the aforementioned high uniformity directional backlight module.

[0026] Furthermore, the three-dimensional display system also includes a liquid crystal modulation element and a light field control element.

[0027] The liquid crystal modulation element is disposed in the outgoing light path of the backlight module and is used to modulate the illumination intensity emitted by the backlight module to achieve image display.

[0028] The light field modulation element is set in the output light path of the liquid crystal modulation element, and three-dimensional viewpoint reconstruction is performed through beam modulation to realize three-dimensional display.

[0029] The present invention further provides a beam control method using the aforementioned high uniformity directional backlight module. The beam emitted by the light source passes through the aperture and is incident on the lens. Due to the limiting effect of the aperture, the incident beam just fills the aperture of the corresponding lens. The lens is an aspherical or freeform lens with optical power on both surfaces, so the intensity and wavefront of the beam can be controlled simultaneously to achieve beam homogenization and collimation. The outgoing beam after passing through the lens passes through a microprism homogenizing film to smooth its illumination defects and viewing problems, thereby achieving directional illumination with high uniformity, high collimation and suitable viewing.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) By simultaneously controlling the wavefront and intensity of the emitted light through a freeform lens, the constructed backlight module has both high uniformity and high collimation, overcoming the problem that uniformity and collimation are difficult to achieve simultaneously in the prior art.

[0032] (2) By smoothing the imperfections in the illumination area through the microprism light-diffusing film, the imperfections in the illumination area and the problem of dark seams in the splicing due to lens manufacturing errors and splicing are overcome, providing a better viewing effect.

[0033] (3) By using a microprism light-diffusing film, the problem of viewing the surface shape of the lens still being visible through subsequent components in the prior art is solved, and a better viewing effect can be provided.

[0034] (4) Inclined emission can be achieved by off-axis placement of the lens and aperture and adjustment of the surface shape, without the need to add additional components.

[0035] (5) By designing microprism structures on the film to achieve uniform light, it can be manufactured based on the existing prism film processing technology. The processing system is mature and can achieve large-size mass production. Attached Figure Description

[0036] Figure 1 This is a system diagram of the high uniformity directional backlight module and a three-dimensional display system diagram including the backlight module, as shown in Example 1.

[0037] Figure 2 This is a schematic diagram of the backlight module array configuration in an embodiment of the present invention;

[0038] Figure 3 This is a system diagram of the high uniformity directional backlight module and a three-dimensional display system diagram including the backlight module, as shown in Example 2.

[0039] Figure 4 This is an illuminance distribution diagram on the illumination surface of the backlight module designed in Example 1;

[0040] Figure 5 This is a diagram showing the intensity distribution of emitted light from the backlight module designed in Example 1;

[0041] Figure 6 This is a schematic diagram of the principle of a 90° apex microprism homogenizing film. Figure 1 ;

[0042] Figure 7 This is a schematic diagram of the principle of a 90° apex microprism homogenizing film. Figure 2 ;

[0043] Figure 8 This is a schematic diagram of the principle of a microprism light-diffusing film with a specific apex angle;

[0044] Figure 9 This is a schematic diagram of the optical transmission path of the microprism homogenizing film;

[0045] Figure 10 This is a schematic diagram of a microprism light-diffusing film smoothing out imperfections in the illumination area.

[0046] Figure 11 This is a schematic diagram showing the arrangement of the microprisms in a two-layer microprism light-diffusing film. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below in conjunction with the accompanying drawings.

[0048] Figure 1 This is a system diagram of the high uniformity directional backlight module of Example 1, and a three-dimensional display system diagram including the backlight module. Figure 1As shown, the high-uniformity directional backlight module includes a substrate 101, a light source array 102, an aperture array 103, a lens array 104, and two layers of microprism homogenizing films 105 and 106. The light source array includes several light sources arranged on the substrate, which are MiniLEDs, MicroLEDs, or LEDs. The aperture array includes several apertures arranged on the substrate, each aperture corresponding to a light source, defining the beam angle entering the directional homogenizing control unit and avoiding crosstalk between light sources. The lens array includes several lenses corresponding to the apertures, homogenizing and collimating the light emitted from the light sources. The microprism homogenizing film is an optical film with microprism structures covering its upper and lower surfaces. The microprism structures on the upper and lower surfaces are arranged in the same direction but the prisms face opposite directions, which can improve lighting defects caused by manufacturing errors and splicing problems, as well as viewing problems caused by lens surface shape, without affecting the collimation of the emitted light. The backlight module can achieve continuous, large-area, highly uniform, and highly collimated directional illumination that completely covers the emission surface of the backlight module.

[0049] The lenses in the lens array have freeform or aspherical surfaces; both surfaces of the lenses in the lens array have optical power, allowing simultaneous control of beam intensity and wavefront; the lenses in the lens array are made of optical plastic, and their refractive index is 1.4 to 1.8.

[0050] There is a one-to-one correspondence between the light source array, aperture array, and lens array. A set of corresponding light sources, apertures, and lenses constitutes a directional homogenization control unit. The surface shape of the lens includes, but is not limited to, freeform surfaces and aspherical surfaces. The surface shape of the lens is designed according to the spatial and luminous characteristics of the light source to achieve the control of the light emitted by the light source, and to collimate and homogenize it.

[0051] Furthermore, to achieve better uniformity and collimation, both surfaces of the lenses in the lens array have optical power, allowing for simultaneous control of beam intensity and wavefront. The lens surface shape is designed based on the spatial and luminous characteristics of the light source within a certain collection angle range. In this embodiment of the invention, an aperture is used to limit the beam angle entering the directional uniform beam control unit and to avoid crosstalk between light sources. The aperture is designed according to the designed light source collection angle and includes, but is not limited to, a through-hole column. The opening size and shape of the two ends of the through-hole column can be the same or different. After the aperture is defined, the shape and size of the light spot formed at the corresponding lens position should match the shape and size of the corresponding lens to prevent crosstalk between adjacent lenses. The aperture is a through-hole cylinder. The size and shape of the openings at both ends of the through-hole cylinder can be obtained by reverse ray tracing calculation based on the design of the lens and the light source. The shape and size of the light spot formed at the corresponding position of the corresponding lens after the light beam emitted by the light source passes through the aperture should match the shape and size of the corresponding lens. This limits the light exceeding the set light source collection angle from entering the lens array, and also avoids the light emitted by the light source from entering the lenses of other directional homogenization control units, which can effectively avoid crosstalk between directional homogenization control units.

[0052] In this embodiment of the invention, the size of the light source is smaller than the size of the lens, according to the law of optical dilatation:

[0053] Etendue=n 2 ∫∫cos(θ)dAdΩ

[0054] In the formula, Etendue is the optical extension, n is the refractive index of the space, dA is the surface element on the optical surface, dΩ is the solid angle of the beam, and θ is the angle between the normal of the surface element and the central axis of the beam.

[0055] In an ideal optical system where energy loss due to scattering and absorption is not considered, the optical spread of the beam is conserved after passing through the optical system. Therefore, the divergence angle of the beam output by the lens array should be smaller than the divergence angle of the beam emitted by the light source, and the illumination light output by the aforementioned backlight module has high collimation.

[0056] Furthermore, since the backlight module uses a lens array to achieve beam homogenization and collimation, the light source used in the backlight module can be a white light source, a monochromatic light source, or a combination of monochromatic light sources.

[0057] Furthermore, the backlight module is composed of an array of several directional uniform light control units. In this embodiment of the invention, the light source and aperture array are arranged on the substrate, and the lenses are arranged in an array with the same spacing, located above the substrate.

[0058] Furthermore, the three-dimensional display system includes the aforementioned backlight module, liquid crystal modulation element 107, and light field control element 108.

[0059] In this embodiment of the invention, the liquid crystal modulation element 107 is located above the lens array and modulates the illumination intensity emitted by the backlight module to achieve image display;

[0060] The light field control element is located above the liquid crystal modulation element. It reconstructs three-dimensional viewpoints through beam control to achieve three-dimensional display. Light emitted from the backlight module passes through the liquid crystal modulation element 107 to load an image, and then the beam is deflected by the light field control element 108, pointing towards a designated viewpoint. Images from different viewpoints are transmitted to the corresponding viewpoints, thereby achieving viewpoint reconstruction. The light field control element 108 includes, but is not limited to, one-dimensional gratings, two-dimensional gratings, surface relief gratings, holographic optical elements, and other refractive, diffractive, or mixed refractive-diffractive elements.

[0061] Figure 2 This is a schematic diagram of the directional uniform light control unit array in an embodiment of the present invention. Figure 2 As shown, a directional homogenization control unit is composed of a set of corresponding light sources, apertures, and lenses. In this embodiment of the invention, the light sources in the light source array are all identical, and the required emission characteristics of the directional homogenization control unit are also identical. Therefore, the aperture array and lens array are both composed of identical aperture and lens arrays, and each directional homogenization control unit has the same output characteristics. The directional homogenization control units are arranged in a continuous rectangular pattern, and each directional homogenization control unit can output uniform and collimated directional illumination light. Therefore, the backlight module obtained by arraying in this way can output continuous, highly uniform, and highly collimated directional illumination.

[0062] In Embodiment 1 of the present invention, the illumination light emission direction of the backlight module is perpendicular to the liquid crystal modulation element. Furthermore, the present invention can also realize directional illumination with tilted emission, that is, the direction of the emitted collimated light is at a certain angle to the normal of the liquid crystal modulation element.

[0063] Figure 3 This is a system diagram of the high uniformity directional backlight module in Example 2, and a three-dimensional display system diagram including the backlight module. Figure 3 As shown, in this embodiment of the invention, the aperture stop is not placed perpendicular to the substrate, and the lens array is not placed parallel to the substrate. Therefore, the collection range defined by the aperture stop is also tilted. Since the light emission spatial characteristics of the light source include, but are not limited to, cosine light emitters, the surface shape of the lens is also designed according to the light emission spatial characteristics of the light source to achieve collimation and homogenization. The surface shape is designed as a freeform surface. Light within the range limited by the aperture stop is collimated and homogenized by the lens array and then emitted at a certain angle to the normal of the liquid crystal control element.

[0064] Similarly, according to the law of optical spread, in an ideal optical system where energy loss due to scattering and absorption is not considered, the optical spread of the beam after passing through the optical system is conserved. Therefore, the divergence angle of the beam output by the lens array should be smaller than the divergence angle of the beam emitted by the light source, and the illumination light output by the aforementioned backlight module has high collimation.

[0065] Figure 4 This is an illuminance distribution diagram on the illumination surface of the backlight module designed in Example 1. For example... Figure 4 As shown, a backlight module was designed according to Embodiment 1 of the invention. The light source is a white miniLED, the distance from the light source array to the lens array is 5mm, the lens surface is aspherical, and the thickness of the lens array is 10mm. Since the emitted beam has high collimation, its illumination distribution does not change significantly within a certain distance. Therefore, the illumination surface is set 1mm above the lens array to simulate the illumination distribution of the directional homogenizing control unit array on the subsequent microprism homogenizing film. A directional homogenizing control unit consisting of a corresponding light source, aperture, and lens has dimensions of 10mm*10mm*15mm. Since the units have the same design parameters, a 3*3 unit array was tested. Figure 4 This demonstrates the illuminance distribution on the illuminated surface. The pixel size sampled on the illuminated surface is 0.2*0.2mm. We selected a 20mm*20mm area at the center of the illuminated plane, i.e. Figure 4 The area marked with a black border uses the average error to measure the uniformity of illumination. The average error is the ratio of the standard deviation of illuminance to the average illuminance.

[0066]

[0067]

[0068] In the formula, σ is the standard deviation of illuminance, N is the number of sampled pixels, and x i Let be the illuminance value at the i-th sampled pixel. Let V be the average illuminance on the illuminated surface, and let V be the average error of the illuminance.

[0069] The uniformity U is then:

[0070] U = (1-V) × 100%

[0071] like Figure 4 As shown, the backlight module designed according to Embodiment 1 has an illumination uniformity of 97% on the illumination plane, indicating that this backlight module has a very high illumination uniformity. Considering that it is difficult to achieve illumination uniformity through beam divergence in a backlight module with high collimation, achieving both uniform output on the illumination plane and collimation of the output beam is very challenging. The design method provided by this invention can effectively solve this problem.

[0072] Figure 5 This is an intensity distribution diagram of the emitted light from the backlight module designed according to Embodiment 1. For example... Figure 5 As shown, the designed backlight module emits light perpendicular to the substrate direction. The full width at half maximum (FWHM) in the two orthogonal directions perpendicular to the emission direction is 1.20° and 1.71°, respectively, and the cutoff is sharp. This indicates that the designed backlight module has extremely high collimation, which is very beneficial for the viewpoint reconstruction of the true 3D display system. This enables the true 3D display system to accurately transmit images to the specified viewpoint and effectively avoid crosstalk between viewpoints, thereby improving viewing comfort.

[0073] Current directional backlight module designs typically have an output beam collimation angle exceeding 5°, and cannot simultaneously achieve both homogenization and collimation, resulting in performance that falls short of practical requirements. This design utilizes a numerical solution method based on partial differential equations to design freeform or aspherical lenses and optimizes the design of each component in the backlight module. This allows for simultaneous control of the output light's wavefront and intensity, resulting in a backlight module that exhibits both high uniformity and high directionality.

[0074] Figure 6 This is a schematic diagram of the principle of a 90° apex microprism homogenizing film. Figure 1 . Figure 6 It includes microprism structures on the upper and lower surfaces of a microprism homogenizing film, with the apex angle of each microprism structure being 90°. Because the central part of the microprism homogenizing film is a high-transmittance matrix and has no light refraction effect, therefore... Figure 6 The middle section between the upper and lower surfaces is omitted. For example... Figure 6 As shown, the microprism structures on the upper and lower surfaces of the microprism homogenizing film have different periods, which can avoid the generation of moiré fringes on the two surfaces.

[0075] Light ray 609 is incident from the left side 601 of the lower surface microprism, making an angle α1 with the normal to the left side. After refraction, the angle with the normal to the left side is β1. According to the law of refraction:

[0076] sin(α1)=n p ·sin(β1)

[0077] In the formula, n p Let be the refractive index of the diaphragm.

[0078] After traveling a certain distance within the diaphragm, light 609 exits from the right side 602 of the upper surface microprism. Geometrically, since the apex angles of the microprism structures on the upper and lower surfaces are identical, surfaces 601 and 602 are parallel. Therefore, the incident angle of light 609 on surface 602 is β1, and its exit angle on surface 602 remains α1. Light 609 essentially passes through a tilted parallel plate. Compared to the original transmission path of light 609, the refraction occurring on the microprism structures of the upper and lower surfaces only causes a certain lateral displacement of light 609, without changing its transmission direction.

[0079] The above describes only one scenario of light transmission. The period of the microprism structure is very small, within 50 μm, and the thickness of the microprism homogenizing film is greater than 0.5 mm. Light incident at the same point on the lower surface, even with only a small divergence angle, will cover tens of micrometers at its landing point on the upper surface, equivalent to several prism periods. Furthermore, because the periods of the microprism structures on the upper and lower surfaces are different, it is possible for light to reach the left or right side of the upper surface microlens regardless of whether it is incident on the left or right side of the lower surface microlens.

[0080] For the case where light ray 610 is incident on the left side of the lower surface microlens and reaches the right side of the upper surface, it is shown as ray 610. Ray 610 is incident on the left side 603 of the lower surface microprism, and its propagation direction is the same as that of ray 609, with an angle of α1 to the normal of the left side. Similarly, after refraction, its angle with the normal of the left side is β1. After propagating a certain distance in the diaphragm, ray 610 reaches the left side 604 of the upper surface microprism. From the geometric relationship, we can know that:

[0081] β2=90-β1

[0082] For α1 = 45 ± 5°, n p In the case of application 1.4-1.8, ray 610 will undergo total internal reflection at surface 604, and then reach the right side surface 605 of the upper surface microprism. Geometrically, the angle between ray 610 and the normal to surface 605 is β1. After refraction, the angle between ray 610 and surface 605 is α1. However, unlike ray 609, its exit direction is on the other side of the normal. Therefore, ray 610 will be incident on the left side surface 606 of the adjacent microprism on the upper surface, with an angle of α2 between ray 610 and the normal to surface 606. After refraction, it reaches the right side surface 607 of the upper surface microprism, undergoes total internal reflection, and reaches the lower surface, exiting from the right side surface 608 of the lower surface microprism. The angle between ray 610 and the normal to surface 608 is α2. Geometrically, we know that...

[0083] α2=90-α1

[0084] Therefore, α2 = 45 ± 5°, and the ray 610 returns to the optical system under the microprism homogenizing film, with the same angular range as at incidence. If the ray 610 reaches the left side of the lower surface microprism structure after total internal reflection on the surface 607, total internal reflection will occur, and the subsequent process is similar to the previous one. In general, the rays incident on the microprism homogenizing film in this way either exit at the original angle or return to the optical system under the film with the same angular range.

[0085] Figure 7 This is a schematic diagram of the principle of a 90° apex microprism homogenizing film. Figure 2 This diagram illustrates the light transmission from the right side of the lower surface microprism. Due to the symmetrical structure of the microprism, light rays incident on the right side and the left side of the lower surface microprism have similar light transmission characteristics. If these rays reach the left side of the upper surface microprism, they are equivalent to passing through a parallel plate and still exit along their original transmission direction. If they reach the right side of the upper surface microprism, total reflection occurs, and the light rays are incident on the adjacent microprism structure, then undergo total internal reflection back to the lower surface microprism structure, or continue the total internal reflection process, or exit from the lower surface microprism structure and return to the optical system under the microprism homogenizing film.

[0086] Figure 6 and Figure 7 The diagram illustrates the light path when light is incident perpendicularly to the microprism homogenizing film. If the light is incident at an angle, a portion of the beam incident from the left / right sides of the lower microprism structure reaches the right / left side of the upper microprism structure, essentially passing through a parallel plate, and the light transmission direction remains unchanged. The other portion reaches the left / right sides of the upper microprism structure, where it undergoes total internal reflection and returns to the optical system below the film, or forms stray light. Generally, this stray light has very low intensity and a large exit angle, having minimal impact on the subsequent 3D display system.

[0087] Figure 8 This is a schematic diagram illustrating the principle of a microprism homogenizing film with a specific apex angle. In a microprism homogenizing film with a 90° apex angle, stray light exists due to total internal reflection. However, by specifically designing the apex angle of the microprism, stray light can be further reduced. For example... Figure 8 As shown, the half-apex angle of the microprism structure is γ3. Ray 801 is incident perpendicularly to the film onto the left side of the lower surface microprism, with an angle α3 between it and the normal to the left side. After refraction on the left side, the refracted ray 802 makes an angle β3 with the normal to the left side. According to the law of refraction:

[0088] sin(α3)=n t ·sin(β3)

[0089] In the formula, n t denoted as the refractive index of the diaphragm.

[0090] It can be deduced from geometric relationships that:

[0091] α3=90-γ3

[0092] δ3=α3-β3

[0093] In a microprism homogenizing film with a specific apex angle, the refracted ray 802 is parallel to the left side 804 of the upper microprism. Thus, the refracted ray 802 must reach the right side of the upper microprism, preventing total internal reflection and thus avoiding some light returning to the optical system below the film or becoming stray light. That is, the following exists:

[0094] δ3=γ3

[0095]

[0096] Because of the symmetry of the microprism structure, light rays incident on the right side of the lower microprism have similar transmission characteristics. As shown in the above equation, the apex angle of the microprism can be designed based on the refractive index of the microprism homogenizing film. This microprism homogenizing film with a specific apex angle has higher energy utilization efficiency, and even if the incident light has a certain divergence angle, the generated stray light energy is very small.

[0097] Figure 9 This is a schematic diagram of the optical transmission path of the microprism homogenizing film. In this invention, the period of the microprism structure is very small, within 50 μm, and the thickness of the microprism homogenizing film is greater than 0.5 mm. The microprism structure is extremely small relative to the film size. The previous figures were enlarged to illustrate the principle of the microprism structure, but the actual situation is as follows: Figure 9 As shown, the spacing and tooth height of the microprism structure have negligible influence relative to the size of the diaphragm. A collimated beam 901 of a certain width is incident perpendicularly to the diaphragm. Light incident on the left side of the lower surface microprism is refracted and propagates to the right, while light incident on the right side is refracted and propagates to the left. Some light returns to the optical system below the diaphragm due to total internal reflection, while most light exits from the upper surface of the diaphragm. Since the left and right light propagate in different directions within the diaphragm, beam 901 is split into two beams 902 and 903 of equal width. Both beams 902 and 903 exit perpendicularly to the upper surface of the diaphragm. The relative displacement Δx between them is related to the thickness, refractive index, and apex angle of the microprism diaphragm. Figure 6 Taking the microprism homogenizing film shown as an example, the relative displacement between its emitted beams is:

[0098] Δx = 2·h·tan(α1-β1)

[0099] In the formula, h is the thickness of the diaphragm.

[0100] Figure 10 This is a schematic diagram illustrating the smoothing of imperfections in the illumination area using a microprism light-diffusing film. In direct-lit collimated backlight modules, dark seams typically exist between illumination areas due to processing and splicing errors. Figure 10 The relationship between normalized illuminance and coordinates along the microprism arrangement direction of the microprism homogenizing film is shown. 1001 is the illuminance distribution emitted from the directional homogenizing control unit, 1004 is the illuminance distribution of a single unit, and 1005 is the illuminance distribution of three adjacent units. Between the uniform illuminance regions of each unit, there exists a dark slit with a width of d, and the illuminance of the dark slit is 0.

[0101] Figure 1002 shows the illuminance distribution after passing through a microprism homogenizing film. Due to the extremely small size of the microprism structure, even in areas where only the left or right side emits light, the tiny divergence angle and distance are sufficient for the emitted light to fill the entire area, rather than forming bright and dark fringes. Therefore, the influence of the microprism's fine structure is not considered here. As seen in Figure 1002, the illuminance region of a single unit becomes the superposition of two regions with a normalized illuminance of 1 / 2, with a relative displacement of Δx. The illuminance region of three units is the superposition of such illuminance regions. The regions with a normalized illuminance of 1 / 2 in adjacent units superimpose, thus becoming a region with a normalized illuminance of 1. However, due to geometric relationships, regions with a normalized illuminance of 1 do not superimpose. This is because as Δx increases, the region with a normalized illuminance of 1 decreases, while the region with a normalized illuminance of 1 / 2 increases accordingly, until the two regions completely separate, forming two regions with a normalized illuminance of 1 / 2. Through this blending process, in a single unit area between the dashed lines, a dark slit with a width of d and a normalized illuminance of 0 is transformed into two imperfection slits with a width of d and a normalized illuminance of 1 / 2, with a distance of Δx between them. During the design process, Δx should be selected with a reasonable value based on the parameters of the dark slits. If Δx is too small, the two imperfection slits will remain in close proximity after smoothing, resulting in a poor visual effect; if Δx is too large, the relative displacement will exceed the size of the directional uniform light control unit, and the required film thickness will be too thick, which is detrimental to the thinning of the backlight module. As can be seen from the above calculations, Δx is related to the film's refractive index, the microprism's apex angle, and the film thickness. Therefore, these parameters need to be reasonably selected based on the value of Δx.

[0102] 1003 represents the illuminance distribution after passing through two layers of microprism homogenizing films. After two such transformation processes, the normalized illuminance of a single unit is transformed into a fourth-order normalized illuminance, with normalized illuminances of 1 / 4, 1 / 2, 3 / 4, and 1, respectively. After superimposing with the illuminance regions of adjacent units, the two slits with a width of 2 / d and a normalized illuminance of 1 / 2 in a single unit region are transformed into four secondary slits with a width of d and a normalized illuminance of 3 / 4. In this process, the difference between the normalized illuminance of the slits and the uniformly illuminated area gradually decreases. On the one hand, this improves the overall uniformity, smoothing abrupt dark slits into imperfections that are almost invisible to the human eye, significantly improving the viewing experience. On the other hand, the smaller illuminance difference makes it possible to homogenize through the small divergence angle of the beam itself. At the same time, during this superposition process, the viewer cannot see the curved surface of the rear lens through the LCD screen, greatly improving the viewing experience.

[0103] This blending and smoothing effect occurs along the arrangement direction of the microprism structure. Therefore, during the design process, the appropriate microprism arrangement direction can be selected based on the direction and location of the seams and imperfections to achieve the best smoothing effect.

[0104] Figure 11 This is a schematic diagram showing the arrangement of the microprisms in a two-layer microprism homogenizing film. (Example:) Figure 11 As shown, when two layers of microprism homogenizing films are used in combination, 1103 is the illumination area formed by the array of directional homogenizing control units. In this invention, the directional homogenizing control units are arranged in a rectangular array, and dark seams caused by manufacturing and splicing errors appear at the intersection of the units, such as... Figure 11 As shown, the microprisms are arranged in a horizontal and vertical grid pattern. Direction 1101 is the arrangement direction of the microprisms in one layer, and direction 1102 is the arrangement direction of the microprisms in another layer. Direction 1101 is along the diagonal of the directional homogenization control unit, and direction 1102 is along the other diagonal of the homogenization control unit. In this way, each layer of microprism homogenization film can smooth the dark slits in both directions. At the same time, the orthogonal placement of the upper and lower layers can effectively avoid the generation of moiré fringes.

[0105] In summary, the backlight module of the present invention can achieve continuous, highly uniform, and highly collimated directional illumination that completely covers the emission surface of the backlight module. The backlight module is thin and light, and can smooth out illumination defects caused by manufacturing errors and splicing problems. It also prevents viewers from seeing the lens structure through subsequent components, and can be well adapted to 3D display systems, thereby realizing true 3D display.

[0106] In this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, which includes not only the elements listed but also other elements not expressly listed.

[0107] In this document, the directional terms such as front, back, top, and bottom are defined based on the location of the components in the accompanying drawings and their relative positions to each other, solely for the purpose of clarity and convenience in expressing the technical solution. It should be understood that the use of these directional terms should not limit the scope of protection claimed in this application.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-uniformity directional backlight module, characterized in that, It includes a substrate, a light source array, an aperture array, a lens array, and one or more microprism homogenizing films. The light source array includes a plurality of light sources arranged on a substrate; The aperture array includes several apertures arranged on the substrate, each aperture corresponding to a light source. The apertures limit the transmission angle of the light beam emitted by the light source to avoid crosstalk between light sources. The lens array includes several lenses that correspond one-to-one with the aperture stop, which homogenize and collimate the outgoing light beam after passing through the aperture stop. The microprism homogenizing film is an optical film. Both the upper and lower surfaces of the microprism homogenizing film are covered with microprism structures. The microprism structures on the two surfaces are arranged in the same direction but the prisms face opposite directions. The refractive index, prism apex angle, and thickness of the microprism homogenizing film are designed to improve the illumination defects caused by manufacturing errors and splicing problems, as well as the viewing problems caused by the lens surface shape, without affecting the collimation of the emitted beam. When the microprism light-diffusing film is multilayered, each of the microprism light-diffusing films is parallel to the substrate, and the multilayered microprism light-diffusing films are placed one after the other in the optical path direction of the beam. A set of light sources, apertures and lenses with one-to-one correspondence constitutes a directional uniform light control unit. The backlight module is composed of the directional uniform light control unit arranged in an array and a microprism uniform light film. The design steps for the microprism homogenizing film are as follows: 1) Lens splicing and manufacturing errors can cause dark seams and defects in the backlight module. The light beam after passing through the lens is injected into the microprism uniform light film. The incident light beam is divided into two outgoing light beams of equal width, thereby achieving aliasing and broadening. A diffusion screen is set on one side of the outgoing surface of the microprism uniform light film to observe the outgoing light beam of the microprism uniform light film. 2) Based on the law of refraction, the structure of the microprism and the geometric relationship of the transmitted beam, calculate the relative relationship between the refractive index of the microprism homogenizing film and the apex angle of the prism. Select the material of the microprism homogenizing film according to the pre-set refractive index, and determine the apex angle of the prism according to the refractive index of the microprism homogenizing film, so that the transmission direction of the incident beam in the microprism homogenizing film is parallel to the side of the prism. 3) Based on the law of refraction and according to the determined refractive index and prism apex angle, the thickness of the microprism homogenizing film is designed. The incident beam illuminates the lens array to form an outgoing beam with a dark slit. The outgoing beam with the dark slit is split by the microprism homogenizing film to form two slits. When observed on the diffusion screen, if there is an overlapping area between the two slits after beam splitting, it indicates that the relative displacement between the outgoing beams of the microprism homogenizing film is too small, and the thickness of the microprism homogenizing film needs to be increased. If the relative displacement between the two slits after beam splitting exceeds the size of the directional homogenization control unit, it indicates that the relative displacement between the outgoing beams of the microprism homogenizing film is too large, and the thickness of the microprism homogenizing film needs to be reduced. In order to ensure the thinness of the backlight module, the thickness of the microprism homogenizing film should not be too large. Finally, the thickness of the microprism homogenizing film to improve the lighting defects and viewing problems is obtained according to the uniformity of the illumination area on the diffusion screen and the visual effect.

2. The high uniformity directional backlight module as described in claim 1, characterized in that, When the microprism light-diffusing film is multilayered, the design steps described in claim 1 are first used to design the first layer of the microprism light-diffusing film. Furthermore, based on the determined upper layer microprism homogenizing film, the thickness of the lower layer microprism homogenizing film is designed. In this process, any slits in the emitted beam of each upper-layer microprism homogenizing film are split into two secondary slits after passing through the current microprism homogenizing film. A diffusion screen is placed on one side of the emitted surface of the current microprism homogenizing film for observation. If the two secondary slits formed by splitting a single slit have an overlapping area, it indicates that the relative displacement between the emitted beams of the current microprism homogenizing film is too small, and the thickness of the microprism homogenizing film needs to be increased. If the relative displacement between the two secondary slits formed by splitting a single slit exceeds the size of the directional homogenizing control unit, it indicates that the relative displacement between the emitted beams of the current microprism homogenizing film is too large, and the thickness of the microprism homogenizing film needs to be decreased. Finally, based on the uniformity and visual effect of the illumination area on the diffusion screen, the thickness of the microprism homogenizing film to be designed is obtained, which can improve illumination defects and viewing problems. Repeat the above steps until the design of all microprism homogenizing films is completed.

3. The high uniformity directional backlight module as described in claim 1, characterized in that, The light source is a MiniLED, MicroLED, or LED; the aperture is used to limit the angle of the beam entering the directional uniform light control unit and to avoid crosstalk between light sources; the size and dimensions of the aperture match the required light source collection angle; the aperture is a through-hole cylinder, and the size and shape of the openings at both ends of the through-hole cylinder are calculated by reverse ray tracing based on the corresponding lens; the shape and size of the light spot formed by the beam emitted by the light source at the corresponding position of the corresponding lens after passing through the aperture should match the shape and size of the corresponding lens. The lenses in the lens array have freeform or aspherical surfaces; both surfaces of the lenses in the lens array have optical power, allowing simultaneous control of beam intensity and wavefront; the lenses in the lens array are made of optical plastic, and their refractive index is 1.4~1.

8.

4. The high uniformity directional backlight module as described in claim 1, characterized in that, The full width at half maximum (FWHM) of the emitted beam intensity of the backlight module is less than 5°.

5. The high uniformity directional backlight module as described in claim 1, characterized in that, The prism apex angles of the microprism structures on the two surfaces of the microprism homogenizing film are the same. The microprisms on the two surfaces of the microprism homogenizing film have different prism spacings, or the microprisms on either surface of the microprism homogenizing film have non-periodic prism spacings, in order to avoid the influence of moiré fringes. The microprisms are arranged in a direction that avoids the direction of dark seams caused by lens splicing and manufacturing errors.

6. The high uniformity directional backlight module as described in claim 1, characterized in that, The backlight module emits light along the normal direction of the substrate or at a certain angle to the normal direction of the substrate.

7. A three-dimensional display system, characterized in that, Includes the high uniformity directional backlight module as described in any one of claims 1-6.

8. The three-dimensional display system as described in claim 7, characterized in that, It also includes liquid crystal modulation elements and light field control elements. The liquid crystal modulation element is disposed in the outgoing light path of the backlight module and is used to modulate the illumination intensity emitted by the backlight module to achieve image display. The light field modulation element is set in the output light path of the liquid crystal modulation element, and three-dimensional viewpoint reconstruction is performed through beam modulation to realize three-dimensional display.

9. A beam control method using the high uniformity directional backlight module according to any one of claims 1-6, characterized in that, The light beam emitted by the light source passes through the aperture and then enters the lens. Due to the limiting effect of the aperture, the incident light beam just fills the corresponding aperture of the lens. The lens is an aspherical or freeform lens with optical power on both sides, so the intensity and wavefront of the light beam can be controlled at the same time to achieve beam homogenization and collimation. The outgoing light beam after passing through the lens will pass through a microprism homogenizing film to smooth its illumination defects and viewing problems, thereby achieving directional illumination with high uniformity, high collimation and suitable viewing.

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