Volume holographic grating assembly for ultrathin Mini LED backlight, backlight module and method

Abstract

The invention discloses a volume holographic grating assembly for ultrathin Mini LED backlight, a backlight module and a method, and belongs to the technical field of liquid crystal display. The volume holographic grating assembly is composed of a reflection type volume holographic grating array, the thickness of a single grating unit is 5-15 microns, and the reflection type volume holographic grating array is of a three-dimensional refractive index modulation structure which is formed through interference recording of two beams of coherent light and has the Bragg diffraction characteristic. The backlight module comprises a reflecting film, a Mini LED light source, a diffusion film and an optical film provided with the volume holographic grating assembly. The reflecting film and the diffusion film are arranged in parallel; the optical film is arranged between the reflecting film and the diffusion film and is close to the diffusion film; the Mini LED light source is arranged close to the reflecting film and right faces the optical film. The optical path can be increased, and the problem that the uniformity requirement of the ultrathin backlight module cannot be met by means of the prior art is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid crystal display, and particularly relates to a volume holographic grating component, a backlight module and a method for ultra-thin MiniLED backlight. Background Art

[0002] After years of development, liquid crystal display has become the mainstream technology of flat panel display. Since liquid crystals do not emit light, a backlight is required to provide illumination light. The brightness, chromaticity and volume of the backlight module largely determine the performance of the final display. The thinning of display products has become a popular trend, which requires the backlight module to minimize the thickness to the greatest extent. However, when the thickness requirement of the backlight module is reduced to less than 3 mm, due to the too short optical path, existing solutions such as diffusion films and refractive lenses cannot fully open the light, so a uniform surface light source cannot be formed at a small distance.

[0003] It can be seen that the level of the existing technology has shown deficiencies in ultra-thin MiniLEDs, and cannot meet the high requirements of the current and future fields for the ultra-thinning and miniaturization of liquid crystal displays. How to improve the opening degree of light to form a uniform surface light source under the conditions of ultra-thinning and miniaturization has become a key point. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems in the above related technologies to some extent.

[0005] To this end, the object of the present invention is to provide a volume holographic grating component, a backlight module and a method for ultra-thin MiniLED backlight, which can reflect the light emitted by MiniLEDs back to the lamp board of the backlight module to the greatest extent through the volume holographic grating, and reflect the light upward through the reflective film on the surface of the lamp board, thereby increasing the optical path and solving the problem that the existing technical means cannot meet the uniformity requirements of the ultra-thin backlight module.

[0006] In order to solve the above technical problems, the present invention is implemented as follows:

[0007] The embodiment of the present invention provides a volume holographic grating component for ultra-thin MiniLED backlight. The volume holographic grating component is composed of a reflective volume holographic grating array. The thickness of a single grating unit is 5 μm to 15 μm. The reflective volume holographic grating array is a three-dimensional refractive index modulation structure with Bragg diffraction characteristics formed by the interference recording of two coherent light beams.

[0008] In addition, the volume holographic grating component for ultra-thin MiniLED backlight according to the present invention may further have the following additional technical features:

[0009] In some of these embodiments, the value range of the first exposure distance of the reflective volume holographic grating array is 1 mm to 2 mm, and the value range of the second exposure distance is 0 mm to 2 mm;

[0010] The first exposure distance is the distance between the first coherent point light source and the prepared holographic volume grating material;

[0011] The second exposure distance is the distance between the second coherent point light source and the prepared holographic volume grating material.

[0012] In some of these embodiments, the grating radius of the reflective volume holographic grating array is determined by the light source divergence angle and the exposure area, and the value range is 0.5 mm to 2 mm.

[0013] An embodiment of the present invention also provides an ultra-thin MiniLED backlight module, which is characterized in that the backlight module includes: a reflective film, a MiniLED light source, a diffusion film, and an optical film provided with the volume holographic grating component for ultra-thin MiniLED backlight according to any one of claims 1-3;

[0014] The reflective film and the diffusion film are arranged in parallel;

[0015] The optical film is arranged between the reflective film and the diffusion film and is close to the diffusion film;

[0016] The MiniLED light source is arranged close to the reflective film and faces the optical film.

[0017] In addition, the ultra-thin MiniLED backlight module according to the present invention may further have the following additional technical features:

[0018] In some of these embodiments, the distance between the diffusion film and the optical film is less than 1 mm;

[0019] The distance between the optical film and the reflective film is greater than 0.5 mm.

[0020] In some of these embodiments, the distance between the diffusion film and the optical film is 0 mm;

[0021] The distance between the optical film and the reflective film is 2 mm.

[0022] In some of these embodiments, the first exposure distance of the volume holographic grating is 1.5 mm to 2 mm, the second exposure distance is 0.75 mm to 1.2 mm, and the exposure radius is 0.75 mm to 2 mm;

[0023] The first exposure distance is the distance between the first coherent point light source and the prepared holographic volume grating array material;

[0024] The second exposure distance is the distance between the second coherent light spot light source and the prepared volume holographic grating array material.

[0025] In some of these embodiments, the first exposure distance of the optical film is 2 mm, the second exposure distance is 0.9 mm, and the exposure radius is 2 mm.

[0026] In some of these embodiments, the reflective film is a diffuse reflection plate.

[0027] The embodiment of the present invention also provides a preparation method for a volume holographic grating component for ultra-thin MiniLED backlight as described in any one of the above, and the steps of the preparation method include:

[0028] S1. Determine the parameters of the volume holographic grating component;

[0029] The parameters include the first exposure distance, the second exposure distance, and the exposure radius of a single grating, the light-emitting characteristics and the light-emitting angle of the MiniLED light source, the refractive index of the volume holographic grating material and the refractive index of air, the maximum divergence angle, the light-emitting angle, the light intensity of each discrete light-emitting angle, and the diffraction angle of the light and the uniformity of the diffraction-formed light spot at the exposure distance after the light enters the grating material;

[0030] Select the structure with the best uniform diffraction effect to determine the final parameter values of the volume holographic grating component;

[0031] S2. Prepare the volume holographic grating component:

[0032] Build an exposure optical path for preparing the volume holographic grating, and adjust the focal length and position of the convex lens in the exposure optical path according to the exposure distance and the exposure radius set in S1; obtain a three-dimensional grating structure through the interference superposition of two coherent lights in a photosensitive medium; and then perform mass production through nanoimprinting and roll-to-roll processes.

[0033] Compared with the prior art, the present invention has at least the following beneficial effects:

[0034] In the embodiment of the present invention, the volume holographic grating for ultra-thin MiniLED backlight can make the light source diffuse a larger distance at a shorter distance to achieve the effect of light homogenization; on the one hand, the light diffracts and diffuses in the reverse direction after passing through the volume holographic grating to increase the diffusion angle; on the other hand, the light is reflected upward at the reflection surface to increase the optical path of the light; in addition, the diffusion film above the optical film receives the light and further diffuses the light, improving the diffusion effect and the light homogenization effect of the light.

[0035] The additional aspects and advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 FIG. 1 is a schematic diagram of an optical module of an existing backlight module using two layers of diffusion films disclosed in the present invention;

[0037] Figure 2 FIG. 2 is a light path diagram of a MiniLED backlight module using a volume holographic grating disclosed in an embodiment of the present invention;

[0038] Figure 3 FIG. 3 is a schematic diagram of a preparation optical path structure used when preparing a volume holographic grating disclosed in an embodiment of the present invention;

[0039] Figure 4 FIG. 4 is a simulated illuminance diagram when the volume holographic grating optical film of the present invention is used as a backlight module in an embodiment;

[0040] Figure 5 FIG. 5 is a ray tracing diagram disclosed in an embodiment of the present invention;

[0041] Figure 6 FIG. 6 is a simulated illuminance diagram when only a diffusion film is used as a backlight module in an embodiment of the present invention.

[0042] DESCRIPTION OF THE REFERENCE NUMERALS:

[0043] 101 - First reflective film; 102 - First MiniLED light source; 103 - First diffusion film; 104 - Second diffusion film;

[0044] 201 - Second reflective film; 202 - Second MiniLED light source; 203 - Optical film; 204 - Third diffusion film. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings through specific embodiments and their application scenarios.

[0047] In some embodiments of the present invention, a volume holographic grating for ultra-thin MiniLED backlighting is provided. The volume holographic grating is arranged above the MiniLED chip and diffracts incident light in all directions in the opposite direction. After the light reflected by the volume holographic grating reaches the light guide plate at the bottom of the MiniLED backlight module, it is reflected upward again by the white paint coated on the surface of the light guide plate at the bottom of the backlight module, reaches the diffusion film located above the volume holographic light spot, and forms a uniform surface light source above the diffusion film after passing through the diffusion film.

[0048] In some embodiments of the present invention, the volume holographic gratings form an array to constitute an optical film. The MiniLED backlight module includes a diffusion film, an optical film, a reflective film, and a MiniLED light source. Among them, the diffusion film is arranged at the upper end of the optical film; the reflective film is arranged at the lower end of the optical film; the MiniLED light source is arranged between the reflective film and the optical film. The optical film is prepared by the principle of interference recording. The MiniLED emits light in all directions as a light source; the optical film receives the light emitted by the light source and changes its direction. Among them, part of the light remains in the original optical path unchanged while part of the light changes direction, and the change in the direction of the light is related to the preparation parameters of the optical film; the diffracted light changes direction again through the reflective film; the reflected light and the previously mentioned transmitted light are further diffused through the diffusion film together, and finally the diffused light meets the requirements of uniform backlighting.

[0049] In some embodiments of the present invention, the optical film is a pure phase element, and its function is to adjust the light angle of the light emitted by the MiniLED light source; diffract the light that meets the diffraction angle, so that the part with higher central light intensity of the light source diffracts to the surroundings.

[0050] In some embodiments of the present invention, the optical film is optimized and solved by Zemax least squares method simulation.

[0051] In some embodiments of the present invention, the optical film is recorded by laser interference and can be mass-produced by nanoimprinting and roll-to-roll processes.

[0052] In the above embodiments, the reflective film can be replaced with a diffuser plate to further improve the diffusion effect. The reflective film can also directly use white paint to form a low-cost diffused area.

[0053] The design process of the volume holographic grating is as follows:

[0054] 1. Calculate the light source diffusion angle. Record the light radius of the light at the output end of the backlight module without a diffusion film; according to the distance between the light source and the output end, the light source diffusion angle can be calculated by the formula

[0055] 2. Calculate the optical parameters required for the preparation of volume holographic gratings. The preparation of volume holographic gratings relies on the interference of two coherent light beams. The two light beams are superimposed within the medium to form a three-dimensional interference fringe pattern with bright and dark intervals; the photosensitive medium (such as photopolymer, photorefractive crystal, etc.) undergoes physical or chemical changes under the exposure in the interference region, resulting in a periodic modulation of the refractive index inside the medium (i.e., a three-dimensional grating structure). The grating structure can reproduce the phase of another coherent light beam through diffraction after receiving a coherent light beam. The main parameters of the two coherent light beams are the light beam divergence angle, the light beam angle, and the light source position. All three parameters of the light beam divergence angle, the light beam angle, and the light source position can be transformed by establishing a coordinate system. A three-dimensional rectangular coordinate system xyz is established with the center of the grating as the coordinate origin. The light source position can be represented by the xyz coordinates. The light beam angle is the angle of the line connecting the light source coordinates and the coordinate origin. The divergence angle of the light beam can be represented by the light beam position and the exposure area together.

[0056] In some embodiments of the present invention, the optical film is composed of a volume holographic grating array; the Bragg diffraction center wavelength of the volume holographic grating is λ; the required parameters of the holographic grating array are the three-dimensional coordinates xyz and the radius r of a single volume holographic grating.

[0057] In some embodiments of the present invention, the volume holographic grating is exposed by two opposite diffused light beams, so the three-dimensional coordinates xy of the exposure light source are both taken as 0. The volume holographic grating is exposed by two coherent light beams diverging from a MiniLED light source, so the received light beam will diffract into a diverging light beam after passing through the optical film.

[0058] In the above embodiment, the exposure distance z of the first exposure light beam 1 , to make the light emitted by the MiniLED satisfy the Bragg diffraction condition with the volume holographic grating, so the exposure distance z 1 is 1 mm to 2 mm. The exposure distance z of the second exposure light beam 2 is 0 mm to 2 mm; the exposure area is determined by the divergence angle of the MiniLED light source itself and its exposure area at the detector position, and the radius of the volume holographic grating is calculated by scaling an isosceles triangle proportionally. The volume holographic grating is a reflective volume holographic grating with a thickness of 5 μm to 15 μm.

[0059] In some embodiments of the present invention, the volume holographic grating can be a monochromatic volume holographic grating, a multiplexed volume holographic grating, or a multi-layer stacked structure volume holographic grating.

[0060] Please refer to Figure 1As shown in the figure, the existing backlight module adopts a two-layer diffusion film method. It includes a reflective film 101, a MiniLED light source 102, a first diffusion film 103, and a second diffusion film 104. When the diffusion film on the market is directly placed on the MiniLED or at a very close distance, there is no diffusion effect. Therefore, the technical solution using the existing diffusion film will result in a very large mixing distance of light.

[0061] See Figure 2 As shown in the figure, in some embodiments of the present invention, a MiniLED backlight module includes a second reflective film 201, a second MiniLED light source 202, an optical film 203, and a third diffusion film 204. The MiniLED light source emits divergent light L21 outward; the divergent light L21 enters the optical film 203 at a certain angle and undergoes Bragg diffraction with the volume holographic grating to become divergent light L22 in the opposite direction; the divergent light L22 contacts the second reflective film 201 and undergoes total reflection to become reflected light L23 (similarly, if a diffuse reflection plate is used, scattered light L23 will be formed); because the volume holographic grating on the optical film 203 only exists at a certain position above the light source, most of the reflected light L23 will pass through the optical film 203 and continue to propagate, and another part of the light will almost completely transmit through the optical film 203 when the incident angle does not satisfy the Bragg diffraction condition when contacting the volume holographic grating area on the optical film 203; the reflected light L23 will pass through the optical film to the third diffusion film 204, and the light forms diffused light L24 through the third diffusion film 204, finally meeting the uniformity conditions required by the backlight module.

[0062] In the above embodiments, the optical film 203 is an array composed of a plurality of volume holographic gratings, and the preparation of the volume holographic grating depends on the interference of two coherent light beams. The two light beams are superimposed in the medium to form an alternating bright and dark three-dimensional interference fringe pattern. The grating exposure parameters include the first exposure distance z of the MiniLED light source of the two coherent light beams from the grating material 1 , the second exposure distance z 2 and the spot size formed by the MiniLED light source at the material position, that is, the exposure radius r. The first exposure distance is the distance between the first coherent point light source and the holographic volume grating material to be prepared. The second exposure distance is the distance between the second coherent point light source and the holographic volume grating material to be prepared.

[0063] In some embodiments of the present invention, the first exposure distance z 1 is 1 mm to 2 mm; the second exposure distance z 2is from 0.5 mm to 1.5 mm; the exposure radius is from 0.5 mm to 2 mm. Further, the first exposure distance is from 1.5 mm to 2 mm; the second exposure distance is from 0.75 mm to 1.2 mm; the exposure radius is from 0.75 mm to 2 mm. Further preferably, the first exposure distance of the optical film 203 is 2 mm; the second exposure distance is 0.9 mm; the exposure radius is 2 mm.

[0064] In some embodiments of the present invention, the distance between the third diffusion film 204 and the optical film 203 is the first distance, and the first distance is greater than 0.5 mm; the distance between the optical film 203 and the second reflective film 201 is the second distance, and the second distance is less than 0.5 mm. Further, the first distance is 2 mm; the second distance is 0 mm.

[0065] In some embodiments of the present invention, the optical film 203 is used to diffract the light emitted by the MiniLED chip back to the bottom of the backlight to the greatest extent; the third diffusion film 204 is used to further diffusely scatter the reflected light.

[0066] In some embodiments of the present invention, there is also provided a method for preparing an optical film for a MiniLED backlight module, including the following steps:

[0067] Step 1: Set the parameters of each individual volume holographic grating on the optical film;

[0068] 1.1. Set the first exposure distance z of each individual volume holographic grating 1 , z 1 is between 1 mm and 2 mm;

[0069] 1.2. Set the second exposure distance z of each individual volume holographic grating 2 , z 2 is between 0.5 mm and 1.5 mm;

[0070] 1.3. Set the exposure radius of each individual volume holographic grating to be between 0.75 mm and 2 mm;

[0071] 1.4. Set the discrete MiniLED light source P corresponding to each volume holographic grating i , i = 1, 2, 3,..., m, and the light-emitting characteristics of each MiniLED light source are the same as those of each MiniLED chip;

[0072] 1.5. Set the light-emitting angle range of each MiniLED light source P i to be (-α max , α max );

[0073] 1.6. Set the refractive index of the volume holographic grating material to be n, and the refractive index of air to be n0 ;

[0074] 1.7. MiniLED light source P i After the light emitted enters the optical film, the maximum divergence angle is The emission angle range is (-β max , β max );

[0075] 1.8. Discretize from 0 to β max into β n ,

[0076] 1.9. Discretize z 1 into z i ,

[0077] 1.10. Discretize z 2 into z j ,

[0078] 1.11. Derive and analyze the absorption-free diffraction efficiency of the micro-grating through the coupled-wave theory, and then derive the actual light intensity of each β n to obtain the diffraction angle of the light and the uniformity of the diffraction-formed light spot at the exposure distance; select the structure with the best uniform diffraction effect from them to determine the structure of the optical film.

[0079] Step 2: Fabricate the micro-structure on the surface of the optical film obtained in Step 1.

[0080] 2.1. Set up the exposure optical path for fabricating the volume holographic grating as shown in Figure 3 . The figure shows the exposure optical path for fabricating a monochromatic volume holographic grating. If needed, a color volume holographic grating can also be fabricated through grating multiplexing or grating superposition; adjust the focal length and position of the convex lens to correspond to the first exposure distance z 1 and the second exposure distance z 2 and the exposure radius r in Step 1 above;

[0081] 2.2. Through the interference of two coherent light beams. The two light beams are superimposed in the medium to form an alternating light and dark three-dimensional interference fringe pattern; the photosensitive medium (such as photopolymer, photorefractive crystal, etc.) undergoes physical or chemical changes under the exposure in the interference region, resulting in a periodic modulation of the refractive index inside the medium (i.e., a three-dimensional grating structure); the grating structure can reproduce the phase of another coherent light beam through diffraction when receiving a coherent light beam; use a black diaphragm to control the optical film to prevent the multiple exposure from affecting the volume holographic grating structure that has been exposed and completed when forming an array (it can also be exposed in multiple pieces and then cut and glued together with optical glue to form an array);

[0082] 2.3. After confirming the structural reliability, mass production can be carried out through nanoimprinting and roll-to-roll processes.

[0083] The nanoimprinting and roll-to-roll processes can adopt existing processes and will not be elaborated here.

[0084] Among them Figure 4 is the simulated illuminance diagram when the volume holographic grating optical film disclosed in an embodiment of the present invention is used as a backlight module. The distance between each MiniLED light source is 6 mm, the length and width of the MiniLED are both 0.524 mm, and the volume holographic grating array and the relevant backlight module parameters are the same as those in step 1 above.

[0085] Among them Figure 5 is the ray tracing diagram disclosed in an embodiment of the present invention. The image shown in the figure is the ray path of the rays emitted by the MiniLED light source when the ray source angle x is 76°, the ray source angle y is 76°, and the ray source angle z is 20° in this embodiment.

[0086] Among them Figure 6 is the simulated illuminance diagram when only a diffusion film is used as the backlight module without using the volume holographic grating array of the present invention, which is placed here for comparison with the effect of the present invention.

[0087] For the parts not detailed in the present invention, reference can be made to the prior art or the well-known technology in the art. This embodiment does not limit this and will not be described in detail here.

[0088] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit and scope protected by the claims of the present invention, and all belong to the protection scope of the present invention.

Claims

1. A volume holographic grating component for ultra-thin MiniLED backlight, characterized in that: The volume holographic grating component is composed of a reflective volume holographic grating array, the thickness of a single grating unit is 5μm~15μm, and the reflective volume holographic grating array is a three-dimensional refractive index modulation structure with Bragg diffraction characteristics formed by interference recording of two coherent light beams.

2. The volume holographic grating assembly for ultra-thin MiniLED backlight according to claim 1, characterized in that: The first exposure distance of the reflective volume holographic grating array has a value range of 1 mm to 2 mm, and the second exposure distance has a value range of 0 mm to 2 mm; The first exposure distance is the distance between the first beam of coherent light point light source and the prepared holographic grating array material; The second exposure distance is the distance between the second beam of coherent light point light source and the prepared holographic grating array material.

3. The volume holographic grating assembly for ultra-thin MiniLED backlight according to claim 1, characterized in that: The grating radius of the reflective volume holographic grating array is determined by the divergence angle of the light source and the exposure area, and the value range is 0.5mm~2mm.

4. An ultra-thin MiniLED backlight module, characterized in that: The backlight module comprises: a reflective film, a MiniLED light source, a diffusion film, and an optical film provided with a volume holographic grating component for ultra-thin MiniLED backlight according to any one of claims 1 to 3; The reflective film and the diffusion film are arranged in parallel; The optical film is disposed between the reflective film and the diffusion film and is close to the diffusion film; The MiniLED light source is disposed close to the reflective film and facing the optical film.

5. The ultra-thin MiniLED backlight module according to claim 4, characterized in that: The distance between the diffusion film and the optical film is less than 1 mm; The distance between the optical film and the reflective film is greater than 0.5 mm.

6. The ultra-thin MiniLED backlight module according to claim 5, characterized in that: The distance between the diffusion film and the optical film is 0 mm; The distance between the optical film and the reflective film is 2 mm.

7. The ultra-thin MiniLED backlight module according to claim 4, characterized in that: The first exposure distance of the optical film is 1.5 mm to 2 mm, the second exposure distance is 0.75 mm to 1.2 mm, and the exposure radius is 0.75 mm to 2 mm; The first exposure distance is the distance between the first beam of coherent light point light source and the prepared holographic grating array material; The second exposure distance is the distance between the second beam of coherent light point light source and the prepared holographic grating array material.

8. The ultra-thin MiniLED backlight module according to claim 7, characterized in that: The first exposure distance of the optical film is 2 mm, the second exposure distance is 0.9 mm, and the exposure radius is 2 mm.

9. The ultra-thin MiniLED backlight module according to claim 4, characterized in that: The reflective film is a diffuse reflective plate.

10. A method for preparing a volume holographic grating component for ultra-thin MiniLED backlight according to any one of claims 1 to 3, characterized in that: The steps of the preparation method include: S1. Determine various parameters of the volume holographic grating component; The parameters include the first exposure distance, the second exposure distance and the exposure radius of a single grating, the luminous characteristics and luminous angle of the MiniLED light source, the refractive index of the volume holographic grating material and the refractive index of air, the maximum divergence angle of the light after entering the grating material, the luminous angle, the light intensity of each discrete luminous angle, and the diffraction angle of the light at the exposure distance and the uniformity of the light spot formed by the diffraction; Select the structure with the best uniform diffraction effect to determine the final parameter value of the volume holographic grating component; S2. Preparation of volume holographic grating components: Build an exposure light path for preparing volume holographic gratings, and adjust the focal length and position of the convex lens in the exposure light path according to the exposure distance and exposure radius set in S1; obtain a three-dimensional grating structure through the interference superposition of two coherent light beams in the photosensitive medium; and then mass produce it through nanoimprinting and roll-to-roll processes.

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