Optical film for mini-led backlight module and design method thereof

Abstract

The present application relates to a kind of optical film for MiniLED backlight module and its design method, belong to MiniLED backlight display technical field.The optical film includes first microstructure layer and second microstructure layer arranged in turn along the direction of light propagation, two layers are by periodic arrangement inverted V type microstructure and the arrangement direction is perpendicular to each other.The design method includes: first microstructure layer with first receiving surface energy distribution variance minimum in first direction as target, by ray tracing to the inclination angle is scanned and optimized, obtains optimal inclination angle;Second microstructure layer with the angle distribution of first layer exit light in vertical direction as input, with second receiving surface energy distribution variance minimum as target to scan and optimize inclination angle, realize two-layer accurate optical matching.The present application can efficiently convert MiniLED point light source into uniform surface light source in short light mixing distance, significantly improve light uniformity.

Description

Technical Field

[0001] This invention belongs to the field of MiniLED backlight display technology, specifically relating to an optical film for MiniLED backlight modules and its design method. Background Technology

[0002] LEDs have become the mainstream light source for LCD backlight modules. With the development of semiconductor technology, the size of LED chips has shrunk to a few hundred micrometers, resulting in MiniLEDs. MiniLEDs are small in size and generate little heat, and are densely arranged in a matrix in the backlight module. A diffusion film is usually used to transform the point light source of MiniLEDs into a surface light source that meets the uniformity requirements, in order to ensure the final display effect.

[0003] To meet the demand for thinner end products, the overall thickness of backlight modules is constantly being reduced, and the mixing distance between the light source and the light-emitting surface is continuously decreasing. Traditional single-layer diffusion films rely on the scattering effect of medium particles on light to achieve uniform light distribution. However, at short mixing distances, they cannot fully diffuse MiniLED light, which easily leads to obvious bright and dark stripes on the light-emitting surface, making it difficult to meet the requirements for high uniformity of light emission.

[0004] To address the aforementioned issues, multilayer optical film solutions have emerged in this field, achieving light control through the combined effect of multiple layers. However, current multilayer optical films generally employ an independent design approach for each layer's parameters, failing to consider the changes in the angle distribution of light after passing through the previous layer and neglecting the transmission and matching relationship of light angle distribution between layers. This results in poor optical synergy of the multilayer structure, low overall optical efficiency, limited improvement in light uniformity, and an inability to achieve high-quality point source to surface source conversion at extremely small mixing distances. Summary of the Invention

[0005] The purpose of this invention is to provide an optical film for MiniLED backlight modules and its design method. Through the cascaded collaborative design of two orthogonal inverted V-shaped microstructures, optical precision matching is achieved based on the interlayer angle distribution, so as to efficiently convert MiniLED point light sources into highly uniform surface light sources at short mixing distances, thereby improving the light output uniformity and overall optical efficiency of the backlight module.

[0006] On the one hand, the present invention provides an optical film design method for MiniLED backlight modules, which adopts the following technical solution: An optical film design method for a MiniLED backlight module, the optical film comprising a first microstructure layer and a second microstructure layer arranged sequentially along the light propagation direction, the first microstructure layer and the second microstructure layer being formed on the upper surface of a corresponding PET substrate and arranged perpendicularly to each other, the first microstructure layer and the second microstructure layer being composed of periodically arranged inverted V-shaped microstructures. The design method includes: The design steps of the first microstructure layer are as follows: with the goal of minimizing the variance of energy distribution along the first direction of the first receiving surface, the tilt angle of the first microstructure layer is scanned and optimized by ray tracing to obtain the optimal tilt angle; The design steps for the second microstructure layer are as follows: obtain the angular distribution of the emitted light from the first microstructure layer in a plane perpendicular to the first direction as the input of the incident light field, take the minimum variance of the energy distribution along the second direction of the second receiving surface as the objective, and perform scanning optimization on the tilt angle of the second microstructure layer through ray tracing to obtain the optimal tilt angle, thereby achieving optical matching between the first and second microstructure layers.

[0007] Preferably, the optimization steps for the first microstructure layer specifically include: The MiniLED is discretized into multiple uniformly distributed point light sources, and the light emitted by each point light source is distributed in a Lambertian pattern in the plane formed by the first direction and the optical axis. Set the period and half-width parameters of the first microstructure layer, and preset the tilt angle scan range; Ray tracing is performed on each candidate tilt angle. The first receiving surface is evenly divided into several equal-width intervals along the first direction as partitions. The energy obtained by accumulating all rays in each partition is counted to form the partition energy distribution of the first receiving surface along the first direction. Calculate the variance of the energy distribution in each partition, and select the tilt angle with the largest negative variance as the optimal tilt angle for the first microstructure layer.

[0008] Preferably, the ray tracing process is as follows: Light rays are incident on the lower surface of the PET substrate through the air and are refracted. They then propagate inside the PET to the inclined surface of the microstructure. The incident angle is calculated at the inclined surface. If the incident angle is greater than or equal to the critical angle for total internal reflection, total internal reflection occurs. If it is less than the critical angle, the light rays are refracted out into the air and finally reach the first receiving surface.

[0009] Preferably, the energy weight of the light emitted by the Lambertian light source is proportional to the cosine of the angle between the light emission direction and the optical axis; The variance of energy distribution is calculated as follows: first, calculate the mean of energy in all partitions, then calculate the average of the squared differences between the energy in each partition and the mean, and thus obtain the variance.

[0010] Preferably, the second microstructure layer collaborative optimization step specifically includes: The obtained angular distribution is discretized and normalized to obtain the probability density function and cumulative distribution function; The first microstructure layer's emitting surface is equivalent to a line light source, and discretized into multiple point light sources along the second direction. Each point light source is sampled at an angle with equal probability according to the cumulative distribution function. Perform ray tracing on the sampled rays: Divide the second receiving surface into several equal-width intervals along the second direction as partitions, and count the energy of all rays in each partition to form the partition energy distribution of the second receiving surface along the second direction; Calculate the variance of the energy distribution in each partition, and select the tilt angle with the largest negative variance as the optimal tilt angle for the second microstructure layer.

[0011] Preferably, an optical model of the first microstructure layer is established using optical simulation software, and the angle-intensity distribution of the emitted light from the first microstructure layer is obtained using a far-field receiver.

[0012] Preferably, the first microstructure layer and the second microstructure layer have the same period and the same half-width.

[0013] On the one hand, the present invention also provides an optical film for a MiniLED backlight module, which adopts the following technical solution: An optical film for a MiniLED backlight module includes a first PET substrate and a second PET substrate arranged sequentially along the light propagation direction, with an air gap between the first PET substrate and the second PET substrate. A first microstructure layer is formed on the upper surface of the first PET substrate, the first microstructure layer being composed of inverted V-shaped microstructures arranged periodically along a first direction; a second microstructure layer is formed on the upper surface of the second PET substrate, the second microstructure layer being composed of inverted V-shaped microstructures arranged periodically along a second direction, the second direction being perpendicular to the first direction. The tilt angles of the first microstructure layer and the second microstructure layer are determined using the design method described in any one of claims 1-7, and the tilt angle of the second microstructure layer is matched and set according to the angular distribution of the emitted light from the first microstructure layer. The two layers constitute a cascaded optical system.

[0014] Preferably, the height of the inverted V-shaped microstructure is equal to the product of its half-width and the tangent of its tilt angle.

[0015] Furthermore, the present invention also provides a method for preparing the optical film for a MiniLED backlight module, which adopts the following technical solution: The method for preparing optical films for MiniLED backlight modules includes the following steps: Using the above design method, the optimal tilt angles of the first microstructure layer and the second microstructure layer are determined; The inverted V-shaped structure geometric parameters of the first microstructure layer are generated based on the optimal tilt angle, and a one-dimensional periodic array is arranged on the first PET substrate along the first direction to obtain the first microstructure layer. Based on the optimal tilt angle, the inverted V-shaped structure geometric parameters of the second microstructure layer are generated, and a one-dimensional periodic array is arranged on the second PET substrate along the second direction to obtain the second microstructure layer. The first PET substrate and the second PET substrate are arranged sequentially along the light propagation direction, such that the first microstructure layer and the second microstructure layer both face the light-emitting side, and an air gap is maintained between the first PET substrate and the second PET substrate.

[0016] In summary, the present invention has the following beneficial technical effects: 1. This invention employs a first microstructure layer and a second microstructure layer arranged sequentially along the light propagation direction. Each layer is composed of inverted V-shaped microstructures arranged periodically in mutually perpendicular directions. This allows the light emitted from the MiniLED point light source to be orthogonally modulated by the first and second microstructure layers, resulting in uniform expansion in two mutually perpendicular directions. Ultimately, this achieves a high-quality conversion from a point light source to a uniform surface light source within a short mixing distance. Experimental data shows that, with mixing distances of only 2mm and 0.5mm, this invention effectively eliminates bright and dark stripes on the light-emitting surface, significantly improving the light emission uniformity of the backlight module.

[0017] 2. This invention uses variance minimization as the objective function for microstructure tilt angle optimization, directly quantifies and optimizes the flatness of energy distribution in each zone of the receiving surface, overcomes the local uniformity defect of "high at both ends and low in the middle" that is easy to occur when the maximum / minimum ratio is used as the uniformity evaluation index in the traditional method, and ensures the global optimal uniformity of light output across the entire surface.

[0018] 3. This invention proposes a two-layer microstructure design method based on "angle distribution transfer and collaborative optimization." After completing the design of the first microstructure layer, the actual angular distribution of the emitted light from the first microstructure layer is used as the input light source condition for the design of the second microstructure layer. This ensures that the tilt angle optimization of the second microstructure layer is strictly based on the actual angular distribution of the emitted light from the first microstructure layer, rather than using the same initial Lambertian distribution as the first microstructure layer design. This design method avoids the optical efficiency loss caused by the mismatch in interlayer angular distribution in traditional multilayer independent designs, achieves precise optical matching between the two microstructure layers, and effectively improves the overall optical efficiency.

[0019] 4. The design method of this invention has good universality and engineering applicability. By simply substituting the parameters of MiniLEDs of different sizes, the corresponding optimal structural parameters can be quickly obtained through ray tracing and parameter scanning, without the need to redesign the overall scheme. At the same time, the solution can achieve mass production based on conventional PET substrates and microstructure processing technology, without the need for additional special processes, and has high industrial application value. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the MiniLED backlight module and optical film. Figure 2 A schematic diagram of the two-dimensional outline of the inverted V-shaped microstructure; Figure 3 Angle-intensity distribution diagram of light emitted from the first microstructure layer corresponding to a 0.78mm chip; Figure 4 Angle-intensity distribution diagram of light emitted from the first microstructure layer corresponding to a 0.508mm chip; Figure 5 Two-dimensional illuminance distribution diagram of the final receiving surface of the double-layer microstructure corresponding to the 0.78mm chip; Figure 6 The image shows the two-dimensional illuminance distribution on the final receiving surface of the dual-layer microstructure corresponding to the 0.508mm chip. Figure 7 Two-dimensional illuminance distribution diagram of the final receiving surface after adding a diffusion film to the 0.78mm chip; Figure 8 Two-dimensional illuminance distribution diagram of the final receiving surface after adding a diffusion film to the 0.508mm chip; Figure 9 A comparison of two-dimensional illuminance on the receiving surface of a traditional single-layer diffusion film scheme; Figure 10 A two-dimensional comparison diagram of the receiving surface of two independent design schemes.

[0021] Explanation of reference numerals in the attached figures: 1. MiniLED; 2. First PET substrate; 21. First microstructure layer; 3. Second PET substrate; 31. Second microstructure layer; 4. Diffusion film. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, the scope of protection of this invention is not limited to the following specific embodiments. Those skilled in the art can make several improvements and modifications without departing from the concept of this invention, and these all fall within the scope of protection of this invention.

[0023] Example Example 1 Reference Figure 1 The MiniLED backlight module provided in this embodiment is provided with a MiniLED1, a first PET substrate 2, a second PET substrate 3 and an optional diffusion film 4 arranged sequentially from bottom to top along the light propagation direction (Z direction); wherein the air gap between the first PET substrate 2 and the MiniLED1 is D1, the air gap between the first PET substrate 2 and the second PET substrate 3 is D2, and the air gap between the second PET substrate 3 and the diffusion film 4 is D3.

[0024] Reference Figure 1 A first microstructure layer 21 is formed on the upper surface of the first PET substrate 2. The first microstructure layer 21 is composed of inverted V-shaped microstructures arranged periodically along a first direction (X direction). A second microstructure layer 31 is formed on the upper surface of the second PET substrate 3. The second microstructure layer 31 is composed of inverted V-shaped microstructures arranged periodically along a second direction (Y direction), which is perpendicular to the first direction. The tilt angle of the second microstructure layer 31 is matched to the angular distribution of the light emitted from the first microstructure layer 21. The two microstructure layers together constitute a cascaded optical system.

[0025] Reference Figure 2 The inverted V-shaped microstructure is a symmetrical two-dimensional prism structure. Its height H is equal to the product of the half-width W and the tangent of the tilt angle θ, i.e., H = W·tanθ. The bottom of the inverted V-shaped microstructure is flush with the upper surface of the PET substrate, and the tip faces the light-emitting side. The two inclined planes on the left and right are symmetrical about the central vertical axis.

[0026] Reference Figure 1 In this embodiment, the thickness of the first PET substrate 2 and the second PET substrate 3 is 0.1 mm, and the refractive index n = 1.49. This embodiment provides two sets of examples with different MiniLED chip sizes: Set 1: MiniLED diagonal length is 0.78 mm; Set 2: MiniLED diagonal length is 0.508 mm. The basic optical parameters are as follows: the air gap D1 between MiniLED1 and the lower surface of the first PET substrate 2 is 2mm; the period of the first microstructure layer 21 is P1=20μm, the half-width W1=10μm, and the distance from its tip to the first receiving surface above the layer is d1=0.5mm; the air gap D2 between the first PET substrate 2 and the second PET substrate 3 is 0.5mm; the period of the second microstructure layer 31 is P2=20μm, the half-width W2=10μm, and the distance from its tip to the second receiving surface above the layer is d2=0.5mm; the air gap D3 between the second PET substrate 2 and the upper diffusion film 4 is 0.5mm; the range of the final receiving surface is ±3mm in the X direction and ±3mm in the Y direction.

[0027] In a preferred embodiment, the first microstructure layer 21 and the second microstructure layer 31 have the same period and the same half-width.

[0028] Example 2 The design method for optical films used in MiniLED backlight modules includes the following steps: S1, Design of the First Microstructure Layer In this embodiment, the first microstructure layer aims to minimize the variance of the energy distribution along the X direction of the first receiving surface. The tilt angle θ1 is optimized by ray tracing to obtain the optimal tilt angle. The specific design steps are as follows: S1.1, Discretization of the light source The MiniLED is discretized into N uniformly distributed point light sources. The light emitted by each point light source follows a Lambertian distribution in the XZ plane formed by the X direction and the optical axis (Z axis), with a divergence angle of ±α. max The discrete angle step size is Δα.

[0029] In this embodiment, the LED line light source is uniformly discretized into 79 point light sources. The light emitted by each point light source is discretized into 316 angles in the XZ plane according to the Lambertian distribution, with a divergence angle range of ±31.5° and an angle step size of 0.2°. For the Lambertian light source, when the angle between the light ray and the optical axis is α0, its energy weight is assigned the value E0=cosα0, that is, the energy weight of the light ray is proportional to the cosine value of the angle between the emission direction and the optical axis.

[0030] S1.2, Parameter and Scan Range Settings Set the period P1 and half-width W1 of the first microstructure layer, and preset the scanning range [θ] of the tilt angle θ1. 1min ,θ 1max The scanning step size is Δθ1. In this embodiment, the scanning range of the tilt angle θ1 is set to 30°-70°, and the scanning step size is 0.5°.

[0031] S1.3 Geometric Model Construction For each candidate tilt angle θ1, construct a geometric model of an inverted V-shaped microstructure: the bottom of the microstructure is located on the upper surface of the PET substrate, the tip height is H1=W1·anθ1, the left and right inclined planes are symmetrical about the vertical axis, and the outer normal of the inclined planes points to the air side.

[0032] S1.4, Ray Tracing and Energy Statistics For each candidate tilt angle, ray tracing is performed on all discrete rays. The first receiving surface is uniformly divided into several equal-width intervals along the X-direction as partitions. The energy of all rays within each partition is accumulated to form the partition energy distribution E1(x) of the first receiving surface along the X-direction. In this embodiment, the first receiving surface is divided into 600 equal-width partitions along the X-direction. The specific process of ray tracing is as follows: A ray of light emanating from the light source (x0, y0=0, z0=0) forms an angle α0 with the optical axis and propagates upwards in the air; Calculate the relationship between the light rays and the lower surface of the PET substrate (z=z bottom The intersection of the two points is refracted into the PET substrate according to Snell's law, and the refraction angle α1 satisfies sinα1=sinα0 / n; The light propagates in a straight line along the direction of the refraction angle inside the PET, and the intersection point with the nearest microstructure slope is calculated; Calculate the angle of incidence (the angle between the ray and the normal to the slope) on the microstructure's inclined surface. If the angle of incidence is greater than or equal to the critical angle of total internal reflection θ... c If the angle of incidence is equal to arcsin(1 / n), total internal reflection occurs, the light direction is updated after reflection, and it continues to propagate within the PET. If the angle of incidence is less than the critical angle, the light refracts and exits into the air, and the exit angle satisfies n. sinα i =sinα2; After the light rays are refracted and emitted, calculate the distance to the first receiving surface z=z. rec The intersection point is used to obtain the X-axis coordinate of the landing point; if the light undergoes total internal reflection at the lower surface of the substrate, it continues to propagate upwards; if it refracts downwards and escapes into the air, the tracking terminates. Specifically, if the direction angle of the light after refraction from the last segment is α... out Then from the intersection point (X) last Z last The propagation distance from the z-side to the receiving surface is: t = (z - z) rec -z last ) / cosα out The X-coordinate of the landing point is: X rec =X last +t·sinα out When performing partitioned statistics, the width of each partition is: Δx = (X... max -X min ) / M1; Landing point X rec The partition index is: idx=floor((X rec -X min ) / Δx)+1; The energy E0 of this ray is added to the energy array of the corresponding partition: binE(idx)=binE(idx)+E0.

[0033] The energy of each ray is accumulated into the corresponding partition where the ray falls. After traversing all the rays, the total energy distribution E1(x) of each partition is obtained.

[0034] S1.5, Variance Calculation and Optimization Calculate the variance Var1 of the partitioned energy distribution E1(x), use the negative variance as the fitness function, and select the tilt angle θ1 that maximizes the fitness as the optimal tilt angle of the first microstructure layer.

[0035] In this embodiment, the variance is calculated as follows: first, the mean energy of all partitions is calculated as μ = (1 / M1)∑E(x i ), where M1 is the total number of partitions; then calculate the variance Var = (1 / M1)∑(E(x) i )-μ) 2The variance is the average of the squared differences between the energy of each partition and the mean. The smaller the variance, the more uniform the energy distribution. Therefore, using negative variance as the fitness function, maximizing fitness is equivalent to minimizing variance.

[0036] Calculations show that the optimal tilt angle θ1 of the first microstructure layer in group 1 is 59.5°; and the optimal tilt angle θ1 of the first microstructure layer in group 2 is 53.5°.

[0037] S2, Design of the Second Microstructure Layer The second microstructure layer uses the actual emission angle distribution of the first microstructure layer as the incident light field input, and performs collaborative optimization with the goal of minimizing the variance of the energy distribution along the Y direction of the second receiving surface, to achieve optical matching of the two microstructure layers. The specific design steps are as follows: S2.1, Collect the emission angle distribution of the first microstructure layer. An optical model of the first microstructure layer was established using the optical simulation software LightTools. A far-field receiver was placed on the receiving surface at a distance d1 above the tip of the first microstructure layer, and the angle-intensity distribution I(α) of the emitted light in the YZ plane was recorded. In this embodiment, the angle range of the far-field receiver was set to -90° to 90°, and the angle resolution was set to 0.2°. After running ray tracing, the angle-intensity curve of the emitted light was obtained.

[0038] Reference Figure 3 and Figure 4 Ultimately, two angle-intensity curves in orthogonal planes were obtained. The red curve represents the angle distribution in the XZ plane (i.e., the expansion direction of the first microstructure layer), and the blue curve represents the angle distribution in the YZ plane (i.e., the expansion direction of the second microstructure layer). The emission angle in the YZ plane exhibits a narrow distribution with a half-width at half-maximum of approximately ±10°. This distribution data serves as the design input for the second microstructure layer.

[0039] S2.2 Constructing a probabilistic sampling model The angular distribution I(α) of the rays emitted from the first microstructure layer is discretized and normalized to obtain the probability density function PDF(α), and then the cumulative distribution function CDF(α) is constructed. Here, the probability density function PDF(α) = I(α) / ∫I(α)dα describes the probability of a ray appearing within a unit angular interval; the cumulative distribution function CDF(α)... , which represents the proportion of rays with an angle of incidence less than or equal to α, and its value ranges from 0 to 1.

[0040] S2.3, Parameter and Scan Range Settings Set the period P2 and half-width W2 of the second microstructure layer, and preset the scanning range of the tilt angle θ2 [θ]. 2min ,θ 2maxThe scanning step size is Δθ2. In this embodiment, the scanning range of the tilt angle θ2 is set to 30°-70°, and the scanning step size is 0.5°.

[0041] S2.4 Equivalent Light Source and Light Sampling The emitting surface of the first microstructure layer is used as the equivalent light source surface of the second microstructure layer. It is uniformly discretized into N² point light sources along the Y-direction. The angle of the light emitted by each point light source is sampled with equal probability according to the cumulative distribution function CDF(α), and each sampled light ray carries equal energy. In this embodiment, the equivalent light source in the Y-direction is uniformly discretized into 101 point light sources, each emitting 300 light rays, and the angles are sampled with equal probability according to CDF.

[0042] S2.5, Ray Tracing and Energy Statistics For each candidate tilt angle, ray tracing is performed on all sampled rays. The second receiving surface is uniformly divided into several equal-width intervals along the Y direction as partitions. The energy of all rays within each partition is accumulated to form the partition energy distribution E2(y) of the second receiving surface along the Y direction. In this embodiment, the second receiving surface is divided into 600 equal-width partitions along the Y direction. The ray tracing process is consistent with the tracing logic of the first microstructure layer, except that the extension direction is replaced by the Y direction instead of the X direction, and the incident angle distribution adopts the actual angle distribution obtained from the above sampling.

[0043] S2.6 Variance Calculation and Optimization Calculate the variance Var2 of the partitioned energy distribution E2(y), use the negative variance as the fitness function, and select the tilt angle θ2 that maximizes the fitness as the optimal tilt angle of the second microstructure layer.

[0044] Calculations show that the optimal tilt angle θ2 of the second microstructure layer in group 1 is 53°; and the optimal tilt angle θ2 of the second microstructure layer in group 2 is 55°.

[0045] After obtaining the optimal tilt angles of the two layers, the geometric parameters of the corresponding inverted V-shaped structures are generated and arranged in a one-dimensional periodic array on the PET substrate in the corresponding direction. The relative rotation angle of the two microstructures is 90°.

[0046] Example 3 The method for preparing an optical film includes the following steps: Using the design method of Embodiment 2 above, the optimal tilt angle θ1 of the first microstructure layer and the optimal tilt angle θ2 of the second microstructure layer are determined; Based on the optimal tilt angle and preset period and half-width parameters, the inverted V-shaped structure geometry parameters of the first microstructure layer are generated, and the first microstructure layer arranged periodically along the first direction is processed on the upper surface of the first PET substrate. Based on the optimal tilt angle and preset period and half-width parameters, the inverted V-shaped structure geometry parameters of the second microstructure layer are generated, and the second microstructure layer is formed on the upper surface of the second PET substrate by periodically arranging along the second direction, the second direction being perpendicular to the first direction. The first PET substrate and the second PET substrate are aligned sequentially along the direction of light propagation, so that the first microstructure layer and the second microstructure layer both face the light-emitting side, and an air gap is left between the two substrates to complete the preparation and assembly of the optical film.

[0047] Test case Test Example 1: Verification of Overall Light Uniformity Reference Figure 5 and Figure 6 The optimal tilt angles θ1 and θ2 were substituted into the complete optical model, and ray tracing was performed using optical simulation software to obtain the two-dimensional illuminance distribution of the final receiving surface. The results show that the optical film of this embodiment can convert the MiniLED line light source into a highly uniform surface light source within a short mixing distance (2 mm from the light source to the first layer, 0.5 mm between layers), effectively eliminating bright and dark stripes.

[0048] Test Example 2: The Optimization Effect of Adding a Diffusion Membrane Reference Figure 7 and Figure 8 To further improve the light uniformity, a diffusion film was added 0.5 mm above the second microstructure layer. After adding the diffusion film, the illuminance uniformity of the light-emitting surface was further optimized, local brightness differences were further smoothed out, and the light uniformity effect was better.

[0049] Test Example 3: Comparison with Traditional Diffusion Membrane Solutions Reference Figure 9 A traditional single-layer diffusion film is used in MiniLED backlight modules with the same light mixing distance. Figure 9 It is evident that traditional diffusion films rely on the scattering effect of medium particles to achieve uniform light distribution. However, they cannot achieve sufficient light diffusion at short mixing distances, resulting in noticeable bright and dark stripes on the light-emitting surface. Their uniformity is far inferior to the double-layer microstructure solution of this invention. Compared to traditional diffusion plate solutions, this solution significantly reduces the overall thickness and significantly improves the uniformity of light emission.

[0050] Test Example 4: Comparison of the effects of collaborative design and independent design A control experiment was set up to verify the technical advantages of the interlayer angle collaborative design: Experimental group: The two-layer collaborative optimization method of this embodiment was adopted, with the actual emission angle distribution of the first microstructure layer as the design input for the second layer. The final simulated illuminance diagram is as follows. Figure 7 As shown; Control group: A two-layer independent design method was used. The second layer directly used the original MiniLED light source angle distribution as the design input, without considering the change in light angle distribution caused by the first layer. The simulated illuminance diagram is shown below. Figure 10 As shown.

[0051] Reference Figure 7 and Figure 10 The independent design scheme did not consider the transmission relationship of light angle distribution between layers, and the second layer's control precision of light was insufficient, resulting in large fluctuations and poor uniformity of the brightness of the final light-emitting surface. The collaborative design scheme in this embodiment, through precise matching of interlayer angles, significantly improved the uniformity of illuminance, verifying the technical advantages of collaborative design for angle distribution transmission.

[0052] Test Example 5: Verification of the effect of variance minimization optimization This embodiment uses variance minimization as the optimization objective, directly controlling the energy flatness of the entire receiving surface. Compared to the traditional uniformity index using the extreme value ratio (min / max), variance optimization effectively avoids the pseudo-uniformity problem of "energy accumulation at both ends and low brightness in the middle," ensuring consistent energy distribution across the entire light-emitting surface and achieving higher quality uniform light distribution. Combined with... Figure 7 The test results show that the brightness difference between the center and the edge of the light-emitting surface is very small, and there is no obvious distribution defect of bright ends and dark middle.

[0053] Test Example 6: Verification of universality across different chip sizes Reference Figures 5 to 8 The design method described in this embodiment was used to optimize MiniLEDs of two different sizes, 0.78mm and 0.508mm. Results show that both chip sizes achieve good light emission uniformity. This solution only requires substituting the corresponding chip parameters to complete the adaptation, without needing to redesign the overall architecture, demonstrating good universality for MiniLEDs of different sizes.

[0054] The embodiments shown in this specification are only used to illustrate the technical solutions of the present invention and are intended to help those skilled in the art understand the principles and advantages of the present invention. They do not constitute a limitation on the scope of protection of the present invention. Although the present invention has been specifically described, those skilled in the art can still make any modifications, equivalent substitutions or other reasonable variations to the implementation methods without departing from the spirit and scope of the present invention. All equivalent technical solutions resulting therefrom should be considered within the scope of protection of this patent.

Claims

1. A method for designing an optical film for a MiniLED backlight module, characterized in that, The optical film includes a first microstructure layer and a second microstructure layer arranged sequentially along the direction of light propagation. The first microstructure layer and the second microstructure layer are respectively formed on the upper surface of the corresponding PET substrate and arranged in a direction perpendicular to each other. Both the first microstructure layer and the second microstructure layer are composed of periodically arranged inverted V-shaped microstructures. The design method includes: The design steps of the first microstructure layer are as follows: with the goal of minimizing the variance of energy distribution along the first direction of the first receiving surface, the tilt angle of the first microstructure layer is scanned and optimized by ray tracing to obtain the optimal tilt angle; The design steps for the second microstructure layer are as follows: obtain the angular distribution of the emitted light from the first microstructure layer in a plane perpendicular to the first direction as the input of the incident light field, take the minimum variance of the energy distribution along the second direction of the second receiving surface as the objective, and perform scanning optimization on the tilt angle of the second microstructure layer through ray tracing to obtain the optimal tilt angle, thereby achieving optical matching between the first and second microstructure layers.

2. The design method according to claim 1, characterized in that, The optimization steps for the first microstructure layer specifically include: The MiniLED is discretized into multiple uniformly distributed point light sources, and the light emitted by each point light source is distributed in a Lambertian pattern in the plane formed by the first direction and the optical axis. Set the period and half-width parameters of the first microstructure layer, and preset the tilt angle scan range; Ray tracing is performed on each candidate tilt angle. The first receiving surface is evenly divided into several equal-width intervals along the first direction as partitions. The energy obtained by accumulating all rays in each partition is counted to form the partition energy distribution of the first receiving surface along the first direction. Calculate the variance of the energy distribution in each partition, and select the tilt angle with the largest negative variance as the optimal tilt angle for the first microstructure layer.

3. The design method according to claim 2, characterized in that, The process of ray tracing is as follows: Light rays are incident on the lower surface of the PET substrate through the air and are refracted. They then propagate inside the PET to the inclined surface of the microstructure. The incident angle is calculated at the inclined surface. If the incident angle is greater than or equal to the critical angle for total internal reflection, total internal reflection occurs. If it is less than the critical angle, the light rays are refracted out into the air and finally reach the first receiving surface.

4. The design method according to claim 2, characterized in that, The energy weight of light emitted from a Lambertian light source is proportional to the cosine of the angle between the light's exit direction and the optical axis. The variance of energy distribution is calculated as follows: first, calculate the mean of energy in all partitions, then calculate the average of the squared differences between the energy in each partition and the mean, and thus obtain the variance.

5. The design method according to claim 1, characterized in that, The second microstructure layer collaborative optimization step specifically includes: The obtained angular distribution is discretized and normalized to obtain the probability density function and cumulative distribution function; The first microstructure layer's emitting surface is equivalent to a line light source, and discretized into multiple point light sources along the second direction. Each point light source is sampled at an angle with equal probability according to the cumulative distribution function. Perform ray tracing on the sampled rays: Divide the second receiving surface into several equal-width intervals along the second direction as partitions, and count the energy of all rays in each partition to form the partition energy distribution of the second receiving surface along the second direction; Calculate the variance of the energy distribution in each partition, and select the tilt angle with the largest negative variance as the optimal tilt angle for the second microstructure layer.

6. The design method according to claim 1, characterized in that, An optical model of the first microstructure layer was established using optical simulation software, and the angle-intensity distribution of the light rays emitted from the first microstructure layer was obtained using a far-field receiver.

7. The design method according to claim 1, characterized in that, The first microstructure layer and the second microstructure layer have the same period and the same half-width.

8. An optical film for a MiniLED backlight module, characterized in that, It includes a first PET substrate and a second PET substrate arranged sequentially along the direction of light propagation, with an air gap between the first PET substrate and the second PET substrate; A first microstructure layer is formed on the upper surface of the first PET substrate, the first microstructure layer being composed of inverted V-shaped microstructures arranged periodically along a first direction; a second microstructure layer is formed on the upper surface of the second PET substrate, the second microstructure layer being composed of inverted V-shaped microstructures arranged periodically along a second direction, the second direction being perpendicular to the first direction. The tilt angles of the first microstructure layer and the second microstructure layer are determined using the design method described in any one of claims 1 to 7, and the tilt angle of the second microstructure layer is matched and set according to the angular distribution of the emitted light rays from the first microstructure layer. The two layers constitute a cascaded optical system.

9. The optical film according to claim 8, characterized in that, The height of the inverted V-shaped microstructure is equal to the product of its half-width and the tangent of its tilt angle.

10. A method for preparing an optical film for a MiniLED backlight module, characterized in that, Includes the following steps: Using the design method described in any one of claims 1 to 7, determine the optimal tilt angle of the first microstructure layer and the optimal tilt angle of the second microstructure layer; The inverted V-shaped structure geometric parameters of the first microstructure layer are generated based on the optimal tilt angle, and a one-dimensional periodic array is arranged on the first PET substrate along the first direction to obtain the first microstructure layer. Based on the optimal tilt angle, the inverted V-shaped structure geometric parameters of the second microstructure layer are generated, and a one-dimensional periodic array is arranged on the second PET substrate along the second direction to obtain the second microstructure layer. The first PET substrate and the second PET substrate are arranged sequentially along the light propagation direction, such that the first microstructure layer and the second microstructure layer both face the light-emitting side, and an air gap is maintained between the first PET substrate and the second PET substrate.

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