Open Access
Add to BibSonomy
Abstract
The preparing method of UV resin compound optical film (COF) by curing under the help of mold has been first proposed in the paper. The simulation results indicate that the theoretical values of the full width at half maximum (FWHM) for the horizontal and vertical direction are 14 degrees and 24 degrees, respectively. Then, the collimated ultraviolet light has been used to prepare the UV resin COF sample with the help of the mold. The experiment results claim the FWHMs of the horizontal and vertical direction for the sample are 16 degrees and 25 degrees when the uniformity is 86%, and it is consistent with the simulation results. The performance parameters in the BLM with COF fabricated are greater than those in the traditional one. Therefore, the COF can provide a collimated uniform plane light source and the new fabrication method is effective.
© 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
In recent years, the liquid crystal display (LCD) still occupy the display industry domain from the smartphones, tablets, computer monitors, and televisions to data projectors, that is due to its advantage in the cost, but the market for the emerging new displays, such as organic light-emitting diode (OLED) displays, micro-scale light emitting diode (micro-LED) and so on, has grown rapidly and gradually started to challenge the LCDs’ applications in all aspects, especially in the small-sized display market [1–5]. Therefore, the performance of the LCD need to be further improved. As we know that the LCD is non-self-emitting, so it needs a backlight module (BLM). The BLM furnishes the LCD with wide color gamut and quasi-collimated uniform planar light source by converting a point array- or line-light source [6,7]; and it can be classified into two types according to the location of the original emitting light source, one is direct-lit and the other is the edge-lit [8–13]. With regard to the direct-lit, the LED array light source is laid on the bottom surface of the BLM [14,15]. And the LED light source for the edge-lit BLM is placed on the edge of the light guide plate (LGP) [16,17].
The performance of the BLM will affect the LCD’s quality, for example, uniformity, collimated degree and integrated degree. Especially, collimated degree is an important parameter, the light produced by the backlight is more or less isotropic, with light incident on the LCD panel at all directions. It is desirable to have the light incident at directions close to the normal of the LCD panel for two reasons. First, the LCD panel does not work well for light with large incident angle. Second, viewers usually look at the display in the normal direction and thus light coming out at large angles is wasted [18]. Therefore, many researchers have tried to improve the performance mentioned above. There are mainly two types of technology to promote the performance of the BLM. The first kind of technology utilizes the optical film to concentrate the emitting light into the normal, which is suitable for both direct-lit and edge-lit types mentioned above. The typical representatives are as follows: Teng [19] proposed the optical film to provide a highly collimated planar light source, Wang [20] introduced an integrated light guide plate to provide the highly directional backlight, but the optical films cannot well adjust the distribution of the light. The second kind of technology utilizes the special-designed LGP that can be used alone or collocate with the proper optical film to achieve the goal, which is suitable only for the edge-lit type. The typical representatives are as follows: Pan [21] presented a hybrid BLM, which consists of a hybrid light guide plate (HLGP) and a brightness enhancement film (BEF), but there are three layers in the structure of the HLGP and one BEF is still needed to concentrate the light, and the complicated structure is difficult to fabricate. An integrated micro-optical LGP was proposed in Ref. [22,23], but the preparation process has not been maintained in detail; Huang [24] proposed the novel integrated backlight design module, but they have not pointed out the principle of optimizing the microstructure in detail, and the experiment has not been verified. Quesada proposed all-glass micro-groove light guide plate by mask and etch, the uniformity reached 80% for 9-points, but the full width at half maximum (FWHM) was about at 50 degrees [25].
The compound optical film (COF) researched in the paper is based on the second kind of technology mentioned above, and the optimization method for the COF have been firstly introduced; secondly, optimal model has been simulated, comparing with the traditional BLM, the FWHM indices decrease from 52 degrees to 24 degrees; finally, the method of preparing the sample has been explained in detail, and the test result indicates that the FWHMs of the horizontal and vertical direction for the sample are 16 degrees and 25 degrees when the uniformity is 86%, it is consistent with the simulation results. Therefore, the new fabrication method are effective.
2. Method of optimization
It is well known that the edge-lit BLM uses special microstructure to provide uniform light distribution at a certain light-emitting angle after the light entering the module experiences the refraction and total internal reflection (TIR) process.When light travels from the optical medium to the air, the critical angle of total reflection can be calculated by the following formula:
where ${\mathrm{\theta }_C}\; $ denotes the critical angle of TIR, ${n_0}$ and ${n_1}$ are the index of the air and the optical materials, respectively. The PMMA has been used as the materials of the LGP in the expreiment, therefore, the refractive index of ${n_0}$ and ${n_1}$ are 1 and 1.49 for the visible light (25°C), and the corresponding critical angle of the TIR is 42.2°.2.1 Opptimization for the slope of the inclined surface
According to the related research report from our researcher team [24], the relationship can be concluded as follows:
It can be clearly seen that the value of $\alpha $ will directly affect the angle of ${{\theta }_2}$ between the exit beam and the normal direction, and the smaller the value of ${{\theta }_2}$, the more collimated the exit beam will be. The special case is that when ${\theta _1}$ is equal to twifold $\alpha $, ${{\theta }_2}$ takes the value of 0 degrees, then the exit beam will propagate along the normal direction.
The relationship shows that the value of ${{\theta }_2}$ is determined by both ${\theta _1}$ and $\alpha $. Therefore, the value of reflection angle ${{\theta }_2}$ can be minimized by setting appropriate value of $\alpha $, so that the angle between the reflected light and the normal direction can be minimized. In order to find the optimal value $\alpha $, the range of ${\theta _1}$ should be determined, and its value equal to that of ${\theta _3}$ when the refractive index of COF equal to that of LGP, therefore, we should firstly analyze the ${\theta _3}$.
There is not films covered on LGP surface as shown in Fig. 1; the light path 1 and 2 are taken for example to illustrate the principle of the light propagation, and the emit angle from the LED for the light path 1 and 2 is 30 degree and −30 degree, respectively. The angle of incidence to LGP is 30 degrees, and the refraction angle is 19.6 degrees after the light enters LGP according to refraction law. The angle of incidence to both upper and lower surfaces of LGP is 70.4 degrees. The angle value is obviously larger than the critical angle of the TIR. Therefore, light path 1 and 2 will always propagate far away from the light source in the form of the TIR after entering LGP. Similarly, when the light emitted by the LED light source spreads to LGP interface at approximate 90 degrees, the refraction angle of the incident plane is close to 42.2 degrees when it enters LGP, and the first reflection angle of the upper or lower surface is 47.8 degrees in LGP, which is also larger than the critical angle of the TIR; therefore, the light will also propagate far from the light source in the LGP in the limit case. From the analysis above, it can be seen that the light emitted by the light source will propagate on the surface of LGP without microstructures in the form of the TIR when it is incident into the interior of LGP, so the light can not be emitted out from the LGP’s surface. From the discussion mentioned above, we can induce the conclusion that the light emitted from the light source will propagate in the form of the TIR after it enters the LGP without any microstructure, and the angle obeys the constraint as follows:
where ${\theta _3}$ is the incidence angle with respect to the normal direction on the LGP’s exit surface. In Fig. 1, when the incident light of the LED is perpendicular to the incident plane of the LGP, the transmission direction of the incident light in the LGP and the normal direction of the light emerging plane is 90°, which determines that the upper limit value is 90 °The index of the COF is equal to the one of the LGP in the experiment, as shown in Table 1, therefore, when the light enters the surface of the COF from the LGP, the direction of the light path remains unchanged, therefore, ${\theta _1}$ is equal to ${\theta _3}$.
Table 1. The parameters for the COF and LGP
The Matlab software are used to calculate the value of ${{\theta }_2}$ varying with the $\alpha $ and the ${\theta _1}$ according to Eq. (2). When the value of $\alpha $ is larger than ${\theta _1}$ as shown in Fig. 2(a), the value of ${{\theta }_2}$ is equal to ${\theta _1}$, when the material of the microstructure is same as the one of the LGP, the value of ${{\theta }_2}$ is from 47.8 and 90 degrees according to Eq. (3). Obviously, this angle range is too divergent for normal direction, which is not conducive to improve the utilization of light.
When the setting of $\alpha $ is less than ${\theta _1}$ as shown in Fig. 2(b), that is, $\alpha $ is less than 47.8 degrees. The value of $\alpha $ is substituted into Eq. (2) from 1 degree to 46 degrees at intervals of 5 degrees. The relationship between the reflection angle ${{\theta }_2}$ and the incident angle ${\theta _1}$ can be plotted in Fig. 3(a). It can be clearly seen that the maximum value of the corresponding reflection angle ${{\theta }_2}$ is less than 40 degrees when the values of $\alpha $ are 26, 31, 36 and 41 degrees, respectively. Therefore, when the values of $\alpha $ are 26 to 41 degrees, the maximum value of the corresponding reflection angle ${{\theta }_2}$ is less than 40 degrees.
Fig. 3. The varying curve of ${{\theta }_2}$ when the value of α range (a) from 1 degrees to 46 degrees, (b) from 25 degrees to 41 degrees.
In order to further get the optimal value of $\alpha $, the range of ${{\theta }_2}$ is calculated by sampling the value of $\alpha $ from 25 to 41 degrees at intervals of 2 degrees, and the relationship between ${{\theta }_2}$ and ${\theta _1}$ is analyzed. As shown in Fig. 3(b), it is obvious that from the graph the maximum value of ${{\theta }_2}$ is 24 degrees when the value of $\alpha $ is set to 33 degrees, while the maximum value of reflection angle ${{\theta }_2}$ is more than 24 degrees when other values are taken. Therefore, the optimal value of $\alpha $ is 33 degrees, and the range of reflection angle ${{\theta }_2}$ is from 0 to 24 degrees correspondingly.
The relationship among ${{\theta }_1}$, ${{\theta }_2}$ and $\alpha $ discussed above are the case of light incident from the positive direction to the inclined plane A as shown in Fig. 2. If the light incident from the direction to the inclined plane B, the analysis process is the same, it will not be repeated here. At the same time, the optimum $\alpha $ value of the inclined plane B is also 33 degrees, and the corresponding reflection angle ${{\theta }_2}$ ranges from 0 degrees to −24 degrees.
From the analysis above, we can see that when the value of $\alpha $ is selected as 33 degrees, the value of ${{\theta }_2}$ is between ±24 degrees, that is to say, ${{\theta }_2}$ falls in the symmetrical region of −24 degrees to 24 degrees, it’s convenient for the further collimation design in the top free curve. The computational complexity for the free curve can be reduced by half, because the light source enter the free curve is symmetrical, so only the half of free curve can been calculated out, the whole free curve can be obtained.
2.2 Optimal design for the top free curve
The free curve further collimating the light can be calculated by using the following relationship reported in our research literature [24]:
The position of the perceived point light source should shift from the origin to point E by 25 microns along the X-axis direction, and the position of point E is shown in Fig. 4(a); the free curve FC can be calculated by using Eq. (4), and the curve is shown in Fig. 4(a). The optimized microstructure model can be obtained by rotating the profile of the microstructure optimization design around OO’ 360 degree, and the model has been shown in Fig. 4(b).
3. Simulation and analysis
The model has been embedded in the edge-lit BLM, and the LEDs’ light distribution is the typical Lambertian. Size of the model is 4 inch (16: 9). The model’s thickness, materials, and angles for the microstructures are shown in Table 1.
In order to compare the optimized module with traditional backlight, the traditional edge-lit BLM is taken as the reference object, and the module consists of an LGP, a reflector, two BEFs and a diffuser. The uniformity surpass 90% for both the BLM with the COF and traditional backlight. Figure 5 is the comparing diagram for the relationship of luminance and off-axis angle between optimized module and traditional BLM in the simulation. The FWHM indices of the intensity angle distribution in the vertical and horizontal directions are 24 degrees and 14 degrees for the BLM with the COF. The FWHM indices of the intensity angle distribution in the vertical and horizontal directions are both 52 degrees for the traditional backlight. Comparing to the traditional edge-lit BLM, the axial brightness of the BLM with the COF increased by 3 times. By calculating the area enclosed by the curve and transverse axis in Fig. 5, the integral area in Table 2 can be obtained. The integral area is increased by 74% for proposed BLM comparing with the traditional BLM in the same density of the microstructure.
Fig. 5. The comparing diagram for the relationship of luminance and off-axis angle between proposed and traditional BLM in the simulation.
Table 2. The average integral area for the proposed and traditional BLM
The main reason why the BLM with the COF has a fine performance in efficiency is that the principle of extracting is different, the one is mainly by reflecting, but the another one is mainly by scattering, moreover, for the traditional edge-lit BLM, most rays circulate between the LGP and the two BEFs; therefore, more power wastage occurs due to the energy absorption and the Fresnel loss.
Compared with the traditional edge-lit BLM, axial brightness of the BLM with the COF increased by 3 times, and the FWHM indices decrease from 52 degrees to 24 degrees.
4. Experiment
4.1 Preparation of the microstructure
The principle of adjusting the light distribution is to vary the density of the microstructure in the experiment, and it is similar to the one of the net dot on the bottom surface of the LGP, hence pattern of the microstructure is irregularly arranged on the film. Moreover, the dimension of the microstructure proposed in the paper is small, therefore, the microstructure of the COF needs to be manufactured by means of a mold, and the UV resin has been used to prepare the microstructures with the help of the mold. The UV light was used to cure the UV resin, the UV light can be used without collimating light, but it needs uniform light distribution to illuminate the UV resin through the PET in Fig. 6(c); the UV light must be collimated and uniform in Fig. 6(f), the reason is that the bottom of the microstructure is relatively long, therefore the superstructure of the microstructure can be used to gather into the conical position at the bottom of the microstructure by adopting collimated light. The process of the microstructure fabricated are described as follow.
Fig. 6. The schematics for sample preparation step1 and 2 (a) mold A coated with UV resin (b) PET covered over UV resin (c) UV resin crosslinking by light (d) upper part for the COF (e) mold B coated with UV resin (f) UV resin crosslinking by light.
Step 1: The UV resin is coated on the mold A as shown in Fig. 6(a); then, the polyethylene terephthalate (PET) substrate is covered over the UV resin as shown in Fig. 6(b); finally, the ultraviolet light is used to irradiate the UV resin as shown in Fig. 6(c), and the mold A is removed after crosslinking, PET and the UV resin bonded together as shown in Fig. 6(d).
Step 2: The UV resin is coated on the mold B as shown in Fig. 6(e); then, the upper part for COF is covered over on the UV resin according to alignment mark as shown in Fig. 6(f), the collimated UV light passing through the collimated upper surface ensures that the resin in the micro-collimation structure can be crosslinked, because the microstructure on the upper surface can focus the collimated UV light source; Finally, remove the mold B.
Step 3: Soak the sample into isopropanol solution and dissolve the unexposed resin.
Step 4: Wash the sample with deionized water and then dry it, and the samples are finished.
4.2 Testing and analysis
The microstructure captured by optical microscopy is shown in Fig. 7. From the cross section of the microstructures sample in Fig. 7(a), it can be seen intuitively that the upper and lower microstructures can be well aligned. Therefore, the collimated UV light source used in this section can ensure that the upper and lower parts of the microstructures are aligned.
Fig. 7. The graph captured by optical microscope (a) profile (b) upper and (c) lower microstructures.
Although the optical microscope pictures in Fig. 7(a) show that the experimental samples are consistent with the design model, the relationship between the samples and the design values cannot be explained from the profile. Therefore, the upper and lower surfaces of the microstructures are scanned by step instrument, and the outline data are extracted for comparison with the design values.
Figure 8(a) is the contour map of the upper part of the microstructures. The illustration is a comparison between the measured contour values (MCV) and the theoretical design values (TDV). It can be seen from the illustration that the upper part of the sample is basically consistent with the designed shape. Figure 8(b) is the contour map of the lower part of the microstructures. Among them, the illustration is a comparison between the MCV and the TDV. From the illustration, it can be seen that the slope of the sample is roughly the same as the TDV. From the analysis above, we can see that the shape of the microstructure samples produced in this section is almost the same as that of the TDV. Next, we will use the fabricated samples to build the test samples and analyze their uniformity and collimation performance.
In order to verify the performance of COF, COF sample has been tested in the edge-lit BLM. Figure 9(a) is the actual diagram of the sample, which includes COF, LGP, reflector and outer frame, respectively; Fig. 9(b) is the structure schematic diagram of the sample module, in which LGP and COF are shown from bottom to top, and the light source is 1pc-WLED. Figure 9(c) is a sample-lit photograph; the assembled sample is placed in the integrated distributed photometer (Everfine Co., Ltd.) to measure the angular brightness of the sample in Fig. 9(d).
Fig. 9. (a) The actual diagram of the sample; (b) the sketch of the tested BLM; (c) the sample-lit photograph; (d) the sample tested by the integrated distributed photometer.
The data measured by the integrated distributed photometer are normalized and compared with the simulation results. Their comparison diagrams are shown in Fig. 10(a). It can be seen from the diagrams that the horizontal FWHM of the sample is 16 degrees and the vertical FWHM is 25 degrees. The deviations are 2 degrees and 1 degree, respectively, compared with the simulation TDV of 14 degrees and 24 degrees. This shows that although there is a deviation between the upper part of the microstructures and the theoretical design value, the alignment effect of the microstructures is still good.
Fig. 10. (a)The comparing diagram for the relationship of luminance and off-axis angle between sample and simulation; (b) the sketch map of the 17-points test method for the BLM.
The uniformity and average brightness of the samples are measured by the 17-point test method of the BLM shown in Fig. 10(b). The measurement position of 17 points is not distributed by equal spacing, but by the spacing shown in Fig. 10(b), and the edge is deducted by 1.5 mm.
The luminance of the sample is tested by SRC-200M (Everfine Co., Ltd.), and the maximum brightness value is at point 16, and the brightness value is 4156 cd/m2; the minimum brightness value is at point 12, and the brightness value is 3575 cd/m2. The uniformity is calculated to be 86% [26]. it is still significantly higher than the requirement of 75% uniformity in the design phase in the display industry. Therefore, the test sample can provide a collimated uniform plane light source.
5. Conclusion
In the paper, the new fabrication method has been proposed. Firstly, the structure on the COF has been optimized, and the simulation results maintain that the TDV of FWHM for the horizontal and vertical direction are 14 degrees and 24 degrees when the uniformity surpass 90%, respectively. Secondly, the method of fabricating has been maintained in detail. Finally, the experiment results indicate that the FWHMs of the horizontal and vertical direction for the sample are 16 degrees and 25 degrees when the uniformity is 86%, respectively. Therefore, the optimal model can provide a collimated uniform plane light source and the new fabrication method is effective.
Funding
Doctoral Research Start Project of Fujian Chuanzheng Communications College (20200304).
Acknowledgment
The authors gratefully acknowledge the financial support provided to this study by Doctoral Research Start Project of Fujian Chuanzheng Communications College (20200304), China.
Disclosures
The authors declare no conflicts of interest.
Data availability
No data were generated or analyzed in the presented research.
References
1. M. Froebel, F. Fries, T. Schwab, S. Lenk, K. Leo, M. C. Gather, and S. Reineke, “Three-terminal RGB full-color OLED pixels for ultrahigh density displays,” Sci. Rep. 8(1), 9684 (2018). [CrossRef]
2. H.-W. Chen, J.-H. Lee, B.-Y. Lin, S. Chen, and S.-T. Wu, “Liquid crystal display and organic light-emitting diode display: present status and future perspectives,” Light: Sci. Appl. 7(3), 17168 (2018). [CrossRef]
3. Y.-J. Wang, J.-G. Lu, W.-C. Chao, and H.-P. D. Shieh, “Switchable viewing angle display with a compact directional backlight and striped diffuser,” Opt. Express 23(16), 21443–21454 (2015). [CrossRef]
4. F. Gou, E.-L. Hsiang, G. Tan, P.-T. Chou, Y.-L. Li, Y.-F. Lan, and S.-T. Wu, “Angular color shift of micro-LED displays,” Opt. Express 27(12), A746–A757 (2019). [CrossRef]
5. S.-W. H. Chen, Y.-M. Huang, K. J. Singh, Y.-C. Hsu, F.-J. Liou, J. Song, J. Choi, P.-T. Lee, C.-C. Lin, Z. Chen, J. Han, T. Wu, and H.-C. Kuo, “Full-color micro-LED display with high color stability using semipolar (20-21) InGaN LEDs and quantum-dot photoresist,” Photonics Res. 8(5), 630–636 (2020). [CrossRef]
6. E. Chen, H. Xie, J. Huang, H. Miu, G. Shao, Y. Li, T. Guo, S. Xu, and Y. Ye, “Flexible/curved backlight module with quantum-dots microstructure array for liquid crystal displays,” Opt. Express 26(3), 3466–3482 (2018). [CrossRef]
7. H. Xie, E. Chen, Y. Ye, S. Xu, and T. Guo, “Highly stabilized gradient alloy quantum dots and silica hybrid nanospheres by core double shells for photoluminescence devices,” J. Phys. Chem. Lett. 11(4), 1428–1434 (2020). [CrossRef]
8. A. Travis, T. Large, N. Emerton, and S. Bathiche, “Collimated light from a waveguide for a display backlight,” Opt. Express 17(22), 19714–19719 (2009). [CrossRef]
9. B.-L. Huang, T.-L. Guo, and J.-M. Yao, “Design of slanted zigzag staggered barrier for autostereoscopic display,” Acta Photon. Sin. 41, 1176–1179 (2012). [CrossRef]
10. S. R. Park, O. J. Kwon, D. Shin, S.-H. Song, H.-S. Lee, and H. Y. Choi, “Grating micro-dot patterned light guide plates for LED backlights,” Opt. Express 15(6), 2888–2899 (2007). [CrossRef]
11. D. Feng, Y. B. Yan, X. P. Yang, G. F. Jin, and S. H. Fan, “Novel integrated light-guide plates for liquid crystal display backlight,” J. Opt. A: Pure Appl. Opt. 7(3), 111–117 (2005). [CrossRef]
12. Z. Feng, Y. Wu, B. Surigalatu, X. Zhang, and K. Chang, “Large transparent display based on liquid crystal technology,” Appl. Opt. 59(16), 4915–4920 (2020). [CrossRef]
13. E. Chen, S. Lin, Z. Jiang, Q. Guo, S. Xu, Y. Ye, Q. F. Yan, and T. Guo, “Analytic design of light extraction array for light guide plate based on extended sources,” Opt. Express 27(24), 34907–34920 (2019). [CrossRef]
14. Z. Qin, K. Wang, F. Chen, X. Luo, and S. Liu, “Analysis of condition for uniform lighting generated by array of light emitting diodes with large view angle,” Opt. Express 18(16), 17460–17476 (2010). [CrossRef]
15. J.-G. Chang and P.-H. Yang, “A generalized model for luminance prediction in a bottom-it backlight with cold cathode fluorescent lamps,” Journal of Optics a-Pure and Applied Optics 8(11), 981–990 (2006). [CrossRef]
16. B.-L. Huang and T.-L. Guo, “Fast optimization method based on the diffuser dot density for uniformity of the backlight module,” Appl. Opt. 55(6), 1494–1499 (2016). [CrossRef]
17. B.-L. Huang, T.-L. Guo, E.-G. Chen, and S. Xu, “Study on the optimal scale of the average netted dot density for light guide plate,” Acta Opt. Sin. 35(5), 0506006 (2015). [CrossRef]
18. D.-K. Yang and S.-T. Wu, Fundamentals of Liquid Crystal Devices (2nd Edition) (John Wiley & Sons, 2014).
19. T.-C. Teng and J.-C. Ke, “A novel optical film to provide a highly collimated planar light source,” Opt. Express 21(18), 21444–21455 (2013). [CrossRef]
20. Y. J. Wang, S. H. Ouyang, W. C. Chao, J. G. Lu, and H. P. D. Shieh, “High directional backlight using an integrated light guide plate,” Opt. Express 23(2), 1567–1575 (2015). [CrossRef]
21. J.-W. Pan and C.-W. Fan, “High luminance hybrid light guide plate for backlight module application,” Opt. Express 19(21), 20079–20087 (2011). [CrossRef]
22. P. Xu, Y. Huang, X. Zhang, J. Huang, B. Li, E. Ye, S. Duan, and Z. Su, “Integrated micro-optical light guide plate,” Opt. Express 21(17), 20159–20170 (2013). [CrossRef]
23. P. Xu, T. Luo, X. Zhang, Z. Su, Y. Huang, X. Li, and Y. Zou, “Design and optimization of a partial integrated backlight module,” Opt. Commun. 427, 589–595 (2018). [CrossRef]
24. B.-L. Huang and T.-L. Guo, “Integrated backlight module to provide a collimated and uniform planar light source,” Appl. Opt. 55(26), 7307–7313 (2016). [CrossRef]
25. M. Quesada, S. Li, and A. Sullivan, “All-glass micro-groove light guide plate by mask and etch,” Opt. Mater. Express 11(2), 497–508 (2021). [CrossRef]
26. B.-L. Huang, J.-T. Lin, Y. Ye, S. Xu, E.-G. Chen, and T.-L. Guo, “Pattern optimization of compound optical film for uniformity improvement in liquid-crystal displays,” Optics & Laser Technology 97, 254–259 (2017). [CrossRef]
