Moir -Free Collimating Light Guide with Low-Discrepancy Dot Patterns

1. 7/26/2012 SID'02 45-2: Ide et al. 1 Moir�-Free Collimating Light Guide with Low-Discrepancy Dot Patterns T. Id�, H. Numata, H. Mizuta, and Y. Taira IBM Tokyo Research Lab. M. Suzuki, M. Noguchi, and Y. Katsu International Display Technology [Your presentation will be strictly limited to 15 minutes with an additional 5 minutes for discussion. ] Thank you, Mr.Chairman. I am Ide. This work is the fruits of the collaboration with these people including Suzuki-san.[Your presentation will be strictly limited to 15 minutes with an additional 5 minutes for discussion. ] Thank you, Mr.Chairman. I am Ide. This work is the fruits of the collaboration with these people including Suzuki-san.

2. 7/26/2012 SID'02 45-2: Ide et al. 2 Agenda Background Why must we optimize irregular dot patterns? Conventional methods Why is a breakthrough needed? Our approach How do we generate the initial pattern? How do we remove inter-dot overlap? Implementation How did our approach improve the luminance uniformity? Summary Here is the agenda of my talk. Background, conventional methods, our proposed approach, implementation of our method, and summary. I will explain these items.Here is the agenda of my talk. Background, conventional methods, our proposed approach, implementation of our method, and summary. I will explain these items.

3. 7/26/2012 SID'02 45-2: Ide et al. 3 Background Edge-lit backlight units Diffusive reflection on the bottom surface of LGs Shape of micro-scatterers Distribution of micro-scatterers Let�s start with the background of this research. What you can see here is the the structure of the conventional edge-lit backlight units. As shown, light rays emitted from the cold cathode fluorescence lamp are guided into the light-guide, and come out through prism sheets and the diffuser films. As you can see, the diffusive reflection on the bottom surface of the LG plays an essential role in backlight units. Because the emitted light is some projection of the diffusive reflection. So, you should design carefully the shape of micro-scatterers and the Distribution of micro-scatterers formed here. Recently, there is a great need for higher luminance to improve the quality of backlight units. There are strict restrictions on physical dimensions and power consumption when used in laptop PCs.Let�s start with the background of this research. What you can see here is the the structure of the conventional edge-lit backlight units. As shown, light rays emitted from the cold cathode fluorescence lamp are guided into the light-guide, and come out through prism sheets and the diffuser films. As you can see, the diffusive reflection on the bottom surface of the LG plays an essential role in backlight units. Because the emitted light is some projection of the diffusive reflection. So, you should design carefully the shape of micro-scatterers and the Distribution of micro-scatterers formed here. Recently, there is a great need for higher luminance to improve the quality of backlight units. There are strict restrictions on physical dimensions and power consumption when used in laptop PCs.

4. 7/26/2012 SID'02 45-2: Ide et al. 4 A new type light guide Integration of a prism sheet Lower loss of flux To enhance the luminance, integrated-type light guides, like this, have been proposed by several researchers such as Dr. K�r�nt�r. The integration of one prism sheet with carefully designed prismatic grooves leads to lower loss of flux, and the carefully designed micro-scatteres in stead of the conventional diffusing white spots greatly improve the luminance. But, this is NOT the end of the story. What is important is that this type of light guides is very transparent in a sense, so that you often clearly observe moir� patterns caused by optical interference between liquid crystal cells and the distribution of the micro-scatterers. You can eliminate the moir� patterns by adding more diffuser films, but it is not a good solution. Therefore, in order to enhance the luminance uniformity without harming the collimating nature, we have to consider an effective method to optimize the distribution of microstructures.To enhance the luminance, integrated-type light guides, like this, have been proposed by several researchers such as Dr. K�r�nt�r. The integration of one prism sheet with carefully designed prismatic grooves leads to lower loss of flux, and the carefully designed micro-scatteres in stead of the conventional diffusing white spots greatly improve the luminance. But, this is NOT the end of the story. What is important is that this type of light guides is very transparent in a sense, so that you often clearly observe moir� patterns caused by optical interference between liquid crystal cells and the distribution of the micro-scatterers. You can eliminate the moir� patterns by adding more diffuser films, but it is not a good solution. Therefore, in order to enhance the luminance uniformity without harming the collimating nature, we have to consider an effective method to optimize the distribution of microstructures.

5. 7/26/2012 SID'02 45-2: Ide et al. 5 Simple pseudo-random number method The coordinates are determined directly with pseudo-random numbers Sufficiently irregular No moir� pattern Let me explain conventional methods to optimize the distribution of the micro-scatterers. The most simple one is the simple pseudo-random method, where the coordinates of the micro-scatterers are determined directly with pseudo-random numbers. As you can see, the created patterns are of sufficient irregularity, but they are very rough. The roughness will be visible to the eye. Also, there is inter-dot overlap everywhere. So, we conclude that this method is not suitable for the present purpose.Let me explain conventional methods to optimize the distribution of the micro-scatterers. The most simple one is the simple pseudo-random method, where the coordinates of the micro-scatterers are determined directly with pseudo-random numbers. As you can see, the created patterns are of sufficient irregularity, but they are very rough. The roughness will be visible to the eye. Also, there is inter-dot overlap everywhere. So, we conclude that this method is not suitable for the present purpose.

6. 7/26/2012 SID'02 45-2: Ide et al. 6 �Pseudo-random perturbation� method To generate patterns without inter-dot overlap The next one is the pseudo-random perturbation approach in out terminology. The main subject of this method is to generate dot patterns without inter-dot overlap. Starting form regular lattice points, The next one is the pseudo-random perturbation approach in out terminology. The main subject of this method is to generate dot patterns without inter-dot overlap. Starting form regular lattice points,

7. 7/26/2012 SID'02 45-2: Ide et al. 7 �Pseudo-random perturbation� method To generate patterns without inter-dot overlap Small random perturbation is given to each dot, Small random perturbation is given to each dot,

8. 7/26/2012 SID'02 45-2: Ide et al. 8 �Pseudo-random perturbation� method To generate patterns without inter-dot overlap So that irregular dot patterns are obtained. But this method has several drawbacks: It exhibits visible roughness due to the pseudo-random numbers. In addition, especially in higher density domains, you have intractable inter-dot overlap and more or less survival of the original lattice. Moreover, it has less flexibility in realizing arbitrary density distributions. This is because mesh generation is generally a tough task when the local density continuously changes.So that irregular dot patterns are obtained. But this method has several drawbacks: It exhibits visible roughness due to the pseudo-random numbers. In addition, especially in higher density domains, you have intractable inter-dot overlap and more or less survival of the original lattice. Moreover, it has less flexibility in realizing arbitrary density distributions. This is because mesh generation is generally a tough task when the local density continuously changes.

9. 7/26/2012 SID'02 45-2: Ide et al. 9 Summary of the conventional methods Here is the summary of the conventional approaches. Notice that there are two metrics to evaluate these ones: Moir� prevention and Uniformity. As explained they all are not adequate for the present purpose. Here is the summary of the conventional approaches. Notice that there are two metrics to evaluate these ones: Moir� prevention and Uniformity. As explained they all are not adequate for the present purpose.

10. 7/26/2012 SID'02 45-2: Ide et al. 10 Low-discrepancy sequences (LDS) Controlled homogeneity with sufficient irregularity Have been applied for speed-up of Monte Carlo integration/simulations Now, let me explain our approach. A class of sequences called LDS is known to have controlled homogeneity with sufficient irregularity. It has been applied for speed-up of Monte Carlo integration/simulations so far. What I am showing here is the comparison between LDS and pseudo-random numbers. As you can see, the LDS pattern is much more homogeneous than that of pseudo-random numbers, conserving good irregularity. The present approach is the first attempt to apply the LDS to the physical dot patterns. Notice that there is inter-dot overlap everywhere even in the LDS pattern. We must remove this.Now, let me explain our approach. A class of sequences called LDS is known to have controlled homogeneity with sufficient irregularity. It has been applied for speed-up of Monte Carlo integration/simulations so far. What I am showing here is the comparison between LDS and pseudo-random numbers. As you can see, the LDS pattern is much more homogeneous than that of pseudo-random numbers, conserving good irregularity. The present approach is the first attempt to apply the LDS to the physical dot patterns. Notice that there is inter-dot overlap everywhere even in the LDS pattern. We must remove this.

11. 7/26/2012 SID'02 45-2: Ide et al. 11 Dynamical redistribution method Give each dot a repulsive force To remove the overlap, we introduce a dynamical theory, which is schematically explained here. Repulsively interacting dots are shown here. Small distance results in a strong repulsion, and large distance results in weak repulsion. The inter-dot overlap is expected to be removed gradually as time evolves. In addition, to reproduce continuous density distributions, a dynamical scaling method is introduced. With this rule, the range of force varies with local density. In fact, the range of force is the order of the minimum separation between adjacent dots. This rule is related with the principal wavelength in the theory of digital half-toning.To remove the overlap, we introduce a dynamical theory, which is schematically explained here. Repulsively interacting dots are shown here. Small distance results in a strong repulsion, and large distance results in weak repulsion. The inter-dot overlap is expected to be removed gradually as time evolves. In addition, to reproduce continuous density distributions, a dynamical scaling method is introduced. With this rule, the range of force varies with local density. In fact, the range of force is the order of the minimum separation between adjacent dots. This rule is related with the principal wavelength in the theory of digital half-toning.

12. 7/26/2012 SID'02 45-2: Ide et al. 12 We can summarize our approach like this. Our approach provides a method such that improves initial patterns to be final patterns, which meets the requirements. For initial patterns, we use the notion of LDS and a probabilistic sampling method, which is not explained here because of the limitation of time. And for the redistribution process, we use the dynamical redistribution method and the dynamical scaling method.We can summarize our approach like this. Our approach provides a method such that improves initial patterns to be final patterns, which meets the requirements. For initial patterns, we use the notion of LDS and a probabilistic sampling method, which is not explained here because of the limitation of time. And for the redistribution process, we use the dynamical redistribution method and the dynamical scaling method.

13. 7/26/2012 SID'02 45-2: Ide et al. 13 What I am showing here is a result of calculation. You can see that a very smooth irregular dot pattern was obtained in spite of the very seep density gradient.What I am showing here is a result of calculation. You can see that a very smooth irregular dot pattern was obtained in spite of the very seep density gradient.

14. 7/26/2012 SID'02 45-2: Ide et al. 14 Here is another example. Starting from these initial patterns, pseudo-random and LDS, which are shown in a previous slide, Here is another example. Starting from these initial patterns, pseudo-random and LDS, which are shown in a previous slide,

15. 7/26/2012 SID'02 45-2: Ide et al. 15 These final patterns are obtained via our dynamical approach. You can see visible roughness in this one, but quite uniform and sufficiently irregular pattern is obtained here. Form this comparison, we conclude that the dynamical redistribution method proves its true merits when used with the LDS.These final patterns are obtained via our dynamical approach. You can see visible roughness in this one, but quite uniform and sufficiently irregular pattern is obtained here. Form this comparison, we conclude that the dynamical redistribution method proves its true merits when used with the LDS.

16. 7/26/2012 SID'02 45-2: Ide et al. 16 Implementation Now we proceed to the section of implementation of our methods. What was prototyped is showing here. It has prismatic grooves and rectangular dimples. Experiments were conducted under these conditions. Now we proceed to the section of implementation of our methods. What was prototyped is showing here. It has prismatic grooves and rectangular dimples. Experiments were conducted under these conditions.

17. 7/26/2012 SID'02 45-2: Ide et al. 17 Here is the result of measurements. These pictures show snapshots of the bottom surface of the light guides. The upper one is based on the PRP method, and the lower one is based on our method. You can see that the lower pattern exhibits more uniformity with sufficient irregularity. In the upper picture, you find that cretain periodicity survives to some extent due to an original lattice. These pictures shows the surface of the UXGA LC cells. For illumination these light guides are used. Notice the clear difference between them. You observe a clear moir� pattern in the upper picture. On the other hand, the moir� pattern disappears here, and also good luminance uniformity is achieved. Here is the result of measurements. These pictures show snapshots of the bottom surface of the light guides. The upper one is based on the PRP method, and the lower one is based on our method. You can see that the lower pattern exhibits more uniformity with sufficient irregularity. In the upper picture, you find that cretain periodicity survives to some extent due to an original lattice. These pictures shows the surface of the UXGA LC cells. For illumination these light guides are used. Notice the clear difference between them. You observe a clear moir� pattern in the upper picture. On the other hand, the moir� pattern disappears here, and also good luminance uniformity is achieved.

18. 7/26/2012 SID'02 45-2: Ide et al. 18 Summary Here is the summary of the present research. First we proposed the integrated-type light guide, and stated what the problem is. Next, our novel approach was explained. Here is the summary of the present research. First we proposed the integrated-type light guide, and stated what the problem is. Next, our novel approach was explained.

19. 7/26/2012 SID'02 45-2: Ide et al. 19 Finally, we demonstrate that our novel approach enables the implementation of the moir�-free collimating light guide. We believe that our approach is currently the best randomization method. Actually, the IBM flex view displays are the fruits of our research. Thank you for your attention.Finally, we demonstrate that our novel approach enables the implementation of the moir�-free collimating light guide. We believe that our approach is currently the best randomization method. Actually, the IBM flex view displays are the fruits of our research. Thank you for your attention.

20. 7/26/2012 SID'02 45-2: Ide et al. 20 Addenda

21. 7/26/2012 SID'02 45-2: Ide et al. 21