CHAPTER 7. CONCLUSION AND FUTURE WORK
7.1.3 Gradient Driven Liquid Crystal Lens (GD-LC lens)
The most important topic, the third one: Gradient Driven Liquid Crystal Lens (GD-LC lens), was proposed to intrinsically solve the issue of high driving voltage. Compare to previous papers or the newly reports, we demonstrated a dramatic improvement for reducing the driving voltage from tens voltages or even higher than hundred voltages down to less than 5 Vrms for focal length from 6cm to infinity. The structure of GD-LC lens utilized a resistant
layer connected by tree electrodes as the control electrode. The first one benefit of this structure is that the applied electric field can be conserved inside the LC cell to be effectively employed the without leaking out. The second one is that the resistance layer controlled by these tree electrodes can initially produce gradient voltage distribution for yielding lens profile. Furthermore, the structure also can be controlled by operating voltage and frequency to achieve the concept of multi-control. In our experiment, the focusing profiles of each focal length can be optimized by this dual-control which has benefited the image quality in our auto-focusing (AF) experiments. The most important breakthrough was that the focusing time has been improved from the typical larger than 10 sec or over 1 min down to less than 1sec (~600ms) for focusing from infinity to 6cm closed object, as Figure 7-4 illustrates.
Figure 7-4 The dramatic improvement in driving voltage and focusing time with GD-LC lens combined with the volt. & freq. dual-control and OD method.
To compare with results of the world’s leading groups, as shown in Table 7, not only the driving voltage was reduced to a reasonable range that the normal IC could drive but also the
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other solutions for AF mentioned in section 1.4.1 after the improvement of our group. As mentioned, the issues of driving and focusing time have almost been solved, although the image quality still cannot compete with conventional lens-head.
Table 7 The comparisons of single tunable lenses.
Table 8 The comparison of the AF solutions after the improvements of our group for LC lens.
7.2 Future work
7.2.1 Optical design for LC lens
In current status, we significantly improve the issues of LC lenses, especially the slow focusing time and high driving voltage. In the optical quality part, however, although the
concept of multi-control can be used to optimize the focusing profiles of each focal length, the spot size still cannot be competed with that of conventional lens-heads, as well as its aberration values also cannot be corrected by this single-lens system. For camera industry, diffraction-limit performance is usually required even for the use in mobile phones. To improve this issue, the optical design of conventional lens for LC lens can be take into consideration. In the first step, the focusing performance of LC lens should be optimized, and then utilize solid lens to correct the image quality, image aberrations, and enhance MTF. The role of the solid lens is to obtain a balance solution for focusing at infinity and close objects.
Finally, the simulation tools for lens design, such as CodeV and Zemax, and LC cells, such as 2Dimos and ExpertLCD, should be linked to simulate the imaging result of LC lens and to analysis items such as aberrations, MTF, imaging result, and tolerance. Optimization is also importance for the lens modifying. The relation of the link is shown in Figure 7-5.
Figure 7-5 The relation of lens design tool for LC lens design
7.2.2 Polarizer free LC lens
In the application of lens with LCs, polarized light is necessary to distinct the ordinary-rays and extraordinary-rays. However, this property results in a half of incoming light losing due to the usage of polarizer. To make the application of LC lens more feasible, polarizer free LC lens is required. The general method for polarizer free LC lens is to use two crossed LC lenses with perpendicular rubbing direction. Each of the lens is used to deal with one polarization.
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Therefore, our group would use DIP to compute the imaging result without employing polarizer. In such a LC lens without polarizer, it can be used for the hyper distance shooting without losing gathering light. For AF usage, the lens system firstly takes an original image before AF which includes information from ordinary-rays and extraordinary-rays, and takes another one after AF ready. The difference of these two images is that the extraordinary-rays in the second image were focused. By DIP, the information coming from ordinary-rays can be eliminated, and according to the original luminance to restore the AF image in the second image with proper intensity, as shown in Figure 7-6.
Figure 7-6 The concept of DIP for polarizer free LC lens.
7.2.3 Optical Zoom
As discussed in section 4.4, GD-LC lens can be easily performed in convex and concave mode. This feature is benefit for the application in LC optical zoom lens because zoom lens usually requires a convex and a concave lens group as the variator and compensator.
Therefore, we add another LC lens in front of the LC AF system, as shown in Figure 7-7. The structure consist of two LC lenses To achieve the concept of zoom lens, Equation (7-1) and Equation (7-2) can be used to obtain the optical power of the zoom system and fix the imaging plane on position of image sensor.
⇒ (7-1)
1
(7-2) and are the lens power of two LC lens, and other parameters are the spacing and fix optical power. As we utilize and as the variator and compensator respectively. The lens power of the system was simulated, as Figure 7-8 shows. In the simulation result, although lens power of the system, K, can be varied, but the lens power of LC lenses were limited within 0.03 mm . Therefore, the zoom ratio, as shown in Equation (7-3)
≡ (7-3)
is only around 1.5X. The next step is to demonstrate the feasibility of the LC zoom lens concept and to improve the zoom ratio.
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Figure 7-8 The variation of lens power, K, changed by LC lens power, K1 and K2
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Curriculum Vitae
L IN- Y AO L IAO
‧National Chiao Tung University‧Rm.502 CPT Building, 1001 Ta Hsueh Road, Hsinchu, Taiwan 300,
‧Tel: +886-3-5712121 ext 59210‧Fax: +886-3-5737681
‧E-mail: finalhome.eo95g@nctu.edu.tw
PERSONAL PROFILE
The 1st in Ph.D. qualify exam of optics in Institute of Electro-Optical Engineering, National Chiao Tung University (NCTU).
Led national scale project relative to Liquid Crystal Lens design for 3 years and acquired breakthrough in performance.
Experienced in lens design for consumer mobile devices as well as programming of optimized
designs in doublet and triplet lens for initial lens designs.
Experienced in design of Liquid Crystal Displays with dynamic backlights, and led projects for the purpose of contrast ratio enhancement and motion blur suppression during period of master study.
Won the Excellent Project Award for project, High Dynamic Rang LCDs, during intern in AU Optronics Corp.
EDUCATION
Ph.D., Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan
* Research Topic－“Liquid Crystal Lens Design”
* Advisors－Prof. Yi‐Pai Huang
M.S., Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan
* Research Topic－“High Image Quality with Low Power Consumption LCDs”
* Advisors－Prof. Yi‐Pai Huang
B.S., Electric Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan
Classical Electrodynamics
Digital Signal Process
Digital Image Process
Statistical Optics and Image Formation
Thin Film Optics
Advanced Geometrical Optics
Quantum Mechanics
EXPERIENCE
Liquid Crystal Lens Design Project with National Science Council 2008/9 ~ present
* The study of a novel heterogeneous integrated compact camera module Project number: NSC 98-2220-E-009-019
Joined the national scale project and cooperate with several groups in other fields, and led a group to develop high efficient Liquid Crystal Lens module for mobile devices.
Realized fast-focusing Liquid Crystal Lens exhibiting 0.2sec focusing time, only driven by 3~5 Vrms. Compare to that of the other world leading groups, which require around 30~60sec focusing time and usually driven by 50~100Vrms.
Technology transfers of patents with companies for the Liquid Crystal Lens developments were done.
Internship in Large-size Panel EE Dep., AU Optronics Corporation, Hsinchu , Taiwan
2007/7 ~ 2007/9
* Project－“High Dynamic Range LCDs”
Won the Excellent Project Award.
High Dynamic Range LC Display Project with AU Optronics Corporation, Hsinchu, Taiwan
2006/7 ~ 2007/6
Led project, High Dynamic Range LCDs, to design a display with the benefits of high image quality, and low power consumption.
Published 3 journal papers in Journal of Display Technology and Journal of Society of Information Display, 4 conference papers in Society of Information Display 2007 ~ 2010 (SID 07
~ 10), and 3 patent packages in Taiwan, United States, and People’s Republic of China.
ACADAMIC HONORS AND AWARDS Ranked 1st in Ph.D. qualify exam of optics
Institute of Electro-Optical Engineering Scholarship
Awarded to 5 out of 150 PhD students in Institute of Electro-Optical Engineering, NCTU
Pre-Ph.D. Scholarship
Awarded to Ph.D. students for being Teaching Assistant in NCTU AU Optronics Corporation Excellent Project Award 2007 The best project during the internship in AU Optronics Corp.
OPT ’07 (Optics & Photonics Taiwan 2007) Student Paper Award Paper Subject – “High Dynamic Range LCDs”
2006/7
1. Yi-Pai Huang, Lin-Yao Liao, and Chih-Wei Chen, ” 2D/3D Switchable Autostereoscopic Display with Multi-electrically Driven Liquid Crystal (MeD-LC) Lenses,” accepted by J. Soc.
Crystal Lens Exhibiting Ultra-fast Focusing by Low Operating Voltages,” submitted to Optics Express.
3. Lin-Yao Liao, Po-Yuan, Shieh, and Yi-Pai Huang, “ 3-Dimentional Imaging and Analysis for Liquid Crystal Lenses by Fluorescence Confocal Polarizing Microscopy,” submitted to Optics Express.
4. Lin-Yao Liao, Po-Yuan, Shieh, and Yi-Pai Huang, “Over-drive Method for Fast Focusing Liquid Crystal Lens Applications,” is under writing.
5. Lin-Yao Liao, and Yi-Pai Huang, ” Blur-Mask Approach for Real-Time Calculation of Light Spreading Function (LSF) on Spatial Modulated High Dynamic Range LCDs,” J. of Display Technology, vol. 6, issue 4, pp. 121-127, 2010.
6. Lin-Yao Liao, Chih-Wei Chen, and Yi-Pai Huang, “Local Blinking HDR LCD Systems for Fast MPRT with High Brightness LCDs.” J. of Display Technology, vol. 6, issue 5, pp. 178-183,
6. Lin-Yao Liao, Chih-Wei Chen, and Yi-Pai Huang, “Local Blinking HDR LCD Systems for Fast MPRT with High Brightness LCDs.” J. of Display Technology, vol. 6, issue 5, pp. 178-183,