Variously subdivided layers of a constant liquid crystal thickness affect electro-optical performance in the hole-patterned electrode liquid crystal lenses

Abstract

SUMMARY In this thesis electro-optical performance of hole-patterned electrode liquid crystal lenses with a constant liquid crystal layer affected by variously subdivided layers was investigated As a result the experiment found that under the same non-uniform electric field distribution the thicker liquid crystal layer reduces the average horizontal component of the electric field As a result it obviously reduces the threshold voltages of vertical electric field to effectively prevent disclination line occurrence when the LC lens with an upper layer of 75 μm and a lower layer of 25 μm Meanwhile the tunable focuses achieve larger increase and better imaging performance than others Key words: hole-patterned electrode subdivided layers of liquid crystal lens dual driving voltage disclination line INTRODUCTION Although the stacked structure of liquid crystal layers brings many improvements to the liquid crystal lens it also causes additional defects to lens that is the disclination lines at the short focal length Due to the upper LC layer closing to the hole-patterned electrode there is a larger electric field gradient If we extend the upper LC layer to the bottom of lens for a short thickness the average horizontal components of the electric field in the layer will be reduced to a certain extent By restraining part of LC molecules from reversed rotating we can prevent the occurrence of disclination lines and the voltage controlling the vertical field also be operated with a lower value In this study three type of LCLs fabricated with subdivided LC layers are demonstrated and evaluated their optical performance ? EXPERIMENTAL MATERIALS Fig 1 Cross-section view of the subdivided layers in a hole-patterned liquid crystal lens structure Figure 1 shows the cross-section view of the subdivided layers in a hole-patterned liquid crystal lens which is composed of top glass substrate (0 55 mm thickness) and bottom glass substrate (1 1 mm thickness) with whole ITO films and the second substrate (0 55 mm thickness) is a hole-patterned (radius 3 mm) with aluminum film There is a cover slip between upper and lower LC layers (filled with E7 LCs purchased from ECHO CHEMICAL CO ) In this experiment we fabricate three type of LCLs subdivided LC layers of a constant liquid crystal thickness (100μm) LCL (50-50) is the lens with 50 μm upper and lower layers LCL (75-25) is the lens with 75 μm upper layer and 25 μm upper The last one which is LCL (25-75) with 25 μm upper layer and 75 μm upper RESULT AND DISCUSSION Figure 2 is shown comparisons of interference patterns at the beginning of disclination lines for three type of above LC lenses when we control the driving voltage V2 at 80 Vrms As a result we observe that a small area of disclination line starting to appear in the center of LCL(25-75) and LCL(50-50) when V1 operated to a value lower than the threshold voltage This area will slowly spread as time goes on and eventually extend to both sides of the lens edge However there is the smaller average horizontal component of the electric field in the LCL(75-25) the threshold voltage of V1 can be operated at a lower value than the other two structures as shown in Fig 2 (c) Fig 2 Comparisons of interference patterns at the beginning of disclination lines for three type of LC lenses when V2 at 80 Vrms (a) LCL (25-75) with V1 at 30 Vrms (b) LCL (50-50) with V1 at 5 Vrms (c) LCL (75-25) with V1 at 0 Vrms Finally various experimental parameters to affect the image performance of LCLs are evaluated which results are shown in Fig 3 We control the three type lenses at the same focal length of 7cm Black and white line pair imaging it is obvious that the edge of LCL (75-25) is sharper than LCL (50-50) and single LC layer lens Fig 3 Observation of imaging performance in three types of lenses (a) LCL (50-50) applied voltage V2=80 Vrms and V1=15 Vrms (b) LCL (75-25) applied voltage V2=80 Vrms and V1=0 Vrms (c) LCL with single LC layer applied voltage V2=80 Vrms and V1=10 Vrms (d) glass lens ? CONCLUSION This study has demonstrated the stacked structure liquid crystal lens with thicker upper LC layer effectively reducing the average horizontal component of the electric field It obviously reduces the threshold voltage of vertical field and restrain disclination line at the same time The proposed LCL (75-25) with 40 Vrms operated by V2 obtained the focal length reduction effectively and good imaging quality is also maintained compared to another two LCLs

Date of Award	2020
Original language	English
Supervisor	Chia-Rong Sheu (Supervisor)