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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 21 — Oct. 21, 2013
  • pp: 24721–24735
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Refraction effect in an in-plane-switching blue phase liquid crystal cell

Daming Xu, Yuan Chen, Yifan Liu, and Shin-Tson Wu  »View Author Affiliations


Optics Express, Vol. 21, Issue 21, pp. 24721-24735 (2013)
http://dx.doi.org/10.1364/OE.21.024721


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Abstract

We develop a refraction model to analyze the electro-optic effects of an in-plane-switching blue phase liquid crystal (IPS-BPLC) cell. Good agreement with experiment is obtained. Based on this model, we optimize the parameters affecting the electro-optics of IPS-BPLC, such as electrode dimension, saturated induced birefringence, saturation electric field, and cell gap. An IPS-BPLC with low operation voltage (<10Vrms) and high transmittance (~80%) with single gamma curve can be achieved by optimizing the BPLC material and device structure.

© 2013 Optical Society of America

1. Introduction

Polymer-stabilized blue phase liquid crystal (PS-BPLC) [1

1. H. Kikuchi, M. Yokota, Y. Hisakado, H. Yang, and T. Kajiyama, “Polymer-stabilized liquid crystal blue phases,” Nat. Mater. 1(1), 64–68 (2002). [CrossRef] [PubMed]

4

4. J. Yan, L. Rao, M. Jiao, Y. Li, H. C. Cheng, and S. T. Wu, “Polymer-stabilized optically isotropic liquid crystals for next-generation display and photonics applications,” J. Mater. Chem. 21(22), 7870–7877 (2011). [CrossRef]

] is emerging as a promising candidate for next-generation display [5

5. L. Rao, Z. Ge, S. Gauza, K. M. Chen, and S. T. Wu, “Emerging liquid crystal displays based on the Kerr effect,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 527(1), 186–198 (2010). [CrossRef]

, 6

6. L. Rao, J. Yan, and S. T. Wu, “Prospects of emerging polymer-stabilized blue-phase liquid-crystal displays,” J. Soc. Inf. Disp. 18(11), 954–959 (2010). [CrossRef]

] and photonic devices [7

7. Y. H. Lin, H. S. Chen, H. C. Lin, Y. S. Tsou, H. K. Hsu, and W. Y. Li, “Polarizer-free and fast response microlens arrays using polymer-stabilized blue phase liquid crystals,” Appl. Phys. Lett. 96(11), 113505 (2010). [CrossRef]

, 8

8. J. Yan, Y. Li, and S. T. Wu, “High-efficiency and fast-response tunable phase grating using a blue phase liquid crystal,” Opt. Lett. 36(8), 1404–1406 (2011). [CrossRef] [PubMed]

]. Different from mainstream nematic liquid crystals [9

9. S. T. Wu and D. K. Yang, Fundamentals of Liquid Crystal Devices (John Wiley & Sons, 2006).

11

11. Y. Chen, F. Peng, and S. T. Wu, “Submillisecond-response vertical-aligned liquid crystal for color sequential projection displays,” J. Disp. Technol. 9(2), 78–81 (2013). [CrossRef]

], PS-BPLC is a self-assembly nanostructure electro-optic medium which exhibits three attractive features: (1) self-assembly process to form three-dimensional lattices without the need of surface alignment layer (e.g., polyimide), (2) microsecond response time [12

12. Y. Chen, J. Yan, J. Sun, S. T. Wu, X. Liang, S. H. Liu, P. J. Hsieh, K. L. Cheng, and J. W. Shiu, “A microsecond-response polymer-stabilized blue phase liquid crystal,” Appl. Phys. Lett. 99(20), 201105 (2011). [CrossRef]

] resulted from nanoscale (~100 nm) double-twisted cylinder diameter and short coherence length, and (3) optically isotropic dark state. Since no surfactant is needed to generate uniform molecular alignment for PS-BPLC, the device fabrication process can be much simplified. And fast response time is particularly desirable because it not only reduces motion blurs but also enables color-sequential display using RGB LED backlight with negligible color breakup [13

13. H. Haseba and S. Kobayashi, “A full-color sequential LCD using modulated backlight,” SID Int. Symp. Digest Tech. Papers 16, 81–83 (1985).

15

15. S. Gauza, X. Zhu, W. Piecek, R. Dabrowski, and S. T. Wu, “Fast switching liquid crystals for color-sequential LCDs,” J. Disp. Technol. 3(3), 250–252 (2007). [CrossRef]

]. With an isotropic voltage-off state, PS-BPLC is able to achieve high contrast ratio and wide view [16

16. Y. Liu, Y. F. Lan, H. Zhang, R. Zhu, D. Xu, C. Y. Tsai, J. K. Lu, N. Sugiura, Y. C. Lin, and S. T. Wu, “Optical rotatory power of polymer-stabilized blue phase liquid crystals,” Appl. Phys. Lett. 102(13), 131102 (2013). [CrossRef]

].

In terms of device configuration, both in-plane-switching (IPS) [17

17. Z. Ge, S. Gauza, M. Jiao, H. Xianyu, and S. T. Wu, “Electro-optics of polymer-stabilized blue phase liquid crystal displays,” Appl. Phys. Lett. 94(10), 101104 (2009). [CrossRef]

, 18

18. Z. Ge, L. Rao, S. Gauza, and S. T. Wu, “Modeling of blue phase liquid crystal displays,” J. Disp. Technol. 5(7), 250–256 (2009). [CrossRef]

] and vertical field switching [19

19. H. C. Cheng, J. Yan, T. Ishinabe, and S. T. Wu, “Vertical field switching for blue-phase liquid crystal devices,” Appl. Phys. Lett. 98(26), 261102 (2011). [CrossRef]

, 20

20. H. C. Cheng, J. Yan, T. Ishinabe, N. Sugiura, C. Y. Liu, T. H. Huang, C. Y. Tsai, C. H. Lin, and S. T. Wu, “Blue-phase liquid crystal displays with vertical field switching,” J. Disp. Technol. 8(2), 98–103 (2012). [CrossRef]

] have been developed. Between these two, IPS is commonly employed because of its simpler backlight system. In an IPS cell, electric field is mainly in lateral direction and the Kerr-effect-induced birefringence is along the electric field direction if the BPLC with a positive dielectric anisotropy (Δε > 0) is employed. However, IPS-BPLC mode has three drawbacks: high operation voltage, low transmittance and relatively large hysteresis. High operation voltage originates from that the electric fields are confined near the IPS electrodes and cannot penetrate deeply into the BPLC bulk [21

21. L. Rao, Z. Ge, S. T. Wu, and S. H. Lee, “Low voltage blue-phase liquid crystal displays,” Appl. Phys. Lett. 95(23), 231101 (2009). [CrossRef]

]. Low transmittance results from the “dead zones” on the top of the electrodes since only the horizontal electric field contributes to the transmittance of the IPS-BPLC cell. Moreover, the electric fields are not uniform in an IPS-BPLC cell, especially in the vicinity of electrode edges, the strong electric fields could cause lattice deformation which in turn leads to hysteresis [22

22. K. M. Chen, S. Gauza, H. Xianyu, and S. T. Wu, “Hysteresis effects in blue-phase liquid crystals,” J. Disp. Technol. 6(8), 318–322 (2010). [CrossRef]

].

To reduce operation voltage and hysteresis, both large Kerr constant BPLC materials [23

23. L. Rao, J. Yan, S. T. Wu, S. Yamamoto, and Y. Haseba, “A large Kerr constant polymer-stabilized blue phase liquid crystal,” Appl. Phys. Lett. 98(8), 081109 (2011). [CrossRef]

26

26. Y. Haseba, S. Yamamoto, K. Sago, A. Takata, and H. Tobata, “Low-voltage polymer-stabilized blue-phase liquid crystals,” SID Int. Symp. Digest Tech. Papers 44, 254–257 (2013). [CrossRef]

], and modified IPS structures, such as protrusion electrodes [21

21. L. Rao, Z. Ge, S. T. Wu, and S. H. Lee, “Low voltage blue-phase liquid crystal displays,” Appl. Phys. Lett. 95(23), 231101 (2009). [CrossRef]

], wall-shaped electrodes [27

27. M. Kim, M. S. Kim, B. G. Kang, M. K. Kim, S. Yoon, S. H. Lee, Z. Ge, L. Rao, S. Gauza, and S. T. Wu, “Wall-shaped electrodes for reducing the operation voltage of polymer-stabilized blue phase liquid crystal displays,” J. Phys. D Appl. Phys. 42(23), 235502 (2009). [CrossRef]

], etched electrodes [28

28. L. Rao, H. C. Cheng, and S. T. Wu, “Low voltage blue-phase LCDs with double-penetrating fringe fields,” J. Disp. Technol. 6(8), 287–289 (2010). [CrossRef]

], and corrugated electrodes [29

29. M. Z. Jiao, Y. Li, and S. T. Wu, “Low voltage and high transmittance blue-phase liquid crystal displays with corrugated electrodes,” Appl. Phys. Lett. 96(1), 011102 (2010). [CrossRef]

] have been proposed. With these combined effects, the on-state voltage can be reduced to <10V. However, the transmittance is still limited to 65-70%. Therefore, to develop a high-transmittance IPS-BPLC with a low operation voltage is urgently needed.

To enhance transmittance, Chen, et al. [30

30. K. M. Chen, J. Yan, S. T. Wu, Y. P. Chang, C. C. Tsai, and J. W. Shiu, “Electrode dimension effects on blue-phase liquid crystal displays,” J. Disp. Technol. 7(7), 362–364 (2011). [CrossRef]

] observed an interesting phenomenon during the study of electrode dimension effects on IPS-BPLC. It was reported that by reducing the width (w) and gap (l) of the IPS electrodes, the operation voltage is reduced while the transmittance keeping above 80%. Such a high transmittance is not expected from the model developed by Ge, et al. [17

17. Z. Ge, S. Gauza, M. Jiao, H. Xianyu, and S. T. Wu, “Electro-optics of polymer-stabilized blue phase liquid crystal displays,” Appl. Phys. Lett. 94(10), 101104 (2009). [CrossRef]

, 18

18. Z. Ge, L. Rao, S. Gauza, and S. T. Wu, “Modeling of blue phase liquid crystal displays,” J. Disp. Technol. 5(7), 250–256 (2009). [CrossRef]

], which predicts the peak transmittance is independent of electrode dimension as long as the same l/w ratio is used. Meanwhile, IPS-2/4 (w = 2μm and l = 4μm), IPS-5/10 and IPS-5/5 are able to achieve over 80% transmittance in experiment, which is much higher than that predicted by Ge’s model, in which the peak transmittance for l/w = 1 and 2 should be ~50% and ~64%, respectively. More recently, Chen, et al. [24

24. Y. Chen, D. Xu, S. T. Wu, S. Yamamoto, and Y. Haseba, “A low voltage and submillisecond-response polymer-stabilized blue phase liquid crystal,” Appl. Phys. Lett. 102(14), 141116 (2013). [CrossRef]

] reported a low voltage IPS-BPLC with peak transmittance ~60% for IPS-5/5 cell. Therefore, Ge’s model predicts a lower transmittance than the experimental data.

In this paper, we propose a refraction model to explain the dimension effect of IPS-BPLC and obtain good agreement with experimental data. From this model, the electro-optics of IPS-BPLC on electrode dimension, saturated induced birefringence, saturation electric field, and cell gap is analyzed. Promising approaches for achieving high transmittance and low operation voltage are presented. Finally, a new method for achieving single-gamma IPS-BPLC is also proposed.

2. Refraction model

2.1 Numerical modeling

In Ge’s model, the incident light is assumed to travel in straight lines in an IPS cell. On the top of IPS electrodes, the electric fields are mainly in the vertical direction. Thus, the transmittance in these regions is very low, known as “dead zones”. Let us take IPS-5/5 cell as an example. According to this model, in a voltage-on state it should have bright and dark lines with nearly the same width. However, it was reported in [30

30. K. M. Chen, J. Yan, S. T. Wu, Y. P. Chang, C. C. Tsai, and J. W. Shiu, “Electrode dimension effects on blue-phase liquid crystal displays,” J. Disp. Technol. 7(7), 362–364 (2011). [CrossRef]

] that the effective aperture ratio for the IPS-5/5 sample is ~75% rather than ~50%. This oversized bright region indicates that the LCs near the edges of ITO electrodes also contribute to the overall transmittance. To explain this increased aperture ratio, we need a new model.

According to the extended Kerr model [31

31. J. Yan, H. C. Cheng, S. Gauza, Y. Li, M. Jiao, L. Rao, and S. T. Wu, “Extended Kerr effect of polymer-stabilized blue-phase liquid crystals,” Appl. Phys. Lett. 96(7), 071105 (2010). [CrossRef]

], the induced birefringence (Δn) is dependent on the electric field in an IPS-BPLC cell. Consequently, in a voltage-on state the ordinary index (no) and extraordinary index (ne) should be different at different positions of the cell. Therefore, the BPLC in an IPS cell cannot be regarded as a uniform medium and the incident light would no longer propagate in a straight path. In our refraction model, we take the nonuniform BPLC profile into account so that the incident light is bent by the refraction effect. In particular, on top of the electrodes the incident light would be refracted toward the center of the electrodes, as depicted in Fig. 1
Fig. 1 Principle of refraction effect in IPS-BPLC.
. These refracted rays would have a larger angle with respect to the optic axis of BPLC. Meanwhile, their optical path in the cell would become longer due to the bent propagation direction. These two factors contribute to the increased phase retardation on the top of electrodes, resulting in a higher transmittance.

For intensity modulation, an IPS-BPLC cell is placed between two crossed linear polarizers. The electric fields generated from interdigitated pixel electrodes are used to induce phase retardation for the incident light. In the voltage-off state (V = 0), BPLC is assumed to be optically isotropic (with refractive index ni), leading to a very good dark state [16

16. Y. Liu, Y. F. Lan, H. Zhang, R. Zhu, D. Xu, C. Y. Tsai, J. K. Lu, N. Sugiura, Y. C. Lin, and S. T. Wu, “Optical rotatory power of polymer-stabilized blue phase liquid crystals,” Appl. Phys. Lett. 102(13), 131102 (2013). [CrossRef]

]. When an electric field E is applied, the induced birefringence is along the electric field direction. Macroscopically speaking, such an isotropic-to-anisotropic transition can be described by the Kerr effect and the induced birefringence characterized by the extended Kerr model [31

31. J. Yan, H. C. Cheng, S. Gauza, Y. Li, M. Jiao, L. Rao, and S. T. Wu, “Extended Kerr effect of polymer-stabilized blue-phase liquid crystals,” Appl. Phys. Lett. 96(7), 071105 (2010). [CrossRef]

]:
Δn=Δns(1exp[(EEs)2]),
(1)
where Δns stands for saturated induced birefringence and Es the saturation electric field.

2.2 Modeling physics

When a light passes through the boundary of two uniform isotropic media, the refraction effect is governed by the Snell’s law. However, in a voltage-on state the incident light propagates in an anisotropic BPLC medium so that the e-ray (TM) and o-ray (TE) should be considered separately. Since the polarizer is oriented at 45° with respect to the IPS electrodes, the incident linearly polarized light can be decomposed into 50% TE and 50% TM waves. Let’s take two arbitrary neighboring layers, the mth and (m + 1)th layers, as an example, among which the mth layer is closer to the bottom substrate, as shown in Fig. 3
Fig. 3 Refraction at the boundary between the mth and (m + 1)th layers in an IPS-BPLC cell.
.

For TE polarization, it experiences an ordinary refractive index no. At the interface between these two layers, the incident angle is:
θinc=θm+αm,
(3)
where θm is the angle between incident light and vertical direction, and αm is the inclination angle between the electric field (Em) and the horizontal axis.

Let us assume no,m and no,m + 1 represent the ordinary refractive indices of the mth and (m + 1)th layers, respectively. Because TE polarization is ordinary wave, its refraction effect can still be described by Snell’s law:
θtrans=no,mno,m+1sin(θinc).
(4)
And because the mth layer is closer to the electrodes, the electric field in this layer is stronger. According to Eqs. (1) and (2), stronger electric field would result in a larger induced Δn and smaller no. Therefore, the transmitted angle θtrans in the (m + 1)th layer is smaller than the incident angle θinc in the mth layer. In the electrode gap, the electric field is nearly horizontal so that θinc is very small and the refraction effect is negligible, as Eq. (4) indicates. However, on top of the electrodes, the electric fields are tilted along vertical direction. Therefore, θinc is larger and the light is bent toward the center of electrodes.

For TM polarization, the situation is more complicated. The incident angle at the interface between these two layers can still be calculated by Eq. (3). Because the electric field of TM polarization is in the plane of incidence, it’s an e-ray propagating in an anisotropic media. Hence, we cannot use Snell’s law to determine its transmitted angle. The wave vector km in the mth layer should be determined by following equations:
{kCm,m2ne,m2+k//Cm,m2no,m2=k02k//Cm,mkCm,m=tan(θinc),
(7)
where kCm,m and k//Cm,mare the components of wave vector km normal and parallel to the direction of optic axis Cm, which is also the direction of electric field in the mth layer. And ne,m and no,m are the extraordinary and ordinary refractive indices of the mth layer, respectively. After obtaining kCm,m andk//Cm,m, the normal-to-Cm component of wave vector in the (m + 1)th layer k//Cm,m+1can be determined according to the boundary matching of tangential wave vectors:

k//Cm,m+1=k//Cm,m.
(8)

To calculate the wave vector in the (m + 1)th layer, we need to do a coordinate transformation as below:
{kCm+1,m+1=kCm,m+1sinβ+k//Cm,m+1cosβmk//Cm+1,m+1=kCm,m+1sinβk//Cm,m+1sinβm.
(9)
Here, βm = αm - αm + 1 is the angle between optic axes in the mth and the (m + 1)th layers. Then we plug Eq. (9) into the following equation for wave vector km+1:
kCm+1,m+12ne,m+12+k//Cm+1,m+12no,m+12=k02.
(10)
By solving Eqs. (9) and (10), we can obtainkCm,m+1. The phase change of TM polarization in the mth layer is:
φTM,m=2πλneff,mtTM,m,
(11)
where neff,m is the effective refractive index and tTM,m is the optical path of TM polarization in the mth layer, respectively.

The direction of TM polarization in the (m + 1)th with respect to the vertical direction is:

θm+1=90°tan1(kCm,m+1k//Cm,m+1)αm.
(12)

After computing the phase change for TE and TM in each layer, we use Eq. (13) to calculate the phase retardation and Eq. (14) for the transmittance of light:

Γ=mϕTM,mmϕTE,m,
(13)
T=sin2(Γ/2).
(14)

3. Results

3.1 Simulation vs. experiments

To compare the refraction model with experimental results, we prepared an IPS-BPLC sample using JC-BP06. The blue phase precursor consists of 88.17 wt. % liquid crystal host JC-BP06N (JNC) with 2.92 wt.% of chiral dopant R5011 (HCCH), 5.24 wt.% di-functional reactive monomer RM257 (Merck), 3.46 wt.% TMPTA (1,1,1-Trimethylolpropane Triacrylate, Sigma Aldrich) and 0.21 wt.% photoinitiator. Then we filled the precursor into an IPS-5/5 cell in its isotropic phase. The IPS cell is comprised of interdigitated pixel electrodes on the bottom substrate, but without polyimide alignment layer. The cell gap is 7.5 μm. Next, the cell was placed on a Linkam heating/freezing stage controlled by a temperature programmer (Linkam TMS94). The cell was cooled to the temperature near the transition temperature from chiral nematic phase to blue phase and then cured at BP-I phase with a UV light (λ ~365 nm and intensity ~2 mW/cm2) for 30 min.

After UV curing, nanostructured BPLC composites were self-assembled. The measured Bragg reflection wavelength is λB ~380 nm. Afterwards, the IPS cell was sandwiched between two crossed polarizers for measurement. It’s worth mentioning that in [30

30. K. M. Chen, J. Yan, S. T. Wu, Y. P. Chang, C. C. Tsai, and J. W. Shiu, “Electrode dimension effects on blue-phase liquid crystal displays,” J. Disp. Technol. 7(7), 362–364 (2011). [CrossRef]

], the VT curves were measured under crossed (T) and parallel (T//) polarizers, respectively; and then calculated the normalized transmittance as T/(T+T//). However, this normalization method only measures the VT curve of the 0th order of diffraction and usually shows higher operation voltage and transmittance than real. Therefore, in our experimental setup we focused the transmitted light with a lens so that different diffraction orders can be collected by the detector. We measured the VT curve of the sample with this lens and normalized the transmittance to that of two open polarizers.

Figure 4
Fig. 4 Comparison between experimental VT curve and simulated results using Ge’s model [18] and the refraction model. BPLC cell: JC-BP06 in IPS-5/5 at 25°C and λ = 633 nm. The parameters used in the refraction model are Δns = 0.09 and Es = 2.2 V/μm.
compares the simulated VT curves using Ge’s and refraction models with the experimental data (IPS-5/5 at λ = 633 nm). The red solid line in Fig. 4 represents the measured VT curve. The black solid line shows the simulated VT curve using Ge’s model. The general trend is similar, but the peak transmittance is lower than that of measured value. However, when we take the refraction effect into account the simulated VT curve (blue line) overlaps with the experimental data well. So our refraction model describes the VT characteristics of IPS-BPLC quite accurately.

It was reported in [30

30. K. M. Chen, J. Yan, S. T. Wu, Y. P. Chang, C. C. Tsai, and J. W. Shiu, “Electrode dimension effects on blue-phase liquid crystal displays,” J. Disp. Technol. 7(7), 362–364 (2011). [CrossRef]

] that the transmittance profiles of IPS-5/5 and 10/10 at their voltage-on state using JC-BP01 are different under the polarizing optical microscope: the IPS-5/5 sample shows an increased aperture ratio of ~75% while IPS-10/10 keeps at the expected ~50%. From Ge’s model, both IPS-5/5 and IPS-10/10 cells exhibit ~50% aperture ratios, as shown in Figs. 5(a)
Fig. 5 Simulated transmittance profiles of JC-BP01 in (a, c) IPS-5/5 and (b, d) IPS-10/10 at λ = 633 nm and 25°C. Cell gap d = 7.5 μm. (a, b): Ge’s model, and (c, d): refraction model.
and 5(b), because only the induced Δn from electrode gaps contribute to the overall transmittance. Our refraction model can also explain well the difference in aperture ratios. Figures 5(c) and 5(d) depict the position dependent transmittance profiles of these two cells at their voltage-on states, respectively. Due to refraction, some rays penetrate into the electrode region, especially at the edges of the electrodes. This is why in [30

30. K. M. Chen, J. Yan, S. T. Wu, Y. P. Chang, C. C. Tsai, and J. W. Shiu, “Electrode dimension effects on blue-phase liquid crystal displays,” J. Disp. Technol. 7(7), 362–364 (2011). [CrossRef]

] the electrode edges look brighter than electrode gaps. The lower aperture ratio of IPS-10/10 can be explained as follows: the light at electrode edges (where the electric fields are mostly inclined) cannot be refracted towards the center of the electrode as much as the IPS-5/5 cell because of its larger electrode dimension and same cell gap (d = 7.5 μm). More detailed explanation of this phenomenon including the discussion of electrode dimension and cell gap effects will be addressed later.

In brief, our refraction model explains well the increased aperture ratio experimentally observed in IPS-5/5 versus IPS-10/10 BPLC cells. Therefore, our refraction model can be used to accurately predict the electro-optic properties of IPS-BPLC. From here on, we will use this model to optimize the BPLC device designs.

3.2 Electrode dimension effect

The electrode dimension plays an important role in the electro-optics of IPS-BPLC. Figure 6(a)
Fig. 6 Simulated VT curves of IPS cells with (a) l/w = 1 and (b) l/w = 2 using JC-BP01 at 25°C and λ = 550 nm.
shows the simulated VT curves of JC-BP01 IPS-BPLC with different electrode dimensions (l/w = 1) using our refraction model. The fitting parameters for JC-BP01 at λ = 550 nm are Δns = 0.154 and Es = 4.05 V/μm. Their on-state voltages and peak transmittances are listed in Table 1

Table 1. Comparison Between Refraction and Ge’s [18] Models for IPS-BPLC Cells with l/w = 1. BPLC: JC-BP01 at 25°C and λ = 550 nm

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. For comparison, we also included the peak transmittance calculated by Ge’s model and the gained transmittance resulted from the described refraction effect.

As shown in Fig. 6(a), the on-state voltage (Von) decreases as electrode dimension decreases from IPS-10/10 to −5/5 and then −3/3. However, for IPS-2/2 this trend is reversed. To explain this, we need to consider two determining factors for Von: penetration depth of electric field and induced birefringence Δn. A smaller electrode dimension requires a lower voltage to achieve comparable induced birefringence, that’s why IPS-3/3 shows a lower Von than IPS-5/5 and −10/10 as mentioned above. On the other hand, a smaller electrode dimension also leads to a shallower penetration depth, which in turn demands a larger induced birefringence in order to accumulate sufficient phase retardation for achieving high transmittance. These two factors compete with each other and result in a higher Von for IPS-2/2 because the deficiency of shallow penetration depth outweighs the merit of strong electric field. However, for IPS-3/3 and 5/5, although their electric field intensities are weaker than that of IPS-2/2, their deeper penetration helps to lower Von. Another clear trend shown in Fig. 6(a) is that the peak transmittance decreases as the electrode dimension increases. IPS-BPLCs with different electrode dimensions have different on-state voltages and electric field intensities. According to the extended Kerr model, stronger electric field would result in a higher induced Δn. As a result, the difference in refractive indices between neighboring layers would be larger as explained above and the light would bend more by the refraction effect. Especially on the top of electrodes, the larger angle with respect to the optical axis and higher Δn would result in a higher transmittance and reduced dead zones. This is why IPS-5/5 exhibits a larger aperture ratio than IPS-10/10.

Next, we use our refraction model to simulate the VT curves of IPS-BPLC (JC-BP01) with l/w = 2, as depicted in Fig. 6(b). Table 2

Table 2. Comparison Between Refraction Model and Ge’s Model [18] for IPS-BPLC with l/w = 2, 3 and 4 Structures. BPLC: JC-BP01 at 25°C and λ = 550 nm

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lists the on-state voltage and peak transmittance with and without the refraction effect. The l/w = 2 cells show following similar trend to l/w = 1: as the electrode dimension increases the peak transmittance decreases. Although a larger l leads to a deeper penetration depth, the electric field is weaker so that the induced birefringence is smaller. Moreover, a larger electrode width (w) causes more dead-zone area, which in turn lowers the transmittance. From Table 1 and Table 2, we find that the cells with l/w = 2 have less refraction effect than the l/w = 1 cells. This originates from that the IPS cells with a larger l/w ratio generates a flatter electric field profile so that the incident light is less affected by the refraction effect. As a result, in comparison with Ge’s model, the increase in peak transmittance due to refraction effect is smaller. We also simulated the VT curves for IPS-BPLC with l/w = 3 and 4 ratios. The results are also included in Table 2, and they show the same trend as expected.

3.3 Cell gap effect

In a nematic IPS cell, both transmittance and response time are affected by the cell gap. However, the transmittance of IPS-BPLC is insensitive to the cell gap as long as the cell gap exceeds the penetration depth of electric field [17

17. Z. Ge, S. Gauza, M. Jiao, H. Xianyu, and S. T. Wu, “Electro-optics of polymer-stabilized blue phase liquid crystal displays,” Appl. Phys. Lett. 94(10), 101104 (2009). [CrossRef]

]. This feature is particularly desirable for fabricating large LCD panels, in which uniform cell gap control is a big concern. Here we revisit this important feature by including the refraction effect.

Figure 7(a)
Fig. 7 (a) Induced Δn profile of a 10-μm-thick IPS-5/5 cell at 31V and (b) simulated VT curves of IPS-5/5 with different cell gaps using JC-BP01 (25°C and λ = 550 nm).
depicts the induced birefringence distribution of a 10-μm-thick IPS-5/5 cell and Fig. 7(b) shows the VT curves of the IPS-5/5 cell with different cell gaps simulated by our refraction model. The material employed here is JC-BP01. From Fig. 7(a), the induced birefringence is the largest near the electrode surface and it gradually decreases as the distance increases. For JC-BP01, as the depth increases to 5.5 μm the induced birefringence decreases to 0.05. Hence, for IPS-BPLC the VT curve is insensitive to cell gap as long as the cell gap is larger than the field’s penetration depth, which is governed by the electrode dimension through Poisson equation. This is verified in Fig. 7(b). Therefore, similar to Ge’s model our refraction model also shows that the VT curve is indeed insensitive to the cell gap variation, as long as the cell gap is above the field’s penetration depth.

Shown in Figs. 8(a)-(d)
Fig. 8 Transmittance profile of IPS-5/5 with different cell gaps: (a) 5 μm, (b) 7 μm, (c) 8 μm and (d) 10 μm. BPLC: JC-BP01 at 25°C and λ = 550 nm.
are the spatial transmittance profiles of IPS-5/5 with cell gap d = 5, 7, 8, and 10 μm, respectively. As the cell gap increases, the light would be bent more toward the center of the electrode by the refraction effect due to its longer optical path. This explains why the IPS-5/5 with d = 10 μm (Fig. 8(d)) shows a slightly larger aperture ratio than the corresponding 7-μm cell (Fig. 8(b)). Nevertheless, the electric fields beyond the penetration regions are very weak and the BPLC in that region can be regarded as isotropic, so the light wouldn’t accumulate additional phase retardation and transmittance wouldn’t change although they have longer optical path. As a result, the VT curves are not critically dependent on the cell gap as long as the cell gap is larger than the field’s penetration depth. Moreover, the cell gap effect can be used to explain the above mentioned lower aperture ratio of IPS-10/10 because its larger electrode dimension.

3.4 Saturated birefringence and saturation field effects

A larger saturated birefringence Δns not only helps boost the Kerr constant [2

2. S. W. Choi, S. Yamamoto, Y. Haseba, H. Higuchi, and H. Kikuchi, “Optically isotropic-nanostructured liquid crystal composite with high Kerr constant,” Appl. Phys. Lett. 92(4), 043119 (2008). [CrossRef]

] but also makes direct impact on the electro-optics due to the refraction effect. Based on JC-BP01, Fig. 9(a)
Fig. 9 Simulated VT curves of IPS-2/4 using BPLCs with (a) different Δns but same Es = 4.05 V/μm, and (b) different Es but same Δns = 0.154 at 25°C and λ = 550 nm. Red dashed lines: JC-BP01.
shows the simulated VT curves of IPS-2/4 with different Δns while keeping Es unchanged (Es = 4.05 V/μm). The red dashed lines represent JC-BP01. As Δns increases, the peak transmittance increases while on-state voltage decreases. For a BPLC with higher Δns, according to Eq. (2), the refractive index difference between neighboring layers would increase and the light would bend more. Thus, the light would propagate at a larger angle with respect to the optical axis. Moreover, a higher Δns helps enhance phase retardation. These two factors combine together to result in a higher transmittance and reduced dead zones.

Figure 9(b) shows how Es affects the VT curves of IPS-2/4 based on JC-BP01. It’s clearly shown that as Es increases the on-state voltage also increases while peak transmittance remains unchanged. This indicates that Es only determines the voltage where the BPLC reaches its Δns, but the maximum induced Δn still remains unchanged at the on-state voltage.

Therefore, in IPS-BPLC structures a larger Δns helps reduce the operation voltage and enhance the transmittance, not only from increasing the Kerr constant on material side but also from stronger refraction effect in the cell. A smaller Es is effective in lowering operation voltage but doesn’t affect the peak transmittance. In order to achieve low voltage while keeping high transmittance, we should boost Δns while keeping Es low.

3.5 Protruded electrodes

Based on the discussion above, we can enhance the transmittance by increasing the l/w ratio of an IPS structure. The reasons are twofold: 1) a larger l/w ratio leads to smaller dead zone area, and 2) it increases the field’s penetration depth. However, the major tradeoff is increased voltage because of the wider electrode gap. An effective way to overcome this problem is to employ protrusion electrodes [21

21. L. Rao, Z. Ge, S. T. Wu, and S. H. Lee, “Low voltage blue-phase liquid crystal displays,” Appl. Phys. Lett. 95(23), 231101 (2009). [CrossRef]

, 32

32. S. Yoon, G. H. Yang, P. Nayek, H. Jeong, S. H. Lee, S. H. Hong, H. J. Lee, and S. T. Shin, “Study on the light leakage mechanism of a blue phase liquid crystal cell with oblique interfaces,” J. Phys. D Appl. Phys. 45(10), 105304 (2012). [CrossRef]

], which enable the horizontal electric fields to penetrate deeply into the bulk LC layer. The detailed performance depends on the protrusion height and the l/w ratio.

To investigate the influence of refraction effect on the transmittance of protruded IPS cell, we used rectangular protruded electrodes in our simulations, as depicted in Fig. 10(a)
Fig. 10 (a) Cell structure and parameter definitions of protrusion IPS-BPLC, and simulated VT curves of the protrusion IPS-BPLC with different electrode dimensions employing (b) JC-BP01 and (c) JC-BP06 (25°C and λ = 550 nm).
. Shown in Figs. 10(b) and 10(c) are the simulated VT curves of planar and protruded IPS cells with protrusion height h’ = 1 µm and 2 µm for IPS-2/4 and IPS-3/6 employing two different BPLC materials: JC-BP01 (Δns = 0.154, Es = 4.05 V/μm) and JC-BP06 (Δns = 0.09, Es = 2.2 V/μm). Compared to a planar IPS, the protruded IPS shows about the same transmittance because the protrusion electrodes mainly generate electric fields in the electrode gaps and don’t change the field distribution above the electrodes. But due to the dimension effect described above, IPS-3/6 exhibits a slightly lower transmittance than IPS-2/4 with the same protrusion height. From the comparison of these curves, we find that by enhancing the protrusion height the operation voltage can be reduced dramatically. However, high-protrusion electrodes are more difficult to make with current fabrication technique. On the other hand, JC-BP06 shows a higher voltage than JC-BP01 for planar IPS-2/4 structure (40V vs. 34V). This is because JC-BP06 has a relatively small induced birefringence (Δns = 0.09) and IPS-2/4 has a relatively shallow penetration depth. Thus, it requires a higher operation voltage to reach the peak transmittance. However, when we utilize protrusion electrodes, the relatively small Δns of JC-BP06 can be compensated with the increased penetration depth. Therefore, with the same device structure JC-BP06 exhibits a lower operation voltage than JC-BP01 because JC-BP06 has a larger Kerr constant. As Fig. 10(c) shows, for IPS-2/4 with h’ = 2 μm its operation voltage is reduced to 10V while keeping 80% transmittance. This is an important milestone to enable BPLC to be addressed by a-Si TFT technology. To boost transmittance further, we can increase the birefringence of the BPLC material. For example as Fig. 10(b) shows, JC-BP01 has a higher induced birefringence so that its peak transmittance can reach 83%.

3.6 Etched electrodes

In contrast to protruded electrodes, etching is another option to lower the operation voltage [28

28. L. Rao, H. C. Cheng, and S. T. Wu, “Low voltage blue-phase LCDs with double-penetrating fringe fields,” J. Disp. Technol. 6(8), 287–289 (2010). [CrossRef]

, 33

33. C. Y. Tsai, T. J. Tseng, L. Y. Wang, F. C. Yu, Y. F. Lan, P. J. Huang, S. Y. Lin, K. M. Chen, B. S. Tseng, C. W. Kuo, C. H. Lin, J. K. Lu, and N. Sugiura, “Polymer-stabilized blue phase liquid crystal displays applying novel groove cell structure,” SID Int. Symp. Digest Tech. Papers 44, 182–183 (2013). [CrossRef]

]. The cell structure of an etched-IPS is depicted in Fig. 11(a)
Fig. 11 (a) Cell structure and parameter definitions of etched-IPS, and simulated VT curves of etched-IPS cells with different electrode dimensions: (b) l/w = 2 and (c) l/w = 3, 4 and 5 using JC-BP06 (25°C and λ = 550 nm).
. In an etched-IPS structure, say IPS-2/4, the etching takes place along the 4-µm electrode gaps. As a result, the fringe fields are above and under the 2-µm ITO electrodes. These doubled penetrating fringe fields help to reduce the operation voltage. Similar to protruded IPS, etched-IPS using JC-BP06 also shows lower operation voltage than that using JC-BP01 since the bottom fringe fields provide an extra phase retardation to compensate for the relatively small Δns of JC-BP06. Therefore, in our simulation we use JC-BP06 as an example to demonstrate the effectiveness of this etched-electrode approach.

Figure 11(b) compares the simulated VT curves of IPS-2/4 structure with etching depth h increasing from 0, 0.5, 1, 2 to 4 µm. As the etching depth increases, the operation voltage decreases rapidly and then gradually saturates. With h~2 μm, the operation voltage is reduced to ~10 Vrms. This saturation phenomenon has been reported in [28

28. L. Rao, H. C. Cheng, and S. T. Wu, “Low voltage blue-phase LCDs with double-penetrating fringe fields,” J. Disp. Technol. 6(8), 287–289 (2010). [CrossRef]

], which originates from the finite penetration depth of the electric field. Hence, when the etching depth is larger than the penetration depth, the operation voltage does not decrease anymore. This feature makes the etched-electrode IPS easy to fabricate since we don’t need to control the etching depth very precisely as long as it’s larger than the penetration depth. Similar to the protruded IPS, the etched electrodes have minor influence on the transmittance since the electric field distribution on the top of the electrode is not changed.

To improve transmittance, we can increase the l/w ratio, such as IPS-2/6 or −2/8, while still using the etched electrodes. Similar to the etched IPS-2/4, both etched IPS-2/6 and −2/8 show the saturation effect, but at a deeper etching depth (4 µm for IPS-2/6 and 6 µm for IPS-2/8), due to their larger penetration depths. Figure 11(c) includes the simulated VT curves of etched IPS-2/6 and IPS-2/8 cells with 4-µm and 6-µm etching depths, respectively. Compared to IPS-2/4, although their transmittance can exceed 80% due to their larger l/w ratios, a tradeoff is increased voltage. As nanotechnology advances, smaller electrode dimension could be fabricated. If we can reduce the electrode width to 1 µm, then the operation voltage as low as 8V while keeping transmittance >80% can be achieved, as Fig. 11(c) shows.

In addition to optimizing device structures, continuous development on large Kerr constant materials [25

25. M. Wittek, N. Tanaka, D. Wilkes, M. Bremer, D. Pauluth, J. Canisius, A. Yeh, R. Yan, K. Skjonnemand, and M. Klasen-Memmer, “New materials for polymer-stabilized blue phase,” SID Int. Symp. Digest Tech. Papers 43, 25–28 (2012).

, 26

26. Y. Haseba, S. Yamamoto, K. Sago, A. Takata, and H. Tobata, “Low-voltage polymer-stabilized blue-phase liquid crystals,” SID Int. Symp. Digest Tech. Papers 44, 254–257 (2013). [CrossRef]

] would help to further reduce the operation voltage. From Gerber’s model [34

34. P. R. Gerber, “Electro-optical effects of a small-pitch blue-phase system,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 116(3-4), 197–206 (1985). [CrossRef]

], Kerr constant is mainly determined by the Δn⋅Δε of the LC host, assuming the pitch length and average elastic constant remain the same. The two BPLC materials we used in simulations are JC-BP01 (Δns = 0.154, Es = 4.05 V/μm) and JC-BP06 (Δns = 0.09, Es = 2.2 V/μm). JC-BP01 has a reasonably large Δns, but its Es is too high, i.e., Δε is not large enough. On the contrary, although JC-BP06 has a large Δε, its Δns is too low. For future material improvement, we should not only emphasize on increasing the Kerr constant, but also need to pay attention to the individual Δn and Δε values.

3.7 IPS-BPLC with a single gamma curve

In an IPS-BPLC cell, the phase retardation depends on the wavelength and induced birefringence. The latter in turn depends on the Kerr constant, which decreases as the wavelength increases [35

35. M. Z. Jiao, J. Yan, and S. T. Wu, “Dispersion relation on the Kerr constant of a polymer-stabilized optically isotropic liquid crystal,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 83(4), 041706 (2011). [CrossRef] [PubMed]

]. Therefore, the VT curves of an IPS-BPLC depend on the wavelength, as shown in Fig. 12(a)
Fig. 12 (a) Simulated VT curves for RGB wavelengths. BPLC cell: etched IPS-2/4 with h = 2.5 μm and JC-BP06, and (b) Simulated VT curves for IPS-2/3.6 (R), −2/4 (G), −2/5.2 (B) with h = 2.5 μm and d = 7.5 μm.
, and three gamma curves are required to drive the red (R = 650 nm), green (G = 550 nm) and blue (B = 450 nm) sub-pixels, which increases the complexity of driving electronics.

To solve this problem, we propose following method to achieve single gamma curve for IPS-BPLC. Based on the discussion above, we know that the on-state voltage of an IPS-BPLC can be adjusted by changing the l/w ratios. Therefore, in order to achieve overlapped gamma curves for RGB colors, we can simply vary the electrode gap (l) for RGB sub-pixels while keeping the same electrode width (w) and etching depth (h). Similar approach of adjusting the electrode gap has been reported in [36

36. Y. Li, M. Z. Jiao, and S. T. Wu, “Transflective display using a polymer-stabilized blue-phase liquid crystal,” Opt. Express 18(16), 16486–16491 (2010). [CrossRef] [PubMed]

] to balance the optical phase retardation between transmissive and reflective regions for transflective displays. Here, let us continue to use IPS-2/4 with h = 2.5 μm and d = 7.5 μm for the green wavelength to illustrate the design principles. From Fig. 12(a), we need to lower the on-state voltage for the red color. Thus, we choose a smaller electrode gap, say l = 3.6 μm, while still keeping h = 2.5 μm and d = 7.5 μm. On the other hand, we increase l to 5.2 μm for the blue wavelength. Figure 12(b) shows the normalized VT curves for the unequally-spaced IPS cell. Indeed, the RGB gamma curves overlap fairly well.

4. Conclusion

We propose a numerical model to account for the refraction effect in an IPS-BPLC cell. Our model agrees with experiment quite well. Based on this model, different effects, such as electrode dimension, cell gap, saturated birefringence and saturation electric field, on the electro-optics of IPS-BPLC cells are investigated in a more insightful way. In addition, we use the refraction model to study the electro-optics of different IPS structures, including planar, protruded electrodes and etched electrodes. An IPS-BPLC with operation voltage <10V and transmittance >80% can be achieved. Moreover, IPS-BPLC with single gamma curve can be achieved by optimizing the l/w ratios for RGB sub-pixels.

Acknowledgments

The authors are indebted to Industrial Technology Research Institute (ITRI), Taiwan, for the financial support.

References and links

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H. Kikuchi, M. Yokota, Y. Hisakado, H. Yang, and T. Kajiyama, “Polymer-stabilized liquid crystal blue phases,” Nat. Mater. 1(1), 64–68 (2002). [CrossRef] [PubMed]

2.

S. W. Choi, S. Yamamoto, Y. Haseba, H. Higuchi, and H. Kikuchi, “Optically isotropic-nanostructured liquid crystal composite with high Kerr constant,” Appl. Phys. Lett. 92(4), 043119 (2008). [CrossRef]

3.

Y. Hisakado, H. Kikuchi, T. Nagamura, and T. Kajiyama, “Large electro‐optic Kerr effect in polymer‐stabilized liquid‐crystalline blue phases,” Adv. Mater. 17(1), 96–98 (2005). [CrossRef]

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J. Yan, L. Rao, M. Jiao, Y. Li, H. C. Cheng, and S. T. Wu, “Polymer-stabilized optically isotropic liquid crystals for next-generation display and photonics applications,” J. Mater. Chem. 21(22), 7870–7877 (2011). [CrossRef]

5.

L. Rao, Z. Ge, S. Gauza, K. M. Chen, and S. T. Wu, “Emerging liquid crystal displays based on the Kerr effect,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 527(1), 186–198 (2010). [CrossRef]

6.

L. Rao, J. Yan, and S. T. Wu, “Prospects of emerging polymer-stabilized blue-phase liquid-crystal displays,” J. Soc. Inf. Disp. 18(11), 954–959 (2010). [CrossRef]

7.

Y. H. Lin, H. S. Chen, H. C. Lin, Y. S. Tsou, H. K. Hsu, and W. Y. Li, “Polarizer-free and fast response microlens arrays using polymer-stabilized blue phase liquid crystals,” Appl. Phys. Lett. 96(11), 113505 (2010). [CrossRef]

8.

J. Yan, Y. Li, and S. T. Wu, “High-efficiency and fast-response tunable phase grating using a blue phase liquid crystal,” Opt. Lett. 36(8), 1404–1406 (2011). [CrossRef] [PubMed]

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S. T. Wu and D. K. Yang, Fundamentals of Liquid Crystal Devices (John Wiley & Sons, 2006).

10.

D. Xu, L. Rao, C. D. Tu, and S. T. Wu, “Nematic liquid crystal display with submillisecond grayscale response time,” J. Disp. Technol. 9(2), 67–70 (2013). [CrossRef]

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Y. Chen, F. Peng, and S. T. Wu, “Submillisecond-response vertical-aligned liquid crystal for color sequential projection displays,” J. Disp. Technol. 9(2), 78–81 (2013). [CrossRef]

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Y. Chen, J. Yan, J. Sun, S. T. Wu, X. Liang, S. H. Liu, P. J. Hsieh, K. L. Cheng, and J. W. Shiu, “A microsecond-response polymer-stabilized blue phase liquid crystal,” Appl. Phys. Lett. 99(20), 201105 (2011). [CrossRef]

13.

H. Haseba and S. Kobayashi, “A full-color sequential LCD using modulated backlight,” SID Int. Symp. Digest Tech. Papers 16, 81–83 (1985).

14.

J. H. Lee, X. Zhu, and S. T. Wu, “Novel color-sequential transflective liquid crystal displays,” J. Disp. Technol. 3(1), 2–8 (2007). [CrossRef]

15.

S. Gauza, X. Zhu, W. Piecek, R. Dabrowski, and S. T. Wu, “Fast switching liquid crystals for color-sequential LCDs,” J. Disp. Technol. 3(3), 250–252 (2007). [CrossRef]

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Y. Liu, Y. F. Lan, H. Zhang, R. Zhu, D. Xu, C. Y. Tsai, J. K. Lu, N. Sugiura, Y. C. Lin, and S. T. Wu, “Optical rotatory power of polymer-stabilized blue phase liquid crystals,” Appl. Phys. Lett. 102(13), 131102 (2013). [CrossRef]

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Z. Ge, S. Gauza, M. Jiao, H. Xianyu, and S. T. Wu, “Electro-optics of polymer-stabilized blue phase liquid crystal displays,” Appl. Phys. Lett. 94(10), 101104 (2009). [CrossRef]

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Z. Ge, L. Rao, S. Gauza, and S. T. Wu, “Modeling of blue phase liquid crystal displays,” J. Disp. Technol. 5(7), 250–256 (2009). [CrossRef]

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H. C. Cheng, J. Yan, T. Ishinabe, and S. T. Wu, “Vertical field switching for blue-phase liquid crystal devices,” Appl. Phys. Lett. 98(26), 261102 (2011). [CrossRef]

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H. C. Cheng, J. Yan, T. Ishinabe, N. Sugiura, C. Y. Liu, T. H. Huang, C. Y. Tsai, C. H. Lin, and S. T. Wu, “Blue-phase liquid crystal displays with vertical field switching,” J. Disp. Technol. 8(2), 98–103 (2012). [CrossRef]

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L. Rao, Z. Ge, S. T. Wu, and S. H. Lee, “Low voltage blue-phase liquid crystal displays,” Appl. Phys. Lett. 95(23), 231101 (2009). [CrossRef]

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K. M. Chen, S. Gauza, H. Xianyu, and S. T. Wu, “Hysteresis effects in blue-phase liquid crystals,” J. Disp. Technol. 6(8), 318–322 (2010). [CrossRef]

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L. Rao, J. Yan, S. T. Wu, S. Yamamoto, and Y. Haseba, “A large Kerr constant polymer-stabilized blue phase liquid crystal,” Appl. Phys. Lett. 98(8), 081109 (2011). [CrossRef]

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Y. Chen, D. Xu, S. T. Wu, S. Yamamoto, and Y. Haseba, “A low voltage and submillisecond-response polymer-stabilized blue phase liquid crystal,” Appl. Phys. Lett. 102(14), 141116 (2013). [CrossRef]

25.

M. Wittek, N. Tanaka, D. Wilkes, M. Bremer, D. Pauluth, J. Canisius, A. Yeh, R. Yan, K. Skjonnemand, and M. Klasen-Memmer, “New materials for polymer-stabilized blue phase,” SID Int. Symp. Digest Tech. Papers 43, 25–28 (2012).

26.

Y. Haseba, S. Yamamoto, K. Sago, A. Takata, and H. Tobata, “Low-voltage polymer-stabilized blue-phase liquid crystals,” SID Int. Symp. Digest Tech. Papers 44, 254–257 (2013). [CrossRef]

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M. Kim, M. S. Kim, B. G. Kang, M. K. Kim, S. Yoon, S. H. Lee, Z. Ge, L. Rao, S. Gauza, and S. T. Wu, “Wall-shaped electrodes for reducing the operation voltage of polymer-stabilized blue phase liquid crystal displays,” J. Phys. D Appl. Phys. 42(23), 235502 (2009). [CrossRef]

28.

L. Rao, H. C. Cheng, and S. T. Wu, “Low voltage blue-phase LCDs with double-penetrating fringe fields,” J. Disp. Technol. 6(8), 287–289 (2010). [CrossRef]

29.

M. Z. Jiao, Y. Li, and S. T. Wu, “Low voltage and high transmittance blue-phase liquid crystal displays with corrugated electrodes,” Appl. Phys. Lett. 96(1), 011102 (2010). [CrossRef]

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K. M. Chen, J. Yan, S. T. Wu, Y. P. Chang, C. C. Tsai, and J. W. Shiu, “Electrode dimension effects on blue-phase liquid crystal displays,” J. Disp. Technol. 7(7), 362–364 (2011). [CrossRef]

31.

J. Yan, H. C. Cheng, S. Gauza, Y. Li, M. Jiao, L. Rao, and S. T. Wu, “Extended Kerr effect of polymer-stabilized blue-phase liquid crystals,” Appl. Phys. Lett. 96(7), 071105 (2010). [CrossRef]

32.

S. Yoon, G. H. Yang, P. Nayek, H. Jeong, S. H. Lee, S. H. Hong, H. J. Lee, and S. T. Shin, “Study on the light leakage mechanism of a blue phase liquid crystal cell with oblique interfaces,” J. Phys. D Appl. Phys. 45(10), 105304 (2012). [CrossRef]

33.

C. Y. Tsai, T. J. Tseng, L. Y. Wang, F. C. Yu, Y. F. Lan, P. J. Huang, S. Y. Lin, K. M. Chen, B. S. Tseng, C. W. Kuo, C. H. Lin, J. K. Lu, and N. Sugiura, “Polymer-stabilized blue phase liquid crystal displays applying novel groove cell structure,” SID Int. Symp. Digest Tech. Papers 44, 182–183 (2013). [CrossRef]

34.

P. R. Gerber, “Electro-optical effects of a small-pitch blue-phase system,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 116(3-4), 197–206 (1985). [CrossRef]

35.

M. Z. Jiao, J. Yan, and S. T. Wu, “Dispersion relation on the Kerr constant of a polymer-stabilized optically isotropic liquid crystal,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 83(4), 041706 (2011). [CrossRef] [PubMed]

36.

Y. Li, M. Z. Jiao, and S. T. Wu, “Transflective display using a polymer-stabilized blue-phase liquid crystal,” Opt. Express 18(16), 16486–16491 (2010). [CrossRef] [PubMed]

OCIS Codes
(160.3710) Materials : Liquid crystals
(230.3720) Optical devices : Liquid-crystal devices

ToC Category:
Optical Devices

History
Original Manuscript: September 5, 2013
Revised Manuscript: September 30, 2013
Manuscript Accepted: October 1, 2013
Published: October 8, 2013

Citation
Daming Xu, Yuan Chen, Yifan Liu, and Shin-Tson Wu, "Refraction effect in an in-plane-switching blue phase liquid crystal cell," Opt. Express 21, 24721-24735 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-21-24721


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References

  1. H. Kikuchi, M. Yokota, Y. Hisakado, H. Yang, and T. Kajiyama, “Polymer-stabilized liquid crystal blue phases,” Nat. Mater.1(1), 64–68 (2002). [CrossRef] [PubMed]
  2. S. W. Choi, S. Yamamoto, Y. Haseba, H. Higuchi, and H. Kikuchi, “Optically isotropic-nanostructured liquid crystal composite with high Kerr constant,” Appl. Phys. Lett.92(4), 043119 (2008). [CrossRef]
  3. Y. Hisakado, H. Kikuchi, T. Nagamura, and T. Kajiyama, “Large electro‐optic Kerr effect in polymer‐stabilized liquid‐crystalline blue phases,” Adv. Mater.17(1), 96–98 (2005). [CrossRef]
  4. J. Yan, L. Rao, M. Jiao, Y. Li, H. C. Cheng, and S. T. Wu, “Polymer-stabilized optically isotropic liquid crystals for next-generation display and photonics applications,” J. Mater. Chem.21(22), 7870–7877 (2011). [CrossRef]
  5. L. Rao, Z. Ge, S. Gauza, K. M. Chen, and S. T. Wu, “Emerging liquid crystal displays based on the Kerr effect,” Mol. Cryst. Liq. Cryst. (Phila. Pa.)527(1), 186–198 (2010). [CrossRef]
  6. L. Rao, J. Yan, and S. T. Wu, “Prospects of emerging polymer-stabilized blue-phase liquid-crystal displays,” J. Soc. Inf. Disp.18(11), 954–959 (2010). [CrossRef]
  7. Y. H. Lin, H. S. Chen, H. C. Lin, Y. S. Tsou, H. K. Hsu, and W. Y. Li, “Polarizer-free and fast response microlens arrays using polymer-stabilized blue phase liquid crystals,” Appl. Phys. Lett.96(11), 113505 (2010). [CrossRef]
  8. J. Yan, Y. Li, and S. T. Wu, “High-efficiency and fast-response tunable phase grating using a blue phase liquid crystal,” Opt. Lett.36(8), 1404–1406 (2011). [CrossRef] [PubMed]
  9. S. T. Wu and D. K. Yang, Fundamentals of Liquid Crystal Devices (John Wiley & Sons, 2006).
  10. D. Xu, L. Rao, C. D. Tu, and S. T. Wu, “Nematic liquid crystal display with submillisecond grayscale response time,” J. Disp. Technol.9(2), 67–70 (2013). [CrossRef]
  11. Y. Chen, F. Peng, and S. T. Wu, “Submillisecond-response vertical-aligned liquid crystal for color sequential projection displays,” J. Disp. Technol.9(2), 78–81 (2013). [CrossRef]
  12. Y. Chen, J. Yan, J. Sun, S. T. Wu, X. Liang, S. H. Liu, P. J. Hsieh, K. L. Cheng, and J. W. Shiu, “A microsecond-response polymer-stabilized blue phase liquid crystal,” Appl. Phys. Lett.99(20), 201105 (2011). [CrossRef]
  13. H. Haseba and S. Kobayashi, “A full-color sequential LCD using modulated backlight,” SID Int. Symp. Digest Tech. Papers 16, 81–83 (1985).
  14. J. H. Lee, X. Zhu, and S. T. Wu, “Novel color-sequential transflective liquid crystal displays,” J. Disp. Technol.3(1), 2–8 (2007). [CrossRef]
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