OSA's Digital Library

Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 11, Iss. 10 — May. 19, 2003
  • pp: 1197–1202
« Show journal navigation

Optical modes for direct-view single-polarizer reflective BTN-LCD

Jesper Osterman and Kent Skarp  »View Author Affiliations


Optics Express, Vol. 11, Issue 10, pp. 1197-1202 (2003)
http://dx.doi.org/10.1364/OE.11.001197


View Full Text Article

Acrobat PDF (195 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

Optical modes for the surface-controlled direct-view single-polarizer reflective BTN (bistable twisted nematic) LCD (liquid-crystal display) are derived with the Jones matrix method. The modes show excellent brightness and high contrast ratio. By use of a quarter-wave retardation film in the optical configuration, the contrast can be increased.

© 2003 Optical Society of America

1. Introduction

Direct-view single-polarizer reflective liquid-crystal displays (LCDs)—in particular, bistable twisted nematic modes (BTN)—are important candidates for next-generation mobile LCD applications. In direct-view reflective displays, ambient light is used to read the information; hence the display does not require any backlight, leading to reduced power consumption and panel weight. Furthermore, reflective displays have outstanding sunlight readability. The single-polarizer reflective LCD is composed of a polarizer, a LC cell, and a reflector as shown in Fig. 1. Owing to the elimination of the rear polarizer that is present in conventional reflective LCDs, the brightness can be increased. Considering a typical high-performance dichroic sheet polarizer with transmittance T =0.90 and T =0.0003 for light polarized parallel and perpendicular to the transmission axes used in the single-polarizer device, the maximum reflectance will be R max=0.41. The corresponding throughput of the double-polarizer configuration is limited to R max=0.33. Another advantage of the single-polarizer configuration is that the parallax problem (double image) that degrades the resolution of the display can be reduced or, if the reflector is placed inside the cell, even eliminated. In recent years, surface-controlled BTN devices in which the two different director configurations differ by a π-twist have been demonstrated. The switching of such devices involves breaking of the anchoring on one of the substrates. Dozov et al. have successfully developed a device in which 0- and π-twisted textures are switched by polar anchor breaking [1

1. I. Dozov, P. Martinot-Lagarde, S. Lamarque-Forget, D. Stoenescu, J. Angelé, R. Vercelletto, B. Pécout, and A. Bossier, “Recent Improvements of bistable nematic displays switched by anchor breaking (BiNem®),” SID Symp. Dig. 32, 224–227 (2001). [CrossRef]

]. Another technique that uses a special three-terminal structure in which a strong horizontal field produces an azimuthal anchoring breaking to realize switching between ϕ and ϕ+π twisted states has been proposed by Guo et al. [2

2. J. X. Guo, Z. G. Meng, M. Wong, and H. S. Kwok, “Three-terminal bistable twisted nematic liquid crystal displays,” Appl. Phys. Lett. 77, 3716–3718 (2000). [CrossRef]

]. Compared with the traditional ϕ, ϕ+2π BTN [3

3. D. W. Berreman and W. R. Heffner, “New bistable cholesteric liquid crystal display,” Appl. Phys. Lett. 37, 109–111 (1980). [CrossRef]

], an intermediate twist state of ϕ+π/2 is not possible in surface-controlled devices. This fact makes these devices truly bistable. Although the anchoring properties and the switching behavior of the surface-controlled BTN have been studied [4

4. M. Giocondo, I. Llelidis, I. Dozov, and G. Durand, “Write and erase mechanism of surface controlled bistable nematic pixel,” Eur. Phys. J. AP 5, 227–230 (1999). [CrossRef]

, 5

5. T. Qian, Z. Xie, H. S. Kwok, and P. Sheng, “Dynamic flow, broken surface anchoring and switching bistability in three-terminal twisted nematic liquid crystal displays,” J. Appl. Phys. 90, 3121–3123 (2001). [CrossRef]

], the optical properties have not been thoroughly investigated. The purpose of this paper is to present optical modes for the direct-view single polarizer ϕ, ϕ+π reflective BTN-LCD, both with and without retardation compensation present in the optical configuration.

Fig. 1. Geometry of the direct-view single-polarizer reflective BTN-LCD.

2. Fundamental equations

According to the 2×2 Jones matrix method, the reflectance of the direct-view single-polarizer reflective BTN for normal incident light is given by

R=VM˜MV2,
(1)

where

M=(cosXiΓsinX2XϕsinXXϕsinXXcosX+iΓsinX2X),
(2)

and

V=(cosαsinα),V=(cosαsinα).
(3)

In the equations above, M is the Jones matrix of the LC cell; V and V’ are the incident and reflected Jones vectors, respectively; and the tilde (~) indicates a transpose operation giving the Jones matrix of the LC cell for light after the reflection, traveling in the opposite direction. After a few steps of matrix algebra the reflectance can be written as

R=12{[cos2X+ϕ2sin2XX2Γ24sin2XX2]2+[ΓsinXX(cos2αcosX+sin2αϕsinXX)]2},
(4)

where X=ϕ2+(Γ2)2 , Γ=2πΔndλ , ϕ is the twist angle of the LC cell, Δn is the birefringence of the LC material, d is the cellgap, λ is the wavelength of the incident light, and α is the azimuth angle between the transmission axis of the polarizer and the local LC director at the entrance side. The factor ½ has to be added because the incident light is assumed to be unpolarized.

3. Possible optical modes

3.1 General twist angles

The parameters that determine the optical properties of the single-polarizer reflective BTN for a given wavelength are the twist angle ϕ, the retardation Δnd, and the polarizer orientation angle α. Differentiating Eq. (4) with respect to the polarizer angle α yields equations for maximum and minimum reflectance. By solving these equations for ϕ1 and ϕ21+π with λ=550 nm, several modes with R max=0.50 and R min=0 can be found. Although the contrast ratio of these modes is infinite for the wavelength used in the calculations, the luminous reflectance given by

RLum=380780R(α,ϕ,Γ)f(λ)D(λ)dλ380780f(λ)D(λ)dλ
(5)

should be considered in evaluating these modes for real display purposes. In Eq. (5), f(λ) is the photopic response of the human eye and D(λ) is the illuminant spectral distribution, here taken as equal energy for all wavelengths. The luminous contrast ratio is then calculated as the ratio RLum2)/RLum1), while the brightness is given by RLum2). Table 1 lists the three modes derived with theoretical luminous contrast ratio >15. These modes are in agreement with the ones derived by Guo et al using a Mueller matrix approach [6

6. J. X. Guo and H. S. Kwok, “Optical Optimisation of Surface-Controlled Bistable Twisted Nematic Liquid Crystal Displays,” in Proceedings of the 20th IDRC20, 241–243 (2000).

].

Table 1. Optical Modes with Luminous Contrast Ratio >15 for General Twist Angles

table-icon
View This Table
| View All Tables

The color dispersion of the two stable twist states of mode 1-1 is shown in Fig. 2. This mode shows perfect brightness and theoretical luminous contrast ratio of 71.6. Common for all three modes are that they all possess excellent brightness, higher than the conventional TN Gooch and Tarry modes. However, the contrast ratio decreases with increasing retardation value, owing to increased leakage of light in the dark state.

Fig. 2. Calculated reflectance spectra of the two stable twist states (ϕ1=-5.7° dashed and ϕ2=174.3° solid) of mode 1-1.

3.2 Fixed twist angles (0°, 180°)

A second group of optical modes were found by plotting the luminous contrast ratio as a function of the polarizer angle, α, and the retardation, Δnd, for the two fixed twist angles 0° and 180°. Two modes were found with contrast ratio > 10, both listed in Table 2. In mode 2-1, the dark state is given by the untwisted state, whereas the twisted state gives the dark state of mode 2-2. Both modes exhibit high brightness. The configuration of the optical parameters of these two modes are however similar to those of modes 1-1 and 1-3, respectively, and can be considered as nonoptimized versions of those modes.

Table 2. Optical Modes with Luminous Contrast Ratio > 10 for Fixed Twist Angles 0° and 180°

table-icon
View This Table
| View All Tables

4. Retardation compensation

The optical modes presented this far all experience limited contrast ratio in response to leakage of light in the dark state. This leakage can be reduced by introduction of a simple uniaxial quarter-wave retardation film into the optical configuration. Two different geometries will be considered: one in which the retardation film is located in the inner position, between the LC cell and the reflector, and one in which there the retardation film is located in the outer position, between the LC cell and the polarizer.

4.1 Inner retardation compensation

The reflectance of the inner retardation compensation geometry is given by

R=VM~W~WMV2,
(6)

where

M=(cosϕsinϕsinϕcosϕ)(cosXiΓsinX2XϕsinXXϕsinXXcosX+iΓsinX2X),
(7)

and

W=(cosψsinψsinψcosψ)(eiπ4eiπ4)(cosψsinψsinψcosψ).
(8)

Fig. 3. Reflectance spectra of the two stable twist states (0° dashed and 180° solid) with inner quarter-wave retardation film for α=0° and ψ=45° with Δnd=558 nm.

4.2 Outer retardation compensation

The reflectance of the outer retardation compensation geometry is given by

R=VWMM˜W˜V2.
(9)

By again plotting the reflectance of the two stable twist states as a function of the retardation value for α=0° and ψ=45°, possible optical modes can be identified. It was found that for Δnd=137.5 nm the luminous contrast ratio of the possible mode is 425, whereas the corresponding brightness value is 0.493. This mode is however not perfectly optimized. When plotting the reflectance as a function of the polarizer angle and the retardation value of the LC cell, it was found that by adjusting the polarizer angle to -1.3°, the theoretical contrast ratio can be increased to >7000, while the bright state with R=0.492, is almost unaffected by the change. The dispersion of this mode can be seen in Fig. 4.

Fig. 4. Reflectance spectra of the two stable twist states (0° dashed and 180° solid) with outer quarter-wave retardation film for α=-1.3° and ψ=45° with Δnd=137.5 nm.

5. Conclusions

In this study, optical modes for the surface-controlled reflective single-polarizer BTN-LCD have been derived with the Jones matrix method. The modes show excellent brightness and high contrast ratio. Furthermore, we present results for optical configurations employing an integrated quarter-wave retardation film to increase the contrast ratio by preventing spectral leakage of light. The results of this investigation will increase the understanding of the optical properties of the direct-view single-polarizer reflective surface-controlled (ϕ, ϕ+π) BTN and will be valuable in considering this type of device for practical applications. In subsequent papers we will evaluate the viewing angle properties and be able to demonstrate experimentally how to realize these new optical modes. Owing to the in-plane direction structure of both stable twist states, the device is anticipated to show wide viewing angle properties.

References and links

1.

I. Dozov, P. Martinot-Lagarde, S. Lamarque-Forget, D. Stoenescu, J. Angelé, R. Vercelletto, B. Pécout, and A. Bossier, “Recent Improvements of bistable nematic displays switched by anchor breaking (BiNem®),” SID Symp. Dig. 32, 224–227 (2001). [CrossRef]

2.

J. X. Guo, Z. G. Meng, M. Wong, and H. S. Kwok, “Three-terminal bistable twisted nematic liquid crystal displays,” Appl. Phys. Lett. 77, 3716–3718 (2000). [CrossRef]

3.

D. W. Berreman and W. R. Heffner, “New bistable cholesteric liquid crystal display,” Appl. Phys. Lett. 37, 109–111 (1980). [CrossRef]

4.

M. Giocondo, I. Llelidis, I. Dozov, and G. Durand, “Write and erase mechanism of surface controlled bistable nematic pixel,” Eur. Phys. J. AP 5, 227–230 (1999). [CrossRef]

5.

T. Qian, Z. Xie, H. S. Kwok, and P. Sheng, “Dynamic flow, broken surface anchoring and switching bistability in three-terminal twisted nematic liquid crystal displays,” J. Appl. Phys. 90, 3121–3123 (2001). [CrossRef]

6.

J. X. Guo and H. S. Kwok, “Optical Optimisation of Surface-Controlled Bistable Twisted Nematic Liquid Crystal Displays,” in Proceedings of the 20th IDRC20, 241–243 (2000).

OCIS Codes
(230.3720) Optical devices : Liquid-crystal devices
(260.1180) Physical optics : Crystal optics

ToC Category:
Research Papers

History
Original Manuscript: March 26, 2003
Revised Manuscript: May 8, 2003
Published: May 19, 2003

Citation
Jesper Osterman and Kent Skarp, "Optical modes for direct-view single-polarizer reflective BTN-LCD," Opt. Express 11, 1197-1202 (2003)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-11-10-1197


Sort:  Journal  |  Reset  

References

  1. I. Dozov, P. Martinot-Lagarde, S. Lamarque-Forget, D. Stoenescu, J. Angelé, R. Vercelletto, B. Pécout, and A. Bossier, �??Recent improvements of bistable nematic displays switched by anchor breaking (BiNem.),�?? SID Symp. Dig. 32, 224-227 (2001). [CrossRef]
  2. J. X. Guo, Z. G. Meng, M. Wong, and H. S. Kwok, �??Three-terminal bistable twisted nematic liquid crystal displays,�?? Appl. Phys. Lett. 77, 3716-3718 (2000). [CrossRef]
  3. D. W. Berreman and W. R. Heffner, �??New bistable cholesteric liquid crystal display,�?? Appl. Phys. Lett. 37, 109-111 (1980). [CrossRef]
  4. M. Giocondo, I. Llelidis, I. Dozov, and G. Durand, �??Write and erase mechanism of surface controlled bistable nematic pixel,�?? Eur. Phys. J. AP 5, 227-230 (1999). [CrossRef]
  5. T. Qian, Z. Xie, H. S. Kwok, and P. Sheng, �??Dynamic flow, broken surface anchoring and switching bistability in three-terminal twisted nematic liquid crystal displays,�?? J. Appl. Phys. 90, 3121-3123 (2001). [CrossRef]
  6. J. X. Guo and H. S. Kwok, �??Optical Optimisation of Surface-Controlled Bistable Twisted Nematic Liquid Crystal Displays,�?? in Proceedings of the 20th IDRC 20, 241-243 (2000).

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1. Fig. 2. Fig. 3.
 
Fig. 4.
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited