Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-11-13
2004-07-20
Ngo, Huyen (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S096000, C349S098000, C349S113000, C349S117000, C349S177000
Reexamination Certificate
active
06765640
ABSTRACT:
TECHNICAL FIELD
The present invention relates to reflective liquid crystal devices and more particularly to reflective liquid crystal display device comprising a bistable twisted nematic (BTN) liquid crystal.
BACKGROUND ART
Reflective liquid crystal devices typically comprise a linear polariser and a mirror, with one or more retarders and a switchable liquid crystal element sandwiched between the polariser and the mirror. In a first state of the liquid crystal element, linearly polarised light passing through the polariser is reflected from the mirror and arrives back at the polariser with the same linear polarisation. Hence the reflected light is transmitted by the polariser and the device appears in the bright state. In a second state of the liquid crystal element, linearly polarised light is converted to have a circular polarisation such that upon reflection at the mirror the “handedness” of the circular polarisation is changed (i.e. from right to left or from left to right). Light arriving back at the polariser is arranged to have a polarisation angle 90° shifted from the axis of the polariser (either the transmission or the absorption axis of the polariser may be considered and both give identical results). Hence, the reflected light to not transmitted by the polariser and the device appears in the dark state. Reflective liquid crystal devices are attractive particularly for low power consumption applications.
GB9622733.5 describes a reflective liquld crystal display device comprising a polariser and a mirror between which are disposed several retarders. One of the retarders is a liquid crystal element whose optic axis is switchable so as to switch the device between a reflective state and a non-reflective state.
EP0018180 describes a liquld crystal cell comprising a cholesteric liquid crystal. The liquid crystal is bistable and can exist in either one of its two metastable states until specific stops are taken to cause a transition to the other metastable state. Energy is expended only when a transition occurs.
The article “Bistable Twisted Nematic Mode with One Polariser for Reflective Liquid Crystal Displays”, Kim, Yu & Lee, IDRC Asia Display 98, Seoul, Korea, p 763, describes a device having in sequence an input linear polariser, a quarter wave retarder, a BTN element, and a mirror.
The article “Reflective Bistable Twisted Nematic Liquid Crystal Display”, Xie & Kwok, Jpn J. Appl. Phys. Vol37, part 1, No. 5a (1998), p 2572, describes a device having an input polariser, a BTN mode and a reflector. The proposed device does not include any additional retarders and states that the contrast ratio measured is about 6:1.
WO98/48320 describes a reflective liquid crystal display device comprising a polariser and a mirror between which are disposed a half wave retarder, a quarter wave retarder, and a liquid crystal element.
Abstract 39.3 (published in the SID 1999 International Symposium, Seminar & Exhibition-Advance program, in advance of a conference to be held in San Jose, Calif. USA, May 16-21, 1999) titled “Reflective Single-Polariser Bistable Nematic LCD with Optimum Twist”, Y. J. Kim & J. S. Patel, describes a single-polariser reflective LCD having a bistable twisted nematic mode. The twist angles of the two bistable states are 63.6° and 423.6°.
The article “Fast bistable nematic display using monostable surface switching”, I. Dozov, M. Nobili and G. Durand, Appl. Phys. Lett. 70 (9), 3 Mar. 1997, describes a device having a two bistable states, namely a metastable uniform (untwisted) state and a half-turn (180°) twist state.
DISCLOSURE OF THE INVENTION
According to a first aspect of the present invention there is provided a reflective liquid crystal device comprising in sequence a linear polariser, a retarder arrangement comprising two retarders, and a reflector, wherein, in at least one state of the device, a first of said retarders acts to rotate linearly polarised light of wavelength &lgr;, and a second of the retarders acts to convert linealy polarised light of wavelength y&lgr; (where 0.7<y<1.3) to substantially circular polarised light, and wherein at least one of the said first and second retarders comprises a Bistable Twisted Nematic (BTN) liquid crystal.
The wavelength &lgr; is an operating wavelength of the reflective liquid crystal device and lies in the visible spectrum and is preferably in the range 400-700 nm, more preferably 420-600 nm, and more preferably still in the region 440-550 nm. Most preferably &lgr; is approximately 550 nm.
Preferably, the retarder comprises a BTN liquid crystal providing a retardation of n&lgr;/4.
According to a second aspect of the present invention there is provided a reflective liquid crystal device comprising in sequence a linear polariser, a retarder arrangement comprising two retarders, and a reflector, wherein a first of said retarders provides a retardation of substantially m&lgr;/2 and a second of the retarders provides a retardation of substantially n&lgr;/4 where m is an integer and n is an odd integer, and wherein at least one of the said first and second retarders comprises a Bistable Twisted Nematic (BTN) liquid crystal and is switchable between a first state in which the retarder provides a retardation of substantially m&lgr;/2 or n&lgr;/4 and a second state in which the retardation is substantially zero.
According to a third aspect of the present invention there is provided a reflective liquld crystal device comprising in sequence a linear polariser, a retarder arrangement comprising at least three retarders, and a reflector, wherein at least one of said retarders comprises a Bistable Twisted Nematic (BTN) liquid crystal and is switchable between first and second retardation states.
The wavelength &lgr; is an operating wavelength of the reflective liquid crystal device and lies in the visible spectrum and is preferably in the range 400-700 nm, more preferably 420-600 nm, and more preferably still in the region 440-550 nm. Most preferably &lgr; is approximately 550 nm.
Preferably, the retarder comprising a BTN liquid crystal providing a retardation in said first state of substantially m&lgr;/2 or n&lgr;/4 where m is an integer and n is an odd integer, and a retardation in said second state of substantially zero. The others of said retarders may provide a retardation of substantially m&lgr;/2 or n&lgr;/4.
“Optic axis” means slow optic axis.
REFERENCES:
patent: 6061042 (2000-05-01), Takahashi et al.
patent: 6104368 (2000-08-01), Bonnett et al.
patent: 6204904 (2001-03-01), Tillin et al.
patent: 6469768 (2002-10-01), Lee
patent: 2003/0128314 (2003-07-01), Dozov et al.
patent: 869470 (1998-10-01), None
patent: 231878 (1998-05-01), None
Acosta Elizabeth Jane
Tillin Martin David
Towler Michael John
Ngo Huyen
Renner , Otto, Boisselle & Sklar, LLP
Sharp Kabushiki Kaisha
LandOfFree
Reflective liquid crystal devices does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Reflective liquid crystal devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reflective liquid crystal devices will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3251850