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4 Opto-Electronics Review

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Antiferroelectric and V-shape liquid crystal on silicon microdisplays

100%

Otón J. M. , Dąbrowski R. , Quintana X. , Urruchi V. , Gayo J. L.

Opto-Electronics Review

2002

tom Vol. 10, No. 1

17-21

In this work, the use of antiferroelectric and V-shape liquid crystals for video projection using LCOS microdisplays has been explored. Antiferroelectric grey levels arise from a double symmetric hysteresis loop that can be stabilised by a constant holding voltage, thus an active matrix is not strictly required in this case. If used, then the voltage levels and the waveform must be adjusted to fulfil the voltage limitations dictated by the matrix. V-shape materials lack hysteresis ; therefore the active matrix is mandatory to stabilise the levels. Voltage limitations, however, are less restrictive int his case, since V-shape smectics require just a few volts for full switching.

Liquid crystal dual-mode band-pass filter with improved performance

100%

Torrecilla J. , Marcos C. , Urruchi V. , Sánchez-Pena J. M. , Chojnowska O.

tom Vol. 23, No. 2

121-125

Over the last twenty years, there has been a growing interest in the design of tunable devices at microwave frequencies by using liquid crystals technology. In particular, the use of liquid crystals with high dielectric anisotropy allows manufacturing voltage-controlled devices to operate in a wide frequency range. In this work the frequency response of a liquid crystal band-pass filter with dual-mode microstrip structure has been studied in depth by using a simulation software tool. A reshaping of a conventional dual-mode square patch resonator band pass filter with a square notch, studied in the literature, has been proposed with the goal of improving the filter performance. The main features achieved are a significant increase in the return loss of the filter and a narrowing of a 3-dB bandwidth. Specifically, a reduction in the filter bandwidth from 800 MHz to 600 MHz, which leads to a return loss increase from 6 dB to 12.5 dB, has been achieved. The filter centre frequency can be tuned from 4.54 GHz to 5.19 GHz.

Antiferroelectric liquid crystal displays

86%

Otón J. M. , Quintana X. , Castillo P. L. , Lara A. , Urruchi V. , Bennis N.

tom Vol. 12, No. 3

263-269

In the last few years, the unique features of antiferroelectric liquid crystals (AFLCs) have been explored to develop high-end displays. A number of passive- and active-matrix prototypes have been presented. However, although their use in a number of application areas has been suggested, no commercial products have been announced yet. This work reviews the state of the art of AFLC displays, the reasons for their present low incidence in display markets, and the latest developments aiming to overcome the main shortcomings that hinder their development. V-shape smectic displays are also included in this study. Although not considered strictly antiferroelectrics nowadays, V-shape materials behaviour and scope are similar to traditional AFLCs.

Video-rate multiplexed driving scheme for passive antiferroelectric liquid crystal displays

86%

Quintana X. , Castillo P. L. , Otón J. M. , Bennis N. , Lara A. , Urruchi V. , Dąbrowski R.

tom Vol. 12, No. 3

291-297

Antiferroelectric liquid crystals have been applied to high-end multiplexed displays. The interest on these materials chiefly comes up from their capability of being multiplex addressed with no need of active matrices. Antiferroelectric grey levels arise from a double symmetric hysteresis loop that can be stabilized by a constant holding voltage. Driving schemes are compatible with passive multiplexing, but limitations appear when the multiplexing rate increases. To avoid these limitations, new driving schemes for high multiplexing level at video rate have been designed. The problem of accumulated voltage on bias level arising from data voltages is tackled as well.