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Proceedings Paper

Liquid crystal based continuous phase retarder: from optically neutral to a quarter waveplate in 200 microseconds
Author(s): Benjamin J. Broughton; Matthew J. Clarke; Ralph A. Betts; Terry Bricheno; Harry James Coles
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Paper Abstract

Liquid crystal variable phase retarders have been incorporated into prototype devices for optical communications system applications, both as endless polarization controllers1,2,3, and as holographic beam steerers4. Nematic liquid crystals allow continuous control of the degree of retardation induced at relatively slow switching speeds, while ferroelectric liquid crystal based devices allow fast (sub millisecond) switching, but only between two bistable states. The flexoelectro-optic effect5,6 in short-pitch chiral nematic liquid crystals allows both fast switching of the optic axis and continuous, electric field dependent control of the degree of rotation of the optic axis. A novel geometry for the flexoelectro-optic effect is presented here, in which the helical axis of the chiral nematic is perpendicular to the cell walls (grandjean texture) and the electric field is applied in the plane of the cell. This facilitates deflection of the optic axis of the uniaxial negatively birefringent material from lying along the direction of propagation to having some component in the polarization plane of the light. The device is therefore optically neutral at zero field for telecommunications wavelengths (1550nm), and allows a continuously variable degree of phase excursion to be induced, up to 2π/3 radians achieved so far in a 40μm thick cell. The retardation has been shown both to appear, on application of the field, and disappear on removal, at speeds of 100-500 μs. The direction of deflection of the optic axis is also dependent on the direction of the field, allowing the possibility, in a converging electrode "cartwheel cell", of endless rotation of the liquid crystal waveplate at a higher rate than achievable through dielectric coupling to plain nematic materials.

Paper Details

Date Published: 12 April 2005
PDF: 7 pages
Proc. SPIE 5741, Emerging Liquid Crystal Technologies, (12 April 2005); doi: 10.1117/12.593301
Show Author Affiliations
Benjamin J. Broughton, Univ. of Cambridge (United Kingdom)
Matthew J. Clarke, Univ. of Cambridge (United Kingdom)
Ralph A. Betts, Pi Photonics Ltd. (United Kingdom)
Terry Bricheno, Pi Photonics Ltd. (United Kingdom)
Harry James Coles, Univ. of Cambridge (United Kingdom)

Published in SPIE Proceedings Vol. 5741:
Emerging Liquid Crystal Technologies
Liang-Chy Chien, Editor(s)

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