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Applied Optics

Applied Optics


  • Vol. 43, Iss. 7 — Mar. 1, 2004
  • pp: 1559–1569

Beam steering experiment with two cascaded ferroelectric liquid-crystal spatial light modulators

David Engström, Sverker Hård, Per Rudquist, Koen D’havé, Tomasz Matuszczyk, Marek Škereň, and Björn Löfving  »View Author Affiliations

Applied Optics, Vol. 43, Issue 7, pp. 1559-1569 (2004)

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The design, construction, and evaluation of a laser beam steerer that uses two binary ferroelectric liquid-crystal (FLC) spatial light modulators (SLMs) operated in conjunction are presented. The system is characterized by having few components and is in principle lossless. Experimentally, a throughput of ∼20% was achieved. The simple system design was achieved because of the high tilt angle FLC material used in the SLMs, which were specifically designed and manufactured for this study. By coherently imaging the first SLM onto the second SLM, pixel by pixel, we obtained an effective four-level phase structure with a phase step of 90°. An appropriate alignment procedure is presented. The beam steering performance of the system is reported and analyzed.

© 2004 Optical Society of America

OCIS Codes
(050.1970) Diffraction and gratings : Diffractive optics
(110.1650) Imaging systems : Coherence imaging
(230.3720) Optical devices : Liquid-crystal devices
(230.6120) Optical devices : Spatial light modulators

Original Manuscript: May 23, 2003
Published: March 1, 2004

David Engström, Sverker Hård, Per Rudquist, Koen D’havé, Tomasz Matuszczyk, Marek Škereň, and Björn Löfving, "Beam steering experiment with two cascaded ferroelectric liquid-crystal spatial light modulators," Appl. Opt. 43, 1559-1569 (2004)

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  11. High-tilt FLCs are notoriously difficult to align in electro-optic cells, and the alignment achieved after the virgin cooling of the CS-2005 LC from the isotropic to the smectic C* phase is often rather inhomogeneous. Hence the boundary conditions (buffed polyimide layers) are by themselves not sufficient for providing satisfactory alignment. However, by cycling the temperature through the nematic to smectic C* transition while applying ac electric fields (with amplitudes similar to the addressing signals), one can significantly improve the alignment.
  12. The distributing circuit, which accepts only positive voltages, contains one binary switch per pixel. When a switch is set in one of its positions, zero voltage is applied to its pixel electrode. When it is set in its other position the raw driving voltage is applied to its pixel electrode. To generate the required positive and negative pixel-cell voltages the common SLM electrode is fed with half of the instantaneous raw driving voltage (virtual ground). The switch settings are controlled by the microprocessor.
  13. The reason why the grating with period 2Np gets repeated after only N pixel shifts is that the phase steps of the SLM pixels are π and π/2.

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