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Polarization properties of a nematic liquid-crystal spatial light modulator for phase modulation
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry, Quantum Chemistry.
2005 (English)In: Optical Society of America. Journal A: Optics, Image Science, and Vision, ISSN 1084-7529, Vol. 22, no 1, 177-184 p.Article in journal (Refereed) Published
Abstract [en]

The polarization properties of a nematic zero-twist liquid-crystal (NLC) spatial light modulator (SLM) were studied. A large ratio between the liquid-crystal (LC) layer thickness and the pixel pitch combined with spatial variations in the applied electric field causes fringing fields between pixels. Depending on the LC alignment, the electric field components within the LC layer can result in a twist deformation. The produced inhomogeneous optical anisotropy affects the polarization of light propagating through the device. We experimentally examined polarization effects in different diffraction orders for both binary and blazed phase gratings. Simulations of the LC deformation together with finite-difference time-domain simulations for the optical propagation were used to calculate the corresponding far-field intensities. It was demonstrated how rigorous simulations of the NLC SLM properties can be used to understand the polarization features of different diffraction orders.

Place, publisher, year, edition, pages
2005. Vol. 22, no 1, 177-184 p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-92441DOI: 10.1364/JOSAA.22.000177PubMedID: 15669628OAI: oai:DiVA.org:uu-92441DiVA: diva2:165518
Available from: 2004-11-24 Created: 2004-11-24 Last updated: 2013-07-05Bibliographically approved
In thesis
1. Nematic Liquid Crystal Spatial Light Modulators for Laser Beam Steering
Open this publication in new window or tab >>Nematic Liquid Crystal Spatial Light Modulators for Laser Beam Steering
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Spatiella ljusmodulatorer med nematisk flytande kristall för laserstrålstyrning
Abstract [en]

Laser beam control is important in many applications. Phase modulating spatial light modulators (SLMs) can be used to electronically alter the phase distribution of an optical wave-front and thus change the direction and shape of a laser beam. Physical constraints set limitations to the SLM and an ideal phase distribution can usually not be realised. In order to understand how such components can be used for non-mechanical beam control three nematic liquid crystal (NLC) SLMs have been thoroughly characterised and modelled.

The pixel structure and phase quantisation give a discrepancy between ideal and realised phase distributions. The impact on beam steering capability was examined by measurements and simulations of the intensity distribution in the far-field.

In two of the studied SLMs the pixel period was shorter than the thickness of the LC layer giving the optical phase shift. This results in a so-called “fringing field”, which was shown to degrade the phase modulation and couple light between polarisation modes. The deformation of the LC was simulated and a finite-difference time-domain (FDTD) algorithm was used to calculate how polarised light propagates through the optically anisotropic SLM.

Non-mechanical beam steering and tracking in an optical free-space communication link were demonstrated. Continual optimisation of the steering angle was achieved by feedback from a video camera.

The optical properties of the SLM in the time period right after a voltage update were studied. It was shown how light is redistributed between orders during the switching from one blazed grating to another. By appropriate choice of the blazed gratings the effects on the diffraction efficiency can be minimised.

The detailed knowledge of the SLM structure and its response to electronic control makes it possible to predict and optimise the device performance in future systems.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 72 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1048
Physics, spatial light modulator, liquid crystal, beam steering, tracking, phase modulation, fringing field, director distribution, finite-difference time-domain, polarization, temporal properties, Fysik
National Category
Physical Sciences
urn:nbn:se:uu:diva-4693 (URN)91-554-6110-7 (ISBN)
Public defence
2004-12-17, Häggsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15
Available from: 2004-11-24 Created: 2004-11-24Bibliographically approved

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