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Nematic Liquid Crystal Spatial Light Modulators for Laser Beam Steering
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry, Quantum Chemistry.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Spatiella ljusmodulatorer med nematisk flytande kristall för laserstrålstyrning (Swedish)
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. , p. 72
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1048
Keyword [en]
Physics, spatial light modulator, liquid crystal, beam steering, tracking, phase modulation, fringing field, director distribution, finite-difference time-domain, polarization, temporal properties
Keyword [sv]
Fysik
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-4693ISBN: 91-554-6110-7 (print)OAI: oai:DiVA.org:uu-4693DiVA, id: diva2:165521
Public defence
2004-12-17, Häggsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15
Opponent
Supervisors
Available from: 2004-11-24 Created: 2004-11-24Bibliographically approved
List of papers
1. Intensity variations using a quantized spatial light modulator for non-mechanical beam steering
Open this publication in new window or tab >>Intensity variations using a quantized spatial light modulator for non-mechanical beam steering
2003 In: Optical Engineering, ISSN 0091-3286, Vol. 42, no 3, p. 613-619Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92439 (URN)
Available from: 2004-11-24 Created: 2004-11-24Bibliographically approved
2. Fringing fields in a nematic liquid crystal spatial light modulator for beam steering
Open this publication in new window or tab >>Fringing fields in a nematic liquid crystal spatial light modulator for beam steering
Show others...
2004 In: Journal of Modern Optics, ISSN 00950-0340, Vol. 51, no 8, p. 613-619Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92440 (URN)
Available from: 2004-11-24 Created: 2004-11-24Bibliographically approved
3. Polarization properties of a nematic liquid-crystal spatial light modulator for phase modulation
Open this publication in new window or tab >>Polarization properties of a nematic liquid-crystal spatial light modulator for phase modulation
2005 (English)In: Optical Society of America. Journal A: Optics, Image Science, and Vision, ISSN 1084-7529, E-ISSN 1520-8532, Vol. 22, no 1, p. 177-184Article 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.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-92441 (URN)10.1364/JOSAA.22.000177 (DOI)15669628 (PubMedID)
Available from: 2004-11-24 Created: 2004-11-24 Last updated: 2017-12-14Bibliographically approved
4. Retrocommunication utilizing electroabsorption modulators and non-mechanical beam steering
Open this publication in new window or tab >>Retrocommunication utilizing electroabsorption modulators and non-mechanical beam steering
Show others...
2005 (English)In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 44, no 4, p. 045001-Article in journal (Refereed) Published
Abstract [en]

A novel retrocommunication link utilizing reflective multiplequantum well (MQW) optical modulators and nonmechanical beamsteering and tracking is demonstrated. Large aperture reflective MQWmodulators using AlGaAs/GaAs are optimized and manufactured. Themodulators exhibit a contrast ratio larger than 4:1 and a modulationbandwidth of 10 MHz. Nonmechanical beam steering and tracking arestudied using nematic liquid crystal (NLC) spatial light modulators(SLMs). The communication link is comprised of a retromodulating arraywith four MQW modulators and a transceiver using a NLC SLM for beamsteering and tracking. Transfer of audio, real-time image data and pseudorandombit sequences over 100-m range while tracking the movingretromodulator is shown. The link is capable of transferring data at approximately8 Mbps.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-92442 (URN)10.1117/1.1883063 (DOI)
Available from: 2004-11-24 Created: 2004-11-24 Last updated: 2017-12-14Bibliographically approved
5. Temporal properties of a nematic liquid-crystal spatial light modulator used for laser beam steering and tracking
Open this publication in new window or tab >>Temporal properties of a nematic liquid-crystal spatial light modulator used for laser beam steering and tracking
In: Applied Optics, ISSN 0003-6935Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-92443 (URN)
Available from: 2004-11-24 Created: 2004-11-24Bibliographically approved

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