Electromagnetic Wave Control Device Laboratory
in Nagaoka University of Technology

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Keywords
Applied optics, Nonlienar optics, Photonics, Terahertz engineering,
Liquid crystal, Photoreactive polymer, Functional dye, Photonic crystal, Graphene,
Difractive optical element, Holography, Terahertz element, Waveguide, Polarimeter,
Jones matrix method, Finite-difference time-domain method, Finite element method, etc.

Objectives
We realize wideband electromagnetic wave controlling using liquid crystals.
Liquid crystals are excellent media for various optical applications because they are highly
transparent in the visible range, have a large optical anisotropy, and respond to external
fields. We utilize liquid crystals in a wide frequency range, and propose functional elements,
devices, and systems using liquid crystals for controlling propagation of electromagnetic waves.



Topics
Terahertz devices using liquid crystal materials
We fabricated a universal polarization terehertz phase controller using a liquid crystal cell with graphene electrodes. The detailes are described in the following paper. In this study, we demonstarted that functionalized active terahertz devices were realized by employing liquid crsytal materials.
*T. Sasaki et al., Opt. Lett. 40, 1544 (2015).


Three-dimensional vector holography
We proposed three-dimensional vector holograms, which were recorded in initially anisotropic media. We demonstrated that spatial molacular alignment of liquid crystals could be controlled in real time by means of three-dimensional vector holography.
*T. Sasaki et al., Holograms- Recording Materials and Applications, pp. 179-196 (INTECH, 2011).


Polarimeters using polymer liquid crystal films
We designed a anisotropic diffraction grating to realize a diffractive polarimeter. The grating was fabricated by vector holographic recording in a photoreactive polymer liquid crystal film. This polarimeter realize robust and high speed polarization analysis.
*Patent No. P5109112 (2012).


Diffraction gratings using liquid crystal cells
We fabricated various liquid crystal diffraction gratings using photocrosslinkable liquid crystalline polymer films for alignment layers of low-molecular-weight liquid crystals. These gratings realize polarization control in the diffraction process.  The fabrication methods diffraction properties were summerized in the following book.
*T. Sasaki et al., Liquid Crystal Polymers, pp. 221-240 (Springer, 2015).


Spatial optical solitons in liquid crystals
Liquid crystals are nonlinear optical media. We study nonlinear propagation properties of gaussian visible light beams in liquid crystal cells to obtain spatial optical solitons.  We showed that highly efficient solitons could be formed in dye-doped liquid crystals.
*KAKENHI 24760265


Surface relief formation in azopolymer films
Surface relief gratings are formed in azopolymer films by vector holographic recordings. However the formation mechanism has not been completely explained yet. We observed the relief formation in real time and analyzed on the basis of the optical gradient force.
*T. Sasaki et al., Appl. Phys. B 114, 373 (2014).


 

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