Browsing by Author "Yang, Zong-Han"

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A thermally tunable narrowband selector based on a chiral nematic containing a binary thermosensitive chiral dopant mixture
(2017-01-01)
Yang, Zong-Han
;
Hsiao, Yu-Cheng
;
Shen, Dong
;
Lee, Wei
;
光電系統研究所
We employed a thermosensitive chiral dopant (CD), characterized by its thermoinduced change in helical twisting power (HTP) in terms of the handedness and strength, to shift the Bragg reflection band of a CLC. A thermally tunable photonic bandgap (PBG) device was demonstrated using a one-dimensional asymmetric photonic crystal (PC) infiltrated with the CLC as a defect layer. With a temperature controller to shift the PBG of the CLC, two narrow transmission bands can be tuned in the spectrum dominated by the asymmetric PC structure. This optical device can find applications as a tunable narrowband wavelength selector or an intensity controller.
Electrically active nanoantenna array enabled by varying the molecular orientation of an interfaced liquid crystal
(2016-01-01)
Hsiao, Yu-Cheng
;
Su, Chen-Wei
;
Yang, Zong-Han
;
Cheypesh, Yevheniia I.
;
Yang, Jhen-Hong
A system comprising a gold nanoantenna array covered with a high-birefringence liquid crystal (LC) material is introduced. By applying voltage across the LC bulk, we demonstrate that the refractive-index and polarization changes significantly modify the hybrid plasmonic-photonic resonances in the system. The hybrid structure enables the active control of the spectrum as well as a large shift in resonance wavelength of the metallic nanoantennas by means of an externally applied electric field. Our modeling supports the observed results, by assuming that the nanoantenna array leads to two orthogonal easy axes with a finite anchoring energy. In combination of the nanostructured surface with birefringent LC, tunability up to 90 nm is achieved in the visible wavelengths, opening the door towards nanoscale displays or nano-optical switches.
Electrically tunable transmission of gold binary-grating metasurfaces integrated with liquid crystals
(2016-07-25)
Chen, Kuo-Ping
;
Ye, Shi-Cheng
;
Yang, Chi-Yin
;
Yang, Zong-Han
;
Lee, Wei
Planar photonics using metasurfaces is of great interest because a metasurface can control the flow of light beyond that attainable with natural materials. The resonance wavelength of a binary-grating metasurface is adjustable by changing the width and thickness of the nanostructure. We propose a novel combination of nematic liquid crystals and a binary-grating metasurface with which the diffraction efficiency can be controlled by adjusting the applied voltage. (C) 2016 Optical Society of America
Red, Green, and Blue Reflections Enabled in an Electrically Tunable Helical Superstructure
(2018-03-05)
Hsiao, Yu-Cheng
;
Yang, Zong-Han
;
Shen, Dong
;
Lee, Wei
;
光電學院
Materials with tunable optical properties in the visible spectrum are intriguingly important in science and technology. Such desired tunability can be conveniently accomplished by controlling optical materials with electric field. Now an organic film of self-organized helical superstructure producing electrically tunable reflection of visible light is introduced in this work. The composite is a dual-frequency thermosensitive cholesteric (DFTC) material consisting of a liquid crystal host doped with a binary chiral-dopant mixture including a thermosensitive chiral switch. The red, green, and blue reflections in the DFTC film can be obtained by varying the frequencies of a 45 V-rms applied voltage to induce dielectric heating. The resulting variation in temperature and, in turn, in helical pitch length, enables various wavelengths of reflection to render full-color display in a single film without the need of film stacking. As far as it is known, this is the first work to demonstrate broad electrical tuning of cholesteric reflection in red, green, and blue.