Circular-polarization and wavelength selective gratings based on polymer templates of holographic cholesteric liquid crystal

  • 鄭 揚臣

Student thesis: Master's Thesis


In this study a cholesteric liquid crystal (CLC) template grating with circular polarization and wavelength selectivity is successfully fabricated by two-beam interference The grating is fabricated by use of CLC template (washing out/refilling) technology and refilling CLCs with different handedness and reflection band When the wavelength of a probe beam is in the CLC reflection band (reflection band of the non-template region) the device works as an amplitude grating because the template and non-template regions reflect distinct wavelengths During the fabrication of the CLC template grating the UV light exposure produces two-dimensional (2D) structures in the sample The formation of the 2D structure reduces the diffraction efficiency of the CLC template grating The exposure UV dose is controlled to avoid the formation of the 2D grating and thus obtain a good one-dimensional (1D) grating Experimental results show that the circular polarization and wavelength selectivity of the CLC template grating can be achieved by refilling different CLCs This principle is based on the selective Bragg reflection characteristic of CLC The Bragg reflection not only allows the CLC template grating to produce diffracted light of a specific wavelength but also provides the CLC with circularly polarized selective characteristics As different CLCs are refilled in CLC template gratings different diffraction efficiencies appear for left-hand circularly polarized and right-handed circularly polarized (LCP and RCP respectively) lights The beam steering element exhibits circular polarization selectivity and dual operation modes The diffraction intensity can be electrically controlled When the electric field is applied the arrangement of the CLC becomes in a focal conic state which presents strong scattering such that the diffraction intensity decreases However after releasing the electric field CLC reorients from the focal conic state to the planer state and the diffraction intensity returns to its original state Therefore this CLC-based device can be potentially used for applied diffraction elements in optics
Date of Award2017 Feb 13
Original languageEnglish
SupervisorChia-Rong Lee (Supervisor)

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