Continuous Optical Phase Modulation in a Copolymer Network Nematic Liquid Crystal

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• 作者：Alexander Lorenz ; Larissa Braun ; Valeria Kolosova
• 刊名：ACS Photonics
• 出版年：2016
• 出版时间：July 20, 2016
• 年：2016
• 卷：3
• 期：7
• 页码：1188-1193
• 全文大小：556K
• 年卷期：0
• ISSN：2330-4022

文摘

A nematic liquid crystal (LC) was doped with a reactive mixture of a mesogenic diacrylate monomer, a monofunctional acrylate monomer, and photoinitiator. This mixture was filled in transparent test cells with planar electrodes and uniform director alignment. Photopolymerization of the monomers was excited by exposure with ultraviolet light. After photoexposure, the test cells were electrically addressed and their electro-optic response properties were studied by polarized optical microscopy. The voltage dependence of the optical retardation was investigated with a Berek tilting compensator. By applying voltages in the range 4–20 V, the optical retardation was continuously tuned. Importantly, the induced optical phase shift had a smooth onset, which is desirable in electro-optic modulators. Low driving voltages of <15 V were sufficient to induce a half-wavelength retardation throughout the visible spectral range. The time dependence of the transmittance was investigated with monochromatized light and converted to optical phase shift data. Square wave signals (2 kHz) of various amplitudes were switched on and subsequently switched off, respectively. The response times were extracted from the measured data, and sums (t_on + t_off) < 3 ms were found at driving voltages of 12–20 V. The copolymer network LC was suitable for 500 Hz modulations. The electro-optic properties of samples with and without added acrylate monomer were compared.