Applying the optical activity of cholesteric liquid crystal for measuring small wavelength differences |
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Authors: | Kun-Huang Chen Jing-Heng Chen |
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Affiliation: | a Department of Electrical Engineering, Feng Chia University, 100 Wenhwa Road, Seatwen Taichung 40724, Taiwan, ROCb Department of Photonics, Feng Chia University, 100 Wenhwa Road, Seatwen Taichung 40724, Taiwan, ROCc Department of Mechatronics Engineering, National Changhua University of Education, No. 2, Shi-Da Road, Changhua City 50074, Taiwan, ROC |
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Abstract: | This work proposes a simple measurement technique based on the optical activity of cholesteric liquid crystal (CLC) and circular common-path heterodyne interferometry for measuring small wavelength differences. A circularly polarized heterodyne light passes through a CLC cell and an analyzer, generating an interference signal. When the CLC cell is properly chosen with a circular regime, it has strong optical activity. Accordingly, the phase difference between the left and right circular light of the interference signal depends strongly on the wavelength. As the wavelength changes, variations of the phase difference can be accurately detected by heterodyne interferometry. Substituting the variation of phase difference into specially derived equations, the wavelength variations can be estimated accurately. The feasibility of this method, which is applicable when the wavelength is larger than the product of the pitch and the refractive index of the CLC cell, was demonstrated; it provides the advantages of simple installation, ease of operation, and high accuracy. |
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Keywords: | Cholesteric liquid crystal Optical activity Wavelength difference Heterodyne interferometry |
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