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Characterization of Second-Order Reflection Bands from a Cholesteric Liquid Crystal Cell Based on a Wavelength-Swept Laser

1
Department of Physics, Chungnam National University, 99 Daehak-ro Yuseong-gu, Daejeon 34134, Korea
2
Core Technology R&D Team, Samsung Electronics, Hwaseong-si, Gyeonggi-do 18448, Korea
3
Instituted of Quantum Systems (IQS), Chungnam National University, 99 Daehak-ro Yuseong-gu, Daejeon 34134, Korea
4
Beckman Laser Institute, UC Irvine, Irvine, CA 92612, USA
*
Author to whom correspondence should be addressed.
These authors contributed equally in this work.
Sensors 2020, 20(16), 4643; https://doi.org/10.3390/s20164643
Received: 30 June 2020 / Revised: 12 August 2020 / Accepted: 15 August 2020 / Published: 18 August 2020
(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)
We report the results of an experimental study of the characterization of second-order reflection bands from a cholesteric liquid crystal (CLC) cell that depends on the applied electric field, using a wide bandwidth wavelength-swept laser. The second-order reflection bands around 1300 nm and 1500 nm were observed using an optical spectrum analyzer when an electric field was applied to a horizontally oriented electrode cell with a pitch of 1.77 μm. A second-order reflection spectrum began to appear when the intensity of the electric field was 1.03 Vrms/μm with the angle of incidence to the CLC cell fixed at 36°. The reflectance increased as the intensity of the electric field increased at an angle of incidence of 20°, whereas at an incident angle of 36°, when an electric field of a predetermined value or more was applied to the CLC cell, it was confirmed that deformation was completely formed in the liquid crystal and the reflectance was saturated to a constant level. As the intensity of the electric field increased further, the reflection band shifted to a longer wavelength and discontinuous wavelength shift due to the pitch jump was observed rather than a continuous wavelength increase. In addition, the reflection band changed when the angle of incidence on the CLC cell was changed. As the angle of incidence gradually increased, the center wavelength of the reflection band moved towards shorter wavelengths. In the future, we intend to develop a device for optical wavelength filters based on side-polished optical fibers. This is expected to have a potential application as a wavelength notch filter or a bandpass filter. View Full-Text
Keywords: fiber laser; wavelength-swept laser; cholesteric liquid crystal; bandpass filter fiber laser; wavelength-swept laser; cholesteric liquid crystal; bandpass filter
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MDPI and ACS Style

Ahn, S.; Ko, M.O.; Kim, J.-H.; Chen, Z.; Jeon, M.Y. Characterization of Second-Order Reflection Bands from a Cholesteric Liquid Crystal Cell Based on a Wavelength-Swept Laser. Sensors 2020, 20, 4643.

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