In this study, the feasibility of a volatile organic compounds (VOC) gas sensor was confirmed through a porous cholesteric liquid crystal film (CLCF) coated on the cross-section of an optical fiber ferrule. The device was fabricated by injecting the CLCF mixture between two ferrules and then UV cured. After separating the two ferrules, porous CLCF was prepared by immersing the CLCF-coated ferrule in acetone. To measure the change in the reflection spectrum of the device for each VOC gas, a broadband wavelength swept laser with a 10dB bandwidth of ~430nm was used. In conclusion, it was found that the reflection band was continuously red-shifted for acetone gas and THF gas.
Wideband wavelength swept lasers (WSLs) are widely used as light sources for dynamic fiber optic sensors. In this study, we implemented an ultra-wideband wavelength-swept laser (WSL) that achieved a 10 dB bandwidth over 430 nm using a single polygonal scanning mirror-based wavelength tunable filter. The wavelength scanning range with a 1.8kHz scanning frequency is 1136.0~1567.2nm. Comparing the WSL output signal in the temporal and spectral domains resulted in an error of 0.7 nm in the mid-crossing region of the two gain media.
To confirm WSL performance, the transmission band was measured by changing the electric field applied to the cholesteric liquid crystal cell, and it was confirmed that the transmitted beam according to the applied electric field matched each other in the spectral and temporal domains.
Many optical devices that can be used in THz systems are continuously being researched and developed. Among them, liquid crystal (LC)-based polarizers and phase shifting devices have also been developed. The LC devices used in the THz system are fabricated in the form of a cell. The substrate of the cell should be transparent with low absorption in the THz frequency range. In the THz frequency band, research and development using various glass materials such as BK7 glass, slide glass, and quartz as substrates have been reported.
In this paper, we report the measurement results of the refractive indices and birefringence of glass materials in the THz band and the possibility of using them as substrates for LC cells. In addition, based on these results, we report the results of measuring refractive indices, absorption coefficient, and birefringence in the THz band after fabricating a LC cell.
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