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.
Recently, with the development of fabrication technology, sub-nm patterning has been developed, and it has become sufficiently possible to make a nanostructure having a sub-wavelength period. For this reason, metasurface has been a topic of increasing interest in the field of nanophotonics. In this paper, we report the results of realizing mode locking by inserting a metasurface in the form of a saturable absorber into an Yb-doped fiber laser. The metasurface-based saturable absorber has the advantage of reducing the loss due to the deterioration of the existing saturable absorber.
In this study, we report the results of confirming the possibility of optical fiber temperature sensors by fabricating cholesteric liquid crystal (CLC) cells combined with optical fibers. The CLC cell was fabricated with a Fabry-Perot etalon using the cross-sections of two optical fiber ferrules as substrates. A 1.2 um wide bandwidth wavelength swept laser was used to measure the spectrum change of the CLC cell according to the applied temperature. The reflection spectra were measured by changing the temperature of the CLC cell at intervals of 2o from 23o to 45o, and it was confirmed that the reflection band shifted discontinuously to a shorter wavelength as the temperature increased.
The wavelength swept laser (WSL) is a promising optical source in optical coherence
tomography, optical fiber sensor, and optical beat source generation. It is demonstrated by employing a
narrowband wavelength-scanning filter, such as a fast rotating polygonal-scanner-filter, a diffraction
grating on a galvo-scan mirror, or a fiber Fabry-Perot tunable filter (FFP-TF). In this manuscript, we
present our researches on the dynamic fiber-optic sensors. Two kinds of WSLs are used to demonstrate
the dynamic measurement in the fiber-optic sensors. One is the WSL using a polygon-scanner-based
wavelength filter and the other is the Fourier domain mode-locked (FDML) WSL using a FFP-TF. The
dynamic fiber Bragg grating (FBG) sensor interrogation up to 2 kHz by using the WSL with a polygonscanner-
based wavelength filter is reported. And by using the FDML WSL with a FFP-TF, we
demonstrate a resonance FBG sensor interrogation. As another application of the WSL, we successfully
measure a dynamic modulation frequency of the applied electric field using a nematic liquid crystal
Fabry-Perot etalon.
A dual-wavelength tunable fiber laser is demonstrated using two polymer waveguide Bragg gratings (PWBGs) as a wavelength tunable filter. The wavelength tuning in the laser could be achieved by changing the applied electrical power to the PWBG. The interval of dual wavelength can be tuned by 18.9 nm for the maximum applied electrical power of 100 mW. The corresponding frequency range is 2.375 THz. The variation of the lasing wavelength is linearly proportional to the applied electrical power. The side mode suppression ratio of the dual wavelength laser has more than 35 dB.
We report a performance comparison of fiber Bragg gratings (FBGs) sensor interrogation using two kinds of
wavelength swept lasers. In a wavelength swept laser with a fiber Fabry-Perot tunable filter (FFP-TF), the reflected
signal from the FBGs in temporal domain has a nonlinear response with respect to the sinusoidal modulation signal. The
output of the time delay for the strained FBGs sensor array in the wavelength swept laser with FFP-TF has different
slope coefficient for each FBGs, while the reflected output of the strained FBGs in the wavelength swept laser with
polygon scanning filter has same slope coefficient for each FBGs.
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