• 전자공학회논문지 IE
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• v.46 no.2
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• pp.18-21
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• 2009

The optical fiber refractive index sensors were fabricated using etching method and their refractive index characteristics have been investigated. Good sensitivity was shown at the region of 1.452-1.46 refractive index and operating point was shifted by wavelength. The sensitivity of sensor increased with decreasing cladding thickness and was stable with heat treatment. The hysteresis under cyclic refractive index changes was negligible.

• Journal of Sensor Science and Technology
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• v.20 no.2
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• pp.107-113
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• 2011

LSPR(Localized Surface Plasmon Resonance) sensor measures the refractive index change on the sensor surface. The detection of biological reaction with the unknown refractive index needs to be converted into the signal sensitivity for the refractive index change for comparison with other measurements. To find the signal sensitivity, the three steps of signal processing are proposed, which are signal modeling, signal calibration and signal normalization of LSPR sensor. The detected signal of biotin-streptavidin interaction has been converted into unit of [RU](Resonance Unit) using the proposed method. The converted signal directly can be compared with the other sensors including commercialized one.

• Journal of Sensor Science and Technology
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• v.21 no.2
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• pp.151-155
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• 2012

We have investigated a refractive index sensor based on a cladded plastic optical fiber taper. The optical transmission and sensing characteristics of the device were illuminated in terms of ray optics. The sensor devices showed that the optical transmittance strongly depends on the refractive index of the external medium surrounding the tapered region.

• Journal of Sensor Science and Technology
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• v.30 no.3
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• pp.139-147
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• 2021

Numerical analysis was performed using FIMMWAVE to optimize the specifications of Si₃N₄/SiO₂ slot and ridge-slot optical waveguides based on confinement factor and effective mode area. The optimized specifications were confirmed based on sensitivity in terms of the refractive index of the analyte. The specifications of the slot optical waveguide, i.e., the width of the slot and the width and height of the rails, were optimized to 0.2 ㎛, 0.46 ㎛, and 0.5 ㎛ respectively. When the wavelength was 1.55 ㎛ and the refractive index of the slot was 1.3, the confinement factor and effective mode area of 0.2024 and 2.04 ㎛², respectively, were obtained based on the optimized specifications. The thickness of the ridge and the refractive index of the slot were set to 0.04 ㎛ and 1.1, respectively, to optimize the ridge-slot optical waveguide, and the confinement factor and effective mode area were calculated as 0.1393 and 2.90 ㎛², respectively. When the confinement coefficient and detection degree of the two structures were compared in the range of 1 to 1.3 of the analyte index, it was observed that the confinement coefficient and sensitivity were higher in the ridge-slot optical waveguide in the region with a refractive index less than 1.133, but the reverse situation occurred in the other region. Therefore, in the implementation of the integrated optical biochemical sensor, it is possible to propose a selection criterion for the two parameters depending on the value of the refractive index of the analyte.

• Journal of Sensor Science and Technology
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• v.30 no.6
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• pp.415-419
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• 2021

We developed a highly accurate, yet inexpensive, refractive index (RI)-based soil moisture sensor. To detect the RI, a light guide was set with a light-emitting diode and photodiode. When the air fills the space between the soil particles, most of the incident light is reflected at the interface between the waveguide and the air because of the large RI difference. As the moisture of the soil increases, the macroscopic soil RI increases. This allows incident light to pass through the interface. The intensity of the light reaching the photodiode was simulated according to the change in the soil RI. Using the simulation results, we designed and manufactured a curved glass waveguide. We evaluated the performance of the RI-based soil sensor by comparing it with a commercially available, high-cost and high-performance time-domain reflectometer (TDR). Our sensor was 96% accurate, surpassing the costly TDR sensor.

• Journal of Sensor Science and Technology
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• v.17 no.4
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• pp.261-266
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• 2008

In this paper, we present thermal characteristics of high-temperature measurement sensor using fiber Bragg grating(FBG), including peak reflectivity, FWHM bandwidth and various normalized refractive index change along temperature variation. The temperature stability of FBG temperature sensor can be changed by varying the refractive index change and grating length. The proposed FBG temperature sensor can measure up to about $600^{\circ}C$ and 1000 hours of heating time.

• Journal of Sensor Science and Technology
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• v.16 no.4
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• pp.254-258
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• 2007

A novel cure sensor based on the side-polished single mode fiber has been proposed and demonstrated. Two different UV curable epoxies were used to verify the feasibility of the side-polished single mode fiber as a high sensitivity cure sensor. The volume change of the epoxy by UV curing results in a corresponding change of the refractive index. The sensor can be used to monitor the curing process, the refractive index variation and the volume change of epoxy in real time during the UV curing process. In addition, small birefringence of the epoxy film can be detected using the sensor.

• Journal of Sensor Science and Technology
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• v.24 no.6
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• pp.423-428
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• 2015

A bimetallic chip made of gold and silver was investigated in intensity interrogation mode to confirm enhancement of the SPR sensor resolution. Both reflectance curves of the bimetallic chip and the conventional gold chip was acquired and compared. The line width of the reflectance curve of the bimetallic chip was narrower than that of the conventional Au chip, resulting in steeper tangential slope. The reflectance was monitored at the angle related to the steepest tangential slope. The change in reflectance of the bimetallic chip was larger than that of the Au chip. The critical angle was analyzed by differentiating the reflectance with respect to incident angle twice. Acquiring the critical angle regarding to the sample informs the refractive index of the sample. Using various concentration of Bovine Serum Albumin, we confirmed that refractive index was linearly related to variation of reflectance of the bimetallic chip.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.37-41
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• 2005

The curing of thermoset resin is accompanied with the changes in chemical and physical properties. The cure monitoring techniques can be designed by tracing these property changes. This paper presents the cure monitoring technique with fiber optic sensors to detect the change of refractive index during the polymerization process of engineering epoxy resin. The fiber optic sensor system was developed to measure the reflection coefficient at the interface between the fiber optic and the resin. The correlation between the sensor output and the degree of cure was performed following Lorentz-Lorenz law. The isothermal data from the sensors are compared with the data from differential scanning calorimeter.

• Journal of Sensor Science and Technology
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• v.29 no.2
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• pp.118-122
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• 2020

This paper proposes a specific sensor-design strategy and the possibility of improving the sensing performance, which can be obtained by replacing part of the existing plasmonic sensor based on the Kretschmann configuration method with an effective refractive-index layer. By replacing the metal layer with an effective refractive-index layer composed of gold and the material to be sensed, an improvement in the detection performance, accompanied by an increase in the sensed incident angle, is observed, and the gold-composition ratio that demonstrates the best result is presented. Subsequently, an increase in the sensed incident angle generated in the previous step can be suppressed by randomly etching a portion of the prism adjacent to the metal layer in a sub-wavelength scale. Finally, this study analyzes the optimization of the metal-layer thickness in a given sensor structure. An effective refractive thin-film surface plasmon resonance sensor design that can achieve optimal sensing performance is then proposed.