• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1100-1109
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• 2006

In this study, two different technologies which can measure temperature simultaneously at many points are introduced. One is to use a thermal sensor cable that is comprised of addressable thermal sensors connected in parallel within a single cable. The other is to use an optic fiber with Distributed Temperature Sensing (DTS) system. The difference between two technologies can be summarized as follows. A thermal sensor cable has a concept of 'point sensing' that can measure temperature at accurate position of a thermal sensor. So the accuracy and resolution of temperature measurement are up to the ability of the thermal sensor. Whereas optic fiber sensor has a concept of 'distributed sensing' because temperature is measured by ratio of Stokes and anti-Stokes component intensities of Raman backscatter that is generated when laser pulse travels along an optic fiber. It's resolution is determined by measuring distance, measuring time and spatial resolution. The purpose of this study is that application targets of two temperature measurement techniques are checked in technical and economical phases by examining the strength and weakness of them. Considering the functions and characteristics of two techniques, the thermal sensor cable will be suitable to apply to the assessment of groundwater flow, geothermal distribution and grouting efficiency within 300m distance. It is expected that the optic fiber sensor can be widely utilized at various fields (for example: pipe line inspection, tunnel fire detection, power line monitoring etc.) which need an information of temperature distribution over relatively long distance.

• Korean Journal of Optics and Photonics
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• v.8 no.5
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• pp.415-419
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• 1997

A novel fiber optic sensor is demonstrated using a FBG in PM(Polarization-Maintaining) fiber. Gratings have been written in a Bow-Tie type fiber using the phase mask. The operation of the sensor simply involves monitoring back-reflected Bragg wavelengths from the grating. Since PM fiber has two principal semi-axes with two indices of refraction, two Bragg wavelengths were observed. We have observed the position of Bragg wavelengths for PM FBG shifted simultaneously by either applying the longitudinal strain or temperature change. The wavelength sensitivity of 1.2pm/$\mu$$\varepsilon$ about a longitudinal strain and the wavelength sensitivity of 11.4pm/$^{\circ}C$ about a temperature have been experimentally achieved. The wavelength sensitivity of both longitudinal strain and temperature are approximately same with the reported values for the single mode FBG. On the other hand, the change of separation between Bragg wavelengths was observed by the applying transverse stress. We observed that the separation between two Bragg wavelengths is proportional to the applied transverse stress. The wavelength sensitivity of 14.6 pm/N about a transverse stress has been achieved. We have demonstrated PM FBG sensors can measure the transverse stress independently from the effects of temperature.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.11
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• pp.160-165
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• 2016

The rapidly developing applications of optical fiber in sensors, sensor system and super high speed optical communication have begun to produce tangible demands for optical coupler and connected WDM. we have designed and made Hopper type WDM (national patent NO:10-1502954). The Hopper type WDM is bi-directional $1{\times}3$ WDM of asymmetry Butt coupling for super high speed optical communication. The Hopper type WDM is used central wavelength of each 850nm,1300nm,1550nm. The Hopper type WDM has an excellent merits which the existing WDM and also it has an excellent signal of super high speed and economic in made. The characteristic of Hopper type WDM is superior in ave 0.02-0.03dB as compared with $1{\times}3$ optical coupler to excess loss. Especially, we can expect the utilization of super high speed optical MUX and also can be developed as the high-sensibility signal detected system in using optical sensor system parts.

• Korean Journal of Materials Research
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• v.19 no.4
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• pp.228-231
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• 2009

Phase transition in ferroelectric polymer is very interesting behavior and has been widely studied for real device applications, such as actuators and sensors. Through the phase transition, there is structural change resulting in the change of electrical and optical properties. In this study, we fabricated the Febry-Perot interferometer with the thin film of ferroelectric P(VDF-TrFE) 50/50 mol% copolymer, and thermo-optical properties were investigated. The effective thermo-optical coefficient of P(VDF-TrFE) was obtained as $2.3{\sim}3.8{\times}10^{-4}/K$ in the ferroelectric temperature region ($45^{\circ}C{\sim}65^{\circ}C$) and $6.0{\times}10^{-4}/K$ in the phase transition temperature region ($65^{\circ}C{\sim}85^{\circ}C$), which is a larger than optical silica-fiber and PMMA. The resonance transmission peak of P(VDF-TrFE) with the variation of temperature showed hysteretic variation and the phase transition temperature of the polymer in heating condition was higher than in the cooling condition. The elimination of the hysteretic phase transition of P(VDF-TrFE) is necessary for practical applications of optical devices.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.1 s.53
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• pp.88-96
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• 2009

This study proposes a wireless measurement system that is a new safety management system by using an FBG sensor and a PDA. The sensor part has many advantages of implementing a wireless measurement system, and the study emploies an FBG-LVDT sensor, FBG-STRAIN sensor, FBG-TEMP sensor, and FBG-ACC sensor, using FBG sensors. Also, the study show a configuration of a signal process system for operating a wireless transmission system of FBG sensors applied to the signal process system, and engrafted the cutting edge information technology industry in order to display from a remote distance using a PDA. In order to verify the applicability of the developed FBG sensors and wireless measurement monitoring system to the field, their accuracy, and usability, the study has conducted a static and dynamic test to a bridge in the field. The study made an assessment of service for the vibration of the bridge by applying dynamic data measured by an FBG-LVDT sensor and FBG-ACC sensor to Meister's curve and prepared methods for assessing the vibration of the bridge by proposing a standard of vibration limitation given the service of vibration of the bridge. As a follow up for this study, it would be necessary to set up an overall model for the standard of service assessment established in this study.

• Journal of Sensor Science and Technology
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• v.11 no.5
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• pp.273-278
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• 2002

An intrusion-sensitive capability of multimode graded-index (GRIN) optical fibers under bending has been investigated. In this system, the data light is transmitted in the fundamental mode while alarm monitor light is launched in a high-order mode at the same time. An attempted intrusion to drain data by bending the fiber results in greater attenuation of a monitor signal in higher order modes, thereby setting off an alarm at the receiver. Light propagation in a multimode graded-index fiber is also analyzed theoretically when the fundamental mode is selectively excited and the fiber is bent around a constant radius mandrel. The bending generates coupling between the various modes of the fiber. Power transitions of the fundamental mode by changing the bending radius were also analyzed numerically using program simulation. It is shown that Asawa-Taylor model[4] is valid up to 1cm of the radius of curvature of the fiber bend.

• Journal of Sensor Science and Technology
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• v.15 no.3
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• pp.186-191
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• 2006

In general, Cerenkov light is produced by a charged particle that passes through a medium with a velocity greater than that of visible light. Although the wavelength of Cerenkov light is very broad, the peak is in the almost visible range from 400 to 480 nm. Therefore, it always causes a problem to detect a real light signal that is generated in the scintillator on the fiber-optic sensor tip for dose measurements of high-energy electron beam. The objectives of this study are to measure, characterize and remove Cerenkov light generated in a fiber-optic radiation sensor tip to detect a real light signal from the scintillator. In this study, the intensity of Cerenkov light is measured and characterized as a function of incident angle of electron beam from a LINAC, and as a function of the energy of electron beam. As a measuring device, a photodiode-amplifier system is used, and a subtraction method using a background optical fiber is investigated to remove Cerenkov light.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.1
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• pp.161-166
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• 2016

We studied the effect of $Co^{60}$ gamma-radiation on the FBGs by a variation of grating the fabrication parameters. The FBGs were fabricated in a different UV KrF laser intensity using the same boron co-doped photo-sensitive fiber and exposed to gamma-radiation up to a dose of 33.8 kGy. According to the experimental data and analysis results, We confirmed that the laser intensity for grating inscription has a highly effect on the radiation sensitivity of the FBGs and the radiation-induced Bragg wavelength shift by the change of laser process condition showed a difference more than about 30 %.

• Journal of Sensor Science and Technology
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• v.24 no.3
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• pp.202-207
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• 2015

As a feasibility study on development of a gamma imaging probe, we developed a scintillating film-based gamma imaging detector that can obtain scintillation images with information of gamma-ray distribution. The scintillating film-based gamma imaging detector was composed of a sensing probe, an image intensifier, and a beam profiler. To detect and transmit scintillation image, the sensing probe was fabricated by coupling a scintillating film, a fiber-optic image conduit, and a fiber-optic taper, consecutively. First, the optical images of USAF 1951 resolution target were obtained and then, modulation transfer function values were calculated to test the image quality of the sensing probe. Second, we measured the scintillation images according to the activity of the 137Cs and the distance between the surface of 137Cs and the distal-end of sensing probe. Finally, the intensities of scintillating light as functions of the activity and the distance were evaluated from the region of interest in the scintillation image. From the results of this study, it is expected that a fiber-optic gamma imaging detector can be developed to detect gamma-rays emitted from radiopharmaceuticals during radioimmunoguided surgery.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.3
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• pp.39-44
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• 2004

Fiber Bragg grating sensors are fabricated by core index modulation using UV laser and phasemask. Bragg wavelength of the grating is changed by the external strain. In this paper, a signal processing system of fiber Bragg grating sensor has studied in the optical wavelength domain. The system is based on the sweep semiconductor light source that consists of SLD, F-P tunable filter and etalon filter. The hysteresis effects of PZT in the F-P tunable filter are compensated. The long term measurement stability is obtained by controlling the temperature of F-P tunable filter and the SLD. We compare the strain data from fiber Bragg grating sensor and that from strain gauge at concrete hume pipe. We also get very good results for the long gauge displacement using fiber Bragg grating sensor which are identical to the data with short gauge length ordinary displacement sensor.