• Journal of Sensor Science and Technology
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• v.21 no.4
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• pp.287-292
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• 2012

A fiber-optic radiation sensor was fabricated using a sensing probe, a plastic optical fiber, a photomultiplier tube, and a multichannel analyzer for gamma-ray spectroscopy. As an inorganic scintillator of the sensing probe, a LYSO crystal was used. In this study, we obtained the relationship between the photon counts of the fiber-optic radiation sensor and the activity of the radioactive isotope. In addition, the gamma-ray energy spectra were also measured using a fiber-optic radiation sensor to discriminate species of gamma-ray emitters.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1400-1409
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• 2001

This paper describes a fiber optic sensor suitable for non-contact detection of ultrasonic waves. This sensor is based on a fiber optic Sagnac interferometer. Quadrature phase bias between two interfering laser beams in Sagnac loop is introduced by a polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output versus phase bias. This method eliminates a digital signal processing for detection of ultrasonic waves using Sagnac interferometer. Interference intensity is affected by the frequency of ultrasonic waves and the time delay of Sagnac loop. Collimator is attached to the end of the probing fiber to focus the light beam onto the specimen surface and to collect the reflected light back into the fiber probe. Ultrasonic waves produced by conventional ultrasonic transducers are detected. This fiber optic sensor based on Sagnac interferometer is very effective for detection of small displacement with high frequency such as ultrasonic waves used in conventional non-destructive testing.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.1
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• pp.73-78
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• 2008

A polarimetric fiber-optic CT has been developed by using a sensing coil made of a length of sun fiber. A Faraday rotator mirror is attached to the end of the sensor coil to double the sensitivity and to suppress the residual linear birefringence effect. From the current measurements, the linear error no more than ${\pm}2[%]$ was obtained. The output of spun fiber sensor coil was compared with those of the twisted- and the flint glass fiber's, and it fumed out to almost 50 times, 2 times more sensitive, respectively.

• Journal of Sensor Science and Technology
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• v.15 no.4
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• pp.263-268
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• 2006

We have demonstrated a highly sensitive temperature sensor using an etched single mode fiber with a thermally expanded core region. Large core size of thermally expanded core facilitates access to evanescent wave by the wet etching. The etched region was surrounded by a low dispersive external medium with high thermo-optic coefficient. Due to the large difference between the dispersion property of the fiber and that of the external medium, the device reveals a cut-off properties at spectral region. The cut-off wavelength was shifted by the variations of the environmental temperatures because of thermo-optic effect of the external medium. The sensitivity of the fabricated device was found to be $45nm/^{\circ}C$.

• 대한공업교육학회지
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• v.32 no.2
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• pp.171-187
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• 2007

The purpose of this study is to measure the lathe tool vibration and verify its usefulness using the fiber optic interferometeric sensor instead of using common accelerometer. To compare two vibration signals a Fabry-Perot fiber optic sensor(FOS) is directly attached to the left-side surface of the lathe tool and an accelerometer is attached near to the fiber optic sensor. Measurement signals from the FOS and theoretical results of receptance simulation are compared. When the amplitude of tool vibration increased the frequency shift phenomena was occurred. This means that mass effect occurred and vibration spectrum moved to the low frequency region. Generally this results is agreement to the regenerative chatter. The chatter frequency is not same as the natural frequency of the tool itself. The FOS can also applied to laboratory experiments for students. This experimental technique is perhaps the first attempts because of directly attachment technique. Therefore, suggested Fabry-Perot fiber optic sensor can be used to monitoring the tool wear and vibration.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.2
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• pp.44-50
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• 2012

When the fiber Bragg gratings are embedded in a fiber-optic Sagnac loop for measuring temperature or strain, it is difficult to separate the Bragg wavelengths. The transmitted light is mixed with the reflected Bragg wavelengths in the photo-detector, working as noises. To suppress the noises, we placed the FBG sensors and a fiber-optic attenuator at asymmetric positions in the loop. With the arrangement the reflected light became much bigger than the transmitted light, enabling the separation of the reflected Bragg wavelengths with almost the same signal-to-noise ratio of the FBG sensors outside the loop.

• Korean Journal of Optics and Photonics
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• v.11 no.2
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• pp.91-96
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• 2000

We propose a novel in-line fiber optic circular polarizing mirror utilizing cholesteric lIquid crystal (CLC) polymer [11m for the fiber laser applications. Ions matrix representation of this device has been derived and venfied experimentally. In a Fabry-Perot cavity configuration, a CLC fiber optic rmrror has been used to achieve longitudinal mode suppression as well as to obtain passively mode~locked laser operations with 630 fs laser pulses via nonlinear polarization evoluhon.oluhon.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.10
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• pp.57-62
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• 2004

We report the fiber-optic current sensors composed of a side-polished single-mode fiber with the thermo-optic Polymer layer and the metal wire as a heater. The index change of polymer layers caused by the resistant heat of the metal wires induces the optical attenuation through the evanescent field of the side-polished single-mode fiber. Two types of the sensors are proposed and their characteristics as a current sensor are investigated.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.10
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• pp.1823-1825
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• 2007

Based on Faraday effect, the variation of current flowing through the conductor can be encoded as that of azimuth angle of light polarization propagating through the fiber coil wound onto the conductor. The amount of current can be obtained by measuring the variation of the light intensity transformed from that of the azimuth angle through a polarization analyzer. In this paper we propose a fiber-optic current sensor system that employs a fiber polarization analyzer as a sensor interrogation device. The fiber polarization analyzer was prepared by inscribing a long-period fiber grating on a high birefringent fiber. At the fixed wavelength of 1522.5 nm, the fabricated fiber device has the polarization extinction ratio of more than 25 dB. The measurement of large current up to 600 Arms was accomplished based on a simple fiber interrogation device and the measurement output of the sensor system showed a good linearity.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.223-236
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• 1999

The need to monitor and undertake remidial works on large structures has greatly increased in recent years due to the appearance of widespread faults in large structures such as bridges and buildings, etc, of 20 or more years of age. The health condition of structures must be monitored continuously to maintenance the structures. In order to do in-situ monitoring, the sensor is necessary to be embedded in the structures. Fiber optic sensors can be embedded in the structures to get the health information in the structures. The fiber sensor was constructed with $3{\times}3$ fiber couplers to sense the multi-point strains and failure instants. The 4 RC (reinforced concrete) beams were made to 2 of A type, 2 of B type beams. These beams were reinforced by the reinforcing bars, and were tested under the flexural loading. The behavior of the beams was simultaneously measured by the fiber optic sensors, electrical strain gages, and LVDT. The states of the beams were interpreted by these all signals. By these experiments, There were verified that the fiber optic sensors could measure the structural strains and failure instants of the RC beams, The fiber sensors were well operated until the failure of the beams. It was shown that the strains of the reinforcing steel bar can be used to monitor the health condition of the beams through the flexural test of RC beams. On the other words, the results were arrived that the two strains in the reinforcing bar measured at the same point can give the information of the structural health status. Also, the failure instants of beams were well detected from the fiber optic filtered signals.