• Journal of the Optical Society of Korea
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• v.9 no.2
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• pp.49-53
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• 2005

We report a new configuration of a reflection-type confocal scanning optical microscope system for measuring the refractive index profile of an optical waveguide. Several improvements on the earlier design are proposed; a light emitting diode (LED) at 650 nm wavelength instead of a laser diode (LD) or He-Ne laser is used as a light source for better index precision, and a simple longitudinal linear scanning and curve fitting techniques are adapted instead of a servo control for maintaining an optical confocal arrangement. We have obtained spatial resolution of 700 nm and an index precision of $2\times10^{-4}$. To verify the system's capability, the refractive index profiles of a conventional multimode fiber and a home-made four-mode fiber were examined with our proposed measurement method.

• Proceedings of the IEEK Conference
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• 2000.06b
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• pp.119-122
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• 2000

The speckle pattern is formed by laser light from a multimode optical fiber. The speckle fluctuation is the result of interference among propagation modes when the optical fiber is subjected to a mechanical distortion at any point along its length. The experiments were carried on for the study of the feasibility of producing an intrusion detection system using the speckle fluctuation. The speckle fluctuation signals were monitored at real time by an oscilloscope which was connected with an amplifier and a filter. The experiment results showed that the intrusion sensor had enough sensitivity to detect an intruder.

• Current Optics and Photonics
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• v.4 no.4
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• pp.286-292
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• 2020

Imaging through multicore fiber (MCF) is of great significance in the biomedical domain. Although several techniques have been developed to image an object from a signal passing through MCF, these methods are strongly dependent on the surroundings, such as vibration and the temperature fluctuation of the fiber's environment. In this paper, we apply a new, strong technique called deep learning to reconstruct the phase image through a MCF in which each core is multimode. To evaluate the network, we employ the binary cross-entropy as the loss function of a convolutional neural network (CNN) with improved U-net structure. The high-quality reconstruction of input objects upon spatial light modulation (SLM) can be realized from the speckle patterns of intensity that contain the information about the objects. Moreover, we study the effect of MCF length on image recovery. It is shown that the shorter the fiber, the better the imaging quality. Based on our findings, MCF may have applications in fields such as endoscopic imaging and optical communication.

• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.366-370
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• 2006

An optical microphone incorporating a reflective diaphragm and a fiber-optic head was demonstrated. The diaphragm was made of a micromirror membrane which is suspended by a silicon bar connected to a frame, allowing fer a displacement induced by acoustic waves. A compact, simple optical head was implemented by exploiting a single multimode fiber. For the assembled microphone, the static characteristics were investigated to find the operation point defined as the optimum distance between the head and the diaphragm, and a flat frequency response with a variation of $\sim$2dB for the range of up to 2 kHz was accomplished.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.214-215
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• 2000

As silica based optical fibers and preforms are processed at a high temperature, residual stresses are bulit in the strucure when cooled down to the room temperature. The magnitude of the residual stress depends on the difference in the thermal expansion coefficients between core and cladding glass as well as on the temperature difference. Residual stress distribution determines the intrinsic strength and could affect the long term reliability of optical fibers. And furthermore, stress can introduces anisotropy into optical fibers by photoelastic effects. The analysis of thermal stress has been intensively studied for multimode fibers$^{(1)}$ and the authors and co-wokers recently reported the stress distribution in a depressed inner cladding structure$^{(2)}$ . The compositions of the glass in the previous studies, however, have been restricted to conventional glass formers, such as GeO2, B2O3, P2O5, Fluorine. (omitted)

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.411-414
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• 2000

Optical Triangulation Probes (OTPs) are widely used for their simple structure. high resolution, and long operating range. However, errors originating from speckle, inclination of the object, source power fluctuation, ambient light, and noise of the detector limit their usability. In this paper, we propose new design criteria for an error-reduced OTP. The light source module for the system consists of an incoherent light source and a multimode optical fiber for eliminating speckle and shaping a Gaussian beam Intensity profile. A diffuse-reflective white copy paper, which is attached to the object, makes the light intensity distribution on the change-coupled device(CCD). Since the peak positions of the intensity distribution are not related to the various error sources, a sub-pixel resolution signal processing algorithm that can detect the peak position makes it possible to construct an error-reduced OTP system

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2447-2449
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• 1999

This paper presents a distributed temperature sensor which uses a multimode optical fiber. The temperature distribution is derived from the intensity of the Raman back scattering light. Testing the sensors on measurement length of 2km of this system shows good temperature characteristics of the heated/cooled section. These performance will useful to design such as monitoring abnormal temperature rise of electric facilities.

• Convergence Security Journal
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• v.8 no.4
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• pp.153-159
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• 2008

Graded-Index Multimode Optical fibers have recently received a lot of attention as regards their application and lightwave behavior in relation to broadband communication links. Accordingly, this aticle presents a novel lightwave mode analysis that solves the wave equation using a numerical analysis based on an eigenvalue problem method, thereby avoiding the typical complicated Bessel function method. Angular depedences and number of modes were observed as well. Future research implications will be possibly noticed such areas as bending effects and mode coupling analyses thru this research.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.7
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• pp.42-49
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• 1999

In this paper, we proposed a simple measurement method to find the behaviors of the fiber-to-waveguide coupler. The polished fiber blocks and planar waveguides on silicon dioxide were fabricated independently and then optically coupled by physical pressure. Several kinds of polymer with different refractive indices were used for waveguide films. The proposed method makes it possible to measure the center wavelength, bandwidth, extinction ratio, and polarization dependence of the coupler during fabrication procedure. The wavelength sensitivity increased with refractive index of polymer. The symmetric planar waveguide structure and isotropic property of guiding materials reduced polarization dependent property. Insertion loss of the coupler was less than 0.5dB. It is expected that our measurement method is useful for developing various optical devices using evanescent coupling between polished fiber and planar waveguide such as optical modulators and filters etc.

• Journal of the Korean Vacuum Society
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• v.6 no.3
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• pp.220-226
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• 1997

An optical intensity-type pressure sensor has been fabricated by coupling multimode optical fiber with 100 nm-Au/30 nm-NiCr/150 nm-$Si_3N_4/300 nm-SiO_2/150 nm-Si_3N_4$ optical reflection layer supported by micromachined frame-shape silicon substrate, and its characteristics was investigated. For the application of $Si_3N_4/SiO_2/Si_3N_4$ diaphragm to the optical reflection layer of the sensor, NiCr and Au films were deposited on the backside of the diaphragm by thermal evaporation , respectively, and thus optical low caused by transmission in the reflection layer could be decreased to a few percents. Dielectric diaphragms with uniform thickness were able to be also reproduced because top- and bottom-$Si_3N_4$ layer of the diaphragm could automatically stop silicon anisotropic etching. The respective pressure ranges in which the sensor showed linear optical output power-pressure characteristics were 0~126.64 kPa, 0~79. 98 kPa, and 0~46.66 kPa, and the respective pressure sensitivities of the sensor were about 20.69 nW/kPa, 26.70 nW/kPa, and 39.33 nW/kPa, for the diaphragm sizes of 3$\times$3 $\textrm{mm}^2$, 4$\times$4 $\textrm{mm}^2$, and 5$\times$5 $\textrm{mm}^2$, indicating that the sensitivity increases as diaphragm size increases.