• Journal of the Korean Institute of Telematics and Electronics
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• v.21 no.1
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• pp.38-44
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• 1984

Subnanosecond optical pulses with 0.8-1.Bum wavelength are generated by experimentally realizing a single pass fiber Raman laser. This fiber Raman laser is pumped by a mode-locked and Q-switched Nd-YAG laser. Two wave sum frequency phenomenon is also obsenred in the course of the experimental work. The fiber Raman laser is then used to measure dispersion characteristics of a sin\ulcorner mode fiber in the long-wavelength lesion.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.376-380
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• 2004

This paper is to develop an optical ruer displacement sensor for monitoring high speed spindle. Proper magnitude of optical power as well as amplification of output signal are necessary to improve sensitivity of the sensor. In this paper, to meet the need of improvement of the sensor resolution, we choose proper optical power and amplification level through speculating on optical power of a laser diode.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.5
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• pp.985-990
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• 2007

The method of enhancing visibility in optical fiber sensor was investigated by improving coherence length of light source. The optical feedback technique is used to enhance coherence length in fiber laser which generates laser in near infrared wavelength region and utilizes low loss characteristics of optical communication grade fiber. In this paper, the effect to coherence length by short and long optical feedback paths are investigated by using Mach-Zehnder interferometer technique. The effect to coherence length by changing optical feedback power and optical modulation are investigated. The spectral drift was calculated by measuring the degree of phase perturbation in unbalanced Mach-Zehnder interferometer having loom path difference. The short optical feedback path was effective to reduce spectral drift to 450kHz/sec and the long optical feedback path in combination with short optical feedback path was found to further reduce spectral drift to 50kHz/sec.

• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.386-389
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• 1996

We report on comparative results obtained from harmonically mode-locked laser operations of ring-type and figure-of-eight(F8) type erbium-doped fiber lasers by using a directional-coupler type electro-optic modulator as an active mode-locker. The mode-locked and transform-limited pulses of 10.6 ps width were obtained at harmonics of the fundamental cavity frequency with the F8 type laser while mode-locked laser pulses greater than 15 ps were achieved with the ring type laser.

• Laser Solutions
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• v.16 no.2
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• pp.12-15
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• 2013

In this paper, we controlled the edge angle of fiber by using $CO_2$ laser. In order to control the angle, tilting angle of fiber on stage and the number of scan repetition are adjusted, and laser power is fixed at 30 W in the experiment. In the polishing result, the edge angle of fiber can be changed from $4^{\circ}$ to $8^{\circ}$, as changing the tilting angle and the number of scan repetition. This $CO_2$ laser polishing can fabricate ball lenses with various curvatures and a sharp probe as well as the edge angled fiber.

• Journal of Welding and Joining
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• v.20 no.1
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• pp.41-46
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• 2002

A new laser welding system far the appendage of bearing pads of PHWR nuclear fuel elements has been developed. This system consists of laser oscillator, a optical fiber transmission, a monitoring device and a welding controller. The basic welding experiments of the appendage of Zircaloy-4 bearing pads were carried out. The laser welded samples were investigated and made by using the optical fiber of GI $400\mu\textrm{m}$. As a result, the seam welding with the bead width of 1.0mm and the weld penetration of 0.3mm could be accomplished.

• Journal of the Optical Society of Korea
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• v.11 no.2
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• pp.63-66
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• 2007

A 9.6 dB gain is observed at 1310 nm in a 5.0 cm bismuth-doped silica fiber. A launched pump power of 100 mW was obtained using an 810-nm laser diode. We demonstrated the simultaneous optical amplification at two wavelengths near second telecommunication windows, which is the range of zero-dispersion for silica fibers.

• Journal of the Optical Society of Korea
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• v.6 no.2
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• pp.37-43
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• 2002

Using the polarization dependence of laser output powers, we measured the characteristics of the birefringence, such as the magnitude of phase retardation, the ellipticity, and the off axis angle to the fiber optical axis, inside the ring type fiber laser cavity.

• Journal of the Optical Society of Korea
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• v.17 no.3
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• pp.231-236
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• 2013

We present both theoretically and experimentally the thermo-optic characteristics of micro-structured optical fiber (MOF) filled with mixed liquid. The performance of MOF depends on the efficient interaction between the fundamental mode of the transmitted light wave and the tunable thermo-optic materials in the cladding. The numerical simulation indicates that the confinement loss of MOF presents higher temperature dependence with higher air-filling ratios $d/{\Lambda}$, longer incident wavelength and fewer air holes in the cladding. For the 4cm liquid-filled grapefruit MOF, we demonstrate from experiments that different proportions of solutions lead to tunable temperature sensitive ranges. The insertion loss and the extinction ratio are 3~4 dB and approximate 20 dB, respectively. The proposed liquid-filling MOF will be developed as thermo-optic sensor, attenuator or optical switch with the advantages of simple structure, compact configuration and easy fabrication.

• Smart Structures and Systems
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• v.9 no.5
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• pp.461-472
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• 2012

This study proposes an optics-based active sensing system for continuous monitoring of underground pipelines in nuclear power plants (NPPs). The proposed system generates and measures guided waves using a single laser source and optical cables. First, a tunable laser is used as a common power source for guided wave generation and sensing. This source laser beam is transmitted through an optical fiber, and the fiber is split into two. One of them is used to actuate macro fiber composite (MFC) transducers for guided wave generation, and the other optical fiber is used with fiber Bragg grating (FBG) sensors to measure guided wave responses. The MFC transducers placed along a circumferential direction of a pipe at one end generate longitudinal and flexural modes, and the corresponding responses are measured using FBG sensors instrumented in the same configuration at the other end. The generated guided waves interact with a defect, and this interaction causes changes in response signals. Then, a damage-sensitive feature is extracted from the response signals using the axi-symmetry nature of the measured pitch-catch signals. The feasibility of the proposed system has been examined through a laboratory experiment.