• 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.

• Current Optics and Photonics
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• v.7 no.6
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• pp.665-672
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• 2023

This study focuses on investigating the impact of the spectral linewidth of a seed laser in a master-oscillator power amplifier (MOPA) configuration on stimulated Brillouin scattering and the beam quality of the output diffracted by a grating. To conduct the study, a distributed feedback (DFB) laser is modulated in a pseudorandom binary sequence (PRBS) and amplified by a two-stage Yb-doped fiber amplifier to achieve an output power of over 1 kW. The spectral linewidth of the seed laser is systematically varied from 1 to 12 GHz in the frequency domain by varying the PRBS modulation parameters. The experimental results reveal a tradeoff between suppressing stimulated Brillouin scattering and enhancing beam quality with increased spectral linewidth. Therefore, the study provides valuable insights into optimizing spectral beam combining to achieve high beam quality and scalable power upgrade in fiber lasers.

• Laser Solutions
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• v.17 no.3
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• pp.1-9
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• 2014

In this study, we analyzed fiber laser welding for the pure copper thin plates in a series of secondary lithium-ion batteries; and performed the experiment for the purpose of the preceding study to replace bolt joints method the with the laser welding method. We have changed the peak power of the laser from 5 to 6kW, the pulse duration by 4, 6, 8, and 10ms, the frequency by 10, 12, 16, and 25Hz, and the focal position by -3, 0, and +3. As a result, when the focal position is at +3, the peak power is 5kW, and the pulse duration and the Frequency are 4ms and 25Hz, respectively, we obtain 2.1 and 2.5 times better tensional strengths, respectively, than the highest values of tensional strengths obtained with the focal positions at 0 and -3.

• Journal of the Optical Society of Korea
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• v.19 no.1
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• pp.7-12
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• 2015

Up to ${\sim}520{\mu}J$ broadband mid-infrared (IR) supercontinuum (SC) generation in telecommunication multimode fiber (MMF) directly pumped by a $2.054{\mu}m$ nanosecond Q-switched Tm, $Ho:YVO_4$ laser is demonstrated. An average output power of 3.64 W is obtained in the band of ~1900 to ~2600 nm, and the corresponding optic-to-optic conversion efficiency is 67% by considering the coupling efficiency. The spectrum has extremely high flatness with negligible intensity variation (<2%) in the wavelength interval of ~2070 to ~2475 nm. The SC long-wavelength edge is limited by the silicon glass material loss, and by optimizing the MMF length, the SC spectrum could extend out to ${\sim}2.6{\mu}m$. The output SC pulse shapes are measured at different output powers, and no splits are found. The SC laser beam is nearly diffraction limited with an $M^2=1.15$ in $2.1{\mu}m$ measured by the traveling knife-edge method, and the laser beam spot is monitored by an infrared vidicon camera.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.9
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• pp.805-811
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• 2014

In this investigation, we constructed and demonstrated a simple Yb-doped fiber laser, of which longitudinal modes are mode-locked without any additional devices to compensate the dispersion caused by optical components. Non-linear polarization rotation (NPR) was adopted for the mode-locking mechanism and a polarization controller (PC) was used for a kind of spectral filters to restrict the bandwidth for mode-locking. As the result, the laser was successfully operated as mode-locked with the repetition rate of 42.2 MHz and the spectrum was broadened up to approximately 16 nm at 1033 nm center wavelength when the laser was mode-locked. In this paper, the operation of the developed Yb-doped mode-locked laser is explained with the concept of Lyot filter realized by a PC, which enables mode-locking under normal dispersion. In the industrial applications, this laser can be used as a seed laser of the high power lasers for optical manufacturing.

• Laser Solutions
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• v.18 no.3
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• pp.14-19
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• 2015

A helical fabricating method using $CO_2$ laser was utilized for producing cone-shaped structure on a silica substrate. Output power and the number of scanning radiation were modified in order to control the structure. The experiment shows that the depth and width of cone-shape were increased with higher output power of the laser and the number of scanning. We demonstrate fabrication of multidirectional side-firing optical fiber with diameter of 440 um using the $CO_2$ laser fabrication technique.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.17-21
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• 2004

We demonstrate an S/S＋band discretely tunable thulium doped fiber laser (TTDFL), anchored on a 50-㎓ ITU-T grid. Investigating the inversion analysis of the thulium doped fiber (TDF) in applying a dual wavelength (1.4 m and 1.5 m) pumping scheme, a laser whose tuning range covers most of the S/S＋band has been obtained. Within the wide 3-㏈ bandwidth of 65.1 nm, the output power of the tunable laser exceeds 6.1 ㏈m with very flat spectral profile and the number of DWDM channels generated is as large as 178. If we increase the subsidiary pump power to 22 ㎽, the bandwidth is expanded up to 66.2 nm. By controlling the temperature of the fine grid filter, we have also shown that the frequency locking capability of the laser can be improved. The laser developed in this work is expected to be utilized as a practical optical source providing reference wavelengths in the S/S＋band.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.322-325
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• 1999

We report fiber guiding experiments on the Photonic Quantum Ring(PQR) laser diode. In the 1km transmission measurements, we find that the PQR performs much better than the VCSEL. This suggests that the PQR laser is very promising candidate for LAN-range optical data communications. On the other hand, we have also fabricated 8$\times$8 PQR laser arrays and measured spatial decays for free space properties without using any guiding optics, which showed about 1m distance of spectral angle sensing.

• Journal of the Optical Society of Korea
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• v.2 no.2
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• pp.64-73
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• 1998

We have theoretically analyzed and experimentally observed the effects of wavelength dependent birefringence inside a laser cavity on the output characteristics of fiber lasers with a figure eight geometry. The spectral and polarization characteristics of fiber lasers are found to be very susceptible to the resultant birefringence composed of the intrinsically existing wavelength dependent birefringence and the externally induced birefringences inside the fiber. For the variation of twist-induced birefringence inside the nonlinear amplifying loop mirror, the laser output power and center wave-length of continuous wave lasers change periodically, but the polarization characteristics remains nearly unchanged. The changes of the birefringence inside the linear loop has little effect on the spectral characteristics but changes the polarization properties such as the polarization direction.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.8
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• pp.75-82
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• 2013

We propose a fiber grating sensor system for condition monitoring of large scale wind turbine blades. For the feasibility test of the proposed sensor system, a down-scaled wind turbine has been constructed and experimented. Fiber grating sensors were attached on a blade surface for distributed strain and temperature measurements. An optical rotary joint was used to transmit optical signals between the FBG sensor array and the signal processing unit. Instead of broadband light source, we used a wavelength-swept fiber laser to obtain high output power density. A spectrometer demodulation is used to alleviate the nonlinear wavelength tuning problem of the laser source. With the proposed sensor system we could measure dynamic strain and temperature profiles at multi-positions of rotating wind turbine blades.