• Journal of the Optical Society of Korea
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• v.17 no.2
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• pp.177-181
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• 2013

We present an all-fiberized power-scalable, sub-nanosecond mode-locked laser based on a frequency-shifted-feedback ring cavity comprised of an erbium-doped fiber, a downshifting acousto-optic modulator (AOM), and a bandpass filter (BPF). With the aid of the frequency-shifted feedback mechanism provided by the AOM and the narrow filter bandwidth of 0.45 nm, we generate self-starting, mode-locked optical pulses with a spectral bandwidth of ~0.098 nm and a pulsewidth of 432 to 536 ps. In particular, the output power is readily scalable with pump power while keeping the temporal shape and spectral bandwidth. This is obtained via the consolidation of bound pulse modes circulating at the fundamental repetition rate of the cavity. In fact, the consolidated pulses form a single-entity envelope of asymmetric Gaussian shape where no discrete internal pulses are perceived. This result highlights that the inclusion of the narrow BPF into the cavity is crucial to achieving the consolidated pulses.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.777-783
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• 2001

This paper is mainly concerned with the state of the practical developments of a constants PWM bridge type resonants DC-DC suitable converter for Nd:YAG Laser with a Microprocessor. (PIC16C54 & 8051) The use of IGBT power supply with feedback control of flashLamp currents imparts a advantages to Nd:YAG Laser for materials processing. these include the alility to tailor the pulseshape and modify pulse parameters on a pulse- by pulse basis. And Correct choice of pulseshape can enhance the repeatability of the process. as higher power IGBT became available, act ive pulseforming power supplies will find greater user in deep hole drilling machine By Using certain control tecniques, utililized in designing Pic16c54 from Microchip technology and Intel 8051, also Mornitoring from Microsoft Visual Basic 5, And it allowed us to designed and fabricate ahigh repel it ion rate and high power(HRHP) pulsed Nd:YAG laser system, As a result of that, the current pulsewidth could be contort led 200s to 350s(step 50s) , and the pulse repetition rate could be adjusted 500pps to 1150pps. In addition, in the case of one laser head consisting of a Nd:YAG laser rod and two flashlamps , the maximum laser output of 240w was produced at the condition of 350s and 1150pps, and that of about 480w was generated at the same condition when two laser heads were arranged in cascade.

• The Transactions of the Korean Institute of Power Electronics
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• v.2 no.3
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• pp.51-57
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• 1997

A new current controlled PWM technique with N.P.C structure is proposed in this paper. A current controlled PWM technique with neutral-point-clamped pulsewidth modulation inverter composed of main switching devices which operates as switches for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential is described. This inverter output contains less harmonic content as compared with that of a conventional current controlled PWM type. In addition, the proposed current controlled PWM technique has lower switching frequency than that of conventional current controlled PWM technique at the same current limit. Two inverters are compared analytically. The improved voltage waveform of current controlled PWM with N.P.C structure is analyzed and the performance is investigated by the computer simulation.

• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.390-396
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• 1996

A pulsed Ti : sapphire laser with a Z-folded cavity, which was pumped by a frequency-doubled Nd : YAG laser, was developed. A laser output energy of 822 $\mu$J with a pulsewidth of 5 ns and an output efficiency of 27.4% was obtained at a center wavelength of 790 nm using an output coupler of 18% reflectance. The slope efficiency was 35%. The output beam diameter was 0.9 mm, and the divergence angle was 1.8 mrad. The spectrum tunability was about 120 nm from 740 nm to 860 nm with a FWHM of 90 nm at an 18% output coupler and a pumping energy of 3 mJ.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.2018-2020
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• 1998

In design of a digital current controller for a 3$\phi$ voltage-source (VS) PWM converter, its conventional model, i.e., stationary or synchronous reference frame model, is used in obtaining its discretized version. It introduces, however, inherent errors since the following practical problems are not taken into consideration: the characteristics of the space vector-based pulsewidth modulation (SVPWM) and the time delays in the process of sampling and computation. In this paper, the new hybrid reference frame model of the 3$\phi$ VS PWM converter is proposed considering these problems. In addition, the direct digital current controller based on this model is designed without any prediction or extrapolation algorithm to compensate the time delay. So the control algorithm is made very simple. The validity of the proposed algorithm is proved by the computer simulation results.

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.490-493
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• 2005

We have experimentally studied supercontinuum generation in a photonic crystal fiber as a function of pump wavelength and intensity with 100 fs pulsewidth. A supercontinuum over 750 nm spectral width with amplitude variation less than 10 dB has been achieved. It was generated by coupling femtosecond pulses from a mode-locked Ti:Sapphire laser into a 2 m long photonic crystal fiber. Adjusting the parameters of the pump source, it was also possible to control different spectral features of the supercontinuum radiation.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.4
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• pp.331-338
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• 2005

In this paper the novel pulsewidth modulation(PWM) technique for the two-leg and four-leg two-phase inverter is proposed. The conventional space vector PWM technique for two-phase inverter was complex. The proposed PWM for two-leg inverter, which is used by sinusoidal PWM method, is simpler than the conventional SVPWU technique. Also, a simple PWM technique for four-leg two-phase inverter is proposed. Such PWM technique is based on PWM technique for two-leg inverter. Practical verification of theoretical predictions is presented to confirm the capabilities of the new techniques.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.1
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• pp.1-10
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• 2002

In this paper the space voltage vector pulsewidth modulation(SVPWM) technique for two-phase inverter is proposed. The two-phase SVPWM technique is applicable to two-phase induction motor drives. The two-phase inverter using two-phase SVPWM technique cannot generate zero voltage vectors, but four space vectors. A reference voltage vector in the square locus is realized by adjusting four space vectors. The switching sequence "two-phase symmetrical modulation" used in two-phase SVPWM is proposed. Practical verification of theoretical predictions is presented to conform the capabilities of the new technique.technique.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.5
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• pp.718-725
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• 2015

This paper proposes a novel level-shifted PWM (LS-PWM) strategy for fault tolerant cascaded multilevel inverter. Most proposed fault-tolerant operation methods in many of studies are based on a phase-shifted PWM (PS-PWM) method. To apply these methods to multilevel inverter systems using LS-PWM, two additional steps will be implemented. During the occurrence of a single-inverter-cell fault, the carrier bands scheme is reconfigured and modulation levels of inverter cells are reassigned in this proposed fault-tolerant operation. The proposed strategy performs balanced three-phase line-to-line voltages and line currents when a switching device fault occurs in a cascaded multilevel inverter using LS-PWM. Simulation and experimental results are included in the paper to verify the proposed method.

• Korean Journal of Optics and Photonics
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• v.6 no.2
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• pp.142-147
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• 1995

Soliton pulse outputs are generated with figure '8' type erbium-doped fiber laser mode-locked by using a fiber loop mirror. The fiber loop mirror consists of an erbium-doped fiber amplifier at the one end of the loop, and 504 m-long dispersion-shifted fiber as a nonlinear medium. By pumping with a $1.48{\mu}m$ wavelength laser diode and adjusting the polarization controllers inside the loop, soliton pulses are generated with 1574 nm center wavelength and 1.2 nm linewidth. The soliton pulses are found randomly spaced within the fundamental period corresponding to cavity round trip time. The autocorrelation trace shows that the pulse width is 2.4 ps, which is in good agreement with the theoretical prediction. The pulsewidth- bandwidth product is found to be 0.348 which means that the pulses are nearly transform-limited.imited.