• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.220-220
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• 2011

The Ne-Xe plasmas in dense plasma-focus device with coaxial electrodes were generated for extreme ultraviolet (EUV) lithography. The influence of gas mixture ratio, Ne-Xe (1, 10, 15, 20, 25, 30, 50%) mixture gas, on EUV emission measurement, EUV intensity and electron temperature in the coaxially focused plasma were investigated. An input voltage of 4.5 kV was applied to the capacitor bank of 1.53mF and the diode chamber was filled with Ne-Xe mixture gas at a prescribed pressure. The inner surface of the cylindrical cathode was lined by an acetal insulator. The anode was made of tin metal. The EUV emission signal of the wavelength in the range of 6~16 nm has been detected by a photo-detector (AXUV-100 Zr/C, IRD). The visible emission line was also detected by the composite-grating spectrometer of the working wavelength range of 200~1100 nm (HR 4000CG). The electron temperature is obtained by the optical emission spectroscopy (OES) and measured by the Boltzmann plot with the assumption of local thermodynamic equilibrium (LTE).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.5288-5293
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• 2014

This paper presents the characterization of the wavelength selective switch using a LCOS display instead of a MEMS device, which is a core technology for the next generation ROADM. We constructed a five-port WSS, and examined the basic characteristics of the WSS, such as the response time, beam steering, insertion loss, and channel isolation. The response time of WSS was 11.6 mS and the beam steering characteristics of LCOS was well performed. The measured insertion loss at 40 channels in the c-band were 5.5~12.7 dB and channel isolation was 16~18 dB. Although the characteristics of LCOS-based WSS are inferior to the conventional MEMS-based WSS, it can be improved by additional experiments that secure the technology competitiveness.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.49-55
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• 2002

In this paper, we present the simulation monitoring of strain and temperature during and after the cure of unsymmetric composite laminate using fiber optic sensors. Fiber Bragg grating/extrinsic Fabry-Perot interferometric (FBG/EFPI) hybrid sensors are used to measure those measurands. The characteristic matrix of the sensor is analytically derived and measurements can be done without sensor calibration. A wavelength-swept fiber laser is utilised as a lighr source. Two FBG/EFPI sensors are embedded in a graphite/epoxy unsymmetric cross-ply composite laminate in different directions and different locations. We perform a real time monitoring of fabrication strains and temperatures at two points of the composite laminate during cure process in an autoclave. Also, the thermal strains and temperatures of the fabricated laminate are measured in a thermal chamber. Through these experiments, we can provide a basis for the efficient smart processing of composite and know the thermal behavior of unsymmetric cross-ply composite laminate.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.155.1-155.1
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• 2011

The Korea Astronomy and Space Science Institute (KASI) and the Department of Astronomy at the University of Texas at Austin (UT) are developing a near infrared wide-band high resolution spectrograph, IGRINS (Immersion Grating Infrared Spectrograph). The white-pupil design of the instrument optics uses 7 cryogenic mirrors including 3 aspherical off-axis collimators and 4 flat fold mirrors. Two of the 3 collimators are H- and K-band pupil transfer mirrors and they are designed as compensators for the system alignment in each channel. Therefore, their mount design will be one of the most sensitive parts in the IGRINS optomechanical system. The other flat fold mirrors are designed within the limited area. Each of those includes the features of 3 axial hard points and 2 radial hard points with one spring plunger in order for the proper deflection of the mirror. The design work will include the computer-aided 3D modeling and finite element analysis (FEA) to optimize the structural stability and the thermal behavior of the mount models. The mount body will also include a tip-tilt and translation adjustment mechanism to be used as the alignment compensators.

• Korean Journal of Optics and Photonics
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• v.10 no.2
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• pp.162-168
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• 1999

A new design of four-pass dye laser amplifier affording a narrow-bandwidth pulsed output is demonstrated to suppress the amplified spontaneous emission(ASE) carried by the amplifier output and reduce the possibility of parasitic oscillation in the amplifier. By the direct pulsed amplification of a cw 100 mW dye laser under a Q-switched doubled Nd:YAG laser pumping with energy of 5.6 mJ/pulse, high-peak-power pulsed output with 1.5-mJ energy in 130-MHz bandwidth is obtained corresponding to a power gain greater than $2{\times}10^6$ and an energy efficiency of 27%. The ASE ratio in the four-pass amplifier output is dramatically reduced by using a diffraction grating in the amplifier. Compared with the results obtained from the normal operation of the amplifier with no frequency-selective device, the ASE ratio is reduced by a factor in excess of 10 to remain under 1.5% of the amplifier output whereas the total output energy is slightly increased by ~4%.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.6
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• pp.607-613
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• 2008

A monitoring system for the subway structures using prestrained FBG sensors fixed with partially stripped fibers was developed. The sensor packages had pre-strain controllable fixtures. Tensile and compressive strain of the structure could be measured without slip. The FBG sensor system was applied to the concrete lining structure in Taegu subway. Near the structure, the narrow tunnel construction, for the electric power cables and telecommunication cables, started. We wanted to measure the deformations of the subway structures due to the construction by the FBG sensor. The applied sensors had the gauge length of 1 meter to overcome the inhomogeneity of the concrete material with enough length. In order to fix tightly to the structure, the partially stripped parts of the sensor glued to the package and slip phenomenon between fiber and acrylate jacket was prevented. Prestrain of the sensor was imposed by controlling the two fixed points with bolts and nuts in order to measure compressive strain as well as tensile strain. The behavior of subway lining structure could be monitored very well.

• Korean Journal of Optics and Photonics
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• v.12 no.4
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• pp.305-311
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• 2001

The new and simple velocimetry model to be perpendicularly arranged with two optical systems with a projected and reduced rotatable line grating is so proposed as to withstand an external vibration. We measured successfully the various velocities (V_{chop}$) of a chopper by using the new velocimeter. As a result, when rotational angles of projected volume gratings in two optical systems are $\alpha=73^{\circ}$ and $\beta=73^{\circ}$, respectively, we measured successfully the chopper velocities within 1 % accuracy from $V_{chop}=43.52cm/s to 249.36cm/s$. In this new velocimetry, we can determine the confidence of .the system by comparing the z-component of velocity, to be measured in one optical system with $V_z$ to be measured in one optical system with $V_z^'$ to to be measured in another optical system, which should be same.e same.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.331-336
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• 1995

The steady-state absorption saturation of the photodarkend SDG was investigated. The absorption saturation intensity was observed to increase for the photodarkened sample. The diffraction efficiency of the permanent grating due to photodarkening was also measured using the backward DFWM technique. For the low backward pump intensity, the diffraction efficiency was proportional to the intensity of the pump beam. The origin of increasing diffraction efficiency is attributed to the difference in absorption between the permanent gratings created by photodarkening. ening.

• Journal of the Optical Society of Korea
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• v.18 no.5
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• pp.436-441
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• 2014

We have demonstrated an amplified wavelength-division multiplexed (WDM) passive optical network (PON) by using broadband light source (BLS) seeded optical sources and chirped fiber Bragg gratings (FBGs) based dispersion compensators. Chirped FBGs located at central office (CO) were fabricated and used as channel-by-channel dispersion compensators in order to mitigate the dispersion-induced distortion of both downstream and upstream signals. Owing to a low insertion loss of chirped FBG based dispersion compensator, the optical signal-to-noise ratio (OSNR) of the downstream signal could be improved to be ~28 dB. Thus, we re-confirmed that an error-free transmission of 1.25 Gb/s signals over a 100 km single-mode fiber (SMF) link could be achieved with a proposed amplified WDM-PON architecture. We have also evaluated the impact of various noises on the system's performance, and found that the low OSNR of the downstream signal would be a main limiting factor on the maximum reach of the proposed amplified WDM-PON architecture. From the measured ~13 dB improvement in OSNR of the downstream signal compared to our previously-proposed dispersion compensating module based scheme, we believe that the proposed architecture can accommodate a reach of longer than 100 km SMF link easily.

• Journal of Korean Association for Spatial Structures
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• v.9 no.3
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• pp.67-74
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• 2009

Presently means of utilizing sensors such as Piezoelectric(PZT) Element for evaluating the affect of oscillator, strain gauge for analyzing physical changes and use of Fiber Bragg Grating(FBG) Sensor are widely practiced in the field. In this study, PZT and FBG sensors were used to tearing damage of cable systems in these sensors. Cable systems are a construction of elements carrying only tension and no compression or bending in membrane structure. But damage detection of cable systems by using existing safety diagnosis is difficult to detect the characteristic change of overall structural action. If cable snaps are occurred to cable release and tear in tension structures, these are set up a vibration. So, we used piezo-electric materials and result of experiment using this was compared with result of experiment using FBG sensors The purpose of this research is to develop of damage detection method of cable system in tensile stress.