• Korean Journal of Optics and Photonics
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• v.14 no.2
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• pp.189-193
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• 2003

A two-stage erbium-doped fiber amplifier (EDFA) with a band pass filter is used to get optical pulses of high peak value. The pulse signal has a 32 ㏈ extinction ratio, 125 W peak power and 79 ㎽ pulse off power. A nonlinear optical loop mirror (NOLM) is used to lower the pulse off power so as to increase the extinction ratio. The pulse signal after the NOLM has a 50.4 ㏈ extinction ratio, 35 W peak power and 0.3 ㎽ pulse off power.

• Korean Journal of Optics and Photonics
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• v.13 no.1
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• pp.9-14
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• 2002

A surface plasmon sensor has been fabricated for detection of concentration and refractive-index of a mixed solution. Based on the Kretschmann-Raether attenuated-total-reflection configuration, the sensor consists of 54 nm-thick Ag metal layer under a prism and a cell containing the mixed solution. We have observed a nonlinear refractive-index change as the ethanol-water concentration increased. The experimental results show us that the detection limit of the SPR sensor is 3$\times$10$^{-2}$ % in ethanol mass ratio. The concentration-to-index curve shows a linear increase in the range of ethanol concentration from 0% to 50%, but a nonlinearity is observed beyond 50%. We have modeled the nonlinearity and compared it with the experimental results.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.229-236
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• 2008

The optimum conditions of second harmonic generation (SHG) can be successfully achieved experimentally using single pass and double pass methods of a pumping beam. The beam has a power of several Watts radiated by a DOFA (Diode Laser Oscillator & Fiber Amplifier) system, which is a high power CW wavelength tunable infrared laser system, in a PPLN (Periodically Poled MgO doped Lithium Niobate) nonlinear crystal. In the case of a single pass method, the parameters are the wavelength of 535 nm for SHG and the output power of 245 mW generated from the pumping input beam with wavelength of 1070 nm and the power of 2.45 W at phase matching temperature of $108.9^{\circ}C$. The conversion efficiency of SHG was 10%. In order to enhance the output of SHG, the double pass method of the SHG system of a PPLN using a concave mirror for the retroreflection and a pair of wedged flat windows for phase compensation was also presented. In this double pass system, we obtained the SHG output beam with the wavelength of 535 nm and the maximum power of 383 mW at optimum phase matching temperature of $108.5^{\circ}C$ by using an incident pumping beam with wavelength of 1070 nm and the power of 2.45 W. The maximum conversion efficiency is 15.6%, which is more than that of the single pass method.

• Korean Journal of Optics and Photonics
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• v.15 no.3
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• pp.248-253
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• 2004

We propose a near- field scanning optical interferometer (NSOI) based on the facet reflection of a nano-sized moveable tapered optical fiber. The interferometer can measure the position and the wave-front of a focused spot simultaneously. The interfering fringes are generated by the reflected beams from the sample surface and from the fiber facet. The wave-front analysis at the focusing position is obtained by using a phase shifting technique with a four-step algorithm. It is found that the resolution for controlling the focal position of our proposed NSOI is less than λ/3 and the measured wave-front aberration at the focal position is in good agreement with the ones obtained by a Twyman-Green interferometer.

• Korean Journal of Optics and Photonics
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• v.16 no.1
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• pp.103-108
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• 2005

Second harmonic generation(SHG) by guided phase matching is observed in waveguide structure using the anomalous dispersion of a poled polymer. The second harmonic TM$_{0}$ guided mode could be generated from the fundamental TM$_{0}$ guided mode and then the second harmonic power was higher than any other phase matchable mode because the overlap integral between the fundamental and the second harmonic wave was the largest in the theoretical analysis. Near UV SHG(370 nm) was obtained from the fundamental wavelength of Ti-sapphire laser(740 nm).

• Current Optics and Photonics
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• v.6 no.5
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• pp.445-452
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• 2022

We developed an adaptive optics test bench using an optical simulator and two rotating phase plates that mimicked the atmospheric turbulence at Bohyunsan Observatory. The observatory was reported to have a Fried parameter with a mean value of 85 mm and standard deviation of 13 mm, often expressed as 85 ± 13 mm. First, we fabricated several phase plates to generate realistic atmospheric-like turbulence. Then, we selected a pair from among the fabricated phase plates to emulate the atmospheric turbulence at the site. The result was 83 ± 11 mm. To address dynamic behavior, we emulated the atmospheric disturbance produced by a wind flow of 8.3 m/s by controlling the rotational speed of the phase plates. Finally, we investigated how closely the atmospheric disturbance simulation emulated reality with an investigation of the measurements on the optical table. The verification confirmed that the simulator showed a Fried parameter of 87 ± 15 mm as designed, but a little slower wind velocity (7.5 ± 2.5 m/s) than expected. This was because of the nonlinear motion of the phase plates. In conclusion, we successfully mimicked the atmospheric disturbance of Bohyunsan Observatory with an error of less than 10% in terms of Fried parameter and wind velocity.

• Korean Journal of Optics and Photonics
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• v.25 no.6
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• pp.340-345
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• 2014

We experimentally demonstrate the use of a gold-deposited side-polished fiber as a $2-{\mu}m$-band polarizing device to produce mode-locked pulses from a thulium/holmium-codoped fiber ring cavity. The mode-locking effect was induced by nonlinear transmission caused by the gold-deposited side-polished fiber, due to nonlinear polarization rotation of the oscillated beam within the fiberized cavity. It is also shown that ~558-fs pulses with a peak power of ~6.7 kW could readily be produced at a wavelength of 1935 nm through subsequent thulium/holmium-codoped fiber amplification, due to the higher-order soliton compression effect.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.4
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• pp.133-140
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• 2006

The growth characteristics and properties of large size $SrAlF_5$ single crystals are described and compared with those of $BaMgF_4$. Transmission spectra in the vacuum ultraviolet wavelength region indicate a high transparency of $SrAlF_5$ (about 90% without considering surface reflection loses) down to 150 nm, on contrast to the optical loses observed for $BaMgF_4$. The ferroelectric character of $SrAlF_5$ is evidenced by the reversal of the spontaneous polarization in a hysteresis loop. The higher potential of $SrAlF_5$ in comparison with $BaMgF_4$ for the realization of all-solid-state lasers in the ultraviolet wavelength region by the quasi-phase matching (QPM) technique is pointed out. $SrAlF_5$, besides a higher grade of transparency, shows a nonlinear effective coefficient similar to that of quartz and uniaxial nature, on contrast to the one order smaller nonlinear coefficient and biaxial character of $BaMgF_4$. The refractive index of $SrAlF_5$ from the ultraviolet to the near-infrared wavelength region is measured by the minimum deviation method. The Sellmeier and Cauchy coefficients are obtained from the fits to the curves of the ordinary and extraordinary refractive indices, and the grating period for the first order QPM is estimated as a function of the wavelength. The poling periodicity for 193 nm SHG from 386 nm is $4{\mu}m$.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.308-314
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• 1997

We have studied the generation of an array of dark spatial solitons in a self-deforcusing medium. Unlike a single fundamental dark spatial soliton, we show numerically that the generation of an array of dark spatial solitons from a spatially sinusoidal input beam needs an adiabatic amplification of nonlinear refractive index with the beam propagation distance. In experiment, we establish a Mach-Zehnder interferometer for making the sinusoidal input beam and use a cylindrical lens for the adiabatic amplification. We observe that the dark soliton's dip-width becomes narrower and the background intensity distribution becomes flatter with increasing the nonlinearity.

• Bulletin of the Korean Chemical Society
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• v.32 no.9
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• pp.3361-3366
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• 2011

New Y-type polyester (3) containing nitrophenylazoresorcinoxy groups as NLO chromophores, which are components of the polymer backbone, was prepared and characterized. Polyester 3 is soluble in common organic solvents such as N,N-dimethylformamide and acetone. It shows a thermal stability up to $240^{\circ}C$ in thermogravimetric analysis with glass-transition temperature ($T_g$) obtained from differential scanning calorimetry near $116^{\circ}C$. The second harmonic generation (SHG) coefficient ($d_{33}$) of poled polymer film at the 1064 nm fundamental wavelength is around $4.63{\times}10^{-9}$ esu. The dipole alignment exhibits a thermal stability even at $4^{\circ}C$ higher than $T_g$, and there is no SHG decay below $120^{\circ}C$ due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.