• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.301-307
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• 2002

The propagation characteristic of an optical waveguide was investigated by measuring with a near-field scanning optical microscope (NSOM) the evanescent field formed at the neighbor of its core-cladding interface. For this purpose, the NSOM system was developed specially as a form of Photon scanning tunneling microscope. The evanescent field distributions of several channel waveguides were measured at the wavelength of 1550 ㎚, and the usefulness of the system was verified by comparing experimental results with simulation results. In particular, the interference phenomena of the guided modes during their propagation along a multimode channel waveguide could be observed directly from the measured evanescent field distribution.

• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.134-141
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• 1997

We design the single mode dispersion-compensating fibers (DCF) which may be necessary for upgrading the previously installed 1.31 ${\mu}{\textrm}{m}$ optical communication system to the 1.55 ${\mu}{\textrm}{m}$ system. To obtain the optimum index profile that allows large negative dispersion at 1.55 ${\mu}{\textrm}{m}$, parabolic-index, double-clad fibers are analyzed by applying the 1-D FEM to the scalar wave equation of optical fibers. In constideration of macro-bending loss, the fibers are designed so that the cutoff wavelength of the $LP_{01}$ mode is greateer than 1.80 ${\mu}{\textrm}{m}$. The computer simulations show that the lower bound of the dispersion at 1.55 ${\mu}{\textrm}{m}$ is limited to about -120 ps/nm . km for the fiber index profiles satisfying the $LP_{01}$'s cutoff condition.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.3
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• pp.309-319
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• 2014

This paper mainly focuses on the conceptual design and stealth performance of the three-surface military aircraft. A three-dimensional (3-D) digital mock-up of the three-surface strike fighter with stealth feature was designed and the schemes of carrying missiles were analyzed in CATIA. Based on physical optics principle and the Method of Equivalent Currents (MEC), a numerical simulation of the RCS feature of the aircraft was carried out with RCSPlus which is a software designed by Beihang University. The paper contributes to the RCS feature analysis of the whole plane and different parts on X-band, S-band and UHF-band and a comparison of RCS feature to Su-37 and T-50 military aircraft is drawn. On X-band, the pitch angle of the incident wave was $0^{\circ}$, and the result shows: (1) Compared with Su-37 aircraft, the forward scattering RCS of the three-surface strike aircraft was reduced to 14.9%, the side scattering RCS to 9.6% and the back scattering RCS to 40.2%. (2) Compared with T-50 aircraft, the forward scattering RCS was reduced to 38.61%, and the side scattering RCS to 67.26%. This paper should be useful for researchers in conceptual design and stealth technology of the military aircraft.

• Current Optics and Photonics
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• v.3 no.6
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• pp.583-589
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• 2019

We report experimental results on 940-nm 350-mW AlGaAs/InGaAs transverse single-mode laser diodes (LDs) adopting graded-index separate confinement heterostructures (GRIN-SCH) and p,n-clad asymmetric structures, with improved temperature and small-divergence beam characteristics under high-output-power operation, for a three-dimensional (3D) motion-recognition sensor. The GRIN-SCH design provides good carrier confinement and prevents current leakage by adding a grading layer between cladding and waveguide layers. The asymmetric design, which differs in refractive-index distribution of p-n cladding layers, reduces the divergence angle at high-power operation and widens the transverse mode distribution to decrease the power density around emission facets. At an optical power of 350 mW under continuous-wave (CW) operation, Gaussian narrow far-field patterns (FFP) are measured with the full width at half maximum vertical divergence angle to be 18 degrees. A threshold current (I_th) of 65 mA, slope efficiency (SE) of 0.98 mW/mA, and operating current (I_op) of 400 mA are obtained at room temperature. Also, we could achieve catastrophic optical damage (COD) of 850 mW and long-term reliability of 60℃ with a TO-56 package.

• Korean Journal of Optics and Photonics
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• v.5 no.3
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• pp.349-355
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• 1994

Superrsolution of an optical imaging system, which resolves $\epsilon_O$ (half width of the square top amplitude impulse function) less than the Rayleigh's resolution limit $\epsilon_R$, is theoretically treated by using the diffraction theory, and an experimental system is proposed. Initially superresolution is stated as an inverse problem, and an integral equation is derived as a function of parameter $\beta$, which is positive. The integration is numerically carried out for the given aperture and those given values of $\beta$, which is 1, 5, 10, 15, and 20. 1/2$\times$FWHM's of the amplitude impulse functions are meassured for the cases of diffrent value of {J and in the case of $\beta=5$, the half-width already approaches to $\epsilon_O=0.1$,urn, which is, in the case of the present work, one fifth of the Rayleigh's resolution limit. It is found both the pupil function and the phase of the Huygens wave are to be modified, and theories of the pupil function modulation plate and the phase modulation hologram plate are also presented. The result obtained may be useful in ultrafine optical lithography.graphy.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.287-292
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• 2004

This paper presents the effect of scratches on an optical connector interface surface on the insertion loss of optical connectors. We propose a model for calculating the insertion loss of optical connectors. The model is expressed in terms of geometrical parameters of scratches assuming that the transmission coefficient of a light wave on the scratch surfaces is linearly varied as a function of scratch depth. Geometrical parameters of scratches such as location, width, and depth of scratches are measured using 3D optical interferometry surface profiler. We obtain the equation of the transmission coefficient in terms of scratch depth comparing the experimental insertion loss data to the insertion loss data using the model presented in this paper. Using the model and the equation of the transmission coefficient presented in this paper, we present the results of the insertion loss of optical connectors for various geometrical parameters of scratches. Scratches which are located at longer than two times the core radius from the center of the core show negligible effect on the insertion loss of optical connectors.

• Korean Journal of Optics and Photonics
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• v.28 no.6
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• pp.334-338
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• 2017

This research aims at investigating science teachers' perception of the refractive index of materials, and thus achieving proper information transmission and teaching of refractive index. Specifically, we have made questionnaires on what physical factors influence the refractive index of a liquid easily available in secondary schools. It was found that 80.0% of science teachers perceived that the density has the greatest influence on the refractive index, among a variety of factors such as molecular structure, the number of molecules per unit volume, mass of each molecule, and the wavelength of light, to mention just a few. This may be due to the fact that current textbooks deal with the refraction of light based on analogy to a mechanical wave. Such a misunderstanding may lead to confusion and misunderstanding for students.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.118-124
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• 2015

The design of radar absorbing structures(RAS) is a discrete optimization problem and is usually processed by stochastic optimization methods. The calculation of radar cross section(RCS) should be decreased to improve the efficiency of designing RAS. In this paper, an efficient method using impedance matching is studied to design RAS for minimizing RCS. Input impedance of the minimal RCS for the specified wave incident conditions is obtained by interlocking physical optics(PO) and optimizations. Complex permittivity and thickness of RAS are designed to satisfy the calculated input impedance by a discrete optimization. The results reveal that the studied method attains the same results as stochastic optimization which have to conduct numerous RCS analysis. The efficiency of designing RAS can be enhanced by reducing the calculation of RCS.

• Korean Journal of Optics and Photonics
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• v.9 no.5
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• pp.307-314
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• 1998

We have studied the effects of interface on polarization dependence of waveguide and designed the polarization independent 2-dimensional waveguides on InP for arrayed waveguide grating. To figure out the effects of interface on polarization dependence, we have solved the 1-dimensional wave equation using a transfer matrix method. It is shown that the birefringence becomes stronger as the number of interfaces increases. In order to design polarization independent 2-dimensional waveguides, we have used effective index method. The structures considered are ridge type, raised strip type, and buried type waveguide. In the cases of ridge and raised strip type, conventional effective index method was used. In the case of buried type corrected effective index method was used. We have determined the height and width of waveguides such that the waveguides become polarization independent.

• Journal of Biosystems Engineering
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• v.28 no.4
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• pp.351-360
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• 2003

This study was carried out to settle the plugging problem which occurs frequently when agricultural wettable powder is used in pest control work using the crushing and the dispersing effects caused by irradiation of ultrasonic wave. Sonication was applied to the wettable powder suspension in a beaker for 30 seconds using a 28 kHz, 200 W PZT BLT, and the image of suspension before and after sonication was observed using a microscope and a SEM. The image of tow commercial wettable powder suspensions in water observed using an optics microscope showed that the agglomerated particles were irregularly distributed over the whole observed region when stirred mechanically, while showing more uniform distribution composed of comparatively single particles in the whole observed region after sonication. Concerning the above, the projected areas of particles in the four suspensions after sonication were decreased distinctively in the observed range of the microscope and the atomization of crystals was much developed. Over the measured range of 5.6∼4,157 ${\mu}$m particle size, the overall projected area of particles was decreased to 58.3∼89.6% on the average after sonication. When the SEM images of sonicated wettable powder suspensions dissolved in water and CH$_3$OH were compared to the suspensions before sonication, such phenomena as the atomization of particles, the expansion of voids between particles, the reduction and the decrease of agglomerated particle groups, and the progress of crack developments on the surface of flake-shaped particles were observed. It seemed possible that the plugging problem that occurs frequently in pest control machine when using wettable powder would be settled by the use of sonication.