• Korean Journal of Optics and Photonics
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• v.31 no.2
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• pp.105-110
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• 2020

A compact beam combiner based on two-mode interference (TMI) in multimode waveguides is proposed, and its feasibility is shown through simulation with the three-dimensional beam propagation method. The input waveguides are separated by about 1 ㎛ at the interface with the multimode waveguide, so that the fabricated waveguide pattern is well repeated. The power transmission to the output port from the red, green, and blue input port is 93.5%, 94%, and 93%, respectively. When the wavelength deviation from a center wavelength is 10 nm, the power transmission is maintained to be greater than 90%. When the waveguide width error is 40 nm, the power transmission is maintained to be greater than 85% for all the three colors. The polarization dependence of the beam combiner is almost negligible, and its size is as tiny as 0.02 × 4 ㎟.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.113-119
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• 2003

During the mission operation time, it is very important to estimate the spacecraft propellant remaining as accurately as possible. This is because the quantity of propellant is related directly to how long the satellite can be operated ín orbit. There are two different methods for spacecraft propellant gauging; the PVT method and the book-keeping method. This paper describes the characteristics and applications of these methods using the flight operation data of KOMPSAT-1. Additionally, propellant consumption rates in delta-V maneuvering and each attitude control submode are analyzed according to spacecraft operation modes. The earth search submode shows the highest propellant consumption rate.

• Journal of the Korean Home Economics Association
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• v.26 no.3
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• pp.13-31
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• 1988

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.9
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• pp.31-37
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• 2004

We have proposed a design methodology for large active-area single-mode VCSELS, which have higher reliability and output power, and are well-suited for high-speed operation. The key idea underlying the design methodology is to reduce the effective index difference between active and cladding regions by controlling the thickness and position of the oxide layer. The idea is confirmed by the self-consistent effective index method. By placing the oxide layer position properly, we can increase the radius of the oxide aperture for single-mode operation by 3 times.

• The Journal of the Korea Contents Association
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• v.10 no.12
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• pp.10-17
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• 2010

In this paper, we design digital D-PHY link chip controling DSI (Display Serial Interface) that meets MIPI (Mobile Industry Processor Interface) standard. The D-PHY supports a high-speed (HS) mode for fast data traffic and a low-power (LP) mode for control transactions. For low power consumption, the unit blocks in digital D-PHY are optionally switched using the clock gating technique. The proposed low power digital D-PHY is simulated and compared with conven tional one about power consumption on each transaction mode. As a result, power consumptions of TX, RX, and total in HS mode decrease 74%, 31%, and 50%, respectively. In LP mode, power reduction rates of TX, RX, and total are 79%, 40%, and 51.5%, separately. We implemented the low power MIPI D-PHY digital chip using $0.13-{\mu}m$ CMOS process under 1.2V supply.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3C
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• pp.271-278
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• 2006

Rate-constrained coding is one of the many coding-efficiency oriented tools of H.264/AVC, but mode decision process of RDO(Rate distortion optimization) requires high computational complexity. Many fast mode decision algorithms have been proposed to reduce the computational complexity of mode decision. In this paper, we propose two algorithms for reduction of mode decision in H.264/AVC, which are the fast reference frame selection and selective intra prediction mode decision. Fast reference frame selection is efficient for inter predication and selective intra prediction mode decision can effectively reduce excessive calculation load of intra prediction mode decision. The simulation results showed that the proposed methods could reduce the encoding time of the overall sequences by 44.63% on average without any noticeable degradation of the coding efficiency.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.10
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• pp.40-50
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• 2003

The operational orbit evolution of the KOMPSAT-l over 3 years was analyzed. During LEOP, four orbit maneuvers were performed to obtain the optimized orbit and eight safe-hold modes happened. The effects of unpredictable occurrence of the safe-hold mode and the highest solar activity on the orbit evolution during the mission life were analyzed. The comparison of orbital elements between long-term predicted orbit and determined orbit from observed data was also performed. The operational orbit started from the optimized one was evolved within the boundary of the designed mission orbit except altitude and it was verified the sun-synchronous orbit was successfully maintained.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.4
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• pp.432-440
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• 2007

In this study, we have investigated the closure behavior of fatigue cracks in SAPH440 steel plates under a mixed-mode I+II loading. A crack image capturing system as a direct measuring method was used to measure the closure levels at a crack tip. The crack closure levels in the fluctuation and stable sections were increased with the increase of the mode mixture ratio. The mode mixture ratio independent fatigue crack propagation rates equation was calculated by considering mixed-mode crack closure levels. The equation was examined according to the application method of crack opening ratio. The fracture surface analysis by C-scan method was also performed in order to investigate the closure mechanism and propagation mode of crack under the mixed-mode I+II loading. The crack closure under the mixed mode I+II is confirmed as a surface roughness closure by the quantitative analysis of fracture surface using the proposed surface roughness parameter.

• Aerospace Engineering and Technology
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• v.12 no.1
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• pp.22-31
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• 2013

Flight tests on flight control performance of helicopter, conversion and airplane mode for the Smart UAV were completed. Automatic take-off and landing, automatic return home as well as automatic approach to hover were performed in helicopter mode. Climb/descent, left/right turn using speed and altitude hold mode were performed in each $10^{\circ}$ tilt angle in conversion mode. The rotor speed in airplane mode was reduced to 82% from 98% RPM in order to increase rotor efficiency with reducing Mach number at tip of rotors. It reached to the designed maximum speed, $V_{TAS}$=440 km/h at 3 km altitude. This paper presents the flight test result on full envelopment of Smart UAV. Detailed test plan and test data on control performance were also presented to prove that all data meets the flying qualities requirement.

• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.248-253
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• 2005

We designed and fabricated a compact multi-mode interference (MMI) wavelength demultiplexer using the concept of 'Improved Quasi-State' modes. The output power and extinction ratio were improved by utilizing modal phase error which is specially occurred in low-index contrast. For a designed demultiplexer, the mode propagation analysis with effective index approximation shows significant improvement of extinction ratio to -25 dB for both $1.31{\mu}m\;and\;1.51{\mu}m$ wavelength region and the split-length was reduced about 1/5 of other MMI devices. The fabricated device shows successful characteristics for both 1.31 and $1.55{\mu}m$ wavelengths. These results demonstrate the potential of low-index materials system and the embossing process for photonic integrated circuits.