• 한국초전도학회:학술대회논문집
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• v.9
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• pp.138-141
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• 1999

For the enhancement of communication system performance, high quality filters are required. Conventional metal filters made of copper can be substituted by high quality high temperature superconductivity(HIS) flms for better performance. In order to reduce the size of the filter for the integration of device in the limited area, we have fabricated hairpin type filters using pulsed laser deposition(PLD) technique. The superconducting YBCO thin films have been grown on MgO substrates by PLD with Nd:YAC laser. The YBCO films were patterned by conventional wet-etching process. We have compared YBCO filters and copper filters which were made with the same spec. Simulated and measured frequency responses reveal that HIS YBCO hairpin type bandpass filters show better performance than copper filters.

• Journal of the Optical Society of Korea
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• v.20 no.4
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• pp.451-463
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• 2016

The misalignment errors and fluctuations in irradiance due to atmospheric turbulence can severely degrade the performance of free-space optical (FSO) systems. In this paper, we investigate the asymptotic bit error rate (BER) performance and diversity orders of FSO links using parallel transmit-diversity schemes. The BER expressions of FSO links with the switch-and-examine transmit (SET), switch-and-examine transmit with post-selection (SETps), dual-branch transmit laser selection (Dual-TLS), and group transmit laser selection (Group-TLS) schemes are derived, based on an approximate channel model. Then numerical simulations for these four schemes in the region of high average signal-to-noise ratio (SNR) are presented under different channel conditions. The results show that the four transmit-diversity schemes can reduce system complexity and overcome the limitation of peak power, without much BER deterioration.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.5
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• pp.899-906
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• 1997

It is known that the Differential Phase Shift Keying (DPSK) modulation scheme in the coherent optical communication system is suitable for design of long-distance transmission system because its receiver performance is 3-5dB better than ASK and FSK. In this paper, we descrive a fundamental understanding of the effects of laser phase noise on the performance of coherent lighwave communication systems. Formulas are derived for the bit error rate in homodyne and heterodyne DPSK. Based on detailed mathematical analysis and estimates, we explain the following finding. DPSK can operates at rates only 300 times greater than the laser linewidth.

• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.12
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• pp.1219-1224
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• 2016

The current wireless power charge technologies are based on induction coupling, magnetic resonant coupling, electromagnetic wave, etc. However, the current wireless power charge technologies has several disadvantages including short transfer range, electromagnetic interference, etc. In this paper, we investigate and demonstrate a laser wireless power charge technology. A laser source is used in the transmitter to convert from electric power to optical power and a solar cell or a photodiode is used in the receiver to convert from optical power to electric power. The laser wireless power charge technology may be the most efficient wireless power charge technology in the long distance over than 10 meters. Our experimental results show a transfer efficiency of 2.15% at the 70-m long distance with a 100 mW laser transmitter and a photodiode receiver.

• Korean Journal of Optics and Photonics
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• v.27 no.4
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• pp.133-142
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• 2016

This paper presents the design and simulation of a three-dimensional pixel-by-pixel scanning light detection and ranging (LIDAR) system with a microelectromechanical system (MEMS) scanning mirror and direct sequence optical code division multiple access (DS-OCDMA) techniques. It measures a frame with $848{\times}480$ pixels at a refresh rate of 60 fps. The emitted laser pulse waves of each pixel are coded with DS-OCDMA techniques. The coded laser pulse waves include the pixel's position in the frame, and a checksum. The LIDAR emits the coded laser pulse waves periodically, without idle listening time to receive returning light at the receiver. The MEMS scanning mirror is used to deflect and steer the coded laser pulse waves to a specific target point. When all the pixels in a frame have been processed, the travel time is used by the pixel-by-pixel scanning LIDAR to generate point cloud data as the measured result.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.10
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• pp.1830-1834
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• 2008

At the present day, devices for measurement and control of data by wireless based computer have been generalized. The devices with low cost and high performance have been spotlighted. If Zigbee communication solution is used in dangerous places and places that can not in use wire communication, computer can process data without limitation. Zigbee communication solution is effective in power consumption as compared with RF or bluetooth and can use battery. System cost of Zigbee also is very low, so can install lots of nodes. The system made in this paper transmit by wireless many LMCs(Laser Measuring Control) of wireless transmission system for distance measurement and many slave Zigbee to a master Zigbee.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1987.10a
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• pp.239-241
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• 1987

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.07a
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• pp.337-337
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• 2004

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.3
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• pp.449-455
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• 1993

In order to investigate the improvements of relatively poor characteristics of short wave length AlGaAs/GaAs laser diodes which are useful as a light source for short distance communication systems, the low temperature $(<680^{\circ}C)$ grown AlGaAs/GaAs GRINSCH-QW laser diodes by molecular beam epitaxy have been studied by photoluminescence as a function of rapid thermal annealing (RTA) temperature. It is shown that guantum well photoluminescence intensity increased substantially by a factor of 10 after RAT at $950^{\circ}C$ for 10 sec. This is related to the reduction of non-radiative recombination in the guantum well region. The threshold current of annealed laser diode is reduced by a factor, of 4, confirming the improvement of laser diode quality by rapid thermal annealing.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.569-574
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• 2004

We stabilized the frequency and power of a CW radio-frequency-excited $CO_2$ laser on the peak of the Doppler broadened gain curve using the photoacoustic effect generated from the laser itself. The condenser microphone is installed in the radio frequency discharge chamber to detect a photoacoustic signal. The photoacoustic signal is fed to a lock-in stabilizer as a reference signal for stabilization. The frequency stability is estimated to be better then 5.4${\times}$10$^{-8}$ at the P(20) line. The stabilized output variation was reduced 9.3%, compared to 100% for a free running laser.