Chang-Bong Kim

Measurement of the refractive index of liquids at 1.3 and 1.5 micron using a fibre optic Fresnel ratio meter

A fibre optic technique based on the Fresnel reflection from the fibre tip is used for measurements of the refractive indices of various liquids at wavelengths of 1310 and 1551 nm. Reflection signals from liquid?fibre interface are compared with reflection signals from air?fibre interface to obtain the refractive index. Values of refractive indices for distilled water measured by this technique compare very well with known values at both wavelengths only if the fibre effective waveguide index is used. Applying the double-pulse measurement technique, it is shown that a measurement resolution of about 2.5 ? 10?5 can be achieved.

Load sharing operation of a 14 kW photovoltaic/wind hybrid power system

In this paper, a design procedure for photovoltaic/wind hybrid power generation system is presented. The hybrid system is composed of a DC/DC converter for photovoltaic energy conversion, a DC/DC converter for wind energy conversion, a four switch IGBT inverter converting the combined DC power to the AC power and a backup power battery. Here, it is very important to select the desired battery size to meet the stable output and economic cost aspect since this system utilizes a fluctuating and finite energy resource. The purpose of this paper is to develop a sizing method for the PV/wind energy hybrid system with load sharing operation. The method demonstrates a simple tool to determine the desired battery size that satisfies the energy demand from the user with the photovoltaic and wind natural source. The proposed method is verified on a 14 kW hybrid power system including a 10 kW PV generator and a 4 kW wind generator established in Cheju island, Korea.

Dynamic gain control of booster amplifier (EDFA) using an optical supervisory channel power adjustment in WDM transmission systems

We present a simple dynamic gain control of a booster amplifier (EDFA-erbium-doped fibre amplifier) with an optical supervisory channel power adjustment in WDM transmission systems. As a result, we performed gain clamping and power clamping of EDFA in the optical link. We can transmit 10 Gbps WDM signals and a 155 Mbps supervisory signal through a single mode fiber 320 km according to the change of signal channel number.

An All-Optically Gain-Controlled Two-Stage Amplifier Using Two Independent Feedback Loops

We propose and demonstrate the scheme to combine a two-staged amplifier with a fixed gain flattening filter and two parallel optical feedback loops. This amplifier all-optically controls constant signal gain and gain level through all C-band with a dynamic input power range of up to -1 dBm while input signals are dynamically changed between one channel and 40 wavelength-division-multiplexing channels. The transient effects of each channel and their wavelength dependency are investigated. It is shown that the amplifier can be used in real field applications through transmission experiments, in which the amplifier performance is kept unchanged under wide dynamic traffic variance.

The Study on the Antireflection(AR) Coating Design Scheme According to the Index Profile in the Thin-Film Silicon Solar Cell

This paper shows an antireflection coating design skill for utilization the thin-film silicon solar cell in the future. The reflectivity of each index profile previously suggested as linear, cubic and quintic function has been calculated and compared. Each index profile is applied to the antireflection coating consisting of 6 layers with 180nm thickness. Also we suggest the graded index profile and compare its reflectivity to the linear, cubic and quintics ones. As a results we find the reflectivity generally decreases as the order goes to higher. However the reflectivity in the graded index profile shows the higher(lower) value than ones in the linear, cubic and quintic especially in the shorter(longer) wavelength range from 500 nm to below 700 nm(above 700 nm to 800 nm). Therefore we find that the graded index profile structure could be applied for the better antireflection coating design scheme especially for optical device and optical filter in the range of from deep red to infrared.

Experimental Study on Economic Long-haul Transmission Link Using standard SMF and All EDFAs

We systematically compare the transmission performance of three different modulation formats, return-to-zero (RZ), chirped RZ (CRZ) and vestigial sideband RZ (VSRZ) on the economically effective transmission link using standard single mode fiber (SSMF) and all Erbium-doped fiber amplifiers (EDFAs). This link is composed of wavelength division multiplexed (WDM) channels at 10 Gbit/s over 24 times 100 km amplifier spans without using new types of fibers and Raman amplifiers. The generation of each modulation format in experiments is optimized for more reasonable comparison, and their optical characteristics are investigated by comparing with simulation results. Optimum input powers into SSMF and dispersion compensation fiber (DCF) for each modulation format signal were explored and transmission performance was compared. In our cost-effective transmission link, CRZ signal showed the lowest input power and best performance among all the formats investigated.

Dynamic Gain Control of Booster Amplifier (EDFA) Using an Optical Supervisory Channel Power Adjustment in Wavelength-Division-Multiplexing Transmission Systems

We present a simple dynamic gain control for a booster amplifier (EDFA) with an optical supervisory channel power adjustment in wavelength-division-multiplexing (WDM) transmission systems. We performed gain clamping and power clamping of an EDFA in optical links. We transmitted 10 Gb/s WDM signals and a 155 Mb/s supervisory signal through a 320 km single mode fiber.

Investigation of polarization tuning mechanism in fiber ring cavity laser

Ring cavity lasers employ an Er doped or a semiconductor gain medium including a wavelength selective element for tuning a lasing wavelength. For a wavelength tuner, a tunable optical filter can be realized using a rotatable grating, Fabry-Perot cavity or an acousto-optic element. In the paper, we demonstrate the fiber ring laser tuned by controlling polarization states along the birefringent optical fiber loop. The ring laser consists of a semiconductor optical amplifier, a polarization controller combined with a rotatable intra-cavity polarizer for a wavelength selective element, and a 9:1 coupler. The ring also includes a polarization independent in-line optical isolator for providing unidirectional operation and an attenuator to adjust a loop loss.

Reduced light induced degradation of a-Si:H thin film transparent solar cells

We fabricated a-Si:H transparent solar cells with thin absorbers. The light induced degradation of 17 % to 22 % was obtained when 130, 150 and 200 nm thick absorbers were used in the fabrication of a-Si:H transparent solar cells. However, the cells with 108 and 120 nm thick absorber showed improved light induced degradation. In particular, the cell with 108 nm thick absorber showed highly improved degradation of 7.3 %. In this case, the p-layer thickness is crucial to determine the degradation rate.

The Study on the Reflection Coating Design Scheme in the Thin-Film Silicon Solar Cell

This paper presents a reflection coating design scheme in the thin-film silicon solar cell. The antireflection(high reflection) coating skill is needed in the front(back) panel of the thin-film solar cell to improve an efficiency of light absorbing. In the single structure a reflectivity is changed according to the thickness of coating for antireflection scheme and its minimum value can be obtained by controlling thickness of coating. In the symmetric multi layer structure low reflectivity can be obtained in the wide wavelength range. And we also find that high reflectivity can be obtained through multi layer structure, which has alternate layers of high and low material, for high reflection scheme in the back panel.