• Journal of Mechanical Science and Technology
• /
• v.15 no.3
• /
• pp.309-319
• /
• 2001

This paper demonstrates the development of optical temperature sensor based on the etched silica-based planar waveguide Bragg grating. Topics include design and fabrication of the etched planar waveguide Bragg grating optical temperature sensor. The typical bandwidth and reflectivity of the surface etched grating has been ∼0.2nm and ∼9%, respectively, at a wavelength of ∼1552nm. The temperature-induced wavelength change is found to be slightly non-linear over ∼200$^{\circ}C$ temperature range. Typically, the temperature-induced fractional Bragg wavelength shift measured in this experiment is 0.0132nm/$^{\circ}C$ with linear curve fit. Theoretical models with nonlinear temperature effect for the grating response based on waveguide and plate deformation theories agree with experiments to within acceptable tolerance.

• KIEE International Transactions on Electrophysics and Applications
• /
• v.5C no.1
• /
• pp.39-43
• /
• 2005

We proposed a structure for a 1.55 ㎛ strained separate confinement heterostructure (SCH) multi- quantum well (MQW) superluminescent diode (SLD), having a tapered active region. SLD was fabricated through a two-step procedure: the first step being metal organic chemical vapor deposition (MOCVD) and the second-step being liquid phase epitaxy (LPE). We used a 15 laterally tilted stripe and window region to suppress the lasing action of the SLD. The performance of the SLD showed output power of 11 mW with no lasing under 200 mA pulse driving. The full-width at half-maximum was 42 nm at 200 mA, 25℃.

• Applied Science and Convergence Technology
• /
• v.24 no.2
• /
• pp.41-46
• /
• 2015

Transparent conductive oxides (TCOs) are essential material in optoelectronics such as solar cells, touch screens and light emitting diodes. Particularly TCOs are attractive material for infrared cut off film due to their high transparency in the visible wavelength range and high infrared reflectivity. Among the TCO, Indium tin oxide has been widely used because of the high electrical conductivity and transparency in the visible wavelength region. But ITO has several limitations; expensive and low environmental stability. On the other hands, fluorine doped tin oxide (FTO) is well known for low cost, weather ability and stable in acidic and hydrogen. In this study, two different magnetron sputtering techniques with RF and DC modes at room temperature deposition of FTO thin film was conducted. The change of oxygen content is influence on the topography, transmittance and refractive index.

• Journal of the Optical Society of Korea
• /
• v.15 no.1
• /
• pp.9-14
• /
• 2011

In this study, the internal structure of an optical waveguide embedded in a flexible optical circuit board is observed with a confocal microscope. In order to increase the light reflection from an internal material interface with a very small index difference, and thus enhance the signal contrast, a theta microscopy scheme has been integrated into a conventional confocal microscope, and a high NA oil-immersion lens has been used. The interface reflectivity is increased from roughly 0.0015% to 0.025% by the proposed method, and the internal structure can thus be successfully measured.

• Korean Journal of Optics and Photonics
• /
• v.21 no.1
• /
• pp.26-32
• /
• 2010

Line lamps, which utilize leaky optical fibers based on periodic bending of plastic optical fibers, are proposed. The LED-optical fiber coupler, the key component of the line lamp, is designed and analyzed. The analysis by the Monte Carlo photon simulation method has shown that the optical coupling efficiency is affected rather sensitively by $\theta_w$, the slanting angle of the reflecting cup sidewall and $\rho_{ref}$, the reflectivity of the reflecting cup. The optical coupling efficiency of the coupler reaches the maximum when $\theta_w$ is about $60^{\circ}$, which is significantly larger than $\theta_w=45^{\circ}$, the typical sidewall slanting angle of the reflecting cup adopted in most LED lamps. When the reflectivity of the reflecting cup is above 0.8, the optical coupling efficiency is larger than 80%, which is the typical efficiency to be achieved in LD-optical fiber coupler.

• Journal of the Korean Vacuum Society
• /
• v.14 no.3
• /
• pp.143-146
• /
• 2005

A new method of x-ray photon correlation spectroscopy (XPCS) using coherent x-rays is developed recently for probing the dynamics of surface height fluctuations as a function of lateral length scale. This emerging technique applies the principles of dynamic light scattering in the x-ray regime. The short wavelength and slow time scales characteristic of XPCS extend the phase space accessible to scattering studies beyond some restrictions by light and neutron. In this paper, we demonstrate XPCS to study the dynamics of surface fluctuations in thin supported polymer films. We present experimental verification of the theoretical predictions for the wave vector and temperature dependence of the capillary wave relaxation times for the supported polymer films at melt for the film thicknesses thicker than 4 times of the radius of gyration of polymer. We observed a deviation from the conventional capillary wave predictions in thinner films. The analysis will be discussed in terms of surface tension, viscosity and effective interactions with the substrate.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.32 no.4
• /
• pp.281-286
• /
• 2019

Raman spectra of a-C:H thin films deposited with an unbalanced magnetron sputtering system showed that the G peak shifted to a higher wavenumber as the target power density increased and $I_D/I_G$ ratio increased from 0.902 to 1.012. Moreover, the transmittance of a-C:H films fabricated at 60 nm tended to decrease with increasing target power density; at 550 nm in the visible light region, the transmittance decreased from 69% to 58%. The rms surface roughness values of the a-C:H thin films decreased with increasing target power density, and varied from 1.11 nm to 0.71 nm. In order to achieve efficient light trapping, the light scattering at the rough interface must be enhanced. Consequently, the surface roughness of the thin film will decrease with the target power density. Further, the refractive index and reflectivity of the a-C:H thin films increased with increasing target power density; however, the Brewster angle decreased with the target power density. Hence, dye-sensitized solar cells using an a-C:H antireflective coating increased the CE, $V_{OC}$, and $J_{SC}$ by approximately 8.6%, 5.5%, and 4.5%, respectively.

• Korean Journal of Materials Research
• /
• v.21 no.10
• /
• pp.573-579
• /
• 2011

Highly textured Ag, Al and Al:Si back reflectors for flexible n-i-p silicon thin-film solar cells were prepared on 100-${\mu}m$-thick stainless steel substrates by DC magnetron sputtering and the influence of their surface textures on the light-scattering properties were investigated. The surface texture of the metal back reflectors was influenced by the increased grain size and by the bimodal distribution that arose due to the abnormal grain growth at elevated deposition temperatures. This can be explained by the structure zone model (SZM). With an increase in the deposition temperatures from room temperature to $500^{\circ}C$, the surface roughness of the Al:Si films increased from 11 nm to 95 nm, whereas that of the pure Ag films increased from 6 nm to 47 nm at the same deposition temperature. Although Al:Si back reflectors with larger surface feature dimensions than pure Ag can be fabricated at lower deposition temperatures due to the lower melting point and the Si impurity drag effect, they show poor total and diffuse reflectance, resulting from the low reflectivity and reflection loss on the textured surface. For a further improvement of the light-trapping efficiency in solar cells, a new type of back reflector consisting of Ag/Al:Si bilayer is suggested. The surface morphology and reflectance of this reflector are closely dependent on the Al:Si bottom layer and the Ag top layer. The relationship between the surface topography and the light-scattering properties of the bilayer back reflectors is also reported in this paper.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.30 no.6
• /
• pp.401-405
• /
• 2017

Because silicon thin film solar cells have a high absorption coefficient in visible light, they can absorb 90% of the solar spectrum in a $1-{\mu}m$-thick layer. Silicon thin film solar cells also have high transparency and are lightweight. Therefore, they can be used for building integrated photovoltaic (BIPV) systems. However, the contact electrode needs to be replaced for fabricating silicon thin film solar cells in BIPV systems, because most of the silicon thin film solar cells use metal electrodes that have a high reflectivity and low transmittance. In this study, we replace the conventional aluminum top electrode with a transparent aluminum-doped zinc oxide (AZO) electrode, the band level of which matches well with that of the intrinsic layer of the silicon thin film solar cell and has high transmittance. We show that the AZO effectively replaces the top metal electrode and the bottom fluorine-doped tin oxide (FTO) substrate without a noticeable degradation of the photovoltaic characteristics.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.15 no.5
• /
• pp.819-826
• /
• 2020

The UHF band wind profiler radars of the Korea Meteorological Administration (KMA), which produces the vertical profile of the wind, need to be calibrated for better performance. The capabilities of the radar in detecting even light precipitation were used for the calibration of which reference takes the hourly series of ground rainfall rate measured by a rain gauge at the radar site. This calibration must be renewed regularly according to the methodology implemented in this work since errors occur on the wind vectors in the clear sky without reflectivity calibration. Comparing the wind by wind profiler with that by radiosonde, the optimal radar constant contributed to the improvement of wind accuracy.