• Journal of Electrical Engineering and Technology
• /
• v.2 no.4
• /
• pp.518-524
• /
• 2007

This paper describes several improved characterizations of the EPIC CCD, which now has modified electrode and channel structures. From a 3-D numerical simulation of the device, its channel doping and potential distributions are then observed for the optimization of the charge transfer. A wavelength-dependence on the device structure is observed in terms of the reflectivity of the incident radiation. The optical properties of ultra-low energy levels, when using an open-electrode structure, are then considered to improve their quantum efficiency.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2007.08b
• /
• pp.1451-1453
• /
• 2007

The electrical and the optical properties of organic light-emitting devices (OLEDs) with or without multiple heterostructures acting as a hole transport layer were investigated. The efficiency enhancement mechanism in the OLEDs with multiple heterostructures is described on the basis of the electrical and the optical results.

• Journal of the Optical Society of Korea
• /
• v.20 no.2
• /
• pp.291-299
• /
• 2016

We have investigated the ultimate limits of nonuniform grating couplers (NGCs) for optimized fiber coupling to silicon waveguides, compared to uniform grating couplers (UGCs). Simple grating coupler schemes, which can be fabricated in etching steps of the conventional complementary metal-oxide semiconductor (CMOS) process on silicon-on-insulator (SOI) wafers without forming any additional overlay structure, have been simulated numerically and demonstrated experimentally. Optimum values of the grating period, fill factor, and groove number for ultimate coupling efficiency of the NGCs are determined from finite-difference time-domain (FDTD) simulation, and confirmed with experimentally demonstrated devices by comparison to those for the UGCs. Our simulated results indicate that maximum coupling efficiency of NGCs is possible when the minimum pattern size is below 50 nm, but the experimental value for the maximum coupling efficiency is limited by the attainable fabrication tolerance in a practical device process.

• Journal of the Optical Society of Korea
• /
• v.18 no.6
• /
• pp.772-776
• /
• 2014

We report a numerical analysis of the light-extraction efficiency (LEE) of light-emitting diodes (LEDs) on patterned sapphire substrates (PSSs). We considered various n-sided, regular convex pyramids, where n is an integer and $n{\geq}3$. We then considered four cross sections: extruded, subtracted, truncated-extruded, and truncated-subtracted. Ray-tracing simulations were carried out with these polygonal pyramid patterns, and the dimensions of the patterns were systematically varied. Optimized pattern shapes were determined for large LEE. An extruded circular pyramid with a slant angle of $45^{\circ}$ was found to be the optimal patterned shape.

• Journal of the Optical Society of Korea
• /
• v.20 no.1
• /
• pp.29-35
• /
• 2016

This paper deals with a design method and capacity loss of an efficient multi-level modulation scheme for dimmable visible light communications (VLC) systems that use light-emitting diodes (LEDs) with efficiency droop. To this end, the impact of such an impairment on dimmable VLC is addressed with respect to multi-level modulations based on pulse-amplitude modulation (PAM) via data-rate optimization formulation.

• Journal of the Optical Society of Korea
• /
• v.18 no.4
• /
• pp.370-376
• /
• 2014

We optimized the design of the flat encapsulant of a light-emitting diode (LED) package to obtain higher light output power (LOP), both by experiment and simulation using three-dimensional ray-tracing software. In the experiment, the refractive index of the encapsulant was varied (1.41 and 1.53). In addition, double-layer structures with these refractive indices (1.41/1.53) were investigated by varying the shape of the interface between the two among flat, concave, and convex. The experiments showed that the LOP of the double-layer encapsulant with convex interface increased by 13.4% compared to the single-layer encapsulant with a refractive index 1.41, which was explained by the increase of the light extraction efficiency (LEE) in connection with the increase of the critical angle (${\theta}_c$) and the decrease of the Fresnel reflection.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2002.08a
• /
• pp.441-444
• /
• 2002

If an antiferroelectric liquid crystal (AFLC) cell is set between crossed polarizers for optical modulators or displays, it has low transmittance efficiency. This happens because AFLC materials have inherent tilt angles of typically $18^{\circ}{\sim}38^{\circ}$, not $45^{\circ}$. To improve the low transmittance efficiency, we propose a new optical configuration for antiferroelectric liquid crystal displays, which also improves color dispersion.

• Korean Journal of Optics and Photonics
• /
• v.10 no.2
• /
• pp.114-119
• /
• 1999

In an interation-free measurement system with the polarization-based Mach-Zehnder interferometer structure, effects of two system imperfections, i.e., the system loss and the low quantum efficiency of photon detectors, on the system perfomance are analyzed, Although both the two system imperfections limit the maximal defection efficiency that can be achievable, we show that the quantum efficiency of photon detectors is less important when the system loss becomes small. In addition, for given system losses and quantum efficiencies, we derive the maximal detection efficiencies that can be achievable.

• Journal of the Optical Society of Korea
• /
• v.20 no.3
• /
• pp.407-412
• /
• 2016

We analyzed through numerical simulations the properties of a square beam homogenizer near the target for laser shock peening. The efficiency was calculated near the target by considering the plasma threshold of the metals. We defined the depth of focus of the square beam homogenizer with a given efficiency near the target. Then, we found the relationship between the depth of focus for the laser shock peening and four main parameters of the square beam homogenizer: the plasma threshold of the metal, the number of lenslets in the array-lens, the focal length of the condenser lens and the input beam size.

• Journal of Astronomy and Space Sciences
• /
• v.10 no.1
• /
• pp.94-102
• /
• 1993

We have develped a four-channel photoelectric photometer for the 61cm telescope of Sobaeksan Astronomy Observatory using optical fiber. We observed a standard star with each channel to check the efficiency difference between the channels, and found no differences. To calibrate the observing accuracy and efficiency, we have observed a short period W UMa type eclipsing binary star, BV Dra. Test observations show that the photometer is very stabel and the accuracy of the data is also increased. The observing efficiency is very increased compared with that of single channel photometer ; at least five times faster than older one in the case of one filter observation.