Se-Geun Park

Photonic crystal power-splitter based on directional coupling

We propose a new power-splitting scheme in two-dimensional photonic crystals that can be applicable to photonic integrated circuits. The proposed power-splitting mechanism is analogous to that of conventional three-waveguide directional couplers, utilizing coupling between guided modes supported by line-defect waveguides. Through the analysis of dispersion curve and field patterns of modes, the position in propagation direction, where an input field is split into a two-folded image, is determined by simple mode analysis. Based on the calculated position, a photonic crystal power-splitter is designed and verified by finite-difference timedomain computation.

Enhancement of electroluminescence in GaN-based light-emitting diodes by metallic nanoparticles

The enhanced electroluminescence of GaN-based light-emitting diodes (LEDs) with noble metallic nanoparticles (MNPs) is demonstrated. The sample with well-designed Ag MNPs has shown the best performance enhancement of 126% in electroluminescent intensity compared with a conventional LED sample, even though the MNPs are placed at least 200 nm away from the quantum-well active layer. The MNPs provide enhanced photon scattering and coupling between localized surface plasmon resonance (LSPR) modes and photon modes internally trapped in a device. To investigate this effect, the peculiarities of the LSPR and the corresponding structural properties of the MNPs are discussed through the effective medium approach.

Photonic Crystal-Based GE-PON Triplexer using Point Defects

In this paper, we newly propose an optical triplexer which is one of key components in Gigabit Ethernet Passive Optical Network for Fiber-To-The-Home network. Based on a photonic crystal structure with local point defects, two types of optical triplexers were optimally designed. The size-tuned optical triplexer shows the extinction ratios of -17.8 dB, -14.4 dB, and -15.9 dB for the wavelengths of 1310nm, 1490nm, and 1550 nm, respectively. And the index-tuned optical triplexer shows the extinction ratios of -19.24dB, -17.09dB, and -22.68dB for the wavelengths of 1310nm, 1490nm, and 1550 nm, respectively. The size of the proposed optical triplexers were about 4 × 3 μm2.

An array of inductively coupled plasma sources for large area plasma

An array of 2 £ 2 inductively coupled plasma (ICP) sources has been built by modifying the conventional reactive ion etching (RIE) type LCD etcher. Each ICP has its own planar circular antenna and quartz dielectric window to the process chamber. One RF power supply and only one impedance matching network are used for delivering the power to all four ICP sources. Distribution of ion and electron densities and electron temperature are measured in terms of the number of acting ICP sources, chamber pressure and RF power. An uniform oxygen plasma density in the order of 10 15 m 23 can be obtained at RF power of 600 W in process chamber of 620 £ 620 mm 2 cross-section, which is higher than that of RIE plasma. By adjusting the power distribution among the four ICP units, uniformity of the plasma can be improved to 10% on substrate stage. Photoresist etching by the oxygen plasma is performed on 320 £ 400 mm glass plates. q 1999 Elsevier Science S.A. All rights reserved.

A new method of Q factor optimization by introducing two nodal wedges in a tuning-fork/fiber probe distance sensor

We report on a new method of achieving and optimizing a high Q factor in a near-field scanning optical microscope (NSOM) by introducing two nodal wedges to a tuning-fork/fiber probe distance sensor and by selecting a vibrational mode of the dithering sensor. The effect of the nodal wedges on the dynamical properties of the sensor is theoretically analyzed and experimentally confirmed. The optimization achieved by the proposed method is understood from the vibration isolation and the subsequent formation of a local vibration cavity. The optimal condition is found to be less susceptible to the variation of the fiber tip length. This method allows effective NSOM measurement of samples placed even in aqueous solution.

NSOM-based characterization method applicable to optical channel waveguide with a solid-state cladding

A new characterization method employing near-field scanning optical microscope (NSOM) is proposed to measure the propagation characteristics of an optical channel waveguide having a solid-state cladding. For the measurement, the cladding material is replaced with the liquid having the same refractive index as that of the removed cladding. Replacing the solid-state cladding with the liquid enables the NSOM probe to reach the core-cladding interface without changing the boundary condition at the interface. The height of the probe immersed into the viscous liquid is done with the information from the surface profile of the naked core. The measured propagation characteristic shows a good agreement with the simulation result.

Novel Grating Design for Out-of-Plane Coupling With Nonuniform Duty Cycle

We propose a waveguide grating coupler with nonuniform duty cycle for the out-of-plane coupling of light from a planar waveguide to an optical fiber, and evaluate the optical performances based on Bloch-wave analysis. The mode profile and focusing performance of the diffracted output beam are investigated in terms of the duty cycle to improve optical coupling efficiency.

POLYMER-BASED OPTICAL PRINTED CIRCUIT BOARD (O-PCB) AS A POTENTIAL PLATFORM FOR VLSI MICROPHOTONIC INTEGRATION

We introduce the concept of optical printed circuit board (O-PCB) and discuss the issues regarding the miniaturization, interconnection, and integration of polymer-based photonic devices with a view to using it as a potential platform for VLSI microphotonic integration. We present new approaches to miniaturize and integrate some examples of microphotonic devices and examine the considerations regarding the design, fabrication, and characterization for miniaturization and integration for O-PCB application. Devices that we have used for our study include mode conversion adaptors, micro-ring resonator devices, multimode interference devices, arrayed waveguide gratings. Scaling rules are also discussed.

Effect of time-varying axial magnetic field on photoresist ashing in an inductively coupled plasma

Time-varying axial magnetic field is added to an inductively coupled plasma. Weak axial magnetic field of about 10–15 G can be obtained by a pair of Helmholtz coils attached to the chamber. This scheme has been applied to etch SiO2 and silylated photoresist, where processing pressures are generally below 7 Pa, and ions are major reaction species. In order to extend this concept to other etching conditions, this method is applied to photoresist ashing, where processing pressure is usually higher than 133 Pa, and downstream oxygen radicals are important species. It is found that 60 Hz of the ac current gives the maximum ash rate and that ash rate is increased from 6.1 to 7.0 μm/min, and uniformity is improved from 8% to 4.5% over an 8 in. wafer. When aluminum baffle is placed between plasma source and reaction chambers, the ash uniformity improves further to 2.0% over a 300 mm wafer. The presence of axial magnetic field increases the plasma density and thus ash rate, and better uniformity comes from redistribution of ions and radicals during the off period in a periodic magnetic field.Time-varying axial magnetic field is added to an inductively coupled plasma. Weak axial magnetic field of about 10–15 G can be obtained by a pair of Helmholtz coils attached to the chamber. This scheme has been applied to etch SiO2 and silylated photoresist, where processing pressures are generally below 7 Pa, and ions are major reaction species. In order to extend this concept to other etching conditions, this method is applied to photoresist ashing, where processing pressure is usually higher than 133 Pa, and downstream oxygen radicals are important species. It is found that 60 Hz of the ac current gives the maximum ash rate and that ash rate is increased from 6.1 to 7.0 μm/min, and uniformity is improved from 8% to 4.5% over an 8 in. wafer. When aluminum baffle is placed between plasma source and reaction chambers, the ash uniformity improves further to 2.0% over a 300 mm wafer. The presence of axial magnetic field increases the plasma density and thus ash rate, and better uniformity comes from redistr...

A triplexer optical transceiver module using cascaded directional couplers

We present the design of a newly conceived triplexing optical microsystem that can provide bases for three wavelengths splitting function for gigabit passive optical network application. Three wavelengths consist of one for the upstream, 1310nm wavelength signal and the other two for downstream, 1490nm and 1550nm wavelength signal. The triplexer module is designed in the form of a planar optical integrated circuit using three directional couplers. In order to increase wavelength splitting performance we arrange the directional coupler by cascaded connecting method and use the asymmetric Y-branch. We analyzed its performance characteristics by BPM. The optical crosstalk of the 1310nm signal to the 1490nm signal and the 1550nm signal are -27.92dB and -66.83dB, respectively in the upstream. In the case of downstream the optical loss is less than 0.5dB with 20nm bandwidth and the optical crosstalk reaching less than -30dB in the downstream is 19nm.