Beom-Hoan O

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.

Vapor sensor realized in an ultracompact polarization interferometer built of a freestanding porous-silicon form birefringent film

A novel vapor sensor that uses polarization interferometry in a form birefringent porous-silicon film is introduced, analyzed, and experimentally characterized. Simulations and analysis of accuracy, versatility, stability, and control of dynamic range of the device are provided. The simulation accurately predicts the polarization interference signal, which is used to estimate the effective refractive indexes characterizing the form birefringence of a porous-silicon film with 0.001 accuracy. The device was tested for the detection of heptane concentration in a range of 342-20 000 ppm (=2.0%).

Novel design concept of waveguide mode adapter for low-loss mode conversion

We proposed a novel design concept of a mode adapter using a new parameter. The overlap integration of two adjacent mode profiles is defined as a single step loss (SSL) parameter for the characterization of optical mode confinement as well as the quantification of mode mismatch. The variation of SSL is described with two parameters. These parameters are V, a normalized frequency, and s, a differential width variation ratio. The contour for constant SSL in the V, s plane provides the optimized s curve as a function of V. The design concept with this constant SSL is shown to provide optimized adapters of minimized conversion loss.

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.

Tiny surface plasmon resonance sensor integrated on silicon waveguide based on vertical coupling into finite metal-insulator-metal plasmonic waveguide

We propose a tiny surface plasmon resonance (SPR) sensor integrated on a silicon waveguide based on vertical coupling into a finite thickness metal-insulator-metal (f-MIM) plasmonic waveguide structure acting as a Fabry-Perot resonator. The resonant characteristics of vertically coupled f-MIM plasmonic waveguides are theoretically investigated and optimized. Numerical results show that the SPR sensor with a footprint of ~0.0375 μm2 and a sensitivity of ~635 nm/RIU can be designed at a 1.55 μm transmission wavelength.

Design and fabrication of polarization-insensitive hybrid solgel arrayed waveguide gratings

We report on the successful design and fabrication of a polarization-insensitive arrayed waveguide grating (AWG), using solgel-derived silica glass films formed on fused-silica substrates. By controlling the waveguide width and making the propagation constants of the polarizations equal, we have found it possible to fabricate polarization-insensitive solgel-based AWGs. Polarization-insensitive design improves the cross talk by approximately 10 dB in the dynamic range.

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.

A nonunitary transfer matrix method for practical analysis of racetrack microresonator waveguide

We report that a nonunitary transfer matrix (NU-TM) method that we have developed is highly accurate and effective in analyzing and designing racetrack microresonator devices. Relatively poor output efficiency of a fabricated racetrack microresonator, unexplained by the conventional unitary transfer matrix (U-TM) method, are analyzed successfully by the NU-TM method. The track-length dependence, which is not obvious in the U-TM analysis, is clearly shown in the NU-TM analysis and is found to stem from the nonorthogonal phase difference between two branching waves in the directional coupling process. The results show excellent agreement with the results obtained by the finite-difference time-domain simulation method, thus confirming the validity and superior capability of the NU-TM method.