Seung Gol Lee

Self-imaging phenomena in multi-mode photonic crystal line-defect waveguides: application to wavelength de-multiplexing

We show that the self-imaging principle still holds true in multimode photonic crystal (PhC) line-defect waveguides just as it does in conventional multi-mode waveguides. To observe the images reproduced by this self-imaging phenomenon, the finite-difference time-domain computation is performed on a multi-mode PhC line-defect waveguide that supports five guided modes. From the computed result, the reproduced images are identified and their positions along the propagation axis are theoretically described by self-imaging conditions which are derived from guided mode propagation analysis. We report a good agreement between the computational simulation and the theoretical description. As a possible application of our work, a photonic crystal 1-to-2 wavelength demultiplexer is designed and its performance is numerically verified. This approach can be extended to novel designs of PhC devices.

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.

Resonance characteristics of waveguide-coupled polyimide microring resonator

We report for the first time on the resonance characteristics of a polyimide-based micro-ring resonator model. The resonator consists of a microring coupled to a pair of waveguides. Using the finite-difference time-domain method, we were able to obtain resonance peaks, from which the resonance wavelength could be identified. For a resonator with a microring of 10 μm diameter, known as the minimum for a lossless microring, we found the free spectral range of 46.65 nm, and quality factor of 588. These are excellent values strongly supporting the outstanding utility and quality of the microring resonators for wavelength-division multiplexing filter applications.

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.

Stimulated Brillouin scattering suppression using cross-phase modulation induced by an optical supervisory channel in WDM links

A stimulated Brillouin scattering (SBS) suppression method is proposed for wavelength-division-multiplexed (WDM) links, based on the cross-phase modulation (XPM) effect induced by an optical supervisory (SV) channel. Since the XPM on each signal channel is induced by the 52-Mb/s optical SV channel, the SBS suppression is nearly insensitive to WDM signal channels. We experimentally demonstrate that the proposed method can increase the SBS threshold and reduce the error floors irrespective of the bit rate, channel power, channel wavelength, and channel spacing of the WDM channels.

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.

More stable algorithm for rigorous coupled wave analysis applied to topography simulation in optical lithography and its numerical implementation

This paper discusses a more stable algorithm of rigorous coupled wave analysis applicable to 2-D exposure simulation in an optical lithography. This algorithm can resolve a divergence problem inherently and can easily be implemented as a full vector model. 2-D exposure simulator based on this algorithm is developed and applied successfully to a very thick photoresist system. Intensity distributions inside the photoresist are simulated and compared with those of other vector models. The adaptive layering technique is introduced to the simulation of bleaching process in order to reduce the computation time. It is found that the technique can greatly reduce memeory size and computation time with reasonable accuracy.

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.

Suppression of polarization dependence in the design of an arrayed-waveguide grating with photodefinable polyimide

We report on an effective means of suppressing polarization dependence in the design of an arrayed waveguide grating (AWG) made of photodefinable polyimide. The polarization dependence of the arrayed-waveguide grating device is excellently suppressed by controlling the grating order (m) for a given refractive index difference between TEand TM-modes within polyimide. The transmission characteristics of two AWGs for two grating orders, m ¼ 70 and 90, show wavelength shift of 5.04 nm and nearly zero, respectively, strongly supporting and confirming the method that we have identified for the birefringence suppression. 2002 Elsevier Science B.V. All rights reserved.

Effect of Incident Beam Width on Light Transmission Enhancement by Bow-Tie-Shaped Nano-Aperture

In this paper, a bow-tie-shaped nano-aperture is proposed to enhance light transmission and obtain a tiny beam spot. The transmission and focusing characteristics of the proposed aperture are analyzed numerically using a dispersive three-dimensional finite-difference time-domain (3D-FDTD) method. The spot size and transmittance enhancement of the light transmitted through the optimized aperture are approximately λ/20 and 400 times, respectively. In contrast to the bowtie antenna, the proposed nano-aperture has a bow-tie-shaped opening at its center and its surroundings are filled with metal. Thus, the transmittance enhancement can be further increased by extending the interaction area between an incident beam and the metal portion of the nano-aperture, which is accomplished by increasing the beam width of an incident light.