Sungchul Kim

Optimal Shape Design of Dielectric Micro Lens Using FDTD and Topology Optimization

In this paper, we present an optimal shape design method for a dielectric microlens which is used to focus an incoming infrared plane wave in wideband, by exploiting the finite difference time domain (FDTD) technique and the topology optimization technique. Topology optimization is a scheme to search an optimal shape by adjusting the material properties, which are design variables, within the design space. And by introducing the adjoint variable method, we can effectively calculate a derivative of the objective function with respect to the design variable. To verify the proposed method, a shape design problem of a dielectric microlens is tested when illuminated by a transverse electric (TE)-polarized infrared plane wave. In this problem, the design variable is the dielectric constant within the design space of a dielectric microlens. The design objective is to maximally focus the incoming magnetic field at a specific point in wideband.

Novel Pilot Scheme for Transmitter IQ Mismatch Compensation in CO-OFDM System

Transmitter in-phase and quadrature (Tx IQ) mismatch is one of the major obstacles preventing coherent optical orthogonal frequency division multiplexing systems from achieving high data rates. Several Tx IQ mismatch compensation methods at the receiver side have been proposed based on the mismatch estimation by the use of pilot signals. In this letter, we propose a novel pilot system for the Tx IQ mismatch estimation to improve the channel-estimation performance. The pilot scheme exploits the conjugate redundancy of the subcarrier mirror images due to the Tx IQ mismatch and allows the estimation of the Tx IQ mismatch factor and channel parameter independently. The advantages of the proposed algorithm are proved via mean square error analysis, and the bit error rate improvement is shown in simulations.

Performance Analysis of Chromatic Dispersion Compensation of a Chirped Fiber Grating on a Differential Phase-shift-keyed Transmission

The properties of the chirped fiber Bragg grating (CFBG) as a chromatic dispersion compensator in differential phase-shift-keyed (DPSK) transmission are analyzed. Comparisons of a performance of a CFBG in between DPSK and On-Off Key (OOK) are shown by simulations using the commercial numerical modeling software,

Neural Network Based Simplified Clipping and Filtering Technique for PAPR Reduction of OFDM Signals

OptSim^{TM}

Simulation of Energy Conversion Efficiency of a Solar Cell with Gratings

. In the simulation, we compared the performance of the CFBG when they were used in the RZ-OOK 40 Gbps and the RZ-DPSK 40 Gbps transmission. The simulation results show the performance of an overall transmission with a CFBG in DPSK is inferior to the case of OOK, although DPSK generally has a 3 dB higher SNR (signal-to-noise ratio) than OOK.

An electronic domain chromatic dispersion monitoring scheme insensitive to OSNR using kurtosis

Many iterative clipping and filtering (ICF) based techniques have been proposed that achieve similar peak-to-average power ratio (PAPR) reduction of orthogonal frequency division multiplexing (OFDM) signals as the original ICF, but with lower complexity, such as the simplified clipping and filtering (SCF) technique. However, these low complexity methods require numerous complex fast Fourier transform (FFT) operations and parameter calculations. In this letter, we introduce a novel ICF method that uses an optimized mapper based on artificial neural network and SCF techniques. Compared to the conventional ICF based methods, the proposed scheme offers desirable cubic metric (CM) and bit error rate (BER) simulation results with significantly reduced computational complexity.

A Simple Numerical Modeling of the Effect of the Incoherent Thick Substrate in Thin-Film Solar Cells Based on the Equispaced Thickness Method

In this work, a numerical analysis of a CIGS (CuIn1-xGaxSex) solar cell with a rectangular grating on the electrode is presented. The effects of the grating on the energy conversion efficiency are calculated using the RCWA (rigorous coupled wave analysis) method. In conventional CIGS solar cells, the thickness of the light absorption layer (CIGS) is 2 µm, at which the incident light is almost absorbed. By adopting a grating on the electrode and using a less than 1 µm CIGS layer, we obtained a higher efficiency compared to the conventional solar cells.

Non-data Aided Timing Phase Recovery Scheme for Digital Equalization of Chromatic Dispersion and Polarization Mode Dispersion

In this paper we present an electronic domain solution for chromatic dispersion (CD) monitoring algorithm based on the estimated time domain channel in electronic domain using channel estimation methods. The proposed scheme utilizes kurtosis as a CD measurement, directly computed from the estimated inter-symbol-interference (ISI) channel due to the CD distortion. Hence, the proposed scheme exhibits robust performance under OSNR variation, in contrast to the existing electronic domain approach based on minimum mean squared error (MMSE) fractionally-spaced equalizer taps [1]. The simulation results verify the CD monitoring ability of the proposed scheme.

Design and Performance Analysis of 2- Dimensional Optical CDMA Encoder/Decoder Using an Array of SSFBGs

We propose a simple numerical modeling method to consider the effect of the incoherent thick substrate on the absorption characteristics of thin-film solar cells. In the proposed “equispaced thickness method” (ETM), the incoherent optical characteristics of the thick substrate are modeled by adding an additional thickness that gives an equispaced phase shift to the incoherent substrate and averaging the coherent simulation results over several equispaced thicknesses. The proposed ETM can be used to consider the effect of the incoherent glass substrate without complicated mathematical and computational procedures and is applicable to not only planar but also surface-textured thin-film solar cells. By applying the proposed method to the numerical modeling based on the finite element method (FEM), we calculate the reflectance spectra in planar and surface-textured thin-film solar cells, respectively. The simulation condition of the FEM, such as mesh size, is determined to match the numerical results based on the ETM with the analytical results obtained by the generalized transfer matrix method. For comparison, the reflectance spectra in the same structures are calculated by taking the average over coherent calculation results for a large number of random thicknesses of the incoherent layer. According to the comparison of the calculated statistical deviations from the exact solution between the ETM and the random thickness method, the ETM reduces the number of simulations by at least a factor of 50 with the same accuracy.

Simulation of Rough Surface of CIGS (CuInGaSe) Solar Cell by RCWA (Rigorous Coupled Wave Analysis) Considering the Incoherency of Light

In this paper we propose an electronic domain timing phase selection scheme for the optical communication systems suffering from inter-symbol-interference (ISI) distortion due to chromatic dispersion (CD) or polarization mode dispersion (PMD). In the presence of CD/PMD a proper timing phase selection is important for discrete time domain equalizers, since different timing phases produce different nonlinear ISI channels of different severity. The proposed timing phase recovery scheme based on dispersion minimization (DM) practically approximates the optimal minimum mean squared error (MMSE) timing phase without training signals which reduces overall throughput substantially, especially in time-varying channels such as PMD. The simulation results show that the proposed DM timing agrees with MMSE timing phase, under proper normalization of the received signals, for various dispersion and OSNR.