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Unidirectional, Efficiency-Controlled Coupling from Microcavity Using Reflection Feedback
Hwang, In-Kag,Lee, Yong-Hee IEEE 2007 IEEE journal of selected topics in quantum electro Vol.13 No.2
<P>We propose a microcavity-to-waveguide side coupling system with a reflector at one end of the waveguide for the feedback. Using this system, one can get a unidirectional output from a microcavity-based light emitter, where the output coupling efficiency and the cavity loss can be enhanced or suppressed through tuning optical phase of the feedback. Theoretical calculations are confirmed by finite-difference time domain (FDTD) simulation of the coupling between a photonic crystal cavity and a microfiber with a perfect mirror attached. Unidirectional coupling from the photonic crystal cavity to the fiber with efficiency of 90% is demonstrated in the simulation</P>
전기 임피던스를 측정할 때 외부 간섭을 제거하기 위한 대역확산 기술의 적용
黃仁德(In-Duk Hwang),姜顯珏(Hyun-Kag Kang) 대한전기학회 2006 전기학회논문지 D Vol.55 No.4
When we measure electrical impedance of a small object, such as an electronic component, external interference or jamming signal can be rejected by shielding the object. However, when we measure impedance of a large object, such as a human body, shielding is not easy and severe error due to the external interference could be introduced. In this paper, spread spectrum technique applicable to bioimpedance measurements for rejecting external interference without shielding is introduced. The improvement in signal-to-jamming ratio by the spread spectrum technique was experimentally confirmed.
Sidelobe suppression in all-fiber acousto-optic tunable filter using torsional acoustic wave
Lee, Kwang Jo,Hwang, In-Kag,Park, Hyun Chul,Kim, Byoung Yoon The Optical Society 2010 Optics express Vol.18 No.12
<P>We propose two techniques to suppress intrinsic sidelobe spectra in all-fiber acousto-optic tunable filter using torsional acoustic wave. The techniques are based on either double-pass filter configuration or axial tailoring of mode coupling strength along an acousto-optic interaction region in a highly birefringent optical fiber. The sidelobe peak in the filter spectrum is experimentally suppressed from -8.3 dB to -16.4 dB by employing double-pass configuration. Axial modulation of acousto-optic coupling strength is proposed using axial variation of the fiber diameter, and the simulation results show that the maximum side peak of -9.3 dB can be reduced to -22.2dB. We also discuss the possibility of further spectral shaping of the filter based on the axial tailoring of acousto-optic coupling strength.</P>
Tunable gratings in a hollow-core photonic bandgap fiber based on acousto-optic interaction
Yeom, Dong-Il,Park, Hyun Chul,Hwang, In Kag,Kim, Byoung Yoon The Optical Society 2009 Optics express Vol.17 No.12
<P>We demonstrate a coherent intermodal coupling in a hollow-core photonic bandgap fibers (PBGF) using an acoustic grating. A theoretical study on the properties of acoustic and optical wave propagating the PBGF is performed indicating that the applied frequency higher than 10 MHz is required to obtain the acousto-optic interaction at the wavelength around 1550 nm. Wavelength-tunable coupling from fundamental mode to higher-order core modes is achieved with more than 90% coupling efficiency at the applied frequency of 11.54 MHz. The low dispersive properties and the mode filed distributions of the higher-order guided modes of the air-core PBGF in the experiment show reasonable agreement with the simulation results.</P>
Polarization-Independent All-Fiber Acousto-Optic Tunable Filter Using Torsional Acoustic Wave
Kwang Jo Lee,In-Kag Hwang,Hyun Chul Park,Byoung Yoon Kim IEEE 2010 IEEE photonics technology letters Vol.22 No.8
<P>The intrinsic polarization dependence of an all-fiber tunable wavelength filter based on polarization coupling by torsional acoustic wave is eliminated by employing a fiber loop configuration. In the fiber loop, two orthogonal polarizations split from input light propagate the single acousto-optic interaction region in opposite directions before being recombined to produce a polarization-independent filter spectrum. The polarization-dependent loss was estimated to be less than 0.1 and 0.3 dB within passband in bandpass and notch type filters, respectively.</P>
Ngoc-Hai Vu,Byung-Chon Jeon,Du-Ho Jo,In-Kag Hwang 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.4
This paper describes computational errors found in finite-difference time-domain (FDTD) analyses of photonic crystal fibers and proposes several techniques to improve the accuracy. We first briefly introduce the FDTD computation scheme and discuss the optimization of various simulation parameters to obtain high accuracy with reasonable computation loads. The calculation of a bending loss with good agreement with the experimental data is demonstrated by proper selection of the computation domain. Finally, we propose a simulation based on a real fiber image to reflect irregularities and fabrication errors for fiber structures. This paper describes computational errors found in finite-difference time-domain (FDTD) analyses of photonic crystal fibers and proposes several techniques to improve the accuracy. We first briefly introduce the FDTD computation scheme and discuss the optimization of various simulation parameters to obtain high accuracy with reasonable computation loads. The calculation of a bending loss with good agreement with the experimental data is demonstrated by proper selection of the computation domain. Finally, we propose a simulation based on a real fiber image to reflect irregularities and fabrication errors for fiber structures.
Experimental excitation and characterization of cladding modes in photonic crystal fiber
Do Lim, Sun,Park, Hyun Chul,Hwang, In-Kag,Lee, Sang Bae,Kim, Byoung Yoon The Optical Society 2010 Optics express Vol.18 No.3
<P>We extend the previous theoretical study on the effect of outer silica cladding to the analysis on real field profiles in a practical PCF. Clear field profiles for the first higher-order cladding modes are presented and discussed. The observed mode fields are reproduced by numerical calculations, and it turns out that they correspond to LP(16) mode groups. Optical properties of the observed modes such as lobe direction and polarization are also investigated. The results of this study will be useful in the design of the PCF-based optical devices utilizing cladding mode coupling.</P>