• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.5
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• pp.775-782
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• 2022

In this paper, a novel small-diameter cylindrical post capacitor inserted into an evanescent-mode rectangular waveguide (EMRWG) is proposed for easier tuning. In order to feed the EMRWG, the proposed structure uses a single ridge rectangular waveguide with the same width and height as the waveguide at the input and output ends. The inserted post capacitor are made up a circular groove formed in the center of the lower part of the broad wall of the EMRWG, and a concentric cylindrical post inserted into the upper part. First, the equivalent circuit model for the proposed structure is presented. When the EMRWG and the single ridge waveguide are combined, the joint susceptance and the turns ratio of the ideal transformer are calculated by two simulations using HFSS (3d fullwave simulator, Ansoft Co.) respectively. The susceptance and resonance characteristics of the inserted post were analyzed by using the obtained parameters and the characteristics of the EMRWG. A 2-post filter with a center frequency of 4.5 GHz and a bandwidth of 170 MHz was designed using a WR-90 waveguide, and the simulation results by using the HFSS and CST, equivalent circuit model were in good agreement.

• Journal of Korea Water Resources Association
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• v.32 no.6
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• pp.675-683
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• 1999

The reflection coefficients of monochromatic waves propagating over a shelf with varying dimensions are theoretically calculated. The diffraction of waves by an abrupt depth change is formulated by the eigenfunction expansion method. Not only propagating mode but also evanescent modes are considered in formulation. The role of evanescent modes in reflection coefficients is investigated in detail. Water waves are obliquely as well as normally incident to the region. The obtained reflection coefficients are verified by checking conservation of wave energy.

• Proceedings of the Optical Society of Korea Conference
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• 2004.02a
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• pp.154-155
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• 2004

• Water for future
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• v.26 no.1
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• pp.71-79
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• 1993

Nonlinear characteristics of air pressure variation and wave transformation of a fixed air-chamber structure are discussed theoretically and experimentally. Two analytical methods(method I and II) based on the perturbation method and Green's formula are employed in order to evaluate nonlinearities by the submerged and semi-submerged air-chamber structure. Moreover, an air compression model is newly developed to estimate the dynamic air pressure in the air-chamber inside the structure, assuming the Boyle-Charles's law with adiabatic process in the air pressure variation. Theoretical values of the method I considering evanescent mode waves at an fictious boundary, are in good agreement with those of method II employing the fictious boundary which is not affected by evanescent mode waves. Both theoretical values are shown to agree well with experimental values.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.1
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• pp.1-9
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• 1992

Eigen Function Expansion Method(EFEM) and Plane Wave Approximation are employed to study the propagation of linear water waves over trenches. The properties of trapped waves due to depth and ambient current discontinuities and the effect of evanescent modes on wave propagations are investigated. Special attention is paid to the trapped waves, and not only 3-D plots but also B-D plots of wave propagation are presented.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.135-139
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• 2016

I propose a vector passive harmonic mode-locked fiber laser based on topological insulator Bi2Se3 interacting with a fiber taper with a diameter of 7 μm. The particles of topological insulator are deposited uniformly onto the fiber taper with light pressure effect. By incorporating the fabricated saturable absorber into an Er-doped fiber laser cavity, stable mode-locked fiber is obtained. Due to the intense evanescent field of the fiber taper, strong confinement of light enhances the nonlinearity of the laser cavity, and passive harmonic mode-locking is performed. I observe a maximum harmonic mode-locking of 356th, corresponding to a frequency of 3.57 GHz. The pulse duration is 824 fs, and the full width at half maximum of the spectrum is about 8.2 nm. The polarization dependent loss of the saturable absorber is ~ 2.5 dB in the wavelength range of the C band. As the cavity contains no other polarization dependent device, the mode-locked laser is functioning in the vector state. The harmonic order vs pump power is investigated. To the best of our knowledge, this report is the highest frequency mode-locked fiber laser based on Bi2Se3. Experimental results indicate that the topological insulator Bi2Se3 functioning with a thin fiber taper is effective for vector harmonic mode-locking.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.82-83
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• 2000

굴절율이 외부보다 큰 실린더 (cylinder)나 스피어 (sphere)는 경계면에서의 전반사에 의해 손실이 매우 적은 high-Q 공진기가 될 수 있음이 잘 알려져 있다. 크기가 수 십 $mu extrm{m}$ 되는 실린더나 스피어에서의 공명모드는 편광(TM, TE), 모드 수 (mode number) n, 모드 순서 (mode order) l에 의해 정의되고 WGM (whispering gallery mode)라고도 불리워진다$^{(1)}$ . 모드 수n 이 클수록 모드 순서 l이 작을수록 공명모드의 Q 값은 큰 경향을 가진다. 액체 방울이나 액체 제트와 같이 열적 섭동에 민감한 마이크로 공진기 (micro-cavity)의 경우 Q값이 $10^{7}$ 정도로 제약되나, 실리카 마이크로 스피어 (micro-sphere)와 같은 고체 구에서 측정된 Q값은 약 $101^{10}$ 정도로 손실이 매우 적은 공진기가 될 수 있다$^{(2)}$ . 이와 같은 마이크로 공진기 특성을 이용하여 다양한 형태의 마이크로 공진기 레이저 대한 연구가 진행되어 왔다. 색소가 첨가된 고체구, 액체 방울, 액체 제트 등에서 기본적인 실험이 이루어졌고 반도체마이크로 스피어 구조에서 WGM 레이저$^{(3)}$ , polymer disc laser$^{(4)}$ , 광양자테 (photonic quantum ring)$^{(5)}$ 특성 연구 등이 실용가능성을 목표로 진행되고 있다. (중략)

• Journal of IKEEE
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• v.24 no.2
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• pp.409-418
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• 2020

In this paper, an integrated optical, evanescent-wave biosensor utilizing a multimode interferometer based on a Si₃N₄ rib-optical waveguide consisting of the Si/SiO₂/Si₃N₄/SiO₂ stacked structure was described. The theoretical background of the multimode interferometer was reviewed, and the structure and design process were presented through numerical computational analysis. We analyzed how the dimension (length, width) of the multimode interferometer affected the sensor performance. It has been confirmed through computational analysis that the changes in the refractive index of an analyte greatly affect the mode pattern formation position and output optical power of a multimode interferometer, and proved that this principle could be applied to integrated-optic biosensor.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.216-217
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• 2001

광섬유와 평면 도파로를 결합한 도파로 구조에서 광 결합 현상은 다양한 응용 가능성 때문에 이론적으로 또는 실험적으로 많은 연구가 되어오고 있다. 광섬유는 단일모드를 이용하고 적당한 곡률이 주어진 블록에 고정한 후 연마하여 클래딩의 일부를 제거하고, 그 상부에 다중모드 평면 도파로(Multi-Mode Overlay Waveguide; MMOW)를 구성한다. 제작된 결합기 구조에서 평면 도파로는 광섬유의 감쇠장 결합(Evanescent field coupling)을 유도하게 되므로, 소자의 특성은 평면 도파로의 구조와 조건에 의해 결정된다. (중략)

• Coupled systems mechanics
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• v.2 no.1
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• pp.53-83
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• 2013

Sea waves induce significant pressures on coastal surfaces, especially on rocky vertical cliffs or breakwater structures (Peregrine 2003). In the present work, this hydrodynamic pressure is considered as the excitation acting on a piezoelectric material sheet, installed on a vertical cliff, and connected to an external electric circuit (on land). The whole hydro/piezo/electric system is modeled in the context of linear wave theory. The piezoelectric elements are assumed to be small plates, possibly of stack configuration, under a specific wiring. They are connected with an external circuit, modeled by a complex impedance, as usually happens in preliminary studies (Liang and Liao 2011). The piezoelectric elements are subjected to thickness-mode vibrations under the influence of incident harmonic water waves. Full, kinematic and dynamic, coupling is implemented along the water-solid interface, using propagation and evanescent modes (Athanassoulis and Belibassakis 1999). For most energetically interesting conditions the long-wave theory is valid, making the effect of evanescent modes negligible, and permitting us to calculate a closed-form solution for the efficiency of the energy harvesting system. It is found that the efficiency is dependent on two dimensionless hydro/piezo/electric parameters, and may become significant (as high as 30 - 50%) for appropriate combinations of parameter values, which, however, corresponds to exotically flexible piezoelectric materials. The existence or the possibility of constructing such kind of materials formulates a question to material scientists.