• Korean Journal of Optics and Photonics
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• v.22 no.6
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• pp.269-275
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• 2011

We propose a metal-dielectric hybrid waveguide structure consisting of a single metal nanowire placed on a flat dielectric slab. Mode size and propagation loss of the surface-plasmons confined in the metal-dielectric gap are compared with those of the complementary structure with a dielectric nanowire on a metal surface. In the case of the nanowire's diameter much smaller than the wavelength the two structures reveal quite different characteristics; the dielectric nanowire-on-metal has longer propagation distance, but only the metal nanowire-on-dielectric exhibits a mode size two fold smaller than the diffraction limit. The proposed hybrid structure may therefore be more suitable for realization of nanocavity lasers.

• Journal of the Korean Vacuum Society
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• v.12 no.S1
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• pp.28-32
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• 2003

Both $LiNbO_3$ and $KTiOPO_4$ samples were implanted with 350 keY $H^+$ and $He^+$ ions at different doses ranging from $1 ${\times}$\times10^{16}$ to of $5 ${\times}$\times10^{16}$ ions/$\textrm{cm}^2$. Single and multi-energy implantations were performed at room temperature. Mono-mode or a few modes in both $LiNbO_3$ and $KTiOPO_4$ waveguides were observed. The effect of temperature on the refractive index profiles of $LiNbO_3$ and $KTiOPO_4$ waveguids was studied. The temperature covered from room temperature, $200^{\circ}C$, 194.5 K (dry ice) and 77K (liquid nitrogen). Different mechanisms are needed to interpret the observed behavior. A n, increased mono-mode $LiNbO_3$ waveguide was formed by multi-energy keV $He^+$ ions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.8
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• pp.1833-1841
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• 1997

Rectangular dielectric waveguides, the most fundamental and indispensible elements in integrated optics, have been investigated by many researchers with various approaching methods including from the relatively approximate techniques to the numerical method. In this paper, the optimum equivalent waveguide model is adopted which is determined by a perturbation feedback process for analyzing the propagation constant by means of computer simulation, we have ascertained that the propagation constant from perturbation feedback method gives the best approximate value because it coincide with more exact value than obtained by other approximating methods. The technique also provides analytical expression for the modal field profile that should be useful in the design of various integrated optical devices.

• Korean Journal of Optics and Photonics
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• v.22 no.3
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• pp.117-121
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• 2011

We propose a saturable absorber reflector based on guided-mode resonance. A carbon nanotube is used as a saturable absorber. By tuning the fill factor, modulation depth can be increased without a change of height of the CNT. We investigate the reflector properties such as modulation depth, bandwidth and peak reflectance as a function of the height of the CNT and the fill factor. The advantage of the proposed reflector is that it can reduce saturation energy by 50 times compared with CNT thin film of 100~200nm.

• Korean Journal of Optics and Photonics
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• v.31 no.5
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• pp.213-217
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• 2020

In this study we report a wet-etching-based fabrication method for adiabatic optical-fiber tapers (OFTs), and describe their adiabaticity and HE₁₁ mode evolution at a wavelength of 1550 nm. The profile of the fabricated system satisfies the adiabaticity properties well, and the far-field pattern from the etched OFT shows that the fundamental HE₁₁ mode is maintained without a higher-order mode coupling throughout the tapers. In addition, the measured far-field pattern agrees well with the simulated result. The proposed adiabatic OFTs can be applied to a number of photonic applications, especially fiber-chip packages. Based on the fabricated adiabatic OFT structures, the optical transmission to the inversely tapered silicon waveguide shows large spatial-dimensional tolerances for 1 dB excess loss of ~60 ㎛ (silicon waveguide angle of 1°) and insertion loss of less than 0.4 dB (silicon waveguide angle of 4°), from the numerical simulation. The proposed adiabatic coupler shows the ultrabroadband coupling efficiency over the O- and C-bands.

• Korean Journal of Optics and Photonics
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• v.33 no.4
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• pp.137-145
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• 2022

A directional coupler device, one of the fundamental components of photonic integrated circuits, distributes optical power by evanescent field coupling between two adjacent optical waveguides. In this paper, the design process for manufacturing a directional coupler device is reviewed, and the accuracy of the design results, as seen from the characteristics of the actual fabricated device, is confirmed. When designing a directional coupler device through a two-dimensional (2D) beam-propagation-method (BPM) simulation, an optical structure is converted to a two-dimensional planar structure through the effective index method. After fabricating the directional coupler device array, the characteristics are measured. To supplement the 2D-BPM results that are different from the experimental results, a 3D-BPM simulation is performed. Although 3D-BPM simulation requires more computational resources, the simulation result is closer to the experimental results. Furthermore, the waveguide core refractive index used in 3D-BPM is adjusted to produce a simulation result consistent with the experimental results. The proposed design procedure enables accurate design of directional coupler devices, predicting the experimental results based on 3D-BPM.

• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.169-173
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• 1997

Most conventional lithography systems have been oriented to fabricate electronic devices. Therefore, it is not so easy to fabricate large aspect ratios of waveguide patterns with those systems. When considering costs and efficiencies, a laser lithography system provides number of benefit in realizing waveguide patterns. However, because the conventional laser lithography system could make only positive tone masks, it is inconvenient in determining the direction of the waveguide. A simple and reliable technique to produce negative tone masks was developed by using the laser beam writing. This technique was not sensitive to environmental situations such as dust, vibration, intensity variation. Making use of the technique a variety of device patterns such as Y-branch, directional coupler, and highly smooth S-shape bend could be successfully fabricated with a good contrast.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.6
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• pp.53-58
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• 2004

A novel UV sensor was manufactured and characterized using evanescent field coupling between photochromic dye dispersed polymer waveguide and side polished fiber. The spiroxazine (photochromic dye) dispersed polymer was used as planar waveguides. The resonant wavelength was shifted owing to refractive index variation of planar waveguide on exposed UV because of its photo-functional properties. The sensitivities are $1.21{\mu}W/mw$ and $2.75{\mu}W/mw$ when UV intensities increased after exposure times were fixed at 3 seconds and 5 seconds, respectively. Output optical power according to UV intensity increases and saturation time decreases as the intensity of UV radiations increases.

• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.99-103
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• 2006

A tunable wavelength filter was proposed and demonstrated by using the UV nanoimprint technique. It consists of a Bragg grating in polymer waveguides and a heating electrode. The manufacturing of the grating was substantially simplified with the introduction of a smart imprint stamp containing a waveguide pattern integrated with the grating pattern. The center wavelength of the filter was successfully tuned by taking advantage of the thermooptic effect in polymers, which was induced by supplying electrical power to the electrode. For the fabricated device, a transmission dip of ${\~}$15 dB and a 3-dB bandwidth of 0.8 nm were obtained at the Bragg wavelength of ${\~}$l560 nm. The achieved thermooptic tuning efficiency was ${\~}$0.28 nm/mW, while the center wavelength was shifted from 1560 nm to 1558 nm with the electrical power consumption of 7 mW.

• Korean Journal of Optics and Photonics
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• v.18 no.6
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• pp.447-451
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• 2007

A triplexer based on a silica planar lightwave circuit Mach-Zehnder nterferometer(MZI) is proposed and its characteristics are analyzed through simulations. To separate 1310 nm band and $1480{\sim}1560nm$ band properly, the path length difference of an MZI is set to be the multiple and half of the wavelength 1310 nm and the balance of the directional coupler is optimized in the $1480{\sim}1560nm$ band. The same MZI is additionally cascaded to provide good crosstalk characteristics. The 1490 nm band and 1550 nm band are further separated using additional two stage MZI's. A three-dimensional BPM and transfer matrix method analysis predicts the low crosstalk characteristics and the fabrication-error-tolerance of the proposed triplexer.