• 정보통신설비학회논문지
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• 제8권2호
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• pp.90-95
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• 2009

All-optical fiber-type gain flattening filer (GFF) for an EDFA (Erbium doped fiber amplifier) were fabricated by using a FBT (fiber biconical tapered) process and the performance of the GFF was tested and athermal package was proposed. Historically, the chief contributor to gain unevenness has been the EDFA. Due to the inherent gain response of the EDFA's operation, there is always a modest imbalance in the gain applied as a function of wavelength. FBT methods have been used to make fiber type couplers and WDM filter since 1980. Attractivity of this methods was simple, cost effective and thermal stability. Simulation program tool is made to design target GFF profile for this paper. Fiber coupler manufacturing machine is modified for the GFF process. The final GFF is obtained by cascading 4 unit filter that has 6 taper stage. Test result shows 1 dB of wavelength flatness in the C band. Polarization dependent loss is under 0.15dB. The center wavelength variation is below ${\pm}$0.35nm at the temperature range of $20^{\circ}C$ to $70^{\circ}C$.

• Journal of the Optical Society of Korea
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• 제9권3호
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• pp.123-128
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• 2005

An electrically controllable fiber Bragg grating inscribed in a hydrogen-loaded standard single-mode fiber with liquid-crystal cladding is presented. Control of the optic axis of liquid crystals by means of external electric fields results in the change of reflectivity and Bragg wavelength of the grating. The increase of surrounding refractive index of a fiber makes effective refractive index of a propagation mode higher, which results in high field confinement and longer Bragg wavelength. The reduction of the fiber diameter by chemical etching process improves the long-range ordering of liquid-crystal molecules and reduces controlling voltage. The tunable ranges of reflectivity and Bragg wavelength of the liquid crystal-cladding fiber Bragg grating were $\~4.6dB\;and\;\~0.3nm$, respectively.

• Journal of the Optical Society of Korea
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• 제9권4호
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• pp.135-139
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• 2005

We demonstrate a simple and effective wavelength-tunable add/drop filter suitable for coarse wavelength division multiplexing (CWDM) systems. The filter consists of two fibers in contact side by side, with identical long-period fiber gratings (LPG) in each fiber. The LPG couples the power in the fundamental core mode to one of the cladding modes, which is then coupled to the same order cladding mode in the other fiber through evanescent-field coupling between two fibers. Finally, the cladding mode in the second fiber is coupled to its core mode with the help of the other LPG. With an optimal longitudinal offset distance of 10 em, coupling efficiency as high as -1.68 dB and side lobes smaller than -24 dB were experimentally obtained. The experimental results agreed well with the theoretical ones. The operating wavelength of the proposed add/drop filter was tunable by varying the temperature. The temperature sensitivity was measured to be -0.43 nm/$^{\circ}C$.

• 한국정밀공학회지
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• 제30권10호
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• pp.1009-1015
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• 2013

Ultra-short laser pulses are effective, when high requirements concerning accuracy, surface roughness and heat affected zone are demanded for surface structuring. In particular, picosecond laser systems that are suited to be operated in industrial environments are of great interest for many practical applications. This paper focused on inducing optimum process parameters for higher volume ablation rate by analyzing a relationship between crater diameter and optical spot size. In detail, the dependency of the volume ablation rate, penetration depth and threshold fluence on the pulse duration 8 ps and wavelength of 515 nm was discussed. The experimental results showed that wavelength of 515 nm resulted in less threshold fluence ($0.075J/cm^2$) on copper than IR wavelength ($0.3J/cm^2$). As a result, it was possible that optimum fluence for higher volume ablation rate was achieved with $0.28J/cm^2$.

• 한국자기학회지
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• 제5권5호
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• pp.561-566
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• 1995

Additional magnetooptical Kerr effect (AMOKE) was observed in several multilayer structures. For Fe/Pd and Co/Cu Multilayers, AMOKE enhanced the Kerr rotation in short wavelength side, while for Fe/Ag and FeSi/Cu multilayer systems the Kerr rotation enhancement appeared in long wavelength side. A number of ferromagnetic/nonmagnetic/ferromagnetic(FM/NM/FM) sandwiches showed that the AMOKE led to oscillations of Kerr rotation and Kerr ellipticity in certain wavelength range with changing NM layer thickness similar to the oscillatory interlayer coupling. The oscillation of effective optical constants related to the MOKE oscillation was observed for the first time. The mechanisms of the AMOKE were discussed.

• 한국재료학회지
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• 제29권9호
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• pp.547-552
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• 2019

In the present study, the thermal conductivity of a silicon nitride($Si_3N_4$) thin-film is evaluated using the dual-wavelength pump-probe technique. A 100-nm thick $Si_3N_4$ film is deposited on a silicon (100) wafer using the radio frequency plasma enhanced chemical vapor deposition technique and film structural characteristics are observed using the X-ray reflectivity technique. The film's thermal conductivity is measured using a pump-probe setup powered by a femtosecond laser system of which pump-beam wavelength is frequency-doubled using a beta barium borate crystal. A multilayer transient heat conduction equation is numerically solved to quantify the film property. A finite difference method based on the Crank-Nicolson scheme is employed for the computation so that the experimental data can be curve-fitted. Results show that the thermal conductivity value of the film is lower than that of its bulk status by an order of magnitude. This investigation offers an effective way to evaluate thermophysical properties of nanoscale ceramic and dielectric materials with high temporal and spatial resolutions.

• 한국광학회지
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• 제14권4호
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• pp.369-376
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• 2003

장파장 적외선 영역에서, 비구면 및 회절면을 동시 또는 단독으로 사용했을 때 렌즈의 성능에 미치는 영향을 분석하였다. 유효초점거리(efl: effective focal length)를 100 mm로 고정하고 반시야 각(half field angle)을 5$^{\circ}$에서 30$^{\circ}$까지 5$^{\circ}$간격으로 증가시켰을 때 수치구경 값의 변화를 고찰하였다. 렌즈의 광학성능은 장점함수(merit function)를 기준으로 사용하였다. 이 분석을 근거로 픽셀 크기 45 $\mu$m, 픽셀 수 320${\times}$240검출기를 기준으로 비냉각 열상장비용으로 사용 가능한 F/l.0인 광학계를 설계하였다.

• 대한의용생체공학회:의공학회지
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• 제31권6호
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• pp.472-480
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• 2010

Mechanically deformed cartilage undergoes a temperature dependent phase transformation resulting in reshaping of cartilage. Laser-assisted cartilage reshaping (LCR) is recently introduced to recreate the underlying cartilage framework in structures such as ear, larynx, trachea, and nose. However, this procedure has not been fully supported by confirmed efficacy because of the lack of scientific research and its safety issues. The purpose of this study is to evaluate current laser sources to determine optimal laser wavelength for LCR using mathematical simulations and investigate optical, thermo-mechanical, and backscattering properties of cartilage after laser irradiation. The results showed that 1444 nm wavelength was effective for reshaping of cartilage with minimal thermal damage in the surrounded tissues by monte carlo simulations. Analysis of bend angle changes, thermo-mechanical characteristics, and backscattered properties may be useful to better identify the biophysical transformation responsible for stress relaxation in cartilage and develop an optical feedback control methodologies.

• 한국광학회지
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• 제23권5호
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• pp.227-232
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• 2012

본 논문에서는 RLD (Reflective Laser Diode)와 FBG (Fiber Bragg Grating)가 하이브리드 집적된 LD (이하 FG-LD)의 정적 및 동적 특성을 해석하기 위하여 대신호 시영역 모델링 방법을 구현하였다. FBG의 유효길이 2.1 mm를 포함한 외부 집적 공진기의 길이가 8 m인 경우에 0.44GHz의 동적 주파수 요동과 6.4 GHz 정도의 동적 주파수 요동 결과를 나타내었다. 또한 10 Gbps NRZ 신호의 아이가 크게 오픈된 상태를 잘 유지함을 확인하였다. FG-LD는 50 km 정도의 길이를 커버하는 10 Gbps 급 단일파장 레이저로서의 효용성이 있을 것으로 기대된다.

• Journal of the Optical Society of Korea
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• 제20권5호
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• pp.557-562
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• 2016

In this paper, for the first time, the transmission performances of long-haul 100-Gb/s direct detection optical OFDM (DDO-OFDM) and coherent optical OFDM (CO-OFDM) wavelength division multiplexing (WDM) systems are compared by simulation. It provides specific guides for system parameter selection to get a high-performance and cost-effective OFDM WDM system. Specifically, the comparison involves three aspects: launched power is investigated to achieve better system performance; laser linewidth is numerically investigated to choose cost-effective laser; system dispersion tolerances with different laser linewidths are analyzed to further reveal the advantages and disadvantages of these two detecting methods, direct detection and coherent detection, in long-haul OFDM WDM system.