• 한국정밀공학회지
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• 제30권12호
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• pp.1273-1279
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• 2013

We propose a dual grating alignment technique for roll-to-roll positioning which allows achieving nanometer scale alignment by using micro-size marks. The high precision alignment system were designed and manufactured. It was confirmed that the optical system was properly adjusted and fully aligned with the dual gratings. The experiment and computer simulation results were presented. Alignment accuracy below 50 nm was achieved.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2013년도 춘계학술대회 논문집
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• pp.603-604
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• 2013

• Journal of Advanced Marine Engineering and Technology
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• 제33권1호
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• pp.153-158
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• 2009

Stable and tunable dual-wavelength erbium-doped fiber ring laser(EDFL) using a single fiber Bragg grating(FBG) and two coil heaters is proposed and demonstrated. Installing two identical coils into a single FBG, the FBG is symmetrically divided into two different portions. While a current supply to the coil, the refractive index of the FBG under the coil is changed. The FBG can operate as a joint of two different FBGs. Due to the thermo-optic effect of a fiber, the resonance wavelength split into two peaks. The spacing between two adjacent channels was changed as much as the difference of heating power. It was tuned up to 3 nm of wavelength under the electrical power with a 1000 mW. Moreover, the lasing wavelength can be individually tuned without influencing to the adjacent channel.

• 한국항공우주학회지
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• 제32권7호
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• pp.43-50
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• 2004

변형률과 파손선호를 동시에 계측하기 위하여 이중복조기를 갖는 광섬유 브래그 격자 센서시스템을 제안하였다. 이중복조기는 가변 패브리-페로 필터를 사용하여 변형률과 같이 변화가 큰 저주파신호를 측정하는 복조기와 수동 마흐 -젠더 간섭계를 사용하여 충격이나 파손신호와 같이 미세한 크기의 고주파 신호를 측정하는 복조기로 구성된다. 제안된 광섬유 브래그 격자 센서시스템을 이용하여 인장하중을 받는 직교적층 복합재 구조물의 변형률과 파손신호를 동시에 계측할 수 있었다. 하나의 광섬유 브래그 격자 센서로 측정한 변형률과 파손신호를 분석한 결과, 복합재 시편의 90도 층에서 기지 균열이 발생할 때 급격한 변형률 변이가 유발되고, 최대 수백 킬로헤르츠에 이르는 주파수 성분을 가진 진동신 호가 발생함을 알 수 있었다.

• Current Optics and Photonics
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• 제5권3호
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• pp.243-249
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• 2021

In this paper, the sensing characteristics of a double cladding fiber (DCF) long-period fiber grating (LPFG) to the surrounding refractive index (SRI) are studied. The outer cladding of the DCF plays the role of the overlay, thus, the mode transition (MT) phenomenon of DCF can be induced by etching the outer cladding radius instead of coating overlays. The response characteristics of the effective refractive index (ERI) of the cladding mode to the outer cladding radius are analyzed. It is found that in the MT range, the change rate of ERIs of cladding modes is relatively larger than that for other ranges. Further, based on the features of the mode transition region (MTR), the phase-matching curve of the 11^th cladding mode is investigated, and the response of the DCF-LPFG to the SRI is characterized by the change of wavelength intervals between the dual peaks under different outer cladding radii. The numerical simulation results show that the SRI sensitivity is greatly improved, which is available to 3484.0 nm/RIU with the fitting degree 0.998 in the SRI range of 1.33-1.37. The proposed DCF-LPFG can provide new theoretical support for designing the DCF-LPFG refractive index sensor with excellent performances of sensitivity, linearity and structure.

• Journal of the Optical Society of Korea
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• 제1권1호
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• pp.23-25
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• 1997

In this paper we will show theoretically that a refractive index grating exhibits a retro-self-focusing effect and an accompanying pinholing effect under the Gaussian intensity distribution of an incident optical field. Those effects result from an effective wave number change of the medium due to the intense optical field.

• Journal of the Optical Society of Korea
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• 제18권5호
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• pp.429-435
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• 2014

We examined the effective utilization of Particle Swarm Optimization (PSO) to enhance the light absorption performance in thin CuIn1-xGaxSe2 (CIGS) solar cells with dual (top and bottom) gratings. The PSO tuned structure was demonstrated to be capable of achieving high and ultra broadband absorption spectra due to well-spaced and well-defined absorption peaks, which were SPPs and photonic modes induced by the metal and dielectric gratings. For only TM polarization and both polarizations, the fully optimized net absorptions exhibit 85.6% and 78.1%, which correspond to ~35.4% and ~23.5% improvement compared to optimized flat structures, respectively.

• 전기학회논문지
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• 제56권11호
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• pp.1995-1997
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• 2007

In this paper we propose a wavelength-switchable fiber ring laser that employs a polarization-dependent fiber band stop filter. The fiber filter was fabricated by inscribing a long-period fiber grating on a high birefringent fiber. Dual-wavelength switching operation was accomplished by controlling the rotatable linear polarizer which rotated the polarization plane of the light circulating through the fiber laser cavity. The amplitude variation of both laser lines was measured to be less than 0.5 dB and the signal-to-amplified spontaneous emission ratio was more than 55 dB.

• 한국광학회지
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• 제16권5호
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• pp.411-416
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• 2005

Optical Time Domain Reflectometry를 이용하여 수백 km 이상의 장거리 광통신망을 감시하기 위해서는 감시광을 증폭시켜야한다. 본 논문에서는 1625 nm OTDR 감시광을 증폭시키기 위해 fiber Bragg grating과 band pass filter를 이용하여 이득과 잡음지수를 각각 5.1 dB 그리고 0.9 dB 향상시킨 2단 구조의 Extended L-band EDFA를 제안하였다. 제안된 Extended L-band EDFA의 1625 nm 대역의 신호 이득은 16.3 dB이고 잡음지수는 7.1 dB였다.

• ETRI Journal
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• 제25권3호
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• pp.149-155
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• 2003

A self-pulsating multisection distributed-feedback laser diode (DFB LD) can potentially realize all-optical clock extraction. This device generally consists of three sections, two DFB sections and one waveguide section. The most important variable in this device is detuning, which is the relative spectral position between the stop bands of two DFB sections. We fabricated a novel structure in which two gratings were located one over and one under the active layers. Each grating structure was independently defined in processing so that detuning, which is the prerequisite for self-pulsation, could be easily controlled. Observing various self-pulsating phenomena in these devices under several detuning conditions, we characterized the phenomena as dispersive Q-switching, mode beating, and self-mode-locking.