• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.18-22
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• 2006

The transmission characteristics of multiply cascaded phase-shifted long-period fiber gratings(LPFGs) were investigated theo-retically and experimentally. Their passband can be changed by increasing the number of p-shifted LPFGs. When two p-shifted LPFGs with different grating lengths are cascaded in series, the bandwidth of the rejection band and passband can be controlled by the pristine characteristics of two gratings. We also investigate the transmission characteristics of phase-shifted LPFG by exposing the half of LPFG region to UV laser. The transmission characteristics strongly depend on the initial coupling strength of the LPFG.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.192-193
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• 2001

높은 파장 선택도를 가지고 광신호를 제어하는 광섬유격자는 단주기 격자, 장주기 격자, 첩 격자 등이 있는데 이러한 격자의 제작 기술은 여러 응용분야에서 활용도 높은 소자를 제작하는 데 이용되어져 왔다. 본 논문에서는, 주어진 반사 파장 내에 매우 좁은 선폭의 여러 투과 스펙트럼 밴드를 가지며 그 응용성이 다양한 격자 제작을 목표로 이미 수행되어진 위상천이 격자의 시뮬레이션[1]을 토대로 $\pi$위상천이 격자를 제작하였다. (중략)

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1583-1584
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• 2006

본 논문에서는 광섬유에 여러 가지의 위상변화를 준 장주기 격자에 대한 센서 특성을 비교하여 분석하였다. 위상변화의 정도에 따라서 센서의 특징을 유효하게 할 수 있는지 비교하여 센서로서의 타당성을 가지는 위상변화 정도의 범위를 알아보았다. 장주기 격자는 아르곤 레이저를 이용하여 Point by point 방식으로 제작되었으며, 위상 변화를 주기 위해서 linear stage를 이용하였다.

• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.643-648
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• 2003

The phase-shifting diffraction-grating interferometer proposed in the investigation uses a diffraction grating that performs manifold functions of beam splitting, beam recombination, and phase shifting. The reference and measurement waves generated by means of diffraction have different amplitudes depending on their orders of diffraction, so the interference fringe pattern resulting from the two waves tends to yield poor visibility. To cope with this problem, we select a phase grating of reflection type and attempt to improve the interference visibility with optimization of the groove shape of the grating through electromagnetic analysis.

• Journal of Software Assessment and Valuation
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• v.15 no.2
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• pp.101-109
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• 2019

Lasers for optical broadband communication systems should have excellent frequency selectivity and modal stability. DFB(Distributed Feedback) lasers have low lasing frequency shift during high speed current modulation. In this paper, I have developed a simulation software and analysed threshold gain and lasing frequency of a lasing mode in longitudinal direction of an 1.55um DFB laser with two mirrors and without anti-reflection coatings, that have both an index- and gain-gratings. The grating phase on a left mirror face is fixed as π/2 and the grating phase on a right mirror face is varied. As the phases of the index and gain gratings on the right mirror facet are π and 0, κL should be in the range of 2~6 in order to enhance the frequency stability. In order to reduce the threshold current of a lasing mode, κL should be greater than 8, regardless of the grating phases on the mirror faces.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.328-334
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• 1999

Methylene blue-sensitized photopolymerizable material based on acrylamide is investigated with two-wave energy coupling experiments. Differently from other studies, self-diffraction oscillations are observed and the grating phase is determined without applying external electric fields, moving nonlinear materials, and phase shifting one of two writing beams. The phase grating showed a phase shift of $\pm$50$^{\circ}$ with respect to the intensity grating. Modified Kogelnik's coupled wave equation considering the mixed gratings of phase and absorption gratings and nonzero spatial phase shifts of the gratings with respect to the intensity interference patterns formed during the two-wave energy coupling is discussed in detail to understand these phenomenon.

• Proceedings of the KAIS Fall Conference
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• 2004.06a
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• pp.247-249
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• 2004

본 논문에서는 격자구조의 유전체에 수직으로 입사된 전자기파의 산란, 투과 특성을 얇은 위상 막 근사화 이론을 이용하여 분석하였다. 위상 막 근사화 이론은 격자구조가 입사되는 전자기파의 위상 변화만을 주는 것으로 간주하는 것으로 이를 이용하여 격자구조를 통과한 직후인 근거리 필드 분포를 TE 모드에서 계산하였다. 기존의 제시된 이론에 비해 비교적 간단하고 빠르게 산란 필드를 분석할 수 있다.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.313-320
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• 2004

We present a null testing method fer aspheric surfaces, utilizing a phase-shifting diffraction grating interferometer along with a binary amplitude computer generated hologram (CGH). The binary amplitude CGH is designed to compensate for the wavefront between a point source and the aspheric surface under test. The fringe visibility of the grating interferometer is controlled easily by selecting suitable grating diffraction orders for the measurement and reference wavefronts or by optimizing the groove shape of the grating used. The binary amplitude CGH is designed by numerical analysis of ray tracing and fabricated using e-beam lithography for autostigmatic testing. Experimental results of a large-scale aspheric mirror surface are discussed to verify the measurement performance of the proposed diffraction grating interferometer.

• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.464-473
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• 1993

The dynamics of phase grating formation with visible light in an optical fiber is investigated. Adopting a simple two-photon local bleaching model, it is shown that the grating self-organize into an ideal grating, where the writing frequency is always in the center of the local band gap, as it evolves. The evolution at each point in the fiber is described in terms of a universal parameter that reduces the coupled partial differential equations describing the system to ordinary differential equatior~s. These equations are used to prove that there exists a fixed point of the grating growth process that corresponds to a perfectly phase-mached grating.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.5C
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• pp.496-499
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• 2002

In this paper, a phase shifter with shifting photonic bandgap(PBG) cell in linear feedforward amplifier is designed and fabricated in 5GHz wireless LAN band. Now a day, the phase shifter has been fabricated with hybrid type. In this paper, a portion of PBG cell is shifted for the tuning phase. The phase shift was achieved maximum 80o in our PBG structure. Shifting PBG cell has been applied in feedforward main loop to cancel the main two tone signal.