• 한국광학회지
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• 제7권4호
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• pp.386-389
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• 1996

We report on comparative results obtained from harmonically mode-locked laser operations of ring-type and figure-of-eight(F8) type erbium-doped fiber lasers by using a directional-coupler type electro-optic modulator as an active mode-locker. The mode-locked and transform-limited pulses of 10.6 ps width were obtained at harmonics of the fundamental cavity frequency with the F8 type laser while mode-locked laser pulses greater than 15 ps were achieved with the ring type laser.

• 한국재료학회지
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• 제12권4호
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• pp.254-258
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• 2002

To realize channel cross-connecting in optical communications systems, a high speed optical matrix switch was fabricated using z-cut $LiNbO_3$. For switch fabrication was design bending structure and coupling length and four $2{\times}2$ directional couplers were integrated on one substrate far construction of a $4{\times}4$ switch. Single-mode optical waveguides were formed by Ti-diffusion at a wet $O_2$ atmosphere. Ti-diffusion profile, refractive index variation and waveguide morphology were analyzed by Prism coupler and optical microscopy, respectively.

• 한국통신학회논문지
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• 제18권7호
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• pp.951-958
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• 1993

방향성 결합기같은 광의 결합현상을 이용한 집적광학 소자에서 결합거리는 소자의 특성을 결정할 수 있는 가장 중요한 요소이다. 또한 결합현상을 이용한 소자들의 연구시 결합거리의 계산은 가장 기본적인 특성 해석방법이 되고 있다. 지금까지 결합거리의 계산시에는 주로 모드결합이론을 사용하였는데 이때 결합계수를 계산하는 과정은 양쪽 도파로가 독립 적으로 존재한때의 모드의 분포를 각각 계산한 후, 그 결과를 가지고 무한적분을 행하여야하는 어려움을 가지고 있었다. 따라서 본 연구에서는 Beam Propagation Method(BPM)를 이용하여 결합계수의 계산없이 결합거리를 계산할것을 제안하였다. 그리고 제안의 타당성을 입증하기 위해서 가장 기본적인 방향성 결합기 모델을 설정하고 모드결합이론과 BPM과의 결과를 비교 검토하였다.

• 한국인터넷방송통신학회논문지
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• 제11권3호
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• pp.47-52
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• 2011

세 채널로 구성된 나노 크기의 플라즈마 방향성 결합기가 모드 결합효과와 립형 전송구조를 사용하여 설계되었다. 종방향 모드 전송선로 해석법을 이용하여 방향성 결합기에서 전파하는 빛의 전파특성과 설계특성들을 분석하였다. 전력분배기로 동작하는 플라즈마 방향성 결합기는 약 200~250 nm의 전송 폭을 갖는 나노 크기로 설계하였다. 최적의 전력분배율을 얻기 위하여 중심 채널의 폭 변화에 따른 전송 모드들의 굴절률을 분석하였다. 결국, 하향 채널에서 입사된 광 신호를 각 채널을 통하여 출력하는 나노 크기의 플라즈마 방향성 결합기가 설계되었다.

• Journal of the Optical Society of Korea
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• 제14권4호
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• pp.326-332
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• 2010

We review the research on specialty fiber couplers with emphasis placed on the characteristics that make them attractive for biomedical imaging, optical communications, and sensing applications. The fabrication of fiber couplers has been carried out with, in addition to conventional single mode fiber, various specialty fibers such as photonic crystal fiber, double clad fiber, and hole-assisted fiber with a Ge-doped core. For the fiber coupler fabrication, the side polishing and the fused biconical tapered methods have been developed. These specialty fiber couplers have been applied to optical coherence tomography, fluorescence spectroscopy, fiber sensors, and optical communication systems. This review aims to provide a detailed statement on the recent progress and novel applications of specialty fiber couplers.

• 대한전자공학회논문지SD
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• 제37권10호
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• pp.42-50
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• 2000

100${\mu}m$ 이하의 길이를 가지는 두 개의 영역으로 구성된 수직 방향성 결합기에서 1% 이하의 안쪽 클래딩 (퓨전층)과 도파로 코어의 굴절율 변화에 의하여 소자의 끝단에서 30dB 이상의 소멸비를 가지는 cross state와 bar state를 모두 얻을 수 있음을 보였다. 향상된 결합모드 이론과 beam propagation method를 사용하여 도파로 코어의 귤절율과 안쪽 클래딩의 굴절율과 두께에 따른 cross state와 bar state의 소멸비 계산 결과의 분석을 통하여 융합된 수직 방향성 결합 스위치의 설계 지침을 제시하였다.

• Current Optics and Photonics
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• 제1권5호
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• pp.514-524
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• 2017

We proposed an integrated wavelength-selective photodetector based on a grating-assisted contradirectional coupler and a graphene absorption layer for a coarse wavelength division multiplexing (CWDM) communication system. The center wavelength of the absorption spectrum of the proposed device can be tuned simply by changing the period of the grating, and the proposed device structure is suitable to forming a cascaded structure. Therefore, an array of the proposed device of different grating periods can be used for simultaneous wavelength demultiplexing and signal detection in a CWDM communication system. Our theoretical study showed that the designed device with a grating length of $500{\mu}m$ could have an absorption of 95.1%, an insertion loss of 0.2 dB, and a 3 dB bandwidth of 7.5 nm, resulting in a -14 dB crosstalk to adjacent CWDM channels. We believe that the proposed device array can provide a compact and economic solution to receiver implementation in the CWDM system by combining functions of wavelength demultiplexing and signal detection.

• Current Optics and Photonics
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• 제1권1호
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• pp.65-72
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• 2017

We propose a nearly lossless, compact, electrically modulated vertical directional coupler, which is based on the controllable evanescent coupling in a previously proposed graphene-assisted total internal reflection (GA-FTIR) scheme. In the proposed device, two single-mode waveguides are separate by graphene-$SiO_2$-graphene layers. By changing the chemical potential of the graphene layers with a gate voltage, the coupling strength between the waveguides, and hence the coupling length of the directional coupler, is controlled. Therefore, for a properly chosen, fixed device length, when an input wave is launched into one of the waveguides, the ratio of their output powers can be controlled electrically. The operation of the proposed device is analyzed, with the dispersion relations calculated using a model of a one-dimensional slab waveguide. The supermodes in the coupled waveguide are calculated using the finite-element method to estimate the coupling length, realistic devices are designed, and their performance was confirmed using the finite-difference time-domain method. The designed $3{\mu}m$ by $1{\mu}m$ device achieves an insertion loss of less than 0.11 dB, and a 24-dB extinction ratio between bar and cross states. The proposed low-loss device could enable integrated modulation of a strong optical signal, without thermal buildup.

• ETRI Journal
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• 제18권1호
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• pp.1-14
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• 1996

We have experimentally observed and theoretically analyzed the gain dependent optimum repetition rates of a hybrid-type active and passive mode locked laser pulses in an erbium-doped fiber laser of the figure-of-eight geometry by utilizing a nonlinear amplifier loop mirror (NALM) as a saturable absorber and a directional-coupler type electro-optic modulator as an active mode locker. Transform-limited mode-locked pulses of about 10 ps width were obtained at repetition rates which correspond to harmonics of the cavity fundamental frequency and depend on the optical amplifier gain in the NALM.

• 전자공학회논문지D
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• 제34D권1호
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• pp.41-48
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• 1997

Design rules of directional coupler optical switches are discussed in consideration of parasitic couplings in the bending section. The parasitic coupling phenomenon is analyzed based on the coupled-mode theory and the solutions are represented in the form of the transfer matrix. The modified switching conditions due to the parasitic coupling are derived and the resultant switching diagrams are illustrated. It is revealed that the parallel section's length needs to be adjustd less than the coupling length $l_c(=\pi/2\textsc{k}o)$ to obtain the desired crosstalk and that the adjustment depends on the strength of the parasitic coupling. However, it is discovered that, for weak parasitic coupling, the switching voltage does not need to be altered but may maintain the same value as if no parasitic coupling is taken into account.