• 한국정밀공학회지
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• 제31권9호
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• pp.805-811
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• 2014

In this investigation, we constructed and demonstrated a simple Yb-doped fiber laser, of which longitudinal modes are mode-locked without any additional devices to compensate the dispersion caused by optical components. Non-linear polarization rotation (NPR) was adopted for the mode-locking mechanism and a polarization controller (PC) was used for a kind of spectral filters to restrict the bandwidth for mode-locking. As the result, the laser was successfully operated as mode-locked with the repetition rate of 42.2 MHz and the spectrum was broadened up to approximately 16 nm at 1033 nm center wavelength when the laser was mode-locked. In this paper, the operation of the developed Yb-doped mode-locked laser is explained with the concept of Lyot filter realized by a PC, which enables mode-locking under normal dispersion. In the industrial applications, this laser can be used as a seed laser of the high power lasers for optical manufacturing.

• 한국통신학회논문지
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• 제33권1C호
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• pp.94-101
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• 2008

본 논문에서는 실시간으로 빛의 편광상태(SOP)를 파악할 수 있는 장치를 소개한다. 소개하는 장치는 광파를 수평 선형편광과 수직 선형편광 성분으로 분리하고, 각각을 기준 광원의 수평 선형편광 및 수직 선형편광 성분들과 중첩시키고 이로부터 발생한 비트신호들을 시간 영역에서 측정하여 비교함으로써 광파의 SOP를 파악해 내는 순방향(feed-forward) 측정 시스템으로서 귀환(feedback) 방식을 이용하는 기존의 방식들에 비해 SOP 측정시간을 실시간으로 단축시키는 장점을 갖고 있다. 본 논문에서는 또한 SOP 측정 과정에서 수반될 수 있는 광소자의 복굴절 변화에 의한 측정 오차를 매우 간편하고 정확하게 제거할 수 있는 새로운 오차 보정 방식을 소개한다. 제안하는 시스템의 동작과 성능을 모의실험 및 광학 실험을 통해 입증하였다.

• Transactions on Electrical and Electronic Materials
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• 제12권6호
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• pp.241-244
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• 2011

An isolator transmits light in the forward direction and blocks light from passing in the reverse direction. It is regarded an essential optical component in medical, industrial, and research lasers for blocking reflection beams that cause optical damage and noise. It is also used as a communicative light intensifier to expand the lifespan of devices and enhance transmission quality. This study analyzed the characteristics of the core components in the construction of a polarization-independent isolator, namely, the walk-off polarizer and the Faraday rotator. Measurement of the extinction ratio of the resultant walk-off polarizer revealed that the ratio between the vertical and horizontal rays was 1,050:1 with a laser output of 0.032 W and 1,010:1 with a laser output of 2.68 W, thus presenting ratios similar to 1,000:1. In addition, the walk-off polarizer and Faraday rotator constructed in this study were used to compare output changes according to changes in power of input light and to check the penetration ratio. Results from the study presented variations in output value according to changes in power of input light. However, the average penetration ratio remained relatively consistent (~81.4%).

• 대한의용생체공학회:의공학회지
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• 제26권1호
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• pp.37-42
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• 2005

We construct and test the polarization-sensitive optical coherence tomography (PS-OCT) system for imaging porcine and human articular cartilages. PS-OCT is a new imaging technology that provides information regarding not only the tissue structures but tissue components that show birefringence such as collagen. In this study, we measure the cartilage thickness of the porcine joint and the phase retardation due to collagen birefringence. Also, we demonstrate that changes of the collagen fiber orientation could be detected by the PS-OCT system. Finally, differences between normal and damaged human articular cartilage are observed using the PS-OCT system, which is then compared with the regular histology pictures. As a result, the PS-OCT system is proven to be effective for diagnosis of the pathology related to the cartilage. In the future, this technology may be used for discrimination of the collagen types. When combined with endoscope technologies, the PS-OCT images may become a useful tool for in vivo tissue testing.

• 대한원격탐사학회지
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• 제25권6호
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• pp.531-546
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• 2009

The main objective of this study is to analyse the polarimetric characteristics of the various terrain targets by ground-based polarimetric SAR system and to confirm the compatible and effective polarimetric analysis method to reveal the polarization properties of different terrain targets by the GB-SAR. The fully polarimetric GB-SAR data with HH, HV, VH, and VV components were focused using the Deramp-FFT (DF) algorithm. The focused GB-SAR images were processed by the H/A/$\alpha$ polarimetric decomposition and the combined H/$\alpha$ or H/A/$\alpha$ and Wishart classification method. The segmented image and distribution graphs in H/$\alpha$ plane using Cloude and Pottier's method showed a reliable result that this quad-polarization GB-SAR data could be useful to classified corresponding scattering mechanism. The H/$\alpha$-Wishart and H/A/$\alpha$-Wishart classification results showed that a natural media and an artificial target were discriminated by the combined classification, in particular, after applying multi-looking and the Lee refined speckle filter.

• Journal of the Optical Society of Korea
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• 제17권1호
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• pp.33-37
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• 2013

In this study a new design concept of the Fabry-Perot filter, constructed with an anisotropic space layer and a couple of isotropic mirrors, was proposed based on the Maxwell equations and the characteristic matrix method. The single- and double-cavity Fabry-Perot filters were designed, and their optical properties were investigated with a developed software package. In addition, the dependence of the transmittance and phase shift for two orthogonal polarization states on the column angle of the anisotropic space layer and the incidence angle were discussed. We demonstrated that the polarization state of electromagnetic waves and phase shifts can be modulated by exploiting an anisotropic space layer in a polarization F-P filter. Birefringence of the anisotropic space layer provided a sophisticated phase modulation with varied incidence angles over a broad range, resulting in a wide-angle phase shift. This new concept would be useful for designing optical components with isotropic and anisotropic materials.

• 전기화학회지
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• 제4권3호
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• pp.125-131
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• 2001

용융탄산염 연료전지의 장기 운전시 각 전극별 분극의 변화를 Au, $CO_2/O_2$ 기준전극이 부착된 단위전지를 이용하여 성공적으로 해석하였다. 서로 다른 구성요소로 조합된 네 가지 단위 전지를 운전하며 각 전극의 분극을 해석한 결과, 이미 알려진 바와 같이 공기극의 분극 크기가 연료극의 경우보다 큰 것을 실험적으로 측정할 수 있었다. 고온 부식 방지를 위해 cell frame의 wet seal부분에 Al코팅을 한 전지는 6,000시간까지 성능을 유지하여 부식이 전지 성능 저하에 큰 역할을 하고 있음을 알 수 있었다. 한편, $LiCoO_2$가 코팅된 안정화 공기극은 일반적으로 사용되는 NiO 공기극보다 lithiation에 필요한 시간이 길어 운전 초기에 공기극 분극이 크고 성능이 낮았으나 지속적인 운전으로 공기극이 충분히 lithiation되면서 공기극의 분극이 작아지고 성능도 점차 증가하였다. $Li_2CO_3/Na_2CO_3$ 전해질을 사용한 전지는 운전 중 성능이 하락과 상승을 반복하는 진동현상을 보였는데 이는 연료극보다는 공기극의 영향으로 해석되었다. 대부분의 단위전지들이 급격한 성능 하락을 보였을 경우의 공기극 분극은 급격히 증가하였으며 이로써 용융탄산염 연료전지의 수명 향상을 위해서는 공기극의 개선이 필수적이라는 것을 알 수 있었다.

• Journal of the Optical Society of Korea
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• 제7권4호
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• pp.211-215
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• 2003

Statistical characteristics of the backscattered light from turbid tissues obtained by polarizationsensitive optical coherence tomography are investigated. The amplitude of the backscattered light is found to faithfully follow the Rayleigh distribution predicted by the scattering theory of electromagnetic waves in random media. The probability density function of the phase difference between the two orthogonal polarization components of the backscattered light is explicitly derived and then verified in comparison with the experimental data measured from in-vitro tissues of porcine ligament.

• Bulletin of the Korean Chemical Society
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• 제24권8호
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• pp.1091-1096
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• 2003

The effects of different polarization conditions on vibrational echo signals are systematically explored for the rigid cyclic dipeptide 2,5-diazabicyclo[2,2,2]octane-3,6-dione. An anharmonic vibrational Hamiltonian is constructed by computing energy derivatives to fourth order using density functional theory. Molecular frame transition dipole orientations are then used to calculate polarization dependent orientational factors corresponding to various Liouville space pathways. Enhancement and elimination of specific peaks in twodimensional correlation plots is accomplished by identifying appropriate pulse configurations.

• Journal of the Optical Society of Korea
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• 제18권6호
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• pp.646-649
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• 2014

Performances of spectrum-sliced channels are strongly affected by their relative intensity noise (RIN). We use polarization-independent optical modulators (PIOMs) for spectrum-sliced channels to suppress their RIN. The PIOM driven by a high sinusoidal voltage signal evenly redistributes optical frequency components in the spectral domain and reduces the RIN. It can be used at a broadband light source (BLS) output to produce spectrum-sliced channels having lower RIN values. Also, it can be used for each spectrum-sliced channel within each optical network unit (ONU). In our experiment, where 12.5-GHz-spaced spectrum-sliced channels are used in 1-GbE speed, the use of PIOM at the BLS output reduces the bit error rate (BER) of the spectrum-sliced channel by more than an order of magnitude. The use of PIOM within the ONU reduces the BER by approximately 3 orders of magnitude.