• 한국ITS학회 논문지
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• 제8권5호
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• pp.114-120
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• 2009

In outdoor visible light communication channels and LED road illumination communications for the intelligent transport systems (ITS), inter symbol interference (ISI) due to multipath propagation prevents high data rate transmission. Indoor wireless optical communication systems utilizing white LED lights and on the road illumination have been studying about it. Generally, plural lights are installed in room and considered to the traffic information system using existing LED traffic lights. Therefore, their optical path difference must be considered. In this paper, the influence of an optical path difference has been investigated and two approaches against this problem are introduced. One uses on-off keying, return-to-zero (OOK-RZ) coding and the other uses optical orthogonal frequency division multiplexing(OFDM).

• Journal of the Optical Society of Korea
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• 제6권3호
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• pp.121-127
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• 2002

The operating principal of a ring laser gyroscope depends on the phase difference for the counter-propagating waves within a closed path. The reflecting mirrors mounted on the monoblock form the traveling waves. The manufacturing accuracy of the monoblock influences the traveling path of ray, the sensitivity of laser resonator for misalignments, and diffraction losses. A 3 $\times$ 3 ray transfer matrix was derived for optical components with centering and squaring errors in a ring resonator. The matrix can be utilized to predict the optical ray paths on the basis of the manufacturing errors of the monoblock as well as the misalignment of mirrors. Then the distance and orientation (o. slope) at the arbitrary plane inside the resonator along the ideal optical path can be calculated from the chain multiplication of the ray transfer matrix for each optical component in one round trip. We also show that the counter-propagating rays In a ring resonator with errors does not coincide in each round trip, which results in gain difference between two beams, and how these errors can be adjusted through the alignment procedure. Finally this 3 $\times$ 3 ray matrix formalism can be used to calculate the beam size and its displacement from the optical axis and the deviation at the diaphragm.

• Journal of the Optical Society of Korea
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• 제15권4호
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• pp.380-385
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• 2011

Common-path interferometers are widely used for endoscopic optical coherence tomography (OCT) because an arbitrary arm length can be chosen for the endoscopic imaging probe. However, the scheme suffers from the limited range of the sample position distance from the end of the imaging probe because the position between the reference reflector and the sample is limited by the optical path-length difference (OPD) to induce an interference signal. In this study, we developed a novel method for compensating the arbitrary sample position in common-path swept-source OCT by adding an extra Mach-Zehnder interferometer in the post-path of the interfered optical signal. Theoretical analysis and an experimental demonstration of imaging depth tuning for the flexible sample position of an endoscopic OCT image are discussed. After post-tuning of sample position distance, the positioning limitation between the reference reflector and the sample can be solved for various sample positions over a range of 26 mm for the cross-sectional images of a fish eye sample.

• Journal of the Optical Society of Korea
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• 제10권4호
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• pp.169-173
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• 2006

This paper describes an efficient optimal design method for an arrayed waveguide grating (AWG) having MMI coupler with flattened transfer function. The objective function is the norm of the difference between calculated and target spectra. To analyze the AWG transfer function, the Fresnel-Kirchhof diffraction formula was employed and the design variable was optical path difference of each array waveguide. The (1+1) Evolution Strategy was applied to an eight-channel coarse wavelength division multiplexing (CWDM) AWG as the optimization tool. For obtaining a broadened spectrum, we use a MMI coupler and the variation in optical path difference at each array waveguide changes the shape of the transfer function to obtain the optimal spectrum shape.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.7-11
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• 2008

Future electric lights will be composed of white LEDs (Light Emitting Diodes). Indoor wireless optical communication systems utilizing white LED lights have been studying about it. Generally, plural lights are installed in room. Therefore, their optical path difference must be considered. In this paper, the influence of an optical path difference has been investigated and two approaches against this problem are introduced. One uses OOK-RZ (On-Off Keying, Return-to-Zero) coding and the other uses optical OFDM (Orthogonal Frequency Division Multiplexing). From the results of computer simulations, we have found that these approaches are feasible for the wireless optical communication systems utilizing white LED lights.

• Journal of the Optical Society of Korea
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• 제13권2호
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• pp.173-177
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• 2009

Digital holographic microscopy allows optical path difference measurement. Optical path difference depends on the both refractive index and morphology of sample. We developed a dual-wavelength in-line digital holographic microscope that can measure simultaneously the refractive index and morphology of a sample, providing highly precise three-dimensional information. Here we propose theoretical and experimental methods for dual-wavelength in-line digital holographic microscopy. The measured data were reasonable, although there was data error. By improving the experimental method, we could measure the refractive index more precisely and obtain more accurate three-dimensional information on samples.

• 한국정보통신학회논문지
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• 제11권5호
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• pp.985-990
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• 2007

코히런트 광섬유 센서의 해상도를 향상시키기 위하여 광원의 코히런스 길이를 향상시키는 방법에 대하여 연구하였다. 넓은 파장범위에 걸쳐서 레이저 광을 생성할 수 있고 발광 파장대역이 장거리 전송이 가능한 통신용 광섬유의 저 손실 대역인 광섬유 레이저의 코히런스 길이를 향상시키기 위하여 레이저의 광궤환 기법을 이용하였다. 본 논문에서는 광섬유 레이저의 단거리 및 장거리 광궤환 루프가 코히런스 길이에 미치는 영향을 Mach-Zehnder Interferometer를 이용하여 연구하였다. 광궤환 전력량과 광궤환 루프에서의 변조형태가 코히런스에 미치는 영향을 조사하였다. 주파수 천이도는 200m 길이차를 갖는 비대칭 간섭계에서의 위상간섭 정도를 측정하여 계산하였다. 광섬유 레이저에서 단거리 광궤환 루프는 450kHz/sec로 주파수 천이도를 축소시키는데 효과가 있었고 장거리 광궤환 루프는 50kHz/sec로 주파수 천이도를 더 향상시키는 효과가 있음을 알 수 있었다. 실제 코히런트 광센서에 응용 시 고감도 침입자 감지가 기대된다.

• Journal of the Optical Society of Korea
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• 제8권3호
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• pp.99-103
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• 2004

This paper describes the optimal design of an AWG spectrum to meet various specifications and improve some physical parameters. The objective function is the norm of the difference between design parameters and target values. To obtain the design parameters, the Fourier model is employed and the design variables arc spacing of array waveguide, width of array waveguide, optical path difference, and focal length. The (1+1) Evolution Strategy is employed as the optimization tool. The optimization procedure is applied to a 16-channel AWG and the optimized design variables will considerably improve the system performance.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2431-2433
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• 1999

Phase errors of arrayed waveguide degrade the performance of AWG router, especially for dense WDM system. So it is necessary to measure the phase error and to compensate. The analysis method of the interference signal from the low coherence interferometer to measure the path length difference phase error is studied. The interference signal generated assuming the intentional path length difference errors of 0.1$\sim$0.4${\mu}m$ are analyzed and the results show that the path length difference phase error of ${\Delta}L$ within ${\pm}14^{\circ}$ of sampling phase error can be accurately measured.

• 한국전기전자재료학회논문지
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• 제19권2호
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• pp.195-199
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• 2006

We report a novel simulation method to calculate optical transmission considering the real paths of optic introduced in a unit pixel of TFT-LCDs using three-dimensional molecular director simulation of the tensor model. The simulation of optical path transmission profile was carried out by calculating new permittivity considered the real paths of optic in liquid crystal cell. As a result, it was clarified that the electro-optic characteristics such as movement of disclination line, contrast ratio and transmittance profile show a large difference according to the viewing angle compared with the conventional method.