• Journal of the Optical Society of Korea
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• 제2권1호
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• pp.1-4
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• 1998

The second harmonic light of an 842 nm diode laser was generated from a KNbO3 crystal in an external ring resonator. The power of the second harmonic light was about 0.8 mV at an input fundamental power of 87 mW. The laser frequency was stabilized to the resonance frequency of the ring resonator, and the frequency fluctuation was measured as about 3 MHz.

• 한국광학회:학술대회논문집
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• 한국광학회 2007년도 하계학술발표회 논문집
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• pp.113-114
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• 2007

• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 하계학술발표회
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• pp.202-203
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• 2000

단원자를 이용한 Cavity-QED실험을 위해서는 고분해능 분광학이 필수적 요소이며, 이에 따라, 좁은선폭의 레이저가 필요하게 된다. 본 실험에서는 기준공진기를 이용한 전류되먹임방법의 1단계와, AOM(Acousto Optic Modulator)을 이용한 주파수 보정의 2단계를 거쳐 다이오드 레이저의 주파수를 안정화하였다. (중략)

• Current Optics and Photonics
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• 제3권1호
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• pp.33-39
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• 2019

We report development of a frequency-stabilized mid-infrared continuous-wave (cw) optical parametric oscillator (OPO) based on a fan-out grating MgO:PPLN crystal pumped at 1064 nm. The OPO resonator was designed as a pump-enhanced standing-wave cavity that resonates to the pump and signal beams. To realize stable operation of the OPO, we applied a modified Pound-Drever-Hall technique, which is a well-known method for powerful laser frequency stabilization. Tuning a poling period of the fan-out grating of the crystal allows wavelength-tunable OPO outputs from 1510 nm to 1852 nm and from 2500 nm to 3600 nm for signal and idler beams, respectively. At the idler wavelengths of 2500 nm, 3000 nm and 3500 nm, we achieved more than 50 mW of output powers at a pumping power of 1.1 W. The long-term stability of the OPO was confirmed by recording the power and wavelength variations of the idler for an hour.

• 한국멀티미디어학회논문지
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• 제20권8호
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• pp.1236-1247
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• 2017

In this paper, we propose a method for evaluating the uncomfortable shaking in the video. When you shoot a video using a handheld device, such as a smartphone, most of the video contains unwanted shake. Most of these fluctuations are caused by hand tremors that occurred during shooting, and many methods for correcting them automatically have been proposed. It is necessary to evaluate the shake correction performance in order to compare the proposed shake correction methods. However, since there is no standardized performance evaluation method, a correction performance evaluation method is proposed for each shake correction method. Therefore, it is difficult to make objective comparison of shake correction method. In this paper, we propose a method for objectively evaluating video shake. Automatically analyze the video to find out how much tremors are included in the video and how much the tremors are concentrated at a specific time. In order to measure the shaking index, we proposed jitter modeling. We applied the algorithm implemented by Optical Flow to the real video to automatically measure shaking frequency. Finally, we analyzed how the shaking indices appeared after applying three different image stabilization methods to nine sample videos.

• 제어로봇시스템학회논문지
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• 제17권2호
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• pp.157-163
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• 2011

This paper proposes a hybrid image stabilizing system which uses both optical image stabilizing system based on EKF (Extended Kalman Filter) and digital image stabilization based on SURF (Speeded Up Robust Feature). Though image information is one of the most efficient data for object recognition, it is susceptible to noise which results from internal vibration as well as external factors. The blurred image obtained by the camera mounted on a robot makes it difficult for the robot to recognize its environment. The proposed system estimates shaking angle through EKF based on the information from inclinometer and gyro sensor to stabilize the image. In addition, extracting the feature points around rotation axis using SURF which is robust to change in scale or rotation enhances processing speed by removing unnecessary operations using Hessian matrix. The experimental results using the proposed hybrid system shows its effectiveness in extended frequency range.

• 항공우주시스템공학회지
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• 제10권4호
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• pp.17-25
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• 2016

본 연구에서는 초점면부 영상안정화 기법 중 렌즈 시프팅 영상안정화 기법에 적용될 광학설계를 수행하였다. 렌즈 시프팅 기법은 광학탑재체로 전달되는 미세진동외란을 보상하기 위해 광 경로를 바꿔주는 영상 안정화 기법이다. 실제 위성카메라의 제원을 참고하여 렌즈 시프팅 기법이 적용될 광학계의 요구도를 수립하였으며, 광학설계 프로그램인 Code-V를 이용해 광학계를 설계하였다. 설계된 광학계가 요구 조건을 충족하였는지 검증하기 위해 시야에 따른 광선 수차분석, 스팟 다이어그램 분석, MTF 선도분석을 수행하였다. 최종적으로 설계된 광학계는 슈미트 카세그라인 타입에 필드 플래트너와 진동보상 렌즈가 삽입된 형태이며, 주반사경 직경은 200 mm, GSD 2.87m, 나이퀴스트 주파수에서 MTF 33%으로 광학계 성능요구도를 만족하였다. 본 연구에서 설계된 진동보상렌즈의 입사광선에 대한 진동계수는 0.95~1.00 으로 성능 요구도를 만족하였다.

• 한국생산제조학회지
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• 제23권3호
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• pp.266-272
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• 2014

This study proposes a closed-loop shaping control method with $H_{\infty}$ optimization for optical image stabilization (OIS) in mobile phone cameras. The image stabilizer is composed of a horizontal stage constrained by ball bearings and actuated by the magnetic force from voice coil motors. The displacement of the stage is measured by Hall effect sensors. From the OIS frequency response experiment, the transfer function models of the stage and Hall effect sensor were identified. The weight functions were determined considering the tracking performance, noise attenuation, and stability with considerable margins. The $H_{\infty}$ optimal controller was executed using closed-loop shaping and limiting the controller order, which should be less than 6 for real-time implementation. The control algorithm was verified experimentally and proved to operate as designed.

• 한국통신학회논문지
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• 제10권4호
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• pp.168-174
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• 1985

半導體 레이저의 出力 및 波長은 溫度에 대단히 敏感하다. 특히 헤테로다인光通信 씨스템이다. 光學用積密 度量衡器, 高分解能 스텍트로스코프 等測量 및 通信에서 發光源으로 使用하기 爲해서는 適當한 安定化 技術이 要求된다. 이 때 溫度의 安定은 絶對的이다 .따라서 本 硏究에서는 桓溫器의 溫度를 -27$-50^{\circ}$에서 +73$^{\circ}C$까지 임의 設定이 可能하게 하였으며 溫度 安定은 ${\pm}2m{\circ}K$보다 좋은 結果를 얻었다.

• Current Optics and Photonics
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• 제5권4호
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• pp.384-390
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• 2021

This paper presents a wide-range tunable wavelength-locking technology based on optoelectronic oscillation (OEO) loops for optical fiber sensors and microwave photonics applications, explains the theoretical fundamentals of the design, and demonstrates a method for locking the relative wavelength differences between a leader semiconductor laser and its follower lasers. The input of the OEO loop in the proposed scheme (the relative wavelength difference) determines the radio-frequency (RF) signal frequency of the oscillation output, which is quantized into an injection current signal for feedback to control the wavelength drift of follower lasers so that they follow the wavelength change of the leader laser. The results from a 10-hour continuous experiment in a field environment show that the wavelength-locking accuracy reached ±0.38 GHz with an Allan deviation of 6.1 pm over 2 hours, and the wavelength jitter between the leader and follower lasers was suppressed within 0.01 nm, even though the test equipment was not isolated from vibrations and the temperature was not controlled. Moreover, the tunable range of wavelength locking was maintained from 10 to 17 nm for nonideal electrical devices with limited bandwidth.