• 한국항행학회논문지
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• 제4권1호
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• pp.1-10
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• 2000

레이다에서 마그네트론을 이용하여 송신펄스를 발생하는 경우에 레이다의 코히어런트 동작을 위해서는 수신기에서 송신펄스의 주파수 및 위상 변화를 감지하여 안정된 중간주파수를 발생할 수 있도록 국부발진주파수를 조정하고, 위상측정을 위하여 송신펄스의 위상에 동기된 신호를 발생하여야 한다. 본 논문에서는 레이다의 수신기 전단부에서 안정된 중간주파수를 발생하기 위한 AFC(Automatic Frequency Control) 회로와 STALO(Stable Local Oscillator)를 설계, 제작하고, 송수신 신호간의 위상측정을 위한 COHO(Coherent Oscillator)를 구현하였다.

• 제어로봇시스템학회논문지
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• 제10권1호
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• pp.96-102
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• 2004

For sensitivity enhancement, the general assisted-GPS acquisition method adopts not only the coherent accumulation technique but also the non-coherent accumulation technique since the long coherent accumulation period increases the number of frequency search cells. But the non-coherent accumulation technique causes tile squaring loss, which is a dominant factor among the acquisition losses of assisted GPS dealing with weak GPS signals. This paper derives the squaring loss of the previous assisted-GPS acquisition method and proposes an assisted-GPS acquisition method for solving the problem of squaring loss in weak signal environment. In this paper, it is explained that the proposed assisted-GPS acquisition method prevents the squaring loss using a coupled coherent accumulation technique and the number of search cells of the proposed assisted-GPS acquisition method is much smaller than that of the previous assisted-GPS acquisition method. Finally, through the simulation by the GPS simulator, the acquisition success rate of the proposed assisted-GPS acquisition method is compared with that of the previous assisted-GPS acquisition method and the acquisition improvements are shown in weak signal environment.

• 한국광학회지
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• 제31권6호
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• pp.247-258
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• 2020

본 논문에서는 대기외란에 따른 SPGD 위상제어 알고리즘 기반 결맞음 빔결합 시스템의 위상제어 동작성능을 논의한다. 대기의 외란에 대한 통계적 이론을 바탕으로 전산모사를 통해 대기외란에 의한 레이저빔의 위상 및 파면 왜곡에 대한 분석과 왜곡된 빔을 통해 얻게 되는 7채널 및 19채널 결맞음 빔결합 결과를 도출하고, 이를 통해 대기외란의 정도에 따른 빔결합 시스템의 위상제어 동작성능 및 효율을 수치적으로 비교분석한다. 분석 결과, 7채널 결맞음 빔결합의 경우, 대기외란 파라미터 cn2 값이 10-13 m-2/3 까지 증가한 상황에서도 SPGD 위상제어 알고리즘을 적절히 적용할 경우 90% 이상의 빔결합 효율로 시스템의 위상 잠금이 가능하다는 것을 확인하였다. 19채널 결맞음 빔결합의 경우, 동일한 대기외란 조건에서도 대기의 굴절률 비균질성(refractive index inhomogeneity)의 영향이 더 커서 빔결합 효율이 60% 수준으로 급격하게 감소할 수 있음을 확인하였다. 또한, 대기외란이 있는 상황에서 위상잠금시점까지 요구되는 알고리즘의 반복연산 횟수와 대기현상의 변화간격을 비교분석함으로써, 다채널 결맞음 빔결합 시스템이 ㎲의 간격을 가지는 대기외란 상황에서도 정상동작을 하기 위해서는 SPGD 위상제어 알고리즘의 연산대역폭이 수백 MHz에서 수 GHz까지 확장되어야 한다는 것을 확인하였다. 향후, 대기외란이 SPGD 위상제어 알고리즘 기반 결맞음 빔결합 시스템의 위상제어 동작성능에 미치는 영향을 정량적으로 분석하고 예측하는 데 있어서 본 논문의 결과가 유용하게 활용될 수 있을 것이라 기대된다.

• 제어로봇시스템학회논문지
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• 제16권7호
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• pp.720-725
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• 2010

In AGPS method, user position can be obtained even in the shadow region by improving signal sensitivity. A hybrid long integration scheme employing both coherent and non-coherent integration method is commonly used in AGPS receivers. Because coherent loss increases as residual frequency become large, residual frequency should be minimized to maximize coherent integration gain. This paper presents performance analysis of residual frequency estimator using FFT in fine-time assistance AGPS method. Considering the hardware complexity and the estimation accuracy, optimal length of FFT is proposed for GPS L1 C/A signal. Signal sensitivity for estimating the residual frequency is also analysed. By field experimental results, it is found that the residual frequency can be successfully estimated using 1 second snap-shot data when GPS signal strength is larger than -150 dBm and its RMS error is 3Hz.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2002년도 ICCAS
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• pp.33.6-33
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• 2002

For RF sensitivity enhancement, the previous assisted GPS acquisition architecture adopts not only the coherent integration technique but also the non-coherent integration technique since the long coherent integration time increases the number of the frequency search cells. But the non-coherent integration technique induces the squaring loss, which is the dominant factor among the acquisition losses of assisted GPS dealing with weak GPS signals. This paper proposes an efficient architecture for weak signal acquisition in assisted GPS. In this paper, it is explained that the proposed architecture reduces the squaring loss using a modified non-coherent integration technique. Furthermore, it is..

• Bulletin of the Korean Chemical Society
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• 제35권11호
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• pp.3294-3298
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• 2014

We theoretically investigated the coherent control of Autler-Townes splitting in photoelectron spectroscopy of K2 molecule within an ultrafast laser pulse by solving the time-dependent Schrodinger equation using a quantum wave packet method. It was theoretically shown that we can manipulate the splitting of photoelectron spectroscopy by altering the laser intensity. Furthermore, it was found that the percentages of each peak in photoelectron spectroscopy can be controlled by changing the envelope of the laser pulse.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 26-27 Oct. 1990
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• pp.1108-1111
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• 1990

Sorce noise effect in 1.5 Mach-Zehnder (MZ) interferometer is analyzed. It is shown numerically that with fine adjustments to the feedback gain and initial phase biases, the operating point of the interferometer to achives common mode compensation can be made to lie in a region where the measurand sensitivity is greater than it would be in a conventional Mach-Zehnder interferometer even if the source is less coherent.

• Current Optics and Photonics
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• 제1권2호
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• pp.85-89
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• 2017

It is shown that polarization singularities of a new type, namely U and P singularities, arise at the transverse cross section of a partially coherent beam, instead of the common singularities such as C points and L lines in a completely coherent vector field. A relationship between the two kind of singularities with respect to intensity is proposed. We also present a setup that can generate the new singularities, and any desired distribution of degree of polarization, using intensity control.

• Current Optics and Photonics
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• 제5권6호
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• pp.627-640
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• 2021

In a free-space coherent optical communication system, wavefront distortion is frequently beyond the correction range of the adaptive-optics system after the laser has propagated through the atmospheric turbulence. A method of residual wavefront correction is proposed, to improve the quality of coherent optical communication in free space. The relationship between the wavefront phase expanded by Zernike polynomials and the mixing efficiency is derived analytically. The influence of Zernike-polynomial distortion on the bit-error rate (BER) of a phase-modulation system is analyzed. From the theoretical analysis, the BER of the system changes periodically, due to the periodic extension of wavefront distortion. Experimental results show that the BER after correction is reduced from 10^-1 to 10^-4; however, when the closed-loop control algorithm with residual correction is used, the experimental results show that the BER is reduced from 10^-1 to 10^-7.

• Journal of the Optical Society of Korea
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• 제11권3호
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• pp.138-141
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• 2007

We suggest that supercontinuum can be used for absorption spectroscopy to observe the exciton levels of a semiconductor nano-structure. Exciton absorption spectrum of a GaAs/AlGaAs quantum well was observed using supercontinuum generated by a microstructrured fiber pumped by a femtosecond (fs) pulsed laser. Significantly narrower peaks were observed in the absorption spectrum from 11 K up to room temperature than photoluminescence (PL) spectrum peaks. Because supercontinuum is coherent light and can readily provide high enough intensity, this method can provide a coherent ultra-broad band light source to identify exciton levels in semiconductors, and be applicable to coherent nonlinear spectroscopy such as electromagnetically induced transparency (EIT), lasing without inversion (LWI) and coherent photon control in semiconductor quantum structures.