• Korean Journal of Optics and Photonics
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• v.11 no.1
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• pp.47-57
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• 2000

A two-stage iterative Fourier transform algorithm, based on hybrid input-output algorithm and new Pnoise algorithm, is used to design continuous and quantized phase-only diffractive pattern elements which produce arbitrary given intensity patterns via Fraunhofer diffraction. Numerical results for two $128\times128$ binary patterns and two grayscale patterns are compared with those of other algorithms. It is found that the algorithm yields better signal-to-noise ratio and even better uniformity with slightly lower diffraction efficiency than other algorithms. We investigated the dependence of performance on parameters used in the algorithm, size of noise region, and the number of phase levels for quantized elements. In the case of quantized phase elements, the size of noise region plays a greater role in determining the performance of the algorithm than given intensity pattern itself. tself.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.6
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• pp.602-612
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• 2013

In this paper, a design and fabrication of miniaturized 5.3 GHz reflection type $360^{\circ}$ analog phase shifter with branch line coupler and $360^{\circ}$ variable reactance load. In order to miniaturize phase shifter, novel branch line coupler is proposed. The novel branch line coupler is miniaturized using transformation of transmission line to T and ${\pi}$ type equivalent circuit. The miniaturized branch line coupler has small size of above 50 % compared with conventional branch line coupler. For wide phase shift range, $360^{\circ}$ variable reactance load structure is adopted. Especially, the structure was improved for linear phase shift by adding transmission line which acts as an impedance transformer. The improved structure was miniaturized using the equivalent lumped-element of transmission line. The fabricated phase shifter with $15{\times}15mm^2$ shows wide phase shift of above $480^{\circ}$, the insertion loss of -4~-6 dB and the reflection loss of below -20 dB at 5.3 GHz under 0~10 V control voltage range.

• Korean Journal of Optics and Photonics
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• v.17 no.6
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• pp.507-513
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• 2006

In this paper, we propose an improved image encryption and fault-tolerance decryption method using phase wrapping and phase encoding in the frequency domain. To generate an encrypted image, an encrypting key which denotes the product of a phase-encoded virtual image, not an original image, and a random phase image is zero-padded and Fourier transformed and its real-valued data is phase-encoded. The decryption process is simply performed by performing the inverse Fourier transform for multiplication of the encrypted key with the decrypting key, made of the proposed phase wrapping method, in the output plane with a spatial filter. This process has the advantages of solving optical alignment and pixel-to-pixel mapping problems. The proposed method using the virtual image, which does not contain any information from the original image, prevents the possibility of counterfeiting from unauthorized people and also can be used as a current spatial light modulator technology by phase encoding of the real-valued data. Computer simulations show the validity of the encryption scheme and the robustness to noise of the encrypted key or the decryption key in the proposed technique.

• Proceedings of the Optical Society of Korea Conference
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• 2002.07a
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• pp.160-161
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• 2002

양자 암호화 키 분배 시스템에서 광자를 code화시키는 방법은 크게 편광coding과 위상 coding으로 대별할 수 있다. 또한 프로토콜은 4개의 상태를 가진 BB82 프로토콜과 2개의 상태를 가진 B92 프로토콜을 사용한 시스템을 많이 연구하고 있다. 본 연구는 B92프로토콜을 적용한, 위상 coding 양자 암호화 키 분배 시스템의 구성에 필요한 위상 변조기에 대한 비교 검토 및 위상 변조기 설계에 관한 것이다. (중략)

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.292-293
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• 2003

반도체 공정에서 위상 소자를 적용하는데 있어, 그 위상항을 ITFA 방법을 적용하여 계산하였고 계산된 위상 소자에 따른 광출력 회절효율을 계산하였다. 이러한 회절 효율의 계산은 출력 평면 내에만 해당되는 것이고, 이외의 영역으로 출력이 소실되는 경우를 고려하지 않았다. 또한, 위상항의 양자화 깊이의 변화에 대하여 입력광이 위상소자를 지난 후의 광출력 효율에 대하여 계산하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.12 no.5
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• pp.478-491
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• 1987

In this paper, an all Digital Phase-Locked Loop(DPLL) has been propoed, which has reduced the phase error by using a half period sampling in order to improve the performance of the conventional DPLL which tracks the phase of incoming sinusoidal signal once per cycle for the Positive Going Zero crossing(PGZC) of the signal. The proposed DPLL tracks the phase of input signal twice per cycle with two samplers for the PGZC. So the loop has a half reduction of the steady state phase error fluctuation ranges without decreasing the lock-range in a whole, comparing with that of the conventional DPLL. Also, it has been known that the proposed loop is rapidly locked to input signal for the same valves of phase differenc between sucessive samples and quantization level. The analytic results of the proposed loop have been verified by computer simulation for the practically requeired conditions.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2019.11a
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• pp.217-218
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• 2019

홀로그램을 재생하기 위한 SLM(Spaital Light Modulator)에서 홀로그램의 실수 정보 혹은 위상 정보를 사용한다. 본 논문에서는 홀로그램의 위상 정보를 효율적으로 압축하기 위한 방식을 제안한다. 홀로그램 압축 표준 코덱 개발에서는 표준 코덱을 기점으로 전후처리를 이용하여 압축효율의 개선 시키는 연구를 진행 중이다. 위상 정보는 -𝜋에서 +𝜋의 제한된 동적 범위를 가진다. 이는 위상 정보 사이의 공간적인 상관도를 낮추며 압축효율을 크게 떨어뜨리는 요인이 된다. 위상 펼침 기법을 이용하여 위상 정보 간의 공간적인 상관도를 확보한다. 공간적인 상관도가 확보된 위상 정보에 JPEG2000 표준 코덱의 입력을 고려하여 양자화한 뒤 압축 후 복원하고 효율을 분석한다.

• Korean Journal of Optics and Photonics
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• v.17 no.5
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• pp.401-411
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• 2006

We propose an optical encryption/decryption technique for a security system based on 2-step phase-shifting digital holography. Phase-shilling digital holography is used for recording phase and amplitude information on a CCD device. 2-step phase-shifting is implemented by moving the PZT mirror with phase step of 0 or ${\pi}/2$. The binary data and the key are expressed with random code and random phase patterns. The digital hologram is a Fourier transform hologram and is recorded on CCD with 256 gray level quantization. We remove the DC term of the digital hologram fur data reconstruction, which is essential to reconstruct the original binary input data/image. The error evaluation fer the decrypted binary data is analyzed. One of errors is a quantization error in detecting the hologram intensity on CCD, and the other is generated from decrypting the data with the incorrect key. The technique using 2-step phase-shifting holography is more efficient than a 4-step method because 2-step phase-shifting holography system uses less data than the 4-step method for data storage or transmission. The simulation shows that the proposed technique gives good results fur the optical encryption of binary information.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.10
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• pp.1-7
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• 2010

A new frequency offset estimation algorithm for chirp spread spectrum based on matched filter is proposed. Generally, the differential phase between successive symbols is used for the conventional frequency offset estimation algorithm. However, if the conventional frequency offset estimation algorithm is used for CSS, phase ambiguity arises because of long symbol duration and guard time. The phase ambiguity causes performance degradation of matched filter since the received signal is corrupted by the integer frequency offset. In this paper, we propose a new frequency offset estimation algorithm which separates integer and fractional frequency offset estimation for removing the phase ambiguity. The proposed algorithm estimates the integer frequency offset by using differential phase between matched filtering results of sub-chirps and successive symbols. Then, the fractional frequency offset is estimated by using the differential phase between successive symbols Simulation results show that the proposed algorithm well removes the phase ambiguity, and have almost same estimation performance compared with conventional one when there is not the phase ambiguity.

• Proceedings of the KIEE Conference
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• 2005.07d
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• pp.2552-2554
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• 2005

제어기 설계에서 이득여유와 위상여유는 견실성 및 안정도 판별의 중요한 척도로 사용되며, 그 중 위상여유는 시스템의 성능지수와 관련된다. 이와 같은 이유로 이득여유와 위상여유의 안정도를 고려한 제어기의 설계방법이 연구되어지고 있다. 근래 Weng Khuen Ho와 Chang Chieh Hang이 제안한 설계방법은 복잡한 계산을 필요로 하는 arctan 함수를 1차 선형함수로 근사화 하여 복잡도를 감소시키면서도 원하는 이득여유와 위상여유를 만족시키는 제어기의 파라미터를 찾았다. 하지만 이 방법은 실제의 arctan 함수를 사용하는 것이 아니라 근사화된 수식을 사용함으로써 오차가 수반되어 원하는 설계조건을 만족 하지 못한다. 따라서 본 논문은 이러한 오차를 최소화하기 위해서 최적화 알고리즘을 이용한 이득여유와 위상여유를 보상하는 PID 제어기를 설계하였다.