Cr4+ : YAG 레이저에서 열 렌즈 효과에 따른 공진기의 안정영역과 빔 허리 및 비점수차의 보상

이봉연 한국광학회 2006 한국광학회지 Vol.17 No.5

We obtained analytic solutions of boundary conditions to the stable region of Z-fold Cr4+ :YAG laser cavity when the conditions are with and without thermal lensing effect. Also we investigated the influence of the thermal lensing effect on the stability of cavity, beam waist, and astigmatic compensation using aberration transformation matrices. The thermal lensing effect almost has no influence on the stable region of the cavity when the crystal is located in the middle of two concave mirrors and when the distances from the concave mirror to the reflecting mirror and the output coupler are the same. The beam waist, however, is affected more in a tangential plane than in a sagittal plane, and so it is difficult to have astigmatic compensation when the thermal lensing effect exists. This result means that the thermal lensing effect should be considered even for the Kerr-lens mode-locking.

다중모드 간섭현상을 이용한 1 × 16 마하젠더 스위치 개발

김성원,홍종균,이상선 한국광학회 2006 한국광학회지 Vol.17 No.5

A 1×16 thermo-optic switch with small excess loss using multimode interference(MMI) couplers is designed, fabricated, and measured. This paper introduces the proposed 1×16 thermo-optic switch, and discusses the measurement results. The 1×16 thermo-optic switch is formed as 4-stage which consists of 15 unit devices. The unit devices are the 2×2 thermo-optic switches with Mach-Zehnder interferometer(MZI) structure. The characteristics of the 1×16 thermo-optic switch depends strongly on each unit device. The unit deviceconsists of two 3-dB general interference MMI couplers and two single mode waveguide arms as a phase shifter. First of all, the 3-dB optical splitter and 2×2 MZI thermo-optic switch have been tested to confirm the characteristics of the unit devices of the 1×16 MZI thermo-optic switch. Using the measurement results of the unit devices, the 1×16 MZI thermo-optic switch can be produced with better characteristics. The resultant structure of the MMI coupler with the optical light source of wavelength of 1550nm for the 1×16 thermo-optic switch is that the width and the optimized length are 25μm and 1580μm, respectively. The smallest excess loss for the unit device is -0.5dB and the average excess loss is -0.7dB.

DUV 피조 간섭계의 자가보정

오혁진,최재혁,김학용 한국광학회 2025 한국광학회지 Vol.36 No.6

본 연구에서는 반도체 광학계 검증을 위해 개발된 193 nm 심자외선(deep ultraviolet, DUV) 피조 간섭계의 측정 정확도를 향상시키기 위한 자가보정기법을 제시한다. 이 방법은 무작위 평면 시험과 삼 평면 시험(three flat test)을 기반으로 하며, 계통 오차에 의해 발생하는 형상 왜곡을 최소화하는 데 목적이 있다. 무작위 평면 시험에서는 측정 평면을 회전 및 병진 이동시키며 총 68회 측정하였고, 평균화를 통해 비대칭 성분을 제거한다. 그러나 이 과정만으로 대칭 성분 보정에 한계가 존재한다. 이를 보완하기 위해 사용한 삼 평면 시험은 세 개의 평면을 네 가지 방식으로 측정하고, 수학적 복원을 통해 대칭 및 비대칭 성분을 모두 제거함으로써 보다 정확한 형상 복원이 가능하다. 본 연구에서 제시한 자가보정기법은 DUV 피조 간섭계의 측정 신뢰성을 높이며, 향후 고분해능 광학계의 성능 개선에 기여할 것으로 기대한다. We have developed a 193 nm deep ultraviolet (DUV) Fizeau interferometer for testing semiconductor optical systems. This study presents a selfcalibration method utilizing the random flat test and three flat test to minimize the shape distortion caused by systematic errors. The random flat test involves rotating and translating the test flat, performing 68 measurements, and averaging the results to cancel out the antisymmetric components of the test flat. By subtracting the average value from the obtained data, systematic errors can be removed. However, this method has limitations in removing symmetric components. To address this problem, the three flat test is applied, measuring three flats in four different ways and using mathematical calculations to eliminate both symmetric and antisymmetric components, thereby restoring the accurate shape. The self-calibration method used in this study enhances the measurement accuracy of the DUV Fizeau interferometer and will improve the performance of high-resolution optical systems under test.

무작위 분할 영상과 결합변환 광 상관기를 이용한 암호화 시스템

최상규,서동환,신창목,김수중,배장근 한국광학회 2003 한국광학회지 Vol.14 No.6

We proposed the optical system using two divided halftone images to hide the original image and a joint transform correlator. The encryption procedure is performed by the Fourier transform of the product of each divided image by visual cryptography and the same random image which is generated by computer processing. As a result, we can obtain two Fourier divided images which are used as the encrypted image and the decrypting key, respectively. In the decryption procedure, both the encrypted image and the decrypting key are located on the joint input plane. Then the original image is reconstructed on a CCD camera which is located in the output plane. An autocorrelation term of joint transform correlator contributes to decrypt the original image. To demonstrate the efficiency of the proposed system, computer simulations and noise analysis are performed. The result show that the proposed system is a very useful optical certification system.

시각 암호화와 가상 위상영상을 이용한 광 암호화 시스템

김인식,서동환,신창목,조규보,김수중,노덕수 한국광학회 2003 한국광학회지 Vol.14 No.6

We propose an encryption method using visual cryptography and virtual phase images. In the encryption process, the original image is shared by virtual images and the decryption key image. We multiply the virtual phase images with each complex image, which has the constant value of its sum after performing the phase modulation of the virtual images and the decryption key. The encryption cards are made by Fourier transforming the multiplied images. It is possible to protect information about the original image because the cards do not have any information from the original image. To reconstruct the original image, all the encryption cards are placed on each path of a Mach-Zehnder interferometer and then the lights passing through them are summed. Since the summed image is inverse Fourier transformed by a Fourier lens, the phase image is multiplied with the decryption key and the output image is obtained in the form of intensity on the CCD plane. Computer simulations show a good performance of the pro-posed optical security system.

줌 구조를 이용하여 물체거리가 변해도 상면과 배율이 고정되는 현미경 광학계의 설계

류재명,조재흥,임천석,정진호,전영세,이강배 한국광학회 2003 한국광학회지 Vol.14 No.6

The multi-configurative microscopic system for inspecting the wire-bonding of reed frame is designed. Rays refracted by objective lens group which is composed of common lens group of x2 and x6 are splitted by beam-splitter, and Rays through the central region and the boundary region of the object imaged at x2 and x6 through imaging lens groups, respectively. The depth of wire structure on the reed frame has about $\pm$3 mm, in order to observe by uniform magnification without the dependency on the variation of objective distance generated by the depth of wire structure on the reed frame, imaging lens groups should be moved on nonlinear locus like mechanically compensated zoom lenses. The nonlinear equations for zoom locus are derived by using the Gaussian bracket. Refraction powers and positions of each groups are numerically determined by solving the equations, and initial design data for each groups is obtained by using Seidel third order aberration theory. The optimization technique is finally utilized to obtain this microscopic system.

위상편이 회절격자 간섭계의 가시도 최적화

황태준,김승우 한국광학회 2003 한국광학회지 Vol.14 No.6

The phase-shifting diffraction-grating interferometer proposed in the investigation uses a diffraction grating that performs manifold functions of beam splitting, beam recombination, and phase shifting. The reference and measurement waves generated by means of diffraction have different amplitudes depending on their orders of diffraction, so the interference fringe pattern resulting from the two waves tends to yield poor visibility. To cope with this problem, we select a phase grating of reflection type and attempt to improve the interference visibility with optimization of the groove shape of the grating through electromagnetic analysis.

위상형 직선격자의 자체결상과 가시도 분석

백승선,이상일,조재흥,김영란 한국광학회 2003 한국광학회지 Vol.14 No.6

The self-imaging effect or lensless imaging effect of a phase line grating is theoretically analyzed by using Fresnel diffraction theory, then experimentally investigated. The self-imaging distance $z_{T,p}$, that is the imaging distance being perfectly copied from the phase distribution of the phase grating to its intensity distribution with the magnification of 1X, can be uniquely defined as the (4n-3) $z_{T,a}$/4(n=positive integers), where rte is the well-known self-imaging distance of an amplitude grating. When the coherent laser beam is illuminated at the phase grating, the self-imaged images were obtained at $z_{T,p}$= $z_{T,a}$/4 and $z_{T,p}$=5 $z_{T,a}$/4 without any optics. On the other side, the phase-reversed self-imaging was obviously observed at $z_{T,p}$ = 3 $z_{T,a}$/4. The visibility of self-imaged images of a phase line grating as a function of the number of slits of the input grating was measured by the FFT(Fast Fourier Transform) results of the self-imaging images. As a result a stationary maximum visibility of V = 0.10 can be obtained from a grating with more than 15 slit pairs.n 15 slit pairs.

위상 변조 Exclusive-OR 연산을 이용한 광학적 암호화 방법

신창목,서동환,김수중 한국광학회 2003 한국광학회지 Vol.14 No.6

In this paper, we have proposed a full phase encryption scheme based on phase-encoded XOR operation. The proposed scheme encrypts a gray-level image by slicing an original image and combining with XORed images which resulted from phase-encoded XOR operations between sliced images and phase-encoded binary random images. Then we produce an encrypted image by combining only XORed images and a key image by only phase-encoded binary random images. The encrypted image and key image are converted into encrypted data and key data by a phase-encoding method. The merits are that the proposed encryption scheme can basically fulfill a high-level encryption using a full phase encryption scheme which has nonlinear and invisible characteristics. The scheme also improves security by encrypting the phase information before full phase encryption. The decryption system based on the principle of interference between a reference wave and a direct pixel-to-pixel mapping image of encrypted data with key data can be simply implemented using a phase-visualization system. Simulation results indicate that our proposed encryption scheme is effective and simple for a gray-scale image and optical decryption system.

링레이저 자이로의 출력오차 최소화를 위한 불규칙 몸체진동잡음 연구

심규민,손승현 한국광학회 2003 한국광학회지 Vol.14 No.6

In this paper we confirm the relation between the phase and phase error of the beat signal at the lock-in region of the dither type ring laser gyroscope by numerical calculation. We also study the requirement of the dither noise of an amplitude modulation type for statistical zero averaging of the beat signal phase error, without accumulation. As a result, we find that the dither noise requires the increase and decrease gradients of the dither amplitude, and those gradients should be combined with similar white noise. The slope of the gradient and maximum/minimum amplitude must be changed randomly. We confirm the error accumulation characteristic related to the dither noise by comparison of the two outputs during temperature change, by operating the two kinds dither noise, one is satisfied with the requirement and the other is not.