• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.37-44
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• 1994

The characteristics of stimulated Brillouin scattering wave for applications to high power laser was experimentally investigated. The peak power reflectivity and the phase conjugation fidelity of Stokes wave with respect to the focal length of lens were measured, and the phase conjugation fidelity for a compressed part of the Stokes wave was also investigated. For the long focal length of lens.(f=100 cm), the peak power of the Stokes wave amounts to about twice as high as that of incident wave. The phase conjugation fidelity for the compressed leading pulse is up to 90%, better than that for other temporal parts of the Stokes pulse. In spatial distribution, the Stokes pulse from the axial region has the largest SBS gain, and it has been ascertained as a best candidate to the application due to excellent pulse compression, peak power reflectivity, and good phase conjugation fidelity.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.208-218
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• 2008

We investigate the effect in terms of yield of the reflectivity of both facets and of the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection complex-coupled (CC) DFB lasers with self-pulsation frequency of the THz region. When the grating phases on both facets of a multisection CC DFB laser are fixed as 0, the variation of SP frequency increases as the reflectivity of both facets increases, while that of SP frequency decreases as the coupling ratio (CR) and the coupling strength increase. For the coupling strength of 3, the range of the phase of a phase tuning section with yields greater than 80% decreases as the CR and the reflectivity of both facets increases. For the coupling strength of 4, the range of the phase of a phase tuning section with yields greater than 80% increases as the CR and the reflectivity of both facets increases.

• Proceedings of the Optical Society of Korea Conference
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• 1991.06a
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• pp.74-79
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• 1991

측뢰 4 광파 혼합법으로 여러 가지 용매와 색소를 매질로 이용하여 위상공파를 발생시키고 발생한 위상공액파를 증폭하였다. 광원은 Q-switching된 루비레이저이다. 위상 공액파의 반사율, R을 증가시키기 위해 여러 가지의 색소와 용매를 이용하여 위상공액파를 방생시키고 이들 중 반사율이 좋은 조합으로 루비봉을 이용한 증폭기를 통과시켜 증폭실험을 수행하였다. 증폭기를 거친 최종적인 반사율은 Renh로 정의하였을 때 실험 결과는 DMSO와 Cryptocyanine의 조합에서 최대 Renh/R = 6.3 $\pm$ 0.38를 얻을 수 있었다.

• Korean Journal of Optics and Photonics
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• v.17 no.6
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• pp.548-555
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• 2006

We investigate the effect of the reflectivity of both facets and the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection index-coupled (IC) DFB lasers composed of two index-coupled DFB sections and a phase tuning section between them in terms of yield. In the case of weak coupling strength, as the reflectivity of both facets increases, the effect of reflected fields from both facets and the other DFB section on the mode characteristics of one DFB section increases. Thus the number of mode hoping increases and yield decreases for the variation of phases of both facets. In the case of strong coupling strength, as the reflectivity of both facets increases, the spatial hole burning effect increases, so that the yield decreases. The maximum yield and the range of the phase of a phase tuning section with yield more than 40% decrease as the facet reflectivity increases irrespective of coupling strength. As the coupling strength increases, the variation of yield for the variation of the phase of a phase tuning section increases and the variation of the phase of a phase tuning section with the maximum yield for the variation of the reflectivity of both facets decreases. The yield characteristics of the cases with the coupling strengths of 2 and 3 are better than those with the coupling strengths of 1.2 and 4.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.11
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• pp.937-950
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• 2015

Microstrip reflectarray is an antenna which controls its radiation pattern with a number of reflective elements. Conventionally, the reflectarray has been researched to replace curved reflector antennas. In this paper, design theories of reflectarray is briefly introduced, and research trends of high gain and broadband reflectarrays are reviewed. To improve the gain of the reflectarrays, it is required that the reflection phase errors on the reflectarray surface be minimized. For this purpose, sufficiently wide reflection phase range and low phase sensitivity should be realized with the designed element. For bandwidth improvement, the reflection phase of the element should be linear with the frequency variation. In this paper, various researches to improve the reflection phase characteristics of the element for high gain and broadband reflectarrays, such as multi-layer and single-layer multi-resonant structures, are reviewed. Also, dual-reflectarray configuration for compact antenna design is reviewed. Finally, various applications of reflectarrays such as contoured beam, near-field focusing, and RCS reduction are reviewed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.3
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• pp.296-303
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• 2003

In this paper, a design method is proposed for the reflection type phase shifter applied to the DTV(Digital TV) receiver, and a phase shifter is designed by using the design equations to satisfy the phase shifting range over 180 degrees for frequency range from 470 MHz to 860 MHz, the receiving band of DTV. From the proposed method, it is possible that the systematic design of the reflection type phase shifter with desired phase shifting range and insertion loss. In addition, it is found that the realized phase shifter satisfies the given specifications.

• Korean Journal of Optics and Photonics
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• v.18 no.5
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• pp.323-332
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• 2007

The effect of the reflectivity of both facets and the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection complex-coupled (CC) DFB lasers is investigated in terms of yield. The lasers are composed of two CC DFB sections and a phase tuning section between them. As the coupling strength and the coupling ratio (CR) decrease, the effect of the reflected fields from both facets and the other DFB section on the mode characteristics of one DFB section increases, so that the yield decreases. As the facet reflectivity increases, the maximum yield and the range of the phase of a phase tuning section with yield more than 60% decrease independent of the coupling strength and CR. The yield characteristics of CR=0.2 are better than those of CR=0.1 with the same coupling strength due to the larger complex coupling effect. The case with ${\mid}{\kappa}L{\mid}=3$ and CR=0.2 shows best yield characteristics among the cases considered in this work.

• The Journal of the Acoustical Society of Korea
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• v.27 no.1
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• pp.1-11
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• 2008

To overcome the mid frequency limitation of geometrical acoustic techniques, the phased geometrical method was suggested by introducing the phase information into the sound propagation from the source. By virtue of phase information, the phased tracing method has a definite benefit in taking the interference phenomenon at mid frequencies into account. Still, this analysis technique has suffered from difficulties in dealing with low frequency phenomena, so called, wave nature of sound. At low frequencies, diffraction at corners, edges, and obstacles can cause errors in simulating the transfer function and the impulse response. Due to the use of real valued absorption coefficient, simulated results have shown a discrepancy with measured data. Thus, incorrect phase of the reflection characteristic of a wall should be corrected. In this work, the uniform theory of diffraction was integrated into the phased beam tracing method (PBTM) and the result was compared to the ordinary PBTM. By changing the phase of the reflection coefficient, effects of phase information were investigated. Incorporating such error compensation methods, the acoustic prediction by PBTM can be further extended to low frequency range with improved accuracy in the room acoustic field.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3A
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• pp.311-317
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• 2004

A low loss reflection type analog phase shifter which is realized with two varactors and branch coupler. is described. A new design technique for the large phase shift is applied using short stub microstripe lines. This paper presented the realization of design and experimental results. Through the experiment using the duroid microstrip line and varactors, the phase of 2.26GHz signal is controlled to the DC voltage with the phase shift range of 170$^{\circ}$. The achieved insertion loss of less than 3㏈ and the return loss of mote than 12㏈ are achieved over all phase states.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.60-61
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• 2000

표면 형상을 측정하는 방법은 샘플표면의 평평도, 곡률, 거칠기, 깊이 측정등의 수많은 상업적 응용을 위해 광범위하게 개발되어왔다. 이중에서도 특히 간섭현상을 이용한 광 표면 프로파일러는 표면의 3차원 구조를 측정하는데 있어서 subangstrom의 매우 높은 깊이 분해능을 가지므로 샘플 표면의 정밀 진단에 많이 사용되어 왔다. [1,2] 광 간섭 현미경은 기본적으로 광위상 변화를 검출하여 그것을 표면구조변화로 바꾸어주는 역할을 한다. 그러나 광위상 변화는 샘플 표면의 구조뿐만 아니라 물질 변화와 박막두께 변화에도 민감하므로 순수한 표면구조측정은 샘플이 단일물질인 경우에만 달성된다는 문제점이 있다. 따라서 이러한 광위상 측정과 관련된 ambiguity를 해결하기 위해서는 일반적인 광 간섭 현미경에서 얻어지는 위상데이터와 더불어 물질변화를 분석할 수 있는 다른 추가적인 데이터가 필요하다. 이러한 필요성 때문에 우리는 광위상 뿐만 아니라 반사율 분포도 동시에 측정할 수 있는 새로운 방식의 다출력단 호모다인 간섭계(Homodyne I/Q Interferometer; HIQI)를 구성하였으며[3], 그 실험장치도는 [Fig. 1]과 같다. HIQI는 in-phase and quadrature 검출방식에 기반을 두며, 이 검출방식은 PBS에서 반사되는 빛살과 투과되는 빛살 사이의 위상차가 $\pi$/4라는 실험결과로부터 달성된다. HIQI는 샘플 표면의 3차원 구조 뿐만 아니라 광학적 특성의 2차원 분포도 동시에 얻을 수 있다. (중략)