• Current Optics and Photonics
• /
• 제2권4호
• /
• pp.356-360
• /
• 2018

We demonstrate continuous-wave operation of an all-fiber thulium-holmium codoped laser operating at a wavelength of 1706.3 nm. To realize laser operation in the short-wavelength region of the emission-band edge of thulium in silica fiber, we employ fiber Bragg gratings having resonant reflection at a wavelength around 1700 nm as a wavelength-selective mirror in an all-fiber cavity scheme. We first examine the performance of the laser by adjusting the central wavelength of the in-band pump source. Although a pump source possessing a longer wavelength is observed to provide reduced laser threshold power and increased slope efficiency, because of the characteristics of spectral response in the gain fiber, we find that the optimal pump wavelength is 1565 nm to obtain maximum laser output power for a given system. We further explore the properties of the laser by varying the fiber gain length from 1 m to 1.4 m, for the purpose of power scaling. It is revealed that the laser shows optimal performance in terms of output power and slope efficiency at a gain length of 1.3 m, where we obtain a maximum output power of 249 mW for an applied pump power of 2.1 W. A maximum slope efficiency is also estimated to be 23% under these conditions.

• 한국전자파학회논문지
• /
• 제27권2호
• /
• pp.147-155
• /
• 2016

본 논문에서는 주파수 변조 연속파(FMCW) 전파고도계의 재밍 환경에서의 강인한 고도 측정을 위한 재밍 탐지/회피 알고리즘을 제안한다. 전파고도계 재밍 탐지 알고리즘은 재밍 탐지를 위해 송수신 구간 앞에 노이즈 측정구간을 두어 노이즈 레벨을 측정하고, 샘플링한 노이즈파형에 대해 재밍 임계치를 넘는 포인트를 산출하여 재밍을 탐지한다. 재밍 회피 알고리즘으로 시간영역에서의 재밍 회피, 송신 출력 및 수신 이득 제어, 주파수 도약을 설계하였다. 제안한 알고리즘은 실제적인 환경에서 평가하기 위한 야외시험을 통해 성공적으로 검증하였다.

• 한국통신학회논문지
• /
• 제15권1호
• /
• pp.71-79
• /
• 1990

逆바이어스 電壓變化에 따라 終端된 바랙터 리액턴스 變化로부터 發生되는 反射波의 連續的인 位相變化를 擴張시키기 위하여 인덕터와 바랙터를 直列로 連結시킨 回路와 하이브리드 링이 結合된 아나로그 移相器를 動作周波數 10GHz에서 設計하였으며, 分散特性 및 不連續 影響을 考慮하여 마이크로 스트립線路로 製作하였다. 實驗結果, 逆바이어스電壓을 20V가지 變化시킴에 따라 位相은 $52.34^{\circ}$에서 $235.01^{\circ}$까지 變化되므로서 $180^{\circ}$이상의 位相變化를 얻을 수 있었으며, 傳送 損失은 -3.6~14.3dB 및 Return loss는 -16~-18dB(1.37 < VSWR < 2.3)을 나타내었다.

• ETRI Journal
• /
• 제38권5호
• /
• pp.972-980
• /
• 2016

An ultra-wideband microwave monolithic integrated circuit high-power amplifier with excellent input and output return losses for phased array jammer applications was designed and fabricated using commercial $0.25-{\mu}m$ AlGaN/GaN technology. To improve the wideband performance, resistive matching and a shunt feedback circuit are employed. The input and output return losses were improved through a balanced design using Lange-couplers. This three-stage amplifier can achieve an average saturated output power of 15 W, and power added efficiency of 10% to 28%, in a continuous wave operation over a frequency range of 6 GHz to 18 GHz. The input and output return losses were demonstrated to be lower than -15 dB over a wide frequency range.

• Structural Engineering and Mechanics
• /
• 제74권1호
• /
• pp.91-104
• /
• 2020

A mathematical analysis has been carried out for understanding the traversal attributes of torsional waves in a Voigt-type viscoelastic porous layer bounded with corrugated surfaces resting over a heterogeneous transversely isotropic gravitating semi-infinite medium. Both the media are assumed to be under the effect of initial stresses acting along horizontal directions. In the presumed geometry, continuous and periodic type of corrugation has been considered. The condensed form of dispersion relation has been obtained analytically with the aid of the Whittaker's function and suitable boundary conditions. The influence of viscoelasticity, porosity, initial stresses, heterogeneity, gravity, undulation and position parameters on the phase and damped velocities has been illustrated graphically. In addition, relative examination investigating the impact of corrugated and planar bounded surfaces on the dispersion and damping characteristics is one of the important highlights of this study.

• 대한기계학회논문집A
• /
• 제28권2호
• /
• pp.165-173
• /
• 2004

Laser beam welding is increasingly being used in welding of structural steels. The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and deep penetration. The thermal cycles associated with laser welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone. Experiments are performed for 304 stainless steel plates changing several process parameters such as laser power, welding speed, shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between the similar and dissimilar plates, etc. The following conclusions can be drawn that laser power and welding speed have a pronounced effect on size and shape of the fusion zone. Increase in welding speed resulted in an increase in weld depth/ aspect ratio and hence a decrease in the fusion zone size. The penetration depth increased with the increase in laser power.

• 한국생산제조학회지
• /
• 제20권3호
• /
• pp.342-349
• /
• 2011

The purpose of this paper is to describe experimental results about the butt welding and bead on plate welding of the high power Continuous Wave (CW) Fiber laser for Ultra-low carbon Interstitial Free(IF) steel plate for gear part of car. After being welded of the gear parts by the fiber laser and electron beam Microstructures of melting zone had been mixed acicular, granular bainitic, quasi-polygonal and widmanstatten ferrite because of a radical thermal diffusion after welding, difference of critical volume and grain size. As a result of experiment, when gear parts were welded by the fiber laser and electron beam, the fiber laser welding has been stable properties without internal defects more than the electron beam welding. Therefore it has the very advantages of welding high quality and productivity more than conventional melting method. The optimal welding processing parameters for gear parts were as follows : the laser power and welding speed were 3kWatt, 30mm/sec respectively. At this time heat input was $21.2{\times}10^3J/cm^2$.

• 전자공학회논문지SC
• /
• 제41권6호
• /
• pp.51-60
• /
• 2004

본 논문은 광역학적 암치료 효율을 높이기 위한 레이저 시스템의 최적화 구현에 관한 연구이다. 레이저 시스템의 최적화를 위해서는 레이저 출력의 출력 변동율과 파장대의 편이가 적어야 한다. 임상에서 암치료의 효율을 높이기 위해서는 악성종양부위에 조사되는 방사방식이 다양하게 구현되어야 한다. 기존에 사용되고 있는 C.W 방식은 정상조직에도 손상을 입힐 수 있는 생체조직의 열적효과를 가져올 수 있다. 이에 새로운 방사모드를 제안하여 생체조직에 대한 열적 안전성과 치료의 효율을 높였다. 실험을 통하여 광파장의 안정성 및 광 출력과 출력의 안정성을 확인 하였고, 피부조직의 열적 손상 방지를 위한 방사모드의 구현은 생체조직에 대한 실험을 통해서 본 연구의 타당성을 검증하였다.

• 전기전자학회논문지
• /
• 제19권2호
• /
• pp.160-167
• /
• 2015

We present an experimental implementation of the inexpensive microwave security sensor that can detect both static and slowly moving objects in cluttered environment. The prototype consists of a frequency-modulated continuous wave radar sensor, control board or computer and software. The prototype was tested in a cluttered indoor environment. In case of intrusion or change of environment the sensor will give an alarm, determine the location of new object, change in its location and can detect a slowly moving target. To make a low-cost unit we use commercially available automotive radar and own signal processing techniques for object detection and tracking. The intruder detection is based on a comparison between current 'image' in memory and 'no-intrusion' reference image. The main challenge is to develop a reliable technique for detection of a relatively low-magnitude object signals hidden in multipath clutter echo signals. Various experimental measurements and computations have shown the feasibility and performance of the system.

• 전기전자학회논문지
• /
• 제15권4호
• /
• pp.313-318
• /
• 2011

10 GHz 고조파 모드잠금 고리형 반도체 광섬유 레이저의 외부 CW 광주입 효과를 연구하였다. 선폭 ~ 100 KHz의 코히어런트 외부 광주입에 의해 40 dB가 넘는 스펙트럼 빗살의 골짜기와 30 dB가 넘는 슈퍼모드 비팅 잡음 억제효과를 얻을 수 있었다. 저가의 주입광원을 이용할 수 있는지를 조사하기 위해 주입광을 대략 10 MHz의 선폭을 갖는 DFB 레이저로 교체하였다. 그 결과, 스펙트럼 빗살의 골짜기는 유사한 특성을 보였으나, 슈퍼모드 비팅 잡음은 억제되기보다는 오히려 증가하는 것으로 관측되었다.