Tunable Multiwavelength Erbium-doped Fiber Laser Based on an In-line Mach Zehnder Interferometer

한영근 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.61

A tunable multiwavelength erbium-doped fiber laser based on an in-line Mach Zehnder interferometer is proposed and experimentally demonstrated. The in-line Mach Zehnder interferometer is realized by using cascaded long-period fiber gratings. The long-period fiber gratings can couple the guided core mode to several cladding modes. If two identical long-period fiber gratings are concatenated, an interference pattern can be generated, which results from an interaction of the core and the cladding modes in the second long-period fiber grating. Therefore, a simple multichannel filter based on an in-line Mach Zehnder interferometer can be realized. The wavelength spacing of the proposed multichannel filter is controlled by the number of long-period fiber gratings. We apply the proposed multichannel fiber to the generation of a multiwavelength erbium-doped fiber laser with a tunability on the order of the wavelength spacing. An erbium-doped fiber amplifier is implemented as a gain medium. The gain competition of erbium ions is suppressed by soaking the erbium-doped fiber in liquid nitrogen. The power fluctuation of the proposed multiwavelength fiber laser is measured to be less than 0.5 dB. A high-quality multiwavelength output with a high extinction ratio of more than 40 dB is achieved. The wavelength spacing of the proposed multiwavelength fiber laser is controlled by increasing the number of long-period fiber gratings. The wavelength spacing is changed from 0.8 nm to 1.6 nm discretely.

장섬유강화 복합재료의 섬유 배향특성이 기계적 특성에 미치는 영향

허몽영,이학성 한국복합재료학회 2019 Composites research Vol.32 No.6

Long-fiber-reinforced composites have the advantages of cost-competitiveness and high degree of freedom of molding compared to continuous-fiber-reinforced composites. On the other hand, it is difficult to ensure uniform characteristics due to the randomly distributed fiber orientation incurred from the process of manufacturing intermediate materials. In this study, the effect of the directionality of LFPS (Long Fiber Prepreg Sheet) materials on the mechanical properties was analyzed. The eddy current measurement method was used to analyze fiber orientations, and tensile and compression tests on LFPS materials were performed according to ASTM standards. In addition, the test results and theoretical values of LFPS materials were verified using the ROM (rule-of-mixtures) theory. These results confirmed the effect of fiber orientation on mechanical properties of discontinuous-fiber-reinforced composites. 장섬유강화 복합재료는 연속섬유강화 복합재료 대비 가격 경쟁력 및 성형 자유도가 높은 장점을 가지고 있다. 반면에 중간재를 제조하는 과정에서 무작위로 분산되는 특성으로 균일한 배향성을 확보하는데 어려움이 있다. 이에 본 연구에서는 LFPS(Long Fiber Prepreg Sheet) 소재의 재현성 검증을 위하여, 섬유의 배향 각도를 측정하고 이를 기반으로 기계적 물성치와의 상관관계를 분석하였다. 배향특성 분석을 위하여 와류측정방식을 사용하였으며, ASTM 기준에 준하여 LFPS 소재의 인장 및 압축 시험평가를 수행하였다. 추가적으로, 탄성강성 예측이론인 ROM(Rule of Mixture)을 활용하여 LFPS 소재의 시험결과와 이론치를 검증하였다. 이러한 결과를 통해 비연속섬유강화 복합재료의 섬유 배향특성이 기계적 특성에 미치는 영향을 확인하였다.

The Fiber Orientation Distribution of Injection Molded Long Fiber Reinforced Polymeric Composites

Kim, Hyuk,Ann, Jongyoon,Yoon, Sungun CHOSUN UNIVERSITY 1997 Basic Science and Engineering Vol.1 No.1

The characteristics of fiber-reinforced plastic composites depend on the quantity and shape of fibers. During a injection molding process of composites, the fiber-matrix separation and fiber orientation are caused by the flow of molten polymer/fiber mixture. As a result, the product tends to be nonhomogeneous and anisotropic. Hence, it is very important to clarify the relations between separation orientation and injection molding conditions. So far, there is no study on the measurement of fiber orientation using image processing. In this study, the effects of fiber length, fiber content, matrix, and molding condition on the fiber distribution and by using image processing technique, a method is achieved for quantitative visualization of fiber orientation of a product which is injection molded of long fiber reinforced polymeric composites. Using the burning method, fiber content distribution in products and the effects of fiber content by weight on the fiber orientation functions are discussed.

하이브리드 섬유보강 콘크리트의 장기 건조수축 및 내동해성 평가

김요셉,배수호,이현진 한국구조물진단유지관리공학회 2019 한국구조물진단유지관리공학회 논문집 Vol.23 No.2

Many researches have been performed on hybrid fiber reinforced concrete for years, which is to improve some of the weak material properties of concrete. Researches on characteristics of hybrid fiber reinforced concrete using amorphous steel fiber and organic fiber, however, yet remain to be done. Therefore, the purpose of this research is to estimate the compressive strength, long term drying shrinkage, and resistance to freezing and thawing of hybrid fiber reinforced concrete(HFRC) using amorphous steel fiber and polyamide fiber as one of organic fibers. For this purpose, HFRCs containing amorphous steel fiber and polyamide fiber were made according to their total volume fraction of 1.0% for target compressive strength of 40 and 60 MPa, respectively, and then the compressive strength, length change, and resistance to freezing and thawing of these were evaluated. As a result, the long term length change ratio of HFRC used in this study decreased by more than 30%, 25% than plain concrete at 365 and 730 days, respectively, and the durability factor of HFRC was very excellent as more than 90%. 콘크리트의 낮은 인장강도 및 균열제어 능력 등의 약한 재료성질을 개선하기 위하여 수년간 하이브리드 섬유보강 콘크리트에 관한 많은 연구가 진행되어 왔다. 그러나 비정질 강섬유와 유기섬유를 이용한 하이브리드 섬유보강 콘크리트에 관한 연구는 이루어지지 않은 실정이다. 따라서, 본 연구의 목적은 비정질 강섬유와 유기섬유로서 폴리아미드 섬유를 이용한 하이브리드 섬유보강 콘크리트의 압축강도, 장기 건조수축 및 내동해성을 평가하는 것이다. 이를 위하여 목표 압축강도 40 및 60 MPa 각각에 대해서 하이브리드 섬유 혼입률을 전체 체적비로 1.0%로 설정하여 비정질 강섬유와 폴리아미드 섬유를 이용한 하이브리드 섬유보강 콘크리트를 제작하였다. 제작된 하이브리드 섬유보강 콘크리트의 장기 건조수축 및 내동해성을 평가한 결과, 재령 365일 및 730일에서의 장기 길이변화율은 플레인 콘크리트보다 각각 30%, 25% 이상 감소된 것으로 나타났으며, 동결융해 300 사이클 후의 내구성 지수는 90% 이상으로, 내동해성이 있는 것으로 나타났다.

Highly Enhanced Mechanical Properties of Polypropylene-Long Carbon Fiber Composites by a Combined Method of Coupling Agent and Surface Modification of Long Carbon Fiber

조성민,정희태 한국고분자학회 2014 Macromolecular Research Vol.22 No.10

The aim of this study was to enhance the mechanical strengths of polypropylene/long carbon fiber thermoplastic(PP/LCFT) composite by increasing the adhesion between the PP matrix and the long carbon fiber (LCF). Bi-functional group grafted polypropylene (BFPP) was used as a coupling agent with surface modified LCF (SMLCF) ina long fiber thermoplastic (LFT) melt impregnation system to increase the interaction between the PP matrix and theLCF. The BFPP was produced by melt compounding of maleic anhydride grafted polypropylene (MAPP) and polyetheramine (PEA). The surface modified LCF (SMLCF) was produced by dipping LCF into a sizing bath with 3-methacryloxypropyltrimethoxysilane (MPTS) to obtain oxygen functional groups. The composites were producedwith a LFT melt impregnation system with PP, BFPP, and SMLCF. Tensile and flexural tests and scanning electronmicroscopy (SEM) results of the PP/BFPP/SMLCFT composite showed significantly enhanced mechanical strengths,compared with those of the common PP/LCF composite with a conventional maleic anhydride grafted polypropylene(MAPP) coupling agent. These improvements in mechanical properties are attributed to better fiber/matrix interfacialadhesion, as confirmed by micro droplet specimen tests and SEM micrographs of the fracture surface afterinter laminar shear testing. The PP/SMLCFT composite with BFPP 5 wt% as coupling agent showed the highesttensile strength and flexural strength, which increased by 1.5 times and 1.7 times respectively, compared with PP/LCFT with a conventional MAPP coupling agent. The composite produced by this effective combination method ofa coupling agent and surface modification of long carbon fiber can potentially be applied to automobile materials,leading to the replacement of metal parts and car weight reduction.

강섬유보강콘크리트 연속슬래브 휨성능의 장기거동 특성

홍건호(Hong, Geon-Ho),정승원(Jung, Seong-Won) 대한건축학회 2019 大韓建築學會論文集 : 構造系 Vol.35 No.10

In spite of various advantages, steel fiber reinforced concrete is still limited in its use due to the insufficient research results on the structural performance and design criteria. This study evaluated the long-term behavior of the steel fiber reinforced concrete slabs by long-term loading experiments based on the short-term load bearing capacity of steel fiber reinforced concrete slabs obtained from previous studies. In this study, long-term loading experiments were carried out on Total four 2-span continuous slab specimens were tested for examining the long-term behavior of steel fiber reinforced concrete members. Long-term behavior characteristics of members were evaluated by measuring the long-term deflection, drying shrinkage, the number and width of cracks. Experimental results showed that the instant deflection of the steel fiber reinforced concrete slab is about 50% of the normal reinforced concrete slab. And, it was analyzed that the long-term deflection of the specimen using steel fiber reinforced concrete was about 10~20% lower than that of normal concrete by the long-term deflection over 100 days. In addition, the slab specimen using steel fiber reinforced concrete was evaluated to have just 70% of the number and width of cracks compared with normal concrete specimens.

기계적으로 유도되는 장주기 광섬유 격자 배열 소자 및 센서 응용

이남권,송재원,박재희,Lee, Nam-Kwon,Song, Jae-Won,Park, Jea-Hee 한국광학회 2007 한국광학회지 Vol.18 No.2

기계적으로 유도되는 장주기 광섬유 격자 배열 소자를 제작하고 격자 배열소자의 광 투과 특성을 측정하였다. 격자 배열 소자는 표면에 $690{\mu}m$부터 $780{\mu}m$ 주기까지 $10{\mu}m$씩 주기가 증가되는 격자들이 만들어져 있는 45 cm 길이의 금속 막대와 고무덮개로 구성되어 있다. 외부 압력이 격자 배열 소자에 인가되면 압력이 인가된 지점에만 장주기 광섬유 격자가 형성되고 장주기 광섬유 격자의 공진 파장은 인가된 지점에 의존한다. 그리고 제작된 장주기 광섬유 격자 배열 소자의 특성측정 결과가 다양한 투과 특성을 갖는 광섬유 대역 제거 필터, 혹은 압력센서로 사용 가능함을 보여주고 있다. A mechanically induced long-period fiber grating array was fabricated and its transmission characteristics were measured. The grating away consisted of a rubber cover and a 45 cm metal bar with 10 grating groups. Each grating group was composed of 60 gratings. The period of the grating of the grating groups was increased by $10{\mu}m$ increments from $690{\mu}m$ to $780{\mu}m$. The long period fiber grating was induced when the pressure was applied on the long period grating array and the resonant wavelength depended on the position of applied pressure. The experimental results shows that this long period fiber grating away can be used as a various band rejection filter or a fiber optic sensor.

Application for multimedia communication using phase-shifted long period fiber gratings (LPFGs)

Min-Sung Kim,Eung Soo Kim,Young-Geun Han 한국멀티미디어학회 2007 한국멀티미디어학회 국제학술대회 Vol.2007 No.-

The transmission characteristics of multiply cascaded phase-shifted long-period fiber gratings (LPFGs) is investigated theoretically and experimentally. Their passband width can be widened by increasing the number of π-shifted LPFGs. When two π-shifted LPFGs with different grating lengths are cascaded in series, the bandwidth of the rejection band and passband can be controlled by the pristine characteristics of two gratings. We also investigate the transmission characteristics of phase-shifted LPFG by exposing the half of LPFG region to UV laser. The phase-shifted LPFG strongly depends on both its initial coupling strength and its length. The phase-shifted LPFGs fabricated by UV exposure can be applied to ubiquitous sensor network.

〈속보논문〉 복굴절이 큰 광섬유에 제작된 장주기 광섬유 격자를 이용한 광섬유 전류 센서

李鎔旭(Lee Yong Wook) 대한전기학회 2007 전기학회논문지 Vol.56 No.10

Based on Faraday effect, the variation of current flowing through the conductor can be encoded as that of azimuth angle of light polarization propagating through the fiber coil wound onto the conductor. The amount of current can be obtained by measuring the variation of the light intensity transformed from that of the azimuth angle through a polarization analyzer. In this paper we propose a fiber-optic current sensor system that employs a fiber polarization analyzer as a sensor interrogation device. The fiber polarization analyzer was prepared by inscribing a long-period fiber grating on a high birefringent fiber. At the fixed wavelength of 1522.5 ㎚, the fabricated fiber device has the polarization extinction ratio of more than 25 ㏈. The measurement of large current up to 600 Arms was accomplished based on a simple fiber interrogation device and the measurement output of the sensor system showed a good linearity.

LFT-D공법을 이용한 탄소 장섬유 강화 열가소성 복합재의 특성에 관한 연구

박명규(Myung-Kyu Park),박시우(Si-Woo Park) 한국산학기술학회 2016 한국산학기술학회논문지 Vol.17 No.5

탄소섬유강화 복합재는 기계적 물성이 우수하여 다양한 산업분야에서 활용되고 있으나 섬유길이가 짧은 단섬유 형태 로 함침 되고 있어 강도와 강성을 증대시키는데 한계가 있다. 이를 보완하기 위한 LFT-D성형은 탄소 또는 유리섬유를 열가 소성 수지와 혼합하여 압출 후 프레스 성형하여 제품을 만드는 공법으로 연속공정이 가능하고 사출성형에 비해 생산성이 높아 자동차 구조용 부품을 제작하는데 사용할 수 있다. 본 연구에서는 LFT-D공법으로 성형된 탄소 장섬유강화 열가소성 복합소재의 기계적 특성을 파악하기 위하여 탄소 장섬유의 함침과 압출공정을 수행할 수 있는 Lab scale의 소형 압출기 시스 템을 제작하였다. Lab scale의 소형 압출기를 사용하여 제작된 탄소 장섬유 복합소재를 프레스 성형하여 시편을 제작하고 재료의 기계적 특성을 평가한 결과, 탄소섬유길이, 프레스 가압압력 및 탄소섬유 함유량이 복합소재의 강도 및 강성의 증가에 영향을 미침을 알 수 있었다. 향후 탄소 장섬유 복합소재의 기계적 성질 향상을 위해서 혼합 스크류 설계, 탄소 섬유코팅 등에 대한 추가적인 연구가 필요하다. Carbon fiber-reinforced composite materials have been widely used in various industrial fields, but there are limits to increasing their strength and stiffness, because of the short-length fibers that are impregnated in them. In this study, a lab-scale small extruder system was developed with the capability to perform the carbon fiber impregnation and extrusion process in order to evaluate the properties of long-length carbon fiber reinforced thermoplastic composite materials molded by the LFT-D method. Specimens were made with the small extruder to press-mold long-length carbon fiber composite materials and evaluate their material properties. As a result, it was found that the carbon fiber length, press load and carbon fiber contents have a considerable influence on the strength and stiffness. Additional studies on such factors as the mixing screw design and coating of the carbon fiber are needed in order to improve the mechanical properties of carbon fiber composite materials.