• Title/Summary/Keyword: single-pass

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Asymmetry of the 1.54${\mu}m$ forward and backward raman gain in methane (라만매질 $CH_4$의 전후방 1.54${\mu}m$ 유도라만 산란광의 비대칭적 발생)

  • 최영수;고해석;강응철
    • Korean Journal of Optics and Photonics
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    • v.10 no.2
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    • pp.89-94
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    • 1999
  • The 1.54 ${\mu}{\textrm}{m}$ forward and backward stimulated Raman scattering (SRS) have been studied in CH$_4$pumped by 1.06 ${\mu}{\textrm}{m}$ Nd:YAG laser. The forward and backward SRS output energy in a single pass were measured at dufferent CH$_4$pressures. Under steady state conditions, the pump input threshold energies and Raman gains in forward and backward directions were for Raman conversion at various CH$_4$pressures for a tight focusing geometry. The forward and backward slope efficiency for Raman conversion were 18% and 34% respectively. The pump input threshold energy of the backward SRS was lower than that of the forward. In backward SRS, the experimental input laser threshold and Raman gain values were in good agreement with the calculated values at different pressures of CH$_4$. The retio of the backward to the forward SRS gain was appoximately 1.4 times above 1200 psi. We obtained that the backward Raman gain coefficient was 0.32 cm/GW, and the forward Raman gain coefficient 0.23cm/GW at 1400 psi. Asymmetry of the forward and backward Raman gain is caused by the interaction between different pump intensities of each direction duting the amplification of the Stokers. The backward Raman gain is proportional to the average pump intensity. However, the forward SRS output grows by depleting the local pump intensity.

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Stimulated Raman scattering at 1.54${\mu}m$ and Brillouin scattering at 1.06${\mu}m$ in $CH_4$ under 5 Hz repetition rate (반복률과 라만매질 압력에 따른 1.54 ${\mu}m$ 전방, 후방 유도라만 및 1.06${\mu}m$ Brillouin 산란광의 출력특성)

  • 최영수;전용근;김재기
    • Korean Journal of Optics and Photonics
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    • v.10 no.2
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    • pp.95-101
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    • 1999
  • We have studied the 1.54$\mu\textrm{m}$ forward and backward stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SRS) for various $CH_4$pressures by 1.06$\mu\textrm{m}$ Q-switched Nd:YAG laser pumping under a repetition rate of Hz in single pass. We obtained that the output of backward SRS was more efficient than that of the forward SRS. The output energy and conversion efficiency of forward and backward SRS were higher than those of SBS since SRS is a steady state, but SBS is a transient state. In a $CH_4$gas uncirculating system, the output energy of the backward SRS and SBS were reduced the about 47% due to a thermal heating of $CH_4$medium in a focusing region for a repetition rate of 5 Hz. But, the output energy of forward SRS was slightly enhanced by about 8.5% due to the increase of the undepleted pump beam in the backward SRS generation. Inthe Raman half resonator using a dichromatic focusing lens, the conversion efficiency of SRS was more than 37% for a input pump laser energy of 40 mJ.

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Optical Design of the Integrated Triplexer Fabricated by Micro Block Stacking Method (MBS 방법으로 제작한 집적형 Triplexer의 광학 설계)

  • Yoon, Hyun-Jae;Kim, Jong-Hyuk
    • Korean Journal of Optics and Photonics
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    • v.22 no.4
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    • pp.191-197
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    • 2011
  • In this paper, we have designed an integrated triplexer which is the basic component for a FTTH(Fiber To The Home) system which can transmit CATV and voice/data at the same time in a single fiber. The integrated triplexer can be fabricated with a novel technique of "Micro-Block Stacking (MBS)" method which automatically aligns the optical components in the optical beam pass using accurate ceramic holders. We analyze the displacement of the optical focus according to the tolerances of the component dimensions and the assembly process using code V simulator. For the transmitter, the most serious shift of the focal points is caused by the displacements of the LD spot. So the focal point moves up to $72{\mu}m$ from the center point for ${\pm}25{\mu}m$, ${\pm}25{\mu}m$, ${\pm}30{\mu}m$ displacements. For the receiver the most serious shift of the focal points is caused by the displacements of a 0.8mm ball lens (for the analog receiving part) and a micro ball lens (for the digital receiving part), and the focal point moves up to $55{\mu}$ for ${\pm}55{\mu}m$, ${\pm}5{\mu}m$, ${\pm}55{\mu}m$ micro ball lens displacements.

Design and Analysis of Pseudorandom Number Generators Based on Programmable Maximum Length CA (프로그램 가능 최대길이 CA기반 의사난수열 생성기의 설계와 분석)

  • Choi, Un-Sook;Cho, Sung-Jin;Kim, Han-Doo;Kang, Sung-Won
    • The Journal of the Korea institute of electronic communication sciences
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    • v.15 no.2
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    • pp.319-326
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    • 2020
  • PRNGs(Pseudorandom number generators) are essential for generating encryption keys for to secure online communication. A bitstream generated by the PRNG must be generated at high speed to encrypt the big data effectively in a symmetric key cryptosystem and should ensure the randomness of the level to pass through the several statistical tests. CA(Cellular Automata) based PRNGs are known to be easy to implement in hardware and to have better randomness than LFSR based PRNGs. In this paper, we design PRNGs based on PMLCA(Programable Maximum Length CA) that can generate effective key sequences in symmetric key cryptosystem. The proposed PRNGs generate bit streams through nonlinear control method. First, we design a PRNG based on an (m,n)-cell PMLCA ℙ with a single complement vector that produces linear sequences with the long period and analyze the period and the generating polynomial of ℙ. Next, we design an (m,n)-cell PC-MLCA based PRNG with two complement vectors that have the same period as ℙ and generate nonlinear sequences, and analyze the location of outputting the nonlinear sequence.

Power Enhance Effect on the Hybrid Cell Based on Direct Current Nanogenerator and an Organic Photovoltaic Device

  • Yun, Gyu-Cheol;Sin, Gyeong-Sik;Lee, Geun-Yeong;Lee, Ju-Hyeok;Kim, Sang-U
    • Proceedings of the Korean Vacuum Society Conference
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    • 2013.08a
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    • pp.298-298
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    • 2013
  • Finding renewable and clean energy resources is essential research to solve global warming and depletion of fossil fuels in modern society. Recently, complex harvesting of energy from multiple sources is available in our living environments using a single device has become highly desirable, representing a new trend in energy technologies. We report that when simultaneously driving the fusion and composite cells of two or more types, it is possible to make an affect the other cells to obtain a greater synergistic effect. To understand the coupling effect of photovoltaic and piezoelectric device, we fabricate the serially integrated hybrid cell (s-HC) based on organic solar cell (OSC) and piezoelectric nanogenerator (PNG). The size of increased voltage peaks when OSC and PNG are working on is larger than the case when only PNG is working. This voltage difference is the Voc change of OSC, not the voltage change of PNG and current density difference between these two cases is manifested more clearly. When the OSC and PNG are working in s-HC at the same time, piezoelectric potential (VPNG) is generated in ZnO and theoretical total voltage is sum of voltage of an OSC (VOSC) and VPNG. However, electrons from OSC are influenced by piezoelectric potential in ZnO and current loss of OSC in whole circuit decreases. As a result, VOSC increases temporarily. Current shows the similar behavior. PNG acts a resistance in the whole circuit and current loss occurs when the electrons from OSC pass through the PNG. But piezoelectric potential recover current loss and decrease the resistance of PNG. Our PNG can maintain piezoelectric potential when the strain is held owing to the LDH layer while general PNG cannot maintain piezoelectric potential. During the section that strain is held, voltage enhancement effect is maintained and same effect appeared even turn off the light. Actually at this time, electrons in ZnO nanosheets move to LDH and trapped by the positive charges in this layer. After this strain is held, piezoelectric potential of ZnO nanosheets is disappeared but potential difference which is developed by negative charge dominant LDH layer is remained. This potential acts similar role like piezoelectric potential in ZnO. Electrons from the OSC also are influenced by this potential and the more current flows.

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A Study on the Development of SSB Modem (디지털 SSB 모뎀 개발에 관한 연구)

  • Kim, Jeong-Nyun
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.11 no.10
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    • pp.1852-1857
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    • 2007
  • The SSB modem performs the modulation process which converts the digital voltage level to the audible frequency band signal and the demodulation process which converts reversely the audible frequency signal to the digital voltage level. The modulator and the demodulator are implemented with a single DSP chip. Because of the SSB specific character, the distortion occurs when the frequency is changed. This distortion has no effect on voice communication but it has an significant effect on data communication. In other words, it is impossible to send data stream with adjacent 2 periods. Therefore, in case of using 2-tone FSK, it is needed to send at least 3 periods to transmit 1 bit. Therefore we implemented the modem using modified phase-delay shift keying to transmit 1 tone signal for high speed transmission. In the 1200[bps] mode, it generates 0, $187{\mu}s$, delay time at 1.3kHz symbol frequency, and in the 2400[bps] mode, 0, $70{\mu}s\;130{\mu}s\;200{\mu}s$, delay time at 1.5kHz symbol frequency. Finally, in the maximum 3600[bps] mode, it generates 0, $100{\mu}s\;160{\mu}s\;250{\mu}s$ 2.0kHz symbol frequency. The measured results of the implemented SSB modem shows a good transfer functional characteristic by spectrum analyzer, almost same bandwidth in pass band and 20dB higher SNR comparing the emu FACTOR and American CLOVER and in the experimental transmitting test, we verified the transmitted data is received correctly in platform.

Integrated Photonic Microwave Bandpass Filter Incorporating a Polymer Microring Resonator (폴리머 마이크로링 공진기를 이용한 광학적 마이크로웨이브 대역통과 필터)

  • Chin, Won-Jun;Kim, Do-Hwan;Song, Ju-Han;Lee, Sang-Shin
    • Korean Journal of Optics and Photonics
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    • v.16 no.5
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    • pp.469-475
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    • 2005
  • An integrated photonic microwave bandpass filter has been proposed and demonstrated incorporating a coherently coupled microring resonator in low-loss polymers. The proposed device may feature compact site, simple structure, tuning via the thermooptic and electrooptic effect, and flexible integration with other electrical and optical devices. The resonator was designed to have an extremely small bandwidth so that it could be used to selectively pass the optical signal carrying the microwave signal to attain efficient bandpass filtering. We made and tested two resonators with a single ring and double rings, and performed a theoretical fitting of their measured transfer curves to predict the performance of the microwave filters based on them precisely. It was found that as the number of the rings used for the resonator increases, the bandwidth gets smaller, the rolloff sharper, and the band rejection higher. Finally our filter exhibited the center frequency of 10GHz, the 3-dB bandwidth of 1.0GHz, the corresponding quality (Q) factor of 10, and the rejection outside of the passband of more than 25dB.

Unsupervised Non-rigid Registration Network for 3D Brain MR images (3차원 뇌 자기공명 영상의 비지도 학습 기반 비강체 정합 네트워크)

  • Oh, Donggeon;Kim, Bohyoung;Lee, Jeongjin;Shin, Yeong-Gil
    • The Journal of Korean Institute of Next Generation Computing
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    • v.15 no.5
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    • pp.64-74
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    • 2019
  • Although a non-rigid registration has high demands in clinical practice, it has a high computational complexity and it is very difficult for ensuring the accuracy and robustness of registration. This study proposes a method of applying a non-rigid registration to 3D magnetic resonance images of brain in an unsupervised learning environment by using a deep-learning network. A feature vector between two images is produced through the network by receiving both images from two different patients as inputs and it transforms the target image to match the source image by creating a displacement vector field. The network is designed based on a U-Net shape so that feature vectors that consider all global and local differences between two images can be constructed when performing the registration. As a regularization term is added to a loss function, a transformation result similar to that of a real brain movement can be obtained after the application of trilinear interpolation. This method enables a non-rigid registration with a single-pass deformation by only receiving two arbitrary images as inputs through an unsupervised learning. Therefore, it can perform faster than other non-learning-based registration methods that require iterative optimization processes. Our experiment was performed with 3D magnetic resonance images of 50 human brains, and the measurement result of the dice similarity coefficient confirmed an approximately 16% similarity improvement by using our method after the registration. It also showed a similar performance compared with the non-learning-based method, with about 10,000 times speed increase. The proposed method can be used for non-rigid registration of various kinds of medical image data.

Comparative Analysis of Training Systems and Curriculums of Early Childhood Educators in Korea and France (한국과 프랑스의 유아교사 양성제도 및 교육내용에 대한 비교 분석)

  • Park, Joo-Won
    • Journal of Korea Entertainment Industry Association
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    • v.15 no.7
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    • pp.107-123
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    • 2021
  • This research aims to review the training systems and curriculums of early childhood educators in Korea and France and seek directions to improve teachers training in Korea. To achieve the research purpose, this article compares three criteria, namely teacher training institutes, training systems, and curriculums based on the legal systems of Korea and France. Below are the summaries of the comparison. First, the training for teachers in France is carried out by the INSPÉ, the state-level single training system, for those who have bachelor's degrees. Second, the second year INSPÉ students or preliminary teachers take national teacher qualification tests. If they pass the tests, they are sent to the teaching fields as licensed teachers. Third, there are 3-year scholarship programs and support for practicums as part of the INSPÉ curriculum through the teacher support system in France to select highly qualified teachers. Fourth, the French curriculums prioritize basic knowledge skills, integration of school systems, teaching practicum experiences that are tied to the teaching fields, and research and analysis of practicum experiences.

Study of Oxygen Barrier Properties of Silk Fibroin Composite Membrane Using Molecular Dynamics Simulation (분자동역학 전산모사를 활용한 실크 피브로인 복합막의 산소 차단성 연구)

  • Young Jin Seo;Na Yeong Kwon;Chi Hoon Park
    • Membrane Journal
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    • v.33 no.6
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    • pp.447-453
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    • 2023
  • The performance of computer systems and the development of various computer simulation programs have made it possible to analyze chemical systems composed of more complex elements, and accordingly, research using molecular dynamics simulation is being actively conducted. Research on calculating the gas permeation characteristics of polymer membranes by molecular dynamics, which was previously conducted mainly through experiments, is receiving attention for gas barrier membranes used in food packaging and pharmaceuticals. Recently, there has been a report that a gas barrier effect appears when a coating film is made using silk fibroin, and in this study, a study was conducted using molecular dynamics simulation to confirm whether an oxygen barrier effect appears when a composite film is made using silk fibroin. We built a single model, calculated the gas permeation characteristics, and compared it with the experimental value to confirm that the model reflects the actual experimental results. Actual composite membrane models were then built and the gas movement path within the polymer was analyzed. As a result, oxygen molecules were found that they could not pass through and was blocked in the fibroin region. Therefore, the composite membrane with silk fibroin has excellent oxygen barrier property and is expected to be useful in food packaging, etc.