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221.
LI Yifeng JIANG Zhuo College of Electronics Information Engineering Nanjing University of Technology Nanjing 《声学学报:英文版》2012,(3):275-284
The conjunction of "Chaotic Cavity Transducer(CCT)" focusing with Nonlinear Elastic Wave Spectroscopy(NEWS)methods has been discussed in the detection of the localization of micro-damage.CCT focusing is a combination process of CCT with the techniques of acoustic Time Reversal(TR)or Inverse Filter(IF),which can improve the ability of localization. In order to improve the quality of focalization,in the experimental process the chirped excitation source signal and inverse filtering techniques have been used.A focusing process in a non-reverberant composite plate sample and an image of a crack in a steel sample demonstrate the focalization ability and high efficiency of imaging of the combination of CCT with NEWS,and proves that CCT can efficiently overcome the problems of "phantom" image and increasement of the strain at the boundary of medium. 相似文献
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谐衍射/折射双波段系统设计 总被引:11,自引:1,他引:10
将谐衍射透镜成功地引入红外凝视阵列探测器双波段系统的设计中,使系统在3.7~4.3μm的中波红外和8.7~11.5μm的长波红外波段同时较好的完成了像差校正。光学传递函数在两个波段范围内,在18lp/mm时的归一化值均大于0.5,接近衍射极限。该系统具有100%冷光栏效率。设计结果表明,谐衍射透镜的光谱特性介于折射透镜与衍射透镜之间,色散大小可以控制,降低了对工艺水平的要求,使红外双波段系统结构紧凑,透镜组片数少、分辨率高。为红外光学设计提供了一种全新的器件。 相似文献
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S波段光纤拉曼放大器中级联受激布里渊散射串扰的实验研究 总被引:2,自引:0,他引:2
研究了光纤激光器前向抽运的S波段分布式光纤拉曼放大器中级联的受激布里渊散射(SBS)串扰现象。用窄光谱带宽(<100MHz)的可调谐激光二极管作为信号源,通过S波段分布式光纤拉曼放大器,当被放大的信号功率超过单模光纤受激布里渊散射的阈值时,出现了前向受激布里渊散射,这是传导声波布里渊散射在光纤放大器中放大的现象。随着拉曼放大器抽运功率的提高,在斯托克斯区,出现了两阶受激布里渊散射线,在实验中观测到偶数阶的受激布里渊散射谱线功率大于奇数阶的布里渊一瑞利散射线。当进一步增加拉曼放大器的抽运功率,出现了前向级联的多阶受激布里渊散射现象,拉曼放大器的增益下降,被放大的信号功率转换为受激布里渊散射,噪声变大。受激布里渊散射的串扰破坏了拉曼放大器的特性,使拉曼放大器无法在密集波分复用光纤传输系统中使用,因此需要严格地控制入纤的信号功率和放大器的抽运功率。在实验中还观测到在光纤拉曼放大器中被放大的信号光和受激布里渊散射线两侧的伴线。 相似文献
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We propose and demonstrate experimentally a novel scheme to realize all-optical up-conversion and wavelength-conversion based on the bi-directional-pump four-wave mixing (FWM) effect in high nonlinear fibers (HNLFs).The pump is generated with optical carrier suppression in a Mach-Zehnder modulator.The two pumps are always parallel and phase-locked.A balance-detection photo-detector for optical signal detection is employed with 3-dB improvement in power penalty.The 2.5-Gb/s signals are transmitted successfully over the 25-km single-mode fiber in 30-GHz radio over fiber (ROF) systems. 相似文献
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A 60-GHz bidirectional radio-over-fiber (RoF) system using two-carrier-injected distributed feedback (DFB) laser is proposed and demonstrated to realize optical single sideband (SSB) modulation for downlink.An injection-locked Fabry-P'erot laser is also carried out to realize wavelength reuse in uplink.Transmission of 2.5 Gb/s on a 60-GHz carrier for downlink and 622-Mb/s baseband signal for uplink are both successfully demonstrated over 50-km single mode fiber without chromatic dispersion compensation. 相似文献
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<正>A reflection-mode photoacoustic microscope(PAM) for rat brain imaging in vivo is constructed.A pulsed laser is used as an excitation source,and a focused ultrasound transducer is adopted to collect the photoacoustic signal.Raster scanning is applied to acquire three-dimensional(3D) data.The obtained measurements of the lateral and axial resolutions of the microscope are 45 and 15μm,respectively.The imaging depth in the chicken breast tissue is 3.1 mm at a signal-to-noise ratio(SNR) of 20 dB without any signal averaging.The imaging speed is 30 A-line/s.Experimental results in vivo demonstrate the capability of 3D imaging of the brain vessels of the rat after removing the skull. 相似文献
229.
A new concept to realize negative refractive index in non-resonance spectrum using chiral metamaterial is proposed.A low-index metamaterial is added to diminish the effective refractive index of the combined structure.Simulation and material parameter retrieval procedures are carried out to determine material performances.Results show evidence of negative refractive index and strong optical activity in the new chiral metamaterial. 相似文献
230.
The highly Ge-doped photosensitive fiber (PSF) has been widely used in the fabrication of fiber Bragg gratings (FBGs). Its birefringence and cladding mode coupling characteristics greatly influence FBG's transmission feature in communication application areas. In this work, a new concept of the PSF is introduced which, along with an optimized birefringence design, a precisely controlled fabrication process, and a cladding mode depressed design, results in a written FBG with -25-dB clad mode-depressed ratio and a polarization mode dispersion value less than 0.045 ps. 相似文献