Semiconductor moirésuperlattices provide great platforms for exploring exotic collective excitations.Optical Stark effect,a shift of the electronic transition in the presence of a light field,provides an ultrafas...Semiconductor moirésuperlattices provide great platforms for exploring exotic collective excitations.Optical Stark effect,a shift of the electronic transition in the presence of a light field,provides an ultrafast and coherent method of manipulating matter states,which,however,has not been demonstrated in moirématerials.Here,we report the valleyselective optical Stark effect of moiréexcitons in the WSe_(2)/WS_(2)superlattice by using transient reflection spectroscopy.Prominent valley-selective energy shifts up to 7.8 meV have been observed for moiréexcitons,corresponding to pseudomagnetic fields as large as 34 T.Our results provide a route to coherently manipulate exotic states in moirésuperlattices.展开更多
Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in tw...Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in two-dimensional(2D)nanospace.As an example,we study the reflectance of few-layered black phosphorus(BP)in the total internal reflection(TIR)mode in detail.We demonstrate that its optical anisotropy can be changed on a large scale by varying the incident angles,polarization states,and the in-plane rotation angles of the BP samples.Theoretical analysis indicates that the phenomena observed are common to all the atom-thick biaxial crystals,so these conclusions can be widely applied to other anisotropic 2D materials.This research furthers the current understanding of the properties of BP more comprehensively,and provides guidance for developing new optoelectronic applications,especially when BP and other atom-thick biaxial crystals are integrated with TIR devices.展开更多
Cholesteric liquid crystals（CLCs） have recently sparked an enormous amount of interest in the development of soft matter materials due to their unique ability to self-organize into a helical supra-molecular architec...Cholesteric liquid crystals（CLCs） have recently sparked an enormous amount of interest in the development of soft matter materials due to their unique ability to self-organize into a helical supra-molecular architecture and their excellent selective reflection of light based on the Bragg relationship.Nowadays,by the virtue of building the self-organized nanostructures with pitch gradient or non-uniform pitch distribution,extensive work has already been performed to obtain CLC films with a broad reflection band.Based on authors＇ many years＇ research experience,this critical review systematically summarizes the physical and optical background of the CLCs with broadband reflection characteristics,methods to obtain broadband reflection of CLCs,as well as the application in the field of intelligent optical modulation materials.Combined with the research status and the advantages in the field,the important basic and applied scientific problems in the research direction are also introduced.展开更多
The quantum fluctuation of photon counting limits the field application of optical time domain reflection. A method of photon counts modulation optics time domain reflection with single photon detection at 1.55 μm is...The quantum fluctuation of photon counting limits the field application of optical time domain reflection. A method of photon counts modulation optics time domain reflection with single photon detection at 1.55 μm is presented. The influence of quantum fluctuation can be effectively controlled by demodulation technology since quantum fluctuation shows a uniform distribution in the frequency domain. Combined with the changing of the integration time of the lock-in amplifier, the signal to noise ratio is significantly enhanced. Accordingly the signal to noise improvement ratio reaches 31.7 dB compared with the direct photon counting measurement.展开更多
Refractive index inhomogeneity is one of the important characteristics of optical coating material, which is one of the key factors to produce loss to the ultra-low residual reflection coatings except using the refrac...Refractive index inhomogeneity is one of the important characteristics of optical coating material, which is one of the key factors to produce loss to the ultra-low residual reflection coatings except using the refractive index inhomogeneity to obtain gradient-index coating. In the normal structure of antireflection coatings for center wavelength at 532 nm, the physical thicknesses of layer H and layer L are 22.18 nm and 118.86 nm, respectively. The residual reflectance caused by refractive index inhomogeneity（the degree of inhomogeneous is between -0.2 and 0.2） is about 200 ppm, and the minimum reflectivity wavelength is between 528.2 nm and 535.2 nm. A new numerical method adding the refractive index inhomogeneity to the spectra calculation was proposed to design the laser antireflection coatings, which can achieve the design of antireflection coatings with ppm residual reflection by adjusting physical thickness of the couple layers. When the degree of refractive index inhomogeneity of the layer H and layer L is-0.08 and 0.05 respectively, the residual reflectance increase from zero to 0.0769% at 532 nm. According to the above accuracy numerical method, if layer H physical thickness increases by 1.30 nm and layer L decrease by 4.50 nm, residual reflectance of thin film will achieve to 2.06 ppm. When the degree of refractive index inhomogeneity of the layer H and layer L is 0.08 and -0.05 respectively, the residual reflectance increase from zero to 0.0784% at 532 nm. The residual reflectance of designed thin film can be reduced to 0.8 ppm by decreasing the layer H of 1.55 nm while increasing the layer L of 4.94 nm.展开更多
We propose a 10-Gb/s Wavelength- Division-Multiplexed Passive Optical Network （WDM-PON） scheme with upstream transmi- ssion employing Reflective Semiconductor Op- tical Amplifier （RSOA） and Fibre Bragg Gra- ting ...We propose a 10-Gb/s Wavelength- Division-Multiplexed Passive Optical Network （WDM-PON） scheme with upstream transmi- ssion employing Reflective Semiconductor Op- tical Amplifier （RSOA） and Fibre Bragg Gra- ting （FBG） optical equaliser. Transmissions of 10-Gb/s non return-to-zero signals using a 1.2- GHz RSOA and FBG optical equaliser with different setups are demonstrated. Significant performance improvement and 40-kin standard single mode fibre transmission are achieved using FBG optical equaliser and Remotely Pum- ped Erbium-Doped Fibre Amplifier （RP-EDFA）, where they are used to equalise the output of the band-limited RSOA and amplify the seed light and upstream signal, respectively.展开更多
The carrier transport layer with reflection reduction morphology has attracted extensive attention for improving the utilization of light.Herein,we introduced single-layer hollow ZnO hemisphere arrays(ZHAs)behaving li...The carrier transport layer with reflection reduction morphology has attracted extensive attention for improving the utilization of light.Herein,we introduced single-layer hollow ZnO hemisphere arrays(ZHAs)behaving light trapping effect as the electron transport layer in perovskite photodetectors(PDs).The singlelayer hollow ZHAs can not only reduce the reflection,but also widen the angle of the effective incident light and especially transfer the distribution of the optical field from the ZnO/FTO interface to the perovskite active layer confirmed by the 3D finitedifference time-domain simulation.These merits benefit for the generation,transport and separation of carriers,improving the light utilization efficiency.Finally,our optimized FTO/ZHA/CsPbBr3/carbon structure PDs showed high self-powered performance with a linear dynamic range of 120.3 dB,a detectivity of 4.2×10^(12) Jones,rise/fall time of 13/28μs and the f_(−3) dB of up to 28 kHz.Benefiting from the high device performance,the PD was demonstrated to the application in the directional transmission of encrypted files as the signal receiving port with super high accuracy.This work uniquely utilizes the features of high-performance self-powered perovskite PDs in optical communication,paving the path to wide applications of all-inorganic perovskite PDs.展开更多
Surface plasmon resonance of noble metal nanoparticles leads to the optical absorption enhancement effects,which have great potential applications in solar cell.By using the general numerical method of discrete dipole...Surface plasmon resonance of noble metal nanoparticles leads to the optical absorption enhancement effects,which have great potential applications in solar cell.By using the general numerical method of discrete dipole approximation （DDA）,we study the absorption and scattering properties of two-dimensional square silver nanodisks （2D SSN） arrays on the single crystal silicon solar cell.Based on the effective reflective index model of the single crystal silicon solar cell,we investigate the optical enhancement absorption of light energy by varying the light incident direction,particle size,aspect ratio,and interparticle spacing of the silver nanodisks.The peak values and position of the optical extinction spectra of the 2D square arrays of noble metal nanodisks are obtained with the different array structures.展开更多
This paper reports that Al1-xInxN epilayers were grown on GaN template by metalorganic chemical vapor deposition with an In content of 7%--20%. X-ray diffraction results indicate that all these Al1-xInxN epilayers hav...This paper reports that Al1-xInxN epilayers were grown on GaN template by metalorganic chemical vapor deposition with an In content of 7%--20%. X-ray diffraction results indicate that all these Al1-xInxN epilayers have a relatively low density of threading dislocations. Rutherford backscattering/channeling measurements provide the exact compositional information and show that a gradual variation in composition of the Al1-xInxN epilayer happens along the growth direction. The experimental results of optical reflection clearly show the bandgap energies of Al1-xInxN epilayers. A bowing parameter of 6.5~eV is obtained from the compositional dependence of the energy gap. The cathodoluminescence peak energy of the Al1-xInxN epilayer is much lower than its bandgap, indicating a relatively large Stokes shift in the Al1-xInxN sample.展开更多
External optical feedback effects due to reflection, Rayleigh backscattering and coherent Rayleigh backseattering in fiber distributed feedback （DFB） fiber laser sensor system have been investigated. If the feedback...External optical feedback effects due to reflection, Rayleigh backscattering and coherent Rayleigh backseattering in fiber distributed feedback （DFB） fiber laser sensor system have been investigated. If the feedback intensity exceeds critical amount, excess noise would be induced in the demodulator. The maximum tolerable intensity back-reflection coefficient Rc and backscattering coefficient Sc into a fiber DFB laser with lead fiber length from I m to 37.5 km before the onset of instabilities are shown. Rc is found to decrease with increasing lead fiber length while Sc was relatively invariable with varying fiber length. The coherent Rayleigh backscattering （CRBS） would induce neglectable noise with a lead fiber exceeding 13.5 kin. To eliminate these noises, one or two isolators should be incorporated in the system.展开更多
In the highest-power chirped-pulse amplification lasers, the pulse must be stretched in time, amplified, compressed in a grating compressor and subsequently focused by off-axis parabola to obtain a high peak power. In...In the highest-power chirped-pulse amplification lasers, the pulse must be stretched in time, amplified, compressed in a grating compressor and subsequently focused by off-axis parabola to obtain a high peak power. In the optical terminal, the temporal and spatial effects of mismatched multigrating tiled compressor on the far-field pulse are critical factors to be analysed. In this paper, a k-space raytracing model is proposed for the temporal and spatial analyses of possible errors in a four-grating single-pass tiled compressor. The results show that the last grating affects mainly the partial focal spot, while the middle two gratings affect the temporal waveform, and the partial focal spot needs much higher error control than that in the temporal domain in a picosecond pulse compression.展开更多
Mini LED背光显示产品使用光学扩散板和复合膜进行亮度提升和均匀性提升,光学膜将大幅改变背光的色坐标和亮度参数。本文测试结果表明,复合膜亮度增益在1.5~2倍,亮度增益排序为POP>DPP>MOP>DOP。经分析这是由于不同复合膜对光...Mini LED背光显示产品使用光学扩散板和复合膜进行亮度提升和均匀性提升,光学膜将大幅改变背光的色坐标和亮度参数。本文测试结果表明,复合膜亮度增益在1.5~2倍,亮度增益排序为POP>DPP>MOP>DOP。经分析这是由于不同复合膜对光束立体角的矫正作用引起,即光学微结构对杂散光收集能量大于扩散剂散射产生的能量耗损。同时复合膜大幅提高了背光色坐标,其中扩散板+DPP色坐标变化Δx为0.01,Δy为0.0187,这是由于扩散粒子的Mie散射使短波段蓝光的光辐射能大幅耗损。对于量子点显示,从多层光学微结构反射回量子膜的蓝光将产生多重光致激发现象,使复合膜对xy色坐标值的增幅进一步加大。光学复合膜产生的亮度增益和色温降低有利于显示产品在出厂时将色温调到低色温从而保证显示亮度。展开更多
为了快速准确地计算电大尺寸目标高频散射场,降低计算代价,本文提出了一种基于八叉树多层结构与二次曲面离散技术的多层快速物理光学(multilevel fast physical optics,MLFPO)算法。八叉树多层结构的引入能够充分利用并行技术对计算加速...为了快速准确地计算电大尺寸目标高频散射场,降低计算代价,本文提出了一种基于八叉树多层结构与二次曲面离散技术的多层快速物理光学(multilevel fast physical optics,MLFPO)算法。八叉树多层结构的引入能够充分利用并行技术对计算加速;二次曲面离散技术可以更好地拟合凸散射体的表面,相较于平面三角形面片能有效降低未知量数目。在此基础上,本文将MLFPO算法应用目标拓展到复杂的多层涂覆目标。数值算例表明,与商业软件FEKO中的PO算法相比,MLFPO算法在S、C、X、Ku四个波段的双站散射场误差在1.54 dB以内,且计算速度随着频率增加可以提升8倍以上,而计算存储度降低98%。说明MLFPO算法在确保物理光学散射场计算精度的同时能够降低计算代价,是分析电大尺寸目标高频电磁散射问题的有效方法。展开更多
伴随着光纤技术的快速发展,光纤网络已部署于航空航天、舰船、数据中心和工业物联网中。传统的光时域反射仪(optical time domain reflectometer,OTDR)因原理限制,难以实现高分辨率测试,在上述复杂场景中应用受限。基于瑞利散射的光频...伴随着光纤技术的快速发展,光纤网络已部署于航空航天、舰船、数据中心和工业物联网中。传统的光时域反射仪(optical time domain reflectometer,OTDR)因原理限制,难以实现高分辨率测试,在上述复杂场景中应用受限。基于瑞利散射的光频域反射(optical frequency domain reflection,OFDR)技术可实现极高的空间分辨率、高传感灵敏度和快速的测试速率,该系列产品适用于光器件、光模块、短距离光网络的测试和故障排除,可实现从器件到光学链路全范围的插损、回损和长度测量。文中基于光频域反射法原理设计实现了一套光纤链路检测系统,针对偏振衰落效应和激光器非线性扫频等难题进行了研究,在112 m的测试链路上实现了20μm空间分辨率。展开更多
Phase measuring deflectometry(PMD)is a robust,noncoherent technique for the characterization of specular surface.For measuring high specular reflectivity surface,PMD can deliver micron radian range local gradient.Howe...Phase measuring deflectometry(PMD)is a robust,noncoherent technique for the characterization of specular surface.For measuring high specular reflectivity surface,PMD can deliver micron radian range local gradient.However,when the measured surface has low specular reflectivity,the accuracy of the measured gradient is low since the captured fringe pattern shows low signal to noise ratio.The phase error characteristics in PMD system when testing low reflectivity surfaces are analyzed.The analysis illustrates that the random phase error increases rapidly while the nonlinear error drops slowly with the decreasing of the tested surface reflectivity.In order to attain high precision measurement of low reflectivity specular surface,a robust error reduction method based on wavelet de-noising is proposed to reduce the phase error.This error reduction method is compared with several other normally used methods in both simulation and experiment work.The method based on the wavelet de-noising shows better performance when measuring the low reflectivity specular surface.展开更多
基金Project supported by the National Key R&D Program of China(Grant Nos.2022YFA1402400 and 2022YFA1405400)the National Natural Science Foundation of China(Grant Nos.11934011 and 12274365)+3 种基金Zhejiang Provincial Natural Science Foundation of China(Grant No.LR24A040001)Open project of Key Laboratory of Artificial Structures and Quantum Control(Ministry of Education)of Shanghai Jiao Tong Universitysupport from the JSPS KAKENHI(Grant Nos.20H00354 and 23H02052)World Premier International Research Center Initiative(WPI),MEXT,Japan。
文摘Semiconductor moirésuperlattices provide great platforms for exploring exotic collective excitations.Optical Stark effect,a shift of the electronic transition in the presence of a light field,provides an ultrafast and coherent method of manipulating matter states,which,however,has not been demonstrated in moirématerials.Here,we report the valleyselective optical Stark effect of moiréexcitons in the WSe_(2)/WS_(2)superlattice by using transient reflection spectroscopy.Prominent valley-selective energy shifts up to 7.8 meV have been observed for moiréexcitons,corresponding to pseudomagnetic fields as large as 34 T.Our results provide a route to coherently manipulate exotic states in moirésuperlattices.
基金supported by the K. C. Wong Education Foundation (GJTD-2018-08)the Natural Science Foundation of China (NSFC) (Grants 11804334, 51705192)+1 种基金the China Postdoctoral Science Foundation (2017M611325)the National Postdoctoral Program for Innovative Talents (BX201600064)
文摘Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in two-dimensional(2D)nanospace.As an example,we study the reflectance of few-layered black phosphorus(BP)in the total internal reflection(TIR)mode in detail.We demonstrate that its optical anisotropy can be changed on a large scale by varying the incident angles,polarization states,and the in-plane rotation angles of the BP samples.Theoretical analysis indicates that the phenomena observed are common to all the atom-thick biaxial crystals,so these conclusions can be widely applied to other anisotropic 2D materials.This research furthers the current understanding of the properties of BP more comprehensively,and provides guidance for developing new optoelectronic applications,especially when BP and other atom-thick biaxial crystals are integrated with TIR devices.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51573006,51573003,51203003,51303008,51302006,51402006,51272026,and 51273022)the Major Project of Beijing Science and Technology Program,China(Grant Nos.Z151100003315023 and Z141100003814011)the Fok Ying Tung Education Foundation,China(Grant No.142009)
文摘Cholesteric liquid crystals（CLCs） have recently sparked an enormous amount of interest in the development of soft matter materials due to their unique ability to self-organize into a helical supra-molecular architecture and their excellent selective reflection of light based on the Bragg relationship.Nowadays,by the virtue of building the self-organized nanostructures with pitch gradient or non-uniform pitch distribution,extensive work has already been performed to obtain CLC films with a broad reflection band.Based on authors＇ many years＇ research experience,this critical review systematically summarizes the physical and optical background of the CLCs with broadband reflection characteristics,methods to obtain broadband reflection of CLCs,as well as the application in the field of intelligent optical modulation materials.Combined with the research status and the advantages in the field,the important basic and applied scientific problems in the research direction are also introduced.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10674086 and 10934004)the National Natural Science Foundation for Excellent Research Team (Grant No. 60821004)+2 种基金the National Key Basic Research and Development Program of China (Grant No. 2010CB923103)the National High Technology Research and Development Program of China (Grant No. 2009AA01Z319)the Program for Top Science and Technology Innovation Teams and Top Young and Middleaged Innovative Talents of Shanxi Province
文摘The quantum fluctuation of photon counting limits the field application of optical time domain reflection. A method of photon counts modulation optics time domain reflection with single photon detection at 1.55 μm is presented. The influence of quantum fluctuation can be effectively controlled by demodulation technology since quantum fluctuation shows a uniform distribution in the frequency domain. Combined with the changing of the integration time of the lock-in amplifier, the signal to noise ratio is significantly enhanced. Accordingly the signal to noise improvement ratio reaches 31.7 dB compared with the direct photon counting measurement.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61405145 and 61235011)the Natural Science Foundation of Tianjin,China(Grant No.15JCZDJC31900)the China Postdoctoral Science Foundation(Grant Nos.2015T80115 and 2014M560104)
文摘Refractive index inhomogeneity is one of the important characteristics of optical coating material, which is one of the key factors to produce loss to the ultra-low residual reflection coatings except using the refractive index inhomogeneity to obtain gradient-index coating. In the normal structure of antireflection coatings for center wavelength at 532 nm, the physical thicknesses of layer H and layer L are 22.18 nm and 118.86 nm, respectively. The residual reflectance caused by refractive index inhomogeneity（the degree of inhomogeneous is between -0.2 and 0.2） is about 200 ppm, and the minimum reflectivity wavelength is between 528.2 nm and 535.2 nm. A new numerical method adding the refractive index inhomogeneity to the spectra calculation was proposed to design the laser antireflection coatings, which can achieve the design of antireflection coatings with ppm residual reflection by adjusting physical thickness of the couple layers. When the degree of refractive index inhomogeneity of the layer H and layer L is-0.08 and 0.05 respectively, the residual reflectance increase from zero to 0.0769% at 532 nm. According to the above accuracy numerical method, if layer H physical thickness increases by 1.30 nm and layer L decrease by 4.50 nm, residual reflectance of thin film will achieve to 2.06 ppm. When the degree of refractive index inhomogeneity of the layer H and layer L is 0.08 and -0.05 respectively, the residual reflectance increase from zero to 0.0784% at 532 nm. The residual reflectance of designed thin film can be reduced to 0.8 ppm by decreasing the layer H of 1.55 nm while increasing the layer L of 4.94 nm.
基金ACKNOWLEDGEMENT This work was supported by the National High Technology Research and Development Pro- gram of China under Grant No. 2011AA01A- 104 the National Natural Science Foundation of China under Grant No. 61302079 and the Fund of State Key Laboratory of Information Photonics and Optical Communications, Bei- jing University of Posts and Telecommunica- tions, China.
文摘We propose a 10-Gb/s Wavelength- Division-Multiplexed Passive Optical Network （WDM-PON） scheme with upstream transmi- ssion employing Reflective Semiconductor Op- tical Amplifier （RSOA） and Fibre Bragg Gra- ting （FBG） optical equaliser. Transmissions of 10-Gb/s non return-to-zero signals using a 1.2- GHz RSOA and FBG optical equaliser with different setups are demonstrated. Significant performance improvement and 40-kin standard single mode fibre transmission are achieved using FBG optical equaliser and Remotely Pum- ped Erbium-Doped Fibre Amplifier （RP-EDFA）, where they are used to equalise the output of the band-limited RSOA and amplify the seed light and upstream signal, respectively.
基金the National Natural Science Foundation of China(Nos.51972101,11874143)the Natural Science Foundation of Hubei Province(No.2019CFB508)the Application Fundamental Research Project of Wuhan Science and Technology Bureau(No.2019010701011396).
文摘The carrier transport layer with reflection reduction morphology has attracted extensive attention for improving the utilization of light.Herein,we introduced single-layer hollow ZnO hemisphere arrays(ZHAs)behaving light trapping effect as the electron transport layer in perovskite photodetectors(PDs).The singlelayer hollow ZHAs can not only reduce the reflection,but also widen the angle of the effective incident light and especially transfer the distribution of the optical field from the ZnO/FTO interface to the perovskite active layer confirmed by the 3D finitedifference time-domain simulation.These merits benefit for the generation,transport and separation of carriers,improving the light utilization efficiency.Finally,our optimized FTO/ZHA/CsPbBr3/carbon structure PDs showed high self-powered performance with a linear dynamic range of 120.3 dB,a detectivity of 4.2×10^(12) Jones,rise/fall time of 13/28μs and the f_(−3) dB of up to 28 kHz.Benefiting from the high device performance,the PD was demonstrated to the application in the directional transmission of encrypted files as the signal receiving port with super high accuracy.This work uniquely utilizes the features of high-performance self-powered perovskite PDs in optical communication,paving the path to wide applications of all-inorganic perovskite PDs.
基金supported by the National Natural Science Foundation of China under Grant No. G050104011004024the Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No. A0901040110018512026
文摘Surface plasmon resonance of noble metal nanoparticles leads to the optical absorption enhancement effects,which have great potential applications in solar cell.By using the general numerical method of discrete dipole approximation （DDA）,we study the absorption and scattering properties of two-dimensional square silver nanodisks （2D SSN） arrays on the single crystal silicon solar cell.Based on the effective reflective index model of the single crystal silicon solar cell,we investigate the optical enhancement absorption of light energy by varying the light incident direction,particle size,aspect ratio,and interparticle spacing of the silver nanodisks.The peak values and position of the optical extinction spectra of the 2D square arrays of noble metal nanodisks are obtained with the different array structures.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60776047, 60506001, 60476021, 60576003 and 60836003)
文摘This paper reports that Al1-xInxN epilayers were grown on GaN template by metalorganic chemical vapor deposition with an In content of 7%--20%. X-ray diffraction results indicate that all these Al1-xInxN epilayers have a relatively low density of threading dislocations. Rutherford backscattering/channeling measurements provide the exact compositional information and show that a gradual variation in composition of the Al1-xInxN epilayer happens along the growth direction. The experimental results of optical reflection clearly show the bandgap energies of Al1-xInxN epilayers. A bowing parameter of 6.5~eV is obtained from the compositional dependence of the energy gap. The cathodoluminescence peak energy of the Al1-xInxN epilayer is much lower than its bandgap, indicating a relatively large Stokes shift in the Al1-xInxN sample.
基金supported by the National 863 Program under Grant No. 2007AA03Z415.
文摘External optical feedback effects due to reflection, Rayleigh backscattering and coherent Rayleigh backseattering in fiber distributed feedback （DFB） fiber laser sensor system have been investigated. If the feedback intensity exceeds critical amount, excess noise would be induced in the demodulator. The maximum tolerable intensity back-reflection coefficient Rc and backscattering coefficient Sc into a fiber DFB laser with lead fiber length from I m to 37.5 km before the onset of instabilities are shown. Rc is found to decrease with increasing lead fiber length while Sc was relatively invariable with varying fiber length. The coherent Rayleigh backscattering （CRBS） would induce neglectable noise with a lead fiber exceeding 13.5 kin. To eliminate these noises, one or two isolators should be incorporated in the system.
基金Project supported by the National High Technology Research and Development Program of China(Grant No.2009AA8044005)
文摘In the highest-power chirped-pulse amplification lasers, the pulse must be stretched in time, amplified, compressed in a grating compressor and subsequently focused by off-axis parabola to obtain a high peak power. In the optical terminal, the temporal and spatial effects of mismatched multigrating tiled compressor on the far-field pulse are critical factors to be analysed. In this paper, a k-space raytracing model is proposed for the temporal and spatial analyses of possible errors in a four-grating single-pass tiled compressor. The results show that the last grating affects mainly the partial focal spot, while the middle two gratings affect the temporal waveform, and the partial focal spot needs much higher error control than that in the temporal domain in a picosecond pulse compression.
文摘为了快速准确地计算电大尺寸目标高频散射场,降低计算代价,本文提出了一种基于八叉树多层结构与二次曲面离散技术的多层快速物理光学(multilevel fast physical optics,MLFPO)算法。八叉树多层结构的引入能够充分利用并行技术对计算加速;二次曲面离散技术可以更好地拟合凸散射体的表面,相较于平面三角形面片能有效降低未知量数目。在此基础上,本文将MLFPO算法应用目标拓展到复杂的多层涂覆目标。数值算例表明,与商业软件FEKO中的PO算法相比,MLFPO算法在S、C、X、Ku四个波段的双站散射场误差在1.54 dB以内,且计算速度随着频率增加可以提升8倍以上,而计算存储度降低98%。说明MLFPO算法在确保物理光学散射场计算精度的同时能够降低计算代价,是分析电大尺寸目标高频电磁散射问题的有效方法。
文摘伴随着光纤技术的快速发展,光纤网络已部署于航空航天、舰船、数据中心和工业物联网中。传统的光时域反射仪(optical time domain reflectometer,OTDR)因原理限制,难以实现高分辨率测试,在上述复杂场景中应用受限。基于瑞利散射的光频域反射(optical frequency domain reflection,OFDR)技术可实现极高的空间分辨率、高传感灵敏度和快速的测试速率,该系列产品适用于光器件、光模块、短距离光网络的测试和故障排除,可实现从器件到光学链路全范围的插损、回损和长度测量。文中基于光频域反射法原理设计实现了一套光纤链路检测系统,针对偏振衰落效应和激光器非线性扫频等难题进行了研究,在112 m的测试链路上实现了20μm空间分辨率。
基金support by the National Nature Science Foundation of China (61421002, 61327004)
文摘Phase measuring deflectometry(PMD)is a robust,noncoherent technique for the characterization of specular surface.For measuring high specular reflectivity surface,PMD can deliver micron radian range local gradient.However,when the measured surface has low specular reflectivity,the accuracy of the measured gradient is low since the captured fringe pattern shows low signal to noise ratio.The phase error characteristics in PMD system when testing low reflectivity surfaces are analyzed.The analysis illustrates that the random phase error increases rapidly while the nonlinear error drops slowly with the decreasing of the tested surface reflectivity.In order to attain high precision measurement of low reflectivity specular surface,a robust error reduction method based on wavelet de-noising is proposed to reduce the phase error.This error reduction method is compared with several other normally used methods in both simulation and experiment work.The method based on the wavelet de-noising shows better performance when measuring the low reflectivity specular surface.
