Spatially modulated polarimetry based on a vortex retarder and Fourier analysis

We report a spatially modulated polarimetry scheme by using a zero-order vortex half-wave retarder(ZVHR)and a spatial Fourier analysis method.A ZVHR is employed to analyze the input polarized light and convert it into a vectorial optical field,and an analyzer is set after the ZVHR to form an hourglass intensity pattern due to the spatial polarization modulation.Then,the input light’s Stokes parameters can be calculated by spatial Fourier analysis of the hourglass pattern with a single shot.The working principle of the polarimeter has been analyzed by the Stokes-Mueller formalism,and some quantitative measuring experiments of different polarization states have been demonstrated.The experimental results indicate that the proposed polarimeter is accurate,robust,and simple to use.     

干涉型复合腔激光束相干合成中分束器的相移特性研究

分析了采用分束器构建干涉型复合腔进行激光束相干合成的过程与原理.利用分束器的特征矩阵研究了分束时产生的反射与透射相移,得到了两束相干光经过分束器分束后进行相干叠加时相移满足的普适关系,从相移的角度解释了分束器一侧发生相长干涉时另一侧必然发生相消干涉这一现象.比较了分束器与光纤耦合器在激光束相干合成应用中的一些特性,并验证了所得相移关系式的正确性.     

利用全光纤耦合环实现三路光纤激光器的相位锁定

利用三个2×2的光纤耦合器按一定规则联接成一个全光纤耦合环,该耦合环将三个独立的掺铒光纤激光器连成一个锁相阵列. 由于耦合环的引入,锁相阵列的整体损耗减小,且三个单元激光器之间可以进行有效的能量相互注入耦合,进而实现阵列的锁相输出. 实验中观察到的远场干涉图样和锁相前后的输出光谱均表明三路光纤激光器实现了相位锁定,当三路抽运源的功率均为100 mW时,获得了92 mW的稳定相干输出. 关键词： 光纤激光器 相干合成 光纤耦合器 相位锁定     

用于光纤激光器阵列锁相的光纤环特性研究

光纤环特性对基于公共光纤环的光纤激光器锁相阵列的性能具有重要影响.介绍了利用公共光纤环构建光纤激光器锁相阵列的结构、特征以及光纤环的作用.建立了研究该光纤环特性的理论模型,分别采用光强叠加和光场叠加法分析了光纤环的能量传输与谐振选模特性,并在考虑输入光波谱宽的情况下证明了两种方法的一致性.研究表明增加成环耦合器的耦合比可以增强锁相阵列各单元激光器间的能量耦合,且在光纤环损耗较低时不会明显降低输出功率和组合效率.实验中观察到了光纤环的滤波选模效应,而输出功率随着耦合比的增加有规律的略微减小.两者均与理论分析结果一致.     

逆透视映射公式的误差分析及准确度验证

从数学上分析了目前普遍使用的逆透视映射公式的误差,给出重新推导的逆透视映射数学公式.设计实验验证了采用本文公式进行逆透视映射的效果,并与现有两公式的效果进行了比较.实验结果表明:无论相机内外参量如何变化,本文推导出的公式其IPM变换效果均好于现有公式,在相机架设高度等参量确定的条件下,采用改进后的公式,逆透视映射变换的...     

Disorder and Itinerant Magnetism in Full Heusler Pd_2TiIn

We report electronic and magnetic properties of full Heusler Pd₂TiIn based on first principles calculations.This compound has been variously characterized as magnetic or non-magnetic.We use first principles calculations with accurate methods to reexamine this issue.We find that ideal ordered Heusler Pd₂TiIn remains non-magnetic,in accord with prior work.However,we do find that it is possible to explain the magnetism seen in experiments through disorder and in particular we find that site disorder can lead to moment formation in this compound.In addition,we find an alternative low energy cubic crystal structure,which will be of interest to explore experimentally.     

基于迈克尔逊型耦合腔光纤激光器相干合成的理论与实验研究

为使光纤激光器在自由空间中进行有效的相干合成,提出了耦合臂上带有会聚透镜的迈克尔逊型耦合腔,并将外腔配置为f－f结构以增强内部反馈.利用高斯光束的ABCD定律分析了外腔的传输特性,详细研究了外腔偏离f－f结构对相互注入耦合效率的影响,指出输出光纤端面与透镜前焦平面的偏差是影响反馈耦合效率的关键因素.基于此特别设计的迈克尔逊型耦合腔,实验上实现了两路光纤激光的有效相干合成.当透镜被移走时,阵列输出功率下降为原始值的78.5％,且相干态变得不稳定.     

Coherent combining of tunable erbium-doped fiber lasers by a single-mode fiber feedback loop

We experimentally demonstrate the coherent combining of two tunable erbium-doped fiber lasers by using a single-mode fiber feedback loop configuration. A single-mode fiber is arranged in the feedback loop to filter the far-field pattern, and the energy of desired in-phase mode is collected and injected into the resonators of two component fiber lasers. The coherently combined laser is tunable over a wide spectrum ranging from 1536 to 1569 nm, which means that the combining scheme is compatible with wavelength tuning. The effects and necessity of whether adopting polarization controlling measures or not in component lasers are investigated in detail. The results indicate that adding polarization controlling can improve the array＇s coherence, whereas it will decrease the output power and efficiency simultaneously.     

基于公共环形腔耦合的光纤激光器相干合成技术

 为提高光纤激光器无源自调整相干合成阵列的效率、稳定性和可扩展性,提出了基于公共光纤环形腔耦合与单模光纤滤波的光纤激光器相干合成方案。将多个2×2的光纤耦合器分别插入各单元激光器的谐振腔,利用耦合器余下的端口,两两相连构成公共环形耦合腔。采用单模光纤滤波技术,提高了各输出激光束之间相位锁定的稳定性。利用该方案在实验上实现了三路光纤激光器的被动锁相输出,实验测得的远场干涉光斑、输出功率及光谱均表明该方案适于构建性能较好的光纤激光器相干合成阵列。     

逆透视映射公式的误差分析及准确度验证

从数学上分析了目前普遍使用的逆透视映射公式的误差,给出重新推导的逆透视映射数学公式.设计实验验证了采用本文公式进行逆透视映射的效果,并与现有两公式的效果进行了比较.实验结果表明:无论相机内外参量如何变化,本文推导出的公式其IPM变换效果均好于现有公式.在相机架设高度等参量确定的条件下,采用改进后的公式,逆透视映射变换的相对误差平均为0.85%,较现有的公式准确度有较大提高,能更好地满足智能导航和路面状况勘测等对近距离图像的逆透视映射变换应用要求.