A novel optical beam splitter based on photonic crystal with hybrid lattices

A novel optical beam splitter constructed on the basis of photonic crystal(PC) with hybrid lattices is proposed in this paper.The band gap of square-lattice PC is so designed that the incident light is divided into several branch beams.Triangular-lattice graded-index PCs are combined for focusing each branch.Computational calculations are carried out on the basis of finite-different time-domain algorithm to prove the feasibility of our design.The waveguide is unnecessary in the design.Thus the device has functions of both splitting and focusing beams.Size of the divided beam at site of full-width at half-maximum is of the order of λ/2.The designed splitter has the advantages that it has a small volume and can be integrated by conventional semiconductor manufacturing process.     

Facile sensitizing of PbSe film for near-infrared photodetector by microwave plasma processing

High quality PbSe film was first fabricated by a thermal evaporation method, and then the effect of plasma sensitization on the PbSe film was systemically investigated. Typical detectivity and significant photosensitivity are achieved in the PbSe-based photodetector, reaching maximum values of 7.6×10⁹ cm·Hz^1/2/W and 1.723 A/W, respectively. Compared with thermal annealing, plasma sensitization makes the sensitization easier and significantly improves the performance.     

十字星形金属纳米粒子的消光性质

单纳米粒子的LSPR光学生物传感器具有空间分辨率高, 可植入生物的细胞和组织里, 检测所需要的剂量少等优势。本文提出一种十字星形的纳米粒子结构以进一步提高单纳米粒子LSPR光学生物传感器的信号强度。模拟和分析表明, 十字星形纳米粒子的消光效率远远高于相同结构尺寸的菱形或三角形纳米粒子的消光效率, 为发展新型结构单或阵列式的金属纳米粒子LSPR光学生物传感器提供了参考依据。     

Flat lenses constructed by graded negative index-based photonic crystals with tuned configurations

Flat lenses are designed by means of graded negative refractive index-based photonic crystals （PCs） constructed using air-holes tuned with different shapes. By gradually modifying the filling factor along the transverse direction, we obtain the graded negative index-based lenses for the purpose of focusing an incident plane wave. The finite-difference and timedomain （FDTD） algorithm is adopted for numerical calculation. Our calculation results indicate that these lenses can finely focus incident plane waves. Moreover, for the same size of air-holes, the focusing properties of the lens with rectangular air-holes are better than those with the other shaped air-holes. The graded negative index PCs lenses could possibly enable new applications in optoelectronic systems.     

菱形金属纳米粒子光学性质的研究

金属纳米粒子的光学性质与金属纳米粒子的组成、形状、尺寸及周围的介电常数有关。利用时域有限差分法研究菱形纳米粒子的尺寸与其消光特性关系, 发现粒子尺寸的大小对其消光谱共振峰有较大影响, 随着粒子尺寸的增大, 消光谱共振峰可分裂成两个或多个共振峰。而且在可见光范围内波长大于480 nm的区域, 表面等离子体共振峰是偶极子激发模式; 而在波长小于480 nm的区域, 共振模式则比较复杂, 有偶极子模式, 也有多极子模式。计算表明, 波长为480~ 600 nm区间与波长大于600 nm的区间, 菱形纳米粒子的尺寸对消光光谱的峰值和谱线宽度影响不同。在波长为480~600 nm之间, 短轴为140 nm时, 其消光效率最高。     

高衍射效率连续面形分束器的设计与制备

为了解决目前光学分束器件衍射效率低的问题,在传统的Gerchberg-Saxton(GS)算法基础上,对初始相位和迭代算法中的振幅限制方式作改进.先利用二次相位来作为迭代算法的初始相位,再在迭代过程中将输出平面分为信号区和噪音区两部分,保持这两部分的相位不变,信号区内振幅乘上一个随迭代次数不断变化的因子,噪音区内振幅保持不变.通过该方法设计9×9连续面形的分束器件,并与传统GS算法设计的分束器进行了对比,结果表明:GS算法设计得到的分束器相位存在严重的突变和不连续等问题,而本文方法设计得到的分束器相位连续平滑,可利用移动掩模技术加工.最终制备出1×3和1×9分束器,其实测的衍射效率分别为83.5%和89.4%,均匀性误差分别为3.56%和15.23%.     

低散斑环形光束整形器件的设计及实验

提出一种可有效抑制散斑噪声的衍射元件设计方法.在传统Gerchberg-Saxton算法的基础上,通过选择一种特殊的初始相位,在不降低衍射效率的同时,有效提升光斑的均匀性.以将高斯光束整形成环形平顶光束为例,开展了数值仿真和光学实验.结果表明,利用该方法和传统Gerchberg-Saxton算法设计得到的环形平顶光束散斑对比度分别为11%和34%,验证了该方法可以获得低散斑噪声的环形平顶光束.     

Tunability of graded negative index-based photonic crystal lenses for fine focusing

Graded negative refractive index-based photonic crystal (PC) lenses are designed by gradually modifying the sizes of air holes along the transverse direction for focusing the incident plane wave. To study the tunability of the graded negative index-based PC, we introduce filling factor A, gradually tune the filling factor, and use the finite-difference and time-domain (FDTD) algorithm for numerical calculation. Our calculation results indicate that the focal length and the spot size increase with A increasing. For the same A value, the focal length of a PC with elliptical air holes is the longest, and those of PC with square and rectangular air holes are the shortest. Moreover, when the focal length is greater than 1 μm, the focal parameters of the PC are highly insensitive to the variation of A. When the focal length is less than 1 μm, the PC lenses have higher transmittances and all well focus with a beam spot size breaking the diffraction limit. This feature possibly makes the graded negative index-based PC lenses have some new applications in optoelectronic systems.     

Experimental investigation of pre-irradiation effect on radiation sensitivity of temperature sensing fiber Bragg gratings

The effect of pre-irradiation on radiation sensitivity of fiber Bragg gratings(FBGs) is verified experimentally.FBGs are fabricated in photosensitive optical fibers and single mode fibers with Ge-concentration in a range from 3 mol% to 23.37 mol% in the core.In experiments,the FBGs are subjected to twice γ-radiation exposures to a Co60 source at a dose-rate of 0.1 Gy/s up to a total dose of 50 kGy.Pre-irradiation treatment can reduce the temperature sensitivity variation of FBGs by 18.12%-35.91%,as well as Bragg wavelength shift(BWS) by 8%-27.08 %.Our research demonstrates that pre-irradiation treatment is a feasible method to improve the radiation tolerance of FBGs.