光栅衍射实验教学中的体会

文中首先介绍了光栅衍射实验教学的难点以及实验的调节目标.之后依次分析了学生在光栅衍射实验调节中经常遇到的问题,例如：分光计的粗调调节不到位;望远镜目镜视场中观察不到由双面平行平面镜反射回来的绿色“＋”字叉丝像;平行光管的光轴没有与望远镜光轴共轴;望远镜目镜视场中观察不到由光栅面反射回来的绿色“＋”字叉丝像.最后,结合实际的教学经验,给出了各个问题相应的解决方法,对教学实践具有一定的参考价值.     

Low divergent diffractive optical element for remote detection

The low divergent Dammann grating is researched for the potential applications in aerospace. A laserbeam writing system is developed for writing the low divergent Dammann grating. The uniformity and efficiency of the Dammann grating are presented in this letter. The novelty of this letter is to demonstrate a low-cost and effective method to fabricate low divergent Dammann grating.     

3D shape measurement of larger complex objects based on fringe cycle correction

The grating fringe on the reference plane is broadened in the intersecting axis system because of oblique-angle projection. In order to solve this problem, we study the theoretical model of the temporal phase unwrapping method based on the fringe cycle correction. We also study the 3D shape measurement theoretical model of the larger complex objects after considering the coordinate deviation and lens distortion. Experimental results demonstrate that the fringe cycle on the reference plane can be corrected to a constant value, the lens distortion can be corrected, and 3D shape of larger complex objects can be accurately measured.     

用于红外探测器的高红外吸收率结构研究进展

高红外吸收是实现高灵敏度红外探测器的一个重要途径。探测器的响应率与热吸收率紧密相关。高红外吸收将提升红外探测器的探测性能。鉴于高吸收率的重要性,对国内外研究中典型的高红外吸收结构的研究进展进行介绍。目前典型新型高吸收结构有基于新型材料(如超材料)的高吸收结构和基于金属光栅高吸收结构。研究表明这些结构在某些波段可实现近100%的完美吸收,是发展高灵敏探测器的新途径。     

Novel wavelength-accurate InP-based arrayed waveguide grating

A 13-channel, InP-based arrayed waveguide grating （AWG） is designed and fabricated in which the on-chip loss of the central channel is about -5 dB and the crosstalk is less than -23 dB in the center of the spectrum response. However, the central wavelength and channel spacing are deviated from the design values. To improve their accuracy, an optimized design is adopted to compensate the process error. As a result, the central wavelength 1549.9 nm and channel spacing 1.59 nm are obtained in the experiment, while their design values are 1549.32 nm and 1.6 nm, respectively. The route capability and thermo-optic characteristic of the AWG are also discussed in detail.     

Spectral analysis of the UFBG-based acousto optical modulator in V–I transmission matrix formalism

In this study, the V-I transmission matrix formalism （V-I method） is proposed to analyze the spectrum characteristics of the uniform fiber Bragg grating （FBG）-based acousto--opfic modulators （UFBG-AOM）. The simulation results demon- strate that both the amplitude of the acoustically induced strain and the frequency of the acoustic wave （AW） have an effect on the spectrum. Additionally, the wavelength spacing between the primary reflectivity peak and the secondary reflectivity peak is proportional to the acoustic frequency with the ratio 0.1425 nm/MHz. Meanwhile, we compare the amount of calculation. For the FBG whose period is M, the calculation of the V-I method is 4 × （2M-l） in addition/subtraction, 8 × （2M - 1） in multiply/division and 2M in exponent arithmetic, which is almost a quarter of the multi-film method and transfer matrix （TM） method. The detailed analysis indicates that, compared with the conventional multi-film method and transfer matrix （TM） method, the V-I method is faster and less complex.     

High-efficiency focusing grating coupler with optimized ultra-short taper

A novel high-efficiency focusing non-uniform grating coupler is proposed to couple light into or off silicon photonic chips for large-scale silicon photonic integration. This kind of grating coupler decreases the transition length of the linking taper between the grating and the single-mode waveguide by at least 80%. The radian of the grating lines and the size of the taper are optimized to improve the coupling efficiency. An experimental coupling efficiency of ~ 68% at 1556.24 nm is obtained after optimization and the whole size of the grating is 12 μm × 30 μm, with a very short taper transition of ~15 μm long.     

中阶梯光栅刻划刀具抗磨损设计

采用DEFORM有限元分析软件模拟中阶梯光栅刻划刀具在光栅刻划过程中的应力分布,并结合金刚石晶体解理特征设计了抗磨损刀具刃口取向。当光栅刻划刀具刃尖点受最大摩擦力方向平行于金刚石晶体周期键连（PBC）方向,且刀具Z向载荷垂直于（111）晶面时,定向面与（111）晶面夹角为27°,非定向面与（111）晶面夹角为63°;光栅刻划刀具在72 g负载条件下,刻程超过17 km时,刀具刃口无崩口等缺陷。采用该方法设计的光栅刻划刀具使用寿命大大超出了传统刀具的使用寿命（刻程约0.8 km）,证明了中阶梯光栅刻划刀具抗磨损设计方法的合理性和有效性。     

Effect of trabecular bone material properties on ultrasonic backscattering signals

In this study, ultrasonic backscattering signals in cancellous bones were obtained by finite difference time domain （FDTD） simulations, and the effect of trabecular material properties on these signals was analyzed. The backscatter coefficient （BSC） and integrated backscatter coefficient （IBC） were numerically investigated for varying trabecular bone material properties, including density, Lame coefficients, viscosities, and resistance coefficients. The results show that the BSC is a complex function of trabecular bone density, and the IBC increases as density increases. The BSC and IBC increase with the first and second Lame coefficients. While not very sensitive to the second viscosity of the trabeculae, the BSC and IBC decrease as the first viscosity and resistance coefficients increase. The results demonstrate that, in addition to bone mineral density （BMD） and microarchitecture, trabecular material properties significantly influence ultrasonic backseattering signals in cancellous bones. This research furthers the understanding of ultrasonic backscattering in cancellous bones and the characterization of cancellous bone status.     

用于抽运铯蒸气激光器的半导体激光器波长稳定与线宽窄化研究

针对铯蒸气激光器对窄线宽与高稳定852nm半导体激光抽运源的要求,采用体布拉格(Bragg)光栅作为外腔输出镜,研究了体Bragg光栅衍射效率对外腔半导体激光器输出光谱特性的影响。研究结果表明,衍射效率为24%、32%与37%的体布拉格光栅均能够改善半导体激光器输出光谱特性;输出光束中心波长锁定在852nm附近、输出线宽约为0.26nm;外腔半导体激光器输出波长随抽运电流、温度的变化速率分别小于10.4pm/A、7.2pm/℃,优于自由运行半导体激光器;随着光栅衍射效率增加,全系统外腔效率从91%降低至86%。