High-efficiency spatial color separation method based on fractional Talbot effect

Based on fractional Talbot effect, Talbot grating is adopted to realize spatial color separation with high light efficiency. For red and green colors, a two-step Talbot grating is optimized and the light efficiency reaches over 95%. The two-step Talbot grating is fabricated and tested. Experimental results show that the Talbot grating indeed has the good ability of spatial color separation.     

Optical Texture Super-Lattices Produced by Talbot Effect at Superimposed Gratings

Fresnel diffraction on periodic gratings results in a two-dimensional periodic distribution of light intensity, also known as the Talbot effect. Here this approach is extended to the family of superimposed structures with translational symmetry, which consist of superposed spatial harmonics. The Talbot effect is demonstrated to be valid for superimposed gratings. The considered superimposed gratings provide a wide range of textures of optical super-lattices. These texture super-lattices represent a Talbot carpets with a complex motif, which can be varied by choosing structure parameters. These results provide a new functionality for structuring optical lattices and can find potential applications in a wide range of light–matter interactions.     

The influence of the polarization effect in Talbot self-imaging of high-density gratings

The Talbot self-imaging of high-density gratings with different period at half Talbot distance for different polarization is analyzed with the finite-difference time-domain (FDTD) method. The numerical results indicate that the Talbot self-imaging of high-density gratings is obviously different for different polarization when the period d of the grating between 2λ and 3λ, which is verified through experimental results with the scanning near-field optical microscopy (SNOM) technique. Furthermore, the Fourier spectrum (far field) generated by the gratings is also given with the rigorous coupled-wave method, which is in agreement with the near field.     

基于X射线塔尔博特效应的纳米光栅制作模拟研究

沿纳米多层膜生长方向切割可制成周期只有几纳米而厚度几十微米的切片多层膜光栅. 基于该切片多层膜光栅塔尔博特自成像效应的X射线光刻是一种新型的纳米图样制作方法. 已有学者用该方法完成了百纳米结构光栅的制作. 采用严格耦合波方法, 本文模拟计算了切片多层膜光栅在满足塔尔博特自成像条件下的后表面光场分布, 详细讨论三个影响光栅后表面成像质量的重要参数:光栅厚度、材料厚度所占比例和多层膜周期. 模拟结果表明, 光栅厚度不仅影响X射线透射率, 还会改变像面条纹衬比度. 材料厚度比的大小直接决定像面是否存在清晰条纹, 选取合适的材料厚度比, 得到了前人实验中近场反常成像现象. 计算还表明, 在一定条件下, 采用周期更小的多层膜光栅有望获得更高分辨率的纳米图形, 这说明使用塔尔博特效应制作更加精细的纳米结构图形具有可行性.     

利用保角变换实现环形光栅的Talbot效应

Talbot效应是一种近场自成像效应,通常只有周期光栅可以产生Talbot效应,而环形光栅无法产生.本文通过引入保角变换,发现可以在环形光栅外部设计适当的折射率渐变层介质,使得其中也能够产生严格的Talbot效应,并计算了对应的自成像半径表达式.本文利用FDTD软件分别将一个环形光栅放置在真空中以及人工设计的折射率渐变层中进行了模拟,并对二者的结果进行了比较分析,发现这种折射率渐变层介质确实对点光源入射的环形光栅的自成像情况有着很好的改善.希望这一工作能够推广Talbot效应的应用范围.     

Spectral Talbot phenomena in sampled arbitrarily chirped Bragg gratings

We derive the general conditions for which spectral Talbot phenomena, both integer and fractional self-imaging, can be observed in sampled arbitrarily chirped fiber Bragg gratings. These results are a generalization of those previously reported in [C. Wang, J. Azaña, L.R. Chen, Opt. Lett. 29(14) (2004) 1590] in which spectral Talbot phenomena were observed in sampled linearly chirped fiber Bragg gratings. We confirm our theoretical derivations with numerical simulations.     

Talbot effect of a high-density grating under femtosecond laser illumination

The Talbot effect of a high-density grating under femtosecond laser illumination is analyzed with rigorous electromagnetic theory which is based on the Fourier decomposition and the rigorous coupled-wave analysis (RCWA). Numerical simulations show that the contrast of the Talbot images steadily decreases as the transmitted femtosecond laser pulses propagate forward and with wider spectrum width of the femtosecond laser pulses. The Talbot images of high-density gratings have much higher sensitivity of the spectrum widths of the incident laser pulses than those of the traditional low-density gratings. In experiments, the spectrums and the pulse widths of the incident pulses are measured with a frequency-resolved optical grating (FROG) apparatus. The Talbot images are detected by using a Talbot scanning near-field optical microscopy (Talbot-SNOM) technique, which are in coincidence with the numerical simulations. This effect should be useful for developing new femtosecond laser techniques and devices.     

部分相干同步辐射照射下光栅分数塔尔博特效应

基于高斯谢尔光束的相干模式分解理论和波动光学,建立了部分相干同步辐射硬X射线光束通过光学器件的传播模型。模拟了微聚焦X射线光束照射下光栅的分数塔尔博特效应,得到了聚焦光束的光强分布和相干特性变化,并分析了散焦光束入射下的光栅自成像。然后通过模拟准直光束入射下的光栅塔尔博特效应,得到了不同传播距离处自成像条纹的变化情况,分析了影响光栅自成像条纹形状的因素。通过光栅衍射条纹测量同步辐射相干度,发现对矩形相位光栅来说,应该对衍射图样进行傅里叶分解,求出各级傅里叶系数随传播距离的变化曲线,从而得到入射光束相干特性。     

用于彩色液晶显示器的色分离光栅的优化设计

利用光栅实现液晶显示器中的色分离可以提高液晶显示器对光能的利用率。为了提高光能利用率,对光栅台阶数进行了优化设计,经矢量衍射理论计算,优化后的多台阶色分离光栅的能量利用率达到了65.3%,与采用滤色片的方法相比,光能利用率提高了近一倍;与三台阶相比,光能利用率提高了9.3%。     

Refractive power mapping of progressive power lenses using Talbot interferometry and digital image processing

A method of refractive power mapping of a lens is presented which is based on Talbot interferometry and utilizes a digital image processor. By adding a digital image processing system, fast measurement of a lens power distribution is feasible. A test lens is placed in front of two collinearly arranged gratings. The light passing through the test lens produces a shifted Talbot image of the first grating on the second grating and generates moiré fringes. Given the inclination angle of moiré fringes, the refractive power of the lens can be calculated. The calculation is performed using a digital image processor. This method is effective in finding the refractive power distribution of progressive power lenses.     

Unveiling Talbot Effect under Fresnel Diffraction at a Fork-Shaped Grating

The near-field effect of diffraction image self-reproduction or self-imaging of a periodic grating illuminated by quasi-monochromatic wave is well-known as the Talbot effect. Introducing a dislocation to a periodic structure provides a fork-shaped modulation of the phase/amplitude, which produces discrete diffraction pattern in a far-field consisting of optical vortices. In this paper, Fresnel diffraction at amplitude fork-shaped grating is theoretically and experimentally studied. The coexistence of spatial ordering and local violation of translational symmetry of the structure manifests itself in a strict diffraction pattern consisting of optical vortices in the far-field, which is shown to be accompanied by formation of a spatially ordered intensity distribution in the near-field, reminiscent the Talbot carpets for periodic structures. These results demonstrate the first evidence of Talbot effect occurred under light diffraction at fork-shaped gratings, being promising for deep understanding of near-field singular optics phenomena.     

Setting sensitivity in Talbot interferometry with modified gratings

A dual field grating has been introduced for use in Talbot interferometry. We report here results of an experimental investigation on setting sensitivity when using these gratings for testing.     

基于Talbot-Moiré法的长焦透镜焦距

 长焦距测量的Talbot Moiré法是研究热点,目前很多方法虽然都是基于Talbot现象和Moiré技术,但基本原理和实验方案各不相同,因此焦距计算公式也不相同。基于透镜位相变换作用,利用Talbot效应和Moiré条纹,通过图像处理的方法获得条纹的斜率变化,根据焦距与莫尔条纹斜率之间的关系求得透镜焦距。由于长焦透镜的焦距相对于被测透镜厚度大得多,完全可以看作是薄透镜对光束的变换,可用薄透镜对球面波的变换作用来近似表示其对高斯光束的变换。因此,该方法测量长焦透镜焦距对于高斯光束与非高斯光束焦距测量结果无差别,均适用。最后全面分析了该测量方法的误差及精度极限。在影响测量精度的各个误差因素中,光栅节距误差对焦距测量的影响最为显著。     

Efficiency Enhancement of Components Based on Talbot Effect

Two ways to improve efficiency of components based on Talbot effect are considered in the present paper. One way is based on optimization of waveguide wall impedance, another one consists in modification of waveguide cross-section shape. Both methods allow correction of waveguide modes spectrum and lead to efficiency enhancement. For the important application of Talbot effect-remote steering antenna of a wavebeam in plasma-the steering band is expanded by 40–50%.     

离焦量和非单色光对二元相位光栅泰伯像的影响

利用平面波衍射的角谱理论,分析计算了二元相位光栅衍射光场的空间分布,特别讨论了离焦量和非单色光对泰伯像的影响.随离焦量和带宽的增加,泰伯像的对比度和衍射效率减小,而压缩比增加.计算结果指出,在带宽<1000或离焦量<0.01时,其对比度和衍射效率减小不到10%,仍能成较高质量的泰伯像;当带宽>5000或离焦量>0.1时,成像质量显著下降.用薄膜沉积法制作了二元相位光栅,实验验证了理论结果.这些结果对泰伯成像和阵列照明器的设计有重要的参考价值.     

畴腐蚀掺镁铌酸锂可调阵列光分束器的研究

研究了不同畴腐蚀深度的掺镁铌酸锂二维六角可调阵列光分束器的分数Talbot效应.对不同Talbot分数β和不同畴腐蚀深度的阵列光分束器Talbot衍射像进行了数值模拟理论研究.模拟结果表明,Talbot分数β可以改变Talbot衍射像的周期及结构分布,而畴腐蚀深度可有效调制衍射像的光强分布.在理论研究的基础上,设计并制备了具有不同畴腐蚀深度的掺镁铌酸锂二维六角阵列光分束器,对其在不同Talbot分数β条件下的分数Talbot效应进行了通光实验研究,实现了畴腐蚀阵列光分束器对近场Talbot衍射光强分布的调制,实验结果与理论研究结果一致.     

一般多值相位光栅菲涅耳衍射光场的分析

基于光栅结构与距离的关系,给出了一种求解一般多值相位光栅菲涅耳衍射光场的解析表达式利用该表达式可以直接分析一般多值相位光栅的分数泰伯数效应及在阵列照明中的应用,克服了间接分析法只能分析某些类型的泰伯阵列照明器的不足之处.     

Use of steel substrates in diffractive optics: Near field of high surface quality steel tape gratings

Steel tape is used in optical applications due to its mechanical properties. However, roughness of steel surfaces affects to wave propagation. The effect can be observed using diffraction gratings with low periods. In such a case, self-images of the grating appear at certain periodic distances from the grating (Talbot planes). When standard steel is used, the contrast of Talbot self-images strongly decreases with the distance from the grating. In this work, we prove that controlling the surface quality of steel, it is possible to improve its optical behavior and, as a consequence, high quality surface steel represents a good choice for diffractive optics when the use of chrome-on-glass masks is not indicated. As an example, we have manufactured a diffraction grating over a high quality steel surface by means of an ablation process with a nanosecond pulsed laser. The contrast of the self-images for these gratings decreases very slowly with the distance, in comparison with the self-images obtained with standard steel tape gratings.     

Talbot interferometry with an adaptive light intensity compensator

Talbot interferometry with a larger applicable scope has been investigated based on the intensity amplification method to weak moiré fringes by using photorefractive crystal as a light amplifier. It not only has function of conventional Talbot interferometry, but also is suitable for situations such as weak incident beam and detected object with strong absorption. The investigation indicates that the method or technique is feasible and the results of theoretical analysis are verified by experiments. Based on this investigation, Talbot interferometry with an adaptive light intensity compensator is proposed and some merits and demerits of the technique have briefly been discussed.     

Self-imaging with curved gratings

We analyze the near field behavior of binary amplitude gratings which present a curved profile. This configuration has an important application in rotary optical encoders. This kind of encoders is used to measure the angular displacement between two different parts of the devices. To our knowledge, its behavior in the near field has not been analyzed yet. We have found that Talbot effect is produced but the period of the self-images and Talbot distances change as we separate from the grating. We have fabricated a curved grating and have performed the experiment to corroborate the behavior theoretically found. This fact could be useful in systems that use Talbot effect to measure displacements, since the mechanical tolerances grow.