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PR Highlights(Vol.8, Iss.4): 高效且紧凑的新型光学多参量探测系统

2020-05-21

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高效且紧凑的新型光学多参量探测系统

振幅、相位和偏振态是描述光波的基本参数。光的偏振和相位信息的实时测量在光学中是非常重要的。然而,目前大多数光电探测器仅对光强敏感,因此,传统的偏振和相位检测系统复杂、笨重且难以集成。

超表面是具有亚波长特征的超薄二维超材料,可以灵活地操控光的振幅、相位和偏振态,因此可以用来开发紧凑型光学器件来取代传统的光学元件,从而产生高度集成且极其紧凑的光学系统。与等离子体超表面相比,介质超表面的透射损耗更小,更适合于可见光和近红外波段。超透镜作为基于超表面的光学领域的研究热点之一,与传统的透镜相比,具有结构紧凑、无球面像差等优点。介质平面超透镜的制造简单、易于集成,可以作为传统折射透镜和衍射透镜的替代或补充,有利于高性能光学设备和系统的进一步小型化。

来自华中科技大学的夏金松教授和杨振宇教授课题组在Photonics Research 2020年第8卷第4期(Yuxi Wang, Zhaokun Wang, Xing Feng, et al. Dielectric metalens-based Hartmann–Shack array for a high-efficiency optical multiparameter detection system[J]. Photonics Research, 2020, 8(4): 04000482)中介绍的装置是一种高效、紧凑的光学多参量检测系统,该系统基于具有2 × 2子阵列超透镜的Hartmann-Shack阵列,工作波长1550 nm。该系统不仅可以通过对焦点振幅的检测来实现对光束空间偏振高效、准确的测量,而且还可以通过对焦点位移的分析来测量光束的相位和相位梯度。

该光学多参量检测系统由介质超透镜阵列和相机组成。超透镜的单位元素是放置在二氧化硅层上的椭圆形硅柱。超透镜阵列包含多个像素,每个像素包含四个不同的超透镜,可以从入射光束中分离出四个不同偏振分量并汇聚到相机上。然后,根据每个焦点的位置和强度信息,可以得到光束的相位和偏振态。该结构具有较高的空间分辨率,有利于在光学成像和光学检测领域的应用。此外,通过设计和优化每个超透镜的晶格单元,可以获得48%的平均聚焦效率。

在实验中,作者首先用阵列中的一个像素精确地描述了22种不同入射偏振光的偏振态。理论计算结果与实验结果的平均相对误差仅为4.24%。接下来,作者检测了两个常见的具有非恒定偏振态的光束(径向偏振光束和方位角偏振光束)和一个具有螺旋波前的涡旋光束,证明这种设计同样适用于具有复杂偏振态和波前的光束。

杨振宇教授认为,该光学多参量检测系统结构紧凑,能够实现对入射光束偏振态和波前分布的实时检测,在光学成像和光学探测中具有重要的应用潜力。此外,通过采用另一种介质代替硅,工作原理便可以转移到其他工作波长。

基于介质超透镜的Hartmann-Shack阵列用于高效光学多参量检测系统的示意图。该系统可以同时测量光的空间偏振和相位。

Dielectric metalens-based Hartmann-Shack array for high-efficiency optical multiparameter detection system

The amplitude, phase, and state of polarization (SOP) are fundamental parameters for describing light waves. The real-time measurement of the polarization and phase information of light is very important and desirable in optics. At present, however, most photodetectors are only sensitive to the light intensity, which makes traditional polarization and phase detection systems complex, bulky and difficult to integrate.

Metasurfaces are ultrathin two-dimensional metamaterials with subwavelength features that can flexibly manipulate the amplitude, phase, and SOP of the light,and can therefore be exploited to develop compact optical devices to replace traditional optical elements, producing a highly integrated and extremely compact optical system. Compared with plasmonic metasurfaces, dielectric metasurfaces have less loss for transmission operation, making them more suitable for visible and near infrared wavelengths.

As one of the most popular directions in the field of metasurface-based optics, metalenses offer the advantages of higher compactness and no spherical aberrations compared with traditional lenses. The fabrication of these planar metalenses is straightforward, easy to integrate, and can potentially replace or complement their conventional refractive and diffractive counterparts, facilitating further miniaturization of high-performance optical devices and systems.

The device introduced by the research groups of Prof. Jinsong Xia and Prof. Zhenyu Yang from Huazhong University of Science and Technology in Photonics Research, Vol. 8, Issue 4, 2020 (Yuxi Wang, Zhaokun Wang, Xing Feng, et al. Dielectric metalens-based Hartmann–Shack array for a high-efficiency optical multiparameter detection system[J]. Photonics Research, 2020, 8(4): 04000482) is an efficient and compact optical multiparameter detection system based on a Hartmann-Shack array with 2×2 sub-array metalenses, operating at 1550 nm. This system not only enables the efficient and accurate measurement of the spatial polarization profiles of optical beams via the inspection of foci amplitudes, but also measures the phase and phase-gradient profiles by analysing foci displacements.

The proposed optical multi-parameter detection system consists of a dielectric metalens array and a camera. The unit element of the metalens is an elliptical silicon pillar placed on a layer of silica. The metalens array contains multiple pixels, and each pixel contains four different metalenses that can separate four differently polarized components from the incident beam and converge these components onto the camera. Then, the phase and SOP profiles of the beam can be derived from the position and intensity information of each focal spot. This configuration affords a high spatial resolution, which is beneficial for applications in optical imaging and optical detection. In addition, by designing and optimizing the unit cell of each metalens, a high average focusing efficiency of 48% can be obtained.

In the experiments, authors first accurately characterize the SOP of 22 different incident polarized beams by one pixel of the array. The average relative error between the theoretical results and experimental results is as small as 4.24%. Next, authors detect two common light beams with nonconstant SOPs (a radially polarized beam and an azimuthally polarized beam) and a vortex light beam with a spiral wavefront, demonstrating that this design is also applicable to beams with complex SOPs and wavefronts.

Prof. Zhenyu Yang believes that this optical multiparameter detection system is very compact and can realize the real-time detection of the SOP and wavefront distributions of the incident beam, which has important application potential in optical imaging and optical probing. By replacing silicon with another dielectric, the operation principle can be transferred to other operation wavelengths.

Dielectric metalens-based Hartmann-Shack array for a high-efficiency optical multiparameter detection system. The system can simultaneously measure the spatial polarization and phase profiles of optical.