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.