A mplitude, phase, polarization, and wavelength are basic parameters of any light wave. Of course, all of these parameters can be characterized experimentally by exist- ing bulk optics. However, miniaturization often makes a big difference concerning usefulness. For example, established Hartmann–Shack wavefront sensors based on arrays of refractive microlenses, which focus the light onto a standard camera system, can simply be placed into a laser beam to analyze its phase and amplitude profile in real time1. Clearly, the same task can be performed by yet more compact metalenses. Metasurfaces and flat lenses based thereupon have recently attracted considerable attention. For example, compact polarimeters2–4, polarization- sensitive elements5–10, holograms11–13, couplers14,15, and meta- lenses16–26 have been demonstrated. Metasurfaces can be based on metals27–31 or dielectrics32–37. The former exhibit larger material contrast, the latter lower losses. Metalenses can be polarization independent38–40 and broadband41–44. Importantly, metalenses can do more than just copying what refractive microlenses can do. Metalenses can, e.g., be designed to exhibit a tailored polarization dependence45–50. On this basis, we generalize the idea of a Hartmann–Shack lens array to not only measure phase profiles but simultaneously map polarization profiles as well. Here, we propose a generalized Hartmann–Shack array based on 2 × 3 sub-arrays of all-dielectric transmission- mode metalenses, and realize it experimentally. The six different metalenses in each sub-array allow to fully determine the Stokes parameters in each pixel of the array. To validate the concept of this generalized “meta-Hartmann–Shack” array, we use it to characterize a radially polarized beam, an azimuthally polarized beam, and a vortex beam. Results Principle of metalens array design. Our system shown in Fig. 1 consists of two main parts: The metalens array and a standard camera, ont
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Generalized Hartmann-Shack array of dielectric metalens sub-arrays for polarimetric beam profiling
Zhenyu Yang, Zhaokun Wang, Yuxi Wang, Xing Feng, Ming Zhao, Zhujun Wan, Liangqiu Zhu, Jun Liu, Yi Huang, Jinsong Xia, Martin Wegener
Research context
To define and characterize optical systems, obtaining the amplitude, phase, and polarization profile of optical beams is of utmost importance. Traditional polarimetry is well established to characterize the polarization state. Recently, metasurfaces have successfully been introduced as compact optical components. Here, we take the metasurface concept to the system level by realizing arrays of metalenses, allowing the determination of the polarization profile of an optical beam. We use silicon-based metalenses with a numerical aperture of 0.32 and a mean measured focusing efficiency in transmission mode of 28% at a wavelength of 1550 nm. Our system is extremely compact and allows for real-time beam diagnostics by inspecting the foci amplitudes. By further analyzing the foci displacements in the spirit of a Hartmann-Shack wavefront sensor, we can simultaneously detect phase-gradient profiles. As application examples, we diagnose the profiles of a radially polarized beam, an azimuthally polarized beam, and of a vortex beam.
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Cite / 引用
Zhenyu Yang, Zhaokun Wang, Yuxi Wang, Xing Feng, Ming Zhao, Zhujun Wan, Liangqiu Zhu, Jun Liu, Yi Huang, Jinsong Xia, Martin Wegener. Generalized Hartmann-Shack array of dielectric metalens sub-arrays for polarimetric beam profiling. Nature Communications (2018). https://doi.org/10.1038/s41467-018-07056-6
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