Spiral Metalens for Phase Contrast Imaging

Abstract

Spiral phase contrast imaging offers an excellent opportunity to observe nonlabeled biological samples with slight variations in refractive index or thickness. However, the overall system covering previous works is still complex and bulky, hindering miniaturization and compatibility with conventional systems. Furthermore, high-resolution imaging, particularly for observing biological specimens such as cellular structures, requires several refractive optical elements like objectives and relay optics which dramatically increases the system form factor. Here, it is demonstrated that a metalens, in which the phase profile is a sum of the hyperbolic phase and spiral phase with a topological charge of 1, performs 2D isotropic edge-enhanced imaging. The metalens achieves a submicrometer resolution of up to 0.78 µm operated under visible broadband range in conjunction with a compact form factor. Furthermore, experiments with biological samples can additionally prove the feasibility of practical usage. Capitalizing on compactness and high-resolution characteristics, it is believed that the scheme provides a stepping stone to biomedical imaging technologies and analog computing.

Revisiting Optical Material Platforms for Efficient Linear and Nonlinear Dielectric Metasurfaces in the Ultraviolet, Visible, and Infrared

“…For example, a-Si:H hologram metasurfaces have been demonstrated with measured and calculated diffraction efficiencies of 61% and 74%, respectively, at λ = 633 nm. 46,48 When a-Si:H metasurfaces are used in the multiwavelength range, the measured diffraction efficiencies are 25.5%, 42.0%, 66.9%, and 53.9% at λ = 497, 532, 580, and 633 nm, respectively 49 (Figure 3c.ii).…”

“…Compared to a-Si, a-Si:H has a higher bandgap energy (1.5–2.0 eV, corresponding to 619.9 < λ < 826.6 nm) and has been used to increase efficiencies of Si-type dielectric metasurfaces. For example, a-Si:H hologram metasurfaces have been demonstrated with measured and calculated diffraction efficiencies of 61% and 74%, respectively, at λ = 633 nm. , When a-Si:H metasurfaces are used in the multiwavelength range, the measured diffraction efficiencies are 25.5%, 42.0%, 66.9%, and 53.9% at λ = 497, 532, 580, and 633 nm, respectively (Figure c.ii).…”

Computation at the speed of light: metamaterials for all-optical calculations and neural networks

“…This functionality is enabled due to the use of achromatic lenses in the 4f system and the broadband response on the metasurface itself. This concept was expanded by exploiting the multiplexing possibilities that metasurfaces offer by Kim et al 89 By integrating the phase required for a metalens with a spiral phase of TC 1, the single device was able to perform isotropic 2D edge detection within an extremely small form factor. Since the metalens phase is also encoded into the metasurface, the requirement for the bulky 4f system was relieved and confined into a single ultrathin device.…”

Recent Progress in Reconfigurable and Intelligent Metasurfaces: A Comprehensive Review of Tuning Mechanisms, Hardware Designs, and Applications

“…In 2011, the generalized Snell's law was proposed, [12] and space-gradient metasurfaces were engineered to undergo abrupt phase change and manipulate EM waves by introducing a phase discontinuity at the interface between two media. Accordingly, metasurfaces have been used to realize a wide range of applications such as holographs, [13,14] anomalous reflection, [15][16][17][18] orbital angular momentum (OAM), [19][20][21][22][23] analog differentiator, [24] EM scattering, [25][26][27] metalens, [28][29][30][31][32][33][34][35][36][37] cloaking, [38][39][40] optical encryption, [41] quantum information, [42,43] and retroreflectors. [44,45] Historically, metasurfaces were designed to realize a singular function for a specific incident wave; therefore, they could not realize dynamic functionalities.…”