High-efficiency broadband achromatic metalens for near-IR biological imaging window

Abstract

Over the past years, broadband achromatic metalenses have been intensively studied due to their great potential for applications in consumer and industry products. Even though significant progress has been made, the efficiency of technologically relevant silicon metalenses is limited by the intrinsic material loss above the bandgap. In turn, the recently proposed achromatic metalens utilizing transparent, high-index materials such as titanium dioxide has been restricted by the small thickness and showed relatively low focusing efficiency at longer wavelengths. Consequently, metalens-based optical imaging in the biological transparency window has so far been severely limited. Herein, we experimentally demonstrate a polarization-insensitive, broadband titanium dioxide achromatic metalens for applications in the near-infrared biological imaging. A large-scale fabrication technology has been developed to produce titanium dioxide nanopillars with record-high aspect ratios featuring pillar heights of 1.5 µm and ~90° vertical sidewalls. The demonstrated metalens exhibits dramatically increased group delay range, and the spectral range of achromatism is substantially extended to the wavelength range of 650–1000 nm with an average efficiency of 77.1%–88.5% and a numerical aperture of 0.24–0.1. This research paves a solid step towards practical applications of flat photonics.

Dielectric metalens for miniaturized imaging systems: progress and challenges

“…With a high refractive index, the electromagnetic field is strongly confined within the nanostructures, enhancing the phasemodulation. Singlet metalenses with focusing efficiency over 90% 34,[53][54][55] have been demonstrated. In particular, the NIL Technology company has reported silicon metalenses possessing 94% efficiency at 940 nm wavelength with anti-reflection coating on the non-structured side of the glass substrate.…”

“…On the one hand, the high diffractive dispersion is utilized for spectral tomographic imaging negating chromatic aberrations 86 , and a metalens-integrated nano-optic endoscope is presented for optical coherence tomography application 87 . On the other hand, achromatic imaging over broad bandwidth has been realized in the VIS 85,88,89 , NIR 55,90,91 , and MIR [92][93][94][95][96] bands. According to Eq.…”

All‐Dielectric Metasurface‐Enabled Multiple Vortex Emissions

“…The designed metasurface was fabricated from an 800 nm TiO 2 film using a combination of electron-beam (E-beam) lithography and reactive ion etching (RIE) (see Experimental Section). [15] Figure 2a,b shows the top-and tilt-view scanning electron microscopy (SEM) images of the metalens, respectively. The sizes of the TiO 2 nanopillars, period, and rotation angles all followed the numerical design in Figure 1c,d.…”

“…Consequently, by placing a microlaser at the focal point, the linearly polarized laser emission is decomposed into RCP and LCP and finally transferred to two collimated vortex beams with topological charges of l L and l R . [14][15][16] The vortex beam arrays or vortex crystals [17] are generated by extending the single metalens into a metalens array (see Figure 1a).…”

Chip-scale metalens microscope for wide-field and depth-of-field imaging

“…13,14 According to the powerful capability in manipulating the phase, polarization, and amplitude of light, [15][16][17][18][19][20][21][22] versatile functional metasurfaces have been well demonstrated, [23][24][25][26][27][28] including image devices. [29][30][31][32][33][34][35][36][37][38][39][40][41][42] Among them, a recent approach of metalens-integrated imaging with a wide FOV shows a promising route to ultracompact and lightweight microscopes. 36 It was implemented by a polarization multiplexed metalens array directly mounted on a complementary metal-oxide semiconductor (CMOS) image sensor, which not only shows its highly compact advantage but also breaks the FOV constraint.…”