Conventional mid-infrared polarization optics assign discrete polarizers, prisms and lens in spatial cascade setup to perform chromatic aberration correction and polarization modulation. Therefore, the complex configuration imposes a severe restriction on the broadband polarization photoelectric integrated detection due to the bulky volume and inaccurate alignment.

In contrast to the traditional bulk elements, metasurfaces, featuring with a lighter, thinner and more compact planar configuration, can selectively and independently manipulate multidimensional information of photons at sub-wavelength scale. However, up to now, little work has been reported on effectively manipulating the polarization, phase and dispersion with broadband multifunctional metadevices. Current metaoptics research mainly focuses on the visible and near-infrared regime.

In a study published online in Science Advances, Assoc. Prof. LI Guanhai, Profs. CHEN Xiaoshuang and LU Wei from Shanghai Institute of Technical Physics of the Chinese Academy of Sciences, cooperating with Prof. Andrey E. Miroshnichenko's group from University of New South Wales in Australia, developed high performance multifunctional meta-photonic devices for mid- infrared polarization detection.

Based on all-silicon metasurface which is compatible with silicon-based semiconductor manufacturing, the researchers in this study proposed a multifunctional metadevice that can be utilized for photodetector integration in the mid-wavelength infrared.

A general broadband achromatic methodlogy was first proposed to simultaneously engineer the phase-dispersion and polarization based on all-silicon birefringent metasurface. The all-Si platform provides a straightforward way to achieve larger phase dispersion control range by selecting more guided modes without additional material’s deposition. The adoption of birefringent metaatoms allows independently and effectively manipulating the phase and dispersion along the orthogonal polarized directions at subwavelength scale over the broad bandwidth.

For the proof of the concept, the researchers then designed and experimentally fabricated the metadevices via exposure and etching processes compatible with silicon-based integrated circuits. The experimental results agreed well with the simulations. Within a continuous bandwidth, different polarized photons modulated by the metadevice are carrying different orbital angular momentum and collected on the predefined focal plane.

Besides, by introducing off-axis phase into the modulated phase spectra of the metadevice, broadband and directional bunching control can be achieved. The experiment results revealed that the focal spots have nearly diffraction-limit sizes and high polarization extinction ratios.

The findings in this study are expected to have applications in the fields of polarization imaging, machine vision, and multidimensional display.