Cover story: Li XT, Seong J, Kim Y et al. Electrically switchable bright-field and interference-synthesized edge-enhanced imaging with a polarization-multiplexed metalens. Opto-Electron Sci 5, 260044 (2026).

Conventional bright-field imaging and optical edge extraction typically require different hardware or digital post-processing. Although metasurfaces can compactly tailor spatial-frequency responses, most multifunctional designs assign a predefined function to each polarization or wavelength channel, treating multiplexed channels as independent information carriers. A key challenge is to use coherent interaction between channels as an additional design degree of freedom, so that a new imaging response can be synthesized and electrically accessed within a single planar device.

In this work, Li et al. integrate a voltage-controlled liquid-crystal (LC) cell with a polarization-multiplexed metalens. The metalens encodes two cofocal channels for X- and Y-polarized light with unequal effective apertures and therefore different numerical apertures and cutoff spatial frequencies. Individually, the channels provide higher- and lower-cutoff low-pass responses for bright-field imaging. Within their overlapping aperture, a relative π-phase offset is deliberately introduced. Under 45°-polarized illumination followed by a 45° analyzer, the two fields are projected onto a common polarization basis and coherently superposed. Their shared low-spatial-frequency components are suppressed, while higher spatial frequencies supported only by the larger aperture are retained. A third edge-enhanced transfer function is thus synthesized rather than independently encoded. Calibrated LC voltages select the X-, Y-, and 45°-polarized states without replacing or rotating the metalens.

Experiments at 635 nm verify the three operating states through focusing characterization, modulation-transfer analysis, USAF resolution-target imaging, and imaging of transparent biological specimens. The X-polarized channel produces higher-resolution bright-field images, the Y-polarized channel provides a lower-cutoff bright-field response, and the 45°-polarized state reveals structural boundaries without digital post-processing. A fabricated control metalens with the same effective apertures and nominal focal length but without the relative π-phase offset did not reproduce the edge-enhanced response, directly confirming the essential role of coherent interference. By transforming polarization channels from independent carriers into interacting optical bases, this work establishes a route toward reconfigurable metasurface transfer-function engineering, with potential applications in compact optical preprocessing, label-free contrast enhancement, and integrated microscopy.

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