Researchers have developed an electrically controlled flat lens that can switch between conventional imaging and edge-enhanced imaging, revealing structural details that may be difficult to distinguish using ordinary optical techniques. The technology could contribute to more compact microscopes and future optical imaging systems.
The international research team, led by scientists at Pohang University of Science and Technology (POSTECH) in South Korea, demonstrated a metalens that changes how it processes light in response to an electrical signal. Their findings, published in Opto-Electronic Science, introduce a way to control image contrast without relying on digital image processing.
Conventional microscopes often struggle to reveal the boundaries of transparent biological structures because these specimens produce relatively little contrast. Techniques designed to overcome this limitation can require additional optical components, increasing the complexity and size of imaging equipment.
The new device addresses this challenge by combining a polarization-sensitive metalens with a voltage-controlled liquid crystal cell. A metalens is an exceptionally thin optical element made from microscopic structures that manipulate light. In this design, electrical signals change the polarization of incoming light, allowing the system to select between three imaging states.
Two states produce conventional bright-field images with different optical resolutions. The third uses interference between two light channels to suppress background information while retaining details associated with structural boundaries. This produces edge-enhanced images directly through the optical system, without digital post-processing.
To demonstrate the technology, the researchers tested the device using a standard optical resolution target and several biological specimens, including earthworm tissue, onion epidermal cells and plant stem sections. The experiments showed clearer structural boundaries in edge-enhanced mode, including cell outlines that were less distinct in conventional images.
The fabricated metalens measures just 570 micrometres in diameter and was tested using light with a wavelength of 635 nanometres. Its electrically controlled operation also eliminates the need to mechanically rotate the metalens when changing imaging modes.
Although the current system remains a proof-of-concept and requires specific illumination conditions and additional optical components, the findings establish a promising approach to reconfigurable optical image processing.
By enabling different imaging functions within a compact optical architecture, the research could support future developments in miniaturized microscopy, label-free biological imaging and integrated optical technologies.
Keywords: polarization-multiplexed metalens, transfer-function engineering, interference, tunable
liquid crystals
