Multiple holographic security images from nanoscale 3D printing

Researchers at the Singapore University of Technology and Design (SUTD)  have used 3D printing to develop something that not only looks cool, but can also be used to deter counterfeiting. The device, which the scientists call “holographic colour prints,” creates images that appear as a regular colour print under white light. But under red, green or blue laser illumination, the device projects up to three different holograms.

Conventional optical security devices provide authentication by manipulating a specific property of light to produce a distinctive optical signature. But the researchers believe these can be easily imitated. So they designed a pixel that overlays a structural colour element onto a phase plate to control both the phase and amplitude of light. They then arrayed the pixels into monolithic prints. Nanostructured posts with different heights were used as structural coloured filters to modulate the amplitude of light.

The researchers also created an algorithm that takes multiple images as its input and generates an output file to determine the positions of different phase and coloured filter elements. They then used a nanoscale 3D printer to create a holoscopic print of painter Luigi Russolo’s 1910 painting “Perfume.” The colour print is visible under ambient white light. Different thicknesses of polymerized cuboid were used to form three multiplexed holograms, projected as a red thumbprint, a green key, and blue letters that read “SECURITY.” The images were embedded within the print.

The holographic colour prints can be easily verified, according to the researchers, but are difficult to imitate. Information in the prints is encoded only in the surface relief of a single polymeric material, so nanoscale 3D printing could then be used to mass manufacture customized masters by nanoimprint lithography.

The research is documented in a paper entitled “Holographic colour prints for enhanced optical security by combined phase and amplitude control.” The research was published in Nature Communications.

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