Soochow University researchers developed an ultrathin film based on light-field imaging — a technology that creates 3D images by capturing the direction and intensity of all light rays in a scene. The 25-µm-thick film, which is made with low-cost materials, provides a glass-free approach to 3D imaging and offers a full field of view. It produces 3D images that are viewable under normal light and without the need for special reading devices. According to the researchers, the algorithm and nanopatterning technique used to make the film could be extended to other applications. For example, the nanopatterns could be created on a transparent display screen instead of a film. In addition to the reflective light-field imaging film, the researchers developed an algorithm that allows both the position and angular information for the light field to be recorded with high density, to overcome drawbacks that affect many current approaches to 3D imaging. These drawbacks include a limited viewing angle and/or low light efficiency. The researchers also developed a self-releasing, ultraviolet-curable nanoimprinting lithography technique that is precise and cost-effective. One side of the film is patterned with a microarray of reflective focusing elements that act like tiny cameras. The other side is patterned with a microarray that encodes the image to be displayed. A plenoptic function built into the film generates a dense reflective light field. “The powerful microfabrication approach we used allowed us to make a reflective focusing that was extremely compact — measuring just tens of microns,” research team leader Su Shen said. “This lets the light radiance be densely collected, creating a realistic 3D effect.” The images created by the film appear to “float” on top of the film and can be clearly viewed from all angles. The created image also appears to have physical depth, Shen said. Researchers developed an ultrathin film that can create a detailed 3D image that is viewable under normal illumination without any special reading devices. They demonstrated the new film by using it to create a 3D image of a cubic die that can be viewed from 360°. Courtesy of Su Shen, Soochow University. To demonstrate the film’s capabilities, the researchers created a 3D image of a cubic die that could be observed clearly from 360°. The die image measured 8 × 8 mm. The depth of the image ranged from 0.1 to 8.0 mm under natural lighting conditions. In addition, the team designed and fabricated an imaging film with a floating logo that can be used as a decorative element — to embellish a mobile phone, for example. “Achieving glass-free 3D imaging with a large field of view, smooth parallax, and a wide, focusable depth range under natural viewing conditions is one of the most exciting challenges in optics,” Shen said. “Our approach offers an innovative way to achieve vivid 3D images that cause no viewing discomfort or fatigue, are easy to see with the naked eye, and are aesthetically pleasing.” With additional development, the film could be incorporated into virtual and augmented reality devices and used as a visual security feature. “It can be easily laminated to any surface as a tag or sticker or integrated into a transparent substrate, making it suitable for use as a security feature on banknotes or identity cards,” Shen said. The team is working to commercialize its fabrication process by developing a double-sided nanoimprinting machine that will make it easier to achieve the precise alignment required between the micropatterns on each side of the film. The research was published in Optics Letters (www.doi.org/10.1364/OL.463117).