High-resolution grayscale image hidden in a laser beam

TLDR: This work proposes and experimentally demonstrates an approach to hide a high-resolution grayscale image in a square laser beam with a size of less than half a millimeter, which provides new opportunities for various applications, including encryption, imaging, optical communications, quantum science and fundamental physics.

Abstract: Images perceived by human eyes or recorded by cameras are usually optical patterns with spatially varying intensity or color profiles. In addition to the intensity and color, the information of an image can be encoded in a spatially varying distribution of phase or polarization state. Interestingly, such images might not be able to be directly viewed by human eyes or cameras because they may exhibit highly uniform intensity profiles. Here, we propose and experimentally demonstrate an approach to hide a high-resolution grayscale image in a square laser beam with a size of less than half a millimeter. An image with a pixel size of 300 × 300 nm is encoded into the spatially variant polarization states of the laser beam, which can be revealed after passing through a linear polarizer. This unique technology for hiding grayscale images and polarization manipulation provides new opportunities for various applications, including encryption, imaging, optical communications, quantum science and fundamental physics. A technique for encoding images in the polarization distribution of a light beam has been demonstrated by a team in the UK and China. Conventionally, black and white images are generated by creating optical patterns in which the light intensity varies with position. Now, Shuang Zhang at the University of Birmingham in the UK, Xianzhong Chen at the Heriot-Watt University in the UK and co-workers have produced grayscale images by spatially varying the polarization in a light beam rather than the light intensity. Since the light beam has a uniform intensity, the images are invisible to the eye until a polarizer is inserted into the beam, thus making the method potentially useful for optical image encryption. The researchers generated an image of the famous physicist James Maxwell by using a reflective metasurface to alter the polarization of a reflected laser beam.