Spatially Selective Imaging in Color: What You See is What You Want

Spatially selective imaging (SSI) involves sampling a group of pixels from different positions on an encoded object to display a decoded image. Here, SSI is achieved by using off-axis cylindrical Fresnel lens arrays to decode multiple images from an encoded print of structural color pixels. Each image is optically retrieved by separately placing different "keys" (arrays of lenses in different pseudorandom configurations) over the same encoded print, and then each image is digitally reconstructed for visualization. In addition, a detailed analysis is presented on the designed lenses and pixels, which are all fabricated by two-photon polymerization lithography. Though Fresnel lenses are susceptible to chromatic aberrations, the results show that they can be used for imaging pixels that produce a wide range of colors at low numerical aperture (NA ≈0.2). The images have acceptable color contrast, corresponding to a simulated normalized modulation transfer function (MTF) of ≈0.6 averaged across wavelengths in the visible spectrum. This work can find applications in optical information security devices.