Demo: PolarTag -- Invisible Data with Light Polarization

Visual tags (e.g., barcodes, QR codes)have become a prominent method of conveying digital information. Existing tags commonly rely on obtrusive visual patterns. Some methods of imperceptibly encoding data include using screens~\citekennedy2013visually or UV ink~\citemeruga2012security, complicating the tags with active components or requiring special manufacturing processes. We propose \name, a new design paradigm of passive visual tags which utilizes light polarization to unobtrusively encode data. \name\ consists of a thin, inexpensive polarizing film with layers of birefringent materials (e.g., everyday transparent tapes) judiciously applied atop. The birefringent layers disperse the polarization direction of outgoing light rays, resulting in color patterns only visible when viewed through a second polarizer. Such patterns are utilized to encode data. This color-changing feature can be used to boost the robustness of tag detection and support arbitrary tag shapes and designs that are not bound by geometric restrictions. In this demo, we present real-time decoding of invisible \name s with a mobile device.