ABSTRACT
A concept for an optical holographic security tag is proposed and demonstrated. When illuminated with a laser beam, the image scattered from the tag projects a Quick Response code which encodes identifying information. The image also carries pseudorandom speckle noise, from which a unique speckle pattern "fingerprint" is derived. We show numerically that the tag is unclonable without access to a secret key - the starting conditions of the design algorithm. However, given the key, it is straightforward to reproduce a tag exhibiting the expected fingerprint. Several tags have been realized, implemented as plasmonic meta-holograms, and characterized experimentally. The robustness of the tag to fabrication error and its resilience to counterfeiting are studied in detail and demonstrated experimentally.
ABSTRACT
We present a direct measurement of short-wavelength plasmons focused into a sub-100 nm spot in homogeneous (translation invariant) 2D space. The short-wavelength (SW) surface plasmon polaritons (SPP) are achieved in metal-insulator-insulator (MII) platform consisting of silver, silicon nitride, and air. This platform is homogeneous in two spatial directions and supports SPP at wavelength more than two times shorter than that in free space yet interacts with the outer world through the evanescent tail in air. We use an apertureless (scattering) near-field scanning optical microscope (NSOM) to map directly the amplitude and phase of these SW-SPP and show they can be focused to under 70 nm without structurally assisted confinement such as nanoantennas or nanofocusing. This, along with the use of visible light at 532 nm which is suitable for optical microscopy, can open new directions in direct biological and medical imaging at the sub-100 nm resolution regime.
