Authors: S. Banu, S. Birtwell, Y. Chen, G. Galitonov, H. Morgan and N. Zheludev
Affilation: University of Southampton, United Kingdom
Pages: 34 - 37
Keywords: diffraction, optical tagging, medical optics, biotechnology
Here we describe a new method for encoding small beads which allows for non-contact reading. The tagging technique is based on fabricating a nano-structured pattern on the surface of the particle, which is only a few microns in size. The pattern is read by detecting the spatial distribution of laser light diffracted by the tag. Encoding information on the tag therefore requires creating many different patterns, which can produce large numbers of unique distributions of diffracted light. In the simplest implementation, the pattern is a miniature diffraction grating, where information is coded in the pitch or spatial dimensions of the grating. The encoding capacity of such a tag can be greatly increased, up to million unique codes by fabricating tags with several overlapping gratings and up to 1012 codes by using two-dimensional diffraction. In order to demonstrate this tagging concept, a chip library of chromium gratings was manufactured on a glass substrate using e-beam lithography. We have been able to demonstrate tags up to order three (containing three superimposed gratings) that are fully distinguishable by diffraction. This provides a capacity of about 68,000 distinguishable tags.<br>We have also created biologically compatible barcodes on SU8 photopolymer, patterned using photolithography.