Optical microbarcodes have recently received a great
deal of interest
because of their suitability for a wide range of applications, such
as multiplexed assays, cell tagging and tracking, anticounterfeiting,
and product labeling. Spectral barcodes are especially promising because
they are robust and have a simple readout. In addition, microcavity-
and microlaser-based barcodes have very narrow spectra and therefore
have the potential to generate millions of unique barcodes. This review
begins with a discussion of the different types of barcodes and then
focuses specifically on microcavity-based barcodes. While almost any
kind of optical microcavity can be used for barcoding, currently whispering-gallery
microcavities (in the form of spheres and disks), nanowire lasers,
Fabry–Pérot lasers, random lasers, and distributed feedback
lasers are the most frequently employed for this purpose. In microcavity-based
barcodes, the information is encoded in various ways in the properties
of the emitted light, most frequently in the spectrum. The barcode
is dependent on the properties of the microcavity, such as the size,
shape, and the gain materials. Various applications of these barcodes,
including cell tracking, anticounterfeiting, and product labeling
are described. Finally, the future prospects for microcavity- and
microlaser-based barcodes are discussed.