Researchers have demonstrated a simple new way to focus laser beams to a much tighter spot than is possible with conventional lenses and mirrors, making it possible to store up to 3T (terabytes) of data on a CD-sized optical disk.
Applied Physics Letters 89: 093120 details the research results of integrating a resonant optical antenna right on a laser (which would make it relatively easy and economical to do commercially.)
Spot sizes of 20 nanometers have already been achieved.
Just by way of comparison, the new high-definition DVDs including Blue-Ray only store about 25G per side with their much larger dot size.
Reading between the lines (so to speak) since I didn’t pay to see the whole article, the new approach appears to use two tiny antennas and thus probably works on an interference pattern basis but that doesn’t really matter unless you are designing lasers, the point is that it appears to work and be commercially viable even for relatively inexpensive devices like today's CD-R and DVD-R drives.
Achieving cheap terabyte storage capacity would probably trigger as big a technology revolution as the original CD-ROM did.