Imaging has always been a major application of optics. Since Abbe and Rayleigh it had been taken for granted that details finer than have a wavelength cannot be resolved. Hence. optical microscopy was limited to micron-size objects.
In the last 20 years, different techniques (Scanning, Near-field Optical Micrscopy, Stimulated Emission Depletion microscopy, Photo Activated Localization Microscopy) have demonstrated that imaging with a resolution on the order of 10nm is possible using aptical wavelengths.
This gives access to the "nano-world". These discoveries were the beginning of the exploration of the interaction of light with matter at the nanscale. This is the subject of nanophotonics. Controlling the interaction between light and matter at the nanoscale allows modifying completly the processes of absorption and emission of light. It paves the way to the design of efficient light sources such as energy saving Light Emitting Diodes (LEDs) or the design of single photon sources that can be used for quantum cryptography for example. Light sources of this kind are nano-objetcs that behave like artificial atoms.
It becomes possible to produce light states wich have quantum properties with no classical counterpart, a key ingredient for the development of quantum information.
Solid-state nanoscale light sources fabrication rely on the development of nanochemistry or semiconductor microfabrication. These powerful techniques are also used to design efficient absorbers that can be used for optimized photovoltaic cells or sensors widely used in bionanoscience and medecine. In order to enhance these interactions, light length using new objects calles optical antennas, often made with nanometallic structures. Let us finally mention that bu structuring the matter at a length scale smaller than the wavelength allows designing new materials called metamaterials with optical properties otherwise not available. Application include negative index materials, materials with magnetic properties at the optical wavelengths, invisibility cloak to name a few.