A relatively basic way to measure the spectra of materials is with micro-photoluminescence (ÁPL). A microscope objective, essentially a lens, focuses light to a small area, on the order of magnitudes of a couple of microns. This area is limited by imperfections in the lens along with other aberrations.
To overcome these limitations, nano-optics uses other techniques and nanostructures, such as the optical fiber probe. An optical probe, or fiber tip, can focus light into areas that are nanometers in diameter.
Light is focused out the diameter of the fiber tip which is nanometers in diameter. Usually light is limited by the diffraction limit: the size which light can be focused is limited by the wavelength of that light. With nano-optics, this limit can be overcome.
Figure 2: Shows the difference between the way a microscope objective and an optical fiber probe are able to focus light into a small area. This small area is what gives us our high spatial resolution.