Nanophotonics studies how light behaves and can be controlled at the nanometer scale, where structures are comparable in size to the wavelength of light. A central goal is to confine and manipulate light in volumes much smaller than its wavelength, enabling strong light–matter interactions and highly integrated optical technologies.

A key platform is the photonic crystal, a material with a periodic variation in refractive index. This periodicity creates photonic band gaps that prevent light of certain frequencies from propagating, similar to how electronic band gaps work in semiconductors. By introducing defects into photonic crystals, light can be tightly confined in cavities or guided along specific paths with minimal loss, which is valuable for compact optical circuits, lasers and sensors.

Another important approach is the use of plasmonic structures, where light couples to collective electron oscillations at metal surfaces. These surface plasmons can localize electromagnetic fields to extremely small regions, greatly enhancing local field strengths. This enables strong enhancement of fluorescence, nonlinear optical effects and sensitivity in nanoscale sensors, although losses in metals remain a challenge.

Nanophotonics also explores hybrid systems where photonic crystals, plasmonic components and quantum emitters are combined. Strong coupling between single photons and individual quantum emitters can be engineered, opening pathways toward quantum information processing, single photon sources and secure communication. Integration of these elements on chips aims to bring together electronics and photonics at similar scales.

Overall, nanophotonics seeks to control light with nanometer precision to achieve compact, efficient and functional optical devices, with applications spanning telecommunication, sensing, imaging and quantum technologies.