Plasmonics and Nanophotonics
Plasmonics and nanophotonics encompass the study and application of light-matter interactions at length scales smaller than the wavelength of light. These fields exploit phenomena including surface plasmon polaritons, localized surface plasmons, photonic crystals, and quantum confinement effects to achieve optical functionalities impossible with conventional optics. By manipulating light at the nanoscale, researchers and engineers can concentrate electromagnetic energy into subwavelength volumes, enhance optical processes by orders of magnitude, and create materials with optical properties not found in nature.
Surface plasmons are collective oscillations of free electrons at metal-dielectric interfaces, coupling to electromagnetic waves to form hybrid excitations that propagate along surfaces or remain localized around nanostructures. These plasmonic modes enable field enhancement for sensing, spectroscopy, and nonlinear optics. Photonic crystals, with periodic dielectric structures, create photonic bandgaps that control light propagation analogous to how semiconductor crystals control electron flow. Metamaterials extend these concepts further, using engineered subwavelength structures to achieve effective optical properties including negative refractive index and perfect absorption.
Quantum-confined nanostructures such as quantum dots, nanowires, and two-dimensional materials exhibit size-dependent optical properties arising from confinement of charge carriers. These materials enable tunable light emission and absorption across the electromagnetic spectrum, with applications ranging from displays and solar cells to biological imaging and quantum information processing. This category provides comprehensive coverage of the physics, materials, devices, and applications that define plasmonics and nanophotonics.
Articles
Nanophotonic Structures
Control light with nanostructures including photonic crystals, photonic crystal fibers, photonic crystal cavities, slow light structures, superprism effects, negative refraction, self-collimation, photonic crystal lasers, photonic crystal sensors, nanobeam cavities, whispering gallery modes, bound states in continuum, Fano resonances, exceptional points, and topological effects.
Plasmonic Devices
Manipulate light at nanoscale using plasmons. Topics include surface plasmon polaritons, localized surface plasmons, plasmonic waveguides, plasmonic modulators, plasmonic sensors, extraordinary optical transmission, plasmonic antennas, spasers and nanolasers, hot electron generation, plasmonic photocatalysis, plasmonic solar cells, metamaterial perfect absorbers, hyperbolic metamaterials, transformation optics, and cloaking devices.
Quantum Dots and Nanocrystals
Exploit quantum confinement effects for tunable optical properties. This section addresses colloidal quantum dots, epitaxial quantum dots, perovskite nanocrystals, carbon dots, silicon nanocrystals, single quantum dot spectroscopy, quantum dot lasers, quantum dot LEDs, quantum dot solar cells, quantum dot photodetectors, quantum dot displays, biological labeling, quantum dot tracking, blinking suppression, and surface functionalization.
Two-Dimensional Materials Photonics
Harness atomically thin materials for next-generation photonic devices. Topics include graphene photonics, transition metal dichalcogenides, black phosphorus, hexagonal boron nitride, MXenes for photonics, van der Waals heterostructures, twisted bilayer systems, exciton-polaritons, valley photonics, strain engineering, electrostatic tuning, photodetectors, modulators, light sources, and nonlinear optics.
Fundamental Concepts
Surface Plasmon Polaritons
Surface plasmon polaritons (SPPs) are electromagnetic waves coupled to collective electron oscillations that propagate along metal-dielectric interfaces. These hybrid modes arise when light couples to the free electrons in metals such as gold, silver, or aluminum at frequencies below the plasma frequency. SPPs exhibit shorter wavelengths than free-space light at the same frequency, enabling subwavelength confinement and field enhancement. The evanescent field extending from the surface into both metal and dielectric makes SPPs sensitive to changes in the local environment, enabling biosensing and chemical detection applications.
Localized Surface Plasmons
When metals are structured at the nanoscale, collective electron oscillations become confined to the nanostructure rather than propagating as surface waves. These localized surface plasmon resonances (LSPRs) occur at frequencies determined by the particle size, shape, composition, and local dielectric environment. At resonance, the local electromagnetic field near the nanostructure is enhanced by factors of hundreds or thousands compared to the incident field. This enhancement underlies surface-enhanced Raman spectroscopy (SERS), where molecules near plasmonic nanostructures exhibit Raman signals enhanced by up to twelve orders of magnitude.
Photonic Crystals
Photonic crystals are periodic dielectric structures with lattice constants comparable to optical wavelengths. The periodic modulation of refractive index creates photonic bandgaps where light cannot propagate, analogous to electronic bandgaps in semiconductors. One-dimensional photonic crystals form Bragg reflectors used in laser mirrors and optical filters. Two-dimensional and three-dimensional structures enable more sophisticated light control, including slow light effects, negative refraction, and complete confinement of light in defect cavities. Photonic crystal waveguides route light along defect channels with sharp bends impossible in conventional optics.
Quantum Confinement
When the dimensions of a semiconductor structure approach the de Broglie wavelength of charge carriers, typically a few nanometers, the continuous energy bands of the bulk material transform into discrete energy levels. This quantum confinement effect enables tuning of optical properties simply by changing the size of the nanostructure. Quantum dots confine carriers in all three dimensions, producing atom-like discrete energy levels with narrow emission linewidths. The ability to tune bandgaps through size control, independent of material composition, revolutionized applications in displays, lighting, solar energy, and biological imaging.
Applications
Sensing and Spectroscopy
Plasmonic sensors exploit the sensitivity of surface plasmon resonances to local refractive index changes for label-free detection of chemical and biological analytes. Surface plasmon resonance (SPR) instruments measure binding kinetics of biomolecular interactions in real time. SERS provides chemical fingerprinting with single-molecule sensitivity when molecules adsorb on roughened metal surfaces or nanoparticle aggregates. Plasmon-enhanced fluorescence increases brightness and photostability of fluorescent labels near metal nanostructures.
Display and Lighting Technologies
Quantum dots have transformed display technology by providing pure, saturated colors impossible with traditional phosphors or organic emitters. Quantum dot enhancement films convert blue LED backlight into precise red and green wavelengths for wider color gamuts in LCD displays. Direct quantum dot electroluminescent displays (QLED) promise even higher efficiency and color purity. In lighting applications, quantum dot phosphors enable warm white LEDs with excellent color rendering.
Solar Energy Conversion
Nanophotonic structures enhance solar cell efficiency through multiple mechanisms. Plasmonic nanoparticles concentrate light into thin absorber layers, enabling reduced material use without sacrificing absorption. Quantum dots provide multiple exciton generation, where single high-energy photons create multiple electron-hole pairs, potentially exceeding the Shockley-Queisser efficiency limit. Photonic crystal structures create optical confinement that increases the effective optical path length in thin-film cells.
Information Processing
Nanophotonic devices enable optical interconnects with bandwidth and energy efficiency surpassing electronic alternatives. Plasmonic waveguides confine light to dimensions compatible with electronic circuits, potentially enabling on-chip optical data transmission. Single quantum dots coupled to photonic crystal cavities provide strong light-matter interactions for quantum information processing. Nonlinear optical processes enhanced by plasmonic fields enable all-optical switching and modulation.
About This Category
Plasmonics and nanophotonics represent the frontier of optical science and technology, where the manipulation of light at the nanoscale enables capabilities beyond the reach of conventional optics. The ability to concentrate, enhance, and control electromagnetic fields at subwavelength dimensions opens possibilities in sensing, energy conversion, information processing, and medicine. This category covers the fundamental physics, materials, fabrication methods, and applications that define these interconnected fields, providing the technical foundation for understanding and advancing nanoscale photonics.