**2.1 Confinements approaches**

Nanophotonics combines many important innovation thrust fields, including lasers, photovoltaics, biotechnology, photonics, and nanotechnology. Recently, growing expertise of fusing nanotechnology and photonics has become fundamental, arising outskirts, challenging basic experimentation. It can be divided into three types of confinement techniques: The first is to create nanoscale connections between light and matter by confining light to nanometer-sized dimensions far less than the light's wavelength. The approach that follows is to confine matter to nanometer range, restricting light-matter interactions to nanoscopic scales and characterizing the world of nanomaterials. The final method requires the nanoscale confinement of a photo-process through photochemistry or a light-induced phase transition, and it is used to fabricate photonic structures and functional units at the nanoscale. One method for confining light to a nanometer scale is to use near-field optical transmission, a model in which light is compressed via a metal-coated, tapered optical fiber and then exudes through a tip with an aperture far smaller than the wavelength of incident light. Different methods of confining the dimensions and producing nanostructures for photonic applications are used in nanoscale matter confinement; for example, nanoparticles with exceptional electronic and photonic properties. It's promising to hear that these nanoparticles are now being used in nanophotonic applications including UV absorbers that are used in sunscreen lotions. These nanoparticles may be composed of organic or inorganic materials, such as nanomers, having size-dependent optical properties as they are nanometersized oligomers (with a finite number of identical units) complexed with monomeric organic analogues, and polymers, which are long chain structures with a large number of repeating units. The field of "plasmonics" is made up of metallic nanoparticles that have an interesting optical reaction and an improved

*Nanophotonics: Fundamentals, Challenges, Future Prospects and Applied Applications DOI: http://dx.doi.org/10.5772/intechopen.98601*

electromagnetic field. There are nanoparticles that can up-convert two absorbed IR photons into a visible UV photon, as well as quantum cutters that can down-convert an absorbed vacuum UV photon to two-visible UV photons. A photonic crystal is a hot field of nanomaterials that refers to a periodic dielectric structure with a repeated unit of the order of wavelength of light. Nano-composites are made up of phase-isolated nano-domains of at least two dissimilar materials on a nanometer scale. Each nano-domain in the nano-composite will give the bulk media a unique optical property. Controlling the flow of optical energy between various domains through an energy move (optical communications) is also possible. Nanolithography can be used to build nanostructures, which can then be used to fabricate nanoscale sensors and actuators using nanoscale photo-processes. The ability to confine photo-processes to all around characterized nano-regions, allowing structures to be fabricated in exact geometry and arrangement, is a key feature of nanofabrication. This section will illustrate the fundamentals of nanophotonics by describing the similarities and variations between photons and electrons, as well as confinement effects on photons and electrons caused by optical and electronic interactions at nanoscale range.

### **2.2 Photons and electrons: a comparison of their similarities and dissimilarities**

Photons and electrons are subatomic elementary particles that can function as both particles and waves. Electrons are negatively charged subatomic particles with the smallest mass, while photons are massless quanta of energy that leads to electromagnetic radiations. The intrinsic angular momentum of an electron is a half integer of ħ (spin = 1/2), indicating that it is a fermion. As a result, if more than one electron occupies the same space, each electron's properties should be unique and conform to Fermi-Dirac statistics. The Pauli's exclusion principle depicts the strong interaction of electrons (fermions). Photon, on the other hand, is an elementary particle with both electric and magnetic fields governed by Maxwell's equations, as well as an inherent angular momentum of integer magnitude of ħ (spin = 1), indicating that it is a boson. According to Bose-Einstein statistics, photons do not associate with other photons, so more than one photon can occupy a single quantum state. There are two ways in which photons differ from electrons: (I) Photons are vector fields (light has the ability to be polarized), while electron wavefunctions are scalar; and (II) Electrons have charge and spin, while photons do not.

Atoms are made up of nuclei (neutrons and protons) surrounded by electrons. Since light (photons) that interacts with nuclei need a lot of energy (gamma rays), hence X-ray to infrared light only interacts with electrons, regulating photon/electron interactions. Light energizes an electron cloud with one particle, which emits a photon, which interacts with another electron cloud in transparent materials, while light can be absorbed and emitted in opaque materials by a resonant electron and photon connection. Quantum representation shows that electrons and photons are analogous and have several characteristics. **Table 1** summarizes the similarities in features of electrons and photons.

### **2.3 Confinement of photons and electrons**

Photon and electron propagation can be dimensionally restricted by reflecting or backscattering these particles in spaces of varying interaction potential along their propagation path, thereby confining their propagation to a single direction or range of directions. According to classical mechanics, electrons and photons are fully confined in confinement areas. Since the energy of electrons trapped within potential energy limits is less than the potential energy due to the boundary, they remain


**Table 1.**

*An overview of similarities in characteristics of electrons and photons.*

## **Figure 1.**

*Confinement of photons and electrons in different dimensions with propagation along z-axis [6].*

completely enclosed within the walls. The wave picture of photons and electrons, on the other hand, does not indicate this. Photons can be used to envision confinement by collecting light in an environment with a high refractive index or high surface reflectivity, whereas a waveguide or cavity resonator can serve as a confining field [5]. The **Figure 1** depicts the classic picture of light direction (trapping) due to total internal reflection using a beam line. The confinement in a planar waveguide is only along the vertical x-direction, while the propagation direction is along the z-axis whereas the confinement of a fiber or a channel waveguide is in the x and y directions. A microsphere is a three-dimensional representation of an optical medium that confines light in all directions by comparing the refractive

*Nanophotonics: Fundamentals, Challenges, Future Prospects and Applied Applications DOI: http://dx.doi.org/10.5772/intechopen.98601*

index of the leading and surrounding mediums. As a result, the disparity n1/n2 functions as a scattering potential, obstructing light propagation. Light functions as a plane wave with a continuous propagation constant, similar to the propagation vector k in free space; the electric field circulation has a distinct spatial profile in the direction of propagation (z axis) and in the confining direction [6].
