Microdisk laser A microdisk laser is a very small laser consisting of a disk with
quantum well structures built into it. Its dimensions can exist on the micro-scale or nano-scale. Microdisk lasers use a
whispering-gallery mode resonant cavity. The light in cavity travels around the perimeter of the disk and the
total internal reflection of photons can result in a strong light confinement and a high quality factor, which means a powerful ability of the microcavity to store the energy of photons coupled into the cavity.
Photonic crystal laser Photonic crystal lasers utilize periodic
dielectric structures with different refractive indices; light can be confined with the use of a photonic crystal microcavity. In dielectric materials, there is orderly spatial distribution. When there is a defect in the periodic structure, the two-dimensional or three-dimensional photonic crystal structure will confine the light in the space of the diffractive limit and produce the
Fano resonance phenomenon, which means a high quality factor with a strong light confinement for lasers. The fundamental feature of photonic crystals is the photonic bandgap, that is, the light whose frequency falls in the photonic
band gap cannot propagate in the crystal structure, thus resulting in a high reflectivity for incident light and a strong confinement of light to a small volume of wavelength scale. The appearance of photonic crystals makes the
spontaneous emission in the photon gap completely suppressed. But the high cost of photonic crystal impedes the development and spreading applications of photonic crystal lasers.
Nanowire laser Semiconductor nanowire lasers have a quasi-one-dimensional structure with diameters ranging from a few nanometers to a few hundred nanometers and lengths ranging from hundreds of nanometers to a few microns. The width of nanowires is large enough to ignore the
quantum size effect, but they are high quality one-dimensional
waveguides with cylindrical, rectangular, trigonal, and hexagonal cross-sections. The quasi-one-dimensional structure and high feedback provided by scattering of light at the nanowire ends makes it have good optical waveguide and the ability of light confinement. Nanowire lasers are similar to
Fabry–Pérot cavity in mechanism, but different in quantitative reflection coefficients High reflectivity of nanowire and flat end facets of the wire constitute a good resonant cavity, in which photons can be bound between the two ends of the nanowire to limit the light energy to the axial direction of the nanowire, thus meeting the conditions for laser formation. Polygonal nanowires can form a nearly circular cavity in cross section that supports whispering-gallery mode.
Plasmonic nanolaser Nanolasers based on surface plasmons are known as plasmonic nanolasers, with sizes far exceeding the diffraction limit of light. If a plasmonic nanolaser is nanoscopic in three dimensions, it is also called a
spaser, which is known to have the smallest cavity size and mode size. Design of plasmonic nanolaser has become one of the most effective technology methods for laser miniaturization at present. A little bit different from the conventional lasers, a typical configuration of plasmonic nanolaser includes a process of
energy transfer to convert photons into surface plasmons. The oscillation of electrons is determined by the geometrical boundaries of different metal nanoparticles. When its resonance frequency is consistent with the incident electromagnetic field, it will form the localized surface plasmon resonance. In 2009, Mikhail A. Noginov of
Norfolk State University in the
United States successfully verified the LSPs-based nanolaser for the first time. Bound states in the continuum laser confines light in an open system via the elimination of radiation states through destructive interference between resonant modes. All of those new types of nanolasers have high quality factor and can achieve cavity size and mode size approaching the diffraction limit of the light. == Applications ==