Highly directional plasmonic nanolaser based on high-performance noble metal film photonic crystal

A fundamental problem in the integration of photonic elements is the problem of the light localization and the creation of nanolocalized laser sources of radiation. A new approach in the miniaturization of lasers is the approach based on using plasmon fields instead of photon fields. Plasmons arise from the interaction of the oscillations of the electron density and the electromagnetic fields that excite them. Accordingly, the electromagnetic effects caused by these fields occur in the subwavelength region near the surfaces, namely, in the nanometer range. Therefore, the approach allows to overcome the diffraction limitation on the laser size. Plasmonic nanolaser is a nanoscale (at least in one dimension) quantum generator of nanolocalized coherent plasmon fields. The nanoscopic in all three dimensions plasmon nanolaser has a different name: SPASER (Surface Plasmon Amplification by Stimulated Emission of Radiation). It is based on patterned metal film. The precision of formed structures and the dielectric properties of the metal are critical factors in determining any plasmonic device performance. Surface and morphology inhomogeneities should be minimized to avoid SPP scattering during propagation and etching anisotropy. Moreover, the metal should have high conductivity and low optical absorption to enhance optical properties and reduce losses. Some researchers focused on developing new low-loss materials (nitrides, highly-doped semiconductors, semiconductors oxides, or two-dimensional materials), but silver and gold are the most commonly used materials in optics and plasmonics due the lowest optical losses in visible and near infrared wavelength range. Recently, we have presented plasmonic nanolaser built on ultra-smooth silver films. Nanoscale structure in metallic films are typically fabricated by a two-step process. Metals are first deposited using evaporation or sputtering on a substrate and then patterned with focused-ion-beam milling or e-beam lithography and dry etching. If the deposited films are polycrystalline, etch rates vary for different grain orientations and grain boundaries. Therefore, the patterned structures could differ from each other. One of the possible solutions is to deposit singlecrystalline metals, which will be etched more uniformly and lead to precise structures. Another approach deals with large grain (<300 nm) polycrystalline film preparation. The fabricated silver films showed ultra-low losses (40 cm−1). Built on it a plasmonic laser demonstrated the lasing at 628 nm with a linewidth of 1.7 nm and a directivity of 1.3.