Plasmonic nanolasers: fundamental properties and applications

Plasmonic nanolasers are a new class of coherent emitters where surface plasmons are amplified by stimulated emission in a plasmonic nanocavity. In contrast to lasers, the physical size and mode volume of plasmonic nanolasers can shrink beyond the optical diffraction limit, and can be operated with faster speed and lower power consumption. It was initially proposed by Bergman and Stockman in 2003, and first experimentally demonstrated in 2009. Here we summarize our studies on the fundamental properties and applications of plasmonic nanolasers in recent years, including dark emission characterization, scaling laws, quantum efficiency, quantum threshold, gain and loss optimization, low loss plasmonic materials, sensing, and eigenmode engineering.

A Low-Threshold Miniaturized Plasmonic Nanowire Laser with High-Reflectivity Metal Mirrors

A reflectivity-enhanced hybrid plasmonic GaAs/AlGaAs core-shell nanowire laser is proposed and studied by 3D finite-difference time-domain simulations. The results demonstrate that by introducing thin metal mirrors at both ends, the end facet reflectivity of nanowire is increased by 30–140%, resulting in a much stronger optical feedback. Due to the enhanced interaction between the surface charge oscillation and light, the electric field intensity inside the dielectric gap layer increases, resulting in a much lower threshold gain. For a small diameter in the range of 100–150 nm, the threshold gain is significantly reduced to 60–80% that of nanowire without mirrors. Moreover, as the mode energy is mainly concentrated in the gap between the nanowire and metal substrate, the output power maintains >60% that of nanowire without mirrors in the diameter range of 100–150 nm. The low-threshold miniaturized plasmonic nanowire laser with simple processing technology is promising for low-consumption ultra-compact optoelectronic integrated circuits and on-chip communications.

Miniaturized GaAs Nanowire Laser with a Metal Grating Reflector

This work proposed a miniaturized nanowire laser with high end-facet reflection. The high end-facet reflection was realized by integrating an Ag grating between the nanowire and the substrate. Its propagation and reflection properties were calculated using the finite elements method. The simulation results show that the reflectivity can be as high as 77.6% for a nanowire diameter of 200 nm and a period of 20, which is nearly three times larger than that of the nanowire without a metal grating reflector. For an equal length of nanowire with/without the metal grating reflector, the corresponding threshold gain is approximately a quarter of that of the nanowire without the metal grating reflector. Owing to the high reflection, the length of the nanowire can be reduced to 0.9 μm for the period of 5, resulting in a genuine nanolaser, composed of nanowire, with three dimensions smaller than 1 μm (the diameter is 200 nm). The proposed nanowire laser with a lowered threshold and reduced dimensions would be of great significance in on-chip information systems and networks.

Electromagnetic analysis of the lasing thresholds of hybrid plasmon modes of a silver tube nanolaser with active core and active shell

Results from the electromagnetic modeling of the threshold conditions of hybrid plasmon modes of a laser based on a silver nanotube with an active core and covered with an active shell are presented. We study the modes of such a nanolaser that have their emission wavelengths in the visible-light range. Our analysis uses the mathematically grounded approach called the lasing eigenvalue problem (LEP) for the set of the Maxwell equations and the boundary and radiation conditions. As we study the modes exactly at the threshold, there is no need to invoke nonlinear and quantum models of lasing. Instead, we consider a laser as an open plasmonic resonator equipped with an active region. This allows us to assume that at threshold the natural-mode frequency is real-valued, according to the situation where the losses, in the metal and for the radiation, are exactly balanced with the gain in the active region. Then the emission wavelength and the associated threshold gain can be viewed as parts of two-component eigenvalues, each corresponding to a certain mode. In the configuration considered, potentially there are three types of modes that can lase: the hybrid localized surface plasmon (HLSP) modes of the metal tube, the core modes, and the shell modes. The latter two types can be kept off the visible range in thin enough configurations. Keeping this in mind, we focus on the HLSP modes and study how their threshold gain values change with variations in the geometrical parameters of the nanotube, the core, and the shell. It is found that essentially a single-mode laser can be designed on the difference-type HLSP mode of the azimuth order m = 1, shining in the orange or red spectral region. Furthermore, the threshold values of gain for similar HLSP modes of order m = 2 and 3 can be several times lower, with emission in the violet or blue parts of the spectrum.