Electric Spaser in the Extreme Quantum Limit

Abstract

We consider theoretically the spaser excited electrically via a nanowire with ballistic quantum conductance. We show that in the extreme quantum regime, i.e., for a single conductance-quantum nanowire, the spaser with the core made of common plasmonic metals, such as silver and gold, is fundamentally possible. For ballistic nanowires with multiple-quanta or non-quantized conductance, the performance of the spaser is enhanced in comparison with the extreme quantum limit. The electrically-pumped spaser is promising as an optical source, nanoamplifier, and digital logic device for optoelectronic information processing with speed ∼ 100 GHz to ∼ 100 THz. Active or gain nanoplasmonics was introduced [1] by spaser (surface plasmon amplification by stimulated emission of radiation). The spaser is a nanoscale quantum generator and ultrafast nanoamplifier of coherent localized optical fields [1][2][3][4][5]. The spaser is a nanosystem constituted by a plasmonic metal and a gain medium. The spaser is based on compensation of optical losses in metals by gain in the active medium (nanoshell) overlapping with the surface plasmon (SP) eigenmodes of the metal plasmonic nanosystem. There are many experimentally observed and investigated spasers where the gain medium consisted of dye molecules [6][7][8], unstructured semiconductor nanostructures and nanoparticles [9][10][11][12][13][14][15][16][17][18], or quantum-confined semiconductor heterostructures: quantum dots (QDs) [19,20], quantum wires (QWs), or quantum wells [21].Classified by mode confinement, there are the spasers with one-dimensional [9,11,13], two-dimensional [10], or three-dimensional (3d) confinement [6,7,18]. The spasers can also be classified by the spasing-eigenmode type, which can be either localized surface plasmons (SPs) [6,7,14,18], or surface plasmon polaritons (SPPs) [22,23] as in the rest of the cases. Among the observed spasers, most are with optical pumping, including all the spasers with the strong 3d confinement [6,7,14,18]. Only few SPP spasers, whose confinement and losses are not strong, are with electric pumping [9,11,13].There have been doubts expressed in the literature regarding viability of the nanospaser with the strong 3d confinement [24], especially with electrical pumping [25]. In a direct contrast, the possibility of the optically pumped strongly 3d-confined spaser has been both theoretically shown [1,3,26,27] and experimentally demonstrated [6,7,14,18]. Here we theoretically establish that the electrically-pumped spaser is fundamentally possible. A principal difference of our theory from the previous works [24,25] is that we consider ballistic, quantum electron transport instead of classical, dissipative one. Another important difference is that the contradicting theoretical work [24,25] on spasers (sometimes also called plasmonic nanolasers) has ignored distinction between the threshold condition of spasing and the condition of developed spasing with N n ∼ 1 quanta (SPs) per generating mode. While for macroscopic lasers with enormousl...

Advances in small lasers

“…Particularly for direct electrical modulation, which will be important for communication applications, factors like non-linear gain compression restrict the modulation bandwidth before the  p limit is reached 23 . Small laser cavities have also been shown to significantly modify the rate of spontaneous emission 17,19,20 which can enhance the modulation bandwidth, particularly if the cavity is used as a light emitting diode rather than a laser [23][24][25][26] . In optical signal processing applications however, optical modulation bandwidth could approach the photon lifetime limit 27 .…”

Fano Resonance in an Electrically Driven Plasmonic Device

“…Finite-difference time-domain (FDTD) calculations reveal that this resonance is due to interference between the nanoparticle and electrodes dipolar fields, and can be conveniently controlled by the structural parameters. Electrically driven plasmonic devices may offer unique opportunities as a research tool and for practical applications [1][2][3][4][5] . In such devices, current that flows across a metallic tunnel junction…”

Spaser operation below threshold: autonomous vs driven spasers

“…A possible solution for this situation could be an increase in the efficiency of an active medium, as was suggested in Ref. [13], in which the use of ballistic quantum wires with low-levels of quantum fluctuations was proposed.…”

“…It seems, however, that a single 3-D confined autonomously generating spaser may only have a limited use [3,9,10,13]. The use of a spaser array distributed in metamaterials may have much better perspective [14][15][16][17][18][19].…”