Khurgin Jacob B, Sun Greg
Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Opt Express. 2012 Jul 2;20(14):15309-25. doi: 10.1364/OE.20.015309.
We develop a theoretical model for the semiconductor generator of the sub-wavelength surface plasmons, operating on a single mode and often referred to as a spaser. We show that input-output characteristics of the single mode spaser does not exhibit nonlinearity inherent in most lasers, but the linewidth of the emission collapses, as in any laser which allows us to define the threshold. Our rigorous derivations show that as long as the mode remains substantially sub-wavelength in all three dimensions, the threshold current (power) shows virtually no dependence on the gain material and geometry of the active layer and is determined solely by the intrinsic loss of the metal in the device. For the semiconductor single mode surface plasmon generators operating in the telecommunication range the threshold current is on the order of 10-20 mA, and the threshold current density grows fast with the decrease of the device size reaching 100's of kA/cm(2) or more. This fact makes coherent sources of sub-wavelength SP's unattainable from our point of view, but there exists a room for efficient broad-band incoherent SP sources either optically or electrically pumped.
我们为亚波长表面等离子体激元的半导体发生器开发了一种理论模型，该发生器工作在单模状态，通常被称为表面等离子体激元激射器（spaser）。我们表明，单模表面等离子体激元激射器的输入-输出特性并不表现出大多数激光器所固有的非线性，但发射线宽会变窄，这与任何激光器一样，使我们能够定义阈值。我们的严格推导表明，只要模式在所有三个维度上基本上仍为亚波长，阈值电流（功率）实际上就不依赖于增益材料和有源层的几何形状，而仅由器件中金属的固有损耗决定。对于工作在电信波段的半导体单模表面等离子体激元发生器，阈值电流约为10 - 20 mA，并且阈值电流密度随着器件尺寸的减小而快速增长，达到数百kA/cm² 或更高。从我们的角度来看，这一事实使得亚波长表面等离子体激元的相干源难以实现，但对于光光学光泵浦的高效宽带非相干表面等离子体激元源仍有发展空间，无论是光泵浦还是电泵浦。
