Investigations of influences of spontaneous emission properties on surface plasmon polariton amplifications with the rate-equation theory

The influences of the position-related spontaneous emission properties of gain media on gain and amplified spontaneous emission (ASE) noise characteristics of surface plasmon polariton (SPP) amplification are investigated with rate-equation theory in this paper. It is found that both the spontaneous emission rate and the probability of spontaneous emission into the SPP mode of the gain media in an SPP waveguide are position related. Based on this, a rate-equation model considering those spontaneous emission properties is presented. With this model, the influences of the position-related spontaneous emission properties on the gain and ASE noise characteristics of a single-mode dielectric-loaded SPP amplifier are discussed. The results show that the spontaneous emission rate of gain media is enhanced near the metal interface and the probability of spontaneous emission into the SPP mode decreases near both the metal and air interfaces of the amplifier. This gives rise to reduced gain and low ASE output power. Moreover, the noise property of the amplifier may be improved because of the great decrease in the output ASE power.