A first 50 Gbps silicon photonic link was demonstrated in 2010 by Intel cooperation integrated with four hybrid silicon lasers [
3]. From many researchers’ viewpoints, such photonic link is very practical and potent, but not a permanent solution because of size mismatch between hybrid lasers and electronic components on the chip. The deeply sub-wavelength size SP emitter has the potential to be the next generation light source for highly compact silicon photonic interconnect [
1]. Analogous to other light sources, an ordinary SP diode produces/excites SPs and an SP laser diode produces coherent SPs, but both of them operate on the interactions (energy coupling) between the optical emitters and the metal. An SP laser is termed surface plasmon amplification by stimulated emission of radiation (SPASER), a nanoplasmonic counterpart of light amplification by stimulated emission of radiation (LASER), and was first suggested by Bergman and Stockman in 2003 [
10]. In 2008, the first lasing SPASER was demonstrated [
11], and then in 2009, two types of nano SPASERs were demonstrated [
12,
13]. These SPASERs were all optically pumped. Recently, quite a few SP diodes including Si-based one have been reported [
14-
17]. A conceptual structure for a (laser) SP diode is shown in Fig. 3(a), which consists of an active (gain) layer and a noble metal layer at least. Additionally, we insert an index matching layer on each side of the active layer for higher efficiency SP generation. When the active layer is organic semiconductor, the structure is known as an organic light emitting diode (OLED), which is naturally an SP diode due to the very thin thickness of the organic layer [
15]. Our group observed a strongly polarized edge-emission from an ordinary OLED with a stacked Sm/Ag cathode. The polarization ratio of transverse magnetic (TM) mode and transverse electric (TE) mode is close to 300 [
16]. The polarization results from the scattering of SPs at the device boundary. Such Si-based OLED is potentially an electrically excited SP source in silicon plasmonics. The operation principal for an SP (laser) diode is depicted in Fig. 3(b).