Surface Plasmon Polaritons (SPPs) are collective oscillations of electrons coupled to an electromagnetic field. They can exist at the interface of a dielectric and metal and exhibit extremely high field intensities near that interface. VCSELs are ideal platforms for studying SPPs and allow for the possibility of integrating an active photonic device with plasmonic structures.
The experiment below shows one application of plasmonic VCSELs. The VCSEL surface is coated with a thin layer of silver and a focused ion beam (FIB) is used to etch a small (sub-wavelength) aperture. Diffracted light exiting from this aperture can couple into a SPP mode. The SPPs are scattered into a propagating mode by the periodic grating surrounding the aperture, creating a larger effective aperture of the radiation. This reduces the far-field divergence of the radiation from 100° to 28° and increases the amount of power collected in the far-field, as shown below.
Fig. 1. (a) Schematic view of plasmonic nano-aperture VCSEL cross-section. (b) Scanning electron microscope image of concentric ring pattern with aperture.
Fig. 2. Light output versus current from VCSELs with a 200 nm Ag aperture (a) as measured (b) with spontaneous emission subtracted.