Efficient insertions of surface plasmon polariton on grating couplers

Abstract

For nanoscale photonic devices, localized and enhanced optical field as surface plasmon polariton (SPP) is applicable. In conventional devices applying SPP, prism coupler is used for generating SPP on metallic surface. Freely propagating light can be converted to SPP by prism coupler efficiently by matching the phase and the field distribution between light and SPP. However, prism coupler has inferiorities as bulky and uncontrollable SPP manipulations. In this paper, we propose the grating coupler for compact and flexible SPP coupler. The grating coupler is consisted with periodic dielectric structures with 300nm-thickness on flat metallic surface. This can be installed at any position, and the directivity can be controlled by the waveform. On the prating coupler with the pitch of 1500nm and the duty ratio of 0.5, the incident beam with the wavelength of 780nm, p-polarization and the incident angle of 45° was irradiated and that was converted to SPP. In the computer simulations, the insertion coupling efficiency became larger than 60% by adjusting of the insertion angle and the beam waist that were corresponded with the phase matching and field distribution matching conditions. Making the prototypes of the grating couplers, the coupling efficiency was evaluated experimentally. Because of larger focus spot of insertion beam, the coupling efficiency was reduced from the predicted value by computer simulations.