Silicon-compatible Ultra-long-range Surface Plasmon Modes
- PDF / 239,515 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 85 Downloads / 154 Views
1077-L06-04
Silicon-compatible Ultra-long-range Surface Plasmon Modes Ali Sabbah1, C. G. Durfee1, R. T. Collins1, T. E. Furtak1, R. E. Hollingsworth2, and P. D. Flammer1 1 Colorado School of Mines, Golden, CO, 80401 2 ITN Energy Systems, Littleton, CO, 80127 ABSTRACT It has long been known that the range of surface plasmons can be extended by sandwiching a thin metal film between dielectrics of equal refractive index. We have modeled the effect of breaking the symmetry of this structure by adding next to the metal film a thin dielectric layer with lower refractive index than the outer dielectric layers. With careful control of the low index layer thickness and dielectric constant, a bound surface plasmon mode with an even greater propagation length can be created for a metal film of finite thickness. We have experimentally confirmed the existence of these modes using an attenuated total reflection measurement to study surface plasmon modes in a Pyrex/Ag/MgF2/oil structure where the oil is index matched to the Pyrex. Shifts in the mode observation angle and mode half width with the MgF2 thickness agree with model predictions. This ultra-long range surface plasmon is of particular interest because a waveguide structure that supports it can have a silicon compatible, metal-oxide-semiconductor (MOS) configuration. INTRODUCTION Electromagnetic waves bound to metal interfaces, or surface plasmons (SPs), have recently attracted considerable interest for their potential to enable sub-wavelength integrated optical devices. SP-based waveguides and modulators would be particularly useful if they could be built and modulated using well developed, MOS compatible Si microelectronics processing allowing a truly integrated optoelectronic technology to be developed. Since silicon lacks an electro-optic effect, efforts to build electrically controlled modulators on silicon (both conventional and plasmonic) are exploring electrically induced free carrier modulation of the dielectric constant in the Si adjacent to a waveguide [1]. This has two major impacts on the design of plasmonic modulators. First, since the dielectric constant modulation is relatively small, the waveguide structure must have very low loss (a long propagation length) to allow sufficient interaction distance for the free carrier modulation to be effective. Second, silicon structures consistent with free carrier modulation, such as metal-oxide-silicon (MOS) capacitors where the carrier concentration under the oxide can be modulated, introduce an asymmetry into the plasmonic waveguide structure. Such asymmetries have previously been reported to complicate SP waveguide performance [2, 3]. Since long propagation length requires limiting the damping of SP modes by the metal layer, it is important to develop devices in which the electric fields associated with the SP are localized outside of the metal. Excitations of this type were predicted and demonstrated (although not in silicon) nearly 25 years ago and are commonly referred to as long range surface plasmon (LRSP) wa
Data Loading...
