Integration of magnetic plasmonic nanoantennas on a silicon chip

Introduction Metallic nanoantennas with subwavelength dimensions have become extremely powerful elements to manipulate light at the nanoscale. Their properties, associated to the existence of localized surface plasmon... [ view full abstract ]

Introduction

Metallic nanoantennas with subwavelength dimensions have become extremely powerful elements to manipulate light at the nanoscale. Their properties, associated to the existence of localized surface plasmon resonances (LSPRs) with either electric or magnetic character, can be used for different applications: directional light scattering, broadband absorption or enhanced nonlinear interactions. In particular, magnetic nanoantennas supporting an LSPR with magnetic character have been used for directional coupling of guided waves, enhanced nonlinear interaction or as fundamental building block of negative-index metamaterials. Taking account this idea, we have demonstrated that a plasmonic nanoantenna showing an magnetic LSPR can be efficiently excited if inserted within a subwavelength gap created into a waveguide and fed by the fundamental TM waveguide mode.

Characterization

Figure 1(a) describes schematically the system we are proposing. A subwavelength gap (g) separates two silicon waveguides with rectangular cross-section. Figure 1(b) shows schematically the distribution of the fields in the sandwich nanoantenna in order to get a magnetic LSPR. When the TM mode is used we can see that the field components (namely the Ez, Fig. 1(c), and Hx, Fig. 1(d)), perfectly match with the requirements in the nanoantenna to obtain a magnetic response. In order to optimize the magnetic field response (Hx) within the insulator several full-3D numerical simulations have been run using CST Microwave Studio. The waveguide is made of silicon with a cross section of 220x450nm². For the nanoantenna we consider indium tin oxide (ITO), with a permittivity of 1.02+j0.96 at the wavelength of 1.6um, and gold. Figure 2 shows the results obtained in the optimization step which has led to a magnetic response at telecom wavelength.

Conclusion

We demonstrate the viability of a magnetic nanoantenna embedded in a photonic waveguide fed by the TM mode of a silicon waveguide. Moreover, we have study the effect of the sandwich-like antenna geometrical parameters, concluding that, first, optimal response occurs for an insulator thickness of 40nm in a gap with a length of 100nm, and secondly, for gap lengths larger than 150nm the resonant magnetic response disappears. Next steps will include the fabrication and testing of the structure under study.