Compact Optical Antenna Coupler for Silicon Photonics Characterized by Third-Harmonic Generation

We exploit the strong interaction between a focused free-space beam and an optical antenna to construct a compact and efficient silicon waveguide coupler operating simultaneously in several telecommunications bands. The antenna is a directional coupler tuned by the spacing and relative size of its two constituent nanoparticles. Moreover, the antenna's compact size and short scattering lifetime provide a bandwidth sufficient to couple 200 fs pulses at both 1500 and 1350 nm simultaneously. By measuring the third-harmonic generation (THG) from waveguide-coupled light we verify our estimates of the high in-coupling efficiency of these antennas. Coupling efficiencies were estimated to be as high as 19% and 14% at the wavelengths of 1500 and 1350 nm, respectively.