Efficient phase-matched third harmonic generation from mid-IR to near-IR regions in a double asymmetric plasmonic slot waveguide

Abstract

Recent years, the research of mid-infrared (mid-IR) photonics has inspired increasingly interest due to their potential applications in a wide variety of areas, including free-space communications, chemical or biological sensors, environmental monitors, thermal imaging, IR countermeasures and medical procedures. On the other hand, third harmonic generation (THG) has been demonstrated to be a versatile tool to realize high speed optical performance monitoring of in-band OSNR and residual dispersion. The mid-IR light sources based third-order frequency conversion opens an entirely new realm of nonlinear interactions. Nevertheless, rare experimental or analytical THG modeling has been published. In this work, we theoretically investigate the possible efficient phase-matched THG in a double symmetric plasmonic slot waveguide (DAPSW) based on a mid-IR light source. Nonlinear organic material DDMEBT with thirdorder susceptibility of χ⁽³⁾= 1×10^-19 m²/V² is integrated into the top metallic slot region as the main slot core medium. Silicon (Si) is used to fill the bottom metallic slot region. Silver (Ag) is considered to be the metal medium due to its low Ohmic loss. The needed phase-matching condition (PMC) is satisfied between the zeroth mode at fundamental frequency (FF) and the first mode at third harmonic (TH) by appropriate designing the waveguide geometrical parameters. The associated parameters such as the width and height of the slot, pump-harmonic modal overlap, figureof- merit (FOM), pump power and detuning have been numerically investigated in detail. Finally, the conversion efficiency comes up to 1.69×10^-5 with pump power of 1 W and the corresponding waveguide length is 10.8 μm.