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<sup>(3) </sup>= 1×10<sup>-19</sup> m<sup>2</sup>/V<sup>2</sup> 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<sup>-5</sup> with pump power of 1 W and the corresponding waveguide length is 10.8 μm.