Quasi-Phase Matched Second Harmonic Generation in Plasmonic–Organic Hybrid Structures

In this article, we propose the design and analyze a plasmonic-organic-hybrid (POH) waveguide structure for efficient forward and backward second harmonic generation (SHG) to bridge the mid-infrared (IR) to near-IR. The required phase matching is satisfied by quasi-phase matching (QPM) technique through periodically altering the material of the metal-insulator-metal slot region between a nonlinear polymer (with second-order nonlinear coefficient of χ
⁽²⁾
≠ 0) and Al
₂
O
₃
(with χ
⁽²⁾
= 0) leading to modulation of χ
⁽²⁾
coefficient along the propagation direction. The strong field confinement offered by surface plasmon polaritons (SPPs) significantly enhances the normalized efficiency up to 1.75 × 10
⁶
W
^-1
cm
^-2
in the case of backward SHG over a short device length of 17 μm with only 20 mW input power. Also, a slightly lower efficiency is achieved for forward configuration with broadband response, high fabrication tolerance, and small temperature-variation sensitivity. Furthermore, our proposed structure is based on standard nanofabrication technologies and can be used for all-optical signal processing, low-noise detection of a mid-IR signal in the near-IR windows, and (mirrorless) optical parametric oscillator.