Quasi-Phase-Matched Frequency Conversion in van der Waals Semiconductors: Thicker May Not Be Better

Area of Science:

• Nonlinear optics
• Condensed matter physics
• Materials science

Background:

• Van der Waals (vdW) crystals exhibit significant optical nonlinearity.
• Nonlinear optical applications require understanding material behavior under lossy conditions.

Purpose of the Study:

• Investigate second-harmonic generation in vdW semiconductors with transmission losses.
• Develop a model for nonlinear transmission in finite-thick, lossy vdW materials.
• Propose a method to enhance nonlinear optical signals in such materials.

Main Methods:

• Utilized 3R-stacked MoS2 as a model system.
• Incorporated dissipation and Fabry-Pérot interference into a nonlinear transmission model.
• Proposed and analyzed a quasi-phase-matching scheme using multilayer stacking with controlled orientation angles.

Main Results:

• Strong second-harmonic absorption causes rapid intensity saturation, limiting conventional phase-matching.
• The proposed quasi-phase-matching scheme effectively enhances second-harmonic signals despite losses.
• Optimized thickness and lattice orientation of layers are key to signal enhancement.

Conclusions:

• Loss mechanisms and quasi-phase-matching behavior in 2D materials are elucidated.
• The findings are vital for developing high-efficiency ultrathin nonlinear devices.
• This research supports advancements in integrated photonic chips and vdW-based quantum photonic technologies.