High-Order Nonlinear Photonic Crystal with Ordered Structures for Giant Enhancement of Frequency Tripling

Area of Science:

• Nonlinear Optics
• Materials Science
• Photonics

Background:

• Second-order nonlinear optical conversion (χ(2)) is well-established for frequency doubling.
• Third-order nonlinear optical conversion (χ(3)) offers direct frequency tripling but suffers from low efficiency and dispersion challenges.
• Existing χ(3) methods have efficiencies between 10⁻¹⁰ to 10⁻⁸, limiting applications.

Purpose of the Study:

• To propose and demonstrate a high-order nonlinear photonic crystal for enhanced third-order optical frequency conversion.
• To overcome the limitations of low efficiency and optical dispersion in third-order nonlinear processes.
• To explore the potential for on-chip photonics and multi-photon entanglement.

Main Methods:

• Designed and fabricated a high-order nonlinear photonic crystal with artificially ordered structures.
• Utilized meta-YAG (Y₃Al₅O₁₂ crystal) as an example material for frequency tripling.
• Investigated phase compensation and efficiency enhancement mechanisms within the engineered crystal structure.

Main Results:

• Achieved a record frequency tripling conversion efficiency of 4.5×10⁻³ in meta-YAG.
• Demonstrated a six-order-of-magnitude improvement in efficiency compared to conventional YAG crystals.
• Obtained wide spectral tunability from 331 to 356 nm, indicating potential for broadband generation.

Conclusions:

• The proposed nonlinear photonic crystal effectively regulates phase compensation and boosts third-order conversion efficiency.
• This advancement opens new avenues for efficient multi-photon entanglement and on-chip photonic devices.
• The study provides a valuable framework for optimizing χ(3)-active nonlinear optical materials.