Terahertz difference frequency generation in a longitudinally coupled LNOI/CPS waveguide: an analytical approach.

Area of Science:

• Photonics and Terahertz Technology
• Materials Science (Lithium Niobate)
• Electromagnetics and Waveguide Theory

Background:

• Current terahertz (THz) technology requires compact, cost-effective, and tunable room-temperature sources for widespread application.
• On-chip integrability and guided-wave approaches offer a promising platform for advanced THz source development.
• Lithium niobate on insulator (LNOI) and coplanar stripline (CPS) waveguides are key components for integrated photonic and electronic devices.

Purpose of the Study:

• To analytically investigate terahertz difference frequency generation in longitudinally coupled LNOI and CPS waveguides.
• To develop a model for efficient optical-to-terahertz conversion in a guided-wave configuration.
• To design and validate a compact, on-chip THz-guided source.

Main Methods:

• Modeling nonlinear interaction in LNOI as a traveling-wave induced current density due to second-order nonlinear susceptibility.
• Applying a semi-analytical approach based on distributed-source transmission line theory to calculate THz signal power.
• Utilizing the multilayer spectral domain method and complex-image technique to compute induced voltage in the CPS.

Main Results:

• A guided source structure satisfying modal phase-matching for efficient 3 THz generation was designed.
• Analytically obtained results showed excellent agreement with full-wave simulations.
• The proposed model enables fast design and optimization of optical-to-terahertz conversion sources.

Conclusions:

• The study successfully demonstrates an analytical model for THz difference frequency generation in coupled LNOI-CPS waveguides.
• The developed approach facilitates the creation of compact, efficient, and tunable on-chip THz-guided sources.
• The general model is applicable to a broad range of integrated optical-to-terahertz conversion devices.