Optical waveguide grating couplers: 2nd-order and 4th-order finite-difference time-domain analysis

Area of Science:

• Photonics and Optical Engineering
• Computational Electromagnetics

Background:

• Optical waveguide grating couplers are essential components in integrated photonics.
• Accurate simulation of these devices is crucial for performance optimization.
• Existing methods face challenges with permittivity discontinuities and computational efficiency.

Purpose of the Study:

• To rigorously analyze volume-holographic and surface-relief grating couplers.
• To compare the accuracy and efficiency of 2-order and 4-order finite-difference time-domain (FDTD) methods.
• To validate FDTD results against rigorous coupled-wave analysis (RCWA) and leaky mode analysis.

Main Methods:

• Finite-difference time-domain (FDTD) method (2-order and 4-order).
• Total field/scattered field (TF-SF) approach.
• Averaging and regularization techniques for permittivity discontinuities.
• Rigorous coupled-wave analysis (RCWA) with leaky modes for comparison.

Main Results:

• Higher-order FDTD methods provide accurate analysis of grating couplers for TE and TM polarizations.
• The 4-order FDTD method demonstrates superior accuracy over the 2-order method.
• FDTD results show good agreement with RCWA and leaky mode analysis.
• Computational efficiency of different FDTD orders is evaluated.

Conclusions:

• The FDTD method, particularly higher-order formulations, is a powerful tool for analyzing optical waveguide grating couplers.
• Advanced techniques effectively mitigate challenges posed by permittivity discontinuities.
• The study provides valuable insights into the performance and simulation of grating coupler designs.