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In the world of optical simulations, designers seek efficient and reliable numerical techniques to model light interactions in complex structures. Rigorous Coupled-Wave Analysis (RCWA) and Finite-Difference Time-Domain (FDTD) are two popular methods, each offering unique strengths and capabilities. In this blog post, we present a comparison of periodic silicon waveguide simulations, examining the results obtained from Lumerical RCWA and FDTD. Our simulation demonstrate a close match between the two methods, while also highlighting RCWA's remarkable speed advantage in handling periodic structures.

RCWA Solver Introduction:

Before delving into the comparison, let's briefly introduce the RCWA method and its prowess in tackling periodic structures. RCWA is a powerful numerical tool extensively used to study light interactions with gratings, photonic crystals, and metamaterials. In this blog, we utilized Lumerical's RCWA solver to investigate the fascinating realm of periodic silicon waveguides.

The Appeal of FDTD and its Limitations:

Finite-Difference Time-Domain simulations have earned popularity for their ease of implementation and ability to handle dispersive materials. FDTD's flexibility makes it a reliable choice for a wide range of optical simulations, from nanophotonics to plasmonics. However, it is known that FDTD can encounter timing simulation challenges when dealing with periodic structures.

The Comparative Analysis:

In our research, we designed a series of simulations, varying parameters such as grating pitch, material properties, and incident angles. The results obtained from both RCWA and FDTD showcased a good agreement. Figure 1 shows the reflection and transmission responses obtained from both RCWA and FDTD simulations for the periodic silicon waveguide. As seen in Figure 1, both RCWA and FDTD exhibit near-identical spectral responses for the periodic silicon waveguide. This convergence in results highlights the reliability and accuracy of both numerical techniques in capturing the optical behavior of the structure.

Figure 1: Reflection and Transmission Responses

RCWA: A Speed Advantage in Periodic Structures:

Beyond the convergence of results, the simulations with RCWA exhibited significantly faster computation times compared to FDTD for these specific waveguide configurations. This speed advantage positions RCWA as an invaluable tool when dealing with large-scale periodic simulations.


Check out the Video Comparison!

For a more detailed visual representation of our simulations, we invite you to watch the video comparison we have prepared. In this video, we showcase the reflection and transmission responses obtained from both RCWA and FDTD simulations for the periodic silicon waveguide. Witness how these numerical techniques closely match each other in capturing the intricate behavior of light within the structure.


The video provides a comprehensive overview of our simulation setup, results, and insightful analysis.

Post by Majid Ebnali Heidari
August 9, 2023