Characterizing femtosecond laser inscribed Bragg grating spectra

Area of Science:

• Photonics and Optical Engineering
• Materials Science and Engineering
• Computational Physics

Background:

• Fiber Bragg gratings (FBGs) are crucial optical components.
• Accurate modeling of FBG spectral characteristics is essential for device design.
• Femtosecond laser inscription offers precise control over FBG fabrication.

Purpose of the Study:

• To present a comprehensive numerical model for femtosecond laser inscribed FBGs.
• To investigate the influence of grating position and symmetry on spectral parameters.
• To validate the model against experimental data and enable predictive analysis.

Main Methods:

• Combined Bidirectional Beam Propagation Method (BPM) and Finite Element Method (FEM).
• Analysis of spectral parameters including insertion loss and cladding/ghost modes.
• Introduction of symmetry breaking in complex grating structures.

Main Results:

• Excellent agreement between numerical modeling and experimental results for FBG spectra.
• Detailed understanding of spectral parameter dependence on grating position within the fiber core.
• Demonstration of the impact of symmetry on spectral quality, particularly for centered gratings.

Conclusions:

• The developed numerical model accurately predicts the wavelength spectra of femtosecond laser inscribed FBGs.
• The model provides insights into optimizing FBG design by controlling grating placement and symmetry.
• The model is capable of handling complex superstructure gratings for tailored wavelength characteristics.