Modified coupled-mode model for thermally chirped polymer Bragg gratings

Area of Science:

• Optics and Photonics
• Materials Science
• Wave Phenomena

Background:

• Classical coupled-mode (CM) models often neglect axial gradients in modulation wavenumber.
• Accurate modeling of thermally chirped Bragg gratings is crucial for optical device performance.
• Nonisothermal conditions introduce complexities in grating behavior.

Purpose of the Study:

• To propose a modified coupled-mode (CM) model for thermally chirped Bragg gratings.
• To incorporate the axial gradient of modulation wavenumber, previously ignored in CM models.
• To characterize the optical behavior of polymer Bragg gratings under nonisothermal conditions.

Main Methods:

• Development of a modified coupled-mode (CM) model.
• Inclusion of axial gradient in modulation wavenumber.
• Application to a polymethyl methacrylate-based polymer Bragg grating.
• Comparison with exact numerical solutions for validation.

Main Results:

• The modified CM model successfully accounts for axial wavenumber gradients.
• Accurate prediction of optical behavior for polymer Bragg gratings under nonisothermal conditions.
• Demonstrated validity of the modified CM model against exact numerical solutions.

Conclusions:

• The modified CM model offers improved accuracy for thermally chirped Bragg gratings.
• This model provides a more robust tool for analyzing polymer gratings in nonisothermal environments.
• The inclusion of axial wavenumber gradients is essential for precise optical characterization.