Tomographic refractive index profiling of direct laser written waveguides

Area of Science:

• Photonics
• Materials Science
• Optical Engineering

Background:

• Direct laser writing (DLW) is a key technology for fabricating complex integrated photonic devices.
• Reliable quantitative characterization of refractive index (RI) changes induced by laser exposure remains a significant challenge in DLW.

Purpose of the Study:

• To develop and validate a novel tomographic reconstruction algorithm for accurate RI characterization of DLW structures.
• To adapt state-of-the-art bioimaging algorithms for photonic applications and extend them to include aberration estimation.

Main Methods:

• Development of a tomographic reconstruction algorithm using accelerated proximal gradient descent based solely on intensity images.
• Adaptation of the algorithm for translation-invariant DLW structures and joint estimation of imaging system aberrations.
• Cross-validation of RI reconstructions using en-face widefield imaging and simulations.

Main Results:

• The developed algorithm accurately reconstructs RI profiles of DLW structures.
• Joint estimation of aberrations is crucial for utilizing larger angle data and enhances reconstruction fidelity.
• Cross-validation confirms the accuracy of the retrieved RI profiles.

Conclusions:

• The proposed method offers a reliable approach for quantitative RI characterization in DLW.
• Accurate aberration estimation is essential for high-fidelity RI profiling.
• This work advances the characterization capabilities for integrated photonic devices fabricated via DLW.