2D refractive index measurement for direct laser writing waveguides with complex structures.

Area of Science:

• Integrated photonics
• Waveguide characterization
• Optical metrology

Background:

• Direct laser writing (DLW) enables complex waveguide structures for advanced photonic devices.
• Precise measurement of the 2D refractive index distribution (RID) is essential for DLW waveguide implementation.
• Existing methods face challenges in accurately characterizing complex DLW waveguide RIDs.

Purpose of the Study:

• To develop and validate a novel method for accurately measuring the 2D RID of complex DLW waveguides.
• To combine modified near field (MNF) and quantitative phase imaging for comprehensive waveguide analysis.
• To enable precise characterization for the wider application of DLW waveguides.

Main Methods:

• Combines the modified near field (MNF) method with quantitative phase imaging.
• MNF method derives qualitative RID and phase from near-field intensity.
• Digital holography (DH) and Mach-Zehnder interferometry extract quantitative phase distribution.
• A hybrid reconstruction algorithm is employed for phase extraction.
• A linear coefficient links qualitative and quantitative phase data for final RID calculation.

Main Results:

• Successfully measured the 2D RIDs of DLW waveguides with both positive and negative refractive index changes.
• Demonstrated efficient acquisition of 2D RIDs for waveguide arrays.
• Validated the proposed method's capability for complex waveguide structures.

Conclusions:

• The proposed combined MNF and quantitative phase imaging method accurately determines the 2D RID of complex DLW waveguides.
• This technique is crucial for the precise characterization and advancement of integrated photonic devices fabricated by DLW.
• The method offers efficient and accurate analysis for diverse DLW waveguide designs and arrays.