Refractive-index measurement of gradient-index microlenses by diffraction tomography

Area of Science:

• Optics and Photonics
• Materials Science
• Computational Imaging

Background:

• Gradient-index (GRIN) materials offer unique optical properties.
• Accurate characterization of GRIN profiles is crucial for device performance.
• Planar GRIN microlenses are fabricated using thermal ion exchange.

Purpose of the Study:

• To apply diffraction tomography for reconstructing the gradient-index distribution of planar GRIN microlenses.
• To validate the reconstruction accuracy using phase-shifting interferometry and the Rytov approximation.
• To compare the obtained results with other measurement and simulation techniques.

Main Methods:

• Fabrication of planar GRIN microlenses via thermal ion exchange.
• Acquisition of single-phase projections using phase-shifting interferometry.
• Reconstruction of the refractive index profile using diffraction tomography with the Rytov approximation.

Main Results:

• Successful reconstruction of the gradient-index distribution was achieved.
• The Rytov approximation proved effective for smooth inhomogeneities.
• Reconstruction results showed good agreement with other experimental and simulation data.

Conclusions:

• Diffraction tomography is a powerful technique for characterizing GRIN microlenses.
• Phase-shifting interferometry and the Rytov approximation are suitable for this application.
• The study validates the potential of diffraction tomography in optical material characterization.