Angular scan optical coherence tomography imaging and metrology of spherical gradient refractive index preforms

Area of Science:

• Optics and Photonics
• Materials Science
• Metrology

Background:

• High-performance spherical gradient refractive index (S-GRIN) optics demand precise, nondestructive metrology for quality control.
• Existing techniques may not fully capture the complex optical properties of S-GRIN preforms.

Purpose of the Study:

• To develop and demonstrate an advanced optical coherence tomography (OCT) system for inspecting polymeric S-GRIN preforms.
• To enable simultaneous mapping of critical optical and physical parameters of S-GRIN preforms.

Main Methods:

• An angular-scan, swept-source Fourier-domain OCT system operating at 1318 nm was utilized.
• The system features 180° polar and 360° azimuthal scanning capabilities for comprehensive sample investigation.
• A novel method was implemented for simultaneous mapping of group optical thickness, physical thickness, refractive index, and transmitted wavefront.

Main Results:

• The OCT system successfully imaged polymeric S-GRIN preforms with a 5 mm imaging depth.
• Simultaneous mapping of group optical thickness, physical thickness, radially-averaged group refractive index, and transmitted wavefront was achieved.
• The metrology provided direct visualization and characterization of molding uniformity and optical properties.

Conclusions:

• The developed angular-scan OCT system is effective for nondestructive metrology of S-GRIN preforms.
• The technique facilitates direct visualization, uniformity assessment, and optical property evaluation, guiding manufacturing improvements.
• Feedback from OCT metrology demonstrated its impact on refining the S-GRIN preform fabrication process across generations.