Simple technique of determining the fibre diameter during etching

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Chemical Metrology

Background:

• Precise control over optical fiber dimensions is crucial for advanced photonic devices.
• In-situ monitoring of fiber etching processes is challenging but essential for achieving target specifications.

Purpose of the Study:

• To develop and validate a novel in-situ technique for measuring optical fiber diameter during etching using fiber Bragg gratings (FBGs).
• To determine the refractive indices of buffered hydrofluoric acid solutions using the developed FBG-based method.

Main Methods:

• Utilizing differential shifts between fundamental and higher-order Bragg resonances generated by etching.
• Employing numerical simulations to analyze evanescent field overlap and calibrate etched fiber diameter.
• Experimentally calibrating the technique against known liquid refractive indices at ~1550nm.

Main Results:

• Achieved ~200nm precision in determining the diameter of standard optical fibers (SMF28) during etching.
• Experimentally determined refractive indices of two buffered hydrofluoric acid solutions: ~1.360 ± 0.005 (20:1) and ~1.370 ± 0.005 (7:1) at ~1550nm.
• Demonstrated excellent agreement between numerical simulations and experimental outcomes.

Conclusions:

• The FBG-based in-situ measurement technique offers a controlled and precise method for achieving target diameters in etched optical fibers.
• This approach provides a reliable tool for real-time process control in optical fiber fabrication and characterization.
• The method is effective for determining the refractive indices of chemical solutions relevant to fiber processing.