Modal coupling in fiber tapers decorated with metallic surface gratings

Area of Science:

• Photonics and optical engineering
• Materials science
• Nanotechnology

Background:

• Optical fiber tapers are crucial for various photonic devices.
• Fabricating precise structures on optical fibers is challenging.
• Metal gratings offer unique optical properties for sensing applications.

Purpose of the Study:

• To develop an interference-based fabrication scheme for periodic metal gratings on optical fiber tapers.
• To characterize the optical properties of the fabricated grating fiber tapers.
• To demonstrate the application of these gratings in a high-sensitivity refractometer.

Main Methods:

• Interference-based lithography for grating fabrication on fiber tapers.
• Optical characterization using spectroscopy to analyze coupling modes.
• Analytical mode-coupling analysis to explain observed optical phenomena.
• Refractive index sensing experiments using the grating fiber taper.

Main Results:

• Successfully fabricated a 5 mm long, 511 nm period gold grating on an optical fiber taper.
• Observed backward coupling to guided and radiation modes, explained by mode-coupling analysis.
• Demonstrated a refractometer with high and constant sensitivity.
• Achieved a wide operating refractive index range from 1 to 1.41.

Conclusions:

• The developed interference-based scheme is effective for fabricating periodic metal gratings on optical fiber tapers.
• The grating fiber tapers exhibit unique optical coupling properties suitable for sensing.
• The grating fiber taper-based refractometer offers high performance over a broad refractive index range.