Highly Regular Laser-Induced Periodic Surface Structures on Titanium Thin Films for Photonics and Fiber Optics.

Area of Science:

• Materials Science
• Optics and Photonics
• Nanotechnology

Background:

• Photonic devices require scalable methods for creating periodic surface patterns, especially on nonplanar surfaces like optical fibers.
• Laser-induced periodic surface structures (LIPSS) present a single-step fabrication route for such patterns, offering robustness to processing variations.

Purpose of the Study:

• To demonstrate LIPSS-assisted oxidation of titanium films using femtosecond laser pulses for fabricating regular rutile gratings.
• To explore the application of these gratings in optical fibers for light coupling and sensing.
• To investigate the use of LIPSS as templates for plasmonic gratings.

Main Methods:

• Near-infrared femtosecond laser pulses were used to induce periodic surface structures on thin titanium films, leading to self-terminating oxidation and rutile ridge formation.
• Gratings were fabricated on optical fiber sidewalls, endfaces, and D-shaped fibers.
• Silver coating was applied to LIPSS for plasmonic applications.

Main Results:

• Fabricated rutile gratings exhibited diffraction efficiency above 7%.
• Efficient free-space light coupling into guided modes was achieved at incidence angles up to 65° on optical fibers.
• D-shaped fibers with gratings showed Bragg grating behavior with a narrow resonance (<1 nm).
• Silver-coated LIPSS demonstrated resonant coupling to surface plasmon waves with a high Q-factor (150).

Conclusions:

• LIPSS-assisted oxidation is a reproducible and stable method for fabricating functional optical fiber gratings.
• These gratings have potential applications in sensing, light management, and plasmonics, including plasmonic biosensing and nonlinear optics.