Metal based grating coupler on a thin-film lithium niobate waveguide

Area of Science:

• Photonics
• Materials Science
• Electrical Engineering

Background:

• Thin-film lithium niobate (LN) is a key material for integrated photonic devices.
• Efficiently coupling light between optical fibers and on-chip waveguides is a significant challenge.

Purpose of the Study:

• To demonstrate an efficient grating coupler for sub-micron lithium niobate waveguides.
• To achieve high coupling efficiency and broad bandwidth for fiber-to-chip integration.

Main Methods:

• Fabrication of a grating coupler using gold (Au) stripes on a lithium niobate (LN) ridge waveguide.
• Utilizing a standard metal film lift-off process for grating fabrication.
• Optimization of the grating structure for maximum coupling efficiency.

Main Results:

• Achieved a peak coupling efficiency of 50.4% (-3 dB loss) at 1.55 µm wavelength for the fundamental transverse-electrical mode.
• Demonstrated a 1-dB coupling bandwidth of 58 nm.
• Experimentally verified coupling efficiencies of 43.8% and 33.7% for LN layers of 400 nm and 600 nm, respectively.

Conclusions:

• The demonstrated gold grating coupler offers a convenient and efficient solution for fiber-to-chip coupling in thin-film lithium niobate integrated photonics.
• The fabrication process is compatible with standard semiconductor manufacturing techniques.
• The results pave the way for more compact and efficient on-chip photonic systems.