Efficient coupling into tapered proton-exchanged LiNbO(3) waveguides fabricated by vertically controlled immersion

Area of Science:

• Photonics and Waveguide Technology
• Materials Science
• Nonlinear Optics

Background:

• Planar lithium niobate (LiNbO3) waveguides are crucial for nonlinear optical applications.
• Efficient light coupling and low propagation losses are key challenges in waveguide fabrication.
• Prism coupling is a common but sometimes inefficient method for coupling light into planar waveguides.

Purpose of the Study:

• To fabricate efficient planar LiNbO3 waveguides using a novel double proton-exchange process.
• To achieve high coupling efficiency and low power transfer loss.
• To provide an alternative to prism coupling for Cerenkov second-harmonic generation (CSHG).

Main Methods:

• Fabrication of LiNbO3 waveguides via a double proton-exchange process.
• Incorporation of a 5-mm tapered region and a 10-mm homogeneous slab waveguide region.
• Characterization of waveguide coupling efficiency and power transfer loss.

Main Results:

• Achieved a high coupling efficiency of up to 93% at the 4-microm waveguide entrance.
• Demonstrated a low 1-dB power transfer loss from the tapered to the working region (0.4-microm depth).
• The developed technique offers an effective alternative to prism coupling.

Conclusions:

• The double proton-exchange method enables the fabrication of high-performance LiNbO3 waveguides.
• Precise control over the tapered region's depth profile is critical for minimizing power loss.
• This advancement facilitates improved efficiency in Cerenkov second-harmonic generation devices.