Laser-written 3D waveguide beam splitters in LBO crystals for second-harmonic generation with tailored modes.

Area of Science:

• Photonics
• Nonlinear Optics
• Materials Science

Background:

• Waveguide beam splitters are crucial components in photonic integrated circuits.
• Efficient frequency conversion is essential for various optical applications.
• Lithium triborate (LBO) is a nonlinear crystal with favorable properties for optical applications.

Purpose of the Study:

• To fabricate three-dimensional (3D) waveguide beam splitters capable of efficient second-harmonic generation (SHG).
• To integrate beam splitting and frequency conversion functionalities into a single device.
• To achieve mode evolution from multi-mode to single-mode at the output ports.

Main Methods:

• Fabrication of 3D waveguide beam splitters using femtosecond laser writing in LBO crystals.
• Depressed-cladding waveguides with circular cross-sections were employed.
• Tailoring of output port cross-sections to achieve mode evolution.

Main Results:

• Achieved a record SHG conversion efficiency of 9.22% with the fabricated beam splitter.
• Successfully demonstrated mode evolution from multi-mode to single-mode at three engineered output ports for both fundamental and SHG waves.
• Integrated 3D beam splitting with frequency conversion in a nonlinear crystal for the first time.

Conclusions:

• The developed 3D waveguide beam splitters offer a novel approach for integrated photonics.
• This technology paves the way for fabricating high-efficiency and energy-saving photonic integrated circuits.
• The integration of beam splitting and frequency conversion in LBO crystals demonstrates significant potential for advanced optical devices.