Femtosecond-laser-written three-dimensional waveguide beam splitters in MgO-doped stoichiometric LiTaO₃ crystal

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Laser Physics

Background:

• Three-dimensional (3D) photonic devices are crucial for advanced optical systems.
• Fabricating complex 3D waveguide structures with high precision remains a challenge.
• MgO-doped stoichiometric lithium tantalate (MgSLT) is a promising material for nonlinear optics and integrated photonics.

Purpose of the Study:

• To design and fabricate compact 3D waveguide beam splitters in MgSLT crystals.
• To demonstrate the capability of femtosecond laser direct writing for creating intricate 3D photonic structures.
• To investigate the microstructural modifications induced by laser irradiation and their impact on optical properties.

Main Methods:

• Utilizing femtosecond laser direct writing to inscribe waveguide structures within MgSLT crystals.
• Implementing photonic-lattice-like cladding waveguides with axial defect-tracks for beam splitting.
• Employing confocal micro-Raman (μ-Raman) spectroscopy for spatial mapping of laser-induced modifications.

Main Results:

• Successfully fabricated 1×2, 1×3, and 1×4 waveguide beam splitters in 3D.
• Achieved nearly equalized splitting ratios for the fabricated beam splitters.
• Confirmed that bulk crystalline properties are well-preserved within the laser-written guiding cores.

Conclusions:

• Femtosecond laser direct writing offers an effective method for fabricating highly compact 3D photonic devices.
• The developed technique enables precise control over light guiding and beam steering in MgSLT.
• This work paves the way for novel 3D integrated optical circuits and devices.