Femtosecond Laser Written Depressed-Cladding Waveguide 2 × 2, 1 × 2 and 3 × 3 Directional Couplers in Tm³⁺:YAG...

Area of Science:

• Integrated Photonics
• Materials Science
• Laser Technology

Background:

• Ion-doped crystals are crucial for integrated photonics, enabling beam splitting and coupling.
• Compact devices are essential for advancing classical and quantum integrated photonics.

Purpose of the Study:

• To fabricate 2D and 3D directional couplers in Tm 3+:YAG crystals.
• To demonstrate the feasibility of femtosecond laser writing for creating complex photonic circuits in crystals.

Main Methods:

• Femtosecond laser writing was employed to fabricate depressed-cladding waveguides.
• Fabricated 2D (2x2, 1x2) and 3D (3x3) directional couplers in Tm 3+:YAG crystals.
• Characterization of coupler performance at 810 nm wavelength.

Main Results:

• Achieved single-mode guidance within the waveguides.
• Demonstrated polarization-independent operation of the couplers.
• Observed finely matched splitting ratios in the fabricated devices.

Conclusions:

• Successfully fabricated 3D directional couplers in Tm 3+:YAG crystals using femtosecond laser writing.
• The demonstrated performance highlights the potential for creating advanced 3D photonic circuits.
• Opens new avenues for fabricating complex crystal-based photonic devices.