Femtosecond laser written waveguides deep inside silicon.

Area of Science:

• Materials Science
• Optics and Photonics
• Nanotechnology

Background:

• Photonic devices are crucial for modern electronics and integrated silicon photonics.
• Efficient light guiding, transfer, and modulation are key challenges.
• Existing methods for creating optical waveguides face limitations.

Purpose of the Study:

• To demonstrate the first creation of optical waveguides deep inside silicon.
• To utilize femtosecond laser pulses for permanent modification of silicon crystal.
• To characterize the properties of the fabricated waveguides.

Main Methods:

• Employing femtosecond pulses (350 fs, 2 μJ, 250 kHz) from an Er-doped fiber laser.
• Focusing laser pulses inside silicon to induce permanent modifications.
• Controlling beam position with pump-probe imaging and scanning focal position for waveguide fabrication (5.5 mm length, 20 μm diameter).

Main Results:

• Successfully fabricated optical waveguides within silicon at a 1.5 μm wavelength.
• Measured refractive index changes of 6×10⁻⁴ (optical shadowgraphy) and 3.5×10⁻⁴ (direct light coupling).
• Demonstrated the feasibility of creating waveguides deep inside silicon using this technique.

Conclusions:

• Femtosecond laser processing is a viable method for creating optical waveguides in silicon.
• This technique offers a new pathway for integrated silicon photonics.
• The precise control and characterization pave the way for advanced photonic device fabrication.