Aberration correction for direct laser written waveguides in a transverse geometry

Area of Science:

• Optics and Photonics
• Materials Science

Background:

• Ultrafast laser writing is a key technique for fabricating optical waveguides.
• Spherical aberration can degrade waveguide quality, particularly at greater depths.
• Transverse writing geometry and slit beam shaping are used in waveguide fabrication.

Purpose of the Study:

• To investigate depth-dependent spherical aberration in ultrafast laser-written waveguides.
• To understand how spherical aberration affects refractive index changes and waveguide mode properties.
• To develop methods for compensating spherical aberration for improved waveguide fabrication.

Main Methods:

• Fabrication of waveguides using ultrafast laser writing in a transverse geometry.
• Utilizing slit beam shaping and low pulse repetition rate.
• Theoretical estimation of aberration compensation by adjusting laser power.
• Experimental demonstration of aberration removal using adaptive optics.

Main Results:

• Spherical aberration causes axial focus elongation, distorting refractive index changes.
• Waveguides designed for single-mode operation become multimode due to aberration.
• Laser power adjustment can compensate for aberration within a specific depth range.
• Adaptive optics successfully removed aberration for single-mode waveguide fabrication > 1 mm deep.

Conclusions:

• Depth-dependent spherical aberration is a critical factor in ultrafast laser-written waveguide quality.
• Simple adjustments in laser power can mitigate aberration effects at shallower depths.
• Adaptive optics provide an effective solution for fabricating high-quality single-mode waveguides at greater depths (> 1 mm).