Fabrication and study of femtosecond laser micromachined few-mode elliptical core waveguides

TL;DR

This study investigates femtosecond laser micromachined elliptical core waveguides, optimizing fabrication parameters to achieve low-loss propagation and analyzing their modal properties compared to theoretical models.

Contribution

It provides a detailed parametric optimization for fabricating low-loss elliptical core waveguides and compares experimental modes with computational predictions.

Findings

Achieved propagation loss of ~0.4 dB/cm with optimized parameters.

Found that V-number depends on core aspect ratio.

Modal analysis shows good correlation with computational models.

Abstract

Femtosecond laser micromachining (FLM) fabricated waveguides inherently form elliptical cores due to differences in focal spot size and the Rayleigh range of the microscope objective. Consequently, it is essential to study their propagation characteristics, which differ from those of conventional circular-core waveguides. In this work, we present the results of a parametric optimization of these waveguides to identify fabrication parameters that lead to minimal loss. A propagation loss characterization study revealed that, for a laser wavelength of 1030 nm, a pulse width of $\sim$300 fs, a pulse energy of 600 nJ, a scan speed of 2 mm/s, and a repetition rate of 100 kHz, a transparent and micro-bubble-free waveguide with a propagation loss of $\sim$0.4 dB/cm was formed. The modal analysis further demonstrated that the V-number depends on the core aspect ratio. The waveguide modes were compared with computationally generated modes, revealing a correlation that aligns well with existing literature.