Title: Transverse Inscription of Silicon Waveguides by Picosecond Laser Pulses

Abstract: In this paper, picosecond laser inscription of segmented waveguides in crystalline silicon based on a deterministic single-pulse modification process is demonstrated.Pulses of 43 ps duration at 1.55 ${\mu}$m wavelength are used to transversely inscribe periodic structures with a pulse-to-pulse pitch of around 2 ${\mu}$m. Infrared shadowgraphy images and Raman spectroscopy measurements indicate that the modifications exhibit a spherical shape. Characterization of waveguide performance at 1.55 ${\mu}$m for various pulse energies and periods is carried out. Direct comparison with numerical simulations confirms the presence of graded index waveguides, encompassing a micrometer core size and a maximum refractive index change of around $7\times 10^{-3}$. This short-pulse inscription approach can pave the way for three-dimensional integrated photonic devices in the bulk of silicon.