New channel guiding structures via femtosecond laser direct writing z-cut LiNbO3 crystals

Abstract

In this work, we use femtosecond laser direct writing to fabricate two kinds of modified structures with opposite refractive index changes to build new dual-line waveguide configurations in z-cut LiNbO3 (LN) crystals for the first time. These hybrid-structure waveguides, in which type-Ⅰ modifications are induced between two type-Ⅱ tracks have been investigated by an end-face coupling system at 532 nm. The results indicate that TEM00 mode is the only transmission mode for all waveguides. Comparing with the single-modification waveguides, experimental results indicate that the new waveguides in which type-Ⅱ tracks with 12 μm interval exhibit lower transmission losses (about 0.98 dB/cm). The reasons for these interesting guiding performances are analyzed by the confocal micro-Raman results. The beam quality is measured in both directions (x and y) and also in the visible (532 nm) and infrared (1064 nm) regions. This work provides a new perspective for improving the transmission efficiency of waveguides, which is the new hybrid structure in LN crystals. The new-waveguides design method has potential application in the field of photonic chips.

Keywords

• New dual-line waveguide
• LN crystal
• Femtosecond laser direct writing
• Micro-Raman spectra