Fabrication of PDMS-based Volume Bragg Gratings by Stitching of Femtosecond Laser Filament

This work demonstrates the fabrication of poly-(dimethylsiloxane) (PDMS)-based volume Bragg gratings (VBGs) by stitching of femtosecond laser filament. The refractive index change induced by femtosecond laser pulses is low (orders of 10−4 to 10−3) in PDMS. Therefore, the VBG thickness is the key parameter to fabricate high-efficiency VBGs in PDMS. With the intention of increasing diffraction efficiency, this paper presents fabrication of multi-layered PDMS-based VBGs. We produce VBGs with 10 μm line pitch using a femtosecond pulse laser (100 fs pulse width, 1 kHz repetition frequency). The modified zone thickness can be controlled by arranging the relative displacement of filament at different depths and the distances between layers. High-efficiency VBGs were created by depth multiplexing of 350 μm long filamentary modification in PDMS. Diffraction efficiency of 87.2% was realized by forming 0.63 mm grating thickness.