Femtosecond laser direct writing of optical waveguides in silicone film

Abstract

For the first time to the authors' knowledge, optical waveguides have been inscribed in silicone ([SiO(CH3)2]n) film by ultrafast laser radiation. The 522 nm femtosecond laser pulses with 3 nJ on target energy at 1 MHz repetition rate were focused into thin silicone film (Quantum Silicone, QSIL216) with a 0.55-NA aspherical lens to induce nonlinear photon absorption in the focal volume of the beam. By scanning the laser beam with respect to the silicone film, a permanent refractive index modification has been created inside the silicone. In the modification tracks, photo-dissociation of SiCH3 and dangling bond of SiOH were observed by time-of-flight secondary ion mass spectrometry. The modification tracks showed multi mode at red (635 nm) wavelength and single mode at infrared (1550 nm) wavelength. Propagation losses were estimated to be < 2.2 dB/cm at 635 nm and < 2.8 dB/cm at 1550 nm by the cut back method.