Glasses are important materials for novel technologies, as their properties can be tailored by doping and compositional changes. Furthermore, glasses can also be microstructured, making them interesting for optical and photonic applications. Corning Gorilla Glass is an alkali aluminosilicate glass commonly used as protective layer in smart phones and tablets thanks to its outstanding mechanical properties. Recently, it has been demonstrated the use of femtosecond direct laser writing of waveguides in Gorilla Glass, prompting it for integrated photonic/electronic devices. Therefore, it is important to study the nonlinear optical properties of Gorilla Glass as well as their laser-inscribed waveguides, since the effects of the laser writing process on the nonlinearity are not totally understood.
Here we investigate the third-order nonlinear optical properties of waveguides fs-pulses written waveguides in Gorilla Glass, by using the Dispersive-scan (D-scan) method. The nonlinear refractive index measured in the waveguide is lower than the one for the pristine material and its value depends on the writing pulse energy. For waveguides fabricated with pulse energy of 250 nJ, for instance, n2 is about three times lower than the one for the pristine sample. Micro Raman measurements were performed in the microstructured material in order to better understand the mechanisms of laser modification. Raman spectroscopy revealed the reduction and broadening of the high-frequency band related to non-bridging oxygens, which can explain the decrease of n2. Therefore, our results not only show the potential of using D-scan for waveguides nonlinear characterization, but also demonstrate and interpret the decrease of the nonlinear index of refraction in fs-laser micromachined waveguides in Gorilla Glass, which potential implications for photonic devices.
Ultrafast waveguide fabrication has been an active research area since its demonstration, leading to numerous applications. Recently reported high quality waveguide in Gorilla Glass has promoted it as a good candidate for optical devices. In this study, 120-fs laser pulses centered at 520, 650 and 775 nm at a repetition rate of 1 kHz were applied to investigate the influence of the wavelength on micromachining. Grooves ablated onto Gorilla Glass surface with different pulse energies and scanning speeds presented similar features and threshold pulse energy, regardless the excitation wavelength. Fifteen millimeter long waveguides were produced 100 μm below sample surface with pulse energy varying from 250 nJ up to 5 μJ (scanning speed of 200 μm/s). Waveguides longitudinal and transversal profiles were analyzed via optical microscopy and its guiding properties characterized in an objective-lens based coupling system at 633 and 775 nm. Guide modes intensity distribution show that for waveguides fabricated with higher pulse energy light is guided further from the core, while for lower fabrication energy light is guided closer to the center in a more fundamental mode. Considering that light traveling through 15 mm of material in confined mode, we coupled 775 nm fs-pulses into fabricated waveguides. By monitoring the spectrum of the guided light as input pulse energy increased, spectral broadening assigned to self-phase modulation effects was observed followed by white-light generation starting at 450 nm. In conclusion, we found that micromachining on Gorilla Glass is wavelength independent and inscribed waveguides present desirable nonlinear features.