Fabrication of single-mode hybrid crystal-glass waveguides by direct femtosecond laser writing and thermal annealing

Ultrafast lasers pave the way for an effective technique for 3D direct space-selective modification of glasses. This work shows that the combination of laser-induced crystallization, isotropic refractive index modification and thermal post-annealing allows the fabrication of single-mode hybrid crystal-glass waveguides. The laser-written waveguides exhibit single-mode behavior and possess the frequency conversion ability due to second harmonic generation by the crystalline waveguide part. The measured level of optical propagation losses of the 9 mm long hybrid optical waveguides is found to be 1.45±0.16 dB at a wavelength of 1550 nm, confirming their improved characteristics. The presented results contribute to the future development of all-optical crystal-in-glass waveguide-based devices and technologies.