SiO2-SnO2:Er3+ planar waveguides: Highly photorefractive glass-ceramics

For different applications in laser photonics and integrated optics, photorefractive materials are surely of great interest and play an important role in miniaturization of devices and fabrication of functional photonic structures such as gratings and waveguides. In this work, high photorefractivity of sol-gel derived SiO2-SnO2:Er3+ glass-ceramic planar waveguides, with negative effective refractive index change, is demonstrated. Through the photorefractivity investigation employing the UV pulsed KrF excimer laser (λ = 248 nm), the glass-ceramic planar waveguides show fast photorefractive response after a cumulative dose of only 0.3 kJ/cm2. A higher SnO2 content in the glass-ceramics leads to a greater change of saturated effective refractive index: Δneff = - (2.60 ± 0.20) x 10-3 at 1550 nm on the TE0 mode, for the 30 mol% SnO2 planar waveguides and Δneff = - (2.00 ± 0.20) x 10-3 on the 1550 nm TE0 mode, for the 20 mol% SnO2 ones. To investigate the structural modifications involved in the photorefractivity of the SiO2-SnO2:Er3+ glass-ceramics, XRD and Raman characterizations are employed. The grating fabrication by direct UV writing on the SiO2-SnO2:Er3+ glass-ceramic planar waveguide as well as an important reduction in the employed energy is demonstrated. The graph presents significant and fast UV-induced effective refractive index change at 1550 nm of the 70SiO2-30SnO2:0.5Er3+ planar waveguide as a function of the cumulative dose of laser exposure. The first dose (0.003 kJ/cm2) caused a change of -1.10 × 10-3 whereas, the saturated value of -2.60 × 10-3 was achieved after the cumulative UV dose of 0.3 kJ/cm2. The inset image shows the direct UV-written optical grating fabricated on a 4 × 4 mm2 area of such glass-ceramic planar waveguide. It was obtained by a CW frequency doubled argon laser λ = 244 nm with a writing fluence of only 1 kJ/cm2, that was one order of magnitude less than in the case of gratings fabrication on germanosilicate glasses. [Display omitted] •SiO2-SnO2:Er3+ glass-ceramic planar waveguides (SnO2: 20 and 30 mol%) exhibit high UV-induced photorefractivity.•Δneff = −2.60 × 10−3 : negative effective refractive index change is observed after 248 nm irradiation.•Fast photorefractive response of SiO2-SnO2:Er3+: Δneff saturated under only 0.3 kJ/cm2 cumulative dose of 248 nm irradiation.•Increasing SnO2 content in glass-ceramic increases the magnitude of negative effective refractive index change.•Direct UV-written gratings on SiO2-SnO2:Er