Luminescent features in double-track type II waveguides made in Er/Yb:LiNbO3 by Ultrafast Laser Inscription

Abstract This work reports the first double-track type II waveguides fabricated by Ultrafast Laser Inscription (ULI) in a z-cut crystal of Er0.5% Yb0.5%LiNbO3. The light-guiding properties were explored and it was found that both polarization modes, TE and TM, are supported at a wavelength of 1550 nm. Also, a thorough spectroscopic characterization of these structures was performed. All luminescence bands of active ions and their corresponding lifetimes were measured and scanning confocal μ-photoluminescence maps were developed. Slight shifts and broadening were found, relative to the bulk, for some specific emission peaks in waveguides. Particularly, Yb3+ ions luminescence within a region up to 2 μm from to where the laser struck during ULI processing, exhibited changes of their positions, heights and widths. The contribution of ULI to the ion environment distortions could be detected by confocal microscopy and could be decoupled from multi-site effects. This procedure can be taken as a quality control tracking of waveguides fabricated by ULI, if one considers variations in micromachining parameters (energy per pulse, speed of writing, repetition rate or pulse duration) as well as in concentration ratios of Er/Yb, or even annealing treatments. Although spectral modifications were resolved, the bulk spectra of these ions are essentially preserved in the waveguide core and surroundings. Therefore, this gives rise to explore these Er/Yb co-doped waveguides as active photonics devices, considering the rich spectra of Er3+ ions: green, red and NIR (1550 nm) emissions and the doping with Yb3+ ions to improve its efficiency.