Rare-earth-ion-doped dielectric waveguides on a silicon chip: Fabrication, spectroscopy, amplification, and lasing

Miniaturization and on-chip integration of high-performance light sources have become major issues for the progress in integrated optics. Over the past decades semiconductor amplifiers and lasers have emerged as the most-preferred choice. However, spatial and temporal gain-patterning effects evoked by the large refractive-index changes that are accompanied with electron-hole-pair excitation limit their performance in several respects. In recent years we have developed low-propagation-loss, rare-earth-ion-doped Al2O3 layers directly deposited onto silicon chips by reactive co-sputtering as viable alternatives. While a lifetime-quenching process limits particularly the performance of Al2O3:Er3+ as an amplifier to 2 dB/cm, this gain is nevertheless higher than the propagation losses in micro-structured channel waveguides of typically 0.2 dB/cm, allowing for efficient lasing. By use of Bragg gratings fabricated by laser interference lithography, we have demonstrated distributed-feedback lasers with ultra-narrow linewidth down to 1.7 kHz in Al2O3:Er3+, lasers with up to 55 mW output power and 67% slope efficiency versus launched pump power as well as dual-wavelength lasers and stable microwave beat-frequency generation in Al2O3:Yb3+, and nano-particle intra-laser-cavity optical sensing.