Microring Lasers Based on Single Crystal Er:Gd₂O₃ Thin Films on Silicon

On-chip Er-doped optical amplifiers and lasers have attracted great attentions recently as active photonic devices for photonic integrated circuits [1], [2]. However, the footprint of the previously reported devices was quite large due to the small optical gain in commonly used Er-doped amorphous host materials. Er-doped crystal materials have potential to realize much larger gain due to their larger optical absorption and emission cross-sections and higher Er doping concentrations. Regarding this, we proposed to use single crystal rare-earth oxide e.g., Er<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>: Gd<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>) thin films epitaxially grown on silicon [3]. Low loss waveguides and large optical gain have been demonstrated in this platform [4], [5]. In this work, we present the first demonstration of lasers based on high Q-factor microring resonators at cryogenic temperatures.