Ultralow-threshold Yb3+:SiO2 glass laser fabricated by the solgel process

A Yb-doped silica microcavity laser on a silicon chip is fabricated from a solgel thin film. The high-Q microtoroid cavity, which has a finesse of 10,000, is evanescently coupled to an optical fiber taper. We report a threshold of 1.8 μW absorbed power that is, to the best of our knowledge, the lowest published threshold to date for any Yb-doped laser. The effect of Yb3+ concentration on laser threshold is experimentally quantified.