Observation of anti-Stokes-fluorescence cooling in commercial Yb-doped silica fibers

Optical cooling of Yb-doped silica fibers using anti-Stokes fluorescence (ASF) has emerged as a powerful technique to produce fiber lasers and amplifiers that generate no heat. This paradigm offers an unprecedented opportunity to engineer a new generation of devices with greater power and frequency stability, smaller size, weight, and power consumption, and greater ease of power scaling. While cooling in silica has been demonstrated so far only in custom compositions, here we show that commercial Yb-doped silica fibers can also be cooled by ASF. The best of seven tested fibers cooled by −85 mK from ambient. This is, however, significantly less than the current record (−250 mK) held by a custom aluminophosphosilicate fiber with a similar core area. We show that the commercial fibers do not cool as well because of a lower Yb concentration, higher quenching, and/or higher background absorption. This work establishes that commercial fibers can be used to carry out valuable research on ASF cooling and athermal lasers. It also quantifies the significant improvements in Yb concentration, quenching suppression, and background-absorption reduction achieved in these custom silica compositions. These fibers are expected to have a major impact on fiber lasers and amplifiers, whose performance also depends critically on these three metrics.