Fiber-coupled microsphere laser

We demonstrate a $1.5‐\mathit{\mu }\mathrm{m}$-wavelength fiber laser formed by placement of glass microsphere resonators along a fiber taper. The fiber taper serves the dual purpose of transporting optical pump power into the spheres and extracting the resulting laser emission. A highly doped erbium:ytterbium phosphate glass was used to form microsphere resonant cavities with large gain at $1.5 \mathit{\mu }\mathrm{m}$. Laser threshold pump powers of $60 \mathit{\mu }\mathrm{W}$ and fiber-coupled output powers as high as $3 \mathit{\mu }\mathrm{W}$ with single-mode operation were obtained. A bisphere laser system consisting of two microspheres attached to a single fiber taper is also demonstrated.