Fiber-coupled microsphere laser.

We demonstrate a 1.5-microm - 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 1.5microm . Laser threshold pump powers of 60muW and fiber-coupled output powers as high as 3 muW with single-mode operation were obtained. A bisphere laser system consisting of two microspheres attached to a single fiber taper is also demonstrated.