  We present the first demonstration of a narrow linewidth, waveguide-based
Brillouin laser which is enabled by large Brillouin gain of a chalcogenide
chip. The waveguides are equipped with vertical tapers for low loss coupling.
Due to optical feedback for the Stokes wave, the lasing threshold is reduced to
360 mW, which is 5 times lower than the calculated single-pass Brillouin
threshold for the same waveguide. The slope efficiency of the laser is found to
be 30% and the linewidth of 100 kHz is measured using a self-heterodyne method.
