We describe a single frequency, unidirectional erbium fiber ring laser. Wavelength selection is performed by a ‘‘continuous fiber’’ filter of the fiber to planar waveguide coupler type. Varying the refractive index experienced by the exposed surface of the filter allowed the single longitudinal mode output from the laser to be tuned, discretely, from 1556–1561 nm with a resolution limited linewidth of 52 kHz. ©1995 American Institute of Physics.