Abstract: The invention relates to an optical waveguide laser comprising a) an active region formed over a length of the optical waveguide, comprising an excitable material emitting light in response to stimulation by pump light thereby defining an optical gain profile and the excitable material comprises Tm; b) a frequency discriminated feedback element adapted to select a single longitudinal lasing mode by coordination with the frequency response of the optical gain of the excitable material; and c) a polarisation asymmetry element adapted for selecting a single polarisation mode of a given longitudinal mode by selectively suppressing propagation of the other polarisation mode of said longitudinal mode. The object of the present invention is to provide relatively simple, compact and economic lasers for single-frequency operation in the wavelength range of 1.7 um to 2.2 um; in particular for a number of applications, including spectroscopy and for eye-safe optical sources in sensing and in LIDAR, etc.