“…The key parameters of the reviewed lasers are given in Table 1. The mechanisms used for creation of wavelength-dependent losses include polarisation effects (birefringent spectral filters [86] introducing minimal losses for radiation that does not change polarisation when passing through the filter; polarisation controller(s) [45,69,73,81] or intra-cavity waveplates [83], whose function is essentially similar to that of a birefringent filter; intensity-dependent variation of birefringence in the cavity [84,85]; Sagnac loop mirror [87] with spectrally controlled reflection), interference effects (various interferometers: Fabry-Pérot [88], Mach-Zehnder [89], and so on), dispersion effects (prisms [90], diffraction gratings [64,68,76,82], acousto-optical filters [49,77]). The majority of the wavelength tuning mechanisms used in pulsed fibre lasers are known; they were earlier applied to other types of lasers.…”