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We have demonstrated the possibility of making a Raman laser with a random distributed feedback ensured by an array of 57 fibre Bragg gratings with random phases and amplitudes inscribed in a 13-m-long polarisation-maintaining passive fibre. The linearly polarised cw output power at a wavelength of 1092.3 nm reaches 5.7 W. The laser linewidth at the highest output power is about 80 pm. In the nearthreshold regime, we observe single-frequency lasing with a linewidth under 100 kHz as determined by self-heterodyne measurements.

Numerical modelling demonstrates the possibility of fabricating an all-fibre multibeam two-mirror reflection interferometer based on a metal–dielectric diffraction structure in its front mirror. The calculations were performed using eigenmodes of a double-clad single-mode fibre. The calculation results indicate that, using a metallic layer in the structure of the front mirror of such an interferometer and a diffraction effect, one can reduce the Ohmic loss by a factor of several tens in comparison with a continuous thin metallic film.

We consider the use of a two-mirror multibeam reflection interferometer as a selector of linear-cavity single-mode fibre laser radiation and present experimental data on continuous wavelength tuning of an erbium-doped fibre laser. Conditions are found for single-longitudinal-mode operation of the fibre laser cavity using a reflection interferometer, with the possibility of broadband wavelength tuning.