Abstract <p>The paper discusses the prospects of using single-frequency fiber lasers based on two different types of active fibers from the point of view of their applying for interrogating hydroacoustic antennas. Two single-frequency fiber lasers fabricated from two different types of erbium-doped fibers have been demonstrated. One of the lasers was made using conventional erbium doped fiber manufactured by vapour phase deposition technique. Another was based on a new type of fiber made by sintering phosphate glass in a silica glass tube (composite fiber). Both fibers were photosensitive to laser radiation at a wavelength of 248 nm (KrF excimer laser), and laser cavities were inscribed directly in the core of these types of active fibers. Stable single-frequency lasing was obtained for both laser configurations. The maximum value of relative intensity noise measured at the frequency of relaxation oscillations was approximately the same for both laser configuration: –82 and –86 dB/Hz, but the generation bandwidth in the conventional fiber laser was lower: 6.5 kHz instead of 14 kHz in composite fiber laser. Due to the high concentration of erbium ions the slope efficiency of the laser based on composite fiber was 0.98% compared to a conventional erbium doped fiber laser (0.19%).</p>