550-mW output power from a narrow linewidth all-phosphate fiber laser

We present a compact monolithic all-phosphate glass fiber laser with up to 550 mW of output power operating on a single longitudinal mode. We measured a linewidth of less than 60 kHz and relaxation oscillation peak amplitudes below -100 dB/Hz without active RIN-supression. The laser cavity has been formed by inscribing fiber Bragg gratings (FBG) directly into heavily Er ³⁺Yb³⁺ doped phosphate glass fiber using femtosecond laser pulses and a phasemask. The compact form factor and higher output power combined with the low noise and narrow line width characteristic make this laser an ideal candidate for ranging, interferometry and sensing applications.