We describe a polarization-maintaining (PM) λ/4-shifted DFB Er-doped fiber laser (EDFL), in which optical pulsation effects caused by Er 3+ ion-pairs were successfully removed by co-doping erbium fiber with 12 wt% aluminum. Stable CW operation was realized at a pump power of 100 mW. The laser exhibited single longitudinalmode oscillation with a single polarization. The output power, linewidth of the longitudinal mode, and RIN at the relaxation oscillation frequency were 0.5 mW, 82 kHz, and −79

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... B/Hz at a pump power of 100 mW, respectively. Stable operation was also obtained at a pump power of 140 mW, where the above values were improved to 0.8 mW, 43 kHz, and −92 dB/Hz, respectively.