Stable and narrow linewidth linear cavity CW-active Q-switched erbium-doped fiber laser

A stable and narrow-linewidth, continuous wave and active Q-switching erbium-doped fiber laser, incorporating a fiber Bragg grating and a fiber Fabry-Perot tunable filter, was designed and experimentally implemented. Here, we proposed combining three approaches to suppress the mode hopping and improve both the output power stability and narrow the linewidth: first, two narrow-band optical filters, fiber Bragg grating and Fabry-Perot tunable filter were utilized in the laser cavity; second, the cavity configuration was optimized as a function of the output coupling ratio; finally, a 1.5 m long segment of unpumped erbium-doped fiber was inserted in the cavity to act as an induced virtual long and weak fiber Bragg grating. Using a 90% output coupling ratio, and monitoring over 120 min at room temperature, the 3 dB linewidth and power fluctuation of the fiber laser emission at 1550 nm were 16 kHz and 0.0025 dB respectively. Also, an optical signal to noise ratio (OSNR) of 82 dB was obtained. Keeping the same fiber laser configuration, laser pulses were also obtained using the Q-switching technique, realized by using dynamic spectral overlapping between the Bragg grating and the tunable filter. A stable output peak power of 5.6 W was achieved with a pulse width of 450 ns at a repetition rate of 1 kHz.