Fig. 1. Experimental setup in different structures (a) with BOA without SIL, (b) with SIL without BOA, and (c) with BOA and SIL. FBG, fiber Bragg grating; PM-NB-FBG, PM narrow-band FBG; BB-FBG, broadband FBG; LD, laser diode; PM-WDM, PM wavelength division multiplexer; PM-CIR, PM circulator; PMI, PM isolator; PM-BPF, PM bandpass filter; PMTI, PM tap isolator; VOA, variable optical attenuator.

Fig. 2. RIN spectra of this single-frequency fiber laser with different conditions. The quantum noise limit of −152.9  dB/Hz is also shown for comparison. (a) 0 to 5 MHz. (b) 0 to 50 MHz.

Fig. 3. Measured signals of coherent light detection of this single-frequency fiber laser in different statuses.

Fig. 4. (a) Optical spectra of this fiber laser at different output ports. The inset shows the degree of polarization of the final laser output (red dot) represented by a Poincaré sphere. (b) Measured single-longitudinal-mode characteristic of the final laser output.

Fig. 5. (a) Measured self-heterodyne spectra of this fiber laser with different conditions. (b) Measured frequency noise spectra and estimation line for evaluation of linewidth.