Fig. 1. Experimental setup. TLS: tunable laser source; Cir: circulator; PC: polarization controllers; OC: optical coupler; SMF: single-mode fiber; ESA: electrical spectrum analyzer; PM-EDF: polarization maintaining erbium-doped fiber; PD: photodetector; OSA: optical spectrum analyzer.

Fig. 2. The foundational concept behind the BFL based on PT symmetric and SA effect. (a) The occurrence of Stimulated Brillouin Scattering in the optical spectrum. (b) The mode selection operational principle when the PT symmetry breaking occurs within the PT-symmetric BFL

Fig. 3. Measured optical spectrum. (a) The optical spectrum of the BFL and 1550 nm pump wavelength and (b) the threshold curve between the pump intensity and BFL output intensity

Fig. 4. The wavelength tunability measurement results of the BFL based on SA effect and PT symmetric

Fig. 5. The spectral analysis results of the frequency beat signals emitted from the PD. (a) Unbroken PT-symmetry and (b) broken PT-symmetry with their magnified view under 0−4 MHz frequency range; (c) and (d) are enlarged views at 100−300 kHz respectively; (e) and (f) present a comparative diagram of the measured spectra, demonstrating the effects of PT-symmetry under 300−500 kHz and 500−700 kHz frequency ranges respectively

Fig. 6. The linewidth measurement setup of the BFL based on PT symmetric and SA effect

Fig. 7. The linewidth measurement results of the BFL under the -20 dB intensity point