Fig. 1. Experimental setup of MPF. TLS, tunable laser; PC, polarization controller; PM, phase modulator; OC, optical coupler; SMF, single-mode fiber; EDFA, erbium-doped fiber amplifier; Cir, optical circulator; PD, photodetector; OSA , spectrum analyzer; VNA, vector network analyzer

Fig. 2. Illustration of tunable narrowband MPF principle. (a) Optical spectra of double sideband swept frequency modulated signal. (b) Optical spectra of SBS. (c) Amplification of the upper sideband of a DSB modulated signal using SBS gain. (d) FSR response of single-ring cavity R₁. (e) Response of MPF

Fig. 3. (a) Schematic diagram of side mode suppression by FSR. (b)The response of MPF based on Brillouin fiber oscillator

Fig. 4. Comparison of Brillouin gain and output light spectra of Brillouin fiber oscillator

Fig. 5. TLS pump spectrum, Brillouin laser output spectrum and combined output spectrum through coupler OC3

Fig. 6. The frequency response of MPF when the wavelength of the pump light is tuned from 1550.232 nm to 1550.392 nm.

Fig. 7. Frequency response of MPF when the wavelength of the pump light varies from 1550.214 nm to 1550.392 nm. (a) Overall comparison diagram in 20 GHz span，(b) expanded diagram with 30 MHz span

Fig. 8. 3-dB bandwidth and side mode suppression ratio at different center frequencies