Microwave photonic filter with a sub-kHz bandwidth based on a double ring Brillouin fiber laser

Abstract

A scheme to achieve a sub-kHz bandwidth microwave photonic filter (MPF) based on a double-ring Brillouin fiber laser (DR-BFL) is proposed and experimentally verified in this study. The stimulated Brillouin scattering gain spectrum can be efficiently narrowed by the DR-BFL, which comprises a main-ring cavity with a 100-m single-mode fiber (SMF) and a sub-ring cavity with a 10-m SMF. A single passband narrow bandwidth MPF is accomplished by the DR-BFL with a single longitudinal mode laser output using the Vernier effect. The bandwidth of the MPF at the center frequency of 10.735 GHz is 114 Hz, and the corresponding Q-factor is 9.42 × 107, which is the highest Q value to the best of our knowledge. Since the measured linewidth of the DR-BFL is 1.2 Hz at the −20-dB power point, the theoretical bandwidth of the DR-BFL-based MPF is 0.16 Hz. This design provides a new idea for realizing high-precision signal extraction in future communication or sensing systems.

Ultra-Narrow Bandwidth Microwave Photonic Filter Implemented by Single Longitudinal Mode Parity Time Symmetry Brillouin Fiber Laser

“…), where the useful RF signal is only distributed within the ultra-narrow bandwidth of kHz order or below. Based on these research foundations, various methods for improving filter bandwidth and compressing it to a narrower range have been reported in many literature [ 19 , 20 , 21 , 22 , 23 ] in recent years. Zhang et al [ 20 ] achieved an MPF which has a bandwidth of 7.8 MHz and a gain response of 24 dB by clipping one Brillouin gain spectra with two Brillouin loss spectra.…”

“…Based on the above analysis, we can see that the MPF technology based on lasers is considered to be one of the most promising means for achieving narrowband filtering and wide tunability [ 22 , 23 , 32 , 33 , 34 ]. Wherein, a MPF [ 32 ] using a multiwavelength erbium-doped fiber laser (EDFL) is demonstrated, but its central frequency is not tunable.…”

“…An approach for achieving single channel MPF utilizing polarization modulators and broadband tunable FP lasers has been presented in [ 34 ]; however, because the modulated signal carried by the signal light is obtained by VNA modulating the electro-optic modulator (EOM) with RF scanning signal, the performance of the EOM limits its adjustable range. Recently, in [ 22 , 23 ], the authors achieved a sub-kHz bandwidth MPF based on a double-ring Brillouin fiber laser. However, the vernier effect used in dual ring resonators has the disadvantage of difficulty in matching different free spectral range (FSR) peaks, which limits mode selection efficiency.…”