Arbitrary-shaped Brillouin microwave photonic filter by manipulating a directly modulated pump

Benefits of Spectral Property Engineering in Distributed Brillouin Fiber Sensing

As one of the most consolidated distributed fiber sensors based on stimulated Brillouin scattering, the Brillouin optical time-domain analyzer (BOTDA) has been developed for decades. Despite the commercial availability and outstanding progresses which has been achieved, the intrinsic Lorentzian gain spectrum restricts the sensing performance from possible further enhancements and hence limits the field of validity of the technique. In this paper, the novel method of engineering the gain spectral properties of the Brillouin scattering and its application on static and dynamic BOTDA sensors will be reviewed. Such a spectral property engineering has not only provided improvements to BOTDA, but also might open a new way to enhance the performance of all kinds of distributed Brillouin fiber sensors.

Tunable dual-passband microwave photonic filter with a fixed frequency interval using phase-to-intensity modulation conversion by stimulated Brillouin scattering

An approach to realizing a highly selective and stable tunable dual-passband microwave photonic filter (MPF) is proposed and experimentally demonstrated, in which two passbands have a fixed frequency interval. The MPF is achieved based on phase-to-intensity modulation (PM-IM) conversion by stimulated Brillouin scattering (SBS). The kernel of the proposed scheme is generating a two-tone pump by first frequency-downshifting the optical carrier through self-induced SBS in a spool of single-mode fiber (SMF), and then modulating it in carrier-suppressed double-sideband modulation mode. Making use of Brillouin frequency shift difference between the SMF and the high nonlinear fiber used for PM-IM conversion, two passbands with a fixed frequency interval equal to 2 times the Brillouin frequency shift difference between the two fibers can be achieved. Through simply varying the modulation frequency, the two passbands can be synchronously shifted back and forth. In the experiment, a tunable dual-passband MPF with a fixed frequency interval of 2.434 GHz is demonstrated in the frequency range of 0-9.644 GHz, where the out-of-band rejection ratio and the 3-dB bandwidth of the passbands are measured to be larger than 20 dB and smaller than 57 MHz, respectively.