Brillouin scattering

About: Brillouin scattering is a research topic. Over the lifetime, 11426 publications have been published within this topic receiving 178306 citations.

Beam cleanup in a self-aligned gradient-index Brillouin cavity for high-power multimode fiber amplifiers

Abstract: We propose a beam cleanup setup to convert a multimode beam into a single-mode beam by use of the Brillouin effect in a multimode gradient-index (GI) fiber. Phase conjugation and beam cleanup regimes in highly multimode fibers are discussed, and the self-aligned GI fiber Brillouin cavity is presented. We report a preliminary conversion from an M2=6.5 beam into an M2=1.3 beam with 31% efficiency.

Microwave Photonic Filter With Two Independently Tunable Passbands Using a Phase Modulator and an Equivalent Phase-Shifted Fiber Bragg Grating

Abstract: A dual-passband microwave photonic filter (MPF) implemented based on phase-modulation to intensity-modulation (PM-IM) conversion using a phase modulator and an equivalent phase-shifted fiber Bragg grating (EPS-FBG) is proposed and experimentally demonstrated. The key component in the system is the EPS-FBG, which is designed and fabricated based on the equivalent phase-shift technique. The unique feature of the EPS-FBG is that equivalent phase shifts are introduced to both of the ±1st channels, leading to a notch in each of the two channels. Thus, by implementing PM-IM conversion in the two channels, two passbands are produced. The central frequency of each passband is determined by the wavelength different between the notch and the optical carrier. In the design and fabrication, two phase shifts are introduced to the EPS-FBG to decrease the shape factor, which is defined as the ratio between the 20- and 3-dB bandwidths. In addition, a stimulated Brillouin scattering (SBS) assisted filter is incorporated in the system for carrier suppression to increase the spurious-free dynamic range (SFDR) and decrease the noise figure (NF) of the MPF. An experiment is performed. A dual passband filter with a 3-dB bandwidth and a shape factor of 167.3 MHz and 3.8, and 143.3 MHz and 3.3 for the 1st and 2nd passband is achieved. The frequency tunable ranges of the 1st and 2nd passbands are 5.4 and 7.4 GHz, respectively, with the magnitude variations of about ±0.5 dB during the turning. Due to the SBS-assisted filter, the SFDRs are increased by 7 dB and the NFs are decreased by 10 dB.

High γ-ray dose radiation effects on the performances of Brillouin scattering based optical fiber sensors

Abstract: The use of distributed strain and temperature in optical fiber sensors based on Brillouin scattering for the monitoring of nuclear waste repository requires investigation of their performance changes under irradiation. For this purpose, we irradiated various fiber types at high gamma doses which represented the harsh environment constraints associated with the considered application. Radiation leads to two phenomena impacting the Brillouin scattering: 1) decreasing in the fiber linear transmission through the radiation-induced attenuation (RIA) phenomenon which impacts distance range and 2) modifying the Brillouin scattering properties, both intrinsic frequency position of Brillouin loss and its dependence on strain and temperature. We then examined the dose dependence of these radiation-induced changes in the 1 to 10 MGy dose range, showing that the responses strongly depend on the fiber composition. We characterized the radiation effects on strain and temperature coefficients, dependencies of the Brillouin frequency, providing evidence for a strong robustness of these intrinsic properties against radiations. From our results, Fluorine-doped fibers appear to be very promising candidates for temperature and strain sensing through Brillouin-based sensors in high gamma-ray dose radiative environments.

Photonic Generation of Triangular-Shaped Microwave Pulses Using SBS-Based Optical Carrier Processing

Abstract: A photonic approach to generate triangular-shaped microwave pulses using stimulated Brillouin scattering (SBS)-based optical carrier processing is proposed and experimentally demonstrated. In the proposed approach, only odd-order optical sidebands are obtained by externally modulating the CW light wave using a Mach–Zehnder modulator (MZM) biased at the minimum-transmission-point (MITP). Then the suppressed optical carrier is recovered by the amplification effect from the SBS gain. After that, all negative-order optical sidebands are removed by using an optical filter. Through opto-electronic conversion in a photodetector (PD), the amplitude of the 1st-order electrical harmonic can be tuned just to be nine times of that of the 3rd-order one when the modulation index is specified as 1.51. Therefore the target pulse is generated and its repetition rate can be flexibly tuned by adjusting the frequency of the radio frequency (RF) signal applied to the MZM. According to the principle above, triangular-shaped microwave pulses with repetition rates of 5, 8, and 10 GHz are generated in our experiments, respectively, showing desired waveforms and excellent tunability.