In X-ray object detection, scale awareness and spatial awareness (SA) are two independent issues. Previous research has attempted to address these two issues separately using different methods but lacked a unified approach to solve both problems simultaneously. This paper presents a single-stage object detector, referred to as scale and SA-based prohibited item detection, which consists of the multi-level fusion module (MLF) and the SA module. MLF is designed to learn multi-level features to enhance scale awareness, and SA is designed to learn and focus on object spatial information to enhance SA. Compared with previous research, our method shows outstanding performance in detection accuracy. Moreover, our single-stage object detector outperforms the accuracy of two-stage object detectors by 1.5 AP.
Based on the polarization vector propagation equation of stimulated Brillouin scattering (SBS) nonlinear effects in fibers, we find the spectral polarization spreading behavior in SBS. As a signal light propagates along a fiber, the state of polarization of different frequency components of the signal light will experience different polarization pulling forces from the counter propagating pump light, resulting in a nearly circular symmetry of spectral spreading of the polarization state at the output end of fiber. Through theoretical analysis and simulation, this paper studies the SBS spectrum polarization spreading effects in the cases of ideal single mode fiber(SMF), practical SMF, and polarization maintaining fiber (PMF). Finally, we demonstrate the SBS spectrum polarization spreading effect in a 200m SMF and a 140m PMF experimentally and good agreement with theory is found.
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