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Highly coherent wave is favorable for applications in which phase retrieval is necessary, yet a high coherent wave is prone to encounter Rayleigh fading phenomenon as it passes through a medium of random scatters. As an exemplary case, phase-sensitive optical time-domain reflectometry (Φ-OTDR) utilizes coherent interference of backscattering light along a fiber to achieve ultra-sensitive acoustic sensing, but sensing locations with fading won't be functional. Apart from the sensing domain, fading is also ubiquitous in optical imaging and wireless telecommunication, therefore it is of great interest. In this paper, we theoretically describe and experimentally verify how the fading phenomena in one-dimension optical scatters will be suppressed with arbitrary number of independent probing channels. We initially theoretically explained why fading would cause severe noise in the demodulated phase of Φ-OTDR; then M-degree summation of incoherent scattered light-waves is studied for the purpose of eliminating fading. Finally, the gain of the retrieved phase signal-to-noise-ratio and its fluctuations were analytically derived and experimentally verified. This work provides a guideline for fading elimination in one-dimension optical scatters, and it also provides insight for optical imaging and wireless telecommunication.

In the distributed optical fiber sensing (DOFS) domain, simultaneous measurement of vibration and temperature/strain based on Rayleigh scattering and Brillouin scattering in fiber could have wide applications. However, there are certain challenges for the case of ultra-long sensing range, including the interplay of different scattering mechanisms, the interaction of two types of sensing signals, and the competition of pump power. In this paper, a hybrid DOFS system, which can simultaneously measure temperature/strain and vibration over 150 km, is elaborately designed via integrating the Brillouin optical time-domain analyzer (BOTDA) and phase-sensitive optical time-domain reflectometry (Ф-OTDR). Distributed Raman and Brillouin amplifications, frequency division multiplexing (FDM), wavelength division multiplexing (WDM), and time division multiplexing (TDM) are delicately fused to accommodate ultra-long-distance BOTDA and Ф-OTDR. Consequently, the sensing range of the hybrid system is 150.62 km, and the spatial resolution of BOTDA and Ф-OTDR are 9 m and 30 m, respectively. The measurement uncertainty of the BOTDA is ± 0.82 MHz. To the best of our knowledge, this is the first time that such hybrid DOFS is realized with a hundred-kilometer length scale.

The full exploration of Si-based photonic integrated circuits is limited by the lack of an efficient light source that is compatible with the complementary metal− oxide−semiconductor process. Highly strained germanium (Ge) is a promising solution, as its band structure can be fundamentally altered by introducing tensile strain. However, the main challenge lies in the incorporation of an electrical structure while maintaining high strain with uniform distribution in the active region. Here we present highly strained Ge LEDs driven by lateral p−i−n junctions and report the strain-induced enhancement of electroluminescence (EL) from Ge. Raman characterization shows that 1.76% strain along the ⟨100⟩ direction with relatively uniform strain distribution is achieved. The observed strain-induced red-shifts of EL spectra agree well with the theoretical prediction, revealing that the direct band gap of Ge can be tuned in the range of 0.785 eV (1580 nm) to 0.658 eV (1885 nm). This work offers a pathway toward a strained Ge laser with low threshold current, as well as opens possibilities for new types of optoelectronics devices based on strain engineering.

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Three‐dimensional porous SnO2/rGO xerogels with superior cycling performance in lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs) are fabricated through a freeze‐drying‐assisted method. SnO2 nanoparticles (5 nm in diameter) are homogeneously attached to the surface of graphene sheets without self‐aggregation. The heterostructured SnO2/rGO xerogel possesses numerous micron‐sized pores that can efficiently buffer the volumetric change of SnO2 during the charge/discharge process and provide multidimensional channels, improving the conductivity between active materials and electrolyte. The SnO2/rGO xerogel exhibits excellent electrochemical performance, both in LIBs and SIBs, owing to its particular porous structure. For LIBs, it delivers a high initial discharge capacity of 1670.5 mAh g−1 in the first cycle and remains at 1139.4 mAh g−1 after 166 cycles at a current density of 0.1 A g−1. The SnO2/rGO xerogel also delivers a high discharge capacity of 189.4 mAh g−1 without capacity loss over 266 cycles at a current density of 0.5 A g−1 for SIBs. The SnO2/rGO xerogel can be used as an electrode material in both LIBs and SIBs, and can maintain an excellent rate performance and cyclic performance, owing to the abundant porosity and high conductivity.

FeCO 3 is a potential anode material, owing to advantages such as facile synthesis, low cost, and abundant natural resources, but its poor cyclic stability and low rate performance seriously limit practical applications in lithium-ion batteries (LIBs). In this paper, the sheath/core hybrid of FeCO 3 /carbon nanofibers (CNFs) as a binder-free anode for high-performance LIBs has been synthesized by using a facile hydrothermal method. Porous FeCO 3 nanosheets grow in a stable manner on the surface of CNFs, and the flexible FeCO 3 /CNF film gives a specific surface area as high as 302.6 m 2 g À1 . The FeCO 3 /CNF film, with its porous architecture, provides open and continuous channels for fast diffusion of Li + to the active material of FeCO 3 , whereas the CNFs effectively play the leading role as the conductive core to efficiently transfer electrons for rapid lithiation/delithiation of FeCO 3 , and offer a buffering network to reduce the volume change during cycling. The hybrid FeCO 3 /CNF film, as a binderfree anode, delivers 592.2 mAh g À1 at the 3rd cycle and 546.2 mAh g À1 at the 200th cycle. As a comparison, bare FeCO 3 drops to 101 mAh g À1 at the 200th cycle. At a current density of 2 Ag À1 , FeCO 3 /CNF delivers 308.2 mAh g À1 , which is far higher than the 11 mAh g À1 of bare FeCO 3 and 52 mAh g À1 of bare CNFs. The FeCO 3 /CNF film presents an applicable hybrid structure as a binder-free anode material for ultrathin and ultralight energy-storage devices.