We propose a compact LIBS system with micro-spectrometers and optical filters, achieving a reduction in size and cost for water heavy metal detection while enhancing sensitivity and portability.
High-capacity S + C + L-multiband dual-polarization optical fiber transmission is proposed and experimentally demonstrated using C/S-interband broadband all-optical wavelength conversion (AOWC) based on low group velocity mismatch (GVM) periodically poled lithium niobate (PPLN) waveguides. The interband AOWC is realized through difference-frequency generation (DFG) in a low-GVM PPLN waveguide pumped by the 764 nm second-harmonic generation (SHG) of a 1528 nm fundamental wave in another PPLN waveguide. A maximum conversion efficiency of −13.2dB and a conversion bandwidth of 146 nm are achieved. By polarization splitting, the dual-polarization AOWC is realized by using two DFG PPLN waveguides in parallel, and the average conversion efficiency is measured to be −16.2dB with a noise figure of about 9.4 dB. Based on the C/S-interband AOWCs, S + C + L-multiband dual-polarization transmission is performed over 125 km, where 128 wavelength channels are uploaded with a single-channel 200 Gb/s DP-QPSK signal. The OSNR difference introduced by S-band transmission is only about 0.5 dB in comparison to the C-band transmission.
Na2FePO4F emerges as a promising cathode material for sodium-ion batteries owing to its low cost, environmental benignity, and reasonably high theoretical capacity. Nevertheless, its practical application is hampered by limited electronic conductivity and ion diffusion rates. This investigation explores low-cost Na2FePO4F1-x (0 <= x <= 0.1) compounds with fluorine defects as potential cathodes for sodium-ion batteries. Specifically, the Na2FePO4F1-x (x = 0.04, denoted as NFPF-0.04) sample demonstrates a narrow band gap of 0.509 eV and a higher Na+ diffusion coefficient of 2.34 x 10-10 cm2 s-1 and also exhibits a volumetric change of only 1.76% during the first charge/discharge cycle. The NFPF-0.04 sample delivers a discharge capacity of 115.3 mAh g-1 at 0.1C, and the capacity retained 75.1% at 10C after 500 cycles. These improved electrochemical performances are attributed to changes in Na-O(F) and Fe-F1/F2 bond lengths induced by a small amount of fluorine defects. The insights into the enhancement of ion diffusion kinetics and mitigation of volume change are expected to accelerate the optimization of Na2FePO4F1-x electrodes for sodium-ion batteries.
In this paper, we analyze the causes and impacts of the misalignment problem in underwater wireless optical communication (UWOC) that arises from the non-common aperture between the optical communication subsystem and the optical alignment subsystem. Subsequently, we propose a new solution that utilizes a dual-spiral position-sensitive detector (PSD). By designing the diameter of the received light spot to match the width D of the spiral PSD, analysis indicates that when the deviation of the spot size remains within 10%, the measurement error for the spot position stays below 2%.
Coherent technology is a promising solution for the future passive optical networks (PONs) to meet the demand for higher bandwidth. Recently, time and frequency division multiplexing (TFDM) PON based on digital subcarrier multiplexing (DSCM) has attracted increasing interest due to its flexible bandwidth allocation and notably low latency advantages. However, upstream burst-mode detection is a critical challenge when adopting a coherent TFDM PON system. To accelerate digital signal processing (DSP) convergence with a minimal preamble length, we propose an upstream system scheme and an efficient burst-mode preamble design. The scheme employs single-polarization and residual carrier modulation combined with specialized spectrum allocation to reduce the cost and shorten the preamble length. The designed preamble uses the same training unit to jointly implement frame synchronization, fine frequency offset estimation (FOE), polarization compensation, and channel estimation. This integration significantly reduces the preamble length. The design is experimentally verified in a 200-Gb/s TFDM upstream transmission over 20-km standard single-mode fiber (SSMF). Using a 20.48-ns preamble with 256 training symbols (TS), a receiver sensitivity of approximately −27 dBm is achieved at the bit error rate (BER) threshold of 1 × 10 −2 .
