Future local area networks require seamlessly converging legacy fiber and future indoor optical wireless (OW) transmission systems, enabling continuous signal propagation across the entire fiber-OW links without intermediate optical-electrical/electrical-optical conversion and/or digital signal processing. As 850 nm is the most imperative wavelength for indoor OW applications, existing ITU-T G.652.D standard single-mode fibers (SSMFs) at such a wavelength support two propagation modes (LP 01 and LP 11 ), and the resulting differential mode delay restricts the achievable 3-dB bandwidths to <250 MHz·km. To effectively address the technical challenge, under strong mode-coupling conditions emulated by multiple cascaded optical connectors, this paper experimentally demonstrates, for the first time, a fiber-OW-converged transmission system incorporating 850-nm two-mode separators, achieving continuous 850-nm signal propagation across ∼1 km SSMF and 2.5 m OW links at bitrates of 23.5 Gbit/s. The two-mode separators are constructed using commercially available 1550-nm polarization controllers and optical couplers, offering effective LP 01 mode extractions with a purity of >99%. With such mode separators, the achievable 3-dB bandwidths of the fiber-OW-converged transmission systems are increased to 7.4 GHz, resulting in 29-fold bandwidth enhancements. Moreover, 850-nm signal propagation characteristics are thoroughly characterized experimentally and numerically in ∼1 km SSMF links with multiple cascaded optical connectors. The experimental and numerical results show that even a single additional optical connector can lead to relatively strong mode coupling, which can be further intensified by increasing the number of optical connectors.

The exploitation of phosphors with tunable color emissions is of great significance in the field of display and lighting. Herein, a series of Eu3+/Dy3+/Eu2+ ions single-/multiple-doped NaMgPO4 phosphors have been successfully synthesized via a high-temperature solid-state reaction method. The luminescence properties of the synthesized NaMgPO4 phosphors were systematically investigated. The incorporation of Dy3+ enables the tuning of emission peaks in NaMgPO4:Eu3+ phosphors through an efficient energy transfer (ET) process from Eu3+ to Dy3+, thereby facilitating white light emission in a single-composition phosphor. Eu3+ and Eu2+ co-activated NaMgPO4 phosphors were achieved by controlling the reduction of Eu3+ to Eu2+ under a reducing atmosphere generated by activated carbon. Photoluminescence (PL) spectra revealed simultaneous blue emission from Eu2+ and red emission from Eu3+. By varying the amount of activated carbon, tunable emission colors can be realized in the Eu3+/Eu2+ codoped NaMgPO4 phosphors. Consequently, through the strategic design of rare-earth ion codoping, the Eu3+/Dy3+/Eu2+ ions single-/multiple-doped NaMgPO4 phosphors exhibit promising practical applications in phosphor-converted white light-emitting diodes (LEDs).

The previously proposed cascaded inverse fast Fourier transform/fast Fourier transform (IFFT/FFT)-based point-to-multipoint (P2MP) flexible optical transceivers have the potential to equip future intensity modulation and direct detection (IMDD) optical access networks with excellent flexibility, adaptability, scalability and upgradability. However, due to their cascaded IFFT-based multi-channel aggregations, P2MP flexible transceivers suffer high peak-to-average power ratios (PAPRs). To address the technical challenge, this paper proposes a novel P2MP flexible optical transceiver, which uses a cascaded discrete Fourier transformation-spread (DFT-Spread) IFFT/FFT-based multi-channel aggregation/de-aggregation and standard signal clipping to jointly reduce its PAPRs. The upstream performances of the proposed transceivers are numerically explored in a 20 km IMDD upstream passive optical network (PON). The results indicate that the proposed transceiver’s PAPRs are mainly dominated by the size of the last IFFT operation of the multi-channel aggregation, and are almost independent of modulation format and channel count. Compared to conventional cascaded IFFT/FFT-based P2MP transceivers with and without clipping operations, the proposed DFT-Spread P2MP transceivers can reduce PAPRs by 2.6 dB and 3.5 dB, respectively, for a final IFFT operation size of 1024. More significant PAPR reductions are achievable when the last IFFT operation size is increased further. As a direct result, compared to conventional P2MP transceivers adopting clipping operations only, the proposed transceiver can improve upstream receiver sensitivities by >1.9 dB and the aggregated upstream transmission capacities by >14.1%. Such aggregated upstream transmission capacity enhancements are independent of channel count and become more pronounced for longer transmission distances.

Point-to-multipoint (P2MP) optical transceivers are promising for meeting the diversified requirements of emerging applications in the 6G era. However, for intensity modulation and direct detection (IMDD) passive optical networks (PONs), the previously reported P2MP optical transceivers cannot effectively accommodate a large number of diversified applications due to their limited flexibility, high digital signal processing (DSP) complexity and latency, as well as relatively high sensitivity to transmission system impairments. To cost-effectively address the challenges, this paper proposes a novel P2MP flexible optical transceiver based on a new parallel multi-channel aggregation/de-aggregation operation and an advanced extended Gaussian function (EGF)-based orthogonal digital filter bank. In comparison with the previously reported transceivers in a >50Gbit/s@25 km IMDD upstream PON with two optical network units (ONUs), our experimental measurements show that for channel counts of 8 (>10), the proposed transceivers can enhance the maximum achievable upstream transmission capacities by >52% (>290%). The new design can also reduce the overall transmitter DSP complexity (transmitter maximum DSP latency) by >70% (>24%) and decrease the receiver multi-channel de-aggregation DSP complexity by >40%. In addition, for the proposed transceivers, the network operation flexibility and scalability are also experimentally explored in a 25 km, >52Gbit/s IMDD upstream PON with five ONUs supporting 70 independent channels of different bandwidths and latencies. It is shown that the proposed transceivers fully support flexible sleep-awake ONU operation, and for a specific ONU, doubling the activated ONU count can only increase its required minimum received optical powers by ∼1.7 dB. Furthermore, the proposed transceivers can also support the ONU count growth without considerably compromising the maximum achievable upstream transmission capacities.

Modulation format identification (MFI) is one of the most critical functions embedded in digital coherent receivers in elastic optical networks (EONs). In view of inherent amplitude and phase characteristics of received signals, different modulation formats exhibit a set of notable features in the polar coordinate system, based on which an MFI scheme incorporating the Gaussian weighted k-nearest neighbors (KNN) algorithm was proposed to identify polarization division multiplexed (PDM)-QPSK/-16QAM/-32QAM/-64QAM/-128QAM signals. The performance of the proposed scheme was numerically verified in 28GBaud coherent optical communication systems. The numerical simulation results show that, to achieve 100% correct identification rates for all of the five modulation formats, the required minimum optical signal-to-noise ratios (OSNRs) were less than their relevant thresholds corresponding to the 20% forward error correction (FEC). The tolerable ranges of the residual chromatic dispersion (CD) for QPSK, 16QAM, 32QAM, 64QAM, and 128QAM were −1920 ps/nm~1920 ps/nm, −720 ps/nm~360 ps/nm, −1200 ps/nm~1680 ps/nm, −600 ps/nm~360 ps/nm, and −600 ps/nm~480 ps/nm, respectively. Meanwhile, the results demonstrate the maximum tolerable differential-group delay (DGD) for the QPSK, 16QAM, 32QAM, 64QAM, and 128QAM signals were 34 ps, 16 ps, 20 ps, 6 ps, and 1.2 ps, respectively. In addition, the simulated results also show that the proposed MFI scheme is robust against the fiber nonlinearities, even if the launch power is increased to 4 dBm.

To cost-effectively meet 6G latency requirements, concurrent upstream and direct inter-optical network unit (ONU) communication passive optical networks (PONs) based on flexible point-to-multipoint (P2MP) optical transceivers and intensity modulation and direct detection (IMDD) have been reported to enable direct communications among different ONUs within the same PON without passing data to the optical line terminal (OLT). However, the previously reported P2MP transceivers suffer from high DSP complexity for establishing ultra-dense connections. For such application scenarios, the PON’s remote nodes also have high inter-ONU signal power losses. To effectively solve these technical challenges, this paper experimentally showcases (a) new P2MP transceivers by utilizing parallel multi-channel aggregation/de-aggregation and advanced extended Gaussian function (EGF)-based orthogonal digital filter banks, along with (b) low inter-ONU signal power loss-remote nodes. By introducing these two techniques into a 27 km, >54.31 Gbit/s concurrent upstream and direct inter-ONU communication IMDD PON, comprehensive experimental explorations of the PON’s performances were undertaken for the first time. The remote node is capable of supporting 128 ONUs. The results show that the new P2MP transceivers lead to >75% (>40%) reductions in overall transmitter (receiver multi-channel de-aggregation) DSP complexity, and they can also equip the PONs with an enhanced capability of providing ultra-dense connections. The experimental results also show that the PON allows each ONU to flexibly change its upstream and inter-ONU communication channel count without considerably compromising its performance. Therefore, the PON outperforms those of previously reported works in terms of ensuring low DSP complexity, highly robust transmission performance, and enhanced capabilities of flexibly accommodating numerous applications with diverse requirements regarding traffic characteristics, thus making it suitable for ultra-dense connection application scenarios.

A phase-sensitive optical time-domain reflectometer (F-OTDR) vibration recognition method using Hilbert-Huang transform (HHT) for feature extraction is proposed. The experimental results show that the proposed method effectively recognizes the real disturbance events, and the recognition accuracy reaches 97.11% by training on a random forest (RF).

A data augmentation method based on multi-scale dense attention-enhanced (MDA) conditional generative adversarial network (CGAN) is proposed for generating high-quality samples, which aims to address the challenge of limited data acquisition in phase-sensitive optical time-domain reflectometry (ci'-OTDR). The raw data from the ci'-OTDR system can be transformed into visualized two-dimensional images to extract real disturbance data, with each disturbance type displaying distinguishable features in the generated images. The MDA U-Net is incorporated as the generator in the CGAN to produce samples for dataset expansion, where the dense convolutional block attention module is added to the skip connection to focus on the key information of events, and the single-layer output of U-Net is replaced with a multi-scale connection output for multi-layer feature fusion. The discriminator adopts a multi-scale convolution structure to enhance the discriminant ability. The multi-event recognition experiments for the fenced fiber optic demonstrate that the augmented dataset enables three testing classification models to achieve recognition accuracy above 97.93%.

Abstract Point‐to‐point (P2P) flexible transceivers are the key technical enabler to cost‐effectively offer fast, dynamic, and ‘just‐the‐right‐size’ ultra‐dense P2P connectivity for various applications including remote equipment control and distributed fibre networks. However, existing flexible transceivers originally designed for hub‐and‐spoke traffic patterns are sub‐optimal. To effectively address such technical issue, a P2P flexible transceiver incorporating a cascaded inverse fast fourier transform/fast fourier transform‐based multi‐channel aggregation/de‐aggregation technique and analogue in‐phase and quadrature (IQ) mixers is proposed and numerically evaluated in a 56Gbps@20 km intensity modulation and direct detection transmission system. The proposed P2P flexible transceivers not only support adaptive and flexible variations in both channel count and channel line rate but also offer additional physical layer network security.

Two kinds of carbon dots with the maximum fluorescence peak of 492 nm (named as G-CDs) and 607 nm (named as R-CDs) were synthesized. In the presence of MoO42− ions, the fluorescence of R-CDs at 607 nm can be quenched, which can probably be assigned to their aggregation caused by MoO42−, while that of G-CDs at 492 nm remained unchanged. For the first time, a ratiometric fluorescence probe was developed for MoO42− ions detection. In the range 0.25 100 μM, the fluorescence ratio (F492/F607) of the probe was linearly related to MoO42− concentration, and the detection limit was 61.5 nM, which fully meets the minimum detection requirements of MoO42− ions in drinking water. On the other hand, when MoO42− was introduced, a significant fading phenomenon of R-CDs can be observed with the naked eye; thereby, the colorimetric method can also be proposed. Based on above, the ratiometric fluorometric/colorimetric dual-mode sensing method was established for MoO42− anion quantification. Compared with the traditional analysis methods, the results obtained by multimodal sensing can be mutually verified, which effectively improves the accuracy and reliability. The dual-mode assay proposed in this work provides an alternative scheme to meet the need of sensing target compounds in complex matrices.

Although pulse compression optical time domain reflectometry (PC-OTDR) exhibits high performance in spatial resolution and dynamic range, it inevitably introduces autocorrelation sidelobes, potentially impacting measurement accuracy. In this letter, an improved CLEAN algorithm is proposed to efficiently suppress sidelobes and enhance the peakto- sidelobe ratio (PSLR) of signals in PC-OTDR. The proposed method introduces an adaptive step factor instead of the traditional fixed factor to reduce the number of iterations. Compared to the traditional method, the proposed method achieves a 2.87 dB improvement of PSLR from a 10 km sensing fiber. In addition, the computation time cost is significantly reduced, which is 1.92 s less than that of the traditional CLEAN algorithm.

Point-to-multipoint flexible optical transceiver-enabled concurrent direct inter-ONU and upstream communications are experimentally demonstrated in >62.47Gbit/s@27km IMDD PONs. The PONs flexibly and adaptively establish simultaneous ONU-to-ONU and ONU-to-OL T communication connections according to end-user's dynamic requirements.

Cascaded inverse fast Fourier transform/fast Fourier transform (IFFT/FFT)-based multi-channel aggregation/de-aggregation offers a promising solution in constructing highly desirable flexible optical transceivers for considerably improving optical networks’ elasticity, flexibility, and adaptability. However, the multi-channel aggregation operation unavoidably results in generated signals having high peak-to-average power ratios (PAPRs). To solve this technical challenge, this paper first explores the PAPR characteristics of the corresponding flexible transceivers in optical back-to-back (B2B) and 20 km intensity modulation and direct detection (IMDD) transmission systems, and then numerically investigates the feasibility and effectiveness of utilizing the conventional clipping techniques in reducing their PAPR reductions. The results show that the last IFFT operation size is the primary factor determining the PAPRs rather than the channel count and modulation format. For a given last IFFT operation size, the optimal clipping ratio can be identified, which is independent of channel count. With the identified optimal clipping ratio, when the channel count is >4, every two-channel increase in the channel count can only lead to <1.2 Gb/s decreases in the maximum aggregated signal transmission capacity.

Point-to-multipoint (P2MP) transceivers offer a promising solution to transform present point-to-point optical access networks into scalable and flexible P2MP networks capable of dynamically meeting, in a cost-effective and high energy consumption efficiency manner, the requirements associated with 5G-Advance and beyond networks, including large signal transmission capacity, fast and dense connection, high network flexibility/adaptability and low latency. However, the previously reported P2MP optical transceivers based on either coherent XR optics or IMDD digital filter multiplexing (DFM) techniques are not suitable for implementing in low-latency and highly cost-sensitive IMDD-dominated optical access networks. This paper proposes, experimentally demonstrates and optimises a novel P2MP flexible transceiver incorporating a new cascaded IFFT/FFT-based multi-channel aggregation/de-aggregation technique and an orthogonal digital filtering technique. The performances of the proposed technique are extensively evaluated experimentally in an upstream 55.3 Gb/s @25 km IMDD PON. It is shown that in comparison with the conventional DFM transceivers, the proposed transceivers can reduce the transmitter DSP complexity by a factor that approximates to aggregated channel count, and simultaneously offer additional physical layer network security, without requiring long digital filter lengths and greatly compromising upstream transmission performances/spectral efficiencies as well as differential ONU launch power dynamic ranges.

Using cascaded IFFT/FFT-based multi-channel aggregation/de-aggregation and orthogonal digital filtering, P2MP flexible transceivers operating in an ‘add-as-you-grow’ mode and offering additional physical-layer security are proposed and experimentally demonstrated in upstream 55.3Gbps@25km IMDD PONs.

To enhance the capability of phase-sensitive optical time domain reflectometers (Φ-OTDR) to recognize disturbance events, an improved adaptive feature extraction method based on NMF-MFCC is proposed, which replaces the fixed filter bank used in the traditional method to extract the mel-frequency cepstral coefficient (MFCC) features by a spectral structure obtained from the Φ-OTDR signal spectrum using nonnegative matrix factorization (NMF). Three typical events on fences are set as recognition targets in our experiments, and the results show that the NMF-MFCC features have higher distinguishability, with the corresponding recognition accuracy reaching 98.47%, which is 7% higher than that using the traditional MFCC features.

Ceramic-based conductive coatings were prepared by sol-gel method with artificial graphite (CGM) as conductive fillers and methyltrimethoxysilane (MTMS) and silica sol as dispersion medias. The graphene (Gr) and carbon black (CB) were added to improve the properties of the resultant coatings. The results showed that the electrical conductivity and thermal stability of coatings were improved by the addition of Gr and the electrical conductivity of coatings was further improved by the addition of CB for decreasing the pores of coatings. When the amount of CGM was 15.0 wt% with adding 1.0 wt% Gr and 0.5 wt% CB in the coating, the resistivity of obtained coating reduced to 1.46 omega center dot cm and its adhesion increased to 3911.62 mN. The prepared coating presented excellent electrical conductivity and adhesion properties, which was much better than the coating prepared without adding Gr and CB.

In traditional radar-communication electronic warfare, independent radar and communication systems can seriously affect the performance of combat platforms due to spectrum overlap. A joint beam-forming algorithm which can be used to transmit and receive radar and communication signals at the same time is proposed to solve this problem. In this approach, the power for the radar and communication are optimally allocated under the signal-to-interference-plus-noise-ratio (SINR) constraint of communication firstly. Then combined with the linearly constrained minimum variance (LCMV) algorithm, the joint beam-forming is optimized using Lagrange multiplier method. The simulation results show that the proposed method can obtain a higher SINR of radar echo and suppress the jamming effectively in other directions.

Yttrium aluminum garnet (YAG) has good optical properties and has been widely used in engineering. The preparation of conventional YAG powder is costly due to its high synthesis temperature, so lowering the synthesis temperature is the most effective way to save cost. The ultrafine oxide composite powder was rapidly synthesized using the microwave hydrothermal method at a low temperature. The effect of temperature and its performance. Differential thermal analysis and XRD phase analysis showed the mixed solution of Al(NO3)(3) and Y(NO3)(3) at pH=9 and C(Al3+)=0.42 mol.L-1. SEM, zeta potential, and particle size analysis revealed that the microwave hydrothermal reaction temperature was 170 degrees C, and the high-purity ultrafine YAG powder was calcined at 928 degrees C, which was lower than conventional calcination temperature. The synthesized ultrafine spherical YAG powder had a small particle size and a uniform distribution.