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In this letter, we proposed and fabricated a single ring uniform erbium-doped ring-core fiber with trench assisted to achieve high modal gain and low differential modal gain (DMG) in amplifying orbital angular momentum (OAM) modes. This is enabled by confining all modes effectively in a highly similar area to improve the overlap integral of erbium ions and mode fields. Theoretical analyses and experimental results suggest the proposed fiber can support four OAM mode groups ( $\vert \text{l}\vert $ = 1 - 4, 14 OAM modes in total). Moreover, the negligible distortion in the intensity and phase patterns of the OAM modes after amplification indicates a stable and effective amplification process. Furthermore, the experimental results exhibit that the RC-EDF amplifier acquires some favorable performances with a high modal gain more than 23 dB and low DMG less than 1 dB for all 14 OAM modes across the whole C-band.

This article proposes and investigates a scheme of Programmable Optical Digital Logic Computing Array (PODLCA) which mainly consists of basic blocks using dual-drive Mach-Zehnder modulators (DD-MZM). By adjusting the parameters of DD-MZM, full coverage of 24 types of logic operations can be implemented, making the Programmable Optical Digital Logic Computing Block (PODLCB) highly reconfigurable. Optimization of each logic operation is achieved through systematic adjustment of the PODCLB to obtain an output optical signal with maximum extinction ratio. Experimental implementation of AND, OR, NAND, NOR, XNOR, and XOR logic operations at a speed of 32 Gb/s is successfully realized using one PODLCB with clear observation of eye diagrams and high extinction ratios. According to the frequency response of the system, the PODLCB demonstrates significant potential for achieving high operating speeds, with the primary limiting factor being the bandwidths of the modulator and photodetector. Furthermore, various complex optical digital logic computing operations can be achieved through different combinations of PODLCBs, validating its high scalability. The proposed scheme features advantages in terms of reconfigurability, operating speed, signal quality and scalability, making it a promising solution for large scale programmable optical digital logic arrays.

Nonlinear Fourier transform (NFT)-based nonlinear frequency division multiplexing (NFDM) system has the potential to overcome the limit of fiber nonlinearity. In the NFDM system, the symbol information is modulated onto the nonlinear spectra, which consist of continuous and discrete spectrum. In theory, the dual-polarization (DP) NFDM system with the continuous and discrete spectrum (full spectrum, FS) modulation has the potential to achieve higher spectral efficiency. However, due to the complexity of the NFT and inverse NFT (INFT) numerical algorithms, the DP-FS modulated NFDM system is rarely reported. For the FS-NFDM system, the existing INFT algorithms either only support q-modulation and present poor performance, or have large discrete spectral error as the continuous spectrum energy increases. In this paper, we propose an INFT algorithm design theory. Based the theory, an accurate DP-INFT algorithm is proposed. The algorithm supports not only q-modulation, but also b-modulation with better performance. Employing the proposed INFT algorithm, we demonstrate, for the first time, a 174.5 Gbit/s FS modulated NFDM transmission system with 1440 km.

The addition of hybrid ceramic reinforcing phases provides the possibility of regulating the in-situ reaction and effective strengthening in laser additive manufactured aluminum matrix composites (AMCs). In this work, AMCs reinforced with (ZrC + TiC) solid solution ceramics with micro/nanoscale microstructural features are fabricated by laser powder bed fusion (LPBF). The influence of laser power on the manufacturing quality, the microhardness and the wear properties of the LPBF-fabricated (ZrC + TiC)/Al composites is investigated. Moreover, the reaction mechanism between the ZrC and TiC ceramics in the LPBF process is revealed. The tensile properties of the (ZrC + TiC)/Al composites with different (ZrC + TiC) contents prepared at optimal process parameters are compared. During the LPBF process, the ZrC and TiC ceramics are incompletely melted. On the ceramic particles, a thin (Ti,Zr)C layer formed and large amounts of (Ti,Zr)C nanoparticles precipitated via a dissolution-precipitation mechanism. When the laser power increases from 375 to 425 W, the manufacturing quality, microhardness, tensile and wear properties of the (ZrC + TiC)/Al composites increase. The tensile strength of 10 wt.% (ZrC + TiC)/Al composites prepared at optimal processing parameters reaches a high strength value of ∼227 MPa with a uniform elongation of ∼6.7%, which is three times higher than that of the unreinforced Al-matrix. This is ascribed to the combined effects of Orowan strengthening, coefficient of thermal expansion (CTE) mismatch strengthening, load-bearing strengthening and grain refinement strengthening.

Significant contributions have been made to understanding the processing of various metal materials using laser powder bed fusion (LPBF) for the design and fabrication of high-performance metal components in many fields. For laser additive manufacturing, aluminum-based materials are regarded as difficult-to-fabricate materials because of their special physical properties, including low density, low laser absorption, high thermal conductivity, and ease of oxidation. Currently, LPBF-formed structural materials require high densification, fine grains, high specific strength, high ductility, and optimized physical or chemical properties. Therefore, comprehensive understanding of the fabrication and performance of Al-based materials processed by LPBF is of significant value. This paper covers emerging research on aluminum-based materials using LPBF, providing an overall view of the basic scientific mechanisms behind manufacturing. The state-of-the-art researches of aluminum-based materials for LPBF formability as well as the microstructures, properties and corresponding metallurgical mechanisms are reviewed. The mechanisms of some of the main defects (pores, cracks, balling, and oxide inclusions) and control measures are also discussed. A summary and outlook for the further development of Al-based materials for LPBF are addressed.

Modulation format identification (MFI) is a key technology in optical performance monitoring for the next-generation optical network, such as the intelligent cognitive optical network. An MFI scheme based on the Calinski–Harabasz index for a polarization-division multiplexing (PDM) optical fiber communication system is proposed. The numerical simulations were carried out on a 28 Gbaud PDM communication system. The results show that the required minimum optical signal-to-noise ratio values of each modulation format to achieve 100% identification accuracy are all equal to or lower than their corresponding 7% forward error correction thresholds, and the proposed scheme is robust to residual chromatic dispersion. Meanwhile, the proposed scheme was further verified by 20 Gbaud PDM-QPSK/16QAM/32QAM long-haul fiber transmission experiments. The results show that the scheme has a good reliability when fiber non-linear impairments exist. In addition, the complexity of the scheme is significantly lower than that of other clustering-based MFI schemes.

A joint scheme introducing probabilistic shaping (PS) at the transmitter and utilizing a neural network (NN) equalizer at the receiver is proposed to improve the performance of the b-modulated nonlinear frequency division multiplexing (NFDM) system. Through a numerical simulation, we demonstrate that PS plays a leading role for low launch power case, which improves the performance of the system effectively, while the NN equalizer’s superiority appears in a high launch power region, whose main role is to weaken the correlation among subcarriers for improving system performance. The proposed scheme would enlighten the optimum modulation and detection schemes of the NFDM system.

Germanium is a promising anode material for lithium ion batteries because of its high theoretical specific capacity and low operation voltage. However, a significant challenge in using Ge-based anodes is the large volume variation during cycling that causes pulverization and capacity fade. Despite intense studies in the past decade, unsatisfactory cycling stability of the Ge-based electrodes still impedes their widespread applications. In this study, we demonstrate a high-performance electrode through the synergistic combination of a high-capacity Ge film grown on a three-dimensional current collector and an in situ formed poly(vinylidene fluoride)–hexafluoropropene/SiO2protective layer. Specifically, the polymer matrix is in continuous contact with the surface of the Ge shell, which provides improved mechanical and ionic transport properties. As a highlight, we present impressive cycling stability over 3000 cycles at 1 C rate with a capacity retention as high as 95.7%. Furthermore, the LiCoO2–Ge full battery operates at an average voltage of 3.3 V at 0.5 C and maintains good electrochemical performance, suggesting great potential for applications in energy storage and conversion devices.

Al-based composites reinforced with TiB2ceramics (1 wt.%, 2 wt.% and 5 wt.%) have been manufactured through selective laser melting (SLM). The results show that the densification, microstructure and mechanical properties of the SLM-processed composites are sensitive to the ceramic particle fraction. The average grain size of the composites decreased from ∼6.32 to ∼1.55 μm with increasing TiB2fraction from 1 to 5 wt.% respectively. Fine equiaxed grains with narrow size distribution were obtained for composites with relatively high amount of TiB2particles. The effects of TiB2ceramic fraction on grain refinement and strengthening mechanisms of SLM-processed composites were discussed. Al-based composite with 2 wt.% TiB2ceramic was determined to be optimum, especially in the view of manufacturing quality, grain refinement and mechanical properties. The composites at an optimum fraction of 2 wt.% TiB2exhibited high microhardness of ∼127 HV0.2, tensile strength of ∼444 MPa, yield strength of ∼283 MPa and elongation of ∼4.2% owing to collective effects of dispersion and grain refinement strengthening as well as high degree of densification. This study can readily offer reference values for laser additive manufacturing of other metal matrix composites to obtain a good compromise of strength and ductility by tuning reinforcement fraction.

Abstract

Al-based composites with micrometer and submicro-TiB2reinforcements (1 wt%) have been produced by selective laser melting (SLM) from mixed powder under different processing conditions. The results show that the densification level of SLM-processed composite with submicro-TiB2particles (>99.0%) was 0.3–2.4% larger than that of micrometer TiB2-reinforced composite under the same processing conditions. The distribution of Si precipitates in the matrix experienced a transform from continuous cellular to directional line-like morphology with reinforcement size decreasing from micron to submicron. The reinforcement size added in the matrix also exhibited a critical influence on preferred orientation and grain size of matrix. The SLM-processed composites exhibited improved tensile strength and ductility with a decrease of reinforcement size. High tensile strength of ∼400 MPa and elongation of ∼3.6% were obtained for the fine TiB2-reinforced samples, increasing by 6 and 13% compared with that of micro-TiB2–added samples, respectively.

A spectrum efficient OFDM scheme named Time Domain Synchronous-OFDM (TDS-OFDM) is introduced into coherent optical transmission system, in which the pseudo noise (PN) sequence is exploited as guard interval to realize frame synchronization, compensate the carrier frequency offset (CFO), and estimate and equalize channel simultaneously. Since there is no pilot signals or training symbols in TDS-OFDM, the proposed scheme can achieve higher spectral efficiency (SE) above 10% improvement comparing with CP-OFDM. The proposed method is implemented and verified in a 28GBaud QPSK OFDM system and a 28GBaud 16QAM OFDM system. It is demonstrated that the proposed scheme shows high CFO estimation accuracy and synchronous accuracy. Under CFO and linewidth of laser source set as 100MHz and 100kHz respectively, BER of QPSK OFDM system is below 3.8e-3 at the optical signal-to-noise ratio (OSNR) of 13dB, and BER of 16QAM OFDM system is below 3.8e-3 at the OSNR of 20dB.

A novel all-fiber broadband mode multiplexer based on an elliptical ring core fiber structure mode selective coupler (MSC) is proposed and analyzed numerically. The MSC is composed of a core-doped single-mode fiber and a polarization-maintaining elliptical ring-shaped core few-mode fiber (FMF). The mode multiplexing can be implemented by a single LP_01 mode excitation that does not introduce insertion loss, which can simplify and promote the multiplexer. The high refractive index difference between the elliptical annular region and the cladding of the FMF, as well as the ellipticity of the ring-shaped core of the FMF could not only decompose the degenerate modes, but also reduce the mode coupling of the adjacent spatial modes to eliminate the multiple-input-multiple-output digital-signal processing in the receiver of the mode division multiplexing system. Finally, a seven-mode multiplexer is modeled and optimized for operation covering the C+L band. Furthermore, the multiplexer provides a high coupling efficiency (>64% for the worst case) for the seven spatial modes, LP_01, LP_11a, LP_11b, LP_21a, LP_21b, LP_31a, and LP_31b, and relatively high mode extinction ratios of more than 15 dB in the C-band.

Abstract Electrochemical measurements on three planes of TiC/Inconel 718 composites fabricated by selective laser melting (SLM) were performed to study the corrosion property. The results showed that the YZ -plane with dense and fine columnar structures possessed high microhardness and superior corrosion resistance in 3.5 wt% NaCl solution. For the XZ -plane, a decreased anti-corrosion property was observed owing to its inhomogeneous microstructures. While the XY -plane with large irregular pores and clustered ring-like structures was more susceptible to corrosion compared with the other two planes. Comparative analysis suggested that the anisotropic corrosion behaviors were significantly dependent on the surface defects, microstructure characteristics and added reinforcements. [ABSTRACT FROM AUTHOR]

We propose a design tool for the family of circular photonic crystal fiber (C-PCF) supporting orbital angular momentum modes. The calibrated normalized parameters for the C-PCF family are presented. The information about the cutoff condition of modes, the number of modes supported in fibers, and the effective index difference between adjacent modes can be obtained by using the design tool. Also, the mode properties, such as confinement loss, effective mode area (A_eff), and spin-orbital coupling are analyzed using the design tool. At the end of paper, we also give some fiber design examples by using the design tool.

We propose a new orbital angular momentum (OAM) erbium-doped fiber amplifier based on a circular photonic crystal fiber, which can support a total of 18 modes (14 OAM modes) over C-band. A correction factor is proposed to modify the overlap factor, with the aim of evaluating the performance of the amplifier more accurately. We found that the confined doping profile can help optimize the differential model gain (DMG). Numerical simulations suggest that the proposed OAM fiber amplifier can provide a gain larger than 20 dB for all 14 OAM modes, with the small DMG less than 0.2 dB and the noise figure lower than 3.5 dB across the C-band.

Exploring highly efficient electrocatalysts is crucial for aprotic Li-O2batteries. Pd/NiO nanomembranes with hierarchical pores are fabricated and employed as cathode catalysts in Li-O2batteries. By means of standard photolithography, ordered macropores were prepared in the nanomembranes. Moreover, we developed a facile template-free method to create nanopores with sizes ranging from 50 to 200nm in the composite. The diverse pores of micro- and nanometer sizes and the resulting loose structure supply fast channels for the transportation of reactants, thus efficiently promoting the performance of Li-O2batteries by lowering the overvoltages and enhancing the rate capability and stability.

This paper investigates the performance of an all-optical logic gate scheme based on a single in-phase and quadrature (I/Q) modulator with direct detection. The proposed scheme of an all-optical logic gate is simple, high speed, and easily reconfigured to realize 24 logic states by adjusting bias voltages, peak-to-peak voltages of the driven RF signals, and the phase shift. As the scheme to realize logic gates is based on the irregular use of a commercially available I/Q modulator and laser source, a specialized logic gate system including a laser, I/Q modulator, and driven RF module should be optimally designed to obtain the best performance. With the system’s extinction ratio (ER) and Q-factor as metrics, the performance of the proposed logic gate scheme is analyzed theoretically and numerically in this paper. We first give a new theoretical model of the I/Q modulator. Next, taking the OR gate as an example, the simulations are carried out to analyze performance under the influence of some key factors in the system. Results show that the extinction ratio of the whole system is affected by the phase shift between the two arms of the I/Q modulator and the extinction ratios of two Mach–Zehnder modulators (MZMs), while Q-factor is further influenced by the output power of the laser and the insertion loss of the MZMs in the I/Q modulator. For an I/Q modulator with MZMs having an extinction ratio of 20 dB, the minimum laser output power to obtain a system’s ER higher than 16 dB is 3 dBm, while in order to obtain a Q-factor higher than 6, the output power of the laser must not be <10  dBm.

The large capacity loss and huge volume change of silicon anodes severely restricts their practical applications in lithium ion batteries. In this contribution, the sandwich nanoarchitecture of rolled-up Si/reduced graphene oxide bilayer nanomembranes was designed viaa strain released strategy. Within this nanoarchitecture, the inner void space and the mechanical feature of nanomembranes can help to buffer the strain during lithiation/delithiation; the alternately stacked conductive rGO layers can protect the Si layers from excessive formation of SEI layers. As anodes for lithium-ion batteries, the sandwiched Si/rGO nanoarchitecture demonstrates long cycling life of 2000 cycles at 3 A g–1with a capacity degradation of only 3.3% per 100 cycles.

Herein we present the preparation of novel multifunctional metallic nickel/oxide (Ni/NiO) hybrid nanomembranes with rough and undulating surface morphologies, by a physical deposition method combined with chemical etching and thermal oxidation. Benefiting from the advantages of intrinsic architecture and electrochemical catalysis of metallic nickel, the anodes can be discharged and charged at an ultrahigh rate of ~115C (1C=718mAg−1) if only the mass of NiO is taken into calculation or 60C if the total mass of Ni/NiO nanomembranes is considered. To our knowledge, this is the best reported rate performance for NiO-based anodes in Li-ion batteries to date. Furthermore, excellent cycling stability is also demonstrated.

A novel compression-induced twisting (CIT)-compliant mechanism was designed based on the freedom and constraint topology (FACT) method and manufactured by means of laser powder bed fusion (LPBF). The effects of LPBF printing parameters on the formability and compressive properties of the laser-printed CIT-compliant mechanism were studied. Within the range of optimized laser powers from 375 to 450 W and with the densification level of the samples maintained at above 98%, changes in the obtained relative densities of the LPBF-fabricated CIT-compliant mechanism with the applied laser powers were not apparent. Increased laser power led to the elimination of residual metallurgical pores within the inclined struts of the CIT mechanism. The highest dimensional accuracy of 0.2% and the lowest surface roughness of 20 μm were achieved at a laser power of 450 W. The deformation behavior of the CIT-compliant mechanism fabricated by means of LPBF exhibited four typical stages: an elastic stage, a heterogeneous plastic deformation stage, a strength-destroying stage, and a deformation-destroying stage (or instable deformation stage). The accumulated compressive strain of the optimally printed CIT mechanism using a laser power of 450 W went up to 20% before fracturing, demonstrating a large deformation capacity. The twisting behavior and mechanical properties were investigated via a combination of finite-element simulation and experimental verification. An approximately linear relationship between the axial compressive strain and rotation angle was achieved before the strain reached 15% for the LPBF-processed CIT-compliant mechanism.

AbstractThe full service access network (FSAN) task group meeting was held in April 2012, where they agreed to adopt time and wavelength division multiplexed passive optical network (TWDM-PON) as a primary solution to NG-PON2. Major requirements includes at least 40 Gbit/s aggregate rate in downstream, 1:64 split ratio, 40 km differential reach, and at least 1 Gb/s access rate per optical network unit (ONU). In this paper, a performance analysis will be carried out for downstream 4-wavelengths group selection from S-band, L-band, and C-band. A comparison for optimal transmitter design is also investigated among probable options of chirp managed laser diode, Lithium Niobate (LiNbo3) Mach Zehnder modulator, besides examining tunable transceivers in contrary to remotely fed colorless ONUs.

AbstractWe propose and present a cost effective and simple technique of simultaneous generation and propagation of millimeter wave with recently standardized 10 giga bit passive optical network (GPON) by mixing of 2.5 Gbit/s, 30 GHz radio wave with 10 Gbit/s based band signal and then modulated by single Mach Zehnder modulator (MZM). In this scheme, we have applied 1490 nm for downstream, 1310 nm for upstream transmission and ON OFF keying (OOK) modulation format to make it fully align with existing standards and infrastructure. Simulation results show error free transmission performance with negligible power penalty over 25 km bidirectional fiber. We also highlight the principles and discuss the main technical challenges for commercial realization of 60 GHz spectrum.

A modified phase recovery algorithm with overlap controlled adaptively used for squared 16-QAM is proposed, which is based on the 4th-power algorithm and relieve the problem of block-size-choosing. By using this modified algorithm, 1.8MHz linewidth tolerance for 25G Baud 16-QAM is improved on traditional 4th-power algorithm.

This paper reports the prototype of optical polarization mode dispersion compensator (OPMDC) we have made to compensate the polarization mode dispersion (PMD) in fibers. The OPMDC prototype designed was tested in a 43Gb/s RZ-DQPSK system either in the back-to-back case, or in a 1200km transmission testbed. It showed a good performance under the tests of fast SOP and PSP rotation, DGD variation, and moderate knock on the testbed in a period of 12 hours.

Amplification and phase regeneration can be realized using a phase-sensitive amplifier (PSA). The phase regeneration of differential phase-shift keying (DPSK) signals based on PSA is analyzed theoretically. We realize the phase regeneration of differential quadrature phase-shift keying (DQPSK) signals based on a structure using two balanced PSAs. Simulations show that nearly ideal phase regeneration can be achieved for the DPSK/DQPSK signals.

Particle swarm optimisation (PSO) algorithm is used in multichannel polarisation-mode dispersion (PMD) compensation systems. As an example, the performances of the two-channel system are simulated. The worse channel is compensated and the performances of the other channel are also improved by using only one compensator. The effect of PMD compensation system is obvious and the searching ability of PSO algorithm is strong. These results shows PSO algorithm is a good choice when it is used in multichannel PMD compensation systems.

Experimental research of simultaneous tunable chromatic dispersion (CD) and adaptive polarization mode dispersion (PMD) compensations in optical fiber communication system was reported. Two different nonlinearly chirped fiber Bragg gratings fabricated through the equivalent chirp technology were adopted in the experiment. One of the gratings was used as CD compensator, with a tunable dispersion range from 300 to 600 ps/nm. The other made of photosensitive polarization maintaining fiber was used as a tunable delay line of PMD compensator, which provided a varying amount of differential group delay (DGD) from 40 to 110 ps. Our experiment was operated at 10-Gb/s non-return-to-zero (NRZ) system and the results showed that the eye pattern recovery is excellent after both PMD and CD are compensated. Especially, the power penalty at a bit error rate (BER) of 10^(-9) is about 1 dB.

An experiment of two-stage adaptive compensation for polarization mode dispersion (PMD) in a 40-Gb/s optical time-division multiplexed communication system is reported. The PMD monitoring technique based on degree of polarization was adopted. The particle swarm optimization (PSO) algorithm was introduced in adaptive PMD compensation. The comparison was made to estimate the effectiveness between PSO algorithms with global neighborhood structure (GPSO) and with local neighborhood structure (LPSO). The LPSO algorithm is shown to be more effective to search global optimum for PMD compensation than GPSO algorithm. The two-stage PMD compensator is shown to be effective for both first- and second-order PMD, and the compensator is shown to be bit rate independent. The optimum searching time is within one hundred milliseconds.

We report the adaptive compensation experiment of polarization mode dispersion (PMD) for 10-Gb/s non return-to-zero (NRZ) and return-to-zero (RZ) optical communication systems using a two-stage PMD compensator and the monitoring technique based on degree of polarization (DOP) feedback-signals. The DOP monitor has its advantages of bit-rate independent and modulation format independent. The twostage compensator has the capacity of compensation for the first- and second-order PMD. The compensated differential group delay (DGD) is up to 80 ps, and compensated principal state of polarization rotation rate is 20 ps. The time used for compensation is less than 1 second.

Selective laser melting (SLM) is an emerging additive manufacturing technology for fabricating aluminum alloys and aluminum matrix composites. Nevertheless, it remains unclear how to improve the properties of laser manufactured aluminum alloy by adding ceramic reinforcing particles. Here the effect of trace addition of TiB2ceramic (1% weight fraction) on microstructural and mechanical properties of SLM-produced AlSi10Mg composite parts was investigated. The densification level increased with increasing laser power and decreasing scan speed. A near fully dense composite part (99.37%) with smooth surface morphology and elevated inter-layer bonding was successfully obtained. A decrease of lattice plane distance was identified by X-ray diffraction with the laser scan speed decreased, which implied that the crystal lattices were distorted due to the dissolution of Si and TiB2particles. A homogeneous composite microstructure with the distribution of surface-smoothened TiB2particles was present, and a small amount of Si particles precipitated at the interface between reinforcing particles and matrix. In contrast to the AlSi10Mg alloy, the composites showed a stabilized microhardness distribution. A higher ultimate tensile strength of 380.0 MPa, yield strength of 250.4 MPa and elongation of 3.43% were obtained even with a trace amount of ceramic addition. The improvement of tensile properties can be attributed to multiple mechanisms including solid solution strengthening, load-bearing strengthening and dispersion strengthening. This research provides a theoretical basis for ceramic reinforced aluminum matrix composites by additive manufacturing.

Strategies for fabricating iron-based materials with high strength and ductility are rare despite intense research efforts within the last decades. This main challenge, which must be overcome in synthesizing such materials, is described by the strength-ductility trade-off dilemma. This study provides a novel approach to achieve the synthesis of highly strong and ductile iron-based composites reinforced with a high weight fraction of WC particles (20 wt%) utilizing laser powder bed fusion (LPBF) as processing technique. Thereby, the LPBF-fabricated composite material has a multi-phase microstructure consisting of ductile austenite (main phase), highly strong martensite and carbidic precipitations extending across different length-scales. The precipitation of (Fe, W)3C type carbide at the Fe/WC interface is well controlled. Thus, a very thin reaction layer (< 500 nm) forms between the WC particles and iron-based matrix. Additionally, nano-scaled precipitations evolve along sub-grain boundaries and within the sub-grains and they show a high coherency with the iron-based matrix. These iron-based composites synthesized by LPBF show an excellent compressive strength of about 2833 MPa and large fracture strain of about 32 %. The following mechanisms contribute to the improved mechanical properties: (1) multiphase material system, (2) grain refinement, (3) substructures, (4) coherent multiscale interfaces and (5) nano-precipitations.

An adaptive polarization mode dispersion (PMD) compensation experiment is reported in a 40-Gb/s phase shaped binary transmission (PSBT) communication system, with the use of a new digital signal processor (DSP)-based optical PMD compensator. PMD tolerance is found to be enhanced by 8 ps after PMD compensation with 1-dB optical signal-to-noise ratio (OSNR) penalty. Under the condition of fast change of states of polarization up to 85 rad/s in the fiber link, the performance of our PMD compensator undergoes the bit error ratio (BER) test for as long as 10 h.

A fast and reliable method to calibrate LiNbO3-based polarization controllers (PCs) presented theoretically and experimentally. Particle swarm optimization (PSO) algorithm is used as an adaptive searching algorithm. Experimental results show that PSO algorithm is powerful in calibrating LiNbO3-based multistage PCs. Only less than one minute is spent for all stages of the PC to be calibrated thoroughly.

In this study, a laser-based additive manufacturing route of selective laser melting (SLM) was applied to fabricate carbon nanotubes (CNTs) reinforced Al-based nanocomposites with tailored microstructures and excellent mechanical properties. The densification behavior, microstructure features and mechanical properties were investigated and the relationship between process and property was established. The results showed that the applied laser power and scan speed were the governing factors of the densification behavior of SLM-processed Al-based nanocomposites. SLM processing of 0.5 wt.% CNTs/AlSi10Mg nanocomposite powder led to the formation of three typical microstructures including the primary Al9Si cellular dendrites decorated with fibrous Si, the in situ Al4C3covered on CNTs, and the precipitated Si inside the cellular grains. As the optimal SLM processing parameters of laser power of 350 W and scan speed of 2.0 m/s were applied, the fully dense SLM-processed CNTs/Al-based nanocomposites exhibited high microhardness of 154.12 HV0.2, tensile strength of 420.8 MPa and elongation of 8.87%, due to the formation of high densification and ultrafine microstructure. The grain refinement effect, Orowan looping system and load transfer are considered as three strengthening mechanisms occurred simultaneously during tensile tests, leading to excellent mechanical properties of SLM-processed CNTs/Al-based nanocomposites.

An experiment of adaptive polarization mode dispersion (PMD) compensation for 40-Gb/s return-to-zero (RZ) optical communication system is reported. In the experiment, degree of polarization (DOP) is used as feedback signal and particle swarm optimization (PSO) method is adopted as logic control algorithm. The compensation time is about 200 ms, the compensated differential group delay (DGD) is up to 30 ps, and bit error rate (BER) of 10^(-9) is reached when PMD compensation is employed.