Publications by authors named "Zixian Wei"

Background: Gestational diabetes mellitus (GDM) can contribute to changes in fetal cardiac structure and function, with potential implications for long-term cardiovascular health. This study focuses on assessing these cardiac adaptations in fetuses from GDM pregnancies by using the innovative Fetal Heart Quantification (Fetal HQ) technology to provide a detailed evaluation of structural and functional parameters.

Methods: A prospective study was conducted from March 2023 to October 2024 at Xiangyang No.

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Most current Data Center Interconnects (DCI) use intensity modulation direct detection (IMDD) configurations due to their low complexity and cost. However, significant scaling challenges allow coherent solutions to become contenders in these short reach applications. We present an O-band coherent optical fiber transmission system based on Quantum Dot-Mode Locked Lasers (QD-MLLs) using two independent free-running comb lasers, one each for the carrier and the Local Oscillator (LO).

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Inspired by the advanced integrated sensing and communication (ISAC), in this Letter, we explore the non-line-of-sight (NLoS) optical channels formed by reflections from the ground or objects to establish an integrated channel model for simultaneous communication and sensing. The integrated channel model can, on the one hand, perceive the changes in the surrounding environment and, on the other hand, determine whether these changes positively or negatively affect the quality of communication simultaneously. To validate the effectiveness of the proposed model, from sensing, we analyze the impact of various floor materials and visible light communication (VLC) users on the integrated channel; from communication, we characterize the influence of perceived environmental changes on communication performance by calculating throughput.

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The short-reach optical transmission systems based on intensity modulation and direct detection (IM/DD) are gradually evolving into the networks with complex link topologies and connections, especially inside the data center. Multipath interference (MPI) introduces irregular fluctuations in the 4-level pulse amplitude modulation (PAM4) signals and therefore affects the transmission performance. This Letter proposes an adaptive decision threshold (ADT) scheme to dynamically update the decision threshold, which can track the signal fluctuations in real time and mitigate the impact of MPI noise on the transmitted PAM4 signals.

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We propose two designs of low-loss and temperature-insensitive single-mode waveguide crossing on silicon-on-insulator (SOI) platform with 415-nm operation bandwidth covering all optical communication bands. Both designs are enabled by subwavelength grating (SWG) modeled as an anisotropic metamaterial. The initial design applies straight SWG as the lateral cladding of the waveguide crossing to minimize the refractive index contrast and reduce the insertion loss (IL), but needs a relatively long taper.

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We present a 2 × 2 polarization-insensitive switch on a 220-nm silicon-on-insulator platform, employing a balanced Mach-Zehnder interferometer (MZI) structure. This design incorporates polarization-insensitive adiabatic couplers, polarization rotators based on mode hybridization and evolution, and thermo-optic mode-insensitive phase shifters with wide waveguides. The switch exhibits broadband polarization-insensitive characteristics, with extinction ratios larger than 15 dB, insertion losses less than 2.

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To develop an adaptive modulation scheme for flexible high-speed multi-user visible light communication (VLC), automatic modulation classification (AMC) is adopted for monitoring the modulation formats of different subcarrier groups. An AMC scheme based on a joint convolutional neural network (CNN), active learning (AL), and data augmentation (DA) is demonstrated over an orthogonal frequency division multiplexing access (OFDMA) VLC system. The configuration of the diffuse white-light VLC system is combined with a pair integrated transceiver module, a light-diffusing fiber (LDF), and a wireless channel, which can provide white-light illumination and ubiquitous access.

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Low-cost underwater wireless optical communication (UOWC) systems are attractive for high-speed connections among unmanned vehicles or devices in various underwater applications. Here we demonstrate a high-speed and low-cost UOWC system using a low-resolution digital to analog converter (DAC), a single-pixel mini-sized light-emitting diode (mini-LED), and digital pre-compensation (DPC). The enabled DPC scheme comprises digital pre-distortion (DPD), digital pre-emphasis (DPE), and digital resolution enhancer (DRE), which pre-compensate for mini-LED nonlinearity, the bandwidth limitation of the mini-LED and avalanche photodiode detector, and DAC resolution limitation, respectively.

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In recent years, visible light communication (VLC) has emerged as a dual-use technique for illumination as well as communication. In VLC system, dimming control is deemed to be an essential functionality for luminous intensity adjusting and energy saving. In this Letter, a noise-suppressed triple-layer hybrid optical orthogonal frequency division multiplexing (NSTHO-OFDM) is proposed and further combined with pulse width modulation (PWM) to achieve the functionality of dimming control.

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To further increase the data rate and rate flexibility of next-generation passive optical networks (PONs), we propose a scheme jointing probabilistic constellation shaping (PCS), constellation diagram identification, and coherent detection. The rate of the coherent PON is dynamically regulated with time-variant entropy, and monitored by the image classifier in real-time. The transmitted cascade frames allocated to different optical network units (ONUs) from the optical line terminal (OLT) can be synchronized, identified, and distinguished by the labeled entropy values.

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High-bandwidth GaN-based mini-LEDs on the c-sapphire substrate are promising candidates for underwater optical wireless communication (UOWC) systems due to their compatibility with the mature LED fabrication process. Here we fabricate and characterize mini-LEDs based on a single-layer InGaN active region with a peak emission wavelength around 484 nm for high-speed UOWC links. Since the LED diameter affects the trade-off between the modulation bandwidth and the optical modulation amplitude, mini-LEDs with varying mesa diameters from 100 µm to 175 µm are fabricated for the measurement.

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Cesium lead halide perovskite nanocrystals have recently become emerging materials for color conversion in visible light communication (VLC) and solid-state lighting (SSL), due to their fast response and desirable optical properties. Herein, perovskite nanocrystal-polymethyl methacrylate (PNC-PMMA) films with red and yellow emission are prepared. The PNC-PMMA films, with optical properties such as a short lifetime and air stability, are used to make broadband color converters based on a high-bandwidth 75 μm blue micro-LED (μLED) for VLC.

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Visible light communication (VLC) beyond 10 Gbps is an important characteristic that can support the future 6 G high-capacity requirements. On the one hand, in order to break the electro-optics (E-O) bandwidth limitation of the light-emitting diodes (LEDs), we fabricated two high-bandwidth (>) single wetting layer micro-LEDs with 50 and 75 µm active regions. On the other hand, for mitigating the nonlinear effects of the VLC system, an artificial neural network equalizer is designed and implemented in offline digital signal processing.

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Infrared optical wireless communication system can achieve ultrahigh capacity and high privacy data transmission. However, for using narrow infrared laser beam as carrier to transmit signal, the high-speed data transmission can only be achieved by point-to-point connection. With the rapid number increasement of consumer electronic devices, such connection method puts a heavy burden on the number of transmitters.

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Visible light communication (VLC) based on a light-emitting diode (LED) suffers from a limited bandwidth of commercial LED, device nonlinearity, channel distortion, and transmitted power caused by a complex free-space channel, power amplifier, and illuminant devices resulting in a limited data rate. In this Letter, to provide an alternative high-speed solution, we first designed and fabricated three 175 µm tricolor mini-LEDs with various wavelengths. They are used to set up a spatial division multiplexing-wavelength division multiplexing VLC system over a 2 m link.

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We built a full-duplex high-speed optical wireless communication (OWC) system based on high-bandwidth micro-size devices, for which micro-LED and VCSEL arrays are implemented to establish downlink and uplink, respectively. The high-capacity downlink based on a single-pixel quantum dot (QD) micro-LED can reach a data rate of 2.74 Gbps with adaptive orthogonal frequency division multiplexing (OFDM).

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We experimentally demonstrated a high-speed multi-user green and blue laser diode based underwater optical wireless communication (UOWC) system using non-orthogonal multiple access (NOMA) with polarization multiplexing. The system affords eight users with a record sum rate of 18.75 Gbps over 2-m underwater plus 0.

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Next-generation visible light communication (VLC) is envisioned to evolve into a high-speed and multi-user system. In this work, a 75-µm single layer quantum dot (QD) micro-LED was fabricated, packaged and used to experimentally demonstrate a 3-meter QAM-OFDMA VLC system affording multiple users with a 1.06-GHz modulation bandwidth.

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Diffuse communication plays a more significant role than the usual point-to-point scenario in indoor optical wireless communication (OWC). We present, for the first time to our knowledge, a Monte Carlo simulation and experiment for a 922.39-nm vertical cavity surface-emitting laser array-based non-line-of-sight OWC system with three common reflective materials.

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Blue/green light-emitting diodes (LEDs) show great potential in medium/short distance underwater optical wireless communication (UOWC) while suffering limited bandwidth caused by a long radiative recombination carrier lifetime and large resistance-capacitance (RC) constant. We designed, fabricated, and packaged a 75-µm single-layer quantum dot (QD) blue micro-LED with a record high modulation bandwidth up to 1.03 GHz.

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