Phase-coded coherent microwave pulse generation based on an actively mode-locked optoelectronic parametric oscillator.

An approach for generating phase-coded coherent microwave pulse trains at high frequencies is proposed and demonstrated based on an actively mode-locked optoelectronic parametric oscillator (AML-OEPO), where an electrical mixer is inserted into the cavity of an optoelectronic oscillator (OEO) to achieve both mode locking and parameter oscillation. The driving signal applied to the mixer is a low-frequency sinusoidal signal with voltage polarity coding, where the frequency is the same as the free spectral range (FSR) of the OEO cavity, and the duration of each voltage polarity coding bit is identical to the loop delay. As a result, phase-coded coherent microwave pulse trains can be generated, where the pulse interval is equal to the loop delay due to the active mode locking effect, and the phase coding period is equal to a multiple integer of the loop delay due to parameter oscillation.

Freely tunable phase-locked dual-frequency microwave signal generation from injection-locked broadband optoelectronic oscillator.

We propose and experimentally demonstrate an injection-locked broadband optoelectronic oscillator (OEO) to generate freely tunable phase-locked dual-frequency microwave signals. When two single-tone signals inside and outside the passband of the electrical broadband bandpass filter (BPF) are, respectively, injected into the OEO, a phase-locked dual-frequency microwave signal with ultra-low near-end side-mode spurs can be generated from the OEO cavity. Therefore, one frequency of the output signal is equal to the frequency of the injected signal within the BPF, and the other frequency is equal to the sum frequency or the differential frequency of two injected signals.

Spatial division multiplexing of LED strips for optical camera communication.

Rolling shutter based optical camera communication (RS-OCC), a promising candidate of optical wireless communication (OWC), has the advantage of unlicensed spectrum and no electromagnetic interference. Since RS-OCC can use the built-in camera of a smartphone as a receiver, it can provide flexible, low-cost, and timely private information exchange between mobile users. However, the enhancement of data throughput for the RS-OCC is challenging.

Schizophrenia and magnetic resonance imaging research: A scientometric analysis during 2014 to 2023.

Background: Recently, magnetic resonance imaging (MRI) has emerged as a leading technique for investigating schizophrenia (SZ) pathological mechanisms, prompting an increase in related studies. This study aims to examine the field's research status and trends via bibliometric analysis.

Method: The publications on SZ and MRI over the past decade were retrieved from the Web of Science Core Collection (WOSCC) On October 15, 2023.

Splicing Hollow-Core Fiber with Standard Glass-Core Fiber with Ultralow Back-Reflection and Low Coupling Loss.

A main, yet-unsolved challenge in splicing hollow-core fiber (HCF) into standard single-mode fiber (SMF) systems lies in managing the strong Fresnel back-reflection that occurs when the light travels from the empty core of the HCF into the glass core of the SMF or vice versa. This impacts the performance of fiber systems that combine SMFs and HCFs due to effects such as multipath interference. Here, we demonstrate a new technique that combines angle-cleaving the HCF, which reduces the back-reflection, with offset-splicing the mode-field adapter to the SMF, which compensates for the refraction at the glass-air interface, enabling us to achieve low coupling loss.

Frame-rate adaptive fractionally spaced equalization enabled high-throughput optical camera communication.

Optical camera communication (OCC) has garnered worldwide research attention, due to its immunity to electromagnetic interference (EMI) and efficient utilization of spectrum resources. However, the limited bandwidth of the OCC system and the timing offset of the camera result in low system throughput. To enhance the OCC throughput, we propose and experimentally demonstrate a frame-rate adaptive fractionally spaced equalization algorithm (FA-FSE) for the joint mitigation of severe inter-symbol interference (ISI) and timing offset arising in OCC.

Multiple-signal-joint-processing-based guard interval shortening method for a CS-NFDM system.

Aiming to further improve the spectral efficiency (SE) of a continuous spectrum modulated nonlinear frequency division multiplexing (CS-NFDM) system, we propose a novel ,to the best of our knowledge, multiple-signal-joint-processing (MSJP)-based guard interval (GI) shortening method. In this method, multiple NFDM time-domain signals are jointly processed as a whole to carry out nonlinear Fourier transform and inverse nonlinear Fourier transform (NFT-INFT) operations. These operations can fuse the multiple NFDM time-domain signals together, which is equivalent to the corresponding inverse process of a fiber transmission.

Improving decryption quality of optical chaos communication using neural networks.

Optical chaos communication is a promising secure transmission technique because of the advantages of high speed and compatibility with existing fiber-optic systems. The deterioration of chaotic synchronization quality caused by fiber optic transmission impairments affects the quality of recovery of information, especially high-order modulated signals. Here, we demonstrate that the use of a convolutional neural network (CNN) with a bidirectional long short-term memory (LSTM) layer can reduce the decryption BER in an optical chaos communication system based on common-signal-induced semiconductor laser synchronization.

Fractionally spaced nonlinear Tomlinson-Harashima precoding with weight clustering for C-band 100 Gbaud/λ PAM-4 transmission.

A nonlinear Tomlinson-Harashima precoding (NTHP) scheme has been verified for its capability to effectively address both the linear and nonlinear inter-symbol interferences (ISIs) arising in the intensity-modulation direct-detection (IM-DD) fiber optics transmission. Nevertheless, the application of the NTHP scheme may significantly increase the number of levels for the intensity modulated signals, resulting in the reduction of both eye width and receiver sensitivity. Here, we propose a fractionally spaced NTHP with a weight clustering (FS-NTHP-WC) scheme.

On the multipath interference mitigation for high-speed IM-DD transmissions with Nyquist subcarrier modulation.

The performance of high-speed intensity modulation direct detection (IM-DD) transmissions is severely degraded due to the occurrence of multipath interference (MPI), especially when a higher-order modulation format is utilized. Here, we propose and demonstrate, for the first time to the best of our knowledge, that a Nyquist subcarrier modulation (Nyquist-SCM) format inherently exhibits resistance to the MPI. We experimentally evaluate the MPI tolerance by transmitting 56 Gbit/s PAM-4 signals and Nyquist-SCM 16QAM signals over the 2 km standard single-mode fiber (SSMF) when the C-band semiconductor laser with a linewidth of 1.

Transverse mode switchable mode-locked laser with narrow bandwidth.

Transverse mode switchable ultrashort optical pulses with narrow bandwidths can create potential for exploring what we believe are new physical effects. We demonstrate the generation of transverse mode switchable ultrashort pulses with narrow bandwidths in an all-fiber mode-locked laser by exploring a mode-selective photonic lantern (MSPL). The laser cavity serves not only as a ring resonator but also as an intrinsic spectral filter.

Optical TTD compensation network-based phase precoding for THz massive MIMO systems.

In sixth generation (6G) communications, terahertz (THz) communication is one of the most important technologies in the future due to its ultra-bandwidth, where hybrid beamforming has been widely used to solve the severe transmission attenuation in the THz band. However, the use of frequency-flat phase shifters in hybrid beamforming leads to the beam split effect. To solve the beam split influence, we propose a novel optical true time delay compensation network (OTTDCN)-based phase precoding structure with low power consumption.

Single wavelength MDM-PDM 800-Gb/s net data rate transmission over a standard multimode fiber employing a Kramers-Kronig receiver.

We propose a high-speed multimode fiber short-reach optical interconnect system based on a Kramers-Kronig (KK) field reconstruction with the mode division multiplexing (MDM) and polarization division multiplexing (PDM) technology. In this work, the LP01, LP21a, LP21b, and LP02 modes are selected as independent channels to carry information. The demonstration achieved the 800 Gb/s net data rate per wavelength with a bit-rate-distance-product (BDP) of 8 Tb/s·km.

Bias-drift insensitive full-field frequency response characterization of a thin-film lithium niobate-based intensity modulator.

We propose a rapid and precise scheme for characterizing the full-field frequency response of a thin-film lithium niobate-based intensity modulator (TFLN-IM) via a specially designed multi-tone microwave signal. Our proposed scheme remains insensitive to the bias-drift of IM. Experimental verification is implemented with a self-packaged TFLN-IM with a 3 dB bandwidth of 30 GHz.

Experimental demonstration of optical waveform transmission with multiple-eigenvalue 16-APSK modulation.

The multi-eigenvalue multiplexing-based discrete spectrum-modulated nonlinear frequency-division multiplexing (DS-NFDM) system with higher-order modulation format has been demonstrated experimentally. After designing the coefficients of the eigenvalue set and the constellation point distribution of 16-amplitude phase shift keying (16-APSK), the realizations of 14-, 30-, and 46-eigenvalue multiplexed DS-NFDM signals have been implemented. The results show that 46-eigenvalue and 30-eigenvalue multiplexed DS-NFDM signals can transmit 50 km and 400 km over a nonzero dispersion-shifted fiber (NZDSF) under soft-decision forward error correction (SD-FEC) threshold of 2.

Blind frequency offset estimation method based on a minimum phase correction error for a full spectrum modulated NFDM system.

To improve the spectral efficiency of a full spectrum modulated nonlinear frequency division multiplexing (FS-NFDM) system, a blind frequency offset estimation (FOE) method has been proposed. The approach based on the minimum phase correction error can achieve high estimation accuracy of sub-MHz without need of any training symbols. Furthermore, in order to reduce the computational complexity, an eigenvalue-shift method is used to get a coarse search interval of FO, and then the one-dimensional optimization algorithm based on golden section search and parabolic interpolation is used to get the optimal FOE for the coarse search interval.

Low-loss and compact photonic lantern based on a step-index double cladding fiber.

The fulfilment of the adiabatic criterion is indispensable for the realization of a low-loss photonic lantern (PL), concurrently imposing a stringent restriction on the taper transition length of the PL. Here, by relaxing the adiabatic criterion, a low-loss and compact PL based on a step-index double cladding fiber (SI-DCF) is theoretically proposed and experimentally demonstrated. The use of SI-DCF can reduce the mode field diameter (MFD) expansion ratio during the tapering processing and greatly decrease the taper transition length required for adiabatic tapering.

Simultaneous realization of high gain and low DMG of four-mode EDFA under bidirectional hybrid-mode pump.

We theoretically and experimentally verify that, the bidirectional hybrid-mode pumping scheme can address the optimization problem of trade-off between high gain and low differential modal gain (DMG) of four-mode erbium-doped fiber amplifier (4M-EDFA), in comparison with traditional both forward and backward hybrid-mode pumping scheme. It is noticed that, when the total pump power is fixed, the bidirectional hybrid-mode pumping scheme can not only achieve higher gain, but also suppress DMG due to different overlap integrals for the forward and backward pumping schemes. The bidirectional hybrid-mode pumped 4M-EDFA is developed with the forward pumping at LP mode and the backward pumping at LP mode, under a pump power ratio of 30%:70%.

Pairwise Tomlinson-Harashima precoding for multiple-lane IM-DD transmissions.

As for the photonic interconnection based on the multiple-lane intensity modulation direct detection (IM-DD) transmission, both intra-channel inter-symbol-interference (ISI) originating from bandwidth constraint, and inter-channel performance discrepancy emerging from inter-channel component differences are the major bottleneck for the throughput enhancement. Here, we propose a pairwise Tomlinson-Harshima precoding (P-THP) scheme, in order to simultaneously deal with both intra-channel ISI and inter-channel performance discrepancy. The effective function of the proposed P-THP scheme is experimentally evaluated by transmitting 4-channel 81-GBaud PAM4 signals over 2 km standard single-mode fiber (SSMF).

Non-sweep DC component estimation method for a virtual-carrier assisted Kramers-Kronig receiver.

The Kramers-Kronig (KK) receiver has attracted much attention in short-range optical interconnection because of its ability to recover the phase of the signal from the intensity information through KK algorithm. In high-speed KK systems, such as virtual-carrier (VC) assisted ones, an alternating current (AC) coupled photo-detector (PD) is preferred due to relaxing the requirements of analog-to-digital converter (ADC) and electronic amplifier by filtering direct current (DC) component. However, the loss of the DC component will cause the KK algorithm to break down, so it is necessary to accurately recover DC value in the digital domain with multiple-sweep.

Mode multicasting without parasitic wavelength conversion.

Optical multicasting, which involves delivering an input signal to multiple different channels simultaneously, is a key function to improve network performance. By exploiting individual spatial modes as independent channels, mode-division-multiplexing (MDM) can solve the capacity crunch of traditional standard single-mode fiber (SSMF) transmission system. In order to realize mode multicasting with high flexibility in future hybrid wavelength-division-multiplexing (WDM) and MDM networks, we propose a mode multicasting scheme without parasitic wavelength conversion, based on the inter-modal four-wave mixing (FWM) arising in the few-mode fiber (FMF).

Towards high spectral efficiency UDWDM-PON based on the simplified coherent reception of pulsed shaped PAM-4 signals.

Enhancing spectral efficiency (SE) of ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) is vital to providing broadband access for massive users. Here, we experimentally demonstrate a high SE UDWDM-PON in the C-band, based on the simplified coherent reception of 10 Gb/s 4-level pulse-amplitude modulation (PAM-4) signals. We investigate the WDM signal reception by mathematical derivation and propose to enhance the SE by adopting both intradyne detection and pulse shaping techniques.

High-speed secure key distribution based on interference spectrum-shift keying with signal mutual modulation in commonly driven chaos synchronization.

The secure key generation and distribution (SKGD) are unprecedentedly important for a modern secure communication system. This paper proposes what we believe to be a novel scheme of high-speed key distribution based on interference spectrum-shift keying with signal mutual modulation in commonly driven chaos synchronization. In this scheme, delay line interferometers (DLI) are utilized to generate two low-correlation interference spectra from commonly driven synchronous chaos, and then a 2 × 2 optical switch can effectively change the relationship between the two interference spectra in post-processing by shifting the states of the switch.

Transmitter dispersion eye closure quaternary assessment based on linear CNN with 1 × 1 convolutional kernel.

Transmitter dispersion eye closure quaternary (TDECQ) is a vital metric to characterize the quality of four-level pulse amplitude modulation (PAM-4) optical signals. However, the traditional TDECQ assessment scheme is complex and time consuming, with heavy iterative operations. Therefore, accelerating the TDECQ assessment has great significance for photonic data-center interconnection (DCI) applications.

Frequency offset estimation for nonlinear frequency division multiplexing with continuous spectrum modulation.

Carrier frequency offset (CFO) estimation is very important for the optical fiber communications and has been studied widely in linear coherent systems, while only a few works have been reported for nonlinear Fourier transform (NFT) based systems. In continuous spectrum (CS) modulation nonlinear frequency division multiplexing (CS-NFDM) systems, frequency offset (FO) has a great influence on its performance, requiring an improved frequency offset estimation (FOE) method. We found that the oversampling rate R adopted in NFDM to ensure the accuracy of the NFT and inverse NFT (INFT) calculations, would cause the estimation accuracy of the traditional FFT-FOE method to decrease by R times.