Xihua Zou

• PhD, Professor / Humboldt Research Fellow
• Professor at Southwest Jiaotong University, China / University of Duisbure-Essen, Germany

Integrated sensing and communication (ISAC), a key technology for next-generation wireless networks (e.g., 5G-A and 6G), aims to provide both large-capacity wireless communication and high-resolution microwave sensing/ranging simultaneously. Microwave photonics (MWP)-ISAC, with its unique features such as high frequency, large bandwidth, low freque...

The Kramers-Kronig (KK) relation, which has been explored in low-complexity receivers for coherent optical communications, is extended to visible light communication (VLC) systems with intensity modulation and direct detection (IM/DD). To generate a real-valued, non-negative signal suitable for IM/DD channels, a KK optical orthogonal frequency divi...

A single photonic reservoir based on a semiconductor ring laser with filtered optical feedback (FOF) is proposed to achieve simultaneous reservoir computing (RC) through multiplexing of the two directional modes and enhance the robustness of RC operations by using a Fabry-Perot filter. Numerical investigations of laser dynamics reveal that the FOF...

The human brain can efficiently handle multiple tasks simultaneously, with the structural segregation of brain regions closely linked to their functional specialization. In this paper, we propose and experimentally demonstrate multifunctional photonic reservoir computing (MPRC), inspired by this biological characteristic. The neuron states of the p...

With the rapid growth of information technology, controlling the synchronization of large-scale networks has become more challenging and costly. To address this, we propose a scalable regulation scheme of cluster synchronization in a directed complex semiconductor lasers (SLs) network. The stability of chaotic synchronization for the entire network...

Chaotic dynamics generated by vertical-cavity surface-emitting lasers (VCSELs) has stimulated a variety of applications in secure communication, random key distribution, and chaotic radar for its desirable characteristics. The application of machine learning has made great progress in the prediction of chaotic dynamics. However, the performance is...

With consideration of the inherent low-pass characteristics of LEDs, this paper proposes a resource allocation strategy for multi-user multiple-input multiple-output visible light communication (MU MIMO-VLC) based on orthogonal frequency division multiple access (OFDMA). We derive theoretical expressions for the achievable rates of MU MIMO-OFDMA VL...

A novel signal quantization scheme based on adaptive differential pulse code modulation (ADPCM) is proposed and experimentally demonstrated. By adaptively adjusting the quantization step size using a small number of quantization bits (QBs), the spectral efficiency (SE) can be improved by a factor of 3∼5 while maintaining a high signal-to-quantizati...

A photonics-assisted compressive sensing (CS) array system based on uniform linear array (ULA) for wideband sparse radio frequency (RF) signals acquisition and direction of arrival (DOA) estimation is proposed. Each branch of the system consists of two cascaded Mach-Zehnder modulators (MZMs), an integrator, and a low-rate analog-to-digital converte...

End-to-End (E2E) learning has increasingly become a dominant method for enhancing the performance of communication systems. In this paper, an E2E Radio Over Fiber (RoF) transmission system utilizing self-supervised learning (SSL) is proposed. This E2E approach enables automatic optimization of the transmission system's transmitter modulator and rec...

High resolution is the decisive factor for detecting, recognizing, and tracking tiny objects in radars. However, high resolution usually requires large instantaneous bandwidth, imposing critical challenges on device bandwidth and available spectrum resources. An emerging approach is the coherent fusion processing over multiple narrow bandwidths, to...

In-band full-duplex (IBFD) operation is essential for both sensing-centric and communication-centric integrated sensing and communications (ISAC) systems. Both types require the monostatic transceiver to overcome the technical challenge of self-interference (SI). To address this challenge, a photonics-assisted self-interference cancellation (SIC) s...

We designed a multi-channel comb filter generation scheme with nearly consistent channel numbers and free spectral range (FSR) in standard 220-nm-thick silicon-on-insulator (SOI) technology. This scheme relies on the formation of optical microcavities using Bragg grating structures, which serve as reflectors. By precisely designing the optical path...

The rapid advancement of the thin-film lithium niobate platform has established it as a premier choice for high-performance photonics integration. High-speed optical coherent receivers are essential for supporting the large communication capacities required by data center interconnects. Although high-speed photodiodes have been demonstrated on the...

Electro–optic phase modulators (PMs) are critical components for modern communication, sensing, and microwave photonics. A recycling PM has been demonstrated to effectively reduce the half‐wave voltage ( V π ) while exhibiting resonant behavior for the driven microwave signals [Nature 612, 252 (2022)]. However, the significant optical delay of the...

We propose and experimentally demonstrate a photonic method for wideband multipath self-interference cancellation using a silicon photonic modulator chip. The chip generates phase-inverted reference signals by leveraging the opposite phase between optical sidebands. Effectively managing amplitude and phase imbalances between self-interference and r...

Orthogonal frequency-division multiplexing (OFDM) waveform is highly preferred as a dual-function candidate for integrated sensing and communication (ISAC) systems. However, the sensitivity to both carrier frequency offset (CFO) and phase noise greatly impedes its applications in millimeter-wave ISAC systems. Here, we propose and experimentally dem...

By adding output feedback and a sliding window, a software-based enhanced reservoir computing (RC) is proposed and verified in intensity modulation direct detection (IMDD)-based short-reach optical transmission systems. Both simulation and experiment confirm the enhanced RC is effective for dispersion and nonlinearity compensation for short-reach I...

Scheduling radar and communication functions in a frequency-division multiplexing (FDM) fashion is a classic solution to achieve mutual-interference-free integrated sensing and communication (ISAC) system. However, it is haunted by poor spectral efficiency (SE) in comparison to the spectrum-sharing scheme. In this paper, we propose a novel photonic...

We report high-power modified uni-traveling carrier photodiodes with 150-GHz bandwidth. To improve the RF output power, the photodiode chips are flip-chip bonded on diamond submounts with high thermal conductivity to enhance heat dissipation. Measured 3-dB bandwidths of 4-μm, 6-μm, 8-μm, and 10-μm diameter photodiodes reach 150 GHz, 129 GHz, 117 GH...

Multipath self-interference (MSI) between the transmitter and receiver is an inevitable problem in realistic in-band full-duplex (IBFD) transmissions. Due to the dynamic and intricate MSI channels, it is crucial for the MSI cancellation system to quickly obtain the optimal configuration of multi-dimensional parameters. To overcome this problem, a p...

Multiband integrated sensing and communication (ISAC) systems towards multiple functions and multiple users will play an important pole in future 6G wireless networks. Here, we propose and experimentally demonstrate a multiband ISAC system using optical frequency upconversion and coherent receiving techniques for millimeter-wave (MMW) high-capacity...

The nonlinear evolution of ultrashort pulses in optical fiber has broad applications, but the computational burden of convolutional numerical solutions necessitates rapid modeling methods. Here, a lightweight convolutional neural network is designed to characterize nonlinear multi-pulse propagation in highly nonlinear fiber. With the proposed netwo...

Nonlinear equalization (NE) plays a pivotal role in the analog intermediate-frequency over fiber (IFoF) mobile fronthaul (MFH) system demanding a high signal fidelity. This work proposes and experimentally validates a novel blind frequency-domain NE (FD-NE) approach for millimeter-wave (MMW) fiber-wireless (FiWi) IFoF MFH systems. This proposed bli...

A data-driven digital demodulator based on a Fourier layer Transformer network (FTnet) for radio over fiber (RoF) transmission system with quadrature amplitude modulation (QAM) is developed and experimentally demonstrated. The FTnet combines the Transformer encoder with the Fourier layer to learn the waveforms and directly recover the bitstreams fr...

With the advantages of a large electro-optical coefficient, wide transparency window, and strong optical confinement, the thin-film lithium niobate (TFLN) technique has enabled the development of various high-performance optoelectronics devices, ranging from the ultra-wideband electro-optic modulators to the high-efficient quantum sources. However,...

Self-interference (SI) due to signal leakage from a local transmitter is an issue in an in-band full-duplex (IBFD) transmission system, which would cause severe distortions to a receiving signal of interest (SOI). By superimposing a local reference signal with the same amplitude and opposite phase, the SI signal can be fully canceled. However, as t...

A high-performance 32-channel silicon arrayed waveguide grating (AWG) with 100 GHz spacing is designed and fabricated using 180-nm lithography platform for massive production. For the arrayed waveguides, a rectangular structure compositing of a straight waveguide and a 90-degree bend waveguide is designed. Moreover, the overall structure only needs...

Electro‐optic (EO) modulation is a well‐known and essential topic in the field of communications and sensing, while ultrahigh modulation efficiency is unprecedentedly desired in the current green and data era. However, dramatically increasing the modulation efficiency is difficult in conventional mechanisms, being intrinsically limited by the monot...

A millimeter-wave (MMW) joint radar-communication (JRC) system with super-resolution is proposed and experimentally demonstrated, using optical heterodyne upconversion and self-coherent detection downconversion techniques. The point lies in the designed coherent dual-band constant envelope linear frequency modulation-orthogonal frequency division m...

The integration of high-speed optical communication and distributed sensing could bring intelligent functionalities to ubiquitous optical fibre networks, such as urban structure imaging, ocean seismic detection, and safety monitoring of underground embedded pipelines. This work demonstrates a scheme of integrated sensing and communication in an opt...

We here propose a novel cost-effective millimeter-level resolution photonic multiband radar system using a single MZM driven by a 1-GHz-bandwidth LFM signal. It experimentally shows an ~8.5-mm range resolution through coherence-processing-free multiband data fusion.

Chromatic dispersion (CD) is one of the key limitations of increasing the transmission performance for short-reach transmission.Theavailableopticaldispersion-compensationtechniques are not favored due to their high complexity and other expenses such as power. Reservoir computing is reviewed as a promising technique to provide equalization with memo...

In this paper, a nonlinear model for Light Emitting Diodes (LEDs) inspired by semiconductor physics, and a corresponding post-compensator are implemented in a Field Programmable Gate Array (FPGA) for real-time Visible Light Communications (VLC). Our experiments demonstrate that the LED model effectively characterizes the dynamic LED nonlinearity, i...

A bidirectional wavelength division multiplexing (WDM) analog radio-over-fiber (A-RoF) mobile fronthaul (MFH) link is enhanced using photonic integrated devices. Two key photonic integrated devices are combined in the A-RoF link: an 8-channel InP directly modulated laser (DML) transmitter and a 32☓100-GHz silicon array waveguide grating (AWG). The...

To improve the receiver sensitivity of the digitized radio-over-fiber (DRoF) transmission system, a vector quantization scheme based on probabilistic quantization codeword shaping (PQCS) is proposed. The PQCS performs quantization bits (QBs) rematching on the original codebook to optimize the proportion distribution of level ‘0’ and level ‘2’ in 4-...

We here propose a novel cost-effective millimeter-level resolution photonic multiband radar system using a single MZM driven by a 1-GHz-bandwidth LFM signal. It experimentally shows an ~8.5-mm range resolution through coherence-processing-free multiband data fusion.

The radio over fiber (RoF) system using optical heterodyne (OH) for broadband up-conversion and envelope detection (ED) for phase-noise-insensitive down-conversion stands out as a simple, robust, and cost-effective solution for exploiting the abundant bandwidth resource at the millimeter-wave (MMW) band. In this paper, we dedicate efforts to experi...

A photonic-assisted approach is proposed for modulation format identification (MFI) on radio frequency (RF) signals under low sampling rate. In this approach, a photonic-assisted interferometer (PAI) is designed for computation-free data augmentation by transforming the signal’s phase and frequency variations into modulation format-sensitive amplit...

A cost-effective millimeter-wave (MMW) joint radar-communication (JRC) system with super resolution is proposed and experimentally demonstrated, using optical heterodyne up-conversion and self-coherent detection down-conversion techniques. The point lies in the designed coherent dual-band constant envelope linear frequency modulation-orthogonal fre...

A digital demodulator based on Fourier layer Transformer network (FTnet) is proposed for radio over fiber (RoF) transmission with intensity-modulation and direct-detection (IM-DD). The FTnet is a new deep learning network, which replaces the self-attention mechanism of the Transformer encoder with a Fourier layer. The FTnet-based digital demodulato...

In phase-sensitive optical time domain reflectometry ( $\Phi \text{-} {\rm OTDR}$ Φ - O T D R ), false phase peaks caused by interference fading have been observed experimentally; however, the statistical law has not yet been disclosed. In this work, after clarifying that the false phase peaks originate from the phase hopping of demodulated phase n...

The stable radio frequency (RF) transmission scheme involving single wavelength has received increasing attention due to the feature of accurate phase information extraction. However in single laser system, the single side band (SSB) phase noise of output signal will be deteriorated by Rayleigh scattering during long-distance optical transmission....

Short reach optical communications are desperate for cost-effective solutions to improve capacity and compatibility in dealing with massive access and applications. Single sideband-direct detection (SSB-DD) is highly recognized for improving capacity with single PD, but it is confronted with signal-signal beating interference (SSBI). Recently, a DC...

A physics-based deep learning (DL) method termed Phynet is proposed for modeling the nonlinear pulse propagation in optical fibers totally independent of the ground truth. The presented Phynet is a combination of a handcrafted neural network and the nonlinear Schrödinger physics model. In particular, Phynet is optimized through physics loss generat...

The joint radar and communication (JRC) system providing both large-capacity transmission and high-resolution ranging will play a pivotal role in the next-generation wireless networks (e.g., 6G and beyond) and defense applications. Here, we propose and experimentally demonstrate a novel photonics-assisted millimeter-wave (mm-wave) JRC system with a...

The publisher's note contains a correction to [Opt. Express 29 32333 (2021)10.1364/OE.438439]. The article was corrected on 17 June 2022.

The ultrashort pulse evolution in fiber optical parametric amplifier (FOPA) systems is a highly complex nonlinear dynamic. Here, the long short-term memory network (LSTM) is applied to predicting the pulse propagation of signal waves in the FOPA system, rather than calculating the nonlinear Schrödinger equation (NLSE) numerically. The LSTM network...

Electro-optic (EO) modulation is a well-known and essential topic in the field of communications and sensing. Its ultrahigh efficiency is unprecedentedly desired in the current green and data era. However, dramatically increasing the modulation efficiency is difficult due to the monotonic mapping relationship between the electrical signal and modul...

An optical frequency comb (OFC)-assisted covert wireless communication system with multiple access and enhanced capacity is proposed and experimentally demonstrated. In the scheme, signals in multiple channels are spread and mixed together to use a single transmitter and then received by individual receivers according to multiple access channels. T...

A novel millimeter-Wave (mm-Wave) joint radar and communication (JRC) system based on photonic spectrum-spreading phase-coding is proposed. The key to the proposed system is the convergence of photonic microwave phase-coding and spectrum-spreading multiplexing techniques. Phase-coding enables the generation of wideband mm-Wave JRC signal, leading t...

IEEE Transactions on Microwave Theory and Techniques, accepted, 2021

The initial state of a nonlinear optical fiber system plays a vital role in the ultrafast pulse evolution dynamic. In this work, a data-driven compressed convolutional neural network, named inverse network, is proposed to predict initial pulse distribution through a series of discrete power profiles at different propagation distances. The inverse n...

Ambiguity resolution (AR) is a fundamental problem for carrier-phase-based signal processing tasks to leverage the superhigh precision of wavelength level range and velocity measurements. With the elaborately designed waveform and coordinated running of the space-based satellite system, the antenna array observations of GNSS signals feature a phase...

This erratum corrects a clerical error in the original manuscript [ Photon. Res. 9 , 1124 ( 2021 ) PRHEIZ 2327-9125 10.1364/PRJ.419605 ].

A 32-channel wavelength division multiplexer with 100 GHz spacing is designed and fabricated by interleaving two silicon arrayed waveguide gratings (AWGs). It has a parallel structure consisting of two silicon 16-channel AWGs with 200 GHz spacing and a Mach–Zehnder interferometer (MZI) with 200 GHz free spectral range. The 16 channels of one silico...

A novel multi-frequency decomposition (MFD) scheme is proposed to achieve a fading-free phase-sensitive optical time-domain reflectometry ( $\Phi $ -OTDR). By performing short-time Fourier transform (STFT) on the detected signal, the spectrum contents of the normal probe pulse can be fully utilized and decomposed in time-frequency domain without s...

Addressing the nonlinearity induced signal degradation is of critical importance for harvesting the transparent benefits of analog radio over fiber (A-RoF architecture, to support mobile fronthaul (MFH with high spectral efficiency and reduced latency. Here, for linearizing the low-latency A-RoF MFH using digital-domain fast Fourier transform /inve...

Radio-over-fiber (RoF) transmission is a quite reliable technology to support the current and future demands of rapidly progressing broadband wireless network with large capacity and high spectral efficiency. In this paper, we report and demonstrate a digital RoF transmission system using two-dimensional discrete cosine transform with vector quanti...