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Optical wireless communication (OWC) can provide the last mile high data rate and broadband access to indoor users. Infrared-based communication (IRC) can also achieve high data rate OWC transmission using a directional and collimated line-of-sight (LOS) optical beam. However, a collimated optical beam with beam steering ability is required to provide the LOS communication channel to different mobile users. Different optical beam steering approaches have their limitations. Although the mechanical-based approach using fast steering mirror (FSM) usually has a large footprint and limited optical steering speed; it can provide a large field-of-view (FOV) and support a wide wavelength window with polarization, optical mode, and modulation format independence operations. These are crucial for the OWC systems as wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM) are employed to boost the transmission capacity. In this work, we propose and reveal a proof-of-concept experimental demonstration of an adaptive fast steering mirror (FSM)-based optical beam tracking and alignment system. To enhance the FOV and the stability of the OWC transmission, high-precision adaptive optical tracking via a two-FSM system with a light spot approaching method is proposed and demonstrated. The operation mechanism of optical alignment using two FSMs to establish the reference optical axis path is discussed in detail. The first FSM is utilized to correct the beam displacement issue from the reference optical axis, while the second FSM is utilized to correct the incident beam angle issue from the reference optical axis. Experimental result shows that the FOV can be enhanced from 0.05° (i.e., using only a single fiber collimator) to 51.85° using the proposed FSM-based system. A high-speed and stable orthogonal frequency division multiplexing (OFDM) OWC transmission at 89.3 Gbit/s, 87.03 Gbit/s, and 84.47 Gbit/s after free space propagation distances of 3 m, 10 m, and 20 m, respectively, can be achieved, fulfilling the hard-decision forward-error-correction (HD-FEC) requirement (i.e., bit-error-rate, BER = 3.8 × 10-3).

Mode-division multiplexing has emerged as an effective approach to increase the capacity of on-chip optical interconnects. Efficient routing and add-drop manipulation of different modes are therefore essential for scalable multimode photonic integrated circuits. However, implementing compact mode routers with low loss, low inter-mode crosstalk, and high-speed signal compatibility remains challenging on the silicon photonic platform. In this work, we propose and experimentally demonstrate a compact four-port optical mode router on a silicon-on-insulator platform. The device enables mode-selective and bidirectional add-drop routing for multiple modes by integrating multimode waveguide crossings, multimode waveguide bends, and mode-selective microring resonators. Low-loss and low-crosstalk operation is achieved through carefully designed mode-matching and multimode waveguide engineering. Experimental results show correct routing for three supported modes with inter-mode crosstalk below -15.4 dB and an insertion loss below 6.6 dB. High-speed data transmission at 40 Gbit/s is demonstrated for all routing paths, resulting in an on-chip aggregate data capacity of 480 Gbit/s. The proposed architecture provides a scalable solution for high-capacity mode-division-multiplexed optical interconnects on a silicon photonic platform.

This Letter experimentally demonstrates a radio-frequency (RF) pilot-aided scheme for joint frequency offset and phase noise compensation in photonics-aided D-band multiple-input multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM) systems. Using 16-quadrature amplitude modulation (16-QAM) and probabilistically shaped 64-QAM (PS-64QAM) signals, the proposed scheme achieves a noticeable signal-to-noise ratio (SNR) improvement while substantially reducing the pilot overhead. Owing to the reduced overhead, the net data rate is increased from 150 to 156 Gbit/s for 16-QAM and from 87 to 91 Gbit/s for PS-64QAM. These results demonstrate that the proposed RF pilot-aided scheme provides a spectrally efficient and low-complexity solution for joint frequency offset and phase noise compensation in broadband photonics-aided OFDM systems.

The conversion between electrical and optical signals underpins modern optical communication systems and increasingly requires tight co-integration with electronics at short length scales. Photonic integrated circuits based on thin-film lithium tantalate has emerged as a promising electro-optic platform due to its large Pockels coefficient, low birefringence, low bias drift, and high power handling, yet its integration with standardized microelectronic processes remains limited. Here we show that incorporating the copper Damascene process into thin-film lithium tantalate modulators enables a scalable, electronics-compatible fabrication approach. The resulting devices exhibit approximately 10% lower microwave loss than conventional gold-electrode designs, while simultaneously supporting watt-level on-chip optical power handling and maintaining a stable quasi-static half-wave voltage from 1 Hz to 1 MHz, with a bias point drift of only 0.4 dB over a 15-hour period when operated at 1.75 mW on-chip optical power. High-speed transmission experiments demonstrate line rates of 416 Gbit/s (PAM4) and 540 Gbit/s (PAM8) below the 25% soft-decision forward-error-correction threshold. These results establish a practical route toward scalable chip-on-wafer integration of electro-optic modulators with microelectronic circuits.

Diffractive neural networks offer a novel physical implementation for optical computing to achieve parallelism, low power consumption, and light-speed processing. However, their limited dispersion engineering necessitates increasingly complex architectures for tasks such as spectrum recognition and simultaneous multi-class classification, which in turn leads to increased energy demands. Here, we propose a spoof plasmonic neural network (SPNN) comprising cross-cascaded spoof surface plasmonic waveguides with strong engineered dispersion properties designed for operation in the terahertz regime. This compact platform efficiently separates spectral components from a broadband input signal, achieving a data rate of 22 Gbit/s across two separated spectral channels. We experimentally show that the SPNN can simultaneously classify multiple inputs from Fashion-MNIST+MNIST or Fashion-MNIST+EMNIST datasets, achieving classification accuracies of 98.3% and 97.4% or 97.4% and 93.8%, respectively. For multi-color CIFAR-10 dataset classification, the network architecture incorporating multiple cascaded SPNNs realizes over 10% higher accuracy than single-color-channel methods by leveraging distinct color channels mapped to respective spectrum channels. These findings highlight the potential of SPNNs for machine learning applications and lay the groundwork for future terahertz chip integration.

In this study, we demonstrate a hardware-efficient post-equalization implementation for PAM8 signals on an FPGA platform by utilizing an additive power-of-two (APoT) quantization scheme. This approach reduces hardware resource consumption by over 70% compared to conventional methods while preserving critical performance metrics. In a 300-m W-band wireless communication experiment, the system reliably transmits 22.1184 Gbit/s PAM8 signals and satisfies the 2.4 × 10-2 soft-decision forward error correction (SD-FEC) standard. Notably, under a host-assisted workflow, the APoT scheme achieves performance equivalent to 16-bit uniform quantization and exhibits superior stability than PoT quantization.

We experimentally demonstrate a high-capacity dense wavelength division multiplexing (DWDM) transmission covering a 12.2 THz bandwidth over a 6×252 km (1512 km) standard single-mode fiber (SSMF) link. To mitigate the severe transmission impairments inherent in wideband systems, such as fiber nonlinearity and inter-symbol interference, we propose an equalizer that cooperatively combines convolutional neural networks (CNN) for local feature extraction, bidirectional long short-term memory networks (BiLSTM) for temporal modeling, and a Bayesian head for uncertainty-aware residual prediction. Experimental results show that with the help of the proposed Bayesian CNN-BiLSTM hybrid equalizer, the generalized mutual information (GMI)-estimated throughput is significantly improved from 97.1 Tbit/s to 102.3 Tbit/s, while the training epochs are reduced by 80% comparing to conventional neural network methods. Consequently, the system achieves a spectral efficiency (SE) of 8.4 bit/s/Hz and an average single-carrier capacity of 838.5 Gbit/s over 1512 km SSMF, validating the effectiveness of the proposed equalizer for wideband long-haul transmission.

Graphene-based optoelectronic devices have shown high bandwidth and easy incorporation in silicon photonics. However, given that graphene is a single-atom-thick material with a large surface-to-volume ratio, the intriguing properties of the graphene optoelectronic devices are very susceptible to surrounding environments, including interfacial states and dangling bonds from dielectrics. This has degenerated the performance of graphene electro-optic modulators that rely on uniform electrical gating. Herein, a facile integration of a Sb2O3/Al2O3 hybrid dielectric on the chemical-vapor-deposited (CVD) graphene is reported for electro-absorption modulators. The Sb2O3 molecular crystal as interfacial layer enables a homogeneous Al2O3 dielectric growth and a van der Waals (vdW) interface with graphene, which can significantly reduce the interfacial scattering centers (such as dangling bonds) and thus preserves the electronic properties of graphene, showing an averaged carrier mobility (μ) of 10880 cm2 V-1 s-1 and residual carrier concentration (n*) of 1.35 × 1011 cm-2. In contrast to the device with a single dielectric, the electro-absorption modulator with the vdW interface shows a 1.6 times higher modulation efficiency (0.0054 dB V-1 µm-1) and 5.8 times higher bandwidth (≈35 GHz). Moreover, modulation rate is up to 30 Gbit s-1. Our work provides a promising dielectric option for graphene optoelectronic devices.

The vulnerability of intensity modulation direct detection (IM-DD) systems to physical-layer eavesdropping poses a significant threat to data center interconnects (DCI). In this Letter, we propose a dual-dynamic strategy for physical-layer encryption to enhance the security of IM-DD systems. The scheme synergistically combines dynamic key update and dynamic rule-based pulse-amplitude modulation (DR-PAM) symbol scrambling to achieve efficient security protection. The master key is dynamically updated according to a pre-negotiated rule, enabling the generation of a distinct session key for each data frame via a hash function. This approach ensures real-time operation without frequent key negotiation. To our knowledge, the DR-PAM is the first universal symbol scrambling scheme supporting arbitrary PAM orders. Experimental results demonstrate that at 56 Gbit/s and 112 Gbit/s data rates, legitimate receivers achieve performance identical to unencrypted links, while illegal receivers are completely unable to decrypt the data. The proposed encryption scheme has better compatibility with existing transmission systems and introduces no performance penalty, thus delivering a secure, real-time, and practical solution for cost-sensitive, high-speed DCI.

Ultrabroadband integrated modulators involving materials beyond those available in silicon manufacturing increasingly rely on the Pockels effect. Among electro-optic materials, lithium tantalate offers comparable Pockels coefficients to lithium niobate but with significantly improved photostability, lower birefringence, higher optical damage threshold, and enhanced DC bias stability. Here we demonstrate wafer-scale heterogeneous integration of lithium tantalate films on low-loss silicon nitride photonic integrated circuits, achieving low optical losses ( ~ 14.2 dB/m) while combining the mature processing of silicon nitride waveguides with the ultrafast electro-optic response of thin-film lithium tantalate. The resulting devices achieve a 6 V half-wave voltage, and support modulation bandwidths of up to 100 GHz. We use single intensity modulators and in-phase/quadrature (IQ) modulators to transmit PAM4 and 16-QAM signals reaching up to 333 and 581 Gbit/s net data rates, respectively. Our results establish lithium tantalate-on-silicon nitride as a viable platform for RF photonics, interconnects, and analog signal processing.

As the scale of reconfigurable photonic chips increases, solutions are needed to address the increasing complexity of the electronic readout circuits needed to monitor the optical functionality. The number of these elements is strictly related to the scale of the photonic chip, and it can represent a significant overhead, in terms of electrical connections and area occupation, when the optical complexity increases. Here, we propose two scalable methods for controlling programmable chips using a single readout circuit, by individually labeling each photonic device. Experimental results at 10 Gbit/s confirm the effectiveness of the approach, while simulation analyses highlight the trade-offs that need to be considered when employing the proposed techniques.

We propose III-V/Si hybrid plasmonic waveguide photodetector incorporating an InGaAs membrane. We confirmed that Ni-InGaAs alloy functions effectively as an electrode for a plasmonic waveguide. Utilizing Ni-InGaAs alloy enabled the integration of plasmonic waveguide photodetectors into the Si photonics platform through a simplified fabrication process. We achieved a responsivity of 0.13 A/W at 1 V with a dark current of 400 nA and confirmed a 32.1 Gbit/s clear eye diagram, demonstrating the potential for high speed InGaAs plasmonic photodetector in Si photonics.

We present a novel, to our knowledge, electro-optic (EO) modulator, integrating slow-light Bragg waveguides with a Michelson interferometer (MI) on a silicon-on-insulator (SOI) platform. By leveraging the slow-light effect, the design enhances the modulation efficiency while reducing the device footprint. Additionally, dual-inductor peaking is employed to improve the bandwidth, with the two circular inductors providing flexibility to adjust their parameters for optimal peaking bandwidth. Experimental results show that the device achieves an electro-optic 3-dB bandwidth of 48 GHz under a 2 V reverse-bias condition in small-signal measurement and a modulation efficiency of 0.26 V·cm. High-speed tests show that the device supports a 100 Gbit/s on-off keying (OOK) eye diagram rate. The device holds significant application prospects in optical interconnection applications.

The mid-infrared spectrum, spanning from 3 to 14 µm, holds great promise for molecular spectroscopy and free space optical communication, benefiting from strong molecular absorption and reduced atmospheric attenuation. While progress in MIR photonics has accelerated due to improved sources and detectors, integrated low-loss, high -performance modulators remain limited. In order to address this gap, we demonstrate a broadband, high speed lithium niobate on sapphire Mach Zehnder electro optic modulator operating from 3.95 to 4.5 µm. The device shows a 3 dB bandwidth above 20 GHz, 17 dB extinction ratio, and Vπ L = 22 V ⋅ cm, with optical output power at the half milliwatt level. We demonstrate 10 Gbit s-1 data transmission and a 70 GHz broad frequency comb, uniquely combining integration, low propagation loss, extinction ratio and high-speed operation.