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An effective solution to enhance the capacity of an optical‐interconnect link is utilizing advanced multiplexing technologies, like wavelength‐division‐multiplexing (WDM), polarization‐division multiplexing (PDM), spatial‐division multiplexing (SDM), bi‐directional multiplexing, etc. On‐chip (de)multiplexers are necessary as key components for realizing these multiplexing systems and they are desired to have small footprints due to the limited physical space for on‐chip optical interconnects. As silicon photonics has provided a very attractive platform to build ultrasmall photonic integrated devices with CMOS‐compatible processes, in this paper we focus on the discussion of silicon‐based (de)multiplexers, including WDM filters, PDM devices, and SDM devices. The demand of devices to realize a hybrid multiplexing technology (combining WDM, PDM and SDM) as well as a bidirectional multiplexing technologies are also discussed to achieve Peta‐bit optical interconnects.

Simultaneous and independent manipulation of light’s propagation direction, polarization state, and wavelength remains a fundamental challenge in photonics, due to the intrinsic entanglement of optical degrees of freedom imposed by reciprocity and structural symmetry. Here, we present a single-layer dielectric Möbius metasurface that achieves fully decoupled control across these three dimensions by leveraging a topology-inspired polarization-path inversion mechanism. Inspired by Möbius topology, our design maps forward and backward polarization trajectories onto a unified Poincaré sphere via a synthetic phase-driven coordinate transformation, enabling direction-selective phase responses for arbitrary elliptical polarization states. To overcome the trade-offs between dispersion and polarization functionality, we introduce a neural network framework that co-optimizes Jones matrix responses across multiple polarizations, wavelengths, and directions. Experimentally, we demonstrate six completely independent holographic channels—defined by three polarization–wavelength combinations under opposite propagation directions—with high-fidelity image reconstructions and inter-channel crosstalk below 6.4%. In contrast to Janus-type or multilayer metasurfaces limited to interleaved or orthogonal polarization encoding, our approach offers a compact, lossless, and fabrication-compatible solution for multidimensional optical multiplexing.

Index modulation (IM) is considered a promising approach for fifth-generation wireless systems due to its spectral efficiency and reduced complexity compared to conventional modulation techniques. However, IM faces difficulties in environments with unpredictable channel conditions, particularly in accurately detecting index values and dynamically adjusting index assignments. Deep learning (DL) offers a potential solution by improving detection performance and resilience through the learning of intricate patterns in varying channel conditions. In this paper, we introduce a robust detection method based on a hybrid DL (HDL) model designed specifically for orthogonal frequency-division multiplexing with IM (OFDM-IM) in challenging channel environments. Our proposed HDL detector leverages a one-dimensional convolutional neural network (1D-CNN) for feature extraction, followed by a bidirectional long short-term memory (Bi-LSTM) network to capture temporal dependencies. Before feeding data into the network, the channel matrix and received signals are preprocessed using domain-specific knowledge. We evaluate the bit error rate (BER) performance of the proposed model using different optimizers and equalizers, then compare it with other models. Moreover, we evaluate the throughput and spectral efficiency across varying SNR levels. Simulation results demonstrate that the proposed hybrid detector surpasses traditional and other DL-based detectors in terms of performance, underscoring its effectiveness for OFDM-IM under uncertain channel conditions.

Background Myoelectric interfaces have emerged as powerful tools for human–machine interaction (HMI), enabling intuitive control of virtual and physical devices. However, most existing systems are limited by low spatial resolution and unidirectional communication. To address these limitations, we developed NeuraLoop, a wearable, high-bandwidth, bidirectional interface that integrates myoelectric (EMG) signal acquisition and electrotactile stimulation feedback within a single wearable textile-based platform. Methods NeuraLoop comprises a flexible matrix of 32 EMG recording and 32 electrotactile stimulation pads controlled by a compact electronic unit. We evaluated the system in two experimental tasks involving ten healthy subjects to demonstrate: (1) online classification of four transient thumb micro-gestures (thumb rightwards, leftwards, upwards, and downwards swipe directions), and (2) closed-loop control of a virtual cursor using micro-gesture commands and spatially encoded tactile feedback. A time-division multiplexing (TDM) strategy was implemented to enable simultaneous stimulation and recording. Results The subjects achieved a median success rate of 82% on the first attempt and over 94% within two attempts during online classification with visual feedback. All four micro-gestures were classified with similar accuracy. In the closed-loop control task with tactile feedback, participants navigated a 3 × 4 grid using only electrotactile stimulation, achieving 70% accuracy for exact target hits and 95% when including the hits in the neighboring cells (1 cell distance error). Conclusions NeuraLoop demonstrates the feasibility of high-bandwidth, bidirectional HMI using a wearable, textile-based interface. The system enables accurate recognition of subtle micro-gestures and effective delivery of spatially encoded tactile feedback. These capabilities open new possibilities for intuitive control in applications such as prosthetics, rehabilitation, and virtual/augmented reality. Future work will explore multimodal feedback encoding and proportional gesture control.

Orthogonal frequency division multiplexing based bidirectional relay network with several antennas at source nodes is the proposed system. To improve outage and bit error rate performance in presence of inphase/quadrature imbalance, concepts of maximal ratio combining and transmit antenna selection are applied at the source nodes in time slot I and time slot II respectively. Analysis of proposed bidirectional relay network with I/Q imbalance are modeled and briefly discussed. Through Monte-Carlo simulations, analytical results have been verified. Performance of proposed work is compared with the like literatures, and better performance is observed in the proposed work.

Terahertz (THz) holography demonstrates immense potential in biomedical detection, virtual reality, and information encryption security. Janus metasurfaces, which can independently control the amplitude and phase of THz waves from opposite directions, offer a promising platform for directional multiplexing in THz holography. However, most existing designs rely on conventional forward design methods, limiting the system to just two degrees of freedom (DOFs) and significantly restricting both channel count and holography imaging quality. In this study, we introduce a bidirectional deep neural network (Bi‐DNN) inverse design method, combined with thermally responsive phase‐change material vanadium dioxide (VO2), for the development of Janus metasurfaces. The proposed design enables independent control of incident direction, frequency, and temperature as three distinct DOFs. The meta‐atoms selected through the Bi‐DNN exhibit a transmittance exceeding 90%, effectively generating low‐crosstalk, eight‐channel THz holographic images with an imaging efficiency of 78%. Furthermore, by combining the metasurface with the inherent superposition properties of Chinese characters to achieve high‐intensity and high‐density holographic encryption in the THz band. This design offers a novel strategy and technical foundation for applications in high‐capacity data storage, holographic encryption, and secure wireless communication. The Janus metasurface that can simultaneously control three DOFs (propagation direction, frequency, and temperature) is designed by Bi‐DNN. The Janus metasurface realizes high‐quality eight‐channel holographic imaging and information encryption functions. Each channel imaging has the characteristics of low crosstalk, large depth of field, and wide frequency band.

This paper investigates the applicability of an intuitive wayfinding system in complex buildings using Visible Light Communication (VLC). Typical scenarios include finding places. Data from the sender is encoded, modulated and converted into light signals emitted by the transmitters. Tetra-chromatic white sources are used providing a different data channel for each chip. At the receiver, the modulated light signal, containing the ID and the 3D geographical position of the transmitter and wayfinding information, is received by SiC photodetector with light filtering and demultiplexing properties. Each luminaire for downlink transmission become a single cell, in which the optical access point (AP) is located in the ceiling and the mobile users are scattered within the overlap discs of each cells underneath. The light signals emitted by the LEDs are interpreted directly by the receivers of the users underneath. The effect of the location of the APs is evaluated and a model for the cellular networks is analyzed using orthogonal topologies. A 3D localization design, demonstrated by a prototype implementation, is presented. Uplink transmission is also implemented and the 3D best route to navigate calculated. The results showed that the system allows to determine the position of a mobile target inside the network, to infer the travel direction along the time and to interact with information received optimizing the route towards the destination.

This paper presents an innovative space laser ranging technology that utilizes time-frequency co-transfer, effectively meeting the critical demand for precision in space laser ranging applications. The aim is to achieve high-precision ranging by calculating the transfer time using a bidirectional comparison scheme for clock synchronization and an active compensation technique for frequency transfer. Experimental results indicate that, over a 500 m optical path, an impressive ranging accuracy of 0.0005 m is achieved, reflecting significant improvements in precision, stability, and resistance to interference. By integrating time synchronization, frequency transfer, and free-space laser ranging into a cohesive system, this technology demonstrates substantial potential for a wide range of applications.

The optical phase conjugation (OPC) process is thoughtfully investigated in a nonlinear bidirectional semiconductor optical amplifier subsystem (SOA), demonstrating the conjugation conversion through the two ports of the SOA, simultaneously. The spectral responses, the nonlinear power curves and the quality optimization of the conjugated are discussed through the simulation in nonlinear bidirectional configuration. The experimental investigation of the polarization-insensitive SOA further confirms the OPC behavior in the bidirectional operation, achieving the error-free conjugation conversion with an output optical signal-to-noise ratio (OSNR) of up to 16 dB. The nonlinear bidirectional SOA configuration tested in the system relaxes the requirement of the conventional four-wave mixing (FWM), enabling the OPC conversion with the signal regeneration in only one unit.

A bidirectional triplexer based on a Bragg grating assisted multimode interference (MMI) coupler has been designed and fabricated. The MMI coupler can multiplex/demultiplex the 1,310 nm wavelength (i.e. upload data) and the 1,490 nm wavelength (i.e. download data). Moreover, the grating written in the waveguide of the MMI can reflect the 1,550 nm wavelength (i.e. download video signals) to the other download port. Using a polarised UV ArF excimer laser irradiation, intrinsic waveguide birefringence can be compensated. Therefore, the fabricated device is polarasation insensitive. The working bandwidths of the final triplexer for 1,310, 1,490, and 1,550 nm are about 110 nm, 50 nm, and 15 nm, respectively.