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Free-space optical (FSO) communication can reduce the routing complexity of data center networks (DCNs), not only ensuring high-capacity optical switching, but also owning similar flexibility to the wireless connectivity. Presently, mainstream wireless-optical switching units (WOSUs) have adopted serial beam control for unicasting. As a two-dimensional planar structure composed of meta-atoms with special electromagnetic properties arranged in a certain way, a passive metasurface (PMF) has strong parallel beam regulating capability. In this paper, we propose a wireless-optical intra-DC interconnection scheme based on PMFs. Through a real PMF chip, by adjusting the polarization of an incident beam, the power distribution between normal and abnormal reflected beams can be controlled. When both reflected beams are assigned with power, we obtain a pair of beams reflected in parallel, thus simultaneously communicating with two racks. In fact, we can perform 1-to-$N$ ($N \ge 2$) multicast by using cascaded PMFs, and 1-to-$N$ means that each source rack can communicate with $N$ destination racks, i.e., a wide communication coverage range. However, the cascaded PMFs may result in huge chip costs and high accumulated power loss. In this paper, we only demonstrate the 1-to-2 communication ability of our PMFs, so the communication coverage may be still limited. Hence, by introducing electrostatic drive to control the PMF rotation, each source rack can achieve a wider communication coverage range than before. As a result, all racks within the coverage range have the ability to establish communication links with the source rack. To this end, we also design a neural network to mimic the PMF rotation, further improving the communication capability between racks. We then propose a DCN-topology reconfiguration algorithm supporting the coexistence of unicasting and multicasting, in order to make real-time decisions on the matching between FSO ports with minimized latency. Finally, we established a proof-of-concept prototype system to demonstrate the parallel beam control of our PMF. The test results show that the angle error is less than 0.1°, satisfying the accuracy requirements of WOSUs, and our PMF always has a good polarization response with the insertion loss of less than 2 dB under various azimuth angles or rotation planes.

High-capacity wireless-optical switches (WOSUs) have broken through the bottleneck of electrical rate, thus enabling low-latency and high-throughput on-board optical switching (OOS). OOS can effectively relieve the service pressure of ground networks, and it also compensates for the sparse deployment of optical fibers in complex terrains. Compared to widely-used silicon-substrate WOSUs, the passively-programmable metasurface (PMF), fabricated by us, has a golden substrate owning better radiation resistance. Without external electrical excitation for beam steering, our passive manner prolongs the service life of satellites. Moreover, by changing the incident beam polarization without consuming additional power, the data can be transferred between normal and abnormal reflected beams, thus the link backup is naturally performed. Based on multiple PMF chips, we design a novel on-board optical switching matrix (POSM), where the neural network controls chip rotation and movement with high precision. To improve OOS reliability, our enhanced optical switching control module (EOSC) solves POSM reconfiguration, once the matrix port or chip fails due to strong atmospheric drag. Finally, we establish a prototype system with the error-free transmission of ultra-high definition (UHD) video streams for the proof-of-concept, especially for verifying the natural link-backup capability of our PMF. The experimental results show <3 dB insertion loss of normal and abnormal reflected beams in the range of incident angle from 0$^{\circ }$ to 35$^{\circ }$, and other meaningful results demonstrate the potential application of our PMF-cascaded POSM in highly-reliable OOS.

Optical networks-on-chip (ONoCs) have emerged as a compelling platform for many-core systems owing to their notable attributes, including high bandwidth, low latency, and energy efficiency. Nonetheless, the integration of microring resonators (MRs) in ONoCs exposes them to vulnerabilities associated with hardware trojans (HTs). In response, we propose an innovative strategy that combines deep-learning-based HT attack prediction with a robust security defense mechanism to fortify the resilience of ONoCs. For HT attack prediction, we employ a multiple-inputs and multiple-outputs long short-term memory neural network model. This model serves to identify susceptible MRs by forecasting alterations in traffic patterns and detecting internal faults within optical routing nodes. On the defensive front, we introduce a fine-grained defense mechanism based on MR faults. This mechanism effectively thwarts HTs during the optical routing process, thereby optimizing node utilization in ONoCs while concurrently upholding security and reliability. Simulation outcomes underscore the efficacy of the proposed HT attack prediction mechanism, demonstrating high accuracy with a loss rate of less than 0.7%. The measured mean absolute error and root mean squared error stand at 0.045 and 0.07, respectively. Furthermore, when compared to conventional coarse-grained node-based defense algorithms, our solution achieves noteworthy reductions of up to 16.2%, 43.72%, and 44.86% in packet loss rate, insertion loss, and crosstalk noise, respectively.

Reconfigurable metasurfaces (R-MTSs) exhibit significant potential for wireless optical switching due to their compact size and rapid beam switching capabilities. However, conventional R-MTSs based on micro-electro-mechanical systems, electrochemical, or chemical reactions often suffer from high losses and bulky dimensions. In this study, we propose a novel R-MTS design utilizing the low-loss phase-change material Sb2Se3. By modulating the crystalline and amorphous states of Sb2Se3, the metasurface achieves reconfigurability. Notably, under circularly polarized light (C-band), it generates two symmetrically high-efficiency anomalous transmission beams corresponding to the two phase states of Sb2Se3. Simulation results indicate that our design covers an angular range of approximately 34.2° through the Sb2Se3 state transition, maintaining a transmission rate >85.3% and polarization conversion efficiency >96.2%.

As a nanometer-level interconnection, the Optical Network-on-Chip (ONoC) was proposed since it was typically characterized by low latency, high bandwidth and power efficiency. Compared with a 2-Dimensional (2D) design, the 3D integration has the higher packing density and the shorter wire length. Therefore, the 3D ONoC will have the great potential in the future. In this paper, we first discuss the existing ONoC researches, and then design mesh and torus ONoCs from the perspectives of topology, router, and routing module, with the help of 3D integration. A simulation platform is established by using OPNET to compare the performance of 2D and 3D ONoCs in terms of average delay and packet loss rate. The performance comparison between 3D mesh and 3D torus ONoCs is also conducted. The simulation results demonstrate that 3D integration has the advantage of reducing average delay and packet loss rate, and 3D torus ONoC has the better performance compared with 3D mesh solution. Finally, we summarize some future challenges with possible solutions, including microcosmic routing inside optical routers and highly-efficient traffic grooming.