Harald Haas

Organic semiconductors offer a compelling platform for high-volume optoelectronic technologies with mechanical flexibility, tuneable properties, and potential for low-cost, sustainable production. Organic photodiodes are promising receivers for visible light communication systems due to their tuneable optical and electronic properties and inexpensive integration. However, their use in high-speed data transmission has been limited by material constraints, including low charge-carrier mobility and parasitic capacitance in thin-film structures. Here we show high-speed organic photodiodes using targeted device engineering that addresses these bandwidth-limiting factors. The devices achieve a record visible light communication data rate of 3.6 gigabits per second over a one-meter link using a single organic photodiode, more than twenty times faster than the previous best visible light communication data rate with organic receivers. These findings establish a new performance level for organic receivers and open a pathway towards their integration in high-speed, flexible, and sustainable applications for the Internet of Things and optical wireless sensors.

Orbital angular momentum (OAM) enables multiplexed optical wireless communication (OWC) with high spectral efficiency but suffers from severe degradation under misalignment-induced power loss and intermodal crosstalk. To the best of our knowledge, this is the first work that embeds experimentally validated, first-principles misalignment-dependent modal coupling with finite-aperture effects directly into a differentiable end-to-end autoencoder framework for BER-driven optimization under IM/DD constraints. Simulation results show that the proposed AE_min-max model outperforms singular value decomposition and turbo-coded systems, achieving signal-to-noise ratio gains of 12.5 dB and 8.5 dB, respectively.

Integrated satellite–terrestrial networks (ISTNs) are envisioned as a key component of 6G to support global connectivity for massive Internet of Things (IoT) devices. However, while terminals operate under strict energy and computational constraints and face additional challenges from satellite dynamics, current designs rarely integrate orbital information with device energy states in a unified system design, leaving significant room for improvement. Motivated by this, we propose a joint trajectory- and energy-aware framework for ISTNs operating in dynamic environments, supported by a low-complexity algorithm tailored for energy-constrained IoT devices. Specifically, we first develop a system model centered on a day–night separated hybrid energy-harvesting (DNEH) mechanism, where each device harvests light energy during the daytime and radio frequency (RF) energy from the gateway (GW) at night. Meanwhile, the GW broadcasts simplified orbital information to assist device operations, thereby forming an integrated communication–energy transfer framework that enhances system sustainability. Analytical characterizations are subsequently derived for the joint coverage probability, and simulations capture orbital dynamics such as the real-time distance variations. Building on the semi-analytical model, the proposed drift-regularized per-frame (DRPF) algorithm determines transmission opportunities that optimize the average Age of Information (AoI) by capturing the coupling between trajectory dynamics and energy availability. Numerical evaluations confirm the theoretical advantages of the proposed framework, showing substantial performance gains over the Immediate and Minimum Distance transmission baselines. Moreover, the optimized TD-SWIPT configuration and transmission scheduling translate these findings into actionable design guidelines for energy-constrained ISTNs.

The increasing proliferation of internet-connected devices, together with the widespread reliance on wireless communication in daily activities, are limiting the capabilities of the radio frequency (RF) spectrum to meet data traffic demands. In particular, the rise in connectivity requirements to realize next generation networks, coupled with the growth in utilization of artificial intelligence (AI) and its associated transmission of massive amounts of data, contribute to the need to leverage the optical spectrum to complement the already-congested RF bands. Optical wireless connectivity encompasses a range of solutions that can support data transfer in various use cases, ranging from intra-chip interconnects to deep-space communication. They benefit from advantages in terms of operation within a broad unlicensed spectrum, minimization of RF interference, and inherent security. On the other hand, optical wireless communication (OWC) systems might experience a decline in performance as a result of factors like atmospheric conditions and link blockage. This requires customizing system designs according to the considered use cases and investigating new solutions for realizing optical wireless connectivity. In this article, we present an overview of OWC, encompassing both its conceptual frameworks and the scientific and technological advancements that hold the potential for shaping its future in next generation networks.

Orthogonal Time Frequency Space (OTFS) modulation has garnered significant attention for its robustness in high-mobility communication scenarios. Existing research predominantly focuses on narrowband time-varying channels, where Doppler effects manifest as uniform frequency shifts across the signal bandwidth. However, OTFS performance degrades in wideband time-varying channels, where the Doppler frequency shift varies substantially across individual frequency bins. To accurately model the wideband time-varying channel, this work proposes a wideband Doppler model, namely Doppler model based on Frequency Domain Subband Partition (FDSP), thereby both the overall frequency shift and spectral spread effect are spontaneously covered. We introduce two novel Doppler spread classifications, i.e., Deterministic Doppler Spread (DDS) and Joint Deterministic-Random Doppler Spread (DRDS), extending beyond traditional Random Doppler Spread (RDS) effects. The closed-form Signal-to-Interference-plus-Noise Ratio (SINR) and Bit Error Rate (BER) for OTFS under these effects are further derived and validated through simulations. Simulations highlight significant differences in the OTFS spectrum between RDS and DRDS effects. While OTFS demonstrates resilience to RDS and DDS effects, performance under DRDS degrades significantly due to wideband time-varying channel characteristics. This underscores the critical need for advanced equalization techniques in wideband OTFS framework.

The rapid growth of the industrial Internet of Things (IIoT) has enabled applications such as smart manufacturing and intelligent inspection, yet large-scale IIoT nodes commonly suffer from energy scarcity. Optical integrated communication, sensing, and power transfer (O-ICSPT) aims to sustainably provide low-power IIoT devices with enhanced data rates and centimeter-level sensing accuracy, and is regarded as a key paradigm for addressing this issue. As waveform design plays a vital role in O-ICSPT systems, this paper proposes a flexible hybrid maximum length sequence (MLS)-orthogonal frequency-division multiplexing (OFDM) waveform design scheme with joint intra-alternating current (AC) and AC–direct current (DC) amplitude allocation, enabling tunable trade-offs among the communication, sensing, and energy harvesting performance. The AC signal is constructed by time-domain concatenation of MLS and OFDM sequences. The intra-AC amplitude allocation controls the power distribution between the MLS and OFDM sequences, where adjusting their ratio strikes a balance for the trade-off between communication and sensing performance. The AC–DC amplitude allocation determines the ratio between the AC signal and the DC component, thus balancing communication–sensing performance and energy harvesting capability. The two amplitude allocation ratios jointly determine the transmitted waveform and the overall system performance under practical non-ideal conditions imposed by cutoff and saturation clipping. Experimental results validate the effectiveness of the proposed waveform design and demonstrate its outstanding potential for deployment in IIoT scenarios.