Integrated sensing and communication (ISAC) is a key pillar for future wireless networks, demanding solutions that simultaneously deliver high-capacity communication and high-accuracy sensing. The terahertz (THz) band, particularly when integrated with fiber-optic networks, emerges as a highly promising candidate, offering the potential for terabit-per-second communication data rates and millimeter-level sensing resolution. Crucially, the integrated waveform is paramount to efficiently and seamlessly combine these dual functionalities, enabling compact frontends design and streamlined baseband processing for photonic THz-ISAC systems. This article presents our recent system-level investigations into diverse integrated ISAC waveform designs. We further synthesize and discuss the latest global research and development progress in advancing this rapidly evolving field.

Free-space optical (FSO) communication is rapidly advancing as a high-capacity wireless technology, with growing interest in extending its operation from the traditional near-infrared to the mid-infrared (mid-IR) spectral region. Particularly, the mid-wave infrared (MWIR) and long-wave infrared (LWIR) atmospheric transmission windows in the mid-IR region provide advantages regarding reduced turbulence effects, scattering and absorption, enabling more robust links under adverse conditions. This review presents recent progress in MWIR and LWIR FSO communication systems, highlighting advances in transmitter and receiver technologies, such as quantum cascade lasers (QCLs), lithium niobate modulators and detectors, including quantum cascade detectors (QCDs), mercury cadmium telluride (HgCdTe and MCT) photodiodes and quantum-well infrared photodetectors (QWIPs). Experimental demonstrations achieving multigigabit to tens-of-gigabit data rates with advanced modulation formats, digital equalisation and coherent detection are summarised. The paper discusses integration trends in MWIR and LWIR photonics, coherent communication strategies and hybrid FSO–radio frequency (RF) architectures. Together, these developments outline the pathway for MWIR and LWIR FSO systems to evolve from laboratory demonstrations towards scalable, practical platforms for next-generation terrestrial and space communication networks.

We report the first system-level MWIR FSO demonstration at 4.65 mu m, combining a directly modulated QCL with an uncooled uni-traveling carrier photodiode (UTC-PD), achieving 14 Gb/s transmission over a 31-m optical path length using a Herriott cell.

We experimentally demonstrate the LWIR FSO communication with advanced modulation formats. Up to 8.4 Gbit/s PAM8 and 5.5 Gbit/s DMT transmission is achieved with 9.15-μm directly-modulated quantum cascade laser and MCT detector at room temperature.

Free space optical (FSO) communication is considered a critical part of future ICT infrastructure, particularly in non-terrestrial communication segments. In this context, the ability to achieve fast and reliable FSO propagation through long-distance atmospheric channels is the most important factor in choosing technological solutions. One property of optics directly related to this factor is the choice of wavelength. It has been identified that the mid-infrared (mid-IR) regime, which includes two atmospheric transmission windows—the mid-wave IR (MWIR, 3-5 μm) and the long-wave IR (LWIR, 8-12 μm)—can potentially offer a promising solution for achieving such performance. Additionally, viable semiconductor sources and detectors that support high-speed and efficient signal transmission are also considered critical to generating sufficient critical mass to advance the application of mid-IR FSO. Unipolar quantum optoelectronics, including quantum cascade lasers (QCL), Stark modulators, quantum cascade detectors (QCD), and quantum-well IR photodetectors (QWIP), among other components, emerge as potential candidates to build such FSO subsystems and systems. We present our recent efforts in conducting subsystem and system-level studies with different variants of these unipolar quantum optoelectronics and demonstrate the potential for feasible transmitter and receiver performance in a laboratory environment. We also discuss the key challenges and considerations of such technologies towards practical development. Finally, we summarize recent research and development efforts worldwide in advancing this highly promising direction.

The development of electrocatalysts with low cost, high efficiency, and long-term durability is crucial for advancing green hydrogen production. Transition metal phosphides (TMPs) have been proved to be efficient electrocatalyst, while the improvement in the performance and durability of the TMPs remains a big challenge. Employing atmospheric pressure chemical vapor deposition (APCVD) and phosphorization, FeP/Ti electrodes are fabricated featuring controllable oxygen ingredients (O-FeP/Ti). This manipulation of oxygen content fine-tunes the electronic structure of the catalyst, resulting in improved surface reaction kinetics and catalytic activity. The optimized O-FeP-400/Ti exhibits outstanding HER activity with overpotentials of 142 and 159 mV at −10 mA cm−2 in 0.5 M H2SO4 and 1 M KOH, respectively. Notably, the obtained O-FeP/Ti cathode also displays remarkable durability of up to 200 h in acidic electrolyte with surface topography remaining intact. For the first time, the low-valence titanium oxide (Ti3O) interlayer is identified in the composite electrode and ascribed for the superior connection between Ti substrate and the surface O-FeP catalyst, as supported by experimental results and density functional theory (DFT) analysis. This work has expanded the potential applications of transition metal phosphides (TMPs) as a cost-effective, highly efficient and durable catalyst for water splitting.

Single-crystal growth of (100) beta-Ga2O3 and the attempt to grow GaP on it by hydride vapor phase epitaxy (HVPE) is been described. The phase purity and (100) orientation of the crystal is confirmed by X-ray diffraction (XRD). The selected area electron diffraction pattern confirms the monoclinic structure with a C2/m space group of beta-Ga2O3. Raman results reveal the stretching and bending vibrations of Ga-O and Ga-O-Ga octahedrons, respectively. The wafer exhibits approximate to 80% optical transmission and surface roughness of approximate to 5 nm. GaP layers are grown on (100)-oriented beta-Ga2O3 substrates by HVPE. The GaP/beta-Ga2O3 heterostructures are characterized using XRD and Raman spectroscopy. Diffraction peak at (111) confirms the zinc blende phase of GaP. The longitudinal optical (405 cm-1) and transverse optical (368 cm-1) phonon modes in the Raman spectra confirm the crystalline GaP. Further optimization is expected to enhance the crystalline quality of the GaP layer on the Ga2O3 wafer. The potential of GaP/(100) beta-Ga2O3 heterostructures are highlighted.

We experimentally demonstrate a room-temperature LWIR FSO link with a 9.1-μm directly modulated QCL and an MCT detector. Net bitrate of up to 16.9 Gb/s is achieved at both 15°C and 20°C over a 1-meter distance.

We experimentally demonstrate a room-temperature LWIR FSO link with a 9.1-μm directly modulated QCL and an MCT detector. Net bitrate of up to 16.9 Gb/s is achieved at both 15°C and 20°C over a 1-meter distance.

This study investigates the potential of long-wave infrared (LWIR) free-space optical (FSO) transmission using multilevel signals to achieve high spectral efficiency. The FSO transmission system includes a directly modulated-quantum cascade laser (DM-QCL) operating at 9.1 µm and a mercury cadmium telluride (MCT) detector. The laser operated at the temperature settings of 15°C and 20°C. The experiment was conducted over a distance of 1 m and in a lab as a controlled environment. We conduct small-signal characterization of the system, including the DM-QCL chip and MCT detector, evaluating the end-to-end response of both components and all associated electrical elements. For large-signal characterization, we employ a range of modulation formats, including non-return-to-zero on-off keying (NRZ-OOK), 4-level pulse amplitude modulation (PAM4), and 6-level PAM (PAM6), with the objective of optimizing both the bit rate and spectral efficiency of the FSO transmission by applying pre- and post-processing equalization. At 15°C, the studied LWIR FSO system achieves net bitrates of 15 Gbps with an NRZ-OOK signal and 16.9 Gbps with PAM4, both below the 6.25% overhead hard decision-forward error correction (6.25%-OH HD-FEC) limit, and 10 Gbps NRZ-OOK below the 2.7% overhead Reed-Solomon RS(528,514) pre-FEC (KR-FEC limit). At 20°C, we obtained net bitrates of 14.1 Gbps with NRZ-OOK, 16.9 Gbps with PAM4, and 16.4 Gbps with PAM6. Furthermore, we evaluate the BER performance as a function of the decision feedback equalization (DFE) tap number to explore the role of equalization in enhancing signal fidelity and reducing errors in FSO transmission. Our findings accentuate the competitive potential of DM-QCL and MCT detector-based FSO transceivers with digital equalization for the next generation of FSO communication systems.