Quantum state transferring has been demonstrated using drones via entanglement distribution. Here, we demonstrate the first drone-based quantum task for quantum key distribution (QKD). Compact and polarization-maintaining acquisition, pointing, and tracking systems and QKD modules are developed and loaded on a homemade octocopter with a takeoff weight of 30 kg. Real-time QKD is performed over a 200 m distance with an 8.48 kHz average secret key rate using a polarization-coded decoy-state BB84 protocol. With the capability of secret key distribution using a drone, wireless communication can be expected with enhanced security in the quantum approach between mobile nodes toward a network.

Periodically poled lithium niobate on insulator (PPLNOI) offers an admirably promising platform for the advancement of nonlinear photonic integrated circuits (PICs). In this context, domain inversion engineering emerges as a key process to achieve efficient nonlinear conversion. However, periodic poling processing of thin-film lithium niobate has only been realized on the chip level, which significantly limits its applications in large-scale nonlinear photonic systems that necessitate the integration of multiple nonlinear components on a single chip with uniform performances. Here, we demonstrate a wafer-scale periodic poling technique on a 4-inch LNOI wafer with high fidelity. The reversal lengths span from 0.5 to 10.17 mm, encompassing an area of ~1 cm² with periods ranging from 4.38 to 5.51 μm. Efficient poling was achieved with a single manipulation, benefiting from the targeted grouped electrode pads and adaptable comb line widths in our experiment. As a result, domain inversion is ultimately implemented across the entire wafer with a 100% success rate and 98% high-quality rate on average, showcasing high throughput and stability, which is fundamentally scalable and highly cost-effective in contrast to traditional size-restricted chiplet-level poling. Our study holds significant promise to dramatically promote ultra-high performance to a broad spectrum of applications, including optical communications, photonic neural networks, and quantum photonics.

Quantum information has the potential to bring revolutionary performance for computation, communication, and metrology applications in terms of speed,^1,2 security,^{3 – 8} and accuracy.^9,10 Similar to the case of classical information, where the system capability relies on the large number of classical bits, the number of qubits is the key resource that defines the overall performance of a quantum system. Benefiting from the superposition of an $N$-qubit state, quantum source further boosts the information exponentially over an $N$-bit classical source.¹¹ In fact, a 300-qubit quantum state has more variations than all the atoms in the known universe classically.^12,13 However, generation of large-size quantum states is a fundamental challenge, whether for electrical or optical systems. Although the strong interacting particles, such as superconductivity electrons and ions, make it easier to generate large-size quantum states and keep the current record of the qubit number;^{14 – 16} their strong interaction also leads to the decoherence problem and can only work in an ultralow temperature and vacuum environment. These electrical quantum sources still suffer from a short-state lifetime even under these conditions.

Free-space optical communication (FSO) can achieve fast, secure, and license-free communication without physical cables, providing a cost-effective, energy-efficient, and flexible solution when fiber connection is unavailable. To achieve FSO on demand, portable FSO devices are essential for flexible and fast deployment, where the key is achieving compact structure and plug-and-play operation. Here, we develop a miniaturized FSO system and realize 9.16 Gbps FSO in a 1 km link, using commercial single-mode-fiber-coupled optical transceiver modules without optical amplification. Fully automatic four-stage acquisition, pointing, and tracking systems are developed, which control the tracking error within 3 μrad, resulting in an average link loss of 13.7 dB. It is the key for removing optical amplification; hence FSO is achieved with direct use of commercial transceiver modules in a bidirectional way. Each FSO device is within an overall size of 45 cm × 40 cm × 35 cm, and 9.5 kg weight, with power consumption of ∼10 W. The optical link up to 4 km is tested with average loss of 18 dB, limited by the foggy test environment. With better weather conditions and optical amplification, longer FSO can be expected. Such a portable and automatic FSO system will produce massive applications of field-deployable high-speed wireless communication in the future.

Lithium-niobate-on-insulator (LNOI) chips have shown outstanding performance in various photonic devices including modulators, lasers, nonlinear converters, and quantum sources. LNOI-based edge couplers are quite important for further promotion of the above devices in practical applications, especially for large-scale multiport photonic uses, where efficient and mode-selective coupling between chips and fibers is of necessity. Previously, several LNOI edge couplers have been demonstrated, but they mainly focus on achieving high coupling efficiency of the fundamental mode, and sub-wavelength etched lithium-niobate (LN) structures are normally needed, which increases fabrication complexity. Here we propose a new type of edge coupler with direct mode-selective excitation ability, using only SiON cladding grating structures without additional etching of LN. By introducing a cladding waveguide with periodic structures on the uniform LNOI waveguide, high-efficiency excitation of multiple modes can be realized directly with easier fabrication. For a specific simulation here, TE₀₀, TM₀₀, and TE₁₀ core modes can be excited, respectively, at optimized periods and grating lengths with a tunable central wavelength, at the launch of the TM cladding mode. The periods of the needed SiON gratings are all over 2 µm, which is feasible with i-line UV lithography. Our results provide a low-cost edge coupler for LNOI photonic circuits with the ability of flexible spatial mode selectivity, which may promote LNOI devices in large-scale multiport photonic integrated circuits in the future.

The self-injection-locked diode laser can significantly reduce the linewidth down to a sub-100 kHz level but requires optical filtering that is much narrower than the laser cavity linewidth. Such optical filtering is usually sophisticated and beyond the capability of the normal dielectric coating approach. Here we develop a 0.16 nm narrowband dielectric coating using a Fabry–Perot dielectric filter (HFFPF) for the narrow linewidth self-injection-locked laser demonstration using a cost-effective Fabry–Perot laser diode. Single-longitude-mode output is achieved, with beat linewidth down to ~66 kHz and a high side mode suppression ratio over 60 dB. This setup of self-injection-locked laser is cost-effective for mass production and thus is suitable for various applications such as laser ranging, LIDAR, optical communication, and holographic.