The stable long-distance transmission of radio-frequency (RF) signals holds significant importance from various aspects, including the comparison of optical frequency standards, remote monitoring and control, scientific research and experiments, and RF spectrum management. We demonstrate a scheme where an ultrastable frequency signal was transmitted over a 50 km coiled fiber. The optical RF signal is generated using a two-section distributed feedback (DFB) laser for direct modulation based on the reconstruction equivalent chirp (REC) technique. The 3-dB modulation bandwidth of the two-section DFB laser is 18 GHz and the residual phase noise of -122.87dBc/Hz is achieved at 10-Hz offset frequency. We report a short-term stability of 1.62×10-14 at an average time of 1 s and a long-term stability of 6.55×10-18 at the measurement time of 62,000 s when applying current to the front section of the DFB laser. By applying power to both sections, the stability of the system improves to 4.42×10-18 within a testing period of 56,737 s. Despite applying temperature variations to the transmission link, long-term stability of 8.63×10-18 at 23.9 h can still be achieved.

Homoepitaxial growth of Si-doped β-Ga₂O₃ films on semi-insulating (100) β-Ga₂O₃ substrates by metalorganic chemical vapor deposition (MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in (100) β-Ga₂O₃ films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga₂O₃ film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the (400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 10¹⁵ – 1.74 × 10²⁰ cm⁻³. Hall measurements demonstrate a high electron mobility value of 51 cm²/(V·s), corresponding to a carrier concentration of 7.19 × 10¹⁸ cm⁻³ and a high activation efficiency of up to 61.5%. Transmission line model (TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10^-4 Ω·cm² for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 10¹⁹ cm⁻³, confirming the effective Si doing in the MOCVD epitaxy.

Power electronic devices are of great importance in modern society. After decades of development, Si power devices have approached their material limits with only incremental improvements and large conversion losses. As the demand for electronic components with high efficiency dramatically increasing, new materials are needed for power device fabrication. Beta-phase gallium oxide, an ultra-wide bandgap semiconductor, has been considered as a promising candidate, and various β-Ga₂O₃ power devices with high breakdown voltages have been demonstrated. However, the realization of enhancement-mode (E-mode) β-Ga₂O₃ field-effect transistors (FETs) is still challenging, which is a critical problem for a myriad of power electronic applications. Recently, researchers have made some progress on E-mode β-Ga₂O₃ FETs via various methods, and several novel structures have been fabricated. This article gives a review of the material growth, devices and properties of these E-mode β-Ga₂O₃ FETs. The key challenges and future directions in E-mode β-Ga₂O₃ FETs are also discussed.

主要介绍了近年来光纤激光相控阵相干合成技术的发展现状，总结了中国科学院光电技术研究所在这方面的最新研究成果，包括基于振幅调制的光纤激光相控阵相干合成能力优化、光纤激光相控阵实现收发一体相干合成、光纤激光相控阵的目标在回路相干合成、光纤激光相控阵在大气湍流下实现耦合接收光束的共相合束、基于多孔径波前探测的相干合成方法、基于自适应光纤准直器和微透镜阵列的光束大角度高精度连续寻址扫描等。以上研究工作将促进光纤激光相控阵技术朝向更多单元、更高功率、更远距离等方向演进，并推动其与激光大气传输、空间激光通信、自适应光学等理论和应用的结合与发展。