An electromagnetic immune Free Space Optical Communication (FSOC) system for an Unmanned Aerial Vehicle (UAV) command and control link is introduced in this paper. The system uses the scheme of omnidirectional receiving and ground scanning transmitting. It has a strong anti-turbulence ability by using a large area detector and short-focus lens. The design of omnidirectional communication improves the ability of anti-vibration and link establishment. Pure static reception has no momentum effect on the platform. The receiver is miniaturized under no use of a gimbal mirror system, beacon camera system, Four-Quadrant Photodetector (QPD) and multi-level lens system. The system can realize omnidirectional reception and the communication probability in 1 s is greater than 99.99%. This design strengthens the ability of the FSOC system, so it can be applied in the UAV command and control, the satellite submarine communication and other occasions where the size of the platform is restricted.

A novel approach to simultaneous radiofrequency self-interference cancellation (SIC) and frequency down-conversion in a unified system is proposed and demonstrated experimentally based on cascade Mach—Zehnder modulators (MZM). The local oscillator signal is injected into the MZM1, whereas the received RF signal and the reference signal are fed into MZM2 and MZM3. After photoelectrical conversion by a balanced photodetector, the desired intermediate frequency signal with SIC is obtained. The cancellation depth for the single frequency SIC with frequency down-conversion is around 38 dB, and that for a wideband signal is around 19 dB. No electrical delay and attenuation are used in the proposed system, so it can potentially reach a wider frequency band and a higher cancellation depth.

We propose a new free-space optical (FSO) communication system for moving platform tracking, which can achieve high precision aiming and tracking. Our prototype system consists of three parts. As a coarse sighting structure, the electro-optical pod module is used for target searching and coarse sighting in the initial stage. As a precise aiming structure, the precise targeting loads module located inside the electro-optical pod module uses miniaturized tubular folding optical path technology for high-precision alignment and tracking. The bottom module of the system is used for communication. In the tracking process, the control unit uses spot offset collected by CCD to perform decoupling calculation and then compensates the offset by swinging tracking and aiming structure. We did track experiments on a mobile platform. The experiment successfully tracked a moving target at 100 m distance, and the tracking error was less than 1 mrad. The proposed system can provide stable communication links between the mobile platforms.

Ultraviolet (UV) communication is considered an effective complement to traditional wireless communication. However, the scattering models of existing non-line-of-sight (NLOS) UV, which are complex, are difficult to combine with the test. In this paper, the single scattering isosceles model with a small elevation angle is proposed first. Then, the relationships between the path loss of single scattering isosceles and elevation angle, emission beam angle, receiving field angle, and transmission distance are studied. Finally, we consider outdoor NLOS UV solar-blind communications test at ranges of up to 100 m and 400 m, with different transmit and receive elevation angles. The results show that the isosceles model is in good agreement with the experiments. In addition, the UV isosceles model exhibits good properties compared with the existing scattering model. The proposed UV isosceles model can be employed as a reference for practical applications in outdoor tests.

In this paper, an efficient photonics time-delayed mixer (PTDM) is proposed and demonstrated. It mainly consists of a dual-parallel Mach-Zehnder modulator (DPMZM) and a dispersion medium (DM). To eliminate the carrier component, the carrier-suppressed dual-sideband (CS-DSB) modulation is implemented without optical filters. Besides, the CS-DSB modulation is also the key to make the phase response is proportional to the converted frequency. Thanks to the controllable DC bias of the modulator, the power response of this PTDM is also tunable. Thus, this property also endows the PTDM able to resist the dispersion-induced power fading (DIPF) when considering the use of large dispersion medium. Experimental results verify the ability of wideband frequency up- and down-conversion. Moreover, a converted signal with linear phase-frequency response is also achieved, which implies the time delay capability. Time delay tuning is realized by altering the wavelength of the carrier with a stable power response. This structure is very compact and thus compresses the signal processing system volume, which is qualified to be integrated into a receiver/transmitter.

This paper presents a miniaturized equipment used in tracking and pointing, and provides a method for free space optical communication among small platform. This scheme uses simple scan mirror and receiver with single photo detector to achieve tracking function. Signal beacon is controlled to rotate around target receiver. Transmitter constantly adjusts emitting direction to track receiver according to received signal intensity, which is send back by reverse laser link. The prototype system is successfully established and its transmitting part consisted by directly modulated laser diode, mechanical collimation lens, and scan mirror is also proved. The receiving end is mainly composed of large area photo detector and short-focal lens. Field-programmable gate array chips set in both ends are used to implement tracking algorithm. This system can track target at speed of 40 mm/s within 2 m distance in an angle range of ±30°. For further application, the system has great potential for miniaturization because of elimination of motors, beacons and cameras in its scheme.