This paper reviews on the latest advances in microwave photonics applied to radar systems, tracing the evolutions of functionalities in the photonic radar toward a new generation of enhanced-performance systems. Photonics is demonstrated to enable a new generation of miniaturized, heterogeneous and distributed radars, i.e. future radars on chip with different features, working in different radio spectral regions, and organized in spatially distributed sensors for the enhanced detection of a wider range of target properties. In these systems, the use of photonics assures benefits in terms of frequency flexibility, accuracy and computational load reduction. Innovative capabilities supported by the photonic approach are presented, such as the use of coherent sparse bands for the synthesis of ultra-wide bands, the use of distributed sensors for multiple-input multiple-output detections, and the use of an ultra-wide band photonics-based receiver for radio frequency (RF) spectrum scanning. The presented novel concepts will open the way to new research activities both in photonic technology and radar systems, contributing to the development of a new generation of remote sensing systems. This expanding cross-fertilization will lead to exciting and challenging research activities in the years to come.

Electronic warfare receivers must satisfy particularly demanding requirements, and current electronic solutions must find a trade-off between the request for high performance (in particular, very wide bandwidth, very high sensitivity, and very linear response) and the need for light and small systems. Photonics has been often proposed as a potential enabler of performance improvements, thanks to its wide tunability and precision, and recently the advancements of the photonic integration technologies are also promising strong reductions of size and weight. In this paper, we present an overview of the photonics-based solutions proposed so far in the field of electronic warfare. In particular, we focus on the specific implementation of a spectrum scanner we have recently proposed. Besides the performance in terms of bandwidth, linearity and sensitivity, which are on par with state-of-the-art electronic commercial systems, here we report on our last advancements in terms of tuning speed. Further improvements are also discussed, in terms of both tuning speed and integrability.

This paper extends a recent demonstration of a hierarchical spatial division network architecture testbed for petabit per second throughput. A spatial cross-connect is implemented to handle 1.08 Pb/s per line side. The spatial crossconnect is based on a low loss 44x44 MEMS switch, which enables switching up to 22 spatial channels, each carrying 202-channel, 24.5 GBaud polarization-multiplexed 64-ary quadrature amplitude modulated signals. Transmission is performed using a 22-core homogeneous multicore fiber. The demonstration includes spatial bypass and spatial add and drop scenarios as well as optical bypass and optical add and drop scenarios. The latter uses wavelength cross-connects implemented using conventional wavelength selective switches. A network scenario implementing 1+1 spatial multiplex section protection is also demonstrated using three 7-core joint spatial switches to protect 21 spatial channels. Finally, the use of hybrid spatial division multiplexing networks with multi-core and few-mode fibers is addressed, showing that skew between spatial channels may be the most significant obstacle to the implementation of such networks. This work concludes with an analysis of the inter-core skew introduced by the 22-core multicore fiber and its impact on a potential implementation of a hierarchical spatial division network.

We demonstrate $640\mathrm{G}\text{bits}/\mathrm{s}$ all-optical A AND $\overline{B}$, and $\overline{A}$ AND B logic functions using pump depletion in a periodically poled lithium niobate waveguide. Bit-error-rate measurements show the effectiveness of the scheme, with a penalty of $<2\mathrm{dB}$.

All-optical digital devices are key components for advanced signal processing in next generation optical networks and optical computing. In most digital systems, photonic integrated circuits are required to carry out high-speed energy efficient functionalities. In this paper, an entire set of integrable all-optical clocked flip-flops and an all-optical binary counter are proposed, as applications of SR latches and logic gates previously introduced in literature. The SR latch is based on gain quenching mechanism between two coupled ring lasers using a semiconductor optical amplifier (SOA) as active element. Photonic logic functions are carried out by exploiting four wave mixing (FWM) and cross gain modulation (XGM) nonlinear effects in SOAs. Different flip-flop logical functionalities, including SR-, D-, T-, and JK-types, as well as an all-optical binary counter, are obtained by adding one of the logic gates, or a combination of them, to the latch scheme. The effectiveness of the proposed schemes is demonstrated by extinction ratio and Q-factor measurements. All solutions are tunable in the whole C-band and can work at different counting rate without any reconfiguration. Photonic integration allows to increase the functioning rate beyond gigahertz and reduce the switching energy.

The Internet-of-Things paradigm is pushing the current fully-automated industry to Industry 4.0, laying on a high degree of end-to-end digitization of all physical assets and their integration into data-based services. A significant contribution to recent advances of digital technologies comes from microwave photonics, whose benefits for RF systems in terms of performance and flexibility have been largely demonstrated. In the radar domain, the high degree of coherence granted by photonics makes possible multiple input-multiple output systems, enabling an enhancement of surveillance and monitoring capabilities, thanks to the possibility of performing centralized processing and raw-data fusion. The advantages offered by photonics for surveillance converge with the Industry 4.0 revolution, helping in the actualization of the “Port of the Future” paradigm, to monitor the freight traffic inside ports, increasing goods distribution efficiency, at the same time reducing carbon footprint. Here, we present the first photonics-based widely distributed multiple input-multiple output dual-band radar network, designed to operate in a real port, showing the achieved enhanced potential detection and imaging capabilities. The integration of the targets radar tracks within the monitoring and control platform of the port is reported, enabling the fusion with other data managed by the multiservice monitoring platform.