We propose a novel architecture for implementing a dual-frequency lidar (DFL) exploiting differential Doppler shift measurement. The two frequency tones, needed for target velocity measurements, are selected from the spectrum of a mode-locked laser operating in the C-band. The tones’ separation is easily controlled by using a programmable wavelength selective switch, thus allowing for a dynamic trade-off among robustness to atmospheric turbulence and sensitivity. Speed measurements for different tone separations equal to 10, 40, 80, and 160 GHz are demonstrated, proving the system’s capability of working in different configurations. Thanks to the acquisition system based on an analog-to-digital converter and digital-signal processing, real-time velocity measurements are demonstrated. The MLL-based proposed architecture enables the integration of the DFL with a photonic-based radar that exploits the same laser for generating and receiving radio-frequency signal with high performance, thus allowing for simultaneous or complementary target observations by exploiting the advantages of both radar and lidar.

This work reports the first realization of a combined radar&lidar system based on silicon-on-insulator photonic integrated circuit (PIC). The software-defined architecture comprises a frequency-flexible and simultaneous multi-band radar operation and an advanced lidar with coherent detection for range and velocity measurements. Both systems are implemented within a single chip, allowing a coherent radar and lidar parallel data acquisition in order to take advantage of their complementary characteristics. This feature potentializes the study of complex environments providing a more complete cognition of the target or scene under observation. Here, we present the first sets of results of the radar and lidar subsystems characterization without any auxiliary frontend that confirms the large frequency flexibility of the radar system and the great potentiality for high resolution range and velocity measurements of the lidar system. These results open the way to an innovative generation of transceivers in the field of microwave photonics, potentially outperforming current systems thanks to its multiband and multifunction capability owing to a unique hybrid radar&lidar coherent architecture. Moreover, by operating in the photonic domain, radar and lidar subsystems are able to share the same optical source and digital electronics unit, allowing for an ultimate reduction of size, weight, and power consumption, thus making the proposed architecture suitable for the most stringent applications.

All-optical digital circuits based on loop memories are demonstrated. These circuits are a variable optical buffer, an optical random access memory, an optical shift register, and an optical linear feedback shift register. Buffers are employed in network nodes to solve the contentions without loosing information. Shift registers are used for error detection and correction techniques. Linear feedback shift registers are employed for generation of pseudo-random bit sequences, data scrambling, and encryption/decryption of information in secure communication systems. Since the role of optical processing is gradually increasing within the communication systems, the possibility to store information directly in the optical domain can lead to a systems simplification and to a performance improvement. In order to make the schemes suitable for practical applications, optical integration is necessary. The use of semiconductor optical amplifier as gain element into the memory loop allows all the proposed schemes to be integrated.

A two-layer switch exploiting orbital angular momentum (OAM) and wavelength of the light as switching domains is presented, aiming to increase the scalability with respect to the single-layer switches. The switch is able to accept 160 optical Gaussian data inputs on a 16-channel wavelength division multiplexing (WDM) grid and direct each input signals to different output ports exploiting 10 OAMs. The optical switch is based on an integrated OAM multiplexer followed by a compact OAM demultiplexer consisting of two refractive elements. Its experimental characterization confirmed a total enabled throughput of 19.2 Tb/s, thanks to the 30 GHz bandwidth available for each port. The switching time can be lower than 1 s. The OAM switch power consumption, solely due to the thermal tuning of the OAM emitters, since the OAM demux is passive, is 1.35 mW/Gb/s. In the proposed switching architecture the number of active components, i.e. the power consumption, scales linear with the number of ports. This is favorable in comparison with single-layer switches that cascade e.g. 2x2 elementary blocks to obtain large port counts, which scale with the square of the number of ports. The switch accepts input and output signals with Gaussian phase profile that propagate through optical fibers and waveguides, thus making it compatible with standard telecom devices. The suitability of the switch to support real data-traffic is proved by successfully testing it with 10G Ethernet and Fiber Channel over Ethernet (FCoE) data traffic and video traffic. A possible application scenario is represented by a data-center network where the switch can be used to create a low-power consumption network parallel to the network based on standard electronic routers, to manage large traffic flows.

A four-orbital angular momentum (OAM) modes converter consisting of the cascade of an OAM demultiplexer and an OAM multiplexer is implemented and characterized. The OAM multiplexer is realized with an integrated photonic circuit based on four tunable OAM emitters, i.e. the order of the emitted OAM mode can be selected by thermal tuning. It works on linearly polarized signals. The OAM demultiplexer, completely passive, consists of the cascade of two patterned refractive elements followed by a lens and can work independently of the polarization of the input signals. The proposed OAM converter can receive at its input a bundle of spatially multiplexed beams mapped on different OAM modes, each one carrying a set of wavelength division multiplexed (WDM) channels. Each WDM channel can be independently converted to a different OAM mode and all the OAM beams are multiplexed at the converter output. The performance of the proposed scheme is assessed as a function of the order of the OAM beam before and after the conversion, as well as of the wavelength of the input signal. The measurements show a power penalty on the bit error-rate (BER) curves of less than 1 dB in all the considered cases. The scheme is tested also with 100 Gb/s real data-traffic generated with commercial network cards, showing full operability. The cascading ability of the proposed scheme is also investigated in an experiment where the signal to be converted is generated by an OAM multiplexer, i.e. the output stage of the OAM converter, showing a penalty of less than 2 dB. Moreover, considerations on scalability, bandwidth and power consumption are also included along with a possible application of OAM conversion within add/drop nodes in an OAM-wavelength multiplexed transmission scenario.

Multi-static SARs from LEO orbits allow the single-pass high-resolution imaging and detection of moving targets. A coherent MIMO approach requires the generation of multi-band, thus orthogonal, signals, the fusion of which increases the system resolution. Up to now the synchronization capability of SAR signals of different satellites is critical. Here, we propose the use of photonics to generate, receive and distribute the radar signals in a coherent multi-static SAR constellation. Photonics overcomes issues in the implementation of MIMO SAR, allowing for the flexible generation of multi-band signals and centralized generation in a primary satellite with coherent distribution to all the secondary satellites of the SAR signals over FSO links. The numerical analysis shows the proposed system has a NESZ < −29.6 dB, satisfying the SAR system requirements. An experimental proof of concept based on COTS, for both signal up- and down-conversion, is implemented to demonstrate the system functionality, showing performance similar to the simulations. The implementation of the proposed systems with integrated technologies could reduce the system SWaP and increase robustness to vibrations. A design based on the consolidated SOI platform with the transfer printing-based hybrid integration of InP semiconductor optical amplifiers is proposed. The amplifiers compensate for the losses of the passive SOI waveguides, decreasing the overall conversion loss. The polarization multiplexing of the modulated and unmodulated combs to be sent from (to) the primary to (from) the secondary satellite over the FSO links avoids complex space-consuming optical filters requiring several control signals.