Swarm of lightsail nanosatellites for Solar System exploration.

This paper presents a study for the realization of a space mission which employs nanosatellites driven by an external laser source impinging on an optimized lightsail, as a valuable technology to launch swarms of spacecrafts into the Solar System. Nanosatellites propelled by laser can be useful for heliosphere exploration and for planetary observation, if suitably equipped with sensors, or be adopted for the establishment of network systems when placed into specific orbits. By varying the area-to-mass ratio (i.e. the ratio between the sail area and the payload weight) and the laser power, it is possible to insert nanosatellites into different hyperbolic orbits with respect to Earth, thus reaching the target by means of controlled trajectories in a relatively short amount of time. A mission involving nanosatellites of the order of 1 kg of mass is envisioned, by describing all the on-board subsystems and satisfying all the requirements in terms of power and mass budget. Particular attention is paid to the telecommunication subsystem, which must offer all the necessary functionalities. To fabricate the lightsail, the thin films technology has been considered, by verifying the sail's thermal stability during the thrust phase. Moreover, the problem of mechanical stability of the lightsail has been tackled, showing that the distance between the ligthsail structure and the payload plays a pivotal role. Some potential applications of the proposed technology are discussed, such as the mapping of the heliospheric environment.

CHARLES: A C++ fixed-point library for Photonic-Aware Neural Networks.

In this paper we present CHARLES (C++ pHotonic Aware neuRaL nEtworkS), a C++ library aimed at providing a flexible tool to simulate the behavior of Photonic-Aware Neural Network (PANN). PANNs are neural network architectures aware of the constraints due to the underlying photonic hardware, mostly in terms of low equivalent precision of the computations. For this reason, CHARLES exploits fixed-point computations for inference, while it supports both floating-point and fixed-point numerical formats for training. In this way, we can compare the effects due to the quantization in the inference phase when the training phase is performed on a classical floating-point model and on a model exploiting high-precision fixed-point numbers. To validate CHARLES and identify the most suited numerical format for PANN training, we report the simulation results obtained considering three datasets: Iris, MNIST, and Fashion-MNIST. Fixed-training is shown to outperform floating-training when executing inference on bitwidths suitable for photonic implementation. Indeed, performing the training phase in the floating-point domain and then quantizing to lower bitwidths results in a very high accuracy loss. Instead, when fixed-point numbers are exploited in the training phase, the accuracy loss due to quantization to lower bitwidths is significantly reduced. In particular, we show that for Iris dataset, fixed-training achieves a performance similar to floating-training. Fixed-training allows to obtain an accuracy of 90.4% and 68.1% with the MNIST and Fashion-MNIST datasets using only 6 bits, while the floating-training reaches an accuracy of just 25.4% and 50.0% when exploiting the same bitwidths.

Integrated optical frequency comb for 5G NR Xhauls.

We experimentally demonstrate the use of optical frequency combs (OFCs), generated by a photonic integrated circuit (PIC), in a flexible optical distribution network based on fiber-optics and free-space optics (FSOs) links, aimed at the fifth generation of mobile network (5G) Xhauls. The Indium Phosphide (InP) monolithically integrated OFC is based on cascaded optical modulators and is broadly tunable in terms of operating wavelength and frequency spacing. Particularly, our approach relies on applying the PIC in a centralized radio access network (C-RAN) architecture, with the purpose of optically generating two low-phase noise mm-waves signals for simultaneously enabling a 12.5-km of single-mode fiber (SMF) fronthaul and a 12.5-km SMF midhaul, followed by a 10-m long FSO fronthaul link. Moreover, the demonstrator contemplates two 10-m reach 5G wireless access networks operating in the 26 GHz band, i.e. over the frequency range 2 (FR2) from the 5G NR standard. The proposed integrated OFC-based 5G system performance is in accordance to the 3rd Generation Partnership Project (3GPP) Release 15 requirements, achieving a total wireless throughput of 900 Mbit/s.

Dynamic switching of a packaged photonic integrated network-on-chip using an FPGA controller.

A packaged photonic integrated network-on-chip (NoC) based on multi-microrings with a controller and scheduler implemented in FPGA is demonstrated under dynamic packet-switched traffic. Multiple transmission scenarios have been investigated, comprising up to three interfering signals at the same wavelength. The dynamic switching exhibits a power penalty of approximately 0.5 dB at a BER of 10-9. The presence of up to three interferers induces a power penalty below 1 dB.

Experimental demonstration of a 24-port packaged multi-microring network-on-chip in silicon photonic platform.

A 24-port packaged multi-microring optical network-on-chip has been tested for simultaneous co- and counter-propagating transmissions at the same wavelength at 10 Gbps. In the co-propagating scenario communications up to five hops with one interfering signal have been tested, together with transmissions impaired by up to three interfering signals. In the counter-propagating scenario the device performance has been investigated exploiting the ring resonators in both shared-source and shared-destination configurations. The spectral characterization is in good agreement with the theoretical results. Bit-error-rate measurements indicate power penalties at BER=10-9 limited to (i) 0.5 dB in the co-propagating scenarios independently from the number of interfering transmissions, (ii) 0.8 dB in the counter-propagating scenario with shared-source configuration, and (iii) 2 dB in the counter-propagating scenario with shared-destination configuration.

BER evaluation of a low-crosstalk silicon integrated multi-microring network-on-chip.

The operation of an integrated silicon-photonics multi-microring network-on-chip (NoC) is experimentally demonstrated in terms of transmission spectra and bit error rates at 10 Gb/s. The integrated NoC consists of 8 thermally tuned microrings coupled to a central ring. The switching functionalities are tested with concurrent transmissions at both the same and different wavelengths. Experimental results validate the analytical model based on the transfer matrix method. BER measurements show performance up to 10(-9) at 10 Gb/s with limited crosstalk and penalty (below 0.5 dB) induced by an interfering transmission.

Silicon-based all-optical multi microring network-on-chip.

An optical multi microring network-on-chip (MMR NoC) is proposed and evaluated through numerical simulations. The network architecture consists of a central resonating microring with local microrings connected to the input/output ports. A mathematical model based on the transfer matrix method is used to assess the MMR NoC performance and to analyze the fabrication tolerances. Results show that the proposed architecture exhibits a limited coherent crosstalk with a bandwidth suitable for 10 Gb/s signals, and it is robust to coupling ratio variations and ring radii fabrication inaccuracies.

A wavelength-preserving photonic integrated regenerator for NRZ and RZ signals.

This paper presents a novel Indium Phosphide based photonic integrated circuit (PIC) for all-optical regeneration of both nonreturn-to-zero (NRZ) and return-to-zero (RZ) on-off-keying (OOK) signals. The PIC exploits cross gain compression in two semiconductor optical amplifiers to simultaneously obtain a wavelength-preserved and reshaped copy, and a wavelength-converted yet inverted copy of the input signal. Regeneration of 10 Gb/s signals on multiple wavelengths is demonstrated, showing a Q-factor improvement from 1.5 to 4 for NRZ-OOK signals and from 2.3 to 3.6 for RZ-OOK signals, and a BER improvement up to 1.5 decades.