Antonio Malacarne

A fully photonics-based coherent radar system

The next generation of radar (radio detection and ranging) systems needs to be based on software-defined radio to adapt to variable environments, with higher carrier frequencies for smaller antennas and broadened bandwidth for increased resolution. Today’s digital microwave components (synthesizers and analogue-to-digital converters) suffer from limited bandwidth with high noise at increasing frequencies, so that fully digital radar systems can work up to only a few gigahertz, and noisy analogue up- and downconversions are necessary for higher frequencies. In contrast, photonics provide high precision and ultrawide bandwidth, allowing both the flexible generation of extremely stable radio-frequency signals with arbitrary waveforms up to millimetre waves, and the detection of such signals and their precise direct digitization without downconversion. Until now, the photonics-based generation and detection of radio-frequency signals have been studied separately and have not been tested in a radar system. Here we present the development and the field trial results of a fully photonics-based coherent radar demonstrator carried out within the project PHODIR. The proposed architecture exploits a single pulsed laser for generating tunable radar signals and receiving their echoes, avoiding radio-frequency up- and downconversion and guaranteeing both the software-defined approach and high resolution. Its performance exceeds state-of-the-art electronics at carrier frequencies above two gigahertz, and the detection of non-cooperating aeroplanes confirms the effectiveness and expected precision of the system.

Ultrafast integrable and reconfigurable XNOR, AND, NOR, and NOT photonic logic gate

A novel, simple, compact, and integrable scheme of reconfigurable and ultrafast photonic logic gate is demonstrated, based on a single semiconductor optical amplifier (SOA) and able to process ultrafast signals. XNOR function has been optically implemented exploiting four-wave mixing and cross-gain modulation in an SOA. The same scheme can be easily reconfigured to obtain AND, NOR, and NOT logic gates. Performances in terms of bit error rate for 20-ps return-to-zero signals at 10 Gb/s show a power penalty limited to 0.5 dB for all logic gates but the AND, which experiences regeneration (-2-dB power penalty) due to nonlinear SOA noise compression.

20 ps Transition Time All-Optical SOA-Based Flip-Flop Used for Photonic 10 Gb/s Switching Operation Without Any Bit Loss

A novel scheme for integrable ultrafast all-optical flip- flop is demonstrated. Transition times as low as 20 ps with a contrast ratio higher than 17.5 dB have been experimentally measured. All-optical switching operation in a 2times2 spatial and wavelength preserving switch is reported with a power penalty of about 1 dB. The proposed solution exploits the fast falling edge provided by a semiconductor optical amplifier (SOA) based optical flip-flop. Numerical investigations already demonstrated high extinction ratios (>40 dB) and low switching energies (15.6 fj) for integrated optical flip-flop. On the other hand, slow rising times, due to the cavity length, intrinsically limit such configurations. By using SOA-based logic gates, two flip-flop outputs are combined in a new bistable signal. Both the new rising and falling edges are related to the primary flip-flop falling edge. This way it is possible to eliminate the intrinsic slow rising time that limits the flip-flop configuration based on the coupled ring lasers, without excessively increasing the complexity of the structure and maintaining a reasonably high contrast ratio. Furthermore, the noise on the high level has been improved due to the regenerative properties of the logic gates based on cross-gain modulation and cross-phase modulation in a single nonlinear SOA. Finally, flip-flop output has been used to drive a 2times2 all-optical spatial and wavelength preserving switch based on SOAs. For cross/bar switch configurations, 10 Gb/s error-free operation has been obtained without bit loss.

Single-shot photonic time-intensity integration based on a time-spectrum convolution system

Real-time and single-shot ultra-fast photonic time-intensity integration of arbitrary temporal waveforms is proposed and demonstrated. The intensity-integration concept is based on a time-spectrum convolution system, where the use of a multi-wavelength laser with a flat envelope, employed as the incoherent broadband source, enables single-shot operation. The experimental implementation is based on optical intensity modulation of the multi-wavelength laser with the input waveform, followed by linear dispersion. In particular, photonic temporal intensity integration with a processing bandwidth of 36.8 GHz over an integration time window of 1.24 ns is verified by experimentally measuring the integration of an ultra-short microwave pulse and an arbitrary microwave waveform.

Demonstration of data and control plane for optical multicast at 100 and 200 Gb/s with and without frequency conversion

Emerging services, such as high-definition Internet Protocol TV (IP-TV) or data center migration, are going to increase the amount of multicast traffic in the Internet. The support of multicast directly in the optical domain, instead of at the IP layer, is a target for reducing the amount of optical-electronic-optical conversions (thus, the network operational and capital expenditure) and energy consumption. In parallel, flex-grid technology (e.g., bandwidth variable wavelength selective switches) is emerging as a candidate solution to be adopted in future optical transport networks given its capacity of improving spectrum efficiency. This paper is focused on optical multicast inflex-grid optical networks and onits control through the Path Computation Element (PCE). First, we present two node architectures supporting optical multicast. The first node architecture achieves optical multicast through passive light split and requires that the multicast connection satisfies the spectrum continuity constraint. The second node architecture achieves optical multicast with frequency conversion. In particular, a specific implementation of the second architecture is proposed in this paper exploiting a periodically poled lithium niobate (PPLN) waveguide. Then, a PCE architecture to control optical multicast (with and without frequency conversion) is proposed. Optical multicasting, based on the proposed node architectures, at 100 and 200 Gb/s is experimentally demonstrated in a flex-grid network testbed. In particular, multicasting is demonstrated with 112 Gb/s polarization multiplexing 16 quadrature amplitude modulation (PM-16QAM) and polarization multiplexing quadrature phase shift keying (PM-QPSK), and with 224 Gb/s PM-16QAM considering the light-split node architecture. Moreover, optical multicast with two frequency conversions, achieved in a single PPLN device, is demonstrated for the first time with a 224 Gb/s PM-16QAM signal. The testbed also includes the PCE, which is extended to control optical multicast in flex-grid optical networks.

A 100-Gb/s noncoherent silicon receiver for PDM-DBPSK/DQPSK signals

An integrated noncoherent silicon receiver for demodulation of 100-Gb/s polarization-division multiplexed differential quadrature phase-shift keying and polarization-division multiplexed differential binary phase-shift keying signals is demonstrated. The receiver consists of a 2D surface grating coupler, four Mach-Zehnder delay interferometers and four germanium balanced photodetectors.

Optical Multicasting of 16QAM Signals in Periodically-Poled Lithium Niobate Waveguide

We experimentally demonstrate multicasting operation of a 16QAM signal, by simultaneously generating multiple copies of the signal through optical wavelength conversion in a single periodically-poled Lithium Niobate (PPLN) waveguide. The simultaneous conversion of the signal on multiple wavelengths is based on the cascade of sum frequency generation and difference frequency generation second order nonlinear effects taking place in the PPLN. Each conversion is potentially tunable in the whole C-band and polarization independent operation is achieved by embedding the PPLN in a polarization diversity scheme. A first experiment reports a 3-fold wavelength conversion of a single polarization 112 Gb/s 16QAM signal. Both DFB lasers and ECLs are used to generate the optical pump signals employed in the scheme; the impact of different phase noise amounts induced by the pumps on the BER curve behavior is also discussed and numerically verified. A second experiment reports a 2-fold wavelength conversion of a 224 Gb/s polarization-multiplexed (PM)-16QAM signal, thus confirming the correct operation for PM signals. At last, the multicasting operation on the PM-16QAM signal is successfully employed in a WDM metro network scenario.

Fiber-Based Programmable Picosecond Optical Pulse Shaper

We experimentally demonstrate a fiber-optic programmable optical pulse shaper based on time-domain binary phase-only linear filtering, which is capable of switching picosecond pulse shapes at unprecedented sub-GHz rates by simply updating the binary signal driving an electro-optic phase-modulator (EO-PM). The required binary phase-filtering functions are computed using a genetic algorithm (GA). One limitation of the binary phase-filtering approach is the inherent symmetry of the output temporal shapes. To generate fully arbitrary time-domain intensity profiles (including asymmetric temporal waveforms) we must employ a multi-level phase-filtering function. However, the size of the solution-space and complexity of the computation multiplies to manifolds as the number of levels in the phase-filtering function increases. Here we numerically demonstrate a simple strategy, by combining the Gerchberg-Saxton algorithm (GSA) and GA, for the fast computation of multi-level phase-filtering functions. The performance of this approach is numerically proven by generating different asymmetric pulse shapes of practical interest, assuming experimentally feasible design parameters.

All-Optical Flip-Flop

Erbium-ytterbium doped fibre absorption and fluorescence are exploited to realize an optical bistable device. An all-optical flip-flop with 10 ns transition time, 18.48 nJ set and 19.82 nJ reset energies, is experimentally demonstrated.

Programmable fiber-based picosecond optical pulse shaper using time-domain binary phase-only linear filtering

We demonstrate a fiber-based programmable arbitrary picosecond optical pulse shaper using binary phase-only linear filtering. The reconfigurable filtering operation is implemented in the time domain using an electro-optical phase modulator driven by a high-speed bit pattern generator. The required binary phase code is designed using a genetic algorithm. Precise matching between the predispersive and postdispersive media in the system is achieved by use of a single linearly chirped fiber Bragg grating subsequently operated from its two input ends. As a proof of concept, different pulse waveforms of practical interest are generated using this new pulse shaper.