Gianluca Berrettini

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.

Push-Pull Defragmentation Without Traffic Disruption in Flexible Grid Optical Networks

In flexi-grid optical networks, fragmentation of spectrum resources may significantly affect the overall network efficiency. Effective techniques for defragmentation (i.e., re-optimization) are then required to limit the wasting of spectrum resources. However, current defragmentation techniques can only be implemented thanks to the presence of additional resources, such as spare expensive transponders. In this study, we propose, discuss and evaluate a novel defragmentation technique called push-pull. The technique is based on dynamic lightpath frequency retuning upon proper reconfiguration of allocated spectrum resources. It does not require additional transponders and does not determine traffic disruption. All the relevant technological limitations that may affect the push-pull applicability are discussed in the context of both optically-amplified direct and coherent detection systems. The technique is then successfully demonstrated in two different flexi-grid network testbeds, reproducing the two aforementioned scenarios. In particular, the reoptimization of a 10 Gb/s OOK lightpath is safely completed in few seconds (mainly due just to node configuration latencies) without experiencing any traffic disruption. Similarly, the push-pull is successfully performed on a 100 Gb/s PM-QPSK lightpath, providing no traffic disruption.

All-Optical Clocked Flip-Flops and Binary Counting Operation Using SOA-Based SR Latch and Logic Gates

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.

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.

Evolution Scenario Toward WDM-PON [Invited]

In this paper we present and critically discuss different wavelength division multiplexing passive optical network (WDM-PON) architectures compatible with pre-existing gigabit PON (GPON) infrastructures. The concurrent use of the trunk fiber permits a hitless evolution from an existing time division multiplexing optical access network to a point-to-point wavelength division access network. System performance has been experimentally evaluated in terms of bit error rate.

Casting 1 Tb/s DP-QPSK communication into 200 GHz bandwidth

We demonstrate the feasibility of a novel time-frequency packing technique to implement DP-QPSK communication with a record spectral efficiency ranging from 5.14 to 4.3 bit/s/Hz over a distance ranging from 3000 km to 5200 km of uncompensated standard fiber, respectively.

Photonic Combinatorial Network for Contention Management in 160 Gb/s-Interconnection Networks Based on All-Optical 2

A modular photonic interconnection network based on a combination of basic 2times2 all-optical nodes including a photonic combinatorial network for the packet contention management is presented. The proposed architecture is synchronous, can handle optical time division multiplexed (OTDM) packets up to 160 Gb/s, exhibits self-routing capability, and very low switching latency. In such a scenario, OTDM has to be preferred to wavelength division multiplexing (WDM) because in the former case, the instantaneous packet power carries the information related to only one bit, making the signal processing based on instantaneous nonlinear interactions between packets and control signals more efficient. Moreover, OTDM can be used in interconnection networks without caring about the propagation impairments because of the very short length (<100 m) of the links in these networks. For such short-range networks, the packet synchronization can be solved at the network boundary in the electronic domain without the need of complex optical synchronizers. In this paper, we focus on a photonic combinatorial network able to detect the contentions, and to optically drive the contention resolution block and the switching control block. The implementation of the photonic combinatorial network is based on semiconductor devices, which makes the solution very promising in terms of compactness, stability, and power consumption. This implementation represents the first example of complex photonic combinatorial network for ultrafast digital processing. The network performance has been investigated for bit streams at 10 Gb/s in terms of bit error rate (BER) and contrast ratio. Moreover, the suitability of the 2times2 photonic node architecture exploiting the earlier mentioned combinatorial network has been verified at a bit rate up to 160 Gb/s. In this way, the potential of photonic digital processing for the next generation broad band and flexible interconnection networks has been demonstrated.

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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.

2 Switching Elements

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.

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

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.