All-optical Label Processing Research Articles

4-Bit All-Optical Serial-to-Parallel Converter With Sub-dB/cm Delay Lines Based on Rib Waveguides

This paper extends our previous work on the microring resonator-type serial-to-parallel conversion scheme aimed for all-optical label processing on the silicon photonic platform. In the previously proposed scheme, the architecture of the delay lines was silicon wires. This resulted in considerable propagation loss, confining multibit operation of serial-to-parallel conversion to a label packet of 2 bits. However, during a practical application, propagation loss at the delay lines has to be improved to support label packets comprising of a greater number of bits. The purpose of this article is twofold. First, we confirm that propagation loss can be lowered to sub-dB/cm values by introducing rib waveguides via simulations and experiment. Second, we demonstrate multibit serial-to-parallel conversion on a 4-bit label “1101” by utilizing a cascaded microring resonator device of which the straight sections of the delay lines are of rib waveguide architecture. In order to focus on free-carrier dispersion effect of silicon during operation, we left out a temporal delay between the pump pulses and probe bits to be extracted. As a result, serial-to-parallel conversion was viable even at peak pump power levels as low as ∼100 mW. We hereby verify that the proposed serial-to-parallel conversion scheme incorporated with rib waveguide delay lines is a realistic solution in realizing a photonics-based solution to all-optical label processing.

MZI-based all-optical serial-to-parallel conversion circuit by free-carrier dispersion effect

Device applications of nonlinear optical phenomena on the silicon-on-insulator platform are attracting significant attention in silicon photonics. We report a novel on-chip Mach–Zehnder interferometer-type serial-to-parallel converter aimed at all-optical label processing of optical packets. We focus on the free-carrier dispersion effect during phase modulation of the serial probe signal, and a pump signal is used to generate sufficient free-carriers within the waveguide structure. By leaving out a delay between the pump and probe pulses, we avoid the effects of pump-induced cross-phase modulation and two-photon absorption, and perform serial-to-parallel conversion at a lower pump power. In the theoretical analysis, serial-to-parallel conversion of a 10-Gbps probe signal is considered. By numerical simulations, the shortest arm length of the Mach–Zehnder interferometric structure required for operation is calculated. When doing so, the pump pulse width and delay between the pulses are varied while the pulse energy of the pump is held constant at 25 pJ, and the combination of values that corresponds to the shortest arm length is taken as optimum values. Our study reveals that the optimum values for delay and pump pulse width are 30 ps and 25 ps, respectively. Finally, we also demonstrate single-bit serial-to-parallel conversion experimentally on a Mach–Zehnder interferometric device. Phase modulation due to free-carrier dispersion was observed at peak pump power levels of 1.0 W at the waveguide input.

160 Gb/s/Port 2$\,\times\,$2 OPS Node Test-Bed Performing 50 Gchip/s All-Optical Active Label Processing With Contention Detection

A 160 Gb/s/port 2×2 optical packet switching node test-bed is implemented by exploiting semiconductor optical amplifier-based label extraction and contention detection. Optical packed switched networks are attractive because they allow packet switching without conversion of the data in the electronic domain, making the nodes transparent to the data format and improving the network scalability. Despite the control of the switching and of the contentions in the network nodes can be implemented in the electronic domain, the use of all-optical processing also in the subsystems devoted to the control can increase the node performance by leading to a reduced packet latency time and to a possibly more efficient implementations. Nevertheless integrated realizations are required to make the all-optical approach attractive and effective also in terms of power consumption and footprint. SOA technology represents a mature and reliable technology suitable for hybrid integrated implementations. The implementation of active label processing in a real testbed with discrete devices demonstrates the validity of the proposed approach. Error-free operations are obtained with a 50 Gchip/s label. To the best of our knowledge this is the first demonstration of active label processing at a chip rate as high as 50 Gchip/s.

Label swapping versus label preserving in packet switched networks: Impact on the label space size

In recent years, switching and networking solutions exploiting all-optical nodes are gaining increasing interest to achieve the target of ultrawide-bandwidth and low-latency packet or burst processing. On the one hand, many prototypes, validated by experimental demonstration of all-optical label processing solutions, have been developed. On the other hand, the primitive available technology for performing label processing poses several constraints on the label structures; this in turn significantly impacts the traffic engineering aspects of such a network. In this paper, the label assignment problem is studied in a network that makes forwarding decision based on optical packet labels and formulated independently of any technology. Specifically, the problem of assigning labels to identify the label switched path (LSP) packets in a unique and disjoint way is defined, with the objective of optimally minimizing the label space size (i.e. number of labels, or bits, required to uniquely identify the LSPs). The network scenarios where (i) labels have local point-to-point significance (i.e. the label is swapped when traversing each node), and (ii) labels have end-to-end significance (i.e. the label is preserved along the LSP traversing multiple nodes) are both investigated. For both scenarios, labels can be uniquely identified at each node or at each node-port. The label assignment strategies for all the possible scenarios are investigated. Both theoretical and practical methods, i.e. integer linear programming formulations and heuristics, respectively, are used to assess the efficiency of the proposed label preserving solution. Numerical results show that, for a significant set of network topologies, the label space size increase experienced by networks with label preserving capabilities is limited or negligible in both per-node and per-port label identification.

A New Loopback Method of All-Optical Label Processing for Label Bit Scalability

We propose and demonstrate a new method to expand the label bit in an all-optical label processor with a multistage switching fabric. It utilizes a loopback configuration, where a probe pulse is fed back to the same switching fabric with wavelength conversion and the output probe pulse is discriminated by arrayed waveguide gratings. The feasibility of the loopback scheme was demonstrated for the two-bit pattern in the two-bit label using a single semiconductor optical amplifier-based Mach-Zehnder interferometer 1x2 all-optical switch. It is effective to reduce the number of switching elements and will expand the number of label bits.

A novel all-optical label processing based on multiple optical orthogonal codes sequences for optical packet switching networks

This paper proposes an all-optical label processing scheme that uses the multiple optical orthogonal codes sequences (MOOCS)-based optical label for optical packet switching (OPS) (MOOCS–OPS) networks. In this scheme, each MOOCS is a permutation or combination of the multiple optical orthogonal codes (MOOC) selected from the multiple-groups optical orthogonal codes (MGOOC). Following a comparison of different optical label processing (OLP) schemes, the principles of MOOCS–OPS network are given and analyzed. Firstly, theoretical analyses are used to prove that MOOCS is able to greatly enlarge the number of available optical labels when compared to the previous single optical orthogonal code (SOOC) for OPS (SOOC–OPS) network. Then, the key units of the MOOCS-based optical label packets, including optical packet generation, optical label erasing, optical label extraction and optical label rewriting etc., are given and studied. These results are used to verify that the proposed MOOCS–OPS scheme is feasible.

All-optical label processing techniques for pure DPSK optical packets

We present two all-optical label processing schemes for pure differential phase shift keying packets. The two techniques are based on the already used optical correlators and on a novel time-to-wavelength conversion of the label information. They require that the label information is encoded by using pulse position modulation, which makes the label processor simpler and can allow very fast processing speed. We investigate and compare the efficiency in terms of packet overhead of pulse position modulation coded labels with ordinary binary coding and show that pulse position modulation is still attractive for medium-size network and for system implementing optical label swapping. We then experimentally demonstrate that the two techniques can distinguish several labels at distinct outputs. Both operate at low optical power, asynchronously, and could allow for photonic integration. Scalability and processing speeds of the two systems are discussed. We also show that the two label processors can be used to implement an optical label swapping system. Experimental results show that the two labels are distinguished at two distinct ports and erased from the incoming packet, so that a new label can be inserted. Scalability and processing speed are discussed as well

Cutting-Edge Technologies on Broadband and Scalable Photonic-Network?Packet switched networks based on all-optical label processing?

Ultra-high speed all-optical label processing methods are proposed and experimentally demonstrated. These methods dramatically increase the label processing capability. Optical packet switch (OPS) systems and networks based on OPS nodes are expressed as an application of optical processing technologies. First, the 40 Gbit/s/port OPS prototype with all-optical label processor, optical switch, optical buffer, and electronic scheduler is described. The feasibility of OPS networks is verified by experimental demonstrations.