Reconfigurable Optical Networks Research Articles

Controllable entangled-state distribution in a dual-rail reconfigurable optical network

The authors introduce a new quantum distribution network architecture enabling control of the propagation direction of an entangled state using linear-optical devices and phase shifters and offering reconfigurable connections between multiple quantum nodes.

Dynamic piezoelectric MEMS-based optical metasurfaces.

Optical metasurfaces (OMSs) have shown unprecedented capabilities for versatile wavefront manipulations at the subwavelength scale. However, most well-established OMSs are static, featuring well-defined optical responses determined by OMS configurations set during their fabrication, whereas dynamic OMS configurations investigated so far often exhibit specific limitations and reduced reconfigurability. Here, by combining a thin-film piezoelectric microelectromechanical system (MEMS) with a gap-surface plasmon-based OMS, we develop an electrically driven dynamic MEMS-OMS platform that offers controllable phase and amplitude modulation of the reflected light by finely actuating the MEMS mirror. Using this platform, we demonstrate MEMS-OMS components for polarization-independent beam steering and two-dimensional (2D) focusing with high modulation efficiencies (~50%), broadband operation (~20% near the operating wavelength of 800 nanometers), and fast responses (<0.4 milliseconds). The developed MEMS-OMS platform offers flexible solutions for realizing complex dynamic 2D wavefront manipulations that could be used in reconfigurable and adaptive optical networks and systems.

Adaptable transmitter for discrete and continuous variable quantum key distribution

We present a versatile transmitter capable of performing both discrete variable and continuous variable quantum key distribution protocols (DV-QKD and CV-QKD, respectively). Using this transmitter, we implement a time-bin encoded BB84 DV-QKD protocol over a physical quantum channel of 47 km and a GG02 CV-QKD protocol with true local oscillator over a 10.5 km channel, achieving secret key rates of 4.1 kbps and 1 Mbps for DV- and CV-QKD, respectively. The reported transmitter scheme is particularly suitable for re-configurable optical networks where the QKD protocol is selected to optimize the performance according to the parameters of the links.

Optimal and near-optimal alpha-fair resource allocation algorithms based on traffic demand predictions for optical network planning

We examine proactive network optimization in reconfigurable optical networks based on traffic predictions. Specifically, the fair spectrum allocation (SA) problem is examined for a priori reserving resources aiming to achieve near-even minimum quality-of-service (QoS) guarantees for all contending connections. The fairness problem arises when greedy SA policies are followed, which are based on point-based maximum demand predictions, especially under congested networks, with some connections highly overprovisioned and others entirely blocked, resulting in highly uneven QoS connection guarantees. To address this problem, we consider predictive traffic distributions allowing the exploration of several combinations of possible SAs. To find a fair SA policy, we resort to an α -fairness scheme, while QoS fairness is evaluated according to a game-theoretic analysis based on the coefficient of variations of the connections’ unserved traffic metric, which measures the dispersion of unserved traffic for a connection around the mean of the unserved traffic over all connections. Non-contending (NC) and link-based contending (LBC) α -fair SA integer linear programming algorithms are proposed, where the optimal NC approach encompasses global network contention information, while the near-optimal LBC approach encompasses partial contention information to reduce problem complexity. We show that as parameter α increases, QoS fairness improves, along with connection blocking, resource utilization, and overprovisioning and underprovisioning. Further, LBC exhibits results close to the optimal, with a significant improvement in processing time.

High-Q nanophotonics: sculpting wavefronts with slow light

AbstractDensely interconnected, nonlinear, and reconfigurable optical networks represent a route to high-performance optical computing, communications, and sensing technologies. Dielectric nanoantennas are promising building blocks for such architectures since they can precisely control optical diffraction. However, they are traditionally limited in their nonlinear and reconfigurable responses owing to their relatively low-quality factor (Q-factor). Here, we highlight new and emerging design strategies to increase the Q-factor while maintaining control of optical diffraction, enabling unprecedented spatial and temporal control of light. We describe how multipolar modes and bound states in the continuum increase Q and show how these high-Q nanoantennas can be cascaded to create almost limitless resonant optical transfer functions. With high-Q nanoantennas, new paradigms in reconfigurable wavefront-shaping, low-noise, multiplexed biosensors and quantum transduction are possible.

Compensation of fiber dispersion induced-power fading in reconfigurable millimeter-wave optical networks

Radio-over-fiber (RoF) systems can be incorporated into a wavelength division multiplexing (WDM) and distributed antenna system (DAS) to vastly increase the data throughput. In this paper, a reconfigurable WDM system at millimeter (mm-wave) frequencies is theoretically proposed and experimentally demonstrated based on an optical frequency comb (OFC) and wavelength selective switch (WSS). The photonic carrier generation using OFC spectra is affected by chromatic dispersion which results in power fading and optical noise. Therefore, the tolerance of the mm-wave heterodyne carrier to fiber propagation is discussed and considered in the proposed architecture. Furthermore, this paper examines how the WSS can pre-compensate the fiber dispersion in terms of power fading on the beating carrier. Experimental measurements show that by variable adjustment of the amount of dispersion compensation applied, power fading of 15 dB can be mitigated and error vector magnitude (EVM) is reduced by 10%. By utilizing the well-known periodic behavior between carrier power penalty and chromatic dispersion, the WSS can also overcome the deep power fading over long fiber lengths (>25 km).

All-Optical Aggregation and De-Aggregation of 4×BPSK-16QAM Using Nonlinear Wave Mixing for Flexible Optical Network

A scheme is proposed for all-optical aggregation from four 10 Gbps binary-phase-shift-keying (BPSK) signals into one 40 Gbps 16-ary quadrature amplitude modulation (16QAM) signal by applying the coherent addition of optical vectors, and de-aggregation for the 16QAM signal to recover the data of four original BPSK signals in high nonlinear fiber (HNLF) without information loss or redundancy using self-phase modulation (SPM) and four-wave mixing (FWM). The simulation results show that the error-vector-magnitude (EVM) curves of BPSK signal before aggregation and the 16QAM signal almost coincide with each other, as well as after the de-aggregation it has about 20% degradation at most. The bit error rate (BER) performance of BPSK signals indicates that when the OSNR of BPSK before aggregation is greater than 21.0 dB, then the wrong code of BPSK signal after de-aggregation can be corrected at the receiving end. Additionally, the expanded methods are also proposed for the aggregation of 8PSK signal and 64QAM signal by employing the similar principle. This proposed method provides a new way for realizing the flexible optical transmission and reception of advanced modulation format signals, and suits for the future dynamically reconfigurable optical network at the gateway nodes between different transmission networks.

Nested Mach–Zehnder interferometer optical switch with phase generating couplers

In reconfigurable optical networks, an optical switch is indispensable to afford routing optical signals without optical/electrical conversion. A nested Mach–Zehnder interferometer (MZI) optical switch is suitable for a silicon-silica hybrid structure compared with a conventional cascaded MZI switch. We proposed to employ phase generating couplers (PGCs) instead of directional couplers (DCs) in the nested MZI optical switch. Calculation results show that the nested MZI switch with PGCs exhibits <−30 dB crosstalk over wider wavelength range than that using DCs.

Global load-balancing ONU assignment for a software-defined reconfigurable PON

Rapidly growing and fluctuating traffic demands lead to unbalanced traffic scenarios in optical access networks, which have an impact on network efficiency. Thus, the flexible software-defined reconfigurable passive optical network (PON) architecture has been proposed to handle this challenge. To improve the efficiency of a reconfigurable PON facing unbalanced traffic demands, this paper proposes a global load-balancing (GLB) optical network unit (ONU) assignment method, which aims to achieve load balancing among the optical line terminals (OLTs) in the OLT pool as well as among the aggregation switch ports that connect the OLTs by optimizing the affiliations between the OLTs and the ONUs. For on-line optimization, a greedy GLB algorithm is introduced that regroups the ONUs and generates load-balanced target ONU-OLT affiliations in accordance with dynamic traffic demands. For off-line optimization, bee colony optimization (BCO) is invoked to search for better ONU regrouping solutions for GLB. Simulation results show that the proposed GLB algorithm can significantly improve the throughput and delay performance of an optical access network faced with unbalanced traffic demands, especially when the network load is heavy. Moreover, the proposed BCO technique for GLB can obviously improve the worst delay performance and reduce the migrated traffic of the GLB solution, especially under network conditions with high peer-to-peer traffic proportions and heavy network loads. Thus, the proposed global load-balancing ONU assignment method is effective for helping a software-defined reconfigurable PON to cope with unbalanced traffic demands.

Reversible Photoalignment of Liquid Crystals: a Path toward the Creation of Rewritable Lenses

In this work, we describe a new reversible photoalignment effect for the director in nematic liquid crystals that provides an approach for the creation of lenses whose optical power can be recorded and erased. The possibility of creating a rewritable lens has very important practical implications, for example, in the ophthalmic lens industry. A rewritable ophthalmic lens could be a convenient solution for patients whose compensation needs change over time due to age-related physiological changes, such as the onset and progression of presbyopia. Using rewritable lenses, small lens power corrections could be implemented through a rewriting procedure on the mounted lens without resurfacing or manufacturing and mounting a new lens. More generally, this new effect multiple potential applications in the creation of rewritable optical systems, such as reconfigurable optical networks, index-tunable antireflective coatings and optically rewritable phase gratings.

Programmable linear quantum networks with a multimode fibre

Reconfigurable quantum circuits are fundamental building blocks for the implementation of scalable quantum technologies. Their implementation has been pursued in linear optics through the engineering of sophisticated interferometers. While such optical networks have been successful in demonstrating the control of small-scale quantum circuits, scaling up to larger dimensions poses significant challenges. Here, we demonstrate a potentially scalable route towards reconfigurable optical networks based on the use of a multimode fibre and advanced wavefront-shaping techniques. We program networks involving spatial and polarisation modes of the fibre and experimentally validate the accuracy and robustness of our approach using two-photon quantum states. In particular, we illustrate the reconfigurability of our platform by emulating a tunable coherent absorption experiment. By demonstrating reliable reprogrammable linear transformations, with the prospect to scale, our results highlight the potential of complex media driven by wavefront shaping for quantum information processing.

Joint and Accurate OSNR Estimation and Modulation Format Identification Scheme Using the Feature-Based ANN

A joint and accurate optical signal-to-noise ratio (OSNR) estimation and modulation formats identification (MFI) scheme based on the artificial neural network (ANN) is proposed and demonstrated via both simulation and the experiment system. The proposed scheme employs ANN to estimate OSNR and modulation formats from the OSNR and modulation formats dependent features, kurtosis, and amplitude variance. Simulation results show that the proposed scheme can achieve high OSNR estimation and MFI accuracy over wide OSNR ranges for the commonly used modulation formats such as QPSK, 8 quadratic-amplitude modulation (QAM), 16QAM, and 64QAM. Meanwhile, experimental results also indicate that the mean OSNR estimation errors are 0.15 dB, 0.41 dB, and 0.49 dB for QPSK, 8QAM, and 16QAM over wide ranges OSNR of 10–17 dB, 14–20 dB, and 17–25 dB, respectively. Additionally, 100% MFI accuracy for the commonly used modulation formats in our scheme is also confirmed experimentally. Compared with the convolutional neural network and the deep neural network, the proposed scheme shows comparable estimation and identification performance, and needs less computational resource. Therefore, our scheme can be considered an attractive technique for joint OSNR estimation and MFI in future reconfigurable optical networks.

All-optical deaggregation from 8PSK to 3×BPSK based on FWM in HNLF.

A scheme is proposed for all-optical deaggregation from one 30 G-bit/s eight-phase-shift-keying (8PSK) signal to three 10 G-bit/s binary-phase-shift-keying (BPSK) signals based on four-wave mixing (FWM) in high nonlinear fiber (HNLF) without information loss or redundancy. The coded information of three BPSK signals after the deaggregation represents every bit of the coded information of the input 8PSK signal. We conducted theoretical analyses and simulations of the proposal. The error-vector-magnitude (EVM), bit-error rate (BER), and constellations were analyzed for system performance evaluation. The results show that when the optical signal-to-noise ratio (OSNR) of the input 8PSK signal is 18 and 30 dB, the phase standard deviations of output BPSK signals decrease about 6.5° and 1.5°, respectively, after the deaggregation. The OSNR-BER performance of the extracted BPSK signals almost coincides with the ideal BPSK signal, with 21 and 12 dB receiver OSNR difference, respectively, at the BER of 10-3, indicating a larger noise tolerance compared to the input 8PSK signal. The scheme provides an effective method of all-optical deaggregation from 8PSK to BPSK, suitable for future dynamically reconfigurable optical networks, and makes it easier and more effectual for the receiving terminal which doesn't have the matching 8PSK receiver.

Characterization of a Low-Cost, Monolithically Integrated, Tunable 10G Transmitter for Wavelength Agile PONs

Dynamically reconfigurable passive optical networks (PONs) using time-division multiplexing and dense wavelength division multiplexing will require low-cost, high-performance customer premises equipment to be economically viable. In particular, substantial cost savings can be achieved through the use of efficient re-growth free, foundry-compatible fabrication techniques. Using this strategy, this paper presents the first detailed characterization of a monolithically integrated transmitter comprised of a discretely tunable slotted Fabry–Perot ridge waveguide laser, an absorptive modulator and a semiconductor optical amplifier (SOA) produced using a standard off-the-shelf AlInGaAs/InP multiple quantum well epitaxial structure. This first generation device demonstrates a discrete single-mode tuning range of approximately 12 nm between 1551nm and 1563 nm with a side-mode suppression ratio ≥30 dB. Moreover, the integrated modulator section is shown to support transmission at 10 Gb/s using non-return to zero on-off keying with an extinction ratio in excess of 8 dB. Furthermore, using a time-resolved chirp measurement technique to examine dynamic deviations in the set carrier frequency, the modulator section exhibits a chirp contribution of $\mu \text{s}$ which are faster than the thermal response time of the transmitter material.

Nonlinear chirped grating based tunable dispersion compensation using strain

Chirped fiber Bragg gratings (CFBGs) offer an attractive solution for dispersion management in long haul and high capacity point to point optical links. The deployment of reconfigurable optical networks however demands dynamic dispersion compensation schemes to address channel degrading effects. Dynamic correction of dispersion can be achieved by tuning the optical characteristics of the non-linearly chirped FBG using external controls like temperature, strain, magnetic, acousto-optic and electro-optic techniques. In this work, simulations are carried out to evaluate the performance of nonlinear chirped gratings as tunable dispersion compensators. The induced dispersion of the grating is found to be tunable from −800 ps/nm to −2657 ps/nm using strain as external perturbation. BER of 1.85 × 10−118 and 1.71 × 10−116 is achieved after the transmission of the information through 90 and 140 km section of single mode optical fiber respectively. This is achieved by adjusting or tuning the dispersion offered by the nonlinear chirped FBG dynamically in the required range.

A novel WDM-MAN enabling cross-regional reconfiguration and comprehensive protection based on tangent-ring

Abstract A reconfigurable and reliable wavelength division multiplexing (WDM) metro-access optical network architecture is proposed in this paper. With the establishment of one optical transmitter in the optical network unit (ONU) and the reuse of optical distribution network, three kinds of reconfigurable WDM optical networks can be successfully built to achieve efficient inter and intra PON communication in the physical layer. With the adoption of multiple topologies based on single ring, four-level protections of feeder and distribution fibers can be achieved. With the creative design of flexible distribution node (FDN), the transmission wavelengths in the central office can be not only transmitted to the express ONUs connected straight with FDN, but also routed to the indirect ONUs hung in the remote node. Finally, large capacity, high reliability, low cost and great transmission performances at 10 Gbps and 2.5 Gbps data rate are obtained via analyses and simulation

De-multiplexing free on-chip low-loss multimode switch enabling reconfigurable inter-mode and inter-path routing

Abstract Switching and routing are critical functionalities for a reconfigurable bandwidth-dense optical network, and great efforts had been made to accommodate mode-division multiplexing technology. Although the reconfigurable routing for spatial-mode groups between different optical paths was realized recently, a demultiplexing-switching-multiplexing process is necessary. Here we present a simplified and compact on-chip 2×2 multimode switch that can be easily upgradable to a larger scale. Fully and reconfigurable routing between not only optical paths but also spatial modes is achieved. To obtain a low loss multimode processing, a novel structure free from demultiplexing and re-multiplexing operations is adopted. The switch enables minimum and maximum insertion losses of 0.3 and 1.2 dB, with a compact footprint of 433 μm×433 μm and low crosstalk of &lt;−16.6 dB for all channels. It is further extended to two types of 4×4 switch fabrics with cross-bar and ring-bus architectures, as demonstrations of high-level integration. System characterization with 32 Gb/s high-speed modulated signals is also carried out, reaching up to 256 Gb/s aggregate throughput. These results verify a general solution of 2×2 multimode switch for reconfigurable inter-mode and inter-path routing applicable in large-scale and high-density multimode optical network.

Reconfigurable Optical Network Intermediate Node With Full-Quadrature Regeneration and Format Conversion Capacity

In this paper, a reconfigurable optical network intermediate node scheme with format conversion capacity and full-quadrature regeneration functionality is proposed. With a degraded input quadrature phase-shift keying (QPSK), the proposed network node can be dynamically reconfigured based on the network situation to output a QPSK or a four-level pulse amplitude modulation (PAM4), both full-quadrature regenerated. The input QPSK is first converted into the two full-quadrature regenerated binary phase-shift keying tributaries after phase sensitive amplifier-based quadrature de-multiplexing and self-phase modulation-based amplitude regeneration. Then the output regenerated QPSK or PAM4 are generated through vector addition by tuning the relative phase and amplitude between two tributaries. For an input 20 Gb/s QPSK with optical signal-to-noise ratio (OSNR) of 15 dB, the output regenerated QPSK gets 10.4% decrease in error vector magnitude (EVM), 2 dB receiver OSNR improvement at the bit error rate of 10 $^{ - 3}$ , and regeneration factors of 6.4 dB and 3.7 dB in amplitude and phase, respectively. In the case with regenerated PAM4 as the output, compared with the input QPSK, it has 10.4% improvement in EVM and regeneration factors of 7.1 dB and 2.5 dB in amplitude and phase, respectively. The numerical simulation results reveal that the system effectively regenerates input signal in full-quadrature with format conversion capacity. The proposed node scheme can be applied as a full-quadrature QPSK regenerator between optical networks, which both employ QPSK to increase the transmission distance, or an all-optical interconnection node between different optical networks where different modulation formats are used individually.

Blind Density-Peak-Based Modulation Format Identification for Elastic Optical Networks

Optical modulation format identification is critical in the next generation of heterogeneous and reconfigurable optical networks. Here, we present a blind modulation format identification method by applying fast density-peak-based pattern recognition in the autonomous receiver of elastic optical networks. In this paper, we find that the different modulation format types show different energy level features which can be used as a metric to identify these modulation formats in two-dimensional Stokes plane. The proposed method does not require training symbols, and is insensitive to carrier phase noise, frequency offset as well as polarization mixing. The effectiveness is verified via numerical simulations and experiments with PDM-BPSK, PDM-QPSK, PDM-8PSK, PDM-16PSK, PDM-8QAM, and PDM-16QAM. The results show that high identification accuracy can be realized using our proposed method over wide optical signal-to-noise ratio ranges. Meanwhile, we also discuss the influence of the residual chromatic dispersion, polarization mode dispersion, and polarization dependent loss impairments to our proposed method. We believe that the simple and flexible identification method would certainly bring a great convenience to the future optical networks.

Energy efficient operation for a reconfigurable and self-interleaved optical access network

This paper presents a resource management of an arrayed waveguide grating for the design of access network in terms of reconfigurable bandwidth allocation and energy efficient operation. Power consumption characteristics of different channel routing mechanisms are investigated for the downstream transmission. Take-up rates of the subscribers are analyzed to estimate the required optical devices at different phases of the system. Traffic mode operation is also considered to realize the power reduction and energy efficiency for different channel routing mechanisms by the optimal use of components with respect to the active users. Proposed mechanisms are discussed in details and simulation results are presented for the energy savings on network scenario. The model which exploits free spectral range wrapping, has the most promising cost efficient device utilization, power consumption of 285 W and a minimum of 45% energy saving characteristics as compared to the conventional model.