Long-haul Networks Research Articles

A New Paradigm in High-Speed and High-Efficiency Silicon Photodiodes for Communication—Part I: Enhancing Photon–Material Interactions via Low-Dimensional Structures

Photodetectors (PDs) used in communication systems require ultrafast response, high efficiency, and low noise. PDs with such characteristics are increasingly in demand for data centers, metro data links, and long-haul optical networks. In a surface-illuminated PD, high speed and high efficiency are often a tradeoff, since a high-speed device needs a thin absorption layer to reduce the carrier transit time, whereas a high-efficiency device needs a thick absorption layer to compensate for the low absorption coefficient of some semiconductors such as Si and Germanium (Ge) or SiGe alloys at wavelengths near the bandgap. In this part of this review, we present the recent efforts in enhancing the photon–material interactions by using low-dimensional structures that can control light for more interaction with the photoabsorbing materials, slow down the propagation group velocity and reduce surface reflection. We present recent demonstrations of high-speed PDs based on nanostructures enabled by both synthetic bottom-up or transformative top-down processing methods. In particular, we detail a CMOS-compatible ultrafast surface-illuminated Si PD with 30-ps full-width at half-maximum, and >50% efficiency at 850 nm. A complementary discussion on device challenges and the integration of low-dimensional structures will be presented in the part II of this review.

Optimized Hybrid Raman/EDFA Amplifier Placement for DWDM Mesh Networks

The minimization of the number of expensive 3R regenerators required at intermediate nodes is a key task when planning long-haul optical transport networks. Combining Raman amplification with Erbium-doped fiber amplifiers (EDFAs) is one of the strategies that can be exploited to achieve this objective, especially in the presence of long fiber spans. Given that hybrid Raman/EDFA amplifiers are more expensive than EDFAs, their deployment should also be minimized. However, determining the number and location of these amplifiers in a mesh optical network is a complex problem because of the overlap of lightpaths with different source and destination nodes at each link. A method to optimize the placement of hybrid Raman/EDFA amplifiers in mesh optical networks is described in this paper. The proposed method analyzes the network as a whole and determines where to introduce Raman amplification such that the 3R regenerator count is minimized while also keeping the number of hybrid Raman/EDFA amplifiers at a minimum. It is shown that, in a reference mesh optical network, the proposed method clearly outperforms the simpler placement approach based solely on fiber span attenuation.

Estimation and Fusion for Tracking Over Long-Haul Links Using Artificial Neural Networks

In a long-haul sensor network, sensors are remotely deployed over a large geographical area to perform certain tasks, such as tracking and/or monitoring of one or more dynamic targets. A remote fusion center fuses the information provided by these sensors so that a final estimate of certain target characteristics—such as the position—is expected to possess much improved quality. In this work, we pursue learning-based approaches for estimation and fusion of target states in long-haul sensor networks. In particular, we consider learning based on various implementations of artificial neural networks (ANNs). The joint effect of 1) imperfect communication condition, namely, link-level loss and delay, and 2) computation constraints, in the form of low-quality sensor estimates, on ANN-based estimation and fusion, is investigated by means of analytical and simulation studies.

TSDX: Enabling Impairment-Aware All-Optical Inter-Domain Exchange

Optical transmission systems exist ubiquitously in data center, access, metro and long-haul networks, and are divided into different autonomous domains based on different carrier ownership, network equipment manufacturers, geographical location, etc. Software-defined Internet exchange methods have been proposed to solve the long-standing problem of inter-domain routing and enable control flexibility in layer-3 networks, and software-defined networking (SDN) has also been introduced to optical networks and much progress has been made to enhance optical network control capability. In this paper, we investigate a transparent software-defined exchange (tSDX) with real-time impairment-aware service level agreement (SLA) guarantees for multidomain optical networks. An SDN-based hierarchical control architecture is designed and implemented. End-to-end, impairment-aware wavelength path provisioning is experimentally realized in a multidomain network. Real-time optical signal to noise ratio based optical performance monitoring, together with inter-domain negotiation enabled by our proposed SDN control architecture, serves as an SLA guarantee for 100-Gbps polarization-multiplexed quadrature phase-shift keying signals in dense wavelength division multiplexed transmission.

Resource Allocation for Elastic Optical Networks Using Geometric Optimization

Resource allocation with quality of service constraints is one of the most challenging problems in elastic optical networks that is normally formulated as a mixed-integer nonlinear optimization program. In this paper, we focus on novel properties of geometric optimization and provide a heuristic approach for resource allocation that is much faster than its mixed-integer nonlinear counterpart. Our heuristic consists of two main parts for routing/traffic ordering and power/spectrum assignment. It aims at minimization of the transmit optical power and spectrum usage constrained to the quality of service and physical requirements. We consider three routing and three traffic ordering procedures and compare them in terms of total transmit optical power, total received noise power, and total nonlinear interference including self- and cross-channel interferences. We propose a posynomial expression for the signal-to-noise ratio in which fiber nonlinearities and amplified spontaneous emission noise have been addressed. We also propose posynomial expressions that relate the modulation spectral efficiency to its corresponding minimum required signal-to-noise ratio. We then use the posynomial expressions to develop six geometric formulations for the power/spectrum assignment part of the heuristic that are different in run time, complexity, and accuracy. Simulation results demonstrate that the proposed solution has very good accuracy and much lower computational complexity in comparison with mixedinteger nonlinear formulation. As an example, for the European Cost239 optical network with 126 transmit transponders, the geometric formulation can be more than 22 times faster than its mixed-integer nonlinear counterpart. Numerical results also reveal that, in long-haul elastic optical networks, considering the product of the number of common fiber spans and the transmission bit rate is a better goal function for routing/traffic ordering that can reduce the total transmit optical fiber (total accumulated noise and nonlinear interference) up to 20% (15%).

Review of CMOS Integrated Circuit Technologies for High-Speed Photo-Detection.

The bandwidth requirement of wireline communications has increased exponentially because of the ever-increasing demand for data centers and high-performance computing systems. However, it becomes difficult to satisfy the requirement with legacy electrical links which suffer from frequency-dependent losses due to skin effects, dielectric losses, channel reflections, and crosstalk, resulting in a severe bandwidth limitation. In order to overcome this challenge, it is necessary to introduce optical communication technology, which has been mainly used for long-reach communications, such as long-haul networks and metropolitan area networks, to the medium- and short-reach communication systems. However, there still remain important issues to be resolved to facilitate the adoption of the optical technologies. The most critical challenges are the energy efficiency and the cost competitiveness as compared to the legacy copper-based electrical communications. One possible solution is silicon photonics which has long been investigated by a number of research groups. Despite inherent incompatibility of silicon with the photonic world, silicon photonics is promising and is the only solution that can leverage the mature complementary metal-oxide-semiconductor (CMOS) technologies. Silicon photonics can be utilized in not only wireline communications but also countless sensor applications. This paper introduces a brief review of silicon photonics first and subsequently describes the history, overview, and categorization of the CMOS IC technology for high-speed photo-detection without enumerating the complex circuital expressions and terminologies.

Remote third shift EAST operation: a new paradigm

General Atomics’ (GA) scientists in the United States remotely conducted experimental operation of the experimental advanced superconducting tokamak (EAST) in China during its third shift. Scientists led these experiments in a dedicated remote control room that utilized a novel computer science hardware and software infrastructure to allow data movement, visualization, and communication on the time scale of EAST’s pulse cycle. This Fusion Science Collaboration Zone infrastructure allows the movement of large amounts of data between continents in a short time scale with a 300-fold increase in data transfer rate over that available using the traditional transmission protocol. Real-time data from control systems is moved almost instantaneously. An event system tied to the EAST pulse cycle allows automatic initiation of data transfers, resulting in bulk EAST data to be transferred to GA within minutes. The EAST data at GA is served via MDSplus to approved US collaborators avoiding multiple US clients from requesting data from EAST and competing for the long-haul network’s bandwidth. At present there are 37 approved scientists from 8 US research institutions.

770-Gb/s PDM-32QAM Coherent Transmission Using InP Dual Polarization IQ Modulator

We experimentally demonstrate 770-Gb/s (77-Gbd PDM-32QAM) transmission on a single wavelength using an indium phosphide dual polarization IQ modulator over 320 km of standard single mode fiber, which is suitable for low-cost metro networks and datacenter interconnects. Moreover with the same setup, we also demonstrate transmissions of 84-Gbd polarization division multiplexed (PDM)-16QAM and 84-Gbd PDM-8QAM signals over 960 and 1980 km distances, respectively, for regional and long-haul networks.

Dynamic mitigation of EDFA power excursions with machine learning.

Dynamic optical networking has promising potential to support the rapidly changing traffic demands in metro and long-haul networks. However, the improvement in dynamicity is hindered by wavelength-dependent power excursions in gain-controlled erbium doped fiber amplifiers (EDFA) when channels change rapidly. We introduce a general approach that leverages machine learning (ML) to characterize and mitigate the power excursions of EDFA systems with different equipment and scales. An ML engine is developed and experimentally validated to show accurate predictions of the power dynamics in cascaded EDFAs. Recommended channel provisioning based on the ML predictions achieves within 1% error of the lowest possible power excursion over 94% of the time. We also showcase significant mitigation of EDFA power excursions in super-channel provisioning when compared to the first-fit wavelength assignment algorithm.

Benefits of sliceable photonic-based transponders in metro and long-haul networks

In this paper, we analyze benefits of photonic integration-based sliceable transponders (sliceable photonics) compared to discrete optics transponder-based solutions (CFP/CFP2--C form-factor pluggable) in metro and long-haul networks. The metrics considered for comparison include the number of transponders, bandwidth use and power utilization. We assumed an OTN-based network with QPSK and 16QAM modulation schemes for both the scenarios. We observed that sliceable photonics is much more advantageous than discrete transponder optics in both metro and long-haul networks. We also compared the effect of modulation schemes on the efficiency of the network by comparing QPSK and 16QAM in discrete transponder optics and show that 16QAM in discrete transponder optics makes the network more inefficient.

Review of Comparative Booster Performances of Semiconductor Optical Amplifier and Erbium-doped-fiber Amplifier for use in Future Long-haul Optical Networks

This study reviews the performance of the Semiconductor Optical Amplifier (SOA) photonic device with the classic Erbium-doped-fiber-amplifier (EDFA). In certain situations, we report that the SOA out-performs the EDFA, particularly in terms of gain and Q-factor and BER of the post-amplified received signal. This substantiates its potential as a viable replacement for the EDFA in future all-optical, long haul networks.

Recent Developments of Fiber Diagnosis Technologies in Optical Communication

This paper reviews novel distributional measurement technologies that were recently developed for monitoring the health of optical fibers in communication systems. The development of these technologies has an extensive history. Physical phenomena of optical fibers have been exploited, and several requirements in managing telecommunication systems have been considered. However, significant progress is still required for diagnosing fibers in long-haul and access networks. In addition, these technologies may stimulate the development of distributional fiber sensors.

Staggered Scheduling of Sensor Estimation and Fusion for Tracking Over Long-Haul Links

Networked sensing can be found in a multitude of real-world applications. We focus on the communication-and computation-constrained long-haul sensor networks, where sensors are remotely deployed over a vast geographical area to perform certain tasks. Of special interest is a class of such networks where sensors take measurements of one or more dynamic targets and send their state estimates to a remote fusion center via long-haul satellite links. The severe loss and delay over such links can easily reduce the amount of sensor data received by the fusion center, thereby limiting the potential information fusion gain and resulting in suboptimal tracking performance. In this paper, starting with the temporal-domain staggered estimation for an individual sensor, we explore the impact of the so-called intra-state prediction and retrodiction on estimation errors. We then investigate the effect of such estimation scheduling across different sensors on the spatial-domain fusion performance, where the sensing time epochs across sensors are scheduled in an asynchronous and staggered manner. In particular, the impact of communication delay and loss as well as sensor bias on such scheduling is explored by means of numerical and simulation studies that demonstrate the validity of our analysis.

Large-Area Low-Loss Fibers and Advanced Amplifiers for High-Capacity Long-Haul Optical Networks [Invited

This paper reviews recent progress on ultra-large-area low-loss fibers for next-generation high-capacity terrestrial long-haul optical networks. The key optical fiber properties of new class fibers are described, and their impact on the transmission performance for 400 Gb/s polarization-multiplexed multilevel modulation coherent transmissions is discussed. The practical consideration of the large-area fibers, such as splicing and cabling for terrestrial transport systems, is also briefly addressed. In addition, we describe two advanced optical fiber amplifier technologies that will improve the efficiency in utilization of optical networking and reduce total system costs. The design and performance of an arrayed optical fiber amplifier using a compact ribbonized Er-doped fiber (EDF) for next-generation reconfigurable optical add/drop multiplexer nodes are discussed, and the performance characteristics of complementary Raman/EDFA, which has +70 nm bandwidth for seamless C+L-band transmissions, are described. Finally, we present the experimental demonstration of transmission of 34.6 Tb/s in 70 nm single band over 2400 km fiber.

Ultrafast gain recovery in a QW-SOA and its application for 40 Gb/s regenerative format conversion from NRZ-DPSK to RZ-OOK

We propose a scheme to realize gain recovery of the order of a few picoseconds in a typical quantum well semiconductor optical amplifier (QW-SOA) using a pump signal with amplitude dips. In the scheme, the gain recovery is determined by the fast carrier density depletion and carrier temperature heating processes. The ultrafast gain recovery is numerically verified by a completed model combining the QW band structure calculation with rate equations in the QW-SOA. In practice, a pump signal with amplitude dips can be partly characterized by a non-return-to-zero differential phase-shift keying (NRZ-DPSK) signal generated by a Mach–Zehnder modulator. Therefore, we experimentally demonstrate 40 Gb/s wavelength-converting and regenerative format conversion from NRZ-DPSK to return-to-zero on–off keying (RZ-OOK), which may be a key function to connect different kinds of modulation formats at gateway nodes between long-haul backbone networks and metro area networks.

Add and Drop Architectures for Multi-Carrier Transponders in EONs

The elastic optical network (EON) is a paradigm for optical networks, based on the combination of a flexible grid, advanced transmission techniques, and bandwidth-variable optical switching. Recent studies on EONs have been focused on multi-carrier transponders with coherent detection. Such transponders can achieve high-rate (e.g., 1 Tb/s) lightpaths through super-channels. A particular case of the multi-carrier transponder is the sliceable bandwidth variable transponder (S-BVT) where the generated flows can also be routed onto different paths and toward different destinations. The add and drop (A&D) module connecting transponders to the optical cross connect plays an important role in the design of the network node. In particular, depending on the A&D architecture, the flexibility provided by the multi-carrier transponder and the S-BVTs may be partially limited. This paper gives first a technological overview of different A&D architectures. In particular, the coupler/splitter, multicast switch, and wavelength-selective switch technologies for A&D are reviewed. Then, we investigate how different A&D architectures influence the benefit of elastic spectral efficiency in a long-haul meshed network scenario, looking for a trade-off between costs and performance.

Cognitive algorithm using fuzzy reasoning for software-defined optical network

We propose a cognitive algorithm based on Fuzzy C-Means (FCM) technique for the learning and decision-making functionalities of software-defined optical networks (SDONs). SDON is a new optical network paradigm where the control plane is decoupled from the data plane, thus providing a degree of software programmability to the network. Our proposal is to add the FCM algorithm to the SDON control plane in order to achieve a better network performance, when compared with a non-cognitive control plane. In this context, we illustrate the use of the FCM algorithm for determining, in real time and autonomously, the modulation format of high-speed flexible rate transponders in accordance with the quality of transmission of optical channels. The performance of this FCM algorithm is evaluated via computational simulations for a long-haul network and compared to the case-based reasoning (CBR) algorithm, which is commonly used in optical cognitive networks. We demonstrate that FCM outperforms CBR in both fastness and error avoidance, achieving 100 % of successful classifications, being two orders of magnitude faster. Additionally, we propose a definition of cognitive optical networking and an architecture for the SDON control plane including the FCM engine.

Controllable pulse width of bright similaritons in a tapered graded index diffraction decreasing waveguide.

We obtain the bright similariton solutions for generalized inhomogeneous nonlinear Schrödinger equation (GINLSE) which governs the pulse propagation in a tapered graded index diffraction decreasing waveguide (DDW). The exact solutions have been worked out by employing similarity transformations which involve the mapping of the GINLSE to standard NLSE for the certain conditions of the parameters. By making use of the exact analytical solutions, we have investigated the dynamical behavior of optical similariton pairs and have suggested the methods to control them as they propagate through DDW. Moreover, pulse width of similariton is controlled through various profiles. These results are helpful to understand the similaritons in DDW and can be potentially useful for future experiments in optical communications which involve optical amplifiers and long-haul telecommunication networks.

Simulative Analysis on Hybrid Optical Amplifier in Fiber Distributed Ring for WAN

tremendous growth of the high speed Internet and data traffic has created an enormous demand for transmission bandwidth of dense wavelength division multiplexed (DWDM) optical communication systems. With the advancement of wideband fiber-optical amplifiers, DWDM optical transmission systems are capable of providing capacities in excess of hundreds of gigabits per second over hundreds of kilometers on a single pair of fibres in long-haul networks. In this paper the investigations in FIBRE Distributed ring for wide area network for six nodes, 45 channels. The main target of this research work is to reduce the data impairment in the data transmission. In this manuscript we investigate the performance on the basis of Q factor, Eye diagram and BER from the simulation setup designed on Hybrid Optical Amplifier in Fiber Distributed Ring for Wide Area Network.

Effect of Retransmission and Retrodiction on Estimation and Fusion in Long-Haul Sensor Networks

In a long-haul sensor network, sensors are remotely deployed over a large geographical area to perform certain tasks, such as target tracking. In this paper, we study the scenario where sensors take measurements of one or more dynamic targets and send state estimates of the targets to a fusion center via satellite links. The severe loss and delay inherent over the satellite channels reduce the number of estimates successfully arriving at the fusion center, thereby limiting the potential fusion gain and resulting in suboptimal accuracy performance of the fused estimates. In addition, the errors in target-sensor data association can also degrade the estimation performance. To mitigate the effect of imperfect communications on state estimation and fusion, we consider retransmission and retrodiction. The system adopts certain retransmission-based transport protocols so that lost messages can be recovered over time. Moreover, retrodiction/smoothing techniques are applied so that the chances of incurring excess delay due to retransmission are greatly reduced. We analyze the extent to which retransmission and retrodiction can improve the performance of delay-sensitive target tracking tasks under variable communication loss and delay conditions. Simulation results of a ballistic target tracking application are shown in the end to demonstrate the validity of our analysis.