Metropolitan Optical Networks Research Articles

Energy-Efficient Regional Area Metropolitan Optical Access Network (RAMOAN) Using Modified Load Adaptive Sequence Arrangement (M-LASA) Methodology

Energy efficiency in optical networks is one of the important criteria to attain enhanced performance. Better energy efficiency can be attained in optical networks if the resources are properly scheduled. Polling sequences perform resource scheduling based on load requirements, and various methodologies have evolved in recent times for better efficiency. Load adaptive sequence arrangement (LASA) is one of the familiar and efficient methodologies adopted in various methodologies. However, the power consumption and idle time of optical network units are high which should be reduced to attain optimal network performances. Considering this, a modified LASA is presented in this research work for the regional area metropolitan optical access network (RAMOAN). The modified LASA is obtained by integrating the first-in-last-out polling sequence such that the proposed arrangement provides a better coverage radius, minimal power cost, maximum access reach, maximum energy saving, and minimal delay and energy cost. The better performance of the proposed approach is compared with traditional time and wavelength division multiplexed (TWDM), TWDM-protected, and RAMOAN with LASA through simulation analysis to validate the better performances of the proposed model.

Small-form-factor Gaussian-modulated coherent-state transmitter for CV-QKD using a gain-switched DFB laser.

We report a directly modulated distributed feedback laser operating in gain-switching mode for preparing the coherent states required for the Gaussian-modulated coherent-state (GMCS) continuous-variable quantum key distribution (CV-QKD) protocol. The proposed single-component quantum transmitter design eliminates the need for external modulators, decreasing the complexity of GMCS CV-QKD systems. The experimental results demonstrate a potential asymptotic secret key rate value of 2.63 Mbps over an 11-km fiber link, making the directly modulated GMCS transmitter particularly suitable for metropolitan optical networks where compactness, robustness, and low cost are key desirable features.

Coexistence of quantum key distribution and optical transport network based on standard single-mode fiber at high launch power.

There is an increasing demand for multiplexing of quantum key distribution with optical communications in single fiber in consideration of high costs and practical applications in the metropolitan optical network. Here, we realize the integration of quantum key distribution and an optical transport network of 80 Gbps classical data at 15 dBm launch power over 50 km of the widely used standard (G.652 Recommendation of the International Telecom Union Telecom Standardization Sector) telecom fiber. A secure key rate of 11 Kbps over 20 km is obtained. By tolerating a high classical optical power up to 18 dBm of 160 Gbps classical data on single-mode fiber, our result shows the potential and tolerance of quantum key distribution being used in future large capacity transmission systems, such as metropolitan area networks and data centers. The quantum key distribution system is stable, practical, and insensitive to the polarization disturbance of channels by using a phase coding system based on a Faraday-Michelson interferometer. We also discuss the fundamental limit for quantum key distribution performance in the multiplexing environment.

Modelling and performance analysis of DWDM passive optical network

Passive optical networks are emerging as the main technology for building access networks. The current metropolitan optical communication networks operate at 1Gbps, which appears to be insufficient for the future development and exponential growth of traffic from IP services. The existing various traffic-intensive services and the growing interest in 4K video content and streaming services require the introduction of new solutions within passive optical networks (PON). A promising option is the combination of 10 Gbps and above high-speed data transmission with spectral multiplexing. DWDM will provide the required high spectral efficiency, but in contrast will require the use of a proper modulation scheme to achieve a longer distance. In this paper a model for performance analysis and solving optimization problems for DWDM-PON networks is developed. Different signal modulations are considered and a comparative analysis is performed. The behaviour of the system at different input parameters is modelled. Performance analysis is performed by evaluating the spectral characteristics and values of BER and Q-factor.

An effective integration of the PM 16-QAM modulation in enhanced metropolitan networks with the EDFA amplification

Abstract This paper deals with the integration of polarization multiplexed 16-ary quadrature amplitude modulation format in optical metropolitan networks enhanced with the signal amplification. Before expensive experimental setup or practical testing and demonstration, we prefer creating of appropriate simulation platform for the optical transmission system. A novelty can be found in adjusting, optimizing and construction of the proposed optical system and functional parts for any modulation format used. So, such simulation platform is first introduced along with possibilities for numerical simulations of its optical components - laser and amplifier. By this way, essential noise tolerances for comparison with the data under real conditions are included. Subsequently, there are characterized implementations of terminal devices in detail with a possibility for upgrading to the dual-polarization mode operation. Finally, simulation results from the simulation platform are presented and a discussion about demands for effective exploitation of the polarization multiplexed 16-ary quadrature amplitude modulation in enhanced optical metropolitan networks concludes our contribution.

Plug-and-play continuous-variable quantum key distribution for metropolitan networks.

We report a plug-and-play continuous variable quantum key distribution system (CV-QKD) with Gaussian modulated quadratures and a true local oscillator. The proposed configuration avoids the need for frequency locking two narrow line-width lasers. To minimize Rayleigh back-scattering, we utilize two independent fiber strands for the distribution of the laser and the transmission of the quantum signals. We further demonstrate the quantum-classical co-existing capability of our system by injecting high-power classical light in both fibers. A secret key rate up to 0.88 Mb/s is obtained by using two fiber links of 13 km and up to 0.3 Mb/s when adding 4 mW of classical light in the optical fiber used for transmitting the quantum signal. The reported performance indicates that the proposed QKD scheme has the potential to become an effective low-cost solution for metropolitan optical networks.

Utilization of 10 Gbps DWDM System with Duobinary Modulation into Passive Optical Network

Passive optical networks are considered to be the most promising solution for future access networks. Growing demand for capability and high bit rate transmission has become an important part of metropolitan optical communication networks in recent years. Currently deployed 1 Gbps passive optical networks do not seem to be suitable for future demands. This paper deals with the utilization of 10 Gbps DWDM (Dense Wavelength Division Multiplex) in PON (Passive Optical Network) using simulation tool OptSim. Our goal was to create passive optical network based on the real passive optical distribution path using OTDR and to show the possibility of utilization of DWDM in such network. We also describe optical duobinary modulation as a future candidate for such network and its advantages over commonly used intensity modulation. Performance of DWDM-PON with optical duobinary modulation and intensity modulation with direct detection is analyzed using BER (Bit Error Rate) and Q factor measurements.

Experimental Validation of Time-Synchronized Operations for Software-Defined Elastic Optical Networks

Elastic optical networking (EON) has been proposed as a solution to efficiently exploit the spectrum resources in the physical layer of optical networks. Moreover, by centralizing legacy generalized multiprotocol label switching control-plane functionalities and providing a global network view, software-defined networking (SDN) enables advanced network programmability valuable to control and configure the technological breakthroughs of EON. In this paper, we review our recent proposal [Optical Fiber Communication Conf., 2017, paper W4J.6] of time-synchronized operations (TSO) to minimize disruption time during lightpath reassignment in EON. TSO has been recently standardized in SDN, and here we discuss its implementation using NETCONF and OpenFlow in optical networks. Subsequently, we update our analytical model considering an experimental characterization of the WSS operation time. Then, we extend our previous work with an experimental validation of TSO for lightpath reassignment in a five-node metropolitan optical network test-bed. Results validate the convenience of our TSO-based approach against a traditional asynchronous technique given its reduction of disruption time, while both techniques maintain a similar network performance in terms of optical signal-to-noise ratio and optical power budget.

SDN control of optical nodes in metro networks for high capacity inter-datacentre links

Worldwide demand for bandwidth has been growing fast for some years and continues to do so. To cover this, mega datacentres need scalable connectivity to provide rich connectivity to handle the heavy traffic across them. Therefore, hardware infrastructures must be able to play different roles according to service and traffic requirements. In this context, software defined networking (SDN) decouples the network control and forwarding functions enabling the network control to become directly programmable and the underlying infrastructure to be abstracted for applications and network services. In addition, elastic optical networking (EON) technologies enable efficient spectrum utilization by allocating variable bandwidth to each user according to their actual needs. In particular, flexible transponders and reconfigurable optical add/drop multiplexers (ROADMs) are key elements since they can offer degrees of freedom to self adapt accordingly. Thus, it is crucial to design control methods in order to optimize the hardware utilization and offer high reconfigurability, flexibility and adaptability. In this paper, we propose and analyze, using a simulation framework, a method of capacity maximization through optical power profile manipulation for inter datacentre links that use existing metropolitan optical networks by exploiting the global network view afforded by SDN. Results show that manipulating the loss profiles of the ROADMs in the metro-network can yield optical signal-to-noise ratio (OSNR) improvements up to 10 dB leading to an increase in 112% in total capacity.

DSP-enabled reconfigurable and transparent spectral converters for converging optical and mobile fronthaul/backhaul networks.

Dynamically reconfigurable and transparent signal spectral conversion is expected to play a vital role in seamlessly integrating traditional metropolitan optical networks and mobile fronthaul/backhaul networks. In this paper, a simple digital signal processing (DSP)-enabled spectral converter is proposed and extensively investigated, for the first time, which just utilizes a single standard dual-parallel Mach-Zehnder modulator (DP-MZM) driven by SDN-controllable RF signals and DC bias currents. As an important thrust of the paper, optimum operating conditions of the proposed converter are analytically identified, statistically examined and experimentally verified. Optimum operating condition-supported spectral converter performances in IMDD-based network nodes are explored both theoretically and experimentally in terms of frequency detuning range-dependent conversion efficiency, spectral conversion-induced OSNR/power penalty and transparency to input signal characteristics. The proposed spectral converter has unique advantages including low configuration complexity, strict transparency, SDN-controllable performance reconfigurability and flexibility, as well as negligible spectral conversion-induced latency.

Stabilized microwave-frequency transfer using optical phase sensing and actuation.

We present a stabilized microwave-frequency transfer technique that is based on optical phase sensing and optical phase actuation. This technique shares several attributes with optical-frequency transfer and, therefore, exhibits several advantages over other microwave-frequency transfer techniques. We demonstrated the stabilized transfer of an 8000 MHz microwave-frequency signal over a 166 km metropolitan optical fiber network, achieving a fractional frequency stability of 6.8×10-14  Hz/Hz at 1 s integration and 5.0×10-16  Hz/Hz at 1.6×104  s. This technique is being considered for use on the Square Kilometre Array SKA1-mid radio telescope.

Optimized Superscalar Parallelization-Based Carrier Phase Recovery for Agile Metro Optical Networks

In this paper, we present a format-transparent carrier phase recovery algorithm for the agile metropolitan optical networks based on an optimized superscalar parallelization structure. The pilot overhead and the buffer size in the superscalar parallelization can be minimized by optimizing the parallelization structure depending on the required laser linewidth tolerance of the system. The trade-off between the laser linewidth tolerance and the reduction of buffer size in the proposed superscalar parallelization is revealed in simulations for 16-QAM, 32-QAM, and 64-QAM, respectively. The results indicate that the buffer size in the superscalar parallelization can be reduced significantly when commercially available external cavity lasers (ECL) are employed for coherent detection in metro links beyond 100 Gb/s. Experiments are further conducted in a single-channel system with ECLs as the transmitter and local oscillator lasers to demonstrate the reduction of the pilot overhead and buffer size using the proposed superscalar parallelization compared with the previous superscalar structures.

Implications of in-band crosstalk on DQPSK signals in ROADM-based metropolitan optical networks

Metropolitan optical networks can be designed to transport a multitude of signals with different bit rates and modulations formats. In this way, in-band crosstalk signals, originated from imperfect isolation inside ROADM (Reconfigurable Optical Add and Drop Multiplexer)-based optical nodes, will potentially have a different modulation format than the primary signal. In this paper, the origin of in-band crosstalk in a typical ROADM is analysed and its impact on differential quadrature phase-shift keying (DQPSK) signals is assessed through an analytical formalism based on the moment generating function (MGF) of the receiver decision variable. Various scenarios are analysed including the case of multiple interfering terms with different modulation formats, namely the on-off keying (OOK). It is concluded that the OOK interferer is more detrimental than the DQPSK interferer for DQPSK systems, or than the differential phase-shift keying (DPSK) interferer for DPSK systems.

Entanglement Distribution in Optical Networks

The ability to generate entangled photon pairs over a broad wavelength range opens the door to the simultaneous distribution of entanglement to multiple users in a network by using centralized sources and flexible wavelength-division multiplexing schemes. Here, we show the design of a metropolitan optical network consisting of tree-type access networks, whereby entangled photon pairs are distributed to any pair of users, independent of their location. The network is constructed employing commercial off-the-shelf components and uses the existing infrastructure, which allows for moderate deployment costs. We further develop a channel plan and a network-architecture design to provide a direct optical path between any pair of users; thus, allowing classical and one-way quantum communication, as well as entanglement distribution. This allows the simultaneous operation of multiple quantum information technologies. Finally, we present a more flexible backbone architecture that pushes away the load limitations of the original network design by extending its reach, number of users and capabilities.

Subcarrier Wave Quantum Key Distribution in Telecommunication Network with Bitrate 800 kbit/s

In the course of work on creating the first quantum communication network in Russia we demonstrated quantum key distribution in metropolitan optical network infrastructure. A single-pass subcarrier wave quantum cryptography scheme was used in the experiments. BB84 protocol with strong reference was chosen for performing key distribution. The registered sifted key rate in an optical cable with 1.5 dB loss was 800 Kbit/s. Signal visibility exceeded 98%, and quantum bit error rate value was 1%. The achieved result is a record for this type of systems.

Experimental-based subsystem models for simulation of heterogeneous optical networks

This work presents and analyzes experimental-based subsystem models for Erbium doped fiber amplifiers (EDFAs) and wavelength selective switches (WSSs) under operation in a metropolitan optical network testbed. Firstly, the performance of the EDFAs and two gain control types are analyzed in a heterogeneous experimental setup with lightpaths modulated at 10G/100G/200G. Secondly, the WSS optical shape filter is experimentally characterized. Subsequently, simulation models are proposed accordingly to the experimental data obtained from the experimental setups. Results of output power and spectrum shape for both amplifiers under test showed good agreement between simulation and experiment. In addition, the optical signal-to-noise ratio (OSNR) for all channels was also analyzed and it was obtained error values bellow 1 dB, which are within an acceptable error margin. The developed sub-system models will provide greater flexibility to simulate different network scenarios and enable the development and validation of future optical network intelligence algorithms.

English

In metropolitan optical networks, with the increasing growth and demand for capability, high bit rate transmission has recently become an important part of communication. Duobinary modulation is more efficient format for transmitting high speed optical signals over bandwidth limited channel. The duobinary modulation format for long haul and WDM transmission links is the one that has a narrow spectral width, low susceptibility to fiber nonlinearity, large dispersion tolerance and good transmission performance and has a simple and cost-effective configuration

Quantum metropolitan optical network based on wavelength division multiplexing

Quantum Key Distribution (QKD) is maturing quickly. However, the current approaches to its application in optical networks make it an expensive technology. QKD networks deployed to date are designed as a collection of point-to-point, dedicated QKD links where non-neighboring nodes communicate using the trusted repeater paradigm. We propose a novel optical network model in which QKD systems share the communication infrastructure by wavelength multiplexing their quantum and classical signals. The routing is done using optical components within a metropolitan area which allows for a dynamically any-to-any communication scheme. Moreover, it resembles a commercial telecom network, takes advantage of existing infrastructure and utilizes commercial components, allowing for an easy, cost-effective and reliable deployment.

Two-Color One-Way Frequency Transfer in a Metropolitan Optical Fiber Data Network

Two-color one-way frequency transfer through one strand of optical fiber is an alternative method to two-way frequency transfer, and is useful if unknown asymmetries exist in the link due to different paths for each direction. The term “two-color” refers to the ability to send signals at two different wavelengths utilizing the same fiber in one direction. The method is suitable for implementation in existing urban Single Mode Fiber networks, for instance in networks that are utilized for data and television communication. It is therefore able to coexist with data channels in wavelength-division multiplexing (WDM) systems. It performs as a dynamical control of transit time and simultaneously enables a real-time phase stabilized output signal. This paper presents results from a comparison of two cesium beam frequency standards separated by about 3 km over an optical fiber network located in a metropolitan area in Sweden. The cesium standards were simultaneously compared to each other with a Global Positioning System (GPS) satellite link and over optical fibers, so that the optical fiber technique could be evaluated with respect to the GPS technique. The difference in frequency stability between the two methods is shown to be about 3 × 10-15 over an averaging interval of 10 000 s

Secure Optical Networks Based on Quantum Key Distribution and Weakly Trusted Repeaters

In this paper we explore how recent technologies can improve the security of optical networks. In particular, we study how to use quantum key distribution (QKD) in common optical network infrastructures and propose a method to overcome its distance limitations. QKD is the first technology offering information theoretic secret-key distribution that relies only on the fundamental principles of quantum physics. Point-to-point QKD devices have reached a mature industrial state; however, these devices are severely limited in distance, since signals at the quantum level (e.g. single photons) are highly affected by the losses in the communication channel and intermediate devices. To overcome this limitation, intermediate nodes (i.e. repeaters) are used. Both, quantum-regime and trusted, classical, repeaters have been proposed in the QKD literature, but only the latter can be implemented in practice. As a novelty, we propose here a new QKD network model based on the use of not fully trusted intermediate nodes, referred as weakly trusted repeaters. This approach forces the attacker to simultaneously break several paths to get access to the exchanged key, thus improving significantly the security of the network. We formalize the model using network codes and provide real scenarios that allow users to exchange secure keys over metropolitan optical networks using only passive components. Moreover, the theoretical framework allows to extend these scenarios not only to accommodate more complex trust constraints, but also to consider robustness and resiliency constraints on the network.