Showing papers presented at "International Conference on Transparent Optical Networks in 2012"

Quality metrics for optical signals: Eye diagram, Q-factor, OSNR, EVM and BER

Abstract: Measuring the quality of optical signals is one of the most important tasks in optical communications. A variety of metrics are available, namely the general shape of the eye diagram, the optical signal-to-noise power ratio (OSNR), the Q-factor as a measure of the eye opening, the error vector magnitude (EVM) that is especially suited for quadrature amplitude modulation (QAM) formats, and the bit error ratio (BER). While the BER is the most conclusive quality determinant, it is sometimes difficult to quantify, especially for simulations and off-line processing. We compare various metrics analytically, by simulation, and through experiments. We further discuss BER estimates derived from OSNR, Q-factor and EVM data and compare them to measurements employing six modulation formats at symbol rates of 20 GBd and 25 GBd, which were generated by a software-defined transmitter. We conclude that for optical channels with additive Gaussian noise the EVM metric is a reliable quality measure. For nondata-aided reception, BER below 0.01 can be estimated from measured EVM.

Mobile backhaul in heterogeneous network deployments: Technology options and power consumption

Abstract: Mobile communication networks account for 0.5% of the global energy consumption, a value that is expected to double within the next five years. For this reason, means of reducing the energy consumption in cellular mobile radio networks has recently gained great interest within the research community. In mobile networks the backhaul contribution to the total power consumption is usually neglected because of its limited impact compared to that of the radio base stations. However, meeting the almost exponential increase in mobile data traffic requires a large number of (mainly small) base stations. This means that backhaul networks will take a significant share of the cost and the energy consumption in future systems. Their actual contribution to the energy consumption will depend on the radio base station deployment scenario as well as on the technology and topology choices for the backhaul itself. This paper presents an initial assessment of the power consumption of two established backhaul technologies, i.e., fiber and microwave. For the microwave case, three backhaul topologies are considered, i.e., tree, ring and star, while for the fiber case only one topology is analysed, i.e., a dedicated point-to-point star. The presented results, assuming off-the-shelf products and based on todays network capacity levels, confirm the importance of considering the backhaul when minimizing the total power consumption in heterogeneous network scenarios. They also show the impact of the basic technology and topology choices of the backhaul for minimizing total power consumption.

A survey of recent developments on flexible/elastic optical networking

Abstract: There is a growing awareness that the utilized bandwidth of deployed optical fiber is rapidly approaching its maximum limit. Given the possibility for such capacity crunch, the research community has focused on seeking solutions that make the most out of the scarce network resources (such as the fiber bandwidth) and allow accommodating the ever-increasing traffic demands. In such context, new spectrum efficient optical networking techniques have been introduced as a way to offer efficient utilization of the available optical resources. "Flexible", "elastic", "tunable", "gridless" or "adaptive" are few examples of the terms used in literature to describe solutions that migrate from the fixed WDM single line rate systems to systems that provide support for the most efficient bandwidth utilization. In this paper, we review the recent developments on the research topic of flexible/elastic networking and we highlight the future research challenges.

On the effect of regenerator placement on spectrum usage in translucent Elastic Optical Networks

Abstract: Translucent optical networks are considered as a promising solution for reducing the electronic processing overhead of opaque optical networks thanks to a cost-effective use of regenerator resources. In a translucent Elastic Optical Network (EON), in which each transparent segment of an optical path may have different spectrum requirements, the use of regenerators will have an impact on the spectrum occupancy in the network. In this work, we focus on the spectrum allocation and regenerator placement problem and we show that the use of regenerators reduces considerably the utilization of spectrum resources in a translucent EON.

Wavelength switched hybrid TDMA/WDM (TWDM) PON: A flexible next-generation optical access solution

Abstract: In this paper, we propose the system concepts of a next-generation wavelength switched hybrid time division multiple access and wavelength division multiplexing (TWDM) passive optical network (PON) architecture. In this architecture, wavelength selective switches (WSSs) are used at the remote node to improve flexibility, data security and power budget compared to other TWDM-PON variants. We map the proposed architecture to the requirements of next-generation optical access networks in a 2020 perspective. Finally, we benchmark the proposed architecture with other proposed TWDM-PON solutions.

Numerical and experimental investigation of an optical high-Q spiral resonator gyroscope

Abstract: An integrated optical gyroscope based on a passive silica-on-silicon resonator with a footprint of about 20 cm2 is reported in this paper. The optical characterization of the cavity has been carried out and the main experimental results are discussed. We derive the sensor performance in terms of minimum detectable angular velocity (or resolution) δΩ, underlining also the impact of the insertion loss in the silica-on-silicon device. Finally, we describe some technical approaches for improving the resolution.

Performance analysis of noise cancellation in a diversity combined ACO-OFDM system

Abstract: In this paper we analyze the combined performance of noise-cancellation and diversity-combining in an ACO-OFDM system. Noise cancellation and diversity combining are two techniques which have each been shown to improve the performance of ACO-OFDM, each giving a maximum improvement of 3dB. As noise cancellation reduces the noise at the detection point, while diversity combining adds two different signal components, it might be expected that combining the two techniques could give further performance gains. In this paper we show analytically that no additional performance gain can be achieved by combining the techniques. Simulation results are presented which are consistent with the analysis. It is also observed that the noise cancellation is more computationally efficient than diversity combining.

The effect of defocus blur on a spatial OFDM optical wireless communication system

Abstract: Imperfect focusing of the receiver can be an important impairment in MIMO optical wireless systems using imaging receivers. This paper investigates the effect of defocus blur on an optical wireless system using spatial orthogonal frequency division multiplexing (OFDM). It is shown that when defocus blur is the only impairment, and when transmitter and receiver are perfectly aligned, the defocus blur causes the received constellation points to be attenuated. Simulation results show that the signal-to-noise ratio (SNR) penalty caused by defocus blur is less for a system using spatial asymmetrically clipped optical OFDM than for one using spatial DC biased optical OFDM.

From GMPLS to PCE/GMPLS to OpenFlow: How much benefit can we get from the technical evolution of control plane in optical networks?

Abstract: Control plane techniques are very important for optical networks since they can enable dynamic lightpath provisioning and restoration, improve the network intelligence, and greatly reduce the processing latency and operational expenditure. In recent years, there have been great progresses in this area, ranged from the traditional generalized multi-protocol label switching (GMPLS) to a path computation element (PCE)/GMPLS-based architecture. The latest studies have focused on an OpenFlow-based control plane for optical networks, which is also known as software-defined networking. In this paper, we review our recent research activities related to the GMPLS-based, PCE/GMPLS-based, and OpenFlow-based control planes for a translucent wavelength switched optical network (WSON). We present enabling techniques for each control plane, and we summarize their advantages and disadvantages.

Comparison of OFDM and frequency domain equalization for dispersive optical channels with direct detection

Abstract: In this paper, advanced block-transmission schemes for dispersive optical channels with intensity modulation and direct detection are discussed and compared In the framework of orthogonal frequency division multiplex or its real valued base-band derivate discrete multitone transmission (DMT) we analyze DC-biased DMT, pulse-amplitude modulated DMT as well as asymmetrically clipped DMT The results are compared to those of base-band pulse-amplitude modulation with frequency domain equalization The dispersive optical channel is modeled as a Gaussian type low-pass filter Closed-form expressions to estimate the required optical power are presented Under the constraint of using power loading and no bit loading, we show that frequency domain equalization outperforms DMT

Flexible bandwidth and bit-rate programmability in future optical networks

Abstract: Recent progress in network equipment allows trade-offs to be made between the optical bandwidth, distance-reach, and bit-rate for given optical data channels. We discuss methods to increase the utilization of network resources and thereby to lower the network's cost-per-bit of transport.

A multi-objective approach to design all-optical and translucent optical networks considering CapEx and QoT

Abstract: In this paper we propose a methodology based on an evolutionary multi-objective optimization algorithm, called NSGA-II to design the topology and define the devices for both all-optical and translucent optical network. We aim to define the topology layout and the specification of the optical devices that should be deployed in the network in order to minimize simultaneously the total installation cost of a communication network (CapEx) and the total network blocking probability (performance criterion). To accomplish that, we propose a capital cost model for the network. We considered the following physical layer impairments: losses in optical devices, amplified spontaneous emission in optical amplifier and homodyne crosstalk in optical cross connect, polarization mode dispersion and residual dispersion. Our proposed methodology can solve the network topology design problem taking into account the physical layer impairments and the capital costs simultaneously. We also present a case study to show the effectiveness of our methodology to define the degree of transparency of the network.

Virtual network embedding in optical infrastructures

Abstract: Optical network virtualisation has recently become a hot topic among the research community due to its potential to enable the shaping of the Infrastructure as a Service (IaaS) concept. A major challenge that arises of paramount importance when virtualising a network is the so called Virtual Network (VN) embedding problem. While this problem has been extensively treated for electrical networks, there is very little work regarding Virtual Optical Network (VONs) embedding. This paper addresses the VON embedding problem, giving an insight about the potential challenges and presenting solutions that allow to optimally solving this problem in dynamic network scenarios.

Super-resolution imaging by high-index microspheres immersed in a liquid

Abstract: We demonstrate that the super-resolution imaging of a commercial Blu-ray® disk containing a one-dimensional array of 200 nm width stripes separated by 100 nm width grooves can be achieved using high-index microspheres in a liquid environment. By using barium titanate glass microspheres (2–20 μm diameters) with index around 1.9 totally immersed in isopropanol with index 1.37 we demonstrate better than λ/6 far field resolution, where λ= 600 nm is the peak wavelength of the white-light illumination system. The results of this work can be used in biomedical microscopy, microfluidics and nanophotonics applications for imaging individual cells and/or nanoparticles in a liquid environment.

Laser-induced periodic surface structures (LIPSS) on polymer surfaces

Abstract: Frequently observed structures in laser-surface processing are ripples, also denoted as laser-induced periodic surface structures (LIPSS). Ripples originate from the interference of the incident/refracted laser light with the scattered or diffracted light near the surface. For many polymer surfaces, organized nano-ripple structures surfaces can be induced by irradiation with pulsed UV lasers with pulse lengths in the order of some nanoseconds at fluences well below the ablation threshold and with a large number of laser pulses N. After exposure to linearly polarized radiation at normal incidence, the lateral period of the observed LIPSS is close to the wavelength λ. This type of structures is usually called low spatial frequency LIPSS (LSFL). For femto-second laser light, ripples at polymer surfaces are also observed at a laser fluence above the ablation threshold, even with low numbers of laser pulses N. Under special conditions, another type of ripples with periods as small as λ/3 has been reported. This type of ripples is called high spatial frequency LIPSS (HSFL). We summarize here our work on LIPSS generation at polymers and describe potential applications in the field of self-organized formation of gold nano-wires and nano-structure induced alignment of biological cells cultivated on polymer substrates.

Energy-aware routing optimization in dynamic GMPLS controlled optical networks

Abstract: In this paper, routing optimizations based on energy sources are proposed in dynamic GMPLS controlled optical networks. The influences of re-routing and load balancing factors on the algorithm are evaluated, with a focus on different re-routing thresholds. Results from dynamic network simulations show that re-routing strategies can lower CO 2 emissions compared to the basic energy source routing scheme, and a lower re-routing threshold achieves more savings. The increased blocking probability brought by using re-routing schemes can be compensated by applying load balancing criteria. A trade-off between blocking probability and obtained CO 2 savings is studied.

Planning and designing FTTH networks: Elements, tools and practical issues

Abstract: Fiber-To-The Home (FTTH) provides the offered and new broadband services. Now it is deployed massively worldwide with Passive Optical Networks (PONs), being the EPON and GPON standards the most used. In this paper we consider solutions for planning and designing such optical fiber access networks from the point of view of an incumbent operator; taking into account components administration, mapping tools, design applications and automation resources; therefore, managing infrastructures, materials, geography, houses, buildings and users databases. The networks will be dynamic, so the proposed designs and utilities must also be active to reach thousands of passed homes and to cover the life-cycle of the networks and not only the initial built.

High-speed GaN micro-LED arrays for data communications

Abstract: We report the modulation performance of micro-light-emitting diode arrays with peak emission ranging from 370 to 520 nm, and emitter diameters ranging from 14 to 84 μm. Bandwidths in excess of 400 MHz and error-free data transmission up to 1.1Gbit/s is shown. These devices are shown integrated with electronic drivers, allowing convenient control of individual array emitters. Transmission using such a device is shown at 512 Mbit/s.

Semi-analytical model for linear modal coupling in few-mode fiber transmission

Abstract: This paper proposes a method for the semi-analytical solution of the coupled linear differential equations that describe the linear modal coupling arising in few mode fibers (FMFs) due to waveguide imperfections. The semi-analytical solutions obtained can be used for the modification of the split step Fourier method to include the respective linear effects. Considering a fiber with six linearly polarized modes (or ten modes, taking into account the degenerate versions) the solutions obtained proved to be accurate when compared to the numerical solutions obtained through the Runge-Kutta-Fehlberg method.

Network architectures for CPRI backhauling

Abstract: Mobile networks evolution is heavily driven by the increasing diffusion of broad-band wireless devices. The quickly growing traffic has to be managed by operators drastically reducing CAPEX and OPEX of their networks per transported bandwidth unit: in some cases this may imply the adoption of revolutionary, more than evolutionary approaches. Under this extent, an important case is CPRI backhauling: a new network paradigm implying centralization of mobile base-band units. The paper describes different functional and physical architectures for CPRI backhauling, comparing them under different CAPEX and OPEX impacting aspects.

Selecting the best locations for data centers in resilient optical grid/cloud dimensioning

Abstract: For optical grid/cloud scenarios, the dimensioning problem comprises not only deciding on the network dimensions (i.e., link bandwidths), but also choosing appropriate locations to install server infrastructure (i.e., data centers), as well as determining the amount of required server resources (for storage and/or processing). Given that users of such grid/cloud systems in general do not care about the exact physical locations of the server resources, a degree of freedom arises in choosing for each of their requests the most appropriate server location. We will exploit this anycast routing principle (i.e., source of traffic is given, but destination can be chosen rather freely) also to provide resilience: traffic may be relocated to alternate destinations in case of network/server failures. In this study, we propose to jointly optimize the link dimensioning and the location of the servers in an optical grid/cloud, where the anycast principle is applied for resiliency against either link or server node failures. While the data center location problem has some resemblance with either the classical p-center or k-means location problems, the anycast principle makes it much more difficult due to the requirement of link disjoint paths for ensuring grid resiliency.

Radial polarization of periodically focused modes in chains of dielectric spheres

Abstract: Recently we showed that light focusing and transport properties of chains of dielectric spheres with D>>10λ, where D is the diameter of the sphere and λ is the wavelength, are dominated by periodically focused modes (PFMs) which have extremely small propagation losses [12]. In this work we show that along with a special case of PFMs in chains of spheres with index n = √3 which propagates in such structures without losses, similar periodic modes exist in a broad range of indices from 1.4 to 2.0. For each n such generalized PFMs have various radial extents in the regions between the neighbouring focused beams. We show that for 10-sphere long chains with 1.68 < n < 1.80 such modes have total propagation losses smaller than 1 dB. Using numerical ray tracing, we demonstrate that such chains filter radially polarized beams. Using collimated incident beams, a polarization degree in excess of 0.9 is demonstrated for 10-sphere long chains for 1.68 < n < 1.80 range. These properties make chains of microspheres instrumental for developing novel focusing and polarization components.

A control plane framework for future cognitive heterogeneous optical networks

Abstract: Future optical networks are expected to provide an efficient infrastructure able to deliver a growing number of services, which have to meet various requirements in terms of quality of service. To achieve this objective the physical network is going through an evolution aimed at increasing its flexibility in terms of spectrum utilization and its level of heterogeneity in terms of supported services and technologies. In this context, cognitive optical networks represent a viable solution to fill the gap between the intelligence required by the future networks and the current optical technology. This paper proposes a control plane framework developed to coordinate the interactions among the elements of the future cognitive optical networks. The building blocks of the framework and the involved protocols are presented. Moreover, this paper provides an insight of the control plane issues related to the introduction of the flexible optical technology.

Re-growth free single mode lasers based on slots suitable for photonic integration

Abstract: The single mode laser structure based on etched slots suitable for photonic integration is presented in this paper. The laser is made completely dependent on a group of slots on one side of the laser cavity. The fabricated 750 μm long single section laser exhibits a threshold current and a slope efficiency of about 32 mA and 0.11 mW/mA, respectively. The stable single mode operation has been observed with a side mode suppression ratio (SMSR) of around 47 dB at a current injection of 100 mA for the fabricated laser. To solve the yield problem associated with the cleaving of the laser structure, the two-section single mode laser based on slots was further present. By tuning the back section current, stable single mode performance with a SMSR of more than 42 dB is observed over a wide temperature from 15°C to 65°C for the fabricated 750 μm long two-section laser. The presented laser structure just needs a single wafer growth and can be fabricated by standard photolithography and has very strong potential for use in optical communication systems.

Path-based recovery in flexgrid optical networks

Abstract: With the advent of flexgrid optical networks, the rigid wavelength-division multiplexing (WDM) technology will be enhanced by providing better spectrum efficiency and flexibility. In those future flexible optical networks, optical connections (lightpaths) can allocate a flexible number of spectrum slices, also known as frequency slots, so to match better with its requested bitrate. In this paper, we propose to take advantage of this flexible spectrum allocation in recovery mechanisms to be triggered when a failure occurs to provide recovery of part of the requested bitrate, i.e. the allocated spectrum by backup lightpaths could be lower than that of the working lightpaths provided that client service level agreements are fulfilled. This reduction in the recovered bitrate (bitrate squeezing) allows optimizing the use of network capacity. We propose path-based recovery alternatives, based on protection and restoration, specially designed for flexgrid networks. The performance of the proposed recovery mechanisms is exhaustively evaluated on a national reference network.

Efficient resource management via dynamic bandwidth sharing in a WDM-PON ring-based architecture

Abstract: In this work, we propose an efficient resource management approach for WDM-PON ring architectures that supports dynamic bandwidth allocation and sharing of downstream wavelengths. We propose a modification in the ONU design, to dynamically setup virtual circuits for inter-ONU communication. The reservation mechanism is arbitrated by the OLT, which also monitors the traffic imbalances of downstream channels.

Energy-aware virtual topology reconfiguration under dynamic traffic

Abstract: In an IP over WDM network architecture, IP traffic is carried over a virtual topology (VT), composed of optical transparent channels called lightpaths. We propose an energy-efficient dynamic VT adaptation method with sleep mode, which allows changing only one lightpath connectivity at a time by dynamically monitoring the IP packet traffic load on each lightpath. In order to assure the connectivity of future traffic increase a high-load threshold is used. When the packet traffic load on a specific lightpath becomes higher than a threshold, a new lightpath is added to the virtual topology. However this congestion avoidance policy increases the power consumption by activating transponders in the network. Therefore at the same time lightly loaded lightpaths are eliminated in the virtual topology by using a low-load threshold. Energy-efficient virtual topology adaptation is achieved by traffic offloading considering both lightly loaded and heavily loaded links in the network. In this regard, high- and low-load threshold values need to be carefully determined in order to both gain power and ensure load balancing with keeping the stability of virtual connectivity at a reasonable level. We have analysed the power consumption of the network during 48-hours for different values of low- and high-load thresholds together with the impact of different threshold values on the stability of the virtual topology. We have shown that there is a trade-off between number of changes in the virtual topology and the energy-efficiency. Experimental results demonstrate that a good compromise can be achieved by adjusting the high- and low-load thresholds carefully.

Single-channel wireless transmission at 806 Mbit/s using a white-light LED and a PIN-based receiver

Abstract: For the first time, we present optimized indoor visible light links at up to 806 Mbit/s using a single channel of a low-cost off-the-shelf RGB-LED. While the RGB-LED acts as transmitter, a high bandwidth Si-PIN photodiode is used at the receiver. Discrete multitone modulation (DMT) is applied to optimally adapt to the channel corresponding to each color. With illumination levels in the range of normal working environments at the receiver, the resultant BERs are below the forward-error-correction limit for standard correction mechanisms.

On the role of wireless sensor networks in intelligent transportation systems

Abstract: Currently Vehicular Ad-hoc Networks (VANET) are receiving great attention by researchers because of their potentiality for developing innovative applications in the Intelligent Transportation Systems (ITS) context and are expected to be a widely adopted technology in the medium/long term. However, for the near future, the adoption of this technology is difficult since its performance relies excessively on its penetration rate into vehicles. In addition VANET are only able to gather information about the road while vehicles equipped with the appropriate technology are nearby, otherwise information can only be obtained by expensive and therefore scarcely deployed Roadside Units (RSU). Wireless Sensor Networks (WSN), on the contrary, can be deployed along a road (or in a parking lot area) with very little installation and maintenance costs. They can be used to constantly acquire information related to the road condition and the traffic state and, in addition, execute collaborative in-road processing for safety purposes. These properties make WSN an effective complement to VANET, since they can cooperate with them in order to mitigate their limitations. On the other hand, WSN deployments can also benefit from VANET and other communication technologies such as cellular networks in order to disseminate the information gathered to distant places. Consequently, WSN can also play a major role in ITS.

Availability analysis of optical cross-connect implemented by architecture on demand

Abstract: The provisioning of services in optical networks requires reliable optical cross-connects. The paper presents advantages of architectures on demand (AoD) for optical cross-connects comparing to non AoD architectures in terms of availability. All conclusions come from analytical calculations verified by path set enumeration and Abraham's algorithm.