Showing papers in "Journal of Lightwave Technology in 2015"

TeraHertz Photonics for Wireless Communications

Abstract: Optical fibre transmission has enabled greatly increased transmission rates with 10 Gb/s common in local area networks. End users find wireless access highly convenient for mobile communication. However, limited spectrum availability at microwave frequencies results in per-user transmission rates limited to much lower values, e.g., 500 Mb/s for 5-GHz band IEEE 802.11ac. Extending the high data-rate capacity of optical fiber transmission to wireless devices requires greatly increased carrier frequencies. This paper will describe how photonic techniques can enable ultrahigh capacity wireless data distribution and transmission using signals at millimeter-wave and TeraHertz (THz) frequencies.

Things You Should Know About Fronthaul

Abstract: This paper provides a review of the new fronthaul network segment that appears in centralized radio access network (C-RAN) architecture. C-RAN drivers are presented under an operational, economic, and radio point of view. The different fronthaul interfaces are briefly described as they have to be taken into account to build a fronthaul transport solution. Then, fronthaul requirements are detailed going from the technical ones to the business ones. Finally, different fronthaul solutions are presented. Perspectives for medium term evolution including fronthaul supervision are hinted as well as challenges for future mobile evolution toward 5G.

NG-PON2 Technology and Standards

Abstract: This paper provides a tutorial overview of the latest generation of passive optical network (PON) technology standards nearing completion in ITU-T. The system is termed NG-PON2 and offers a fiber capacity of 40 Gbit/s by exploiting multiple wavelengths at dense wavelength division multiplexing channel spacing and tunable transceiver technology in the subscriber terminals (ONUs). Here, the focus is on the requirements from network operators that are driving the standards developments and the technology selection prior to standardization. A prestandard view of the main physical layer optical specifications is also given, ahead of final ITU-T approval.

VCSEL-Based Interconnects for Current and Future Data Centers

Abstract: The vast majority of optical links within the data center are based on vertical cavity surface emitting lasers (VCSELs) operating at 850 nm over multimode optical fiber. Deployable links have evolved in speed from 1 Gb/s in 1996 to 28 Gb/s in 2014. Serial data links at 40 and 56 Gb/s are now under development and place even more demand on the VCSEL and photodiodes. In this paper, we present the characteristics of VCSELs and photodiodes used in current generation 28 Gb/s links and present several methods to extend link distances using more advanced data encoding schemes. Finally, we will present results on wavelength division multiplexing on multimode optical fiber that demonstrate 40 Gb/s Ethernet connections up to 300 m on duplex OM3 optical fiber, and present results on fiber optimized for modal bandwidth in the 850 to 980 nm range.

Energy Efficient Virtual Network Embedding for Cloud Networks

Abstract: Network virtualization is widely considered to be one of the main paradigms for the future Internet architecture as it provides a number of advantages including scalability, on demand allocation of network resources, and the promise of efficient use of network resources. In this paper, we propose an energy efficient virtual network embedding (EEVNE) approach for cloud computing networks, where power savings are introduced by consolidating resources in the network and data centers. We model our approach in an IP over WDM network using mixed integer linear programming (MILP). The performance of the EEVNE approach is compared with two approaches from the literature: the bandwidth cost approach (CostVNE) and the energy aware approach (VNE-EA). The CostVNE approach optimizes the use of available bandwidth, while the VNE-EA approach minimizes the power consumption by reducing the number of activated nodes and links without taking into account the granular power consumption of the data centers and the different network devices. The results show that the EEVNE model achieves a maximum power saving of 60% (average 20%) compared to the CostVNE model under an energy inefficient data center power profile. We develop a heuristic, real-time energy optimized VNE (REOViNE), with power savings approaching those of the EEVNE model. We also compare the different approaches adopting an energy efficient data center power profile. Furthermore, we study the impact of delay and node location constraints on the energy efficiency of virtual network embedding. We also show how VNE can impact the design of optimally located data centers for minimal power consumption in cloud networks. Finally, we examine the power savings and spectral efficiency benefits that VNE offers in optical orthogonal division multiplexing networks.

Network Function Placement for NFV Chaining in Packet/Optical Datacenters

Abstract: In an operator's datacenter, optical technologies can be employed to perform network function (NF) chaining for larger aggregated flows in parallel with the conventional packet-based fine-grained traffic steering schemes. When network function virtualization (NFV) is enabled, virtualized NFs (vNF) can be placed when and where needed. In this study, we identify the possibility of minimizing the expensive optical/electronic/optical (O/E/O) conversions for NFV chaining in packet/optical datacenters, which is introduced by the on-demand placement of vNFs. When the vNFs of the same NF chain are properly grouped into fewer pods, traffic flows can avoid unnecessary traversals in the optical domain. We formulate the problem of optimal vNF placement in binary integer programming (BIP), and propose an alternative efficient heuristic algorithm to solve this problem. Evaluation results show that our algorithm can achieve near-optimal O/E/O conversions comparable to BIP. We also demonstrate the effectiveness of our algorithm under various scenarios, with comparison to a simple first-fit algorithm.

Replacing the Soft-Decision FEC Limit Paradigm in the Design of Optical Communication Systems

Abstract: The FEC limit paradigm is the prevalent practice for designing optical communication systems to attain a certain bit error rate (BER) without forward error correction (FEC). This practice assumes that there is an FEC code that will reduce the BER after decoding to the desired level. In this paper, we challenge this practice and show that the concept of a channel-independent FEC limit is invalid for soft-decision bit-wise decoding. It is shown that for low code rates and high-order modulation formats, the use of the soft-decision FEC limit paradigm can underestimate the spectral efficiencies by up to 20%. A better predictor for the BER after decoding is the generalized mutual information, which is shown to give consistent post-FEC BER predictions across different channel conditions and modulation formats. Extensive optical full-field simulations and experiments are carried out in both the linear and nonlinear transmission regimes to confirm the theoretical analysis.

Multilayer Silicon Nitride-on-Silicon Integrated Photonic Platforms and Devices

Abstract: We review and present additional results from our work on multilayer silicon nitride (SiN) on silicon-on-insulator (SOI) integrated photonic platforms over the telecommunication wavelength bands near 1550 and 1310 nm. SiN-on-SOI platforms open the possibility for passive optical functionalities implemented in the SiN layer to be combined with active functionalities in the SOI. SiN layers can be integrated onto SOI using a front-end or back-end of line integration process flow. These photonic platforms support low-loss SiN waveguides, low-loss and low-crosstalk waveguide crossings, and low-loss interlayer transitions using adiabatic tapers. Novel ultra-broadband and efficient grating couplers as well as polarization management devices are enabled by the close coupling between the silicon and SiN layers.

Inter-Channel Nonlinear Interference Noise in WDM Systems: Modeling and Mitigation

Abstract: We review the modeling of inter-channel nonlinear interference noise (NLIN) in fiber-optic communication systems, focusing on the accurate extraction of the NLIN variance, the dependence on modulation format, the role of nonlinear phase-noise, and the existence of temporal correlations. We show ways in which temporal correlations can be exploited for reducing the impact of NLIN, and discuss the prospects of this procedure in future systems.

Dynamic Load Balancing With Handover in Hybrid Li-Fi and Wi-Fi Networks

Abstract: In this paper, a hybrid network combining light fidelity (Li-Fi) with a radio frequency (RF) wireless fidelity (Wi-Fi) network is considered An additional tier of very small Li-Fi attocells which utilize the visible light spectrum, offers a significant increase in the wireless data throughput in an indoor environment, while at the same time providing room illumination Importantly, there is no interference between Li-Fi and Wi-Fi A Li-Fi attocell covers a significantly smaller area than a Wi-Fi access point (AP) This means that even with a moderate user movement a large number of handover between Li-Fi attocells can occur, and this compromises the system throughput Dynamic load balancing (LB) can mitigate this issue so that the quasi-static users are served by Li-Fi attocells, while moving users are served by a Wi-Fi AP However, due to the user movement, local overload situations may occur which prevent handover, leading to a lower throughput This research studies LB in a hybrid Li-Fi/Wi-Fi network by taking into account user mobility and handover signalling overheads Furthermore, a dynamic LB scheme is proposed, where the utility function considers system throughput and fairness In order to better understand the handover effect on the LB, the service areas of different APs are studied, and the throughput of each AP by employing the proposed LB scheme is analyzed

Phase-Sensitive Optical Time Domain Reflectometer Based on Phase-Generated Carrier Algorithm

Abstract: We propose a novel approach to generate distributed fiber sensing system based on phase-sensitive optical time domain reflectometer (Φ-OTDR) and phase-generated carrier demodulation algorithm. An unbalanced Michelson interferometer is introduced at the receiving end of the system. The back Rayleigh scattering light from a certain position along the sensing fiber would interfere to generate interference light signal versus time, whose phase carries the sensing information. Phase-generated carrier demodulation algorithm is proposed and carried out to recover the phase information. A single frequency vibration event is applied to a certain position along the sensing fiber and we realize to demodulate it correctly. The noise level of the phase sensitive OTDR system is about $3 \times 10^{-3}$ rad/SHz and a signal to noise ratio about 30.45 dB is achieved. The maximum sensing length and the spatial resolution of the Φ-OTDR system are 10 km and 6 m with pulse repetition rate at 10 kHz and 6 m fiber delay in MI with interrogating pulse width of 30 ns.

Resource Allocation for Space-Division Multiplexing: Optical White Box Versus Optical Black Box Networking

Abstract: Elastic optical networking (EON) with space-division multiplexing (SDM) is the only evident long-term solution to the capacity needs of the future networks. The introduction of space via spatial fibers, such as multicore fibers (MCF) to EON provides an additional dimension as well as challenges to the network planning and resource optimization problem. There are various types of technologies for SDM transmission medium, switching, and amplification; each of them induces different capabilities and constraints on the network. For example, employing MCF as the transmission medium for SDM mitigates the spectrum continuity constraint of the routing and spectrum allocation problem for EON. In fact, cores can be switched freely on different links during routing of the network traffic. On the other hand, intercore crosstalk should be taken into account while solving the resource allocation problem. In the framework of switching for elastic SDM network, the programmable architecture on demand (AoD) node (optical white box) can provide a more scalable solution with respect to the hard-wired reconfigurable optical add/drop multiplexers (ROADMs) (optical black box). This study looks into the routing, modulation, spectrum, and core allocation (RMSCA) problem for weakly-coupled MCF-based elastic SDM networks implemented through AoDs and static ROADMs. The proposed RMSCA strategies integrate the spectrum resource allocation, switching resource deployment, and physical layer impairment in terms of intercore crosstalk through a multiobjective cost function. The presented strategies perform a cross-layer optimization between the network and physical layers to compute the actual intercore crosstalk for the candidate resource solutions and are specifically tailored to fit the type of optical node deployed in the network. The aim of all these strategies is to jointly optimize the switching and spectrum resource efficiency when provisioning demands with diverse capacity requirements. Extensive simulation results demonstrate that 1) by exploiting the dense intranodal connectivity of the ROADM-based SDM network, resource efficiency and provisioned traffic volume improve significantly related to the AoD-based solution, 2) the intercore crosstalk aware strategies improve substantially the provisioned traffic volume for the AoD-based SDM network, and 3) the switching modules grows very gently for the network designed with AoD nodes related to the one with ROADMs as the traffic increases, qualifying AoD as a scalable and cost-efficient choice for future SDM networks.

Channel Characteristics of Visible Light Communications Within Dynamic Indoor Environment

Abstract: Visible light communications (VLC) is a new emerging technology, which provides both data transmission and illumination by utilizing the visible range (370-780 nm) of the electromagnetic spectrum. In order to maximize the available data rate and enhance the users mobility within an indoor environment, it is essential to characterize the communication channel. In this paper, we present both analytical and experimental results for a VLC system affected by movement of people for different indoor conditions (i.e., furnished office room, empty hall, and corridor). VLC systems utilize multiple light-emitting diodes mounted in the ceiling and the configuration is based on the nondirected line of sight. We consider random movement of people within the room, focusing on the impacts of shadowing and blocking on mobility and link system performance by investigating changes in the channel characteristics using the cumulative distribution function of the received power distribution and the delay profile. We demonstrate the behaviour of communication channels for different scenarios from corridor, the most robust against people movement induced fading, to the office rooms and halls, the most vulnerable to the received power fluctuation.

Adaptive Modulation Schemes for Visible Light Communications

Abstract: A major limitation of existing visible light communication (VLC) systems is the limited modulation bandwidth of light-emitting diodes used in such systems. Using adaptive modulation to improve the spectral efficiency for radio communications has been well studied. For VLC with various physical layer schemes, however, how adaptive modulation works is not well understood yet. The goal of this paper is to provide an in-depth analysis of the achievable spectral efficiency of adaptive modulation for three different schemes for high speed VLC: dc-biased optical orthogonal frequency division multiplexing (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), and single-carrier frequency-domain equalization (SC-FDE). We will show that in the low signal-to-noise ratio region, the ACO-OFDM-based adaptive modulation scheme outperforms the other two schemes. SC-FDE-based adaptive modulation achieves a better performance than the DCO-OFDM-based scheme, and it is much simpler than the other two schemes.

Silicon Photonics for Exascale Systems

Abstract: With the extraordinary growth in parallelism at all system scales driven by multicore architectures, computing performance is increasingly determined by how efficiently high-bandwidth data is communicated among the numerous compute resources. High-performance systems are especially challenged by the growing energy costs dominated by data movement. As future computing systems aim to realize the Exascale regime—surpassing 1018 operations per second—achieving energy efficient high-bandwidth communication becomes paramount to scaled performance. Silicon photonics offers the possibility of delivering the needed communication bandwidths to match the growing computing powers of these highly parallel architectures with extremely scalable energy efficiency. However, the insertion of photonic interconnects is not a one-for-one replacement. The lack of practical buffering and the fundamental circuit switched nature of optical data communications require a holistic approach to designing system-wide photonic interconnection networks. New network architectures are required and must include arbitration strategies that incorporate the characteristics of the optical physical layer. This paper reviews the recent progresses in silicon photonic based interconnect devices along with the system level requirements for Exascale. We present a co-design approach for building silicon photonic interconnection networks that leverages the unique optical data movement capabilities and offers a path toward realizing future Exascale systems.

Unified Performance Analysis of Mixed Radio Frequency/Free-Space Optical Dual-Hop Transmission Systems

Abstract: The mixed radio frequency (RF)/free-space optical (FSO) relaying is a promising technology for coverage improvement, while there lacks unified expressions to describe its performance. In this paper, a unified performance analysis framework of a dual-hop relay system over asymmetric RF/FSO links is presented. More specifically, we consider the RF link follows generalized $\kappa$ - $\mu$ or $\eta$ - $\mu$ distributions, while the FSO link experiences the gamma-gamma distribution, respectively. Novel analytical expressions of the probability density function and cumulative distribution function are derived. We then capitalize on these results to provide new exact analytical expressions of the outage probability and bit error rate (BER). Furthermore, the outage probability for high signal-to-noise ratios and the BER for different modulation schemes are deduced to provide useful insights into the impact of system and channel parameters of the overall system performance. These accurate expressions are general, since they correspond to generalized fading in the RF link and account for pointing errors, atmospheric turbulence, and different modulation schemes in the FSO link. The links between derived results and previous results are presented. Finally, numerical and Monte–Carlo simulation results are provided to demonstrate the validity of the proposed unified expressions.

20 Gb/s Mobile Indoor Visible Light Communication System Employing Beam Steering and Computer Generated Holograms

Abstract: Visible light communication (VLC) systems have typically operated at data rates below 10 Gb/s and operation at this data rate was shown to be feasible by using laser diodes (LDs), imaging receivers and delay adaptation techniques (DAT imaging LDs-VLC). However, higher data rates, beyond 10 Gb/s, are challenging due to the low signal to noise ratio (SNR) and inter symbol interference (ISI). In this paper, for the first time, to the best of our knowledge, we propose, design, and evaluate a VLC system that employs beam steering (of part of the VLC beam) using adaptive finite vocabulary of holograms in conjunction with an imaging receiver and a DAT to enhance SNR and to mitigate the impact of ISI at high data rates (20 Gb/s). An algorithm was used to estimate the receiver location, so that part of the white light can be directed towards a desired target (receiver) using beam steering to improve SNR. Simulation results of our location estimation algorithm (LEA) indicated that the required time to estimate the position of the VLC receiver is typically within 224 ms in our system and environment. A finite vocabulary of stored holograms is introduced to reduce the computation time required by LEA to identify the best location to steer the beam to the receiver location. The beam steering approach improved the SNR of the fully adaptive VLC system by 15 dB at high data rates (20 Gb/s) over the DAT imaging LDs-VLC system in the worst-case scenario. In addition, we examined our new proposed system in a very harsh environment with mobility. The results showed that our proposed VLC system has strong robustness against shadowing, signal blockage, and mobility.

Silicon Photonic Hybrid Ring-Filter External Cavity Wavelength Tunable Lasers

Abstract: Si-photonic hybrid ring external cavity wavelength tunable lasers by passive alignment techniques with more than 100-mW fiber-coupled power and linewidth narrower than 15 kHz along the whole C-band are demonstrated. These attractive performances are achieved due to very low loss Si-wire waveguides, of which loss is lower than 0.5 dB/cm. Obtained results show excellent features of Si-photonics toward commercial products.

Mobile Multi-Gigabit Visible Light Communication System in Realistic Indoor Environment

Abstract: The main challenges facing high data rate visible light communication (VLC) are the low-modulation bandwidth of the current transmitters (i.e., light emitting diodes), the intersymbol interference (ISI) caused by the multipath propagation and cochannel interference (CCI) due to multiple transmitters. In this paper, for the first time, to the best of our knowledge, we propose, design, and evaluate the use of laser diodes (LDs) for communication as well as illumination. In addition, we propose an imaging receiver for a mobile VLC system to mitigate ISI. A novel delay adaptation technique is proposed to mitigate CCI, maximize the signal to noise ratio, and reduce the impact of multipath dispersion under user mobility. The proposed imaging system is able to provide data rates of 5 Gb/s in the worst-case scenario. The combination of a delay adaptation approach with an imaging receiver (DAT imaging LD-VLC system) adds a degree of freedom to the link design, which results in a VLC system that has the ability to provide higher data rates (i.e., 10 Gb/s) in the considered harsh indoor environment. The proposed technique (delay adaptation) achieves significant improvements in the VLC channel bandwidth (more than 16 GHz) over an imaging system in the worst-case scenario. The VLC channel characteristics and links were evaluated under diverse situations including an empty room and a room with very strong shadowing effects resulting from minicubicle offices.

Spatially Coupled Soft-Decision Error Correction for Future Lightwave Systems

Abstract: In this paper, we discuss and present some recent advances in the field of error correcting codes and discuss their applicability for lightwave transmission systems. We introduce several classes of spatially coupled codes and discuss several design options for spatially coupled codes and show how rapidly decodable codes can be constructed by careful selection of the degree distribution. We confirm the good performance of some spatially coupled codes at very low bit error rates using an FPGA-based simulation. Finally, we compare all proposed schemes and show how spatially coupled Low-Density Parity-Check (LDPC) codes outperform conventional LDPC and polar codes with similar receiver complexity and memory requirements.

Optical Metasurfaces and Prospect of Their Applications Including Fiber Optics

Abstract: Metasurfaces have emerged in the recent years as a platform to design subwavelength-thick optical components (“flat optics”), which can be used to implement any optical function (beam deflection, focusing, waveplates, etc). These flat optical components can be fabricated using a single lithographic step. The approach is particularly suited for patterning nonconventional substrates, such as semiconductor laser facets and optical fiber facets. In this paper, we review recent applications of metasurfaces to flat optical devices, including their use in semiconductor lasers and fiber optics. Metasurfaces make it possible to design all properties of light (amplitude, phase, and polarization), which enable us to build a large variety of flat optical components, including planar lenses, quarter-wave plates, optical vortex plates, holograms for vector beam generation, and ultrathin perfect absorbers and color coatings. We also review flat collimating lenses integrated on the facets of mid-infrared and far-infrared (terahertz) quantum cascade lasers, and novel techniques to create large arrays of nanostructures on fiber facets.

Mechanism of Dissipative-Soliton-Resonance Generation in Passively Mode-Locked All-Normal-Dispersion Fiber Lasers

Abstract: Numerical simulations on dissipative-soliton-resonance generation in an all-normal-dispersion fiber ring laser are presented. Situations with monotonic and periodical saturable absorption are both considered. The multipulse operation in dissipative soliton laser is found to be caused by the spectral filtering effect that limits the spectral maximum width, and the multipulsing can be fully circumvent by inducing strong peak-power-clamping effect of a sinusoidal saturable absorber in the cavity. When the cavity peak-power-clamping effect is strong enough that the pulse peak power and the pulse spectral width are both confined at a low value, the spectral filtering effect induced multipulse operation is prevented and the dissipative-soliton-resonance is generated. Otherwise, the spectral filtering effect causes pulse breaking before the pulse peak power reaches the saturation point. Further results show that under the dissipative-soliton-resonance, the generated pulse peak power can be directly controlled by the cavity peak-power-clamping effect, which is determined by the saturation power of the saturable absorber.

Demonstration of Cooperative Resource Allocation in an OpenFlow-Controlled Multidomain and Multinational SD-EON Testbed

Abstract: The combination of elastic optical networks (EONs) and software-defined networking (SDN) leads to SD-EONs, which bring a new opportunity for enhancing programmability and flexibility of optical networks with more freedom for network operators to customize their infrastructure dynamically. In this paper, we investigate how to apply multidomain scenarios to SD-EONs. We design the functionalities in the control plane to facilitate multidomain tasks, and propose an interdomain protocol to enable OpenFlow controllers in different SD-EON domains to operate cooperatively for multidomain routing and spectrum assignment. The proposed system is implemented and experimentally demonstrated in a multinational SD-EON control plane testbed that consists of two geographically distributed domains located in China and USA, respectively. Experimental results indicate that the proposed system performs well for resource allocation across multiple SD-EON domains.

Design and Properties of Hollow Antiresonant Fibers for the Visible and Near Infrared Spectral Range

Abstract: Hollow core antiresonant fibers offer new possibilities in the near infrared and visible spectral range. I show here that the great flexibility of this technology can allow the design and fabrication of hollow core optical fibers with an extended transmission bandwidth in the near infrared and with very low optical attenuation in the visible wavelength regime. A very low attenuation of 175 dB/km at 480 nm is reported. A modification of the design of the studied fibers is proposed in order to achieve fast-responding gas detection.

A Novel Statistical Channel Model for Turbulence-Induced Fading in Free-Space Optical Systems

Abstract: In this paper, we propose a new probability distribution function which accurately describes turbulence-induced fading under a wide range of turbulence conditions. The proposed model, termed double-generalized gamma (double GG), is based on a doubly stochastic theory of scintillation and developed via the product of two generalized gamma distributions. The proposed double GG distribution generalizes many existing turbulence channel models and provides an excellent fit to the published plane and spherical waves simulation data. Using this new statistical channel model, we derive closed form expressions for the outage probability and the average bit error as well as corresponding asymptotic expressions of free-space optical communication systems over turbulence channels. We demonstrate that our derived expressions cover many existing results in the literature earlier reported for gamma–gamma, double-Weibull and K channels as special cases.

Connecting Silicon Photonic Circuits to Multicore Fibers by Photonic Wire Bonding

Abstract: Photonic wire bonding is demonstrated to enable highly efficient coupling between multicore fibers and planar silicon photonic circuits. The technique relies on in-situ fabrication of three-dimensional interconnect waveguides between the fiber facet and tapered silicon-on-insulator waveguides. Photonic wire bonding can easily compensate inaccuracies of core placement in the fiber cross-section, does not require active alignment, and is well suited for automated fabrication. We report on the design, on fabrication, and on characterization of photonic wire bonds. In a proof-of-principle experiment, a four-core fiber is coupled to a silicon photonic chip, leading to measured coupling losses as small as 1.7 dB.

Hybrid 3-D Localization for Visible Light Communication Systems

Abstract: In this study, we investigate the hybrid utilization of angle-of-arrival (AOA) and received signal strength (RSS) information in visible light communication (VLC) systems for 3-D localization. We show that AOA-based localization method allows the receiver to locate itself via a least squares estimator by exploiting the directionality of light-emitting diodes (LEDs). We then prove that when the RSS information is taken into account, the positioning accuracy of AOA-based localization can be improved further using a weighted least squares solution. On the other hand, when the radiation patterns of LEDs are explicitly considered in the estimation, RSS-based localization yields highly accurate results. In order to deal with the system of non-linear equations for RSS-based localization, we develop an analytical learning rule based on the Newton–Raphson method. The non-convex structure is addressed by initializing the learning rule based on 1) location estimates, and 2) a newly developed method, which we refer as a random report and cluster algorithm. As a benchmark, we also derive the analytical expression of the Cramer–Rao lower bound for RSS-based localization, which captures any deployment scenario positioning in 3-D geometry. Finally, we demonstrate the effectiveness of the proposed solutions for a wide range of LED characteristics and orientations through extensive computer simulations.

Distance Adaptive Dynamic Routing and Spectrum Allocation in Elastic Optical Networks With Shared Backup Path Protection

Abstract: This paper considers distance adaptive dynamic routing and spectrum assignment (RSA) for elastic optical networks with shared backup path protection (SBPP). Efficient heuristic algorithms based on spectrum window planes are proposed for implementing distance and modulation format adaptive RSA so as to maximize spare capacity sharing among multiple protection lightpaths. A differentiated sharable frequency slot cost was also defined for the first time to more efficiently share protection resource. Network performance is evaluated in terms of bandwidth blocking probability (BBP) through simulations. The proposed SBPP technique is effective in reducing BBP and improving spectral efficiency compared to conventional SBPP schemes and 1+1 path protection. The impact of transponder tunability on bandwidth blocking performance is also evaluated to show that a limited tuning range is sufficient to achieve a BBP performance close to that with full tunability.

Fundamentals of Optical Fiber Sensing Schemes Based on Coherent Optical Time Domain Reflectometry: Signal Model Under Static Fiber Conditions

Abstract: The paper develops a statistical model for the signals received in phase-sensitive optical time domain reflectometry (OTDR) probed by highly coherent sources. The backscattering process is modelled by a set of discrete scatterers with properly chosen parameters. Explicit equations for calculating the amplitude and the phase of the backscattered signal are obtained. The developed model predicts spectral and autocorrelation characteristics of the amplitude signals that are validated by experimental results. Characteristics of the phase signals, practicable for studying the sensing applications of the OTDR system, are presented and studied as well, demonstrating good correspondence with experiment. A more detailed modelling of distributed vibration sensing systems and their response to disturbances along an optical fiber will be possible as an extension of the developed formalism.

Multipoint Two-Dimensional Curvature Optical Fiber Sensor Based on a Nontwisted Homogeneous Four-Core Fiber

Abstract: We have implemented a multipoint two-dimensional curvature optical fiber sensor based on a nontwisted homogeneous four-core fiber. A theoretical approach to model the mechanical behavior of these fibers under curvature conditions has been developed. Two shape sensors composed of an array of FBGs inscribed in the four-core fiber have been implemented to corroborate the theoretical analysis with the experimental results. The characterization of the proposed shape sensors showed their ability to measure the curvature radius, the curvature direction, and any external applied force related to both uniform and nonuniform curvatures with high accuracy.