We study a dynamic WDM network supporting different service classes (SC) containing applications having similar setup delay tolerance. By utilizing delay tolerance we propose scheduling strategies able to significantly reduce blocking probability of each SC.
Energy-efficient optical networks are gaining momentum as environmental-friendly solutions with reduced operational costs. Energy-efficiency can be achieved by using devices in sleep mode, i.e., a low-power, inactive state in which devices can be suddenly waken-up upon occurrence of triggering events. This paper advocates a sleep mode option for the optical devices (e.g., amplifiers, optical switches) installed for protection purposes only. These devices can be put in sleep mode to reduce the network power consumption, but they can be promptly waken up (if necessary) upon a failure occurrence. This principle is proposed and applied in Wavelength Division Multiplexing (WDM) networks with dedicated-path protection to ensure survivability against single-link failures. The main contribution of the paper is the definition of the energy-efficient network planning problem for resilient WDM networks where optical devices can be configured in sleep mode. Optimal results of the integer linear programming (ILP) problem show savings of up to 25% in the overall power consumption.
Discrete coherent states for a system of n qubits are introduced in terms of eigenstates of the finite Fourier transform. The properties of these states are pictured in phase space by resorting to the discrete Wigner function.
We theoretically and experimentally evaluated energy dissipation of nanophotonic devices based on energy transfer via near-field interactions and their interfaces with optical far-fields. The lower bound is about 10(4) times more energy-efficient than electronic devices. We also examined some fundamental differences between near-field-mediated optical energy transfer logic and electrical logic in terms of energy dissipation.
We theoretically analyzed the lower bound of energy dissipation required for optical excitation transfer from smaller quantum dots to larger ones via optical near-field interactions. The coherent interaction between two quantum dots via optical near-fields results in unidirectional excitation transfer by an energy dissipation process occurring in the larger dot. We investigated the lower bound of this energy dissipation, or the intersublevel energy difference at the larger dot, when the excitation appearing in the larger dot originated from the excitation transfer via optical near-field interactions. We demonstrate that the energy dissipation could be as low as 25 mu eV. Compared with the bit flip energy of an electrically wired device, this is about 10(4) times more energy efficient. The achievable integration density of nanophotonic devices is also analyzed based on the energy dissipation and the error ratio while assuming a Yukawa-type potential for the optical near-field interactions.
Enhanced slow light propagation is predicted in a coupled resonator optical waveguide structure possessing highly dispersive elements using the finite-difference time-domain method. The group velocity is shown to be below 0.01c(0).
Analysis of photonic crystal coupled resonator optical waveguide (CROW) structures with a highly dispersive background medium is presented. A finite-difference time-domain algorithm was employed which contains an exact representation of the permittivity of a three-level atomic system which exhibits electromagnetically induced transparency (EIT). We find that the coupling strength between nearest-neighbor cavities in the CROW decreases with increasing steepness of the background dispersion, which is continuously tunable as it is directly related to the control field Rabi frequency. The weaker coupling decreases the speed of pulse propagation through the waveguide. In addition, due to the dispersive nature of the EIT background, the CROW band shape is tuned around a fixed k-point. Thus, the EIT background enables dynamic tunability of the CROW band shape and the group velocity in the structure at a fixed operating point in momentum space.
Time-domain electromagnetic modelling of complex structures which include both non-dispersive media and media exhibiting electromagnetically induced transparency (EIT) require a general, robust calculation method such as finite-difference time-domain (FDTD). We propose a complex-valued, exact two-pole representation of the permittivity of a three-level system which is suitable for integration into the FDTD algorithm via the auxiliary differential equation method. Our calculation model confirmed reported results which were calculated with an approximate representation of the EIT permittivity. Additionally, propagation calculations which mimic slow light experiments were performed. A major advantage of our representation is the ease with which changes in the control field Rabi frequency can be implemented by using a time-dependent permittivity.
We present a theoretical study of an opticalmicroresonator system which contains a electromagneticallyinduced transparency medium within the resonator.We find that a time-dependent tuning of thedispersive properties of the resonator medium resultsin an enhanced transmission spectrum.
This chapter provides an overview of unusual multifunctional, specialty single-mode fibers-macrohole fibers, multicore fibers, fibers with internal electrodes, and fibers for high-temperature resistant fiber Bragg gratings. Macrohole fibers belong to the group of microstructured fibers, which encompass a wide variety of fibers with air holes or other structures extending in the axial direction. Functions performed using macrostructured fibers include supercontinuum generation in tapered hole fibers, dispersion management, fibers with decreased bend loss for compact optical fiber wiring, and fibers for polarimetric sensing, and lasers. The introduction of materials in the holes adds the possibility of manipulating the guiding properties of the fiber. This can be achieved by interaction of the guided mode with actively controllable materials in the holes or by using the inserted materials for other active functions, such as a metal electrode to implement electro-optic control of the fiber. The proposed applications for multicore fibers span over lasers and amplifiers, transport fibers for broadband communications, passive, and active fiber optic components such as filters, multiplexers, and various kinds of sensors. The ultimate multicore fiber is the image fiber used in endoscopes and other such devices.
We study the partial spatial coherence and partial three-dimensional polarization in electromagnetic fields consisting of a superposition of evanescent plane waves generated in total internal reflection. In particular, we investigate the coherence length in such fields, and demonstrate that it can be shorter than the wavelength of the propagating field above the dielectric surface. The higher the refractive-index contrast at the interface is, and the closer to the surface the field is considered, the shorter is the coherence length. Physical explanation for this behavior analogous to the generation of incoherent light in a multimode gas laser is provided. We also assess the degree of polarization in evanescent fields by using a recent threedimensional formulation.
We consider partial spatial coherence and partial polarization of purely evanescent optical fields generated in total internal reflection at an interface of two dielectric (lossless) media. Making use of the electromagnetic degree of coherence, we show that, in such fields, the coherence length can be notably shorter than the light's vacuum wavelength, especially at a high-index-contrast interface. Physical explanation for this behavior, analogous to the generation of incoherent light in a multimode laser, is provided. We also analyze the degree of polarization by using a recent three-dimensional formulation and show that the field may be partially polarized at a subwavelength distance from the surface even though it is fully polarized farther away. The degree of polarization can assume values unattainable by beamlike fields, indicating that electromagnetic evanescent waves generally are genuine three-dimensional fields. The results can find applications in near-field optics and nanophotonics.
We point out an apparently overlooked consequence of the boundary conditions obeyed by the electric displacement vector at air-metal interfaces: the continuity of the normal component combined with the quantum mechanical penetration of the electron gas in the air implies the existence of a surface on which the dielectric function vanishes. This, in turn, leads to an enhancement of the normal component of the total electric field. We study this effect for a planar metal surface, with the inhomogeneous electron density accounted for by a Jellium model. We also illustrate the effect for equilateral triangular nanoislands via numerical solutions of the appropriate Maxwell equations, and show that the field enhancement is several orders of magnitude larger than what the conventional theory predicts.
Multi-layer and multi-period network planning can lead to significant cost reductions. Using linear programming we study the effect of their joint consideration for IP-over-WDM networks. Case studies show cost savings surpassing 20% by including forecast knowledge in multi-layer optimization.
Link state databases maintained in parallel at each node in networks that require link state information for proper operation try to reflect real-time changes of the network state. Information dissemination, however, by its very nature introduces latency in the update of link state information at different nodes, which may in turn lead to faulty decisions that entail additional delay perceived by user traffic. The paper presents a probabilistic model based on simple assumptions in order to derive an upper bound on the probability that such a link state database inconsistency occurs.
This paper investigates what impact optical node failures may have on wavelength-division-multiplexed networks, in which reliable end-to-end optical circuits are provisioned dynamically. At the node level, the optical cross-connect (OXC) equipment availability measure is estimated using proven component level availability models. At the network level, end-to-end optical circuits are provisioned only when the level of connection availability required by the application can be guaranteed. With the objective of yielding efficient utilization of the network resources, i.e., fibers and OXCs, circuit redundancy is achieved by means of shared path protection (SPP) switching, in combination with. differentiated reliability (DiR). The resulting optimal routing and wavelength assignment problem is proven to be NP-complete. To produce suboptimal solutions in polynomial time, a heuristic technique is presented, which makes use of a time-efficient method to estimate the end-to-end circuit availability in the presence of multiple (link and node) failures. Using the proposed heuristic, a selection of representative OXC architectures and optical switching technologies is examined to assess the influence of the node equipment choice on the overall network performance.
Adaptive routing is considered as a promising solution to support flexible resource allocation in wavelength division multiplexing network. Resource advertisement protocols, such as link state advertisement (LSA), are essential to enable routing algorithms to efficiently carry out the required path computation. The LSA nonnegligible convergence time may lead to outdated link information, which in turns may adversely affect the efficiency of the computed path. As a result, traffic engineering is suboptimal and some services may be unnecessarily blocked. This study investigates the impact of outdated information on the blocking probability of adaptive routing schemes focusing on two LSA protocols: one advertising specific resource information and one advertising only a summary of the same. Our simulation results show that compared with the routing scheme requiring specific information LSA, the approach based on LSA with summary information is by its nature not precise and hence able to mitigate the adverse impact of the LSA convergence time on blocking performance.
The simultaneous wireline (600 MHz) and wireless (5.5 GHz) transmission of data over cable service interface specification (DOCSIS) signals in a hybrid fiber-radio access network is presented. The DOCSIS signal wireless replica is generated by means of an optical harmonic up-conversion technique based on a dual-drive Mach-Zehnder modulator. The optical signal is fed to a base station (BS) where a packaged asymmetric Fabry-Perot modulator/detector acts simultaneously as a photodetector and an optical modulator. At the BS, the DOCSIS signals can be fed either to a wireline or a wireless access network, in a highly flexible approach. Full-duplex operation has been demonstrated for both access types, including indoor wireless transmission.
Scanning near-field photoluminescence spectroscopy has been applied to evaluate bandgap fluctuations in epitaxial AlGaN films with the AlN molar fraction varying from 0.30 to 0.50. A dual localization pattern has been observed. The potential of the small-scale (<100 nm) localization, evaluated from the width of the photoluminescence spectra, is between 0 and 51 meV and increases with increased Al content. These potential variations have been assigned to small-scale compositional fluctuations occurring due to stress variations, dislocations, and formation of Al-rich grains during growth. Larger area potential variations of 25-40 meV, most clearly observed in the lower Al-content samples, have been attributed to Ga-rich regions close to grain boundaries or atomic layer steps. The density, size, and bandgap energy of these domains were found to be composition dependent. The lower bandgap domains were found to be strongly correlated with the regions with efficient nonradiative recombination.
Electroluminescence of 285 and 340 nm AlGaN quantum well light emitting diodes (LEDs) has been studied by scanning near-field optical spectroscopy. In the 285 nm devices, the near-field scans revealed hexagonal cross hatch microcracks that can be related to strain relaxation. Besides, mu m size areas emitting with a higher intensity and at a longer wavelength, presumably, due to lower AlN molar fraction, have been observed. Near-field scans performed during subsequent days revealed that with time, intensity from these spots increases and emission wavelength shifts to the red, indicating further change in the quantum well alloy composition. This has allowed distinguishing a novel LED aging mechanism that involves locally increased current, heating and Al atom migration. For the 340 nm emitting device with lower Al content in the active region, no such features have been observed.
Shift of the transition energy after pulsed optical excitation in Al0.35Ga0.65N/Al0.49Ga0.51N quantum well (QW) structures with varying well width has been studied by time-resolved photoluminescence. The shift dynamics, which is due to descreening of the intrinsic electric field, has characteristic times similar to carrier lifetimes revealing negligible influence of trapped carriers on screening. Comparison of the experimental spectral shifts with the calculations has shown that the intrinsic field in our AlGaN QWs is about 0.4-0.5 MV/cm, which is about a factor of two smaller than the value calculated using the theoretical polarization constants.
Photoexcited carrier dynamics in a 280 nm AlGaN quantum well (QW) light emitting diode has been studied by time-resolved photoluminescence at forward and reverse bias. Long ( for AlGaN QWs with high Al content) room temperature carrier lifetimes of about 600 ps were measured with only a slight dependence on bias. These lifetimes are much longer than calculated free carrier tunnelling and thermionic emission times, pointing out the importance of excitonic effects for carrier dynamics in AlGaN QWs.
Band gap fluctuations and carrier localization in AlxGa1-xN films with x values varying from 0.30 to 0.50 has been studied by scanning near-field optical microscopy (SNOM) by measuring photoluminescence. The measurements have revealed a dual localization potential. Microscopic scale potential variations, detected by the SNOM, were most pronounced in the lower Al content samples. The nanoscopic carrier localization potentials, evaluated from the width of the photoluminescence spectra, were largest in layers with the largest AlN molar fraction. The large scale potential fluctuations were attributed to Ga rich regions close to grain boundaries or atomic layer steps. The density, size and band gap energy of these domains were found to be composition dependent. The nanoscopic potential variations have been assigned to small-scale compositional fluctuations, possibly, occurring due to formation of Al rich grains during growth.
Degradation under high current stress of AlGaN quantum well based light emitting diodes emitting at 285 and 310 nm has been studied using electroluminescence, time-resolved photoluminescence and current-voltage experimental techniques. The measurements have revealed that during aging decrease of the emission intensity is accompanied by increase of the tunneling current, increase of the nitrogen vacancy concentration and partial compensation of the p-doping. The main role in the device degradation has been ascribed to formation of tunneling conductivity channels, probably, via activation of the closed core screw dislocations with the help of nitrogen vacancies. Carrier lifetimes in the quantum wells and the p-cladding were found to be unaffected by the aging process, suggesting that the nonradiative recombination has a lesser influence on the device degradation.
Time-resolved photoluminescence measurements performed on proton implanted and annealed GaN layers have shown that carrier lifetime can be tuned over two orders of magnitude and, at implantation dose of 1 x 10(15) cm(-2), decreases down to a few picoseconds. With annealing at temperatures between 250 and 750 degrees C, carrier lifetime, contrary to electrical characteristics, is only slightly restored, indicating that electrical compensation and carrier dynamics are governed by different defects. Ga vacancies, free and bound at threading dislocations, are suggested as the most probable defects, responsible for electrical compensation and carrier lifetime quenching.
Emission from a 285 nm AlGaN quantum well light emitting diode has been studied by scanning near-field optical spectroscopy. The scans revealed micrometer-size domainlike areas emitting with a higher intensity and at a longer wavelength; presumably, because of a lower AlN molar fraction in these regions. Experiments performed on different days have shown that with time, intensity from these spots increases and emission wavelength shifts to the red, indicating a further change in the quantum well alloy composition. This has allowed distinguishing an aging mechanism that involves locally increased current, heating, and atom migration.
Aging under high current stress of AlGaN quantum well based light emitting diodes with high and low Al content in the wells emitting at 270 nm and 335 nm, respectively, has been studied by scanning near field optical spectroscopy and far field electroluminescence, photoluminescence and time-resolved photoluminescence. In the high Al content devices emission band related to optical transitions in the cladding involving nitrogen vacancies has been found. Evolution of this band during aging suggests that the role of N vacancies is crucial in the aging process by aiding defect generation and formation of high conductivity channels.
Wick's theorem in the Schwinger-Perel-Keldysh closed-time-loop formalism is written in a form where the place of contractions is taken by the linear response function of the field. This result demonstrates that the physical information supplied by Wick's theorem for operators is propagation of the free field in space and time.
Tunability has added an important dimension to a variety of laser devices and led to new systems and applications. From laser spectroscopy to Bose-Einstein condensation, the one nexus is the tunable laser. Incorporating nine new chapters since the first edition, Tunable Laser Applications, Second Editionreflects the significant developments in tunable lasers that have taken place over the past decade. Internationally recognized experts describe the physics and architecture of widely applied tunable laser sources, emphasizing biomedical applications of fiber lasers and ultrashort pulsed lasers, as well as laser isotope separation and cancer photodynamic therapy. The Second Edition Covers- Advances in optical parametric oscillators Developments in tunable semiconductor lasers Solid-state dye lasers Laser isotope separation using diode lasers Medical applications of table-top coherent X-rays Outlining applications in biology and medicine, this second edition offers a much-needed account of the most promising tunable laser applications.
Interference of the near optical field caused by evanescent waves leaking a coupled microcavity enhances the optical field between the cavity sections. This enhancement can be used for design of microcavity lasers with outside-cavity modes and for various sensors, for example, to precisely detect the direction of incident wavefront.
Enhanced scattering of the THz radiation caused by the interaction of near field component with plasmons in a substrate material results in sub-wavelength resolution within THz range. Variation of dielectric permittivity of organic materials placed on a metal substrate can improve contrast of the image obtained with such a technique.
For setting the optical gain of an optical amplifier such as a Raman amplifier that is connected in a wavelength division multiplexing (WDM) system, the gain of the amplifier is made dependent on the states of optical polarizers connected to individual inputs of a WDM multiplexer. The polarizers can be actively controlled by a device connected to sense the output power of the Raman fiber at different wavelengths. For an appropriate control the optical gain can be given any desired shape such as for example a reasonable flatness. The control of the polarization states of the WDM-channels allows for the use of a single wavelength pump source of the amplifier, instead of the conventionally used multiwavelength source.
Bragg grating reflectors placed along microcavity facets can improve the efficiency of a polymer dye laser built with such a microcavity. The impact of different reflector designs on the mode pattern and resonance frequencies of the microcavity is numerically simulated and analyzed. This rigorous physical model is based on solving the Maxwell equations and includes such material properties as absorption, dispersion, fluorescence and optical gain. In certain cases, an asymmetrical layout of the reflectors can be more preferable than the pair of reflectors located on opposite sides of the microcavity as it is implemented for typical design.
The effect of in-situ N-ion irradiation on the recombination dynamics of GaInNAs/GaAs semiconductor saturable absorber mirrors has been studied. The samples were fabricated by molecular beam epitaxy using a radio frequency plasma source for nitrogen incorporation in the absorber layers as well as for the irradiation. The recombination dynamics of irradiated samples were studied by pump-probe measurements. The recombination time of the absorbers could be reduced by increasing the irradiation time. The effect of the reduced recombination time on the pulse dynamics of a mode-locked laser setup was studied with a Bi-doped fibre laser. The pulse quality was found to improve with increased irradiation time and reduced recombination time, demonstrating the potential of the in-situ irradiation method for device applications.
Organically modified silica nanoparticles, doped with photosensitizers, are synthesized, characterized and used for photodynamic therapy (PDT) of cancer. These nanoparticles were uptaken by tumor cells in vitro and the effect of photon-induced toxicity was demonstrated.
High-Q surface mode micro-cavities in silicon-on-insulator (SOI) structures are investigated. Cavity structures in amorphous silicon based SOI structures show intrinsic Q values of 2000, while cavities in crystalline SOI structures can have intrinsic Q values larger than 10(4).
We experimentally demonstrate resonance-splitting and enhanced notch as a result of the mutual mode coupling in silicon ring resonator. Dense wavelength conversions, wavelength multicasting and optical up-converter are demonstrated in the split silicon ring resonator. A temporal differentiator and format conversion from NRZ to AMI are demonstrated utilizing the filtering effect of ring resonator. Photonic phase shifter and delay line are demonstrated utilizing the phase shift of ring resonator.
The coupling efficiency between external plane waves and the Bloch waves in photonic crystals are investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air n=l and a photonic crystal with effective index -1. It is also shown that, for point imaging by a photonic crystal slab owing to the negative refraction, the influence of the surface termination to the transmission and the imaging quality is significant. Finally, we present results demonstrating experimentally negative refraction in a two-dimensional photonic crystal.
We present some of our recent results for negative refraction in photonic crystals. The concept of negative refraction in photonic crystals is firstly introduced. Then, the propagation of electromagnetic waves in photonic crystals is systematically studied. By the layer Korringa-Kohn-Rostoker method, the coupling efficiency between external plane waves and the Bloch waves in photonic crystals is investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air with n=1 and a photonic crystal with effective index n(eff)=-1. It is also shown that, for point imaging by a photonic crystal slab, owing to the negative refraction, the influence of the surface termination on the transmission and the imaging quality is significant. Finally, we present results experimentally demonstrating negative refraction in a two-dimensional photonic crystal at optical communication wavelengths.
The exploitation of photonic technology through application of switching principles and system concepts in switch implementation, i.e. photonics in switching, is a very challenging topic in the field of optical networking research. Many European research teams have been involved in high quality studies and trials in this field since several years and obtained funding opportunities for joining their expertise within the e-photon/One+ Network of Excellence. This talk aims at presenting how collaborations on photonics in switching research has been organized within e-Photon/One+ and which actions have been finalized for exploitation and dissemination of this knowledge in science and education. The paper will report a description of research contributions from different partners involved in photonics in switching research.
This paper describes recent research activities and results in the area of photonic switching carried out within the Virtual Department on Switching (VDS) of the European e-Photon/ONe Network of Excellence. Contributions from outstanding European research groups in this field are collected to offer a platform for future research in optical switching. The paper contains the main topics related to network scenarios, switch architectures and experiments, with an effort to investigate synergies and challenging opportunities for collaboration and integration of research expertise in the field.
Hierarchical (multi-core) Wavelength Division Multiplexing (WDM) networks present a challenging design problem to the network designer who wishes to establish all-optical circuits end-to-end and across multiple network cores. Due to the nature of the hierarchical structure and its traffi distribution, it is likely that the inner core requires more capacity when compared to the capacity required by the metro cores, which are individually connected to the inner core. This capacity mismatch cannot be addressed by assigning distinct transmission rates to each core, as this solution would result in using electronic time division add-drop multiplexer to interconnect the traffi across cores with distinct rates. An alternative solution to addressing the capacity mismatch between WDM metro and inner core is explored in this paper, which is based on a limited number of wavelengths (a subset of the full set) being used in the metro core, when compared to the full set of wavelengths being used in the inner core. Two available architectures are presented in the paper, discussing their respective advantages and disadvantages.
PlaNet is a multilayer network planning tool developed at the University of Texas at Dallas. This demo willillustrate some of the features of PlaNet-PTN, one of the modulesavailable in the PlaNet tool. PlaNet-PTN can be used to designand plan a single layer packet transport network (PTN). Qualityof protection, routing constraints, minimization of the networkequipment cost, and user’s desired run time of the tool are justsome examples of the features available in PlaNet. As shown inthe demo, the PlaNet-PTN planning module is able to provide,among others, optimization of LSP-tunnel routes, link capacityplacement, node and link equipment configuration.
A careful wavelength assignment (WA) to lambda services must be performed to reduce the total number of wavelength converters (WCs) that are required when the wavelength continuity constraint cannot be met in wavelength division multiplexing (WDM) networks. With the successful introduction of reconfigurable optical add-drop multiplexers (ROADMs), WDM networks are now growing in size, both in the number of optical nodes and the number of wavelengths supported. Fast and memory efficient WA algorithms are required to design cost effective large WDM networks. This paper presents a scalable and efficient WA heuristic algorithm aimed at reducing the total number of WCs that are required in (large) WDM networks bearing static lambda services. The WA algorithm is applied to both unprotected and (dedicated) protected lambda services. In the latter case, the wavelength continuity constraint between the working and protection path of a lambda service is taken into consideration when non-tunable optical transceivers are employed.
PlaNet is a multilayer network planning tool developed at the University of Texas at Dallas. This paper illustrates some of the features of PlaNet-PTN, one of the modules available in the PlaNet tool. PlaNet-PTN can be used to design and plan a single layer packet transport network (PTN). Quality of protection, routing constraints, minimization of the network equipment cost, and user’s desired run time of the tool are just some examples of the features available in PlaNet. As shown in the paper, the PlaNet-PTN planning module is able to provide, among others, optimization of Label Switched Path (LSP) routes, link capacity placement, node and link equipment configuration.