Autonomous and dynamic reconfigurable waveguide for optical interconnection with large shift-tolerance

Dynamic reconfiguration techniques can greatly improve the flexibility and reliability of manufacturing systems. However, different from static reconfigurable systems, system behavior during dynamic reconfiguration processes is quite complex due to possible concurrence of system structure changes and events inside unaltered components. This increases the difficulty in designing and developing dynamic reconfigurable systems. The current paper deals with the analysis and control of dynamic reconfiguration process of manufacturing systems from the perspective of discrete event systems. To this end, the authors improve the reconfigurable timed net condition/event systems formalism by assigning reconfiguration functions with extra permeating time, action ranges, and concurrent decision functions. As a consequence, nondeterministic behavior of a dynamic reconfigurable system during dynamic reconfigurations can be specified, while the system correctness, coherence, and safety during reconfigurations can be guaranteed. A reconfigurable manufacturing plant is used as a running example to illustrate the contribution of this paper.

Researchers at the University of Adelaide, Australia, and the Islamic University of Technology, Bangladesh, report the optimum design for a porous photonic crystal fibre capable of terahertz frequency transmission. Photonic crystal fibres (PCFs), also known as micro-structured optical fibres (MOFs), are a new class of optical fibre. The significance of PCFs is their remarkable optical properties, such as providing single mode operation, high birefringence, and controllable chromatic dispersion characteristics, which are not obtainable using conventional optical fibres. As a result, PCFs are used extensively in different medical imaging applications, for example, in Optical Coherence Tomography (OCT). OCT is an imaging technology that allows non-invasive cross-sectional imaging of biological tissue. Bringing such techniques into the terahertz domain will be assisted by the development of PCFs that operate in the terahertz regime. There are different types of PCFs, including solid core PCF, hollow core PCF and porous core PCF. A solid core PCF experiences large material loss, which is a property that makes these PCFs unsuitable for terahertz signal transmission. In a hollow core PCF, the loss is greatly reduced, but such fibres operate over a narrow frequency range. To overcome the described disadvantages of solid core and hollow core fibres, porous core fibres were introduced. A porous core fibre contains a number of micro-structured air holes in the core. The advantage of the porous structure is that the fibre global parameters, including air hole size, pitch distance (centre-to-centre distance between air holes), core diameter and shape of air holes can be tuned as required for different applications. Thus, for porous fibre PCFs, the effective material loss, birefringence, dispersion, confinement loss, numerical aperture and other modal properties can be obtained by design. Nowadays, PCFs are used in the field of sensing, biomedical imaging, time domain spectroscopy, security, detecting DNA hybridisation and bio-sensing, skin cancer and breast cancer detection, and in communication applications. However, there are no previously reported articles on terahertz PCFs with sufficient numerical aperture (NA) to be used for OCT applications. In this issue of Electronics Letters, Saiful Islam and colleagues propose a terahertz PCF with high birefringence, high NA, and near zero dispersion variation. The measured high birefringence is reported to be due to the elliptical-shaped asymmetrical structure of the air holes inside the core. The asymmetrical structure of air holes created a refractive index difference between the polarisation modes, thus generating birefringence. The observation of high NA is reported to be due to the high birefringence and high modal effective area. Moreover, flattened dispersion is reported due to the waveguide structure and chosen materials that the waveguide was formed of. The kagome-based PCF has the advantage that it has a significantly lower confinement loss than other PCF structures. Terahertz time-domain spectroscopy set-up in the National T-Ray lab at the University of Adelaide. Saiful Islam at the University of Adelaide. The reported simulations in this Letter have allowed for rapid design optimisation that can now be experimentally tested. The major challenge of a PCF design is to anticipate difficulties in fabrication. Thus, the fabrication possibilities of a PCF must be addressed. For accuracy, obtaining correct parameters to describe the structural and optical properties of the fibre, such as refractive index, material absorption loss, relative permittivity and relative permeability, is of great importance. S. Islam states that ‘‘Our PCF design was produced with ease of fabrication in mind, allowing future realisation. Thus, applications in THz-OCT, chemical sensing, and multichannel communications are envisaged.’’ S. Islam and colleagues are currently using photonic crystal fibres to design chemical sensors for skin cancer detection. Non-invasive breast cancer detection is possible via detecting the presence of certain protein markers in human saliva. The authors are also designing sensors to detect hazardous chemicals for security applications. ‘‘We are planning to extend our PCF designs with the use of graphene or gold coasting to exploit surface plasmons for enhanced sensing’’, explains S. Islam. In practice, PCFs are limited to reasonably simple geometries due to difficulties in fabrication. However, emerging techniques exploiting developments in 3D printing are promising methods to overcome current limitations. S. Islam predicts that ‘‘It is possible that in the next decade will we begin to see more sophisticated PCFs with remarkable properties that are not deemed practical in today's technology.’’

We present experimental analysis of supercontinuum generation obtained for highly birefringent and highly nonlinear dual-mode fiber. A specific difference between the zero dispersion wavelength of fundamental mode and higher order mode in such fiber gives possibility of a normal and an anomalous dispersion regime pumping, depending on the mode, which is excited. The nonlinear effects responsible for the generation of broadband spectrum of the light are analyzed when the fiber is pumped by the pulse pump source operating at the wavelength of 1064nm. Full Text: PDF References J. M. Dudley, G. Goëry, and C. Stéphane, "Supercontinuum generation in photonic crystal fiber", Reviews of modern physics 78(4), 1135 (2006). CrossRef J. C. Knight, and D. V. Skryabin, "Nonlinear waveguide optics and photonic crystal fibers", Opt. Express, 15(23), 15365-15376 (2007). CrossRef Z. Holdynski et al., "Experimental study of dispersion characteristics for a series of microstructured fibers for customized supercontinuum generation", Opt. Express 21(6), 7107-7117 (2013). CrossRef M. Napierala et al., "Influence of photonic crystal fiber manufacturing inaccuracies on supercontinuum generation", SPIE Photonics Europe, International Society for Optics and Photonics, p. 91361M-91361M-6 (2014). CrossRef J. M. Dudley, and J. R. Taylor: Supercontinuum generation in optical fibers (Cambridge University Press, 2010). CrossRef P. Falk, M. H. Frosz, and O. Bang, "Supercontinuum generation in a photonic crystal fiber with two zero-dispersion wavelengths tapered to normal dispersion at all wavelengths", Opt. Express 13(19), 7535?7540 (2005). CrossRef A. Hartung, A. M. Heidt, and H. Bartelt, "Design of all-normal dispersion microstructured optical fibers for pulse-preserving supercontinuum generation", Opt. Express, 19, 7742-7749 (2011). CrossRef B. Jinendra, K. Ranka, R. S. Windeler, and A. J. Stentz, "Optical properties of high-delta air?silica microstructure optical fibers", Opt. Lett., 25, 796-798 (2000). CrossRef J. C. Knight et al., "Anomalous dispersion in photonic crystal fiber", IEEE Photon. Technol. Lett. 12(7), 807?809 (2000). CrossRef T. Tenderenda et al., "Fibre Bragg Gratings written in highly birefringent microstructured fiber as very sensitive strain sensors", SPIE Photonics Europe, International Society for Optics and Photonics, p. 84260D-84260D-8 (2012). CrossRef T. Tenderenda et al., "Highly birefringent dual-mode microstructured fiber with enhanced polarimetric strain sensitivity of the second order mode", Opt. Express, 20, 26996-27002 (2012). CrossRef K. Stepien et al., "Fiber Bragg gratings in hole-assisted multicore fiber for space division multiplexing", Opt. Lett., 39, 3571-3574 (2014). CrossRef http://www.lumerical.com/tcad-products/mode/. DirectLink

A multi-mode circuit implements the functionality of a limited number of circuits, called modes, of which at any given time only one needs to be realised. Using dynamic partial reconfiguration of an FPGA, all the modes can be implemented on the same reconfigurable region, requiring only an area that can contain the biggest mode. This can save considerable chip area. Conventional dynamic partial reconfiguration techniques generate a configuration for every mode separately. As a result, to switch between modes the complete reconfigurable region is rewritten, which often leads to long reconfiguration times. In this paper we give an overview of research we conducted to reduce this overhead of dynamic partial reconfiguration for multi-mode circuits. In this research we explored several joint optimization strategies at different stages of the tool flow.

The dramatic reduction of transmission loss in optical fibers coupled with equally important developments in the area of light sources and detectors has brought about a phenomenal growth of the fiber optic industry during the past two decades. The birth of optical fiber communication coincided with the fabrication of low-loss optical fibers and room-temperature operation of semiconductor lasers in 1970. Ever since, the scientific and technological progress in this field has been so phenomenal that we are already in the fifth generation of optical fiber communication systems within a brief span of 30 years. Recent developments in optical amplifiers and wavelength division multiplexing (WDM) are taking us to a communication system with almost "zero" loss and "infinite" bandwidth. Indeed, optical fiber communication systems are fulfilling the increased demand on communication links, especially with the proliferation of the Internet. This module, Optical Waveguides and Fibers, is an introduction to the basics of fiber optics, discussing especially the characteristics of optical fibers as regards their application to telecommunication (to be covered in Module 1.8, Fiber Optic Telecommunication) and fiber optic sensors.

This study presents the development and modeling of a photonic crystal fiber (PCF) sensor designed for detecting harmful chemicals in polycarbonate plastics. The sensor features a wheel-shaped PCF structure with a floral pattern in the initial cladding layer. The focus is on two significant chemical compounds commonly found in plastics, bisphenol A (BPA) and bisphenol S (BPS). The individual sensitivities of the sensor to these compounds are measured, achieving relative sensitivities of 90.716% for BPS and 84.688% for BPA. The effective refractive indices for BPS and BPA are found to be 1.499 and 1.550, respectively. Additionally, the study analyzes confinement loss and nonlinearity of the proposed structure when exposed to these compounds, demonstrating low confinement loss and high nonlinearity, which are desirable attributes for sensing applications. The octagonal floral structure of the PCF sensor shows potential for a variety of applications, including chemical and biochemical sensing and nonlinear optics. The propagation characteristics and performance of the wheel-shaped hollow-core PCF have been thoroughly analyzed within the wavelength range of 1.5 μm to 2.5 μm. The sensor, utilizing silica as the background material, exhibits high sensitivity and low confinement loss. The analysis indicates that increasing the number of air holes in the cladding and enlarging the core size, where electromagnetic waves interact with the analyte, can further enhance sensitivity and detection accuracy with minimal losses. The PCF sensor offers real-time, label-free detection of chemical compounds with a high birefringence of -9.594×10-5, a highest refractive index (RI) of 1.550, and an effective area of 4.373×10-12 m2 for BPS at 1.2 μm. The proposed method yields negligible confinement loss, making it suitable for applications in optical fiber sensing, optical waveguides, and various photonic devices.

Optical waveguides have assumed major importance, not only in optoelectronic applications but also, quite recently, in a study of fundamental physical properties of materials. The propagation characteristics of linear optical waveguides, and to a lesser extent those of waveguides curved in a single plane, are well understood. However, optical waveguides having three-dimensional curvature, for example the helical waveguide, have been proposed and fabricated and an analysis of its properties is essential. In this paper the scalar wave equations for a three-dimensionally curved optical fibre are solved analytically and boundary conditions are applied to the curved core-cladding interface. An asymptotic formula for computing the propagation constant is proposed and the effects of curvilinearity on the characterization of the bound modes are discussed. By using the equivalent fictitious electromagnetic current method, the far radiative field is established and expressions for the radiation losses for various modes are derived.

In this work, we study a novel type of optical waveguide, whose properties derive from a periodic arrangement of fibers (not necessarily circular), and from a central structural defect along which the light is guided. We first look for propagating modes in photonic crystal fibers of high indexcore region which can be single mode at any wavelength (1-4). Unlike the first type of photonic crystal fibers, whose properties derive from a high effective index, there exists some fundamentally different type of novel optical waveguides which consist in localizing the guided modes in air regions (4-5). These propagating modes are localized in a low-indexstructural defect thanks to a photonic bandgap guidance for the resonant frequencies (coming from the photonic crystal cladding). We achieve numerical computations with the help of a new finite element formulation for spectral problems arising in the determination of propagating modes in dielectric waveguides and particularly in optical fibers (7). The originality of the paper lies in the fact that we take into account both the boundness of the crystal (no Bloch wave expansion or periodicity boundary conditions) and the unboundness of the problem (no artificial boundary conditions at finite distance). We are thus led to an unbounded operator (open guide operator) and we must pay a special attention to its theoretical study before its numerical treatment. For this, we choose the magnetic field as the variable. It involves both a transverse field in the section of the guide and a longitudinal field along its axis. The section of the guide is meshed with triangles and Whitney finite elements are used, i.e., edge elements for the transverse field and node elements for the longitudinal field. To deal with the open problem, a judicious choice of coordinate transformation allows the finite element modeling of the infinite exterior domain. It is to be noticed that the discretization of the open guide operator leads to a generalized eigenvalue problem, solved thanks to the Lanczos algorithm. The code is validated by a numerical study of the classical

Eigenvalue equations for solving full-vector modes of optical waveguides are formulated using Yee-mesh-based finite difference algorithms and incorporated with perfectly matched layer absorbing boundary conditions. The established method is thus able to calculate the complex propagation constants and the confinement losses of leaky waveguide modes. Proper matching of dielectric interface conditions through the Taylor series expansion of the fields is adopted in the formulation to achieve high numerical accuracy. The method is applied to the study of the holey fiber with triangular lattice, the two-core holey fiber, and the air-guiding photonic crystal fiber.

Debugging of Field-Programmable Gate Arrays (FPGAs) is a difficult task due to the limited access to the internal signals of the design. Embedded logic analyzers enhance the signal observability for FPGAs. These analyzers are implemented on the FPGA resources and they use the embedded memory blocks as trace buffers, so a limited number of signals can be observed using these analyzers due to resources constraints. Changing the traced set of signals requires re-synthesis, placement and routing of the whole design. In this paper, we propose a new methodology for FPGA debugging to change dynamically the set of signals to be observed at runtime, and consequently minimize the time required for debugging. The proposed methodology utilizes the Dynamic Partial Reconfiguration (DPR) technique to dynamically switch between different sets of signals. DPR creates a reconfigurable module (RM) to route each set of signals to an embedded logic analyzer. We demonstrate the proposed approach using Xilinx FPGA tools, finding that changing the set of signals to be observed requires only few milli-seconds to re-program the reconfigurable region (RR). The area overhead of the proposed methodology is lower than other traditional methods of using multiplexers as the DPR allows the routing module to only use buffers to connect a set of signals to the embedded logic analyzer.

The Beam Propagation Method (BPM) is the most widely used tool for the investigation of complex photonic structures. Since the original BPM was introduced, many improvements and extensions have been proposed. We have developed a computer program based on the Finite Difference BPM for modeling propagation in optical waveguides. This method has been successfully applied for several 3D problems such as propagation on Bragg Fiber. The main drawback of this method is its complexity and long computation time using a personal computer. In this paper, a simple efficient numerical solution method, we called double 2D-BPM, is proposed. This technique is based on the decomposition of the 3D field propagation equation onto two 2D equations related to transverse plans. Propagation along the x and y axes is computed separately in two steps. Using a similar technique, a finite difference approximation for each propagation step involves the solution of two equations and the complete problem splits into two independent 2D problems. We performed propagation tests in elementary 3D problems but also on Bragg fiber. The numerical results of 3D-BPM and double 2D-BPM have been compared. The propagation step along the propagation axis has been experimentally determined. Parameters that affect the accuracy and the stability of this method were discussed. Losses induced by propagation on Bragg fiber were also considered. We have established that the global effect of the double 2D-BPM is equivalent to 3D-BPM technique. Comparison with exact results obtained from analytical expressions also shows excellent agreement.

The ability to reconfigure around manufacturing defects and operational faults increases FPGA chip yield, reduces system downtime and maintenance in field operation, and increases reliabilities of mission- and life-critical systems. The fault reconfiguration technique discussed in this work use the principle of node covering in which reconfiguration is achieved by constructing replacement chains of cells from faulty cells to spare/unused ones. A key issue in such reconfiguration is efficient incremental rerouting in the FPGA. Previous methods for node-covering based reconfiguration are “static” in the sense that extra interconnects are added a-priori as part of the initial circuit routing so that a specific fault pattern (e.g., one fault per row) can be tolerated [1]. This, however, results in worst-case track overheads and also in an inflexibility to tolerate other realistic fault patterns. In this paper, we develop dynamic reconfiguration and incremental rerouting techniques that are fault specific. In this approach, the FPGA is initially routed without any extra interconnects for reconfiguration. When faults occur, the routed nets have to be minimally perturbed to allow these interconnects to be inserted “on-the-fly” for reconfiguration. These requirements are addressed in our minimally incremental rerouting technique Conv_T-DAG, which uses a cost-directed depth-first search strategy. We prove several results that establishes the near-optimality of Conv_T-DAG in terms of track overhead. To the best of our knowledge, this is the first time that an incremental rerouting technique has been developed for FPGAs. For several benchmark circuits, the static approach to tolerating one fault per row resulted in a 43% to 34% track overhead.Using the dynamic reconfiguration approach and Conv_T-DAG results in an average overhead of only 16%—an improvement of more than 50%. Over all circuits, the reconfiguration time per fault ranges from 16.8 to 72.9 secs. Simulation of smaller fault sets of one to four faults show very small track overheads ranging from 1.75% to 4.49%. Conv_T-DAG can also be used for interconnect fault tolerance.

Devices that incorporate optical dielectric waveguides in their design now play a significant role in communications and signal processing. Optical fibers used in telephone communications are a familiar example of passive waveguides, but research activity is growing in the area of devices that actively switch or modulate light. The increasing interest in optical waveguides and the increasing complexity of waveguide devices have stimulated the development of mathematical tools for waveguide analysis. One set of important but difficult problems is characterizing propagation in inhomogeneous structures, i.e. waveguide structures that vary in the direction of propagation.KeywordsLithium NiobateWaveguide StructureDielectric WaveguideSlab WaveguideBeam Propagation MethodThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Photonic Crystal Fibers (PCFs) have extended the range of capabilities in optical fibers, both by improving well-established properties and introducing new features. PCFs are optical fibers that employ a microstructured arrangement in a background material of different refractive index. The background material is often undoped silica and a low index region is typically provided by air voids running along the length of the fiber.The strong wavelength dependency of the effective refractive index and the inherently large design flexibility of the PCFs allow for a whole new range of novel properties. Such properties include endlessly single-moded fibers, extremely nonlinear fibers and fibers with anomalous dispersion in the visible wavelength region. Fabrication of PCF, like in conventional fiber fabrication, starts with a fiber preform. PCF preforms are formed by stacking a number of capillary silica tubes and rods to form the desired air/silica structure. This way of creating the preform allows a high level of design flexibility as both the core size and shape as well as the index profile throughout the cladding region can be controlled.When the desired preform has been constructed, it is drawn to a fiber in a conventional high-temperature drawing tower and hair-thin photonic crystal fibers are readily produced in kilometer lengths.

Recently, the generation of coherent, octave-spanning, and recompressible supercontinuum (SC) light has been demonstrated in optical fibers with all-normal group velocity dispersion (GVD) behavior by femtosecond pumping. In the normal dispersion regime, soliton dynamics are suppressed and the SC generation process is mainly due to self-phase modulation and optical wave breaking. This makes such white light sources suitable for time-resolved applications. The broadest spectra can be obtained when the pump wavelength equals the wavelength of maximum all-normal GVD. Therefore each available pump wavelength requires a specifically designed optical fiber with suitable GVD to unfold its full power. We investigate the possibilities to shift the all-normal maximum dispersion wavelength in microstructured optical fibers from the near infra red (NIR) to the ultra violet (UV). In general, a submicron guiding fiber core surrounded by a holey region is required to overcome the material dispersion of silica. Photonic crystal fibers (PCFs) with a hexagonal array of holes as well as suspended core fibers are simulated for this purpose over a wide field of parameters. The PCFs are varied concerning their air hole diameter and pitch and the suspended core fibers are varied concerning the number of supporting walls and the wall width. We show that these two fiber types complement each other well in their possible wavelength regions for allnormal GVD. While the PCFs are suitable for obtaining a maximum all-normal GVD in the NIR, suspended core fibers are well applicable in the visible wavelength range.