Optoelectronic Conversions Research Articles

High-Throughput Prediction of the Band Gaps of van der Waals Heterostructures via Machine Learning

Van der Waals heterostructures offer an additional degree of freedom to tailor the electronic structure of two-dimensional materials, especially for the band-gap tuning that leads to various applications such as thermoelectric and optoelectronic conversions. In general, the electronic gap of a given system can be accurately predicted by using first-principles calculations, which is, however, restricted to a small unit cell. Here, we adopt a machine-learning algorithm to propose a physically intuitive descriptor by which the band gap of any heterostructures can be readily obtained, using group III, IV, and V elements as examples of the constituent atoms. The strong predictive power of our approach is demonstrated by high Pearson correlation coefficient for both the training (292 entries) and testing data (33 entries). By utilizing such a descriptor, which contains only four fundamental properties of the constituent atoms, we have rapidly predicted the gaps of 7140 possible heterostructures that agree well with first-principles results for randomly selected candidates.

Intra-node high-performance computing network architecture with nanosecond-scale photonic switches [Invited

We propose a single-stage network architecture for intra-node connectivity that makes use of nanosecond-scale photonic switches. Although buffering at the switch points is of vital importance for complex multistage networks, this is not the case for smaller-scale single-stage networks where the end nodes are located only one hop apart. By limiting the buffering to the end points, the proposed architecture manages to minimize the required electro-optic and opto-electronic conversions, leading in this way to both low end-to-end latency and better energy efficiency. Combining these advantages with nanosecond-scale switching times can allow for high-throughput operation, even for frequent switch reconfigurations. The performance of the proposed architecture is evaluated via discrete-event simulations for a wide range of synthetic-traffic cases. The simulation results show that high-throughput operation of ≥ 90 % can be achieved even for small message sizes, i.e., 32 KB for all-to-all communication and 2 KB for uniform random traffic, at a data rate of 400 Gb/s and a switch reconfiguration time of ≤ 72 n s . Moreover, if 100 ns reconfiguration times are achievable as opposed to 150 ns, then for the all-to-all traffic case a 16% and 28% reduction in completion time can be achieved for message sizes of 8 KB and 1 KB, respectively. In a forthcoming era of optically interfaced processors and accelerators, nanosecond-scale photonic switches appear as a highly promising solution for keeping up with the intra-node bandwidth scaling due to their high-bandwidth, low-latency, and fast-switching capabilities.

Experimental AND and OR Logic Gates With MZI and SOA Using PAM Modulation

One of the main limitations of optical communication systems is the current need for optoelectronic conversions in intermediate devices, which do not reach the transmission rates of optical fibers of terabits per second. In this work, we investigated the obtaining of logic gates through a configuration of a Mach–Zehnder interferometer with a semiconductor optical amplifier (SOA) as the unbalancing element of the interferometer. We experimentally studied three different scenarios of input power for a continuous wave regime and one scenario for the PAM regime, both with varying levels of gain of the SOA. As a result, we obtained the AND and OR logic gates in all scenarios in a wide range of gain of the SOA, besides the logic functions 0 and 1 in some of the cases. We confirm the quality of these logic gates by the precision rate regarding the threshold of 0.4 dB above and below the central limit, according to recommendations from the literature. We highlight that the technique used in this experiment is much less complex than most of those described in the literature. The use of pulse amplitude modulation (PAM) suggests a simpler way for controlling logic gates, once we can obtain those by simply changing the injection current applied by the SOA. The experimental obtaining of such logic gates is relevant for all-optical logic circuits that are proposed to optimize the current optical communication systems.

Transport Mechanisms for Mobility Support in Optical Slot Switching-Based Next-Generation Mobile Backhaul Networks

In order to implement the next-generation (e.g., LTE-A) mobile backhaul networking segment, an optical slot switching solution called packet optical add/drop multiplexer (POADM) was previously proposed. Optical slot switching is at the same time a high capacity, energy-efficient, and low-latency optical transport network technology that relies on the direct transmission of data from base station to base station without resorting to time-consuming electronic processing and energy-hungry optoelectronic conversions. Low latency is an important requirement of mobile backhaul networks for real-time traffic such as Coordinated MultiPoint (CoMP) and POADM was shown to be compatible with the strict latency requirement of CoMP—1 ms end-to-end—even for very high network loads of 80% and above. However, user mobility was not taken into account. The traffic of users moving from one cell to another cell during handovers should also meet this strict requirement. In this paper, we propose and evaluate several transport mechanisms to support User Element mobility at the optical layer in a next-generation mobile backhaul network implemented using our previously proposed optical slot switching technology. We show with simulations that with smart introduction of additional electronic processing for handover traffic only (traffic of user elements that have moved from one cell to another), very strict latency constraints (sub-ms) can be met even for the time-sensitive mobile traffic.

Extracting high electrical currents with large fill factors from core/shell silicon nanopillar solar cells

Although it is possible to improve the optoelectronic conversions of solar cells through the construction of one-dimensional nanostructures on their front surfaces, much effort at such fabrication has led to only modest increases in conversion efficiencies. In this study, we employed i-line lithography and ion implantation to fabricate arrays of well-aligned, contamination-free silicon nanopillars with core/shell p–n junctions for use in high-performance nanostructured solar cells. Such structures provided concurrent improvements in both the optical and electrical characteristics of nanopillar devices. We extracted high currents with large fill factors from these lowly reflective nanopillar arrays, resulting in power conversion efficiencies of up to 11.70 ± 0.22%—that is, 28% higher than that of the planar counterpart. Moreover, when applying 75-nm-thick silicon nitride as a passivation layer on the nanopillars, the average total reflection over wavelengths in the range of 400–1020 nm decreased to 2.56%, while the power conversion efficiency increased further to 12.39%.

Solving the Routing and Wavelength Assignment problem with conflict-driven ASP solvers

The Routing and Wavelength Assignment (RWA) problem is an optical networking problem that aims to improve data transmission by eliminating optoelectronic conversions through the network. The RWA pr...

Solving the Routing and Wavelength Assignment problem with conflict-driven ASP solvers

The Routing and Wavelength Assignment (RWA) problem is an optical networking problem that aims to improve data transmission by eliminating optoelectronic conversions through the network. The RWA problem is in the set of NP-complete problems and thus, it is also an interesting problem from a computational point of view. It can be solved in different flavors, being the Static Lightpath Establishment (SLE) the one studied in this work.In this work we define different Answer Set Programming (ASP) encodings for the RWA–SLE problem and study their performance when solving the problem with a state-of-the-art conflict-driven ASP solver: clasp. We investigate the relation between the performance of the ASP encodings and two different characteristics of the encodings: the number of nogoods and loop nogoods generated during search and a new measure for their tightness that we introduce. We also compare the performance of our ASP encodings with the best performing pseudo-Boolean encoding that we presented in a previous work.

Wavelength layer recovery in transparent optical networks

Ultra-high capacity transmission systems utilizing dynamic photonic switches enable transparent networking with reduced optoelectronic conversions and simplified and automated operations and maintenance. Due to recent advances in control functions for wavelength switching in optical networks, network service providers envision the same level of automated connection provisioning and restoration capabilities at the wavelength layer as offered by time division multiplexing (TDM) or packet switched networks. Implementing Generalized Multiprotocol Label Switching (GMPLS), transparent networks can offer a high level of reliability with automatic restoration as well as reduced resources compared to legacy 1 + 1 protection mechanisms. Based on preplanned path computation, selection, signaling, and allocation of optical resources, three recovery schemes are described in the context of the wavelength connections: protection, dynamic restoration, and a combination of protection and restoration. Through the use of network simulations, we analyze the impact of transparency constraints such as optical switch activation delay and sequential light path establishment on the recovery time. This analysis includes the trade-off between different recovery strategies and transmission system reach. é 2010 Alcatel-Lucent.

New transmission systems enabling transparent network perspectives

Abstract The emergence of new devices and technologies introduces new trends and design issues for optical transport networks. The higher performance of transmission and switch systems enables the reduction of optoelectronic conversions in intermediate nodes with the introduction of transparency in the network. Simultaneously, the system of Automatic Switched Optical Networks (ASON) describes the rules for the construction of a network enabling cost reduction, above all for maintenance, and fast and automatic reconfiguration. Two axes have to evolve to make possible all these proprieties: the control plane and its relative set of protocols, to manage the network working for the network automation, and also the systems and tools enabling transparency and reconfigurability. In this article we focus on the second axis applied to an automatic transparent network. To cite this article: A. Morea et al., C. R. Physique 9 (2008).

Minimal Delay Traffic Grooming in WDM Optical Star Networks

All-optical networks face the challenge of reducing slower opto-electronic conversions by managing assignment of traffic streams to wavelengths in an intelligent manner, while maximizing the bandwidth resources utilization. This challenge becomes harder in networks closer to the end users that have insufficient data to saturate single wavelengths as well as traffic streams outnumbering the usable wavelengths. Traffic grooming has been proposed as a possible solution in the network closer to the end users. However, it requires costly traffic analysis at access nodes. We study the problem of traffic grooming that reduces the need to analyze traffic, for a class of network architecture mostly used by Metropolitan Area Networks; the star network. We first prove that the problem is NP-hard, then provide an efficient greedy heuristics that can be used to intelligently groom traffics at the LANs to reduce latency at the access nodes. Simulation results show that our greedy heuristics achieves a near-optimal solution.

Failure location algorithm for transparent optical networks

Fault and attack management has become a very important issue for network operators that are interested to offer a secure and resilient network capable to prevent and localize, as accurately as possible, any failure (fault or attack) that may occur. Hence, an efficient failure location method is needed. To locate failures in opaque optical networks, existing methods which allow monitoring of the optical signal at every regeneration site can be used. However, to the best of our knowledge, no method exists today that performs failure location for transparent optical networks. Such networks are more vulnerable to failures than opaque networks since failures propagate without being isolated due to optoelectronic conversions. In this paper, we present a failure location algorithm that aims to locate single and multiple failures in transparent optical networks. The failure location algorithm developed in this paper can cope with ideal scenarios (i.e., no false and/or lost alarms), as well as with nonideal scenarios having false and/or lost alarms.

Network control and management challenges in opaque networks utilizing transparent optical switches

There is a potential for significant cost, footprint, and power savings by eliminating unnecessary opto-electronic conversions on a signal path in a core optical mesh network. The article addresses and clarifies some fundamental issues surrounding all-optical networking and all-optical switching, and analyzes the trade-offs between transparent and opaque networking. It investigates a number of networking and interface compatibility issues that arise for an opaque network with transparent switches, and presents a number of ways to address these issues.

A novel self-routing address scheme for all-optical packet-switched networks with arbitrary topologies

Pure all-optical packet-switched networks in which both header processing and packet routing are carried out in the optical domain overcome the bandwidth bottlenecks of optoelectronic conversions and therefore are expected to meet the needs of next generation high speed networks. Due to the limited capabilities of available optical logic devices, realizations of pure all-optical packet-switched networks in the near future will likely employ routing schemes that minimize the complexity of routing control. In this paper, we propose a novel self-routing scheme that identifies the output ports of the nodes in a network instead of the nodes themselves. The proposed address scheme requires single bit processing only and is applicable to small to medium size pure all-optical packet-switched networks with arbitrary topologies. Unlike traditional self-routing schemes, multiple paths between two nodes can be defined. An hierarchical address structure can be used in the proposed routing scheme to shorten the address.

Optical WDM rings using a smart wavelength routing assignment

AbstractFunctionality is inserted into the physical layer of WDM optical networks in order to provide for an efficient carrier routing and packet‐addressing scheme. No optoelectronic conversions are needed along the network nodes, except at the source and destination nodes. Tuned transmitters or receivers are not used. The ancillary network routing management structure is dramatically reduced, together with the total network cost. Simple and efficient mechanisms to avoid optical carrier modulation inefficiency and data collision are introduced. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 121–125, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10392

The design of fiber-optic filters

Fiber-optic filters can be used for processing wideband radio-frequency, microwave, and millimetric signals directly in the optical domain avoiding costly electrooptic and optoelectronic conversions. Because these filters sum signals on an intensity basis, they are bound to be positive and, hence, heavily restricted in their achievable performance. Nevertheless, such filters are the only choice because positivity is a consequence of the underlying physical mechanism. In this paper, the authors present a new design methodology to realize an arbitrary filter as a difference of two positive filters, thus overcoming any performance limitation.

Compact parallel optical modified-signed-digit arithmetic-logic array processor with electron-trapping device

A compact two-step modified-signed-digit arithmetic-logic array processor is proposed. When the reference digits are programmed, both addition and subtraction can be performed by the same binary logic operations regardless of the sign of the input digits. The optical implementation and experimental demonstration with an electron-trapping device are shown. Each digit is encoded by a single pixel, and no polarization is included. Any combinational logic can be easily performed without optoelectronic and electro-optic conversions of the intermediate results. The system is compact, general purpose, simple to align, and has a high signal-to-noise ratio.

Optical versus electronic switching for broadband networks

The authors compare the use of electronic and optical switching for broadband networks. Their technological merits and their ability to meet traffic demand when multimedia communications become ubiquitous are considered. The authors conclude that electronic ATM switches are adequate and commercially mature for local access. An ATM-mesh switch with multihop routing can be used to achieve capacity of several hundreds of gigabits per second. Beyond access, the authors argue that traffic aggregation may allow switching to be performed on much longer time scales than that of ATM cells. Wavelength and mechanical fiber switching may be used economically for trunk switching, avoiding the expensive processes of optoelectronic conversions and demultiplexing.

Investigation of thick, low-temperature plasma deposited silica films for waveguide fabrication

Optical devices, such as directional couplers made from silica waveguides, are used to route optical signals at points where optoelectronic conversions are necessary. We report the fabrication of silica waveguides using low-temperature plasma deposition and etching processes. The devices are buried-ridge, single-mode waveguide structures with a refractive index difference (Δn) of 0.03 between the guiding and cladding layers. Two different plasma deposition processes with different reactant chemistries (SiH4/N2/N2O) and 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS)/O2 were used to fabricate the waveguides. The deposition rates, uniformities, film stress, and refractive index control obtained using the two techniques are discussed. The plasma etching process (CHF3/CF4/Ar chemistry) defining the guiding layer varied from a vertical profile (90°) down to 75°, to minimize void formation in the coupling regions of the devices. The step coverage obtained using the TMCTS process showed marked improvement when compared to silica films deposited using plasma-enhanced chemical-vapor deposition with SiH4/N2/N2O chemistry. The TMCTS chemistry produced plasma deposited films with increased deposition rates and the required precision for both the thickness and refractive index parameters necessary for waveguide device fabrication.

Mathematical modelling of the apparatus channel of an infrared remote sensing system

This paper presents a mathematical model of the apparatus channel of an infrared remote sensing radiometric system. The latter comprises: (1) the sounded object. This may be a medium, such as a cloud or a dense aerosol layer caused by a temperature inversion; (2) background radiation; (3) the atmospheric channel, or the medium where the signal radiation from the sounded object and the background radiations propagate; (4) the apparatus channel or the infrared radiometer itself. The system described is useful for investigating, measuring or controlling objects and media. The apparatus channel modelled is proposed as a lock-in detector. The joint action of all types of noise due to the stochastic nature of the infrared radiation or to the optoelectronic and electronic conversions is discussed. The final results allow calculation of the apparatus channel output signal-to-noise ratio.

Fabrication of waveguides using low-temperature plasma processing techniques

The proliferation of the use of light as the transfer medium in communications has brought about some unique technical challenges. Among these is the development of devices that route optical signals at points where optoelectronic conversions are necessary. In this article we discuss the fabrication of silicon oxide waveguides on silicon substrates, describing low-temperature plasma deposition processes and the relationship between crucial optical parameters of the films and the significant processing parameters. The waveguides are buried-ridge, single-mode waveguide structures fabricated using two deposition techniques: plasma-enhanced chemical vapor deposition and low-pressure chemical vapor deposition. We will present the plasma deposition conditions established to control the two refractive index differences (Δn) of 0.065 and 0.020 between the guiding and cladding layers for two different waveguide designs. Uniformity of the Δn as a function of plasma conditions and dopant species will be presented for the guiding layer. The analytical techniques used to evaluate the properties of the guiding layers doped with fluorine and nitrogen consisted of Auger spectroscopy, infrared spectroscopy, ellipsometry, and prism coupling techniques. In addition, we will present the plasma etching conditions required to fabricate of the waveguiding ridge structures. The etch rates and uniformities obtained in two different reactors using either SF6 or CF4 chemistries will be discussed.