Showing papers presented at "International Conference on Transparent Optical Networks in 2007"

Recent Developments in Optical Wireless Communications using Infrared and Visible Light

Abstract: For future short-range applications, optical wireless communications present a viable and promising supplemental technology to radio wireless systems. This contribution presents a review of infrared and visible light optical wireless indoor communications, including basics, state of the art, challenges and prospects. Advanced approaches based on diversity techniques and adaptive signal processing show potential to achieve both high spatial coverage and high bit rates of more than 100 Mb/s.

Free-Space Optical Communication Using Subearrier Modulation in Gamma-Gamma Atmospheric Turbulence

Abstract: Free-space optical communications (FSO) propagated over a clear atmosphere suffers from irradiance fluctuation caused by small but random atmospheric temperature fluctuations. This results in decreased signal- to-noise ratio and consequently impaired error performance. In this paper, the error performance of the FSO using a subcarrier intensity modulation (SIM) based on a binary phase shift keying scheme in clear but turbulent atmosphere is presented. To evaluate the system error performance in turbulence regimes from weak to strong, the probability density function of the received irradiance after traversing the atmosphere is modelled using the gamma-gamma distribution and the effect of turbulence induced irradiance fluctuation is mitigated using spatial diversity.

Radio over Fiber Technologies and Systems: New Opportunities

Abstract: A key initiative in the deployment of new wireless services is to cost effectively extend and enhance the network's radio coverage. Implementing a Distributed Antenna System (DAS) is a common method of extending radio coverage for multiple operators from multiple base stations to multiple locations. In this paper, how the Radio over Fiber (RoF) techniques can offer technically and economically attractive features compared with other ways to provide coverage is described.

Investigation in Free Space Optical Communication Links Between Unmanned Aerial Vehicles (UAVs)

Abstract: For critical civil and military missions, the Unmanned Aerial Vehicles (UAVs) are continuously attracting attention. UAVs should collect data for a defined area with a variety of sensors. When these UAVs are operating in swarm formation, the observation area could be increased and it would also be possible to deal with a loss of a UAV. The big amount of data produced by the UAVs requires high date rate connectivity, therefore the free space optical (FSO) communication is suitable. When using FSO links some important issues need be considered, the beam attenuation due the atmosphere on one side and the alignment of the FSO units on the other side. The alignment raises technical challenges in tracking and acquisition. The combination of UAVs with the FSO communication is an interesting investigative scenario and some of the important aspects of this ambitious design are the main focus of this paper.

10G EPON Development Process

Abstract: The recent kick-off of the 10G EPON system standardization effort in the IEEE [1] resulted in a lot of interest in the evolution of current PON systems towards high data rate systems capable of providing a future-proof platform for delivery of truly subscriber oriented and personalized triple-play services. The Ethernet in the First Mile (EFM) Task Force was disbanded in June 2004, having completed its task of developing and having ratified the IEEE 802.3ah specifications, now merged in the IEEE 802.3-2005 document. The following 2 years saw unprecedented field deployment of EPON systems [2-6], resulting in the currently installed port capacity, estimated at approximately 6 million deployed lines and 15 million ports installed in the Central Office (CO) of Service Providers (SPs) (port numbers valid for March 2007) [1]. Ethernet PON has therefore become a network of a choice for low cost, subscriber oriented digital service delivery, taking over the market previously dominated by DSL and cable modems. In this paper, we will therefore examine in more detail the current development process of 10 Gbit/s EPON systems, standardized in the framework of the IEEE 802.3av Task Force, looking at the technical challenges, drivers and evolution scenarios of the emerging high data rate access systems. Additionally, a brief comparison between EPON and GPON systems is presented, outlining the differences and similarities between these two PON technologies.

Centralised Optical Monitoring of Tree-structured Passive Optical Networks using a Raman-assisted OTDR

Abstract: Monitoring of tree-structured passive optical networks from a central office is difficult to achieve using a standard OTDR. Switchable reflective elements placed at the ONU can help to discriminate between the branches. In parallel, a Raman assisted OTDR is shown to increase the dynamic range of the reflectometry measurement, thus enabling to detect more faults in the network, and especially fibre breaks after the splitter.

Semiconductor Optical Amplifiers for FTTx

Abstract: Access networking is a hot topic. After Japan and Korea, demand is now picking up also in Europe and the US. After cherry-picking the easy installs, operators find that they could use a power boost in their passive optical networks to reach further out neighbourhoods from their present set of PON central offices. Hence the push for introducing optical amplification in access. As always, the main aim is cost reduction. Fewer COs means lower opex, while amplification before the PON splitter may mean higher split ratios, which in turn means that the same central office equipment can serve more end customers. Given the wavelength plan of a typical PON, the choice of optical amplifiers is limited to SOAs or Raman-assisted SOAs, depending on whether gain-flattened operation in a CWDM-PON is desired. Possible locations of the amplifier are as a booster/preamp at the OLT, or as a line amplifier near the passive splitter. These set different output power / noise figure requirements, where the in-line configuration allows for longer distances between the CO and the end customer, and/or higher split ratios. Operating regimes to be distinguished are NF-limited, gain limited, and power limited. Access networking is a hot topic. After Japan and Korea, demand is now picking up also in Europe and the US. After cherry-picking the easy installs, operators find that they could use a power boost in their passive optical networks to reach further out neighbourhoods from their present set of PON central offices. Hence the push for introducing optical amplification in access. As always, the main aim is cost reduction. Fewer COs means lower opex, while amplification before the PON splitter may mean higher split ratios, which in turn means that the same central office equipment can serve more end customers. Given the wavelength plan of a typical PON, the choice of optical amplifiers is limited to SOAs or Raman-assisted SOAs, depending on whether gain-flattened operation in a CWDM-PON is desired. Possible locations of the amplifier are as a booster/preamp at the OLT, or as a line amplifier near the passive splitter. These set different output power / noise figure requirements, where the in-line configuration allows for longer distances between the CO and the end customer, and/or higher split ratios. Operating regimes to be distinguished are NF-limited, gain limited, and power limited.

Integrating GMPLS in the OBS Networks Control Plane

Abstract: The GMPLS set of protocols have been consolidated as the model for building up a Control Plane for WCS (Wavelength Circuit Switched Networks). GMPLS, which is an extension of the MPLS model adopted in IP networks to introduce traffic engineering, constrained routing and connection oriented facilities, includes extensions to introduce these facilities also to circuit switched networks like SDH and WDM networks. Now, adapting GMPLS to optical networks providing statistical multiplexing capabilities like Optical Burst Switching (OBS) networks means close the cycle, since we are coming back to the origins, a packet switched network. In this paper we first discuss the main characteristics of OBS networks and compare them with those of IP and WDM networks, then based on these characteristics we analyze the potential new requirements of building up a Control Plane for OBS networks, and finally we suggest how to integrate GMPLS the OBS control plane.

Adaptive Multi-Path Routing for OBS Networks

Abstract: In this paper we present a novel adaptive routing strategy for OBS networks aimed at balancing global network load, in order to reduce overall burst loss probability. This strategy dynamically balances load in the output links of core nodes according to local congestion information. The results provided show a significant reduction in the load imbalancement of the links in the network, as well as a lower burst loss probability.

Optoelectronic Components for WDM-PON

Abstract: With the increasing demand for bandwidth, there is an ever growing interest in fibre to the home (FTTH) technologies and its deployments. Wavelength division multiplexing passive optical networks (WDM-PONs) have received a lot of attention as one of the best contenders for next generation optical access networks. In this paper we will overview on WDM-PON architectures, focussing our attention on reflective PON schemes that offer a cost-effective, colourless solution. The critical component required for these schemes is the reflective semiconductor optical amplifier (RSOA) transmitter at the customer premises. This paper will report latest results on RSOA technology for WDM-PON.

Focused-Ion-Beam Processing for Photonics

Abstract: Although focused ion beam (FIB) processing is a well-developed technology for many applications in electronics and physics, it has found limited application to photonics. Due to its very high spatial resolution in the order of 10 nm, and its ability to mill almost any material, it seems to have a good potential for fabricating or modifying nanophotonic structures such as photonic crystals. The two main issues are FIB-induced optical loss, e.g., due to implantation of gallium ions, and the definition of vertical sidewalls, which is affected by redeposition effects. The severity of the loss problem was found to depend on the base material, silicon being rather sensitive to this effect. The optical loss can be significantly reduced by annealing the processed samples. Changing the scanning strategy for the ion beam can both reduce the impact of gallium implantation and the redeposition effect.

SOAs for All-Optical Switching-Techniques for Increasing the Speed

Abstract: This paper reviews some of the most recent methods for increasing the speed of operation of all-optical switches based on semiconductor optical amplifiers (SOAs). We concentrate on two approaches; namely, methods to utilise the high-frequency tail of the nonlinear optical response of SOAs, and ways to reduce their gain recovery time.

BER Characteristic of Ground-to-Train Communication System Using Free-Space Optics Technology

Abstract: We propose a ground-to-train communication system using free-space optics between a train and the ground. In this paper, we evaluate BER characteristic in outdoor experiment using test train. The experimental results lead to the conclusion that the proposed system is a promising candidate for train communication from the viewpoint of BER characteristic.

1.25 - 10 Gbit/s Reconfigurable Access Network Architecture

Abstract: In this paper we propose a novel reconfigurable access network architecture which enables the bidirectional transmission of 1.25 - 2.5 Gbit/s. Optical network units (ONUs) are equipped with a reflective semiconductor optical amplifier (RSOA) and remote nodes (RNs) are based on microring resonators - both contribute to network transparency and flexibility. We also propose ONU upgrade to serve 10 Gbit/s per end-user. Next to the theoretical description and transmission simulations some principle measurement results are presented which show the feasibility of the concept.

OCDMA over WDM Transmission

Abstract: The optical code division multiple access (OCDMA) over wavelength division multiplexing (WDM) passive optical network (PON) system has been proposed as a potential candidate for gigabit-symmetric fiber-to-the- home (FTTH) services. Asynchronous OCDMA over WDM systems have been experimentally demonstrated using superstructured fiber Bragg gratings (SSFBG) and multi-port OCDMA en/decoders. The total throughput has reached above -380 Gbit/s with spectral efficiency of about -0.32.

Over-Stratospheric-Altitude Optical Free Space Links: System Performance Evaluation

Abstract: The wide bandwidth offered by optical communications systems, is attracting more and more interest in space applications. Investigation has been carried out either on suitable modulations or resilient architectures for communications and Earth Observation (EO) missions. New elements have been introduced: High-Altitude- Platforms (HAP's), whose characteristics allow us to carry out an optical link between unmoving terminals, if GEO satellites are involved. This paper is describing an architecture for EO, based on two HAP's linked via a GEO satellite, whose optical payload offers an inline-like amplification for an overall link that can extend over 80,000 km. The aim of our work is to present a low power consumption system that guarantees the required Bit Error Rate (BER) . Both Direct Detection (DD) and coherent (homodyne and heterodyne) systems will be considered.

Multiobjective Genetic Algorithm to Design Cost-Efficient Wavelength-Routed Optical Networks

Abstract: A new algorithm, GAPDELT, is presented to jointly design the resource provisioning and the logical topology of wavelength-routed optical networks. GAPDELT is based on genetic algorithms and uses Pareto optimality to reduce both the network congestion and the number of resources employed. By means of a simulation study, we show that GAPDELT designs a set of good alternatives that achieve up to 50% of reduction in terms of congestion or 75% of reduction in the number of transmitters and receivers required when compared with another well-known

Physical-Layer Considerations for The Realistic Deployment of Impairment-Aware Connection Provisioning

Abstract: Nowadays, impairment-aware connection provisioning is a hot topic due to the evolution of optical networks to all-optical infrastructures and to the need to maintain or enhance Quality of Service (QoS). Most of the research efforts in this field use complex, analytical models of impairments as the basis for the connection provisioning decision. However, these models are not fully feasible in practice due to cost, monitoring limitations and the architectures of impairment-aware Routing and Wavelength Assignment (RWA). This paper discusses key physical-layer considerations for the realistic deployment of impairment-aware connection provisioning, and provides an example of cost-effective, distributed Impairment-aware RWA (IRWA) in the context of the all- optical ADRENALINE testbed.

A Hybrid Optical Switch Architecture with Shared Electronic Buffers

Abstract: In this paper we present a hybrid opto-electronic switch architecture, which can be enhance the performance of optical packet switching (OPS) schemes. The proposed architecture is based on the use of electronic line-cards and packet cross-connect to a limited degree utilizing the large buffering capacity available only by means of electronic subsystems. This hybrid architecture achieves efficient utilization of optical network resources, which can be assigned dynamically in small time scales, limiting loss probability with controlled average latency.

Progress in Large Integration Scale Circuits in SiON Technology

Abstract: In this contribution the potentialities and the limitation of the silicon oxynitride (SiON) technology are reviewed and a number of integrated optical circuits and devices are presented. Mach-Zehnder, ring resonators, variable bandwidth filters, ring resonators based cross-bar matrices and a DQPSK receiver with interleaver and variable attenuators have been realized, characterized and tested in a 10 Gbit/s WDM system.

Theoretical and Experimental Study of Temperature-Dependent Spectral Properties of Multi-Layer Metal-Dielectric Nano-Film Structures

Abstract: We investigate theoretically and experimentally frequency-selective transmission and reflection characteristics of thin-film metal-dielectric multi-layer structures. The thin-film structures were deposited on glass substrates using a thermal evaporation technique, and their optical characteristics were studied in the visible and infrared frequency bands. A computational scheme based on a reiterative method for the calculation of reflection from a multi-layer stack is developed to model interference filters, polarization splitters and surface-plasmon sensors and also to study the effect of temperature change on the device characteristics. The temperature dependence is introduced in the model by taking into account the thermo-optic effect in the dielectrics and contributions from the phonon-electron and electron-electron scattering in metal layers. Detailed analysis of reflectance characteristics of thin-film stacks of various material compositions has been performed with the aim to estimate their temperature sensitivity, to achieve improved device performance and to design sensors and tunable filters.

Ultra High-Speed Optical Transmission based on LDPC-Coded Modulation and Coherent Detection for Employment in All-Optical Network Scenario

Abstract: The coded modulation schemes enabling 100+ Gb/s transmission by using commercially available components operating at 40 Giga symbols/s have been proposed and discussed in this paper. We considered bit-interleaved coded modulation (BICM) in combination with the low-density parity-check (LDPC) codes that are used as component codes, and in combination with coherent detection scheme. It was shown that coherent detection scheme outperforms the direct detection one and provides additional margin needed for application in an all-optical network scenario.

Impact of Mode-Partition Noise in the Performance of 10 Gbit/s Ethernet Passive Optical Networks

Abstract: The enormous success of Ethernet passive optical network (EPON) deployment has been inciting the development of upgrades for this system, namely the data rate upgrade. In these upgraded next generation access networks, low-cost and simplicity should play a fundamental role, and so the use of low cost multimode laser sources should be considered. However, impairments such as Mode-Partition Noise (MPN) will arise and will affect the performance of the network. This paper presents an evaluation of the impact of MPN in 10 Gbit/s EPONs that employ multimode laser sources. It is shown that MPN may have a severe impact, but the use of Forward Error Correction (FEC) is considered as a way to mitigate this effect.

Bandwidth Re-Distribution Techniques for Extended EPON Based Multi-Wavelength Networks

Abstract: The broadband photonics project (BBP) under the Freehand consortium of projects looks into the design of an extended access network. The network is a photonic network which can be dynamically reconfigured to distribute bandwidth in an optimised manner. This paper presents linear programming based formulations to calculate implementation of bandwidth redistribution in the network.

Bistability and All-Optical Switching in Semiconductor Ring Lasers

Abstract: We have studied the emergence of bistability and the switching properties of semiconductor ring lasers by means of a two-modes rate equations model. We find that the bistability is induced by cross-gain saturation of the two counterpropagating modes. Optical switching is theoretically predicted in a single bistable semiconductor ring laser triggered by coherent directional pulse injection, when the trigger energy exceeds a critical amount.

Orthogonal Frequency Division Multiplexing (OFDM) and other Advanced Options to achieve 100Gb/s Ethernet Transmission

Abstract: Based on the demand for transmission technologies offering high ratio of bits per symbol, two promising candidates to achieve a data rate of 100 Gb/s per optical carrier are discussed, namely optical orthogonal frequency division multiplexing and 16-ary multilevel modulation.

Calculating Blocking Probabilities in Single-Hop WDM Traffic Groomed Optical Networks

Abstract: Traffic grooming in Wavelength Division Multiplexing (WDM) optical networks is a promising technology for improving the performance and reducing the network cost. We study the blocking performance of a single-hop WDM traffic groomed optical network, by considering that different connections request service through a single optical link. In each connection the generated calls may come from a single or multiple service-classes. For the case of a single service-class we develop a novel analytical loss model to calculate Connection Blocking Probabilities (ConBP) and Call Blocking Probabilities (CBP). Also, we extend this model to support multiple service-classes. The accuracy of the calculations is verified by simulation and found to be absolutely satisfactory.

Adaptive Burst Assembly Mechanism for OBS Networks Using Control Channel Availability

Abstract: Burst dropping rate is a major issue for OBS networks. Unlike classical circuit switching, contention between bursts may cause blocking and make consequent loss within the network. Since the network can not carry a burst without its control packet, the control channel must be able to carry the complete BCP load. We propose a new assembly mechanism which takes into account the control channel availability. In this mechanism, a burst is created only if its control packet can be transmitted. We present preliminary results that show how monitoring the control channel in the burst assembly mechanism can significantly improve the network performance. Simulations show that the proposed mechanism changes adaptively the burst length, reduces the possibility of continuous blocking problem, reduces the packets loss rate, and increases the throughput while still satisfying the maximum assembly delay.

Multi-Domain Resilience: Can I Share Protection Resources with my Competitors?

Abstract: The Internet consists of a collection of more than 21000 domains called Autonomous Systems (AS) operated mostly under different authorities (operators/providers) that although co-operate over different geographical areas, they compete in a country or other area. Today BGP is the de facto standard for exchanging reachability information over the domain boundaries and for inter-domain routing. The GMPLS controlled optical beared networks are expected to have similar architecture, however, more information has to be carried for TE, resilience and QoS purposes. Therefore, extensions of BGP and of PNNI as well as the PCE have been proposed. Still in all cases emerges the question of protection shareability. For dedicated protection it is enough to know the topology of the network to be able to calculate disjoint paths. However, to be able to perform sharing of protection resources (shared protection) it is not enough to know the topology, but it is mandatory to know exact working and protection path pairs for all the demands, since protection paths can share a certain resource only if there is no such a pair of working paths that contain any element from the same Shared Risk Group (SRG). This can be checked within a domain where the full topology and link-state information is flooded, however, over the domain boundaries for security and scalability reasons no such information is being spread. In this paper we propose using two techniques that do not require flooding the information on working and protection paths while they still allow sharing of resources. These two techniques are the Multi-Domain p- Cycles (MD-PC) and the Multi-Domain Multi-Path Routing with Protection (MD-MPP). After explaining the principles of these methods we give illustrative results.

Solutions for Budget Increase for the Next Generation Optical Access Network

Abstract: After a presentation of the France Telecom Group's optical deployment project based on available technology, our interest for the Next Generation Passive Optical Network is described. With the need for increased bit rate, splitting ratio, as well as the reach extension, more optical budget will be required. Solutions for optical amplification in the target architectures which can ensure the evolution of the access network are presented. These solutions are compared in different schemes and the budget increase for the upgrade of Gigabit PON (GPON) system is deduced.