G. M. Tosi Beleffi

Scalable Extended Reach PON

Extended reach highly-scalable, fully passive WDM/TDM-PON allows reaching >1000 users along protected 100 km by colorless ONUs, centralized light-generation and control, single-fiber access and remote amplification. ONUs are based on 1.25/2.5/5Gbps-capable RSOA and downstream at 10 Gbps.

Free Space Optical Technologies

Free Space Optics (FSO), also known as Optical Wireless or Lasercom (i.e. Laser Communications), is a re-emerging technology using modulated optical beams to establish short, medium or long reach wireless data transmission. Most of the attention on FSO communication systems it was initially boost by military purposes and first development of this technology was dedicated to the solution of issues related to defense applications. Today’s market interest to FSO refers to both civil and military scenarios covering different situations and different environments, from undersea to space. In particular, due to the high carrier frequency of 300 THz and the consequently high bandwidth, the most prominent advantage of Free Space Optical (FSO) communication links may be their potential for very high data rates of several Gbps (up to 40 Gbps in the future (J. Wells, 2009)). Other advantages like license-free operation, easy installation, commercial availability, and insensitivity to electromagnetic interference, jamming, or wiretapping make FSO interesting for applications like last mile access, airborne and satellite communication (L. Stotts et alt, 2009), temporary mobile links and permanent connections between buildings. Mainly, the adoption of FSO is needed when a physical connection is not a practicable solution and where is requested to handle an high bandwidth. As a matter of fact, FSO is the only technology, in the wireless scenario, able to grant bandwidth of several Gigabits per second. The interest in this technology is also due to the low initial CAPEX (Capital Expenditure) requirement, to the intrinsic high-level data protection & security, to the good flexibility and great scalability innate in this solution. For these reasons FSO possible applications cover today, as mentioned, a wide range. Thus this technology generates interest in several markets: the first/last mile in dense urban areas, network access for isolated premises, highspeed LAN-to-LAN (Local Area Networks) and even chip-to-chip connections, transitional and temporary network connection, undersea and space communication. Furthermore FSO can be used as an alternative or upgrade add-on to existing wireless technologies when the climatic conditions permit its full usage. 13

QoE and QoS comparison in an anycast digital television platform operating on passive optical network

We report an experimental investigation on QoE, compared with the QoS, for a complete digital television platform able to deliver broadcast, multicast and unicast services in wide geographical area network, with broadband access based on passive optical network (PON). In particular, we show the service degradation due both to network impairments and to the TCP limits on operating systems. Multicast forwarding was tested in PBB-TE environment to exploit a Carrier Ethernet behavior. Concerning broadcasting, such a network allows the user to see the DVB-T by using the same optical infrastructure by means of the specific wavelength foreseen by the GPON standard.

Remotely pumped Erbium Doped Fibre bidirectional Amplifier for gain transient mitigation

In this paper, we analyze bidirectional Downstream and Upstream amplification for gain transient mitigation in Remote Erbium Doped Fibre Amplifiers. Amplifying a Continuous Downstream and a burst mode Upstream data traffic in the same remotely pumped Erbium Doped Fibre Amplifier, a reduction of the overshoot and BER penalty have been experimentally measured for different packet lengths. In addition, gain transient time constants have been measured.

Model analysis of hydrometeor scattering effects on free space near-infrared links

A promising technology for peer-to-peer connections and urban area networks is represented by wireless communications through free space using optical carrier (Free Space Optics, FSO). This technology ensures high data rates, with relatively low error rates, low power consumption and inherent security. Nevertheless FSO links are quite sensitive to atmospheric condition. Fog droplets, but also raindrops and snowflakes, may introduce severe path attenuation which drastically reduces the channel availability. A parametric model to simulate droplets scattering effects over the FSO link in terms of extinction coefficient, albedo factor and asymmetry coefficient as function of the particle water content will be presented. Both single and multiple scattering effects will be shown.

On field test of a Wavelength Division Multiplexing Free Space Optics transmission at very high bit rates

We report experiments on a fully transparent free space optic system operating at 2.5,10 and 40 Gbps. A on-field system operating on a 100 m link as been implemented and tested. Results demonstrate that this kind of system is able to exploit the high bandwidth provided by the fibers and that it can support WDM transmission; in particular it could be a competitive technology in the last mile/last hundred of meters scenario.

Security issues in optical networks physical layer

Network management and maintenance in optical networks faces additional security challenges arose from increased transparency in optical network components and systems. A review on existing physical security breaches on these types of networks will be presented. From these some of the methodologies for location and detection will be described and characterized in terms of applicability. Special focus will be given to the ones that are more prone to Passive optical networks due to its proximity to the user, leading to increased attack diversity.

Optical fiber bending limits for optical fiber infraestructures

In this work the high power propagation in tight bent fibers was studied. The signal losses and the temperature increase have been experimental measured for single mode optical fibers (SMF) as function of the bending diameter. These results were used to propose an approach to limit the bending diameter, as a function of the injected power, in order to maintain the operational condition bellow the safety limit.

Rateless codes performance tests on terrestrial FSO time-correlated channel model

Free Space Optics (FSO) links are affected by several impairments: optical turbulence, scattering, absorption, and pointing. In particular, atmospheric optical turbulence generates optical power fluctuations at the receiver that can degrade communications with fading events, especially, in high data rate links. A way to mitigate FSO link outages can be to add a coding to communications. Nevertheless, in order to study innovative solutions (software or hardware) and to improve the FSO link performance it needs accurate testing models. In this paper we describe an accurate time-correlated channel model able to predict random temporal fluctuations of optical signal irradiance caused by optical turbulence. Moreover, concerning the same channel, we also report simulation results on the error mitigation performance of Luby-Transform, Raptor, and RaptorQ codes.

Hydrometeor scattering and stochastic modeling for free-space optical channel characterization

Free space communications, using optical carriers (Free Space Optics, FSO) technology, ensure high data rates, with relatively low error rates, low power consumption and inherent security. However, FSO links are quite sensitive to atmospheric conditions. Fog droplets, but also raindrops and snowflakes, may introduce severe path attenuation which drastically reduces the channel availability. A parametric model to simulate droplets scattering effects on FSO links (from visible to near infrared wavelengths) is proposed in terms of scattering coefficients, albedo factor and asymmetry coefficient as function of the particle water content. Both single and multiple scattering effects are shown and discussed. A prototype of a stochastic time series generator of FSO rain attenuation is also presented.