D. Forin

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

All-Optical Conversion From RZ to NRZ Using Gain-Clamped SOA

An all-optical converter from return-to-zero (RZ) pulses to the nonreturn-to-zero (NRZ) format is presented. The converter operates in two stages: the laser generated in a gain-clamped semiconductor optical amplifier (SOA) is modulated with the data signal; afterwards this signal is wavelength-converted by cross-gain modulation in a common SOA. The setup is noninverting and can feature wavelength conversion. Experimental error-free conversion from 5- and 40-ps RZ pulses to NRZ format is presented at 10 Gb/s using a 211-1 bit sequence

All-optical fiber 2+1 auxiliary carrier transponder-regenerator

The authors report simulations and experimental results about a new kind of all-optical reamplification and reshaping (2R) regenerator. The novelty is based on the principle that the ordinary four-wave-mixing process, inside a particular dispersion-shifted fiber, is able to induce input signal replicas on a third copropagating auxiliary carrier even if its state of polarization is orthogonal to that of the pump. Test results on a deployed cable showing improved 2R function and wavelength conversion capability are reported.

Network Performance Investigation in a Wide Area Gigabit Ethernet Test Bed Adopting All-Optical Wavelength Conversion

We experimentally investigate the network performance of a wide area gigabit Ethernet test bed in which we introduced the all-optical wavelength conversion (WC) process. Such a test bed is configured to implement a quality of service (QoS) control based on the virtual private local area network service (VPLS), a technique that, according to the reported results, is well suitable to implement forwarding process based on dedicated wavelengths. We show that the all-optical WC does not degrade the QoS properties of the VPLS and it can be used with very fast switching time.

Experimental Investigation of Quality of Service in an IP All-Optical Network Adopting Wavelength Conversion

We experimentally show how the virtual private large-area network service (VPLS) technique, a layer 2 service, can improve optical network performance in terms of quality of service (QoS), and how a VPLS network behaves when it adopts all-optical wavelength conversion (AOWC), a new optical process that will be introduced in future optical networks. The advantages of VPLS are based on the capability to generate logical reliable paths in each wavelength channel, permitting suitable partitioning of the bandwidth according to the user requirements. In particular, we show the advantages of VPLS in access networks based on passive optical networks, and we test QoS properties of VPLS paths when an AOWC process occurs both in the core and in the access networks. The experimental investigation is carried out in a wide-area, all-optical gigabit Ethernet testbed with an access section based on an Ethernet passive optical network. As far as the core segment is concerned, we chose a high-efficiency AOWC process based on four-wave mixing in dispersion-shifted fiber; conversely in the access segment we chose a cheaper AOWC process based on cross gain modulation in a semiconductor optical amplifier. The reported results show that gigabit Ethernet transmission, with the relative layer 2 techniques, is also well suitable for wide-area WDM architectures, and in particular it is able to guarantee end-to-end QoS for huge bandwidth services such as high-definition TV and also in the case of congestion, restoration, and wavelength conversion processes.

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.

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.

Ultrawide bandwidth λ-converter with regeneration properties based on cross phase modulation effect in highly non linear dispersion flattened fiber

We experimentally demonstrate and theoretically verily for what is believed to be the first time that a almost unlimited bandwidth λ-conversion can be achieved. 2R-functionality is also reported. Effect is based on cross-phase modulation between.

Experimental evaluation of modulation induced by continuous waves in a semiconductor optical amplifier

Many simulative approaches have been proposed to investigate Semiconductor Optical Amplifier (SOA) behaviour, in order to model its performance when used in several scenarios. Most of the applications of SOAs are based on the propagation of maximum two signals within the active medium, thus, higher order phenomena due to beating of more than two signals are not always correctly predicted by usual simulative models. In this paper we report some experimental results which validate an accurate model for SOA nonlinearities. This model is based on calculation of nonlinear susceptibility whose expression depends on multicarrier propagation. In particular, three signals are considered and their nonlinear interaction is evaluated by measuring a modulation arising on one of the signals.

3R all optical regeneration

The authors investigate a possible technique, based on a three stage cascade configuration, in order to implement an all-optical 3R regenerator. A multiwave-mixing based unit is used to perform simultaneously reshaping, re-amplification and wavelength conversion of a propagated signal. A fiber ring based unit is used to perform the all-optical timing extraction while a classical four-wave-mixing process inside a dispersion-shifted fibre is adopted for the retiming process.