N. Caponio

Single‐Layer Optical Platform Based on WDM/TDM Multiple Access for Large‐Scale “Switchless” Networks

The European Union ACTS project SONATA will define and demonstrate a cswitchlessn all-optical network to provide a future single-layer, advanced transport architecture on a national scale. The single-hop, shared-access network employs time and wavelength agility (a WDMA/TDMA protocol), using fast tunable transmitters and receivers to route individual customer connections as well as bandwidth pipes through a single wavelength router (suitably replicated for resilience). No electronic switching nodes or cross-connects (telephony, IP, ATM, SDH) are required within the transport network, nor optical cross-connects (save the wavelength routing node), thus providing major transport architecture simplifications and hardware reductions. The network is scalable to 200 Tbit/s throughput over 1, 000 krn, connecting 20 million terminals operating at 622 Mbit/s over 50.000-way split c<hyperPONss, by means of 800 WDM channels with 0.05 nm channel spacing (6.25 GHz). Details of network dimensioning, physical layer modeling and network control issues are presented.

Analysis and design criteria of three-section DBR tunable lasers

Three-section distributed Bragg reflector (DBR) tunable lasers emitting in the 1.55 mu m region are studied through a theoretical model which takes into account thermal effects and exploits an accurate calculation of the optical parameters. Static modal competition is discussed for transverse and longitudinal modes in operation at and above threshold. The static tuning characteristics are presented; a saturation of the wavelength shift is found for control current densities of approximately=20 kA-cm/sup -2/ due to Auger recombination processes and heating effects. The dependence of the tuning ranges on the section lengths, waveguide thickness results, and some design criteria are derived. >

A simple angular alignment technique for a polarization-maintaining-fiber

Simple and accurate techniques for angular alignment of a polarization-maintaining-fiber (PMF) to a linearly polarized input beam are required for many optical-fiber applications. We consider an alignment technique wherein a short length of PMF undergoes a large temperature excursion and the output beam from the fiber is simply monitored by a linear polarizer and a power meter. Upon carefully considering the results for rotation angles near alignment, an accuracy better than 0.2/spl deg/ as well as a measurement of the fiber crosstalk are obtained.<<ETX>>

Spectral linewidth and frequency chirp of four-wave mixing components in optical fibers

The spectral characteristics of four-wave mixing components in optical fibers have been investigated both theoretically and experimentally, for the first time. The theoretical deductions show different contributions of the spectral linewidth and the frequency chirp of the signal waves to the spectrum of four-wave mixing components. Accurate spectral measurements, relying on a highly sensitive heterodyne detection system, fully confirmed the theoretical evaluations. The spectral broadening of the four-wave mixing components, due to the phase noise and the frequency chirp, may degrade the performance of unequally spaced channel HD-WDM and fiber four-wave mixing application systems.<<ETX>>

Linewidth of a semiconductor laser operating near threshold

The linewidth of a single-mode semiconductor laser operating in the threshold region has been studied both theoretically and experimentally. Due to strong phase-amplitude coupling in a semiconductor laser, its linewidth versus current characteristics exhibit a local minimum below threshold and a local maximum just about threshold. This implies a limitation in the minimum optical bandwidth achievable in a resonant-type semiconductor laser optical amplifier. The theoretical prediction has been verified experimentally on a conventional DFB semiconductor laser.<<ETX>>

Impact of DFB-LD FM response distortion, in amplitude and phase, on FSK coherent systems

The influence of amplitude and phase distortions of the FM response of DFB (distributed feedback) lasers on coherent FSK (frequency shift keying) transmission systems has been investigated. It was found that pattern effects are mainly due to phase distortions, while the IF (intermediate frequency) spectrum broadening is due to both amplitude and phase distortions. Possible remedies are described, including device selection, line coding, and phase and/or amplitude equalization of the FM response. A comparison between observed spectra and computer analysis has been performed, showing a good agreement. Transmission experiments at 140 Mb/s have been carried out, showing the predicted effects on the eye diagram.<<ETX>>

Demonstration of polarisation independent coherent transmission by synchronous intra-bit polarisation spreading

Polarization-independent heterodyne detection of an FSK (frequency shift keying) signal has been demonstrated by the synchronous intrabit polarization spreading technique, which consists in the switching or proper modulation of the state of polarization of the laser output field inside the bit period. This approach is particularly suitable for distribution networks, as the polarization diversity function is shifted to the transmitter, thus resulting in a simpler and cheaper heterodyne receiver. A transmission experiment, making use of a 1.55 mu m DFB (distributed feedback) laser diode, directly FSK modulated at 155 Mb/s, a properly developed high-speed polarization modulator, and single filter heterodyne detection, has been successfully carried out. The penalty resulting from preliminary bit-error-rate measurements ranges from 4 to 6.5 dB, including the 3 dB intrinsic loss common to all polarization spreading techniques.<<ETX>>

Optical Switching for End-to-end Packet Communications and its Potential Advantages over Electronic Switching

The introduction of optical switching could provide high capacity switching nodes cheaper than the current electronic switches and could allows end-to-end connections through the whole network simplifying the structure of the network itself. The key problems related to optical switching are discussed and the main reference switch architectures are reported. The integration of optical functions through the whole network are addressed in order to show the feasibility of end-to-end optical networks.

Operative characteristics and application aspects of synchronous intra-bit polarization spreading for polarization independent heterodyne detection

Operative characteristics and application aspects of synchronous intra-hit polarization spreading (SIB-PS) technique for polarization independent heterodyne detection were investigated. The experimental investigation, carried out on a 622 Mbit/s FSK coherent transmission system, allowed an accurate study of the significant dependence of the IF spectrum broadening and of the baseband pulse-shape on the phase between the polarization spreading waveform and transmitted data, thus resulting in useful design criteria for practical applications of SIB-PS technique.<<ETX>>

Analysis and Dimensioning of Interconnected Single-layer Switchless All-optical Networks

A “switchless” all-optical network requires neither electronic switches nor active optical cross-connects because the switching function is implemented at terminals via time and wavelength agile transceivers. Terminals are grouped into passive optical networks which are connected to a single passive wavelength router. One centralised controller grants the terminals access to the time/wavelength frame. This paper defines a simple non-uniform traffic pattern based on a locality principle and evaluates the hardware/software complexity required to cover the same user population with either one or four fully interconnected “switchless” networks.