Optical technologies represent the main bet for future communication systems. Among the others, digital subsystems for
optical processing are of great interest thanks to their intrinsic properties in terms of bandwidth, transparency, immunity
to the electromagnetic interference, cost, power consumption, as well as robustness in hostile environment. Key basic
functions are represented by logic gate, logic function, flip-flop memories, optical random access memories, etc..
Research in this field is in its very early stages even if some interesting techniques have been already theoretically
addressed and experimentally demonstrated. In this paper we review the state of the art for all-optical flip-flop including
different approaches such as fiber based, semiconductor amplifier based or waveguide and micro-ring solutions. Best
result will be highlighted in terms of transition speed, switching energy, complexity and power consumption. Finally our
best results are discussed.
A modular photonic interconnection network based on a combination of basic 2×2 all-optical nodes where a photonic
combinatorial network manages the packet contention, is presented. The proposed architecture is synchronous, can
operate Optical Time Division Multiplexing (OTDM) packets up to 160Gb/s and exhibits self-routing capability and
very low switching latency.
In such a scenario, OTDM has to be preferred to Wavelength Division Multiplexing (WDM), because in the former case
the instantaneous packet power carries the information related to only one bit, making more simpler the signal processing
based on instantaneous nonlinear interactions between packets and control signals. Moreover OTDM can be utilized in
interconnection networks without caring about the propagation impairments, since these networks are characterized by a
very limited size (< 100m). Finally, in such a limited domain, the packet synchronization can be solved at the network
boundary in the electronic domain, without the need of complex optical synchronizers. The 2×2 switching element is
optically managed by exploiting a photonic combinatorial network able to carry out contention detection, and to drive the
contention resolution and the switching controller blocks. The implementation of such photonic combinatorial network
is based on semiconductor devices, making the solution very promising in terms of compactness, stability, and power
consumption. The network performances have been investigated for bit streams at 10 Gb/s in terms of Bit Error Rate
(BER) and Contrast Ratio. Moreover, the suitability of the 2×2 photonic node architecture exploiting the above
mentioned combinatorial network, has been verified up to 160 Gb/s, demonstrating the potentialities of photonic digital
processing in the next generation broad-band and flexible interconnection networks.
The virtually unlimited bandwidth of optical fibers has caused a great increase in data transmission speed over the past decade and, hence, stimulated high-demand multimedia services such as distance learning, video-conferencing and peer to peer applications. For this reason data traffic is exceeding telephony traffic, and this trend is driving the convergence of telecommunications and computer communications. In this scenario Internet Protocol (IP) is becoming the dominant protocol for any traffic, shifting the attention of the network designers from a circuit switching approach to a packet switching approach. A role of paramount importance in packet switching networks is played by the router that must implement the functionalities to set up and maintain the inter-nodal communications. The main functionalities a router must implement are routing, forwarding, switching, synchronization, contention resolution, and buffering. Nowadays, opto-electronic conversion is still required at each network node to process the incoming signal before routing that to the right output port. However, when the single channel bit rate increases beyond electronic speed limit, Optical Time Division Multiplexing (OTDM) becomes a forced choice, and all-optical processing must be performed to extract the information from the incoming packet.
In this paper enabling techniques for ultra-fast all-optical network will be addressed. First a 160 Gbit/s complete transmission system will be considered. As enabling technique, an overview for all-optical logics will be discussed and experimental results will be presented using a particular reconfigurable NOLM based on Self-Phase-Modulation (SPM) or Cross-Phase-Modulation (XPM). Finally, a rough experiment on label extraction, all-optical switching and packet forwarding is shown.
A highly dispersive fiber behaves like a Fourier transformer with respect to the complex envelope of the input signal. It follows that the best pulse shape for transmission on a dispersive fiber is that one of the most concentrated in frequency and time, and thus related to the prolate spheroidal wave functions. This is used to devise line coding schemes highly insensitive to chromatic dispersion. However, the greater the dispersion, the more complex these schemes become. The effect of filtering and chirping is also taken into account and it is shown that chirping over a bit time is not useful for bit rates greater than 10 Gb/s.
In this paper, forward error correction schemes are discussed for application in the multigigabit-per-second optical channel. The proposed schemes, based on specific convolutional codes which allow simple decoding techniques, represent a valid alternative, in terms of performance and complexity, to the recommended Reed-Solomon codes.
Optical multi-wavelength transport networks (MWTN) have generated considerable recent interests because of their inherent capability to achieve higher information capacity, greater flexibility, efficient routing, transparent switching, reconfugarability etc.. The effect of switch cross-talk, adjacent channel cross-talk, filtering effect, accumulated ASE in MWTN has been recently addressed. However, the performance of closely packed WDM systems with dispersion shifted fibers is highly vulnerable to the effect of FWM. The present study investigates the degradation encountered in multi-wavelength switched optical network due to the combined influence of receiver noise, phase noise, accumulated amplified spontaneous emission (ASE), FWM crosstalk and dispersion. For each channel CPFSK modulation is considered with direct detection receiver employing Mach-Zehnder interferometer (MZI). The analysis is carried out to include the combined effect of accumulated optical amplifiers’ spontaneous emission (ASE) noise and the beat noise components viz. signal-spontaneous emission beat noise, ASE-ASE beat noise, adjacent channel-spontaneous beat noise, signal- FWM beat noise, FWM-spontaneous beat noise etc.. An expression for the probability density function (pdf) of the random phase fluctuation due to FWM effect is developed and the bit error rate is estimated at each node for different number of channels. In the present analysis, a node architecture of the optical mesh network is considered in which an interconnection between two consecutive nodes consists of optical in-line amplifiers, optical space-switches, power splitters, wavelength multiplexers and demultiplexers and the fiber protection switch. All the wavelengths are combined in the multiplexer and amplified before feeding to the transmission fiber. The gains of the in-line amplifiers are adjusted to compensate for the losses in the fiber, splitters and other passive components. The demultiplexer separates the desired signal wavelength from the WDM multiplex and is realized by a Febry-Perot filter (FPF) tuned to the desired signal channel. The node uses M transmitters and M receivers if M is the number of wavelength channels. Computations of results are carried out at a bit rate of 2.5 Gb/s for several fiber spans with different sets of system parameters, viz. number of channels, number of nodes, optical SPIE Vol. 3211 • 0277-786X/97/$10.00? wavelength from the WDM multiplex and is realized by a Febry-Perot filter (FPF) tuned to the desired signal channel. The node uses N transmitters and N receivers if N is the number of wavelength channels