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High-speed broadband services require optical fibres in access networks, in which multiple subscribers are connected to service providers, to satisfy the continuously growing bandwidth demand. The primitive signaling scheme used in access networks enables the use of low-cost equipment but diminishes the bandwidth available to end-users. Thus, current technology will be unable to support future broadband demands. Coherent communication systems offer significantly improved power- and bandwidth-efficiency, but require fundamental simplifications to become economically viable for access networks. Here, we demonstrate a promising simplified coherent receiver exhibiting a robust performance against polarisation fluctuations over an installed fibre network. It enables the realisation of high-order modulation formats and offers high sensitivities, achieving a four-fold increase in the supported number of subscribers and approximately doubling the transmission distance compared to the recently standardized access technology. The proposed solution indicates that digital coherent technology can be feasible and transform the access networks, enabling ubiquitous new services and applications with uncontended, multi-gigabits/user broadband connections. [ABSTRACT FROM AUTHOR]

We introduce a next-generation long-reach access optical network (35 dB loss budget +2 dB margin) delivering up to 40G/40G per passive 1:256 optical distribution network, supporting symmetrical 1 Gb/s rates per home user or up to 40 Gb/s for business users (e.g., enterprises, antenna sites). The proposed system is based on a novel spectrally efficient orthogonal frequency division multiplexing/wavelength division multiplexing OFDM/WDM architecture symmetrically using 16-QAM OFDM polarization diversity in both the downstream and upstream in order to serve low-cost energy-efficient symmetric 1 Gb/s optical network units (ONUs), which are self-coherent, laserless, colorless, and tunable-filter-free. Each ONU comprises a standard semiconductor optical amplifier (SOA), a silicon-based photonic integrated circuit (PIC), and mixed-signal electronic integrated circuits (ICs) performing the signal processing at a relatively slow rate as compared with the overall passive optical network (PON) throughput: digital to analog converters (DACs) and analog to digital converters (ADCs) at 417 MS/s for the home user ONUs. [ABSTRACT FROM PUBLISHER]

It is widely believed that dynamic operation of wavelength-routed optical networks will help overcome the inefficiencies of static allocation in terms of wavelength utilization. In this paper, this hypothesis is reviewed. The wavelength requirements of dynamic wavelength-routed optical networks are quantified and compared to static routing. To do so, new analytical and algorithmic lower bounds for the wavelength requirements of dynamic networks are proposed. They are used to evaluate the optimality of the already proposed algorithms whose wavelength requirements are quantified - by means of simulation- with and without the wavelength continuity constraint, as well as for uniform and nonuniform traffic demand. Results show that, without wavelength conversion capability, the benefit of dynamic wavelength-routed optical networks is not significant: lower wavelengths requirements than static networks are achieved only at low traffic loads (< 0.3 - 0.4). In wavelength convertible networks instead, dynamic operation leads to lower wavelength requirements than static operation over a wide traffic load range (< 0.7 - 0.8), making dynamic operation attractive in this type of network. Under nonuniform traffic it was found that dynamic operation achieves slightly higher wavelength savings than in the uniform traffic case. But the savings were not high enough as to impact on results of the uniform traffic case. These results can aid network operators in the design and optimization of optical WDM networks. [ABSTRACT FROM PUBLISHER]

Advances in the performance and flexibility of future optical networks will be brought about through the use of high-speed digital signal processing (DSP) for the generation of advanced optical signal formats and the compensation of transmission impairments. The use of field-programmable gate arrays (FPGAs) to implement experimental transceivers employing novel DSP techniques is attractive, as they are of low cost and are reprogrammable. In this paper, the design of a reprogrammable FPGA-based 10-Gb/s optical transmitter using real-time DSP is described and assessed through simulation. Using a single Xilinx Virtex-4 FPGA, digital filtering based on lookup tables with up to 12-bit addressing could be implemented. We also present, for the first time, a simulation technique using industry-standard digital design simulation tools (mentor graphics modelsim) in combination with a simulation of analog microwave components, optical transmission, and bit-error-rate estimation to assess the performance of the full transmission system. This simulation technique is used to demonstrate 10-Gb/s transmission over 550 km of standard single-mode fiber (SSMF) using electronic predistortion (EPD) and the generation of optical single sideband signals. A proof-of-principle experiment is described in which a single 10.7-Gb/s Mach-Zehnder modulator drive signal with 4-bit amplitude resolution and 1-sample/bit temporal resolution was generated. This was used as the input to Monte Carlo simulations to assess EPD transmission performance over SSMF links of up to 640 km. [ABSTRACT FROM PUBLISHER]

This paper assesses the regenerative properties of nonlinear semiconductor optical amplifier (SOA)-based optical regenerators cascaded in high-speed transmission networks. It is shown that the fundamental condition that must be ensured to maintain optimum and constant regenerative properties along a chain of concatenated nonlinear optical regenerators is that the extinction ratio at the input of each regenerator is kept constant. This condition determines an important requirement on the regenerator; signal reshaping and noise suppression must take place while performing the necessary extinction ratio enhancement to maintain cascadability. Starting from the SOA nonlinear transfer function, we derive the relationship between the extinction ratio enhancement and the noise suppression for different SOA-based gate configurations and assess their cascadability properties. This analysis is supported by experimental results of transmission with cascaded optical regeneration in a reconfigurable transmission network over transoceanic distances on standard fiber. [ABSTRACT FROM PUBLISHER]

The impact of polarization-mode dispersion (PMD) on the phase of the recovered clock in the receiver is analyzed. The effects of first-order PMD on different clock-recovery configurations utilized for return-to-zero (RZ) and non-RZ (NRZ) formats are studied. Closed-form expressions relating the PMD-induced sampling time shift with the differential group delay and the power ratio between the principal states of polarization are obtained for each high-Q filter-based clock recovery. An experimental validation at 10 Gb/s is also shown for the case of NRZ data format [ABSTRACT FROM PUBLISHER]

This paper investigates the challenges for developing the current local area network (LAN)-based Ethernet protocol into a technology for future network architectures that is capable of satisfying dynamic traffic demands with hard service guarantees using high-bit-rate channels (80...100 Gb/s). The objective is to combine high-speed optical transmission and physical interfaces (PHY) with a medium access control (MAC) protocol, designed to meet the service guarantees in future metropolitan-area networks (MANs). Ethernet is an ideal candidate for the extension into the MAN as it allows seamless compatibility with the majority of existing LANs. The proposed extension of the MAC protocol focuses on backward compatibility as well as on the exploitation of the wavelength domain for routing of variable traffic demands. The high bit rates envisaged will easily exhaust the capacity of a single optical fiber in the C band and will require network algorithms optimizing the reuse of wavelength resources. To investigate this, four different static and dynamic optical architectures were studied that potentially offer advantages over current link-based designs. Both analytical and numerical modeling techniques were applied to quantify and compare the network performance for all architectures in terms of achievable throughput, delay, and the number of required wavelengths and to investigate the impact of nonuniform traffic demands. The results show that significant resource savings can be achieved by using end-to-end dynamic lightpath allocation, but at the expense of high delay. [ABSTRACT FROM PUBLISHER]

The understanding and development of 160-Gb/s transmission systems requires the study of the impact of different dispersion compensation schemes on pulse propagation in nonlinear fiber. In this paper, we present an investigation of 160-Gb/s optical transmission systems, focusing on optimal propagation regimes, and in particular, we analyze different transmission limitations and dominant nonlinear effects by comparing quasi-linear and dispersion managed soliton systems. Two quasi-linear systems, one using nonzero dispersion-shifted fiber (NZDSF) and the other single-mode fiber (SMF), and one short-period (1 km) dispersion managed soliton (DMS) system are studied, both for single-channel and wavelength-division-multiplexed (WDM) transmission. First, the performance of the two quasi-linear systems in single-channel transmission are compared and it is shown that the NZDSF and SMF systems allow similar error-free transmission distances with only small differences in the intrachannel four-wave mixing (IFWM) induced amplitude jitter. The effect of pulsewidth on transmission performance in this regime was investigated and the use of shorter pulses was found to result in lower amplitude jitter. We analyzed the behavior of the DMS system and showed that the reduced pulse broadening during transmission allowed a significantly longer single-channel transmission distance with a smaller impact of nonlinearities compared to quasi-linear propagation. The sensitivity of the DMS system performance to statistical fluctuations in the fiber dispersion was studied and the results show the level of accuracy in the dispersion management map which must be ensured in these systems. Finally, the performance of the DMS in WDM transmission was investigated and it was found that it was subject to very large penalties increasing the minimum channel spacing possible because of the strong impact of interchannel cross-phase modulation (XPM). [ABSTRACT FROM PUBLISHER]

The results of a detailed study of the performance of 40-Gbit/s optical transmission over standard single-mode fiber with alternate-phase return-to-zero (AP-RZ) modulation formats are presented. While in the highly dispersed propagation regime, the use of RZ format signals with alternate phase between adjacent pulses can lead to a significant reduction in nonlinear interaction between pulses, allowing increased launch powers and, hence, increased transmission distances, this has not been systematically investigated. In this paper, we investigate the use of AP-RZ formats, both numerically and experimentally, to explain and quantify the effects of varying the peak-to-peak phase modulation, the amount of precompensation at the transmitter and the presence of multiplexer prefiltering for the case of wavelength-division multiplexing systems with high spectral efficiency. It is shown that, while the use of pulses with alternate π/2 rad phase shifts minimizes the build-up of shadow pulses in the zero bit slots due to intrachannel four-wave mixing, the best overall performance is obtained with π rad peak-to-peak phase modulation. We show experimentally, for the first time, that the optimum value of precompensation to minimize intrachannel nonlinear distortion is dependent on the signal format used. [ABSTRACT FROM PUBLISHER]

The performance of 40-Gb/s transmission systems is limited by the nonlinearity of the transmission and dispersion compensating fibers, and hence, optimized dispersion map designs and signal formats are required to extend error-free transmission distances. In this paper, we describe systematic experiments and simulations of return-to-zero (RZ) and nonreturn-to-zero (NRZ) 40-Gb/s transmission over nonzero dispersion-shifted fiber using higher order mode fiber dispersion management devices. We compare the single channel transmission limits due to nonlinear distortion with dispersion compensators positioned at the start and end of each amplifier span (pre- and postcompensation) and show that the transmission distance of NRZ signals can be extended with the use of precompensation due to the reduced self-phase modulation in the transmission fiber. In contrast, the combination of precompensation and RZ format was found to give poor performance, and analysis shows that this is a result of intrachannel four-wave mixing. The best performance was obtained using an RZ signal format and postcompensated spans. The performance of wavelength-division multiplexing (WDM) signal transmission over the link was then investigated. The simultaneous transmission of multiple 40-Gb/s channels over long-distances was achieved, demonstrating broad-band compensation of the dispersion and dispersion-slope using higher order mode fiber. Results of experiments assessing cross-phase modulation between 40-Gb/s WDM channels spaced by 100 GHz are presented, and the penalties due to inter- and intrachannel nonlinear effects are compared. [ABSTRACT FROM PUBLISHER]

The concept of optical burst switching (OBS) aims to allow access to optical bandwidth in dense wavelength division multiplexed (DWDM) networks at fractions of the optical line rate to improve bandwidth utilization efficiency. This paper studies an alternative network architecture combining OBS with dynamic wavelength allocation under fast circuit switching to provide a scalable optical architecture with a guaranteed QoS in the presence of dynamic and bursty traffic loads. In the proposed architecture, all processing and buffering are concentrated at the network edge and bursts are routed over an optical transport core using dynamic wavelength assignment. It is assumed that there are no buffers or wavelength conversion in core nodes and that fast tuneable laser sources are used in the edge routers. This eliminates the forwarding bottleneck of electronic routers in DWDM networks for terabit-per-second throughput and guarantees forwarding with predefined delay at the edge and latency due only to propagation time in the core. The edge burst aggregation mechanisms are evaluated for a range of traffic statistics to identify their impact on the allowable burst lengths, required buffer size and achievable edge delays. Bandwidth utilization and wavelength reuse are introduced as new parameters characterizing the network performance in the case of dynamic wavelength allocation. Based on an analytical model, upper bounds for these parameters are derived to quantify the advantages of wavelength channel reuse, including the influence of the signaling round-trip time required for lightpath reservation. The results allow to quantify the operational gain achievable with fast wavelength switching compared to quasistatic wavelength-routed optical networks and can be applied to the design of future optical network architectures [ABSTRACT FROM PUBLISHER]

An experimental and theoretical study of the effect of temperature on the static and dynamic characteristics of packaged external fiber grating semiconductor lasers (FGL) is reported on. Operating in single frequency mode, the laser exhibits high output power (> 8 mW), high temperature stability of operating frequency (-3.4 GHz/K), and low static chirp (-60 MHz/mA). The observed hysteresis in wavelength versus temperature dependence is explained in the frame of a time-domain FGL model accounting for asymmetric nonlinear gain. The laser has low dynamic chirp (∼16 MHz/mA) under 2.5 GB/s direct modulation, which is the key factor determining low penalty transmission over 312 km of SSM fiber. Dense WDM transmission performed at 2.6 Gbit/s over 117 km of SSM fiber shows that an FGL-based transmitter is a factor of 7 more tolerant to temperature variations than externally modulated DFB lasers. [ABSTRACT FROM AUTHOR]