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We present a simple, straightforward technique to enable bidirectional transmission of analog and digital signals in single-fiber wavelength division multiplexing passive optical network systems employing reflective semiconductor optical amplifiers (RSOA). An On-Off-Keying (OOK-DL) downlink modulation is effectively erased in a saturated RSOA, reflecting a carrier for retransmitting on the same fiber an in-band analog WiFi orthogonal frequency division multiplexing uplink signal (OFDM-UL). We investigate the operating conditions and the optimization procedure to attain required signal quality for both the uplink and downlink. We demonstrate experimentally the maximum distance and the best attainable performances for different lengths of standard single mode fiber (transmission). Bit error rate below the forward error correction threshold is obtained for WiFi OFDM-UL signal over 40 km and up to 80 km of SSMF using 64QAM and QPSK modulation modes, respectively. In all cases, we achieve error-free operation for the OOK-DL signal at 1 Gb/s. [ABSTRACT FROM PUBLISHER]

We previously proposed inverse source coding (ISC) to maximize the transmission rate in visible light communications with dimming capability using ON-OFF keying. First, this paper extends the proposed ISC approach to -ary pulse amplitude modulation and obtains the optimal probability distributions. Then, dimming capacity is used to compare the existing analog dimming approach, the extended ISC approach, and the hybrid of these approaches. We conclude that ISC is the best approach, and threshold values for adaptive modulation are derived depending on signal quality and dimming target. [ABSTRACT FROM PUBLISHER]

Chromatic dispersion is a limiting factor in intensity-modulated radio-over-fiber links with direct detection. This paper investigates its influence on single-mode fiber links based on mode-locked laser sources through simulation and experiment. A time-based approach is used to describe the impact of chromatic dispersion after transmission across a single-mode fiber link. The simulations presented herein give hints for the design of dedicated mode-locked lasers that can later serve in dispersion-tolerant radio-over-fiber networks. The findings of the simulations are experimentally validated for a laser delivering a 60 GHz radio carrier, and for a link of 400 m length which represents a realistic link length for in-house distribution. Furthermore, the impact of chromatic dispersion on signal quality is demonstrated for WLAN transmission employing direct and external link modulation. [ABSTRACT FROM PUBLISHER]

In the future all-optical network controlled by generalized multiprotocol label switching (GMPLS), the wavelength path between end nodes will change dynamically. This inevitably means that the fiber parameters along the wavelength path will also vary. This variation in fiber parameters influences the signal quality of high-speed-transmission system (bit rates over 40 Gb/s). Therefore, at a path setup, the fiber-parameter effect should be adequately compensated. Moreover, the path setup must be completed fast enough to meet the network-application demands. To realize the rapid setup of adequate paths, a multilayer integration system for all-optical wavelength-path quality assurance is proposed. This multilayer integration system is evaluated in a field trial. In the trial, the GMPLS control plane, measurement plane, and data plane coordinated to maintain the quality of a 40-Gb/s wavelength path that would otherwise be degraded by the influence of chromatic dispersion. It is also demonstrated that the multilayer integration system can assure the signal quality in the face of not only chromatic dispersion but also degradation in the optical signal-to-noise ratio by the use of a 2R regeneration system. Our experiments confirm that the proposed multilayer integration system is an essential part of future all-optical networks [ABSTRACT FROM PUBLISHER]

A 40-Gb/s asynchronous self-routing network and node architecture that exploits bit and packet level optical signal processing to perform synchronization, forwarding, and switching in the optical domain is presented. Optical packets are self-routed on a hop-by-hop basis through the network by using stacked optical tags, each representing a specific optical node. Each tag contains necessary control signals for configuring the node-switching matrix and forwarding each packet to the appropriate outgoing link and onto the next hop. In order to investigate the feasibility of their approach physical-layer simulations are performed, modeling each optical subsystem of the node showing acceptable signal quality and end-to-end bit error rates. In the All-optical self-RouTer EMploying bIt and packet-level procesSing (ARTEMIS) control plane, a timed/delayed resource reservation-based signaling scheme is employed combined with a load-balancing feedback-based contention-avoidance mechanism that can guarantee a high performance in terms of blocking probability and end-to-end delay [ABSTRACT FROM PUBLISHER]

Constraint-based routing (CBR) requires a fast and accurate assessment of the different physical degradation effects in optical communications systems. This paper deals with fast analytical approximation formulas describing the induced system penalty due to the dominant nonlinear effects in 10-Gb/s nonreturn to zero (NRZ) transmission systems. This paper concentrates on the multichannel effects of cross-phase modulation (XPM) and four-wave mixing (FWM). [ABSTRACT FROM PUBLISHER]

This paper addresses the problem of survivable lightpath provisioning in wavelength-division-multiplexing (WDM) mesh networks, taking into consideration optical-layer protection and some realistic optical signal quality constraints. The investigated networks use sparsely placed optical-electrical-optical (O/E/O) modules for regeneration and wavelength conversion. Given a fixed network topology with a number of sparsely placed O/E/O modules and a set of connection requests, a pair of link-disjoint lightpaths is established for each connection. Due to physical impairments and wavelength continuity, both the working and protection lightpaths need to be regenerated at some intermediate nodes to overcome signal quality degradation and wavelength contention. In the present paper, resource-efficient provisioning solutions are achieved with the objective of maximizing resource sharing. The authors propose a resource-sharing scheme that supports three kinds of resource-sharing scenarios, including a conventional wavelength-link sharing scenario, which shares wavelength links between protection lightpaths, and two new scenarios, which share O/E/O modules between protection lightpaths and between working and protection lightpaths. An integer linear programming (ILP)-based solution approach is used to find optimal solutions. The authors also propose a local optimization heuristic approach and a tabu search heuristic approach to solve this problem for real-world, large mesh networks. Numerical results show that our solution approaches work well under a variety of network settings and achieves a high level of resource-sharing rates (over 60% for O/E/O modules and over 30% for wavelength links), which translate into great savings in network costs. [ABSTRACT FROM PUBLISHER]

We investigate new connection-provisioning algorithms to efficiently provide signal-quality-guaranteed connections in an optical wavelength-division-multiplexing (WDM) mesh network operating with high-speed wavelength channels. In an optical network, a connection is set up to carry a data signal via an all-optical channel (lightpath) from its source to destination node. The optical signal transmitted along the lightpath may need to travel through a number of crossconnect switches (OXCs), optical amplifiers, and fiber segments. While the signal propagates toward its destination, the optical components would continuously degrade the signal quality by inducing impairments. When the signal degradation is so severe that the received bit-error rate (BER) becomes unacceptably high, the lightpath would not be able to provide good service quality to a connection request. Such a lightpath, which has poor signal quality due to transmission impairments in the physical layer, should not be used for connection provisioning in the network layer. With increasing channel bit rate to 10 Gb/s or higher, fiber linear and nonlinear impairments become prominent factors, which affect the signal quality. Thus, new techniques in both physical layer and network layer are necessary for mitigating impairments to accommodate high-speed traffic. Therefore, to ensure service quality of high-speed connections, we develop intelligent impairment-aware routing and wavelength assignment (RWA) algorithms, which automatically consider the effects of high-speed transmission impairment when setting up a lightpath. The main contribution of our paper is that we investigate a novel hierarchical RWA model for high-speed connection provisioning where the optical signal-to-noise ratio (OSNR) and polarization mode dispersion (PMD) effect are estimated in the physical layer, and regarded as metrics for lightpath computation in the network layer. The performance of the proposed connection-provisioning strategies is demonstrated to be promising through illustrative numerical examples. [ABSTRACT FROM PUBLISHER]

This paper describes a software-synchronized all-optical sampling system that presents synchronous eye diagrams and data patterns as well as calculates accurate Q values without requiring clock recovery. A synchronization algorithm is presented that calculates the offset frequency between the data bit rate and the sampling rate, and as a result, synchronous eye diagrams can be presented. The algorithm is shown to be robust toward poor signal quality and adds less than 100-fs timing drift to the eye diagrams. An extension of the software synchronization algorithm makes it possible to automatically find the pattern length of a periodic data pattern in a data signal. As a result, individual pulses can be investigated and detrimental effects present on the data signal can be identified. Noise averaging can also be applied. To measure accurate Q values without clock recovery, a high sampling rate is required in order to establish the noise statistics of the measured signal before any timing drift occurs. This paper presents a system with a 100-MHz sampling rate that measures accurate Q values at bit rates as high as 160 Gb/s. The high bandwidth of the optical sampling system also contributes to sampling more noise, which in turn results in lower Q values compared with conventional electrical sampling with a lower bandwidth. A theory that estimates the optically sampled Q values as a function of the sampling gate width is proposed and experimentally verified. [ABSTRACT FROM PUBLISHER]

Progress in optical networking has stimulated interest in optical performance monitoring (OPM), particularly regarding signal quality measures such as optical signal-to-noise ratio (SNR), Q-factor, and dispersion. These advanced monitoring methods have the potential to extend fault management and quality-of-service (QoS) monitoring into the optical domain. This paper reviews OPM applications and techniques, while examining the role of OPM as an enabling technology for advances in high-speed and optically switched networks. [ABSTRACT FROM PUBLISHER]

The design of optical communication networks with network switching elements operating in the optical domain requires careful system analysis and potentially stringent component requirements. We consider here network elements such as transparent optical cross-connects that demultiplex WDM signals, optically switch individual channels, and then multiplex the wavelengths together again before transmission into the next span. Network element optical impairments that can significantly degrade signal quality are in-band (same wavelength) crosstalk and signal distortion from filter concatenation effects. We examine tradeoffs between accumulated crosstalk and filter distortion in the context of the optical filters used in the network elements and demonstrate the balance that must be struck in the design of the filters and network system. As an example, we study a 10-Gb/s network with 50-GHz channel spacing, examining both nonreturn-to-zero (NRZ) and return-to-zero (RZ) modulation formats. In both cases, we find optimal filter bandwidths that minimize the total signal degradation measured in terms of Q penalty, including filter misalignment statistics and signal laser frequency offset. A model is developed to treat the statistical nature of filter misalignment and its effect on filter-generated in-band crosstalk. The optical node penalties suffered by RZ signals can be significantly higher than that of NRZ signals and must be considered when estimating overall system reach. [ABSTRACT FROM PUBLISHER]

We report computer simulation results of the effects on optical signal quality of passage through a cascade of wavelength division multiplexing (WDM) filters-multiplexers and demultiplexers-for directly modulated lasers with different chirp characteristics. In particular, lasers with transient or adiabatic chirp characteristics at 2.5 Gb/s and 10 Gb/s are investigated, and we find clear differences between the laser types with respect to filter concatenation effects. Filters with an optical bandwidth suitable for a 200-GHz channel-spacing system are considered, and we evaluate the system behavior as a function of laser frequency offset for a fixed number of filters. The reference network architecture used for the simulations is an optically transparent metropolitan scale network in which the WDM signals may be demultiplexed and then multiplexed again at multiple optical network elements. The signal quality is evaluated in terms of a distortion-induced eye-closure penalty as well as the excess attenuation or loss suffered. We find that transient chirp-dominated lasers show a generally symmetric distortion penalty response to laser frequency offset, whereas the response for adiabatic chirp dominated lasers is highly asymmetric. Furthermore, the extinction ratio for the latter class of lasers can be improved, in some cases, by the appropriate offset between laser and filter center frequencies [ABSTRACT FROM PUBLISHER]

Simulations of first-order polarization-mode dispersion (PMD) mitigation, based on the electrical power spectrum has been performed. We show that, although first-order compensation significantly improves the signal quality for PMD values of a few tenths of the bit-slot, the improvement still is deficient for telecom purposes when the PMD value neighbors a third of the bit-slot. We, therefore, propose and analyze a novel concept for PMD mitigation in optical multichannel systems, which increases the systems reliability at the expense of the total capacity for the same system. With the proposed method, which uses switching to redundant channels based on measurements of signal quality of all channels in the actual system, the PMD value can be increased to a half of the bit-slot while still keeping the probability for signal outage at acceptable low levels. In the appendixes we simulate the statistical impact of different PMD-emulator models and we show that static bit sequences may induce notches in the electrical power spectrum. These notches may obstruct the extraction of feedback signals for PMD-mitigator schemes based on electrical power spectrum. [ABSTRACT FROM PUBLISHER]

In a wavelength-routed optical network, a transmitted signal remains in the optical domain over the entire route (lightpath) assigned to it between its source and destination nodes. The optical signal may have to traverse a number of crossconnect switches (XCSs), fiber segments, and optical amplifiers, e.g., erbium-doped fiber amplifiers (EDFAs). Thus, while propagating through the network, the signal may degrade in quality as it encounters crosstalk at the XCSs and also picks up amplified spontaneous emission (ASE) noise at the EDFAs. Since these impairments continue to degrade the signal quality as it progresses toward its destination, the received bit error rate (BER) at the destination node might become unacceptably high. Previous work on the lightpath routing and wavelength assignment (RWA) problem assumed an ideal physical layer and ignored these transmission impairments. The main contribution of our work is to incorporate the role of the physical layer in setting up lightpaths by employing appropriate models of multiwavelength optical devices (XCSs and EDFAs) such that the BER of a candidate lightpath can be computed, in advance, to determine if this lightpath should be used for the call. Features from existing RWA algorithms are integrated with our on-line BER calculation mechanism. Our simulation studies indicate that employing BER-based call-admission algorithms has a significant impact on the performance of realistic networks [ABSTRACT FROM PUBLISHER]