Polymorphic Architectures for Optical Networks and their Seamless Evolution towards Next Generation Networks

This paper proposes a novel polymorphic framework for optical networking and a seamless evolution path from optical circuit-switched towards optical packet-switched networks. We show that by simultaneously supporting several optical switching paradigms in a single physical topology, efficient and flexible optical networks can be built. The supported paradigms are associated with different Classes of Service (CoS) in order to provide service differentiation at the optical layer. Two polymorphic architectures are presented, one based on optical circuit switching paradigms with different grades of dynamism, and a second one based on optical labeled burst-switched networks with the added capability of dynamic lightpath provisioning. These architectures provide a seamless evolution path towards an efficient IP-over-WDM approach with service differentiation. Moreover, the proposed polymorphic architectures are fully compatible with the GMPLS unified control plane. We present in a detailed form the proposed polymorphic framework, including the selection of switching paradigms, its support for CoS, the network and control architecture, and a possible seamless evolution towards optical packet-switched networks. Possible implementation examples of optical network nodes that support the proposed polymorphic architectures are also presented.     

Multiwavelength cross-connects for optical transport networks

Multiwavelength cross-connects (M-XCs) will play a key role in future optical multiwavelength transport networks. In this paper, we propose a class of optical wavelength interchange devices that can be used as basic building-blocks for multiwavelength optical cross-connects. We describe three different multiwavelength cross-connect structures that can be constructed using these building blocks. We investigate their blocking performance and examine issues such as complexity, modularity, and wavelength channel spacing associated with the proposed cross-connect structures     

All-Optical Envelope Detection and Fiber Transmission of Wireless Signals by External Injection of a DFB Laser

We outline a novel method for all-optical envelope detection of wireless signals by exploiting cross-gain modulation effects in a distributed feedback laser operating with optical injection. We successfully demonstrate envelope detection of a 20-GHz carrier amplitude-shift-keying modulated signal at 2.5 Gb/s and its transmission over a 70-km optical fiber link. We present results including bit-error-rate measurements, signal waveforms, and receiver sensitivity penalties associated with envelope detection and fiber transmission.     

Low-Current N-Type Quantum Dash Semiconductor Optical Amplifiers

In this letter, we propose the use of light N-type doping to enhance the optical gain of the quantum dash semiconductor optical amplifier (SOA) at low applied current. We find that doping the dashes with light donor concentration increases the unsaturated optical gain and widens the optical gain spectrum range at low applied current. Also, our calculation reveals that the use of N-type doping is associated with a reduction in the slope efficiency and a decrease in the transparency current, which makes N-type quantum dash SOA attractive for low power dissipation applications.     

Nonlinear switching of optical pulses in fiber Bragg gratings

We study numerically the nonlinear switching characteristics of optical pulses transmitted though fiber Bragg gratings. We consider both the uniform and phase-shifted gratings and compare their performance as a nonlinear switch. The nonlinear coupled-mode equations were solved numerically to obtain the pulse-switching characteristics. The steady-state behavior known to occur for continuous-wave optical beams is realized only for pulses wider than 10 ns with long tails. For pulsewidths in the range 0.1-1 ns, the use of phase-shifted gratings reduces the switching threshold, but the on-off contrast is generally better for uniform gratings. We also quantify the effects of rise and fall times associated with an optical pulse on nonlinear switching by considering the Gaussian pulses with smooth tails and nearly rectangular pulses with sharp leading and trailing edges.     

Multidimensional processing: Nonlinear optics and computing

The purpose of this paper is to overview some of the trends and directions in computing, as performed by optical hardware, resulting from the demands made by multidimensional signal processing. Optical information processing or optical computing is a vast field and some of the more significant issues are discussed here. We discuss future developments and architectural consequences for such potentially highly parallel and interconnected processing systems. Particular emphasis is placed on energy and speed considerations, associated with the use of nonlinear optical materials in optical systems and devices.     

Ethernet-based passive optical local-area networks for fiber-to-the-desk application

We introduce optical local-area network (LAN) architectures based on multimode optical fiber and components, short wavelength lasers and detectors, and the widely used fast Ethernet protocol. These architectures are designed to lower the costs associated with passive optical LAN implementation. Further reduction in overall cost is achieved through decreased network downtime, lower maintenance cost, extended geometrical spans, and larger headroom for future capacity increase. These optically transparent networks represent a novel approach for implementing fiber-to-the-desk.     

Large modular expandable optical switching matrices

Large optical switching matrices can be assembled incrementally from identical modules by means of a rearrangement of the Clos architecture that we have labeled SKOL. The design retains the strict-sense nonblocking properties of the Clos design, identical units provide economies of manufacture, and there are also cost advantages associated with the incremental expandability. SKOL modules can be constructed in ways that do not map back to the Clos original. In this form, SKOL is a new multistage switching architecture that is well adapted for construction with integrated optical technologies. We anticipate that the SKOL design can provide the very large, expandable optical switching matrices now demanded for optical networks     

Extending end-to-end optical service provisioning and restoration in carrier networks: opportunities, issues, and challenges

In this article, we address the opportunities, issues and challenges associated with end-to-end optical service provisioning and restoration in carrier networks. A number of scenarios are analyzed from a practical perspective, considering important aspects relevant to the management and control planes. Along the lines of three basic dimensions, to which we refer as locality, granularity, and ownership, we discuss the complexity associated with provisioning and restoring end-to-end optical services in regional (local scale) and national (global scale) networking scenarios. We identify a number of challenges in integrating a unified control plane solution and vendor-specific management and control planes with legacy carrier management systems.     

The optical network control plane: state of the standards and deployment

The notion of an optical control plane has rapidly ascended from being a mere concept to a detailed set of protocol standards developed with broad industry participation. In this article we present a brief overview of optical control plane architecture and the associated protocols. We then examine the business drivers and inhibitors behind the optical control plane effort, the current state of the standards, interoperability status, and the open issues that need to be resolved before widescale deployment of this new technology can begin.     

Shedding light on the future of SP for optical recording

Optical recording has lagged behind magnetic recording in two key areas: writable/erasable/rewritable media and density gains from advanced signal processing. While there are some writable optical-disk products available, their writing capability pales in comparison to magnetic recording. A great deal of research and development in writable/erasable/rewritable optical media continues and we address this in the article. Of particular interest is the use of near-field optical approaches to dramatically increase the storage density in both magnetic and optical recording. To a great extent, this article is about the future of signal processing for optical recording, since advanced signal processing has not been applied to any great extent in optical recording. The intention is twofold: (1) to provide a summary of current and existing optical recording technologies, and (2) to encourage and motivate work in advanced signal processing for these and other optical systems. We begin by summarizing the optical recording and readback processes and then describe writable optical channels and the gains associated with using partial-response coding techniques. We then describe nonbinary recording and the potential gains due to signal processing. The digital versatile disc (DVD), multilayer recording, and holographic recording are also discussed     

Planning of WDM Ring Networks

The rapid introduction of wavelength division multiplexing (WDM) technology to cope with the increased bandwidth requirements of transmission networks has intensified the need for recovery mechanisms at the optical layer. A first step towards survivable optical networking will be seen through the introduction of optical rings. This paper presents different types of optical rings (dedicated and shared protection WDM rings) and the planning issues associated with these WDM rings. In particular, we give mathematical models as well as solution methods for the ring loading and wavelength assignment problem. We compare the wavelength requirement of dedicated and shared protection rings under scenarios with different demand patterns. We also discuss the influence of the WDM equipment cost, and present a mathematical model for the optimization of hybrid networks with both dedicated and shared protection rings.     

Optically-induced molecular reorientation in nematic liquid crystals and nonlinear optical processes in the nanoseconds regime

We present a detailed theoretical analysis and experimental study of purely optically-induced nematic axis reorientation and the associated nonlinear optical processes such as self-phase modulations and optical switching. It is shown that under a sufficiently intense laser field (∼ 100 MW/cm²), nematic liquid crystals will respond in the nanosecond regime. Single nanosecond laser pulse self-phase modulation and intensity switching effects are observed. The magnitude and dynamics of the response are in agreement with theoretical expectations. Optical power limiting and switching effects associated with self-phase modulations are also demonstrated.     

Approaching the Non-Linear Shannon Limit

We review the recent progress of information theory in optical communications, and describe the current experimental results and associated advances in various individual technologies which increase the information capacity. We confirm the widely held belief that the reported capacities are approaching the fundamental limits imposed by signal-to-noise ratio and the distributed non-linearity of conventional optical fibres, resulting in the reduction in the growth rate of communication capacity. We also discuss the techniques which are promising to increase and/or approach the information capacity limit.      

The optical Internet: architectures and protocols for the globalinfrastructure of tomorrow

We present a high-level overview of the current state of the network architectures, protocols, and technologies that will serve as the seed for the optical Internet. We further propose that a two-way ripple effect of technologies penetrating from the edge to the core and vice versa, and the associated transformations that result, represent the keys to unlock the full potential of an optical Internet     

Optical Coding for Enhanced Real-Time Dynamic Bandwidth Allocation in Passive Optical Networks

In this paper, optical pulse encoding and decoding technology is proposed to enable real-time signaling in a passive optical network (PON) setting. Unique optical codes are assigned to selected optical network units (ONUs) equipped with the corresponding encoders. An out-of-band pulse train is broadcast from the optical line terminal (OLT) and is modulated by ONU-based switches. The encoded reflections of pulses are thus used to update the status of the OC-enabled queues at the OLT in real time. We explore the enhanced PON architecture and define its major design parameters. Through extensive simulations, we investigate the design principles and limits of our system parameters. Through a performance comparison of native interleaved polling with adaptive cycle time with its OC-enhanced counterpart, we show that our OC enhancement breaks the fundamental delay lower bound associated to the polling cycle. We propose and investigate new dynamic bandwidth allocation (DBA) algorithms that exploit real-time queue updates enabled through OC-enhanced polling. We also explore the pay-as-you-grow implementation of OC-enhanced polling to realize quality-of-service (QoS) differentiation, elaborate on possible migration paths from conventional PONs, and investigate absolute QoS performance guarantee improvements achieved through OC-enabled real-time DBA algorithms.     

Fundamental limits for linearity of CATV lasers

We have considered nonlinear distortions in a subcarrier multiplexed optical transmission system arising from carrier heating effects in the source laser. We included two sources of carrier heating: free-carrier absorption of the coherent radiation in the cavity, and the power flux into the active layer, associated with the input current. Resulting from the very existence of modulated optical and electrical signals, these effects cannot be avoided in any laser structure. Simple analytic expressions have been derived for the intermodulation distortion in multichannel single-mode lasers. For an 80-channel 60-540 MHz system with 3% optical modulation depth per channel, the composite second-order (CSO) distortion brought about by the hot-carrier effects is near the tolerance limit for CATV systems     

Ultralow chromatic dispersion measurement of optical fibers with a tunable fiber laser

We describe a novel convenient technique to allow for the accurate measurement of the dispersion coefficients till fourth-order in the zero-dispersion wavelength region of single-mode optical fibers. The proposed method is based on a careful spectral analysis of modulation instability occurring in both normal and anomalous dispersion regime and the associated dispersive waves emitted by soliton fission. It simply requires a high-power tunable continuous-wave fiber laser and an optical spectrum analyzer and is able to retrieve both the sign and magnitude of dispersion coefficients with enhanced precision.     

Hybrid optical switch using passive polymer waveguides andsemiconductor optical amplifiers

Optical switching can be performed by using optical amplifiers combined with a passive waveguiding network. Recently, most of the effort in optical amplifier switch modules have been focused on monolithic switches in which the entire device is fabricated on an InP substrate together with the semiconductor optical amplifiers (SOA's). In this paper, we investigate the use of SOA's with passive polymer waveguides to make hybrid switches of varying sizes. The optical amplifiers serve dual purposes, gating the signal and amplifying the signal. Amplification is needed in order to offset the losses associated with the passive waveguide elements as well as the losses from component misalignments in the switch module. Our analysis finds the largest switch module size that can be made with the architecture used. We also calculate the maximum number of switch modules which can be cascaded in order to retain a bit-error rate (BER) under 10^-9