Wavelength Add-drop Multiplexers Research Articles

Compact wavelength add-drop multiplexers using Bragg gratings in coupled dielectric-loaded plasmonic waveguides.

We report a novel design of a compact wavelength add-drop multiplexer utilizing dielectric-loaded surface plasmon-polariton waveguides (DLSPPWs). The DLSPPW-based configuration exploits routing properties of directional couplers and filtering abilities of Bragg gratings. We present practical realization of a 20-μm-long device operating at telecom wavelengths that can reroute optical signals separated by approximately 70 nm in the wavelength band. We characterize the performance of the fabricated structures using scanning near-field optical microscopy as well as leakage-radiation microscopy and support our findings with numerical simulations.

Analysis of reconfigurable multi-channel wavelength add drop multiplexer for intelligent optical networks

This paper presents design of an electro-optically tunable polymer multi-channel wavelength add drop multiplexer (WADM). The proposed WADM with trapezoidal waveguide geometry and poled electro-optical polymer material in the waveguide cores enables the wavelength tuning speed of WADM as 7.5 ps at the resonance wavelength of 1550 nm and coupling length of 1.5 mm. The device can be electro-optically tuned to add/drop multiple channels. Transmission spectra of the device with varying device parameters are simulated. The proposed WADM with high speed, small size and varying tuning capability makes this device, an important element in faster provisioning and routing of light paths in intelligent optical network.

A robust fiber-radio architecture for wavelength-division-multiplexing ring-access networks

In this paper, we propose a dynamic wavelength-allocation scheme for wavelength-division multiplexing (WDM) fiber-radio ring-access networks. This scheme can be used to improve the use efficiency of wavelengths at the burst traffic load on the fiber-radio networks. Moreover, a novel bidirectional wavelength add-drop multiplexer (B-WADM) is designed on the backboned ring, which can connect the working and standby sub-rings. It can provide the self-protected function that uses just a few optical devices under link failures. Furthermore, we carry out this study through the simulation and analysis for carrier-to-noise ratio (CNR), channel capacity, and spurious free dynamic range (SFDR) of the fiber-radio network. Finally, we set up an experimental network to demonstrate its performance. The experimental results illustrate that this fiber-radio architecture can provide the robust, flexible, and reliable characteristics for large radio terminals.

Novel Bidirectional Wavelength Add-Drop Multiplexer in the Wavelength Division Multiplexing Radio-over-Fiber Ring Network

In this paper, we propose and implement a novel bidirectional wavelength add-drop multiplexer (B-WADM) to provide dynamic wavelength allocation employing tunable fiber Bragg gratings (FBGs) and self-protecting function under link failure. This device can be used to improve the efficient use of wavelengths under burst traffic load as well as increase network reliability. The experimental results demonstrate that this B-WADM device can provide robust, flexible and cost-effective characteristics in the wavelength division multiplexing (WDM) fiber-radio ring access network.

Regeneration in synchronous optical network/WDM rings

In today’s WDM all-optical networks, a majority of existing virtual topology design algorithms have ignored link-performance limiting factors such as dispersion, amplified spontaneous emission (ASE), cross talk resulting from signal leakage in optical cross connects (OXCs), and fiber nonlinearities. All these factors result in bit-error-rate (BER) degradation at the receiving end. To maintain a BER below a certain level, some lightpaths in the network will require regeneration at the intermediate nodes, thus, setting up a lightpath in a multihop manner. In synchronous optical network (SONET) ring networks, the terminal equipment cost associated with electronic multiplexing is predominantly high. Wavelength add–drop multiplexers reduce the amount of SONET terminal equipment at each node by allowing certain wavelengths or bands to bypass the node optically without being electronically terminated. Most of the previous research in this area has focused on the virtual topology design and wavelength-routing algorithms to address the cost savings. Here we consider both unidirectional path-switched and bidirectional line-switched rings (UPSR, BLSR/2) with optical bypass. We analytically derive a relationship for the number of regenerators to support both single-hub and all-to-all situations for uniform and nonuniform traffic cases with an arbitrary internodal length distribution. We obtain lower and upper bounds for regeneration cost on a ring when nodes are randomly placed. Equivalency is established between UPSR and BLSR/2 networks in terms of regeneration cost for cases of single link failure. Regeneration cost advantage is shown for nonzero dispersion-shifted fiber (NZDSF) over standard single-mode fiber in dispersion-limited regimes.

Wavelength Assignment Algorithms in SONET/WDM Optical Ring Networks

The terminal equipment costs associated with electronic multiplexing can comprise of a dominating percentage of the total network costs in today's backbone wavelength-division-multiplexed (WDM) synchronous optical network (SONET) ring networks. The deployment of wavelength add-drop multiplexers (WADM) allows certain wavelengths to optically bypass the nodes without being electronically terminated, thus can effectively reduce the total equipment costs if connections and channels are appropriately assigned in traffic grooming. This paper presents a series of wavelength assignment algorithms with the objective to optimize the number of required wavelengths and SONET add-drop multiplexers in both unidirectional and bi-directional rings under an arbitrary grooming factor. In our analysis, we have considered both uniform and non-uniform all-to-all network traffic. As a simple model for realistic traffic pattern, a special case of non-uniform traffic, distance-dependent traffic is analyzed in detail. Significant ADM savings are reported for different traffic scenarios using our proposed algorithms.

On the reconfigurability of single-hub WDM ring networks

We study the benefit of reconfigurability for wavelength division multiplexed (WDM) ring networks with dynamic single-hubbed traffic. We show that the ability to reconfigure wavelength add-drop multiplexers helps to reduce the number of expensive line terminating equipment (LTEs) by a factor of W, where W is the number of wavelengths in the network. In addition, we show that for a general class of traffic, optical networks using reconfigurable wavelength add-drop multiplexers guarantee to be almost as bandwidth efficient as full wavelength add-drop networks, that is, opaque networks. For such traffic, we introduce several fast algorithms that achieve or approximate the optimal performance guarantees. The comparison between reconfigurable networks and opaque networks is quantified using a performance metric called capacity ratio, which captures the relative throughput performance of a reconfigurable network compared to the opaque network.

A DWDM/SCM self-healing architecture for broad-band subscriber networks

A high-capacity dense wavelength-division multiplexing/subcarrier multiplexing (DWDM/SCM) network based on a self-healing star-bus-ring architecture (SBRA) is proposed and demonstrated. This architecture has a star subnet on the upper level to be a high-capacity infrastructure for the network, several bus subnets on the middle level to offer broad-band channels for multiwavelength signals, and many ring subnets on the lower level to serve a number of nodes. We design remote nodes and bidirectional wavelength add-drop multiplexers (WADMs) by using simple optical switches to reconfigure the network under link failure. We further employ M-quadrature amplitude modulation (M-QAM) and frequency shift-keyed (FSK) signals for downstream and upstream channels, respectively. The SBRA ensures an optical-beat-interference-free (OBI-free) and high-reliability optical network. Finally, we set up an experimental network to demonstrate the feasibility of the proposed architecture.

Wavelength Assignment Algorithms in SONET/WDM Optical Ring Networks

The terminal equipment costs associated with electronic multiplexing can comprise of a dominating percentage of the total network costs in today's backbone wavelength-division-multiplexed (WDM) synchronous optical network (SONET) ring networks. The deployment of wavelength add-drop multiplexers (WADM) allows certain wavelengths to optically bypass the nodes without being electronically terminated, thus can effectively reduce the total equipment costs if connections and channels are appropriately assigned in traffic grooming. This paper presents a series of wavelength assignment algorithms with the objective to optimize the number of required wavelengths and SONET add-drop multiplexers in both unidirectional and bi-directional rings under an arbitrary grooming factor. In our analysis, we have considered both uniform and non-uniform all-to-all network traffic. As a simple model for realistic traffic pattern, a special case of non-uniform traffic, distance-dependent traffic is analyzed in detail. Significant ADM savings are reported for different traffic scenarios using our proposed algorithms.

Integrated reconfigurable optical wavelength add-drop multiplexer

A high performance 16-channel integrated optical add-drop multiplexer is described. The device offers both common wavelength and discrete wavelength add and drop ports for all channels. Insertion loss is less than 6 dB and the isolation is greater than 40 dB.

Bidirectional grating wavelength shifter with a broad-range tunability by using a beam of uniform strength

Bidirectional chirp-free tuning in Bragg reflection wavelength by as much as 12.52 mm has been achieved based on the principle of a beam of uniform strength. The experimental results are in good agreement with the theoretical analysis. The tuning device is simple in configuration, low cost, and easy to operate, which can be used in numerous applications, such as tunable fiber grating lasers and reconfigurable wavelength add-drop multiplexers, etc.

Effective wavelength assignment algorithms for optimizing design costs in SONET/WDM rings

In high-speed wavelength-division-multiplexed synchronous optical network (SONET) ring networks, the terminal equipment costs associated with electronic multiplexing can be predominantly high. Placing a wavelength add-drop multiplexer (WADM) at each network node allows certain wavelengths to optically bypass the node without being electronically terminated. This approach can effectively reduce the total equipment cost if connections and channels are appropriately assigned in traffic grooming. In this paper, we present a series of wavelength optimization and wavelength assignment algorithms with the objective to optimize the number of required SONET add-drop multiplexers and yet minimizes the number of wavelengths in both unidirectional and bidirectional rings under an arbitrary grooming factor. In our analysis, we have considered both uniform and general nonuniform all-to-all network traffic. As a simple model for realistic traffic patterns, a special case of nonuniform traffic, distance-dependent traffic, is analyzed in detail. Significant ADM savings are observed for different traffic scenarios using our proposed algorithms.

Bidirectional wavelength add-drop multiplexer using multiport optical circulators and fiber Bragg gratings

We propose and experimentally demonstrate a new of bidirectional wavelength add-drop multiplexer using multiport optical circulators and fiber Bragg gratings. It has the efficient suppression of the unwanted light caused by Rayleigh backscattering and optical reflection and is economical for the effective use of multiport optical circulators.

Wavelength-domain simulation of multiwavelength optical networks

This paper presents an efficient simulation method for the design of the optical transport layer of large-scale multiwavelength optical networks. According to this method, computations are performed in two complementary steps. During the first step, the powers of optical signals, amplified spontaneous emission (ASE) noise, and linear optical crosstalk are calculated at all points in the network. During the second step, the distortion and the overall performance of selected optical paths in the network are calculated. Each simulation step requires a different computer representation of optical signals and network components. A large part of this paper is devoted to the description of the wavelength-domain representation used during the first simulation step. In wavelength domain, optical signals are represented by their carrier wavelength and average power, exclusively. In addition, the network components are fully characterized by their loss or gain as a function of wavelength. The phase-transfer functions of the network components are discarded. These simplifications result in a dramatic increase in execution speed. During the second simulation step, optical signals are represented by their temporal waveforms. Linear optical network segments are replaced by an equivalent channel. The link between the two simulation steps is explained in detail. The remainder of the paper is devoted to the implementation of a network simulation tool based on the above method in the context of the multiwavelength optical networking (MONET) project. To illustrate the capabilities of the MONET simulator, a mesh of 4/spl times/4 wavelength-selective cross-connects (WSXCs) and wavelength add-drop multiplexers (WADMs) is studied and the crosstalk performance is determined.

Experimental investigation of wavelength-tunable WADM and OXC devices using strain-tunable fiber Bragg gratings

Two reconfigurable wavelength add/drop multiplexer (WADM) and optical cross-connect (OXC) devices based on strain-tunable fiber Bragg gratings (ST-FBGs) are proposed. The feasibility of WADM is verified by measuring the bit-error-rate performance of the dropped (cross-connect) and pass-through (no cross-connect) channels over a 50- and 100-km standard single-mode fiber for a 2.5 Gb/s system. Compared to back-to-back transmission, a negligible power penalty of only 0.2 dB is observed.

An Efficient Simulation Model of the Erbium-Doped Fiber for the Study of Multiwavelength Optical Networks

The first part of this paper reviews the spectrally resolved erbium-doped fiber model by Saleh, Jopson et al. (1990, IEEE Photon Technol. Lett.2, 714; 1991, Fiber Laser Sources and Amplifiers III, Vol. 1851, pp. 114–119, SPIE). This model is adequate for fast simulation of erbium-doped fiber amplifiers pumped at 980 or 1480 nm which are not self-saturated by amplified spontaneous emission noise. The second part of this paper reviews the wavelength-domain representation of optical signals and network components at the optical transport layer of multiwavelength optical networks. This representation stems from the spectrally resolved model of erbium-doped fiber amplifiers. Optical signals are represented by their carrier wavelength and average power exclusively and not by their temporal waveform, as is customary in simulation of analog and digital communication systems. In addition, network components are fully characterized by their loss or gain as a function of wavelength. The wavelength-domain representation is adequate for efficient steady-state and transient power-budget computations; i.e., it can be used to evaluate the optical signal, amplified spontaneous emission noise, and linear optical crosstalk average powers at all points in a multiwavelength optical network. To illustrate the capabilities of the spectrally resolved erbium-doped fiber model by Saleh, Jopson et al. and the wavelength-domain representation, transient power fluctuations caused by the dynamic interaction of saturated erbium-doped fiber amplifiers and servo-controlled attenuators in a bidirectional ring composed of four wavelength add–drop multiplexers are studied. The mechanisms responsible for this oscillatory behavior are identified and remedies are proposed.

Quantifying the benefit of wavelength add-drop in WDM rings with distance-independent and dependent traffic

One drawback to deploying wavelength division multiplexed (WDM) synchronous optical network (SONET) rings is the potentially large amount of equipment necessary for their deployment. Wavelength add-drop multiplexers potentially reduce the amount of required SONET terminal equipment by allowing individual wavelengths to optically bypass a node rather than being electronically terminated. We have quantified the maximum terminal-equipment savings attainable using wavelength add-drop for rings carrying uniform traffic and rings carrying distance-dependent traffic. The analysis makes use of both an enumerative methodology, and a "super-node" approximation technique that is applicable to arbitrary ring size and internode demand. In both the uniform and distance-dependent traffic scenarios, maximum terminal-equipment savings are shown to rapidly increase, over the region of interest, with both network size and internode demand. The value of wavelength add-drop is accordingly expected to grow rapidly in rings interconnecting numerous high-capacity nodes.

Multichannel add/drop and cross-connect using fibre Bragg gratings and optical switches

A dynamically selective wavelength add/drop multiplexer (WADM) and a multiwavelength cross-connect (M-XC) configuration for dense wavelength division multiplexed networks are proposed. Multiple channels add/drop and/or cross-connect can be realised according to the control of the optical switches and fibre Bragg gratings arrangement. The selective WADM and M-XC devices could provide more reconfigurable flexibility and survivability in WDM networks.

Simulation of ASE noise accumulation in a wavelength add-drop multiplexer cascade

This letter presents a computer simulation of a cascade of wavelength add-drop multiplexers (WADMs) each consisting of optical amplifiers, a multiplexer/demultiplexer pair, gain equalizing attenuators and 2/spl times/2 optical switches. It is shown that one of the eight wavelengths can propagate through more than 50 equidistant WADMs in a wavelength-division multiplexed (WDM) optical network before its optical signal-to-noise ratio (SNR) drops below acceptable levels. These simulations indicate that a national scale transparent WDM network is feasible.

Optical wavelength add-drop multiplexer in installed submarine WDM network

The authors present a simple, low-loss wavelength add-drop multiplexer and evaluate its implications and performance in a 4/spl times/2.5 Gbit/s system, demonstrating for the first time four-channel WDM transmission with wavelength routing over an installed optically amplified submarine cable system.