Number Of Wavelength Channels Research Articles

High-power multi-wavelength Yb-doped fiber laser with a tunable interval, amplitude, and a number of channels

In recent years, multi-wavelength lasers have attracted much attention due to their wide applications in various fields. In this Letter, we experimentally demonstrate a high-power multi-wavelength Yb-doped fiber laser with the aid of an acoustic-optic tunable filter, in which the wavelength interval, the intensity of each channel, and the number of lasing channels can be tuned independently. As a result, the operating wavelength tuning range covers 1040.0 to 1090.0 nm and the maximal output power reaches 15.7 W, which is higher than the previous reports by more than three orders of magnitude. The wavelength interval can be adjusted from 2.6 to 50 nm and the spectral profile can be arbitrarily controlled. Furthermore, the number of wavelength channels can be adjusted from 1 to 4. This work will provide a reference for achieving high-power spectral-flexible fiber sources.

Routing, Core and Wavelength Allocation in Multi-Core-Fiber-Based Quantum-Key-Distribution-Enabled Optical Networks

Quantum-key-distribution (QKD) enabled optical networks can provide secure keys for different kinds of applications to ensure the high security of communication processes. As the number of wavelength channels in a single-core fiber is limited, space division multiplexing (SDM) has been considered to be a valuable technique to provide more wavelength resources, which solves the problem of insufficient channel capacity. Due to the rapid expansion of data volume, the SDM-based QKD network has been regarded as an important paradigm. At the same time, resource allocation in multi-core optical networks is a problem worthy of studying. In this work, four routing, core, and wavelength allocation (RCWA) algorithms are proposed in the multi-core optical network for quantum service requests and classical service requests, which are referred to as RCWA without perception (RCWA-WP), RCWA with crosstalk perception (RCWA-XTP), RCWA with spectrum perception (RCWA-SP), and RCWA with core perception (RCWA-CP). Simulations are carried out to evaluate the network performance in terms of blocking probability, key utilization, and average crosstalk intensity. The comparative results indicate that the RCWA-SP algorithm can improve network performance and reduce the blocking probability, while the RCWA-XTP algorithm can reduce inter-core crosstalk during transmission.

Performance evaluation of a multihop WDM network with share-per-node L-WIXC architecture

Abstract This paper investigates the impact of coherent and incoherent crosstalks on bit error rate of a multihop wavelength division multiplexing (WDM) transmission system with limited-wavelength-interchanging cross connects (L-WIXCs). The relation between the crosstalk and signal to crosstalk plus noise ratio at the receiver output is analyzed and redefined with an improved mathematical modeling. Quantitative analysis of the bit error rate (BER) in terms of system parameters like number of hops, number of fiber and number of wavelength channels per fiber are evaluated. The power penalty due to accumulated crosstalk at a given BER of 10−9 and the optimum system design parameters are also determined numerically. Results show that there is a significant power penalty of the order of 10–12 dB due to accumulated crosstalk depending on the number of hops. Maximum allowable number of hops at a given BER of 10−9 and number of input fibers are also evaluated.

Sampled fiber gratings for picosecond time delay signal processing

Sampled fiber grating for high-resolution time-domain signal processing is investigated. Sampled fiber grating is useful to introduce precise time delays in picosecond (ps) across many wavelength channels. We analyze and simulate for Sinc2 sampled fiber grating, and show that a large number linear sub-ps time delays can be achieved by the grating. We present that Gaussian sampled fiber gratings can be fabricated by inscribing optical fiber by Gaussian laser beam, and can realize short time delays over a number of wavelength channels with a required time delay profile. For a Gaussian sampled fiber grating fabricated, an average time delay step of 4.49 ps with 10% linearity for 8 wavelength channels, and an average delay step of 2.5 ps with 8% linearity if for 4 channels, are realized. A physical model of cascaded equivalent Fabry-Perot cavities together with rectangular truncation of the inscription laser beam for the Gaussian sampled refractive index is suggested, and used to explain the grating spectra. A technique for time delay step tunability of the grating is presented. Some issues are discussed with conclusions given. We demonstrate that the sampled fiber gratings have capability to provide a large number of picosecond time delays with good linearity. This offers a simple technique for ps-high-resolution signal processing in time-domain and THz signal generation.

An improved approximate network blocking probability model for all-optical WDM Networks with heterogeneous link capacities

Abstract Currently, analytical models are used to compute approximate blocking probabilities in opaque and all-optical WDM networks with the homogeneous link capacities. Existing analytical models can also be extended to opaque WDM networking with heterogeneous link capacities due to the wavelength conversion at each switch node. However, existing analytical models cannot be utilized for all-optical WDM networking with heterogeneous structure of link capacities due to the wavelength continuity constraint and unequal numbers of wavelength channels on different links. In this work, a mathematical model is extended for computing approximate network blocking probabilities in heterogeneous all-optical WDM networks in which the path blocking is dominated by the link along the path with fewer number of wavelength channels. A wavelength assignment scheme is also proposed for dynamic traffic, termed as last-fit-first wavelength assignment, in which a wavelength channel with maximum index is assigned first to a lightpath request. Due to heterogeneous structure of link capacities and the wavelength continuity constraint, the wavelength channels with maximum indexes are utilized for minimum hop routes. Similarly, the wavelength channels with minimum indexes are utilized for multi-hop routes between source and destination pairs. The proposed scheme has lower blocking probability values compared to the existing heuristic for wavelength assignments. Finally, numerical results are computed in different network scenarios which are approximately equal to values obtained from simulations.

Minimization Number of Network-Coded Links Based on Improved Adaptive Genetic Algorithm for Multi-source Optical Networks

Abstract With the rapid development of multi-source optical multicast application, the wavelength division multiplexing (WDM) with limited number of wavelength channels is facing with the new challenge of bandwidth shortage. Optical multicast adopting network coding can improve the bandwidth utilization, but optical network coding needs to increase optical storage and computation overhead in WDM optical network. For reducing the number of optical network-coded links, an improved adaptive genetic algorithm (IAGA) is proposed to minimize the number of network-coded links for multicast. By designing the maximization difference crossover operation, IAGA can guarantee the diversity of population and avoid individuals from falling into a local optimal. By adaptively adjusting the crossover probability, IAGA makes the population diverse at the beginning stages and makes the excellent individuals remain in a stable condition. Compared with other algorithms, the simulation result shows that the proposed algorithm has fastest convergence speed, which means that it takes the shortest time to find the minimum numbers of coded link solutions.

Optimization Techniques for 160 GBPS WDM Optical Links to Minimize Nonlinear Effects

Increased channel capacity of optical transmission system is obtained by either increasing the bit rate of transmission or by using the technique of Wavelength Division Multiplexing (WDM). In long distance communication, higher launched power is required to achieve the required signal-to-noise ratio (SNR) but with increased launched optical powers, rates and the number of wavelength channels, nonlinear optical effects have been increased. DWDM (Dense Wavelength Division Multiplexing) Systems facilitate the maximum channelization of the huge bandwidth offered by Optical Systems. The paper recognizes Cross Phase Modulation (XPM) and Four Wave Mixing (FWM) as major performance limitations for DWDM Systems. We have optimized the 160 GBPS, 16 channel optical link and have observed the optimization by variation of parameters like Dispersion, Channel Spacing and Pulse Width alongside NZDSF (Non-Zero Dispersion Shifted Fiber) and DCF (Dispersion Compensated Fiber) have been employed to further optimize the system performance. System parameters have been proposed for optimum performance yielding a Q –factor value of 34.89 dB and BER (Bit Error Rate) value of the order of 10-268.

A Tunable on-Chip Integrated Plasmonic Filter and Router Based on Metal/Dielectric Nanostructures

An on-chip integrated wavelength filter and router device is realized using two-dimensional metal/dielectric nanostructures. The device can filter wavelengths of light from an incident broadband beam, and further route the filtered signals to different ports on the same chip. The footprint of the entire device is only 3.4 μm × 7.3 μm. Both the number of wavelength channels and the central wavelength of each channel can be tuned by adjusting the structure parameters, or by using a pumped laser. This work demonstrates an ultracompact and robust integrated multifunctional device, and provides a novel and flexible method for the integration of nanophotonic devices.

Wavelength channel minimization-based energy-aware mechanism in a multichannel EPON

We propose an energy-aware mechanism (EAM) applicable to the multichannel Ethernet Passive Optical Network that can minimize the number of wavelength channels used and save energy. Wavelength channel minimization is processed by collecting the information such as request message, allocated grant, and start time of each optical network unit (ONU) transmission in the previously elapsed scheduling cycles and comparing it with the buffer occupancy and packet delay conditions of the ONUs required by the user's quality-of-service requirement. They are exchanged between the optical line terminal (OLT) and the ONUs via the multipoint control protocol. In this way, at the beginning of each scheduling cycle, the ONU's buffer occupancy and packet delay conditions can be evaluated, and then, the OLT decides the smallest number of wavelength channels to be used in the current scheduling cycle. By turning off the OLT receivers corresponding to the unused wavelength channels, the OLT can save energy. The performance of the proposed EAM was evaluated through simulations using nonjoint off-line dynamic bandwidth allocation and dynamic wavelength assignment algorithms. The results showed that the OLT receivers' power consumption could be reduced by 48 % on average.

Bandwidth-variable optical transport network with adjustable time-modulated and inverse-multiplexed wavelength channels

This paper presents a bandwidth-variable and optical-groomable (BVOG) transport network architecture based on time-modulated optical cross-connects that enables efficient switching of periodic burst-sequenced traffic in addition to wavelength streaming traffic; with an elastic control plane that shapes each sub-wavelength traffic stream at the network edge into a sequence of periodic bursts, and inverse-multiplexes a supra-wavelength traffic stream into a group of multiple wavelength traffic streams and a potential sub-wavelength traffic stream to match the bandwidth requirement. BVOG network enables variable-time-slotted lightpaths with variable-length time slots to meet the bandwidth requirements of sub-wavelength traffic; and inverse-multiplexed lightpath-group (IM-lightpath-group) with variable group size to meet the bandwidth requirements of supra-wavelength traffic. For the problem of "routing and wavelength and time assignment" (RWTA) for sub-wavelength traffic; this paper presents an optimal integer linear programming (ILP) formulation that maximizes total network throughput, and a heuristic algorithm to minimize the blocking probability of future connection requests. For the problem of "inverse-multiplexed routing and wavelength assignment" (IMRWA) for supra-wavelength traffic; this paper presents an optimal ILP formulation that minimizes the total number of hops and the total per-hop propagation delays of the IM-lightpath-group, and a heuristic algorithm that minimizes the total number of wavelength channels of the IM-lightpath-group. The RWTA ILP is solved by the ILOG CPLEX optimization tool, and it is used to check the optimality of the RWTA heuristic. Performance tuning of the IMRWA heuristic is investigated to balance the tradeoff between performance and computation complexity. Performance tuning of the BVOG network with the RWTA and IMRWA heuristic is examined through simulation experiments.

Longest Path Reroute to Optimize the Optical Multicast Routing in Sparse Splitting WDM Networks

Limited by the sparse light-splitting capability in WDM networks, some nodes need to reroute the optical packet to different destination nodes with the high cost of routing for reducing packet loss possibility. In the paper, the longest path reroute optimization algorithm is put forward to jointly optimize the multicast routing cost and wavelength channel assignment cost for sparse splitting WDM networks. Based on heuristic algorithms, the longest path reroute routing algorithm calls multiple longest paths in existing multicast tree to reroute the path passing from the nodes which are violating the light-splitting constraint to the nodes which are not violating light-splitting constraint with few wavelength channels and low rerouting cost. And a wavelength cost control factor is designed to select the reroute path with the lowest cost by comparing the multicast rerouting path cost increment with the equivalent wavelength channel required cost increment. By adjusting wavelength cost control factor, we can usually get the optimized multicast routing according to the actual network available wavelength conversion cost. Simulation results show that the proposed algorithm can get the low-cost multicast tree and reduce the required number of wavelength channels.

Topology and investigation of a polymer 8-port optical router with scalable 7N channel wavelengths using N-stage cascading structure

Eight-port optical routers are widely used in Cluster-Mesh photonic networks-on-chip (NoC). In this paper, by using 24 groups of cross-coupling two-ring resonators, a 1-stage 8-port polymer optical router is proposed, which can optically route 7 channel wavelength data streams along definite-path in 2-D plane. Under the selected 7 channel wavelengths with standard 0.8-nm spacing, the insertion losses along all routing paths are within 0.02–0.58dB, the maximum crosstalk of all routing operations is less than −39dB, and the device footprint size is about 0.79mm2. Then, to improve bandwidth capability, a universal novel structure and routing scheme of N-stage cascaded 8-port optical router are presented, which can optically routes 7N channel wavelengths. As N increases, the insertion losses of most wavelength channels increases, and a maximum N of 43 is required to drop the insertion loss below 10dB. In this case, the maximum allowed number of wavelength channel is as large as 300. So due to good scalability in wavelength, this device shows potential application of wideband signal routing in optical NoC.

Optically transparent integrated metro-access network

High-capacity optical transmission technologies have made possible very high data rates and a large number of wavelength channels. Further, optical network functionality has made progress from simple point-to-point WDM links to automatically switched optical networks. In the future, dynamic burst-switched and packet-switched photonic networks may be expected. This paper describes a novel architecture of transparent WDM metropolitan area network (MAN) that is capable of switching on both packet-by-packet and burst-by-burst basis, thereby having the potential to achieve high throughput efficiency. The optically transparent MAN also includes a large part of the access network infrastructure. It is scalable, flexible, easy upgradeable and able to support heterogeneous network traffic. Some results of a preliminarly study on network performance are shown.

Optimal Packet Scheduling in WDM Optical Switches With Output Buffer and Limited Wavelength Conversion

All-optical packet switching is a promising candidate for future high-speed switching. However, due to the absence of optical random access memory, the traditional Virtual Output Queue (VOQ) based input-queued switches are difficult to implement in the optical domain. In this paper we consider output-buffered optical packet switches. We focus on packet scheduling in an output-buffered optical packet switch with limited-range wavelength conversion, aiming at maximizing throughput and minimizing average queuing delay simultaneously. We show that this problem can be converted to a minimum cost maximum network flow problem. To cope with the high complexity of general network flow algorithms, we present an algorithm that can efficiently find an optimal schedule in O(min{NW,BW}) time, where <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> is the switch size, W is the number of wavelength channels per fiber and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> is the length of the longest FDL at the output of the switch. The complexity of the new algorithm asymptotically matches the lower bound of the scheduling problem. We also conduct extensive simulations to test the performance of the proposed scheduling algorithm under different traffic models.

On the Conditions That Justify Requiring Dynamic Reconfigurability in WDM–TDMA Optical Access Networks

In a passive optical network with a hybrid wavelength division multiplexing time division multiple-access scheme, implementing reconfigurable wavelength assignment is complex; hence the need to determine the conditions for which the capacity improvements justify requiring reconfigurability over adopting a more inexpensive fixed wavelength assignment. Fixed and reconfigurable approaches to wavelength assignment are modeled and evaluated under nonstationary traffic conditions. The performance improvement is obtained in terms of bit rate gain relative to the nominal bandwidth and depends on the number of wavelength channels as well as the magnitude of the load offered by the optical network units. In addition, frame delay and frame loss in relation to the bit rate performance are obtained for Pareto and exponentially distributed traffic. Simulations show that when introducing reconfigurability, typical peak bit rate gains with respect to the fixed case are 17%, and maxima of 175% are potentially possible when traffic demands are particularly uneven.

Traffic grooming, routing, and wavelength assignment in an optical WDM mesh networks based on clique partitioning

In wavelength routed optical networks, the number of wavelength channels is limited due to several constraints and each wavelength as well as each lightpath support traffic in the Gbps range. On the other hand, the traffic requested by an individual connection is still in the Mbps range. Therefore, to utilize the network resources (such as bandwidth and transceivers) effectively, several low-speed traffic streams have to be efficiently groomed or multiplexed into one or more high-speed lightpaths. The grooming problem of a static demand is considered as an optimization problem. In this work, we have investigated the traffic grooming problem with the objective of maximizing the network throughput for wavelength-routed mesh networks and map this problem to the clique partitioning problem. We have proposed an algorithm to handle general multi-hop static traffic grooming based on the clique partitioning concept. The efficiency of our approach has been established through extensive simulation on different sets of traffic demands with different bandwidth granularities for different network topologies and compared the approach with existing algorithms.

An integrated reconfigurable optical add-drop multiplexer based on using an opto-VLSI processor and a 4-f imaging system

A novel integrated reconfigurable optical add-drop multiplexer (ROADM) structure is proposed and demonstrated experimentally. The ROADM employs an interface substrate that enables the integration of a fiber-lens collimator array and an Opto-VLSI processor to realise a 4-f imaging system through optical beam steering. Phase hologram optimization of the Opto-VLSI processor is investigated, for maximizing the number of wavelength channels while keeping adequate insertion loss and crosstalk levels. Experimental results are shown, which demonstrate a broadband operation and the principle of the ROADM with crosstalk of less than −30.5 dB and insertion loss of less than 6 dB for the drop and through operation modes.

Effective utilization of optical transponders in WDM mesh networks

We consider a multi-degree optical node configuration, which can provide multiple fiber links to the other nodes in wavelength-division-multiplexing (WDM) mesh networks. In the node, optical transponders are utilized for the wavelength channels sources and 3R-wavelength converters. It is shown that blocking originated from both the limited signal impairment threshold (SIT) problem and wavelength contentions can be resolved by the optical transponders. Moreover, the number of optical transponders per fiber link can be reduced down to half of the number of wavelength channels without degrading the network performance.

Performance Study of Optical Packet Switching Node based on Shared Wavelength Conversion

Contention resolution is one of the key issues for optical packet switching (OPS). Wavelength converter is an effective contention resolution for the contending optical packet. In this paper, an architecture model equipped with a band of shared tunable wavelength converters for optical packets node is put forward. Shared wavelength conversion corresponds to the case of a number of converters shared amongst a larger number of wavelength channels. For studying the packets blocking, we assumed packet arrivals at the optical switch with Poisson process to cope with very general traffic patterns whereas packet lengths are assumed to be exponentially distributed. The analysis and simulation results show that this architecture reduces both the packet loss ratio and the number of wavelength converters.

Dynamic optical packet/burst-switched metropolitan area network

The development of key technologies for high-capacity optical transmission has made possible transmission experiments with very high data rates and a large number of wavelength channels. Based on the recent development of enabling technology, optical network functionality has made progress from simple point-to-point wavelength division multiplexed (WDM) links to automatically switched optical networks. In the future, dynamic burst-switched and packet-switched photonic networks may be expected. This paper summarizes recent research progress in the area of optical metro networks and proposes an architecture for a transparent WDM metropolitan area network (MAN) that enables switching on both packet-by-packet and burst-by-burst basis, thereby having the potential to achieve high throughput efficiency. The optically transparent MAN also includes a large part of the access network infrastructure. It is scalable, flexible, easy upgradeable and able to support heterogeneous network traffic.