S. J. B. Yoo

Spectral and spatial 2D fragmentation-aware routing and spectrum assignment algorithms in elastic optical networks [invited]

This paper investigates the spectrum fragmentation issue, which undermines the bandwidth efficiency in elastic optical networks. After categorizing the two-dimensional fragmentation problem as the fragmentation and misalignment subproblems, this paper proposes joint routing and spectrum assignment (RSA) algorithms to alleviate the spectral fragmentation in the lightpath provisioning process. The time complexity of the two proposed algorithms are analyzed in detail, and both algorithms can run in 0(kdnC log C) time, where k is the number of the shortest path in the routing algorithm, d is the maximum node degree in the network, n is the number of nodes in the network, and C is the link capacity expressed as the number of spectral slots. Simulation results indicate that the proposed fragmentation-aware (FA) RSA algorithm and the FA algorithm with congestion avoidance (CA) outperform the existing schemes in terms of blocking probability (BP) reduction. Compared with the benchmark K-shortest-path routing and first-fit assignment (KSP-FF) algorithm, the proposed FA and FA-CA algorithms can achieve a BP reduction of [100%, 4.43%] and [100%, 6.45%], respectively, according to the traffic load in a sample NSFNET topology.

Fragmentation-aware routing, modulation and spectrum assignment algorithms in elastic optical networks

We investigate the principle of how dynamic service provisioning fragments the spectral resources on links along a path, and propose corresponding RMSA algorithms to alleviate spectrum fragmentation in dynamic network environments.

Demonstration of Cooperative Resource Allocation in an OpenFlow-Controlled Multidomain and Multinational SD-EON Testbed

The combination of elastic optical networks (EONs) and software-defined networking (SDN) leads to SD-EONs, which bring a new opportunity for enhancing programmability and flexibility of optical networks with more freedom for network operators to customize their infrastructure dynamically. In this paper, we investigate how to apply multidomain scenarios to SD-EONs. We design the functionalities in the control plane to facilitate multidomain tasks, and propose an interdomain protocol to enable OpenFlow controllers in different SD-EON domains to operate cooperatively for multidomain routing and spectrum assignment. The proposed system is implemented and experimentally demonstrated in a multinational SD-EON control plane testbed that consists of two geographically distributed domains located in China and USA, respectively. Experimental results indicate that the proposed system performs well for resource allocation across multiple SD-EON domains.

OpenFlow-assisted online defragmentation in single-/multi-domain software-defined elastic optical networks [invited]

Spectrum fragmentation limits the efficiency of spectrum utilization in elastic optical networks (EONs). This paper studies how to take advantage of the centralized network control and management provided by software-defined EONs (SD-EONs) for realizing OpenFlow-assisted implementation of online defragmentation (DF). We first discuss the overall system design and OpenFlow protocol extensions to support efficient online DF and conduct DF experiments with routing and spectrum assignment (RSA) reconfigurations in a single-domain SD-EON. Then, we propose to realize fragmentation-aware RSA (FA-RSA) in multi-domain SD-EONs with the cooperation of multiple OpenFlow controllers. In order to provision inter-domain lightpaths with restricted domain visibility on intradomain resource utilization, we design and implement an inter-domain protocol to facilitate FA-RSA in multi-domain SD-EONs and demonstrate controlling the spectrum fragmentation on inter-domain links with FA-RSA. Our experimental results indicate that the OpenFlow-controlled DF systems perform well and can improve the performance of SD-EONs effectively.

Mode-multiplexed transmission over conventional graded-index multimode fibers

We present experimental results for combined mode-multiplexed and wavelength multiplexed transmission over conventional graded-index multimode fibers. We use mode-selective photonic lanterns as mode couplers to precisely excite a subset of the modes of the multimode fiber and additionally to compensate for the differential group delay between the excited modes. Spatial mode filters are added to suppress undesired higher order modes. We transmit 30-Gbaud QPSK signals over 60 WDM channels, 3 spatial modes, and 2 polarizations, reaching a distance of 310 km based on a 44.3 km long span. We also report about transmission experiments over 6 spatial modes for a 17-km single-span experiment. The results indicate that multimode fibers support scalable mode-division multiplexing approaches, where modes can be added over time if desired. Also the results indicate that mode-multiplexed transmission distance over 300 km are possible in conventional multimode fibers.

Monolithic InP 100-Channel

We demonstrate monolithic integration of a 100-channel arrayed-waveguide grating (AWG) with 10-GHz channel spacing and 100 optically controlled Michelson-interferometer-based phase and amplitude modulators. The high-resolution AWG showed better than -15-dB crosstalk, and the modulator extinction ratio was better than 20 dB with either electrical or optical modulation control. The twin-integrated devices comprise a 50-mm diameter InP wafer with 1200 independent optoelectronic components.

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This paper proposes and demonstrates optical 3R regeneration techniques for high-performance and scalable 10-Gb/s transmission systems. The 3R structures rely on monolithically integrated all-active semiconductor optical amplifier-based Mach-Zehnder interferometers (SOA-MZIs) for signal reshaping and optical narrowband filtering using a Fabry-Peacuterot filter (FPF) for all-optical clock recovery. The experimental results indicate very stable operation and superior cascadability of the proposed optical 3R structure, allowing error-free and low-penalty 10-Gb/s [pseudorandom bit sequence (PRBS) 223-1 ] return-to-zero (RZ) transmission through a record distance of 1 250 000 km using 10 000 optical 3R stages. Clock-enhancement techniques using a SOA-MZI are then proposed to accommodate the clock performance degradations that arise from dispersion uncompensated transmission. Leveraging such clock-enhancement techniques, we experimentally demonstrate error-free 125 000-km RZ dispersion uncompensated transmission at 10 Gb/s (PRBS 223-1) using 1000 stages of optical 3R regenerators spaced by 125-km large-effective-area fiber spans. To evaluate the proposed optical 3R structures in a relatively realistic environment and to investigate the tradeoff between the cascadability and the spacing of the optical 3R, a fiber recirculation loop is set up with 264- and 462-km deployed fiber. The field-trial experiment achieves error-free 10-Gb/s RZ transmission using PRBS 223-1 through 264 000-km deployed fiber across 1000 stages of optical 3R regenerators spaced by 264-km spans

10-GHz Device for Optical Arbitrary Waveform Generation

We demonstrate, for the first time, an error-free, 320-Gb/s optical code division multiple access (O-CDMA) network testbed employing the spectral phase encoded time spreading (SPECTS) technique. Results with and without forward error correction (FEC) are presented.

High-Performance Optical 3R Regeneration for Scalable Fiber Transmission System Applications

This paper discusses multihop routing, all-optical label swapping operation of optical label switching routers that make real-time decisions based on the label and the forwarding table. The switching fabric conducts data regeneration and label rewriting.

320-Gb/s Capacity (32 Users × 10 Gb/s) SPECTS O-CDMA Local Area Network Testbed

We report optical-label switched optical packet routing with wavelength, time, and space domain contention resolution. Testing of the packet routing system under three contention scenarios demonstrated the successful contention resolution in the three domains and error free performance.