Optical Time Division Multiplexing Technology Research Articles

Chirped-apodized Thue-Morse quasiperiodic structures for multichannel optical dispersion compensation

Nowadays, optical data transmission systems are significantly involved in telecommunication networks. Particularly, hundreds of data channels can be sent concurrently over a single optical fiber through dense wavelength division multiplexing (DWDM) and optical time division multiplexing technologies. Nevertheless, dispersion imposes main limitations for having high capacity systems with high transmission rates. This paper suggests a new dispersion compensating scheme by introducing one-dimensional chirped and apodized Thue-Morse quasiperiodic structures. Numerical investigations of the dispersion features of the proposed structure is presented. According to the acquired relatively smooth and negative slope group delay (GD) along with corresponding negative constant group velocity dispersion (GVD) of the reflection bands, it would be possible to apply the suggested structure in an efficient way in DWDM applications for multiband dispersion compensation in optical communication systems. The designed multilayer structure with short physical length and ultrahigh negative dispersion coefficient and with the free spectral range (FSR) of about 0.8 nm meets the International Telecommunication Union-Telecommunication Standardization (ITU-T) Sector requirements. Besides, the impact of main structural design parameters on the spectral features of the suggested system are presented in this paper.

Resource Assignment Strategy in Optical Networks Integrated With Quantum Key Distribution

Data transmission with optical fiber is vulnerable to eavesdropping. Moreover, conventional key distribution technology suffers from increasing computational power and upgraded attack algorithms. To address these issues, quantum key distribution (QKD), a quantum technology that secures secret information (such as a cryptographic key) exchange between two parties, can be used to guarantee secure data transmission. Integrating QKD into existing wavelength division multiplexing optical networks has been verified through a series of experiments, which contribute to ensuring network security and saving fiber resources. This paper addresses the resource assignment problem in QKD-enabled optical networks. First, a QKD-enabled optical network architecture is introduced. A small fraction of wavelength channels are segmented into multiple time slots with optical time division multiplexing technology to construct quantum key channels (QKChs) and measuring-basis channels, and then the remaining wavelengths can construct traditional data channels. Second, a static routing, wavelength, and time-slot assignment (RWTA) strategy is proposed and verified by the integer linear programming formulation and a heuristic algorithm. In the RWTA, QKChs are assigned for service requests according to the security levels specified by relevant key-updating periods. Thus, the secret keys for data encryption can update periodically to enhance security. Simulation results indicate that there is a trade-off between security (i.e., security levels and security-level types) and resource utilization.

Fiber-connected UWB sensor network for high-resolution localization using optical time-division multiplexing

A fiber-connected ultra-wideband (UWB) sensor network for high-resolution localization which consists of a central station and several sensor nodes is proposed and demonstrated. To make the central station easily identify the received UWB pulses from different sensor nodes, optical time-division multiplexing (OTDM), realized by inserting a certain length of optical fiber between every two sensor nodes, is implemented. Due to the OTDM technology, the UWB pulses received by different sensors are mapped into different time slots, so neither parameter estimation nor clock synchronization is required in the UWB sensor node. All complex signal processing is completed in the central station, which greatly improve the localization accuracy and simplify the system. A proof-of-concept experiment for two-dimensional localization is demonstrated. Spatial resolution as high as 3.9 cm is achieved.

Optical regenerative NRZ to RZ format conversion based on cascaded lithium niobate modulators

Optical regenerative nonreturn-to-zero (NRZ) to return-to-zero (RZ) format conversion using a lithium niobate phase modulator and a lithium niobate intensity modulator is proposed and demonstrated. The key advantage of the proposed format converter is that the converted RZ signal has a very small pulse width, which can be multiplexed to a higher bit rate using optical time division multiplexing technology. The operation can greatly reduce the timing jitter of the degraded NRZ signal due to the regenerative property of the proposed scheme. Besides, the format converter can also support multi-channel operation. An experiment is performed with the feasibility of the scheme demonstrated.

Experimental Demonstrations of All-Optical Phase-Multiplexing Using FWM-Based Phase Interleaving in Silica and Bismuth-Oxide HNLFs

We propose an all-optical phase-interleaving technology based on dual-pump four-wave mixing (FWM) in highly nonlinear fiber (HNLF). The proposed all-optical phase-interleaving technology is applied in an all-optical phase-multiplexing scheme to successfully phase-multiplex 2times or 3 times 10-Gb/s DPSK-WDM signals to a 20- or 30-Gb/s DPSK in non-return-to-zero (NRZ) formats. The proposed all-optical phase multiplexing scheme is demonstrated using dual-pump FWM in highly nonlinear silica and bismuth fibers. In contrast with optical time-division multiplexing technology, the proposed all-optical phase-multiplexing technology does not require pulse-carving, thus offering a high spectral-efficiency. Differential precoder for each input tributary is operated independently, and no additional encoder or postcoder is required to recover the original data after demodulation on the receiver side.

OTDM-based optical communications networks at 160 Gbit/s and beyond

The virtually unlimited bandwidth of optical fibers has caused a great increase in data transmission speed over the past decade and, hence, stimulated high-demand multimedia services. Nowadays, opto-electronic conversion is still required at each network node to process the incoming signal. However, when the single channel bit rate increases beyond electronic speed limit, optical time division multiplexing (OTDM) becomes a forced choice, and all-optical processing must be performed to extract the information from the incoming packet. In this paper the state of art, the advantages and drawbacks of the OTDM technology will be discussed in order to highlight its potentialities in different application scenarios for optical communications networks, and its perspectives in different temporal horizons. In detail, a recent experiment of a 160 Gbit/s OTDM system is presented. Furthermore, a photonic node architecture suitable for optical packet switching networks is proposed, and possible solutions for the implementation of all the required subsystems are presented and compared in order to optimize the node performance. In particular innovative schemes for optical add/drop multiplexer, optical logic gates, optical switches, and optical flip-flop are introduced with a particular emphasis on emerging nonlinear materials and enabling technologies.

160 Gbit/s OTDM Long-Haul Transmission with Long-Term Stability Using RZ-DPSK Modulation Format

We describe a transmission system having a data rate of 160 Gbit/s based on the RZ-DPSK modulation format. The 160 Gbit/s single-polarization signal is generated by optical time division multiplexing technology using the base rate of 40Gbit/s. The setup is explained and results are given with a special focus on the stability issue of the transmission system. The pulse source, the optical gate for demultiplexing, the clock recovery and the balanced photo-detector are based on semiconductor components. We present long-term bit error measurements (10 hours) over two different long-haul fiber links. The first link comprises 3 ×106 km standard single mode fiber and uses a PMD mitigation scheme. The other link consists of 4 dispersion managed 80 km fiber spans without the need for an additional PMD compensation. Using EDFA amplification solely and also no FEC, error-free operation was achieved over several hours, only limited by slow drift effects in the laboratory system.

Ultrafast and Wideband All-Optical Processing Technologies Towards Flexible Photonic Networks

Recent progress in ultrafast and wideband all-optical processing technologies to realize flexible and transparent optical time-division multiplexing (OTDM)/wavelength-division multiplexing (WDM) photonic networks is reviewed covering ultrafast OTDM technologies handling more than 100 Gbit/s per wavelength channel and wideband WDM technologies handling more than 1000 wavelength channels over the 200 nm range.

Petastar: a petabit photonic packet switch

This paper presents a new petabit photonic packet switch architecture, called PetaStar. Using a new multidimensional photonic multiplexing scheme that includes space, time, wavelength, and subcarrier domains, PetaStar is based on a three-stage Clos-network photonic switch fabric to provide scalable large-dimension switch interconnections with nanosecond reconfiguration speed. Packet buffering is implemented electronically at the input and output port controllers, allowing the central photonic switch fabric to transport high-speed optical signals without electrical-to-optical conversion. Optical time-division multiplexing technology further scales port speed beyond electronic speed up to 160 Gb/s to minimize the fiber connections. To solve output port contention and internal blocking in the three-stage Clos-network switch, we present a new matching scheme, called c-MAC, a concurrent matching algorithm for Clos-network switches. It is highly distributed such that the input-output matching and routing-path finding are concurrently performed by scheduling modules. One feasible architecture for the c-MAC scheme, where a crosspoint switch is used to provide the interconnections between the arbitration modules, is also proposed. With the c-MAC scheme, and an internal speedup of 1.5, PetaStar with a switch size of 6400 /spl times/ 6400 and total capacity of 1.024 petabit/s can be achieved at a throughput close to 100% under various traffic conditions.

A highly-scalable, rapidly-reconfigurable, multicasting-capable, 100-Gb/s photonic switched interconnect based upon OTDM technology

We describe an ultrafast photonic switched interconnect based upon technologies developed for optical time division multiplexing (OTDM). The system uses a time-interleaved broadcast-and-select star architecture that is functionally equivalent to a crossbar switch. The interconnect offers full connectivity and low uniform latency among the input and output ports. The enabling technologies include ultrafast gated time slot tuners and all-optical demultiplexers. By utilizing these advanced optical technologies, it is possible to construct a highly scalable, rapidly reconfigurable, ultra-high-speed switch with performance beyond the capacity of current electronics. In the experimental demonstration, we constructed an interconnect with a peak bit rate of 100 Gh/s and the capability of connecting 16 OTDM ports. The system successfully demonstrated error-free operation of 100 Gb/s-multiplexing and demultiplexing in addition to rapid inter-channel switching capability on the order of the single channel bit period. The system also supports multicasting functions among many nodes. To scale the system to accommodate a large number of ports, we provide an analysis of the coherent crosstalk requirements through the network to show the potential to support hundreds of ports within practical constraints of the optical components. We believe that this system offers an approach to meet the demands of high bandwidth and fast switching capability required in current high-speed lightwave networks.