A linearization scheme based on two cascaded intensity modulators is proposed and experimentally demonstrated. By optimizing the biases, the power ratio and the phase difference between the drive signals applied to the two Mach–Zehnder modulators (MZMs), the third-order intermodulation distortion (IMD3) can be effectively eliminated over a wide operating bandwidth of 1 to 12 GHz without the same RF phase at two modulators, which is required in previous works. The ratio of the fundamental output to the IMD3 reaches 50.21 to 63.28 dB, which has an improvement of 18.35 to 31.42 dB compared to that of a single MZM link.
We describe and demonstrate a practical method for improving the performance of an injection-locked optoelectronic oscillator (IL OEO). An improved IL theory model, which helps to set the optimal locking range and reduce the phase noise of the OEO, is proposed. The IL OEO with an extra feedback loop exhibits good long-term operating stability and can produce a 10 GHz output signal with 80 dB side-mode suppression ratio and better than ±0.0005 ppm frequency drift within 12 h. The presented results can be used to guide the design of high-quality OEOs.
An intensity modulator is a key component in an optoelectronic oscillator (OEO). It is necessary to investigate the effects of some of the operating parameters of the modulator on OEO phase noise. Since the OEO optimized oscillation power is related to the nonlinear effect of the modulator, an extended analysis is made by considering both the saturation effects of the modulator and the radio frequency amplifier. Experimental results show that a 5-dB improvement of phase noise performance is achieved. In addition, a theoretical and experimental study on the DC bias-drifting problem of the modulator and its induced phase noise fluctuations is proposed. It is found that the saturated operation of the amplifier is helpful in reducing the fluctuation range. The presented results can be used to guide the design of high-quality OEOs.
This paper focuses on the problem of optical buffer control strategies for recirculation shared optical buffer in optical packet switching. Five control algorithms are presented, and their performances are evaluated and compared by computer simulations. Issues on the optimal configuration of optical buffers are also discussed. The numerical results show that the time delay resolution of fiber delay line has significant influence on the system performance in all three discussed switching mode. The results are valuable in designing the optical packet switch.
Optical burst switching (OBS) is a viable solution to support next generation optical Internet. This paper addresses the problem of inter-class bandwidth management for OBS supporting multi-class services. Bandwidth management should be simple to implement and optimally designed to maximize the network performance. We propose here a wavelength based inter-class bandwidth management approach for optical burst switched networks (OBSN). Three different wavelength allocation schemes are presented respectively. In our schemes, each class of service is endued with a weight according to its importance, which is proportional to the charge on corresponding class of service by the network operator. The static scheme allocates wavelengths based on the weight of class, while the dynamic allocation scheme is based on the weighted traffic load with the help of a traffic predictor. The merit optimized allocation aims to achieve the maximized weighted throughput of the network based on a traffic predictor and a dynamic optimization algorithm. The performance of the proposed three schemes are evaluated and compared by computer simulations, where the weighted loss rate is chosen to be a merit used in performance evaluations. From the viewpoint of the network operator, the merit-based scheme provides the maximized profit since it improves the weighted throughput of the system, which is approved by simulation results.
In this paper, inefficiencies of the QoS scheme based on extra-offset-time-based priority for variable-length optical burst-switched network were pointed out, and a novel fixed-length burst assembly scheme is proposed. This scheme is not only practical, but also able to decrease the latency of bursts at the edge nodes. Compared to variable-length (traditional) scheme, a smaller blocking probability for the highest priority service and almost one third offset time delay for every class were obtained in fixed-length scheme.
A novel, simple and controllable bandwidth allocation scheme, called bandwidth on Demand (BoD), is proposed for optical burst-switched network in this paper. It assures every service class to consume bandwidth no more than its granted percentage by examining the bandwidth usage of each class periodically. The burst loss ratios under arbitrary input loads are theoretically analyzed as well as numerically simulated. The theoretical descriptions accord with the simulated results very well. The scheme can be used as an effective scheme of bandwidth allocation and management.
In Optical Burst Switched (OBS) networks, the requirements on packet loss probability vary for different class users. In order to meet different packet loss probability demands, besides the traditional methods to support Differentiated services (DiffServ) by resource allocation and contention resolution, the scheduling of control
packets should also support DiffServ. A new type of scheduling strategy, Priority-based Weight Fair Queuing (PWFQ) scheduling strategy, is proposed. An equivalent analysis model is also presented to simplify the solving process of scheduling weight of each class. We also define a parameter, normalized deviation factor, to evaluate
the validity of our analysis model as well as the fairness of scheduling strategy on supporting DiffServ. Numerical results confirm that, it is feasible to analyze queue system, in which PWFQ scheduling strategy is adopted, with our equivalent model. At the same time, it confirms that our scheduling strategy performs well on providing fair DiffServ in terms of packet loss probability.
In order to improve the processing ability in the switching node, a lot of optical packet switching schemes were proposed, one of them is multi-wavelength label switching. In the scheme, a case of using K bit-long label and W different wavelengths can obtain WK unique labels at most. Here A novel label-coding scheme was put forward, which can produce more labels than before, For an example, if using 2 bit-long label and 2 different wavelengths, we can get 9 different labels, instead of 4 different labels using the old coding method proposed in the paper. At last, we give the design of the transceiver in detail.
Wavelength-division multiplexing appears to be the solution of choice for providing a faster networking infrastructure that can meet the explosive growth of the Internet. Future networks are expected to utilize the WDM technology for optical functionalities capable of handling multi-Teragabit signals and thus the cost, therefore it is very important that the Optical cross-connects (OXCs) and optical Add-drop Multiplexers (OADMs) have performed routing and switching capacities. Optical Packet Switch (OPS) technology allows us to rapidly deliver the enormous network bandwidth. OPS offers high-speed data rate and format transparency. But there are still many technologies and key components need to solve. In this paper we propose a novel architecture for OPS using Tunable Wavelength Converters (TWC) and Fiber Delay-Lines (FDLs). We use wavelength converters and demuxes connected with several FDLs that provide different delay periods. Input wavelengths can be tuned to different ones in order to acquire different delay periods. Wavelength converters are shown to improve the traffic performance of the switch blocks for both random and burst traffic. It can also provide contention resolution solution in wavelength and time domains. This architecture improves packet switching speed and significantly decreases the use of optical switches comparing with general architecture. Finally, the simulation results show that the packet blocking can be decreased.
The realization technology of a new kind of multi-wavelengths label optical packet switching technology is discussed. In this switching, optical header is labeled by several optical pulses at different wavelengths in the same optical communication channel band as optical payload. The optical transmitter with header generation and packet formation, receiver with data restoration and switching node with route processing are introduced. The switching principle is verified by a simplified experiment.
Optical Label Switching (OLS) is one of the practical manners of optical packet switching. It is a main research domain in optical networks. The advantage of OLS is its bandwidth efficiency and ability to support various network devices. There are a lot of practical problems need to be resolved. Today, research into OLS technology has focused on key networking and hardware issues such as high-speed optical switch, optical storage component, and network nodes source distribution optimization algorithm. The optical Label Header contains header synchronizing bits, routing address bits, etc. Header reading and rewriting includes synchronizing, routing and checking technologies. So it is the key issue in the OLS, and has very important research and application values. In this paper, a novel proposed fabric scheme was discussed to achieve the function of the header reading and rewriting. It can be applied to the high-speed header reading and rewriting to satisfy the requirements of practical applications. The fabric scheme adopts a high-speed tunable laser and wavelength converter to rewrite the header. The high-speed tunable laser is based on Grated Coupler Sampled Reflector (GCSR) structure and the wavelength converter is based on Cross-Phase Modulation (XPM) in a Semiconductor Optical Amplifier (SOA) and a Mach-Zehnder Interferometer (MZI) structure. The synchronization of the packet in the node also be discussed.
This article focuses on the problem of switch control strategy for optical burst switch with optical buffer supporting variable length packets and under asynchronous mode. Two novel control algorithms are proposed, and their performances as well as that of the well-known reserve-switching mode, are evaluated and compared by computer simulations. Issues on the optimal configuration of optical buffers are also discussed. The numerical results show that the time delay resolution of fiber delay line has significant influence on the system performance in all three switching modes.
ATM based passive optical networks can provide broadband services as defined by the international telecommunication union. The medium access control protocol is of great importance to the access scheme as it controls the flow of traffic in the access network. This paper presents a novel MAC protocol with the ability of traffic profile distortions control for APON system at low cost of bandwidth consumption. We evaluate the protocol performance in the term of cell transfer delay and cell delay variation at different traffic load by computer simulations, which approve the validity of the protocol and the bandwidth allocation algorithm.
Coarse wavelength-division multiplexing (CWDM) is an ideal solution to the tradeoff between the cost and the capacity. Compared with DWDM, CWDM system deploys uncooled distributed feedback (DFB) lasers and wideband optical filters. These technologies provide several advantages to CWDM systems such as lower power dissipation, smaller size and less cost. For these merits mentioned above, the CWDM system will be widely used in the metro and access networks in the future. The CWDM system is scalable, but the scalability is limit. So, in some metro networks, it can¡¯t meet the increasing needs of the capacity. To solve this problem, there are a few of solutions proposed now, such as the TDM techniques and the combination with the DWDM that is applied in C band. In this paper, firstly, we will introduce the techniques of the CWDM, and explain the reasons of the less cost, and then the solutions to the scalability are presented in detail. At last we introduce the applications in the metro and access networks at present.
Several tunable optical splitter techniques and some of their applications, including some prospective schemes, are discussed in this paper. It is explained by specific examples that all the variable transmission/reflection film technology, variable fiber couple length technology, acousto-optic/electro-optic deflection technology, and Mach-Zehnder interference technology are the capable technologies to realize tunable optical splitter, and tunable splitter technology to be applied to optical transmission networks, other devices and optical measurements.
Optical label switching is a promising optical packet switching technology to ease the process of getting the route information from the packet label in optical domain. In this paper, a promising kind of multi-wavelength label is adopted and to which a simple label extraction and recognition technology through a array of tunable Fiber Bragg Gratings (FBGs) is presented.
A novel depolarizer composed of two quartz sedges is presented. The depolarization mechanism of this depolarizer lies in the double effects of integration over both frequency and space domain. The conditions of the depolarizer for effect depolarization are concluded: (1) the slope of retardance should be large enough; (2) retardance of the depolarizer should be large enough; (3) the angle between optical axes of two crystals should be 45 degrees. Furthermore, the image characteristics of the depolarizer is analyzed and image tripling is demonstrated. The experiment results show that our theoretical analysis is responsible. This depolarizer can be applied in many fields such as astronomy, remote sensor and spectroscopy.