We propose and demonstrate an electro-optical chaotic communication system with additional chaotic phase-shift based on the mutual coupling structure. Under the condition of complete concealment of time-delayed signatures (TDSs), the key space of the system is greatly enhanced and highly reliable chaotic communication is finally realized. The additional-phase introduced by the new branch is nonlinearly superimposed on the phase generated by the chaotic signal of the original branch, which improves the complexity and aperiodicity of chaos. For security performance, the system only needs a very small feedback gain (i.e., βi = 2.5) to conceal TDSs. Moreover, since the system has only one chaotic signal transmitted in the transmission link, it overcomes the exposure of TDSs caused by the cross-correlation characteristics between different links. At the same time, the system has strong synchronization robustness and can achieve high-quality communication when the parameters are well-matched. To sum up, the proposed system can effectively resist eavesdropping, which provides security for the physical layer of optical networks.
A scheme is proposed to realize the all-optical phase regeneration of four-channel quadrature phase shift keying (QPSK) signal based on phase-sensitive amplification. By utilizing conjugate pump and common pump in a highly nonlinear optical fiber, degenerate four-wave mixing process is observed, and QPSK signals are regenerated. The number of waves is reduced to decrease the cross talk caused by undesired nonlinear interaction during the coherent superposition process. In addition, to avoid the effect of overlapping frequency, frequency spans between pumps and signals are set to be nonintegral multiples. Optical signal-to-noise ratio improvement is validated by bit error rate measurements. Compared with single-channel regeneration, multichannel regeneration brings 0.4-dB OSNR penalty when the value of BER is 10−3, which shows the cross talk in regeneration process is negligible.
A modified Mach–Zehnder interferometric phase sensitive amplifier (MMZI-PSA) configuration is proposed and simulated, which combined the four-wave mixing phase-sensitive amplifier (FWM-PSA) with the fiber interference phase-sensitive amplifier (FI-PSA). This modified scheme for an all-optical communication system can not only eliminate phase noise, but also reduce additional amplitude noise, reducing intrinsic amplitude noise and suppressing phase-to-amplitude noise conversion tremendously. Compared with the traditional FWM-PSA configuration, the proposed configuration can obtain higher gain, as well as reduce bit-error rate (BER) and error vector magnitude (EVM). The simulation results suggest that MMZI-PSA can effectively regenerate QPSK signals and obtain 6.9-dB gain. Furthermore, it can reduce BER to 3.98×10−6 and reduce EVM to 22%, which improves system noise tolerance.
We propose to use a semiconductor optical amplifier as the nonlinear medium to realize data exchange of two differential quadrature phase-shift keying (DQPSK) signals based on the nondegenerate four-wave mixing (FWM) process. This scheme exploits the parametric depletion effect of the FWM process, when proper pump power and wavelength result in almost negligible noise of the original signal for the converted signal after data exchange. Optical data exchange of two DQPSK signals at 10 Gbps is achieved with a power penalty of less than 4 dB at the bit-error rate of 10−9.
Recently, optical burst switching (OBS), which represents a balance between circuit and packet switching, has opened up
some exciting new dimensions in optical networking. Burstification is an important process in OBS networks. Due to the
burstification, there are two opposite effects on TCP throughput in OBS networks: delay penalty and amplification
effects. In this paper these two effects are experimentally investigated simultaneously for the first time based on an OBS
mesh network testbed and some valuable experimental results are achieved. Experimental results show that when BTT is
less than 1.5ms, and BLT is in the BLT window, the positive effect on TCP throughput is dominant. On the other hand,
if BTT is larger than 1.5ms, the BLT window will be closed, thus the delay penalty will become the dominant effect in
the OBS networks.
KEYWORDS: Receivers, Distortion, Transmitters, Dispersion, Modulation, Signal processing, Signal detection, Optical signal processing, Telecommunications, Transmittance
Electronic dispersion compensation (EDC) has recently gained attention as a cost-effective, power-effective solution
used to counteract the distortion occurred in fiber optical communication system Transmitter side EDC (EDC-TX) and
receiver side EDC (EDC-RX) are investigated in optical system for NRZ pulse shape and RZ pulse shape. The results
show that each EDC mechanism has its corresponding preponderant effective range, for every pulse format.
Token scheme is one of methods to overcome burst collision problem in Optical Burst Switch Ring Network with Fixed
Transmitters and Tunable Receivers, but it brings big End-to-End delay and decreases bandwidth utilization. In this
paper a novel token protocol is proposed, which can make better performance on End-to-End delay and bandwidth
utilization.
With the development of diversity requirements, researches on service management based on QoS guaranteed have been
paid more and more attention. On the perspective of service-orientation, this paper presents an integrated suite of
network management system on optical burst switching (OBS) ring network, which combines network services and
management services referencing the traditional models of network management. In the first place, an introduction of
service-oriented management architecture in aspect of conceptions and significances is given, and then extend several
key technologies within the existing service-oriented architecture according to OBS ring's special characteristics. Also
some superiorities and shortages of the implemented system are explained in the end.
Light-trail is a solution to providing high resource utilization and sub-wavelength support [1]. A light-trail is a
multi-point light-path, such that multiple users can take part in communication along the trail, through time
(differentiated) non-overlapping connections. This multi-point flow model leads to a new set of problems in the area of
protecting and restoring light-trail based networks. Conventional link protection which just protects the existed
connection in the light-trail at the time of the failure is not sufficient for light-trails because of the potential of having
multiple possible source-destination pairs in the same trail over time. The fact is demonstrated and explained detailedly
in [4]. In this paper, a novel protection mechanism is proposed for light-trail WDM mesh network, which is Backup
Light-trail Expending scheme. Subsequently the performance of this scheme is evaluated and compared to conventional
Connection Dedicated Protection Scheme. Numerical results obtained by simulation indicate that, Backup Light-trail
Expending Scheme has a faster restoration time and better wavelength utilization.
In this paper, both numerical and simulated modeling techniques were applied to analyze the influence on the
performance of the token-based Optical Burst Transport (OBT) ring networks caused by the parameters, such as the
minimum and maximum burst length, the circumference of the ring, and so on.
We first analyze the issue by numerical analysis in the case that each node has only one token. After that, we confirm the
analytical results and made further researches in the case that each node has multiple tokens by simulated analysis. All
the results show that to design a high-performance token-based OBT ring network, not only the common parameters,
such as the number of nodes and wavelengths, and the circumference of the ring, but also the special parameters, such as
the minimum and maximum burst length, and the offset time should be taken into account.
Furthermore, a testbed of Three-node Token-based OBT ring network Using Fixed Transmitter and Tuneable Receiver
(FTTR) is constructed. With it, the variations of the network performance caused by the maximum burst length are
investigated.1
The path-protection scheme in WDM optical networks is addressed, and also the conception of the SRLG (Shared Risk Link Group) is introduced. A new link protection method is proposed, i.e. unrelated SRLG-based Shared-path protection (uSS). The concept of the
spare-path set and wavelength-levels cited, the complexity of the algorism is analyzed. The simulations results show that the developed iSS performs well in terms of protection efficiency and the viability of the whole networks , while resource utilized ratio is improved enormously by contraries the possibility of invalidation of both the work-path and the protection-path.
Traditional transportation networks adopt the static resource configuration while the backbone of IP data with varieties
of characteristics (such as the burst, randomicity), and here arises the problem of how to allocate proper resources to
them. Because some type of IP data services are very sensitive to packet loss, the quality of service drops dramatically.
So it is critical to change the original static control-based mode to traffic-driven mode so as to achieve bandwidth
allocation according to demand.
A service-driven mechanism in IP over WDM is proposed. It adapt to the burst and randomicity characteristics of IP
services. To meet different requirements, QoS of different levels and working modes is provided for users, with which
network resources can be utilized more sufficiently.
We established a principle experiment to demonstrate this mechanism. Due to the burst and random characteristics of IP
services, the traffic flow over the allocated bandwidth is lost under the static resource configuration while the problem
does not occur under the service-driven mechanism because new light path is applied and acquired to transport the extra
services when the traffic flow exceeds the traffic threshold. We've tested packet loss rate of IP services running under
the static resource configuration mode and the service-driven mode. From the result, we can see that the throughput of
networks can be greatly improved with low packet loss rate by adopting service-driven mechanism.
We demonstrate an optical burst switched network test-bed with three nodes in ring topology. A fixed burst-length
assembly algorithm is adopted in data assembly schedule. Through simulation and experimental analysis, this algorithm
is testified and the optimized assembly burst length is found at 1024 Bytes.
An adaptive double-stage PMD compensator capable of compensating first- and second-order PMD simultaneously is experimentally researched by introducing genetic algorithm for the first time. In order to verify the effect of the double-stage PMD compensator, an experimental optical transmission system at a bit rate of 10 Gbit/s is setup. In experiments, degree of polarization (DOP) of received optical signal is adopted for PMD monitoring. Experimental results show that genetic algorithm is effective and powerful in first- and second-PMD compensation. The DOP of received optical signals after PMD compensation can reach a value larger than 0.97 within 180 milliseconds during which genetic algorithm runs 50 iterations. PMD measurement indicates that the first- and second-order PMD in transmission link can simultaneously reach the minima after PMD compensation at the operation wavelength.
The optimal length of the fixed delay line (FDL) for a one-stage optical polarization mode dispersion (PMD) compensator with two degrees of freedom (DOF) is investigated for a 40 Gbit/s NRZ optical fiber transmission system by implementing genetic algorithm in the logic-control unit. It is found that there exists an optimal length of FDL for such an optical PMD compensator (PMDC), and the optimal length of the FDL is equal to the PMD value of the preceding transmission fiber to be compensated for. Such an optimized one-stage PMDC with a fixed delay line can achieve a close performance to that of a one-stage PMDC with a variable delay line.
The impact of XPM on the 1st-order PMD compensator is numerically simulated for a two-channel WDM system with the bit rate in each channel of 40-Gbit/s. Simulation results show that a 1st-order PMDC does not change the distribution of the remaining EOP in a single channel system; but in a WDM system, the EOP distribution will disperses over the whole EOP range and the occurrence probability of larger EOPs increases heavily due to the XPM effect when a 1st-order PMD compensator is used to compensate for the DGD of the preceding fiber link. Furthermore, in WDM systems, the larger the input average power in the pump channel, the severer the impact of XPM on 1st-order PMD compensation is. When the XPM-inducing input average power reaches 0dBm, the impact of XPM on the 1st-order PMD compensator is visible.
Optical Burst Switching (OBS) provides statistical multiplexing capabilities at the optical layer with relaxed hardware requirements when compared to optical packet switching. Burst blocking probability of OBS networks is a very serious problem without efficient wavelength converter or optical buffer so that OBS is not available in the near future. We proposed a new switching architecture and technical implementation issues. The technical features of the proposed network are use of ring topology, one-way reservation, out-of-band transmission of the burst packet control signal, optical burst transmission unit, loss-free transmission of burst, small delay jitter, and dynamical intelligent wavelength add-drop multiplexer (DI-WADM) module. Our proposed switching architecture and technical implementation issues can make most use of both optic and electric technology and provide a good resolution of optical burst packet contention with our proposed access protocols. The implementation frameworks of the proposed network and node are simple.
By modeling a long optical fiber as 1000 small fiber segments, we simulate the statistical characteristics of PMD up to second order including the DGD, the parallel component of DGD slope, the perpendicular component of depolarization, and second-order PMD (SOPMD) denoted as the sum of the both components for 106 fiber realizations. Through simulations, we found that the higher PMD value, the larger the covered range of the DGD slope, PSP rotation rate, depolarization, and SOPMD is. For certain PMD value, although the maximum (average) PSP rotation rate decreases rapidly with instantaneous DGD value increasing, the maximum depolarization increases with instantaneous DGD before DGD reaches 2 times of PMD value, then begins to decrease. The average depolarization increases almost linearly with instantaneous DGD value. Maximum DGD slope also increases firstly, then decreases with instantaneous DGD, but
average DGD slope almost does not change with DGD value. Also, we found by simulations that depolarization dominates in second-order PMD and DGD slope only has little contribution.
Polarization mode dispersion (PMD) is a serious limiting factor for high bit rate optical communication systems. It is important and necessary for PMD researchers to know the joint statistical characters of the second order PMD (SOPMD) vs. differential group delay (DGD) and how about the penalty contributions of PMD vector’s components. In this letter, we first get the joint statistical distributing range and joint probability distributing density of normalized DGD slope, depolarization, and the SOPMD vs. normalized DGD, and the average values of normalized DGD slope and depolarization vs. normalized DGD. The results are independent with PMD value, and the depolarization is the main contributor for SOPMD value. We secondly analyze the system penalties induced by PMD vector’s components. The DGD is the main contributor for the maximum system penalty. When the sate of input polarization (SOIP) is
principle state of polarization (PSP) input and fixing DGD value, the SOPMD is the main contributor for penalty varieties, the main penalty contributors are DGD and depolarization. Ignoring DGD slope effect, with PSP input and fixing DGD value, the system penalty first keeps constant (near zero dB) and then increases linearly with depolarization value increasing; with PSP input and fixing depolarization value, the system penalty decreases with DGD value
increasing and the curve has slightly fluctuant.
Optical burst switching (OBS) is a promising solution for building terabit optical routers and realizing IP over WDM. In this paper, we describe the basic concept of OBS and present a simulation model. The objective of our simulation is to estimate the throughput and the burst loss probability in such a network of OBS nodes. The traffic characteristics and reservation schemes are essential on burst loss probability. We give some comparison of these schemes by using our simulation model, as we can see, while low self-similarity traffic distribution and JET (just enough time) reservation schemes may have a potential positive effect on the overall blocking probability of the OBS network.
We demonstrate the combined effects of SPM, GVD, and PMD-induced eye-diagram penalties by means of numerical simulations for 40Gbit/s NRZ and RZ modulation formats. Considering all orders of PMD, we choose a fixed state of input polarization (SOIP) and do the simulation 1000 times for each input average power, and then get the Q-penalty of eye-diagram by exponential extrapolation method for cumulative probability 10-5. When input average power is less than 0dBm, SPM effect is very weak and GVD is compensated completely, only PMD takes effect in this power area. The Q-penalties are constants for NRZ and RZ with different PMD values. As input average power increasing, SPM takes effect gradually. First order PMID can suspend the SPM affection, and the higher PMD value, the more postponement is observed. The Q-penalty contributed by higher order PMID has close relation with spectrum width of signal. For NRZ signal with chirp=-0.7, the interactions between SPM and chirp can decrease spectrum width of signal; the Q-penalty contributed by higher order PMD will decrease correspondingly. For RZ with duty 0.3, the changing of the root mean square (RMS) spectrum width induced by the interactions of SPM and chirp is not obviously in this case, the Q-penalties of SPM+GVD+PMD increase consistently. When SPM effect is too strong (For example: for NRZ, average power larger than 10dBm; for RZ with duty 0.3, average power larger than 6dBm.), the interactions of SPM+GVD+PMD will cause the seriously degradation of system performance for any duty cycle and PMID value. Under our simulation conditions, the narrower pulse-width, the less Q-penalty until duty cycle decreases to 0. 1.
As bit-rate in optical fiber communications system increases to 4OGbit/s or beyond in single channel, polarization mode dispersion (PMD), especially higher-order PMD, has become one of major obstacles in high-speed and long-distance transmission systems. Therefore, it is obvious that there are two ways to think of higher-order PMD, one is to investigate that how the higher-orderPMD affect system performance and its critical limitation value; the other is to find effective methods to mitigate or compensate higher-order PMD to improve system performance. Therefore, in this paper, firstly a detailed discussion will focus on the system impairment due to higher-order PMD, secondly, a improved first-order PMD compensation method is proposed to compensate part of higher-order PMD and checked with numerical simulation.
Based on the modeling of considering polarization mode dispersion (PMD) and polarization-dependent loss (PDL) simultaneously, the impact ofPDL on high-speed PMD compensation systems is discussed in this paper. The simulation result shows that for the 4OGbit/s NRZ systems being PMD value 8ps, if the PDL value of single device increases to 0.7dB, the infkience of PDL on the systems performance is obvious. Furthermore, if it reaches to 1.5dB, the outage probability of eye-opening penalty of PMD compensation system will increase from 10-6 (in case no PDL effect) to 10-4.Therefore, it is necessary to considering the impact of PDL on systems performance in the PMD compensation systems design ifthe PDL value ofdevice reaches to 0.7dB or beyond
Based on the segmented bi-refringent fiber model, the penalties due to PMD, GVD and nonlinearity effects in 4x400bit/s WDM systems is calculated by solving the coupled nonlinear Schrodinger equation in bi-refringent fiber with split-step Fourier method for different PMD values in this paper. The simulation results show that in a WDM system the outage probability for one channel is not much larger than that in other channels. For PMD compensation in WDM system it runs a dangerous risk to only compensate the worst channel at a time, and it might be necessary to compensate all channels simultaneously.
An effective way to evaluate the performance of PMD compensation, which uses a proposed polarization-mode dispersion (PMD) emulator, has been studied recently. In this paper, we first present a theoretical analysis on a special model of PMD-emulator (PMDE), then explain the first and second-order PMD effects, which are very useful to value the impact of high-order PMD on pulse. Numerical and experimental results show that PMDE can emulate the statistics property and cover the range of high-order parameter of the real fiber successfully. The impact of second-order PMD on pulse for 40Gbit/s optical fiber communication is also presented as the simulation results.
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