Flexi-grid elastic optical network (EON) provides a promising infrastructure for datacenter (DC) interconnection with its flexible spectrum allocation and high-capacity transmission. Since failures in inter-datacenter elastic optical networks (IDC-EONs) will result in vast amounts of request interruptions and data loss, much recent research has focused on the survivability of IDC-EONs. In this paper, we investigate how to improve network survivability and provide 100% request protection under single-datacenter and single-link failures (single-DLFs) scenario by leveraging multiple DCs that can provide the same services. A shared backup path protection based on minimum spectrum occupancy combination strategy (SBPP-MSOCT) is proposed, which combines the existing spectrum occupancy of the network and select working and protection paths with the least spectrum consumption. Numerical results demonstrate that SBPP-MSOCT can effectively enhance network survivability while reducing spectrum resource consumption and request blocking probability compared to reference algorithms.
In this paper, we propose a two-stage bit mapping based irregular QC-LDPC coded BICM scheme to further improve the BER performance of BICM system. Firstly, with the aid of EXIT chart, the irregular code ensemble with optimal convergence threshold can be found, then PEG algorithm is used to construct the required irregular QC-LDPC code with possibly enlarged girth from the ensemble. Secondly, a two-stage bit mapping design method is introduced to find the optimal bit mapping distribution and the near optimal bit mapping table, which can further improve the convergence threshold of the BICM system. Simulation results show that, when applying the proposed scheme to BTB coherent optical PM-64QAM system, additional 0.13dB net coding gain can be achieved compared with the traditional BICM scheme at the BER of 10-5.
In this paper, we propose a multi-level non-binary quasi-cyclic low density parity check (NB-QC-LDPC) coded modulation (CM) scheme to reduce the decoding complexity while maintaining and/or exceeding the super BER performance of the traditional NB-QC-LDPC CM scheme. Firstly, local optimal searching combined with the classical superposition construction is proposed to construct the required NB-QC-LDPC codes with possibly enlarged girth and less number of the shortest cycles. Secondly, by analyzing the changing trend of the BER performance and decoding complexity of the NB-QC-LDPC code defined over ๐บ๐น(๐) incident to ๐. We find that the decoding complexity increases proportionally with the increase of ๐, but the best BER performance usually corresponds to a smaller ๐. Finally, by replacing the high-order NB-QC-LDPC code based CM scheme to the multi-level low-order NB-QC-LDPC code based CM scheme, the decoding complexity can be effectively reduced. Simulation results show that the designed two-level ๐บ๐น(4)/๐บ๐น(8) QC-LDPC code based 16QAM/64QAM CM system can perform almost the same or even better BER performance with/than the corresponding traditional ๐บ๐น(16) / ๐บ๐น(64) QC-LDPC code based 16QAM/64QAM CM system.
Receiver in-phase/quadrature (Iโโ/โโQ) imbalance caused by imperfect analog receiver front end can rapidly degrade system performance in a coherent optical transmission system. These imbalances, including Iโโ/โโQ gain and phase imbalance, become increasingly important when higher symbol rate, higher modulation order, and low roll-off pulse shape are used. Here, a low-complexity blind equalization algorithm, cascaded phase, and gain imbalance equalizers, is designed to mitigate these interferences. Furthermore, a field-programmable gate array hardware realization with 128-parallel processing units is performed to demonstrate the proposed algorithm in a 32-GBaud 16-quadrature amplitude modulation off-line transmission experiment. Based on the obtained results, the proposed blind Iโโ/โโQ imbalance compensation algorithm can provide very good compensation performance with low logic element consumption, which is more suitable for high order and high baud rate transmission system.
In recent years, the integrated space-ground network communication system plays an increasingly important role in earth observation and space information confrontation for the civilian and military service. Their characteristic on wide coverage, which may be the only way to provide Internet access and communication services in many areas, has extensively promoted its significance. This paper discusses the architecture of integrated space-ground communication networks, and introduces a novel routing algorithm named Improved Store-and-forward Routing Mechanism (ISRM) to shorten the transmission delay in such a network. The proposed ISRM algorithm is based on store and forward mechanism, while it trying to find several alternative delay-constraint paths by building the route-related nodes encounter-probability information table and communication timing diagram. Simulation is conducted at the end, and comparisons between ISRM and baseline algorithm are given. The results show that ISRM can achieve relatively good performance in terms of transmission latency in integrated space-ground networks.
Variable-rate intensity modulation and direct detection-based optical transceivers with software-controllable reconfigurability and transmission performance adaptability are experimentally demonstrated, utilizing M-QAM symbol mapping implemented in MATLABยฎ programs. A frequency division multiplexing-based symbol demapping and wavelength management method is proposed for the symbol demapper and tunable laser management used in colorless optical network unit.
KEYWORDS: Digital signal processing, Signal processing, Process control, Polarization, Receivers, Optical signal processing, Finite impulse response filters, Optical engineering, Networks, Computer simulations
We propose a method of digital signal processing for a burst-mode coherent receiver, which can recover the burst data rapidly aided by a control signal. The feasibility and effectiveness of our proposed method are demonstrated in a 128ย Gbps polarization division multiplexed quadrature phase shift keying modulation experiment, and the results show that the proposed method can reduce the 70% convergence time on average compared with the traditional digital signal processing without any training overhead or additional computing complexity.
KEYWORDS: Orthogonal frequency division multiplexing, Receivers, Signal to noise ratio, Detection and tracking algorithms, Passive optical networks, Numerical simulations, Signal processing, Analog electronics, Computing systems, Transmitters
An extensive comparison between iteration interference cancellation and symbol predistortion in an analog domain generated ratio frequency tone based virtual single sideband direct detection orthogonal frequency division multiplexing system is presented on the basis of equalization principles, computational complexity, algorithm performance, and robustness. The analysis results show that the two algorithms have the same computational complexity. Symbol predistortion is more suitable for the downstream scheme in the passive optical network, while iteration interference cancellation is suitable for the upstream scheme since, for these two scenarios, the computational complexities are both located at the optical line terminal. The numerical simulation and 40 Gbps experimental results both indicate that the iteration interference cancellation algorithm exhibits a better performance and is more robust.
Intensity modulation and direct detection signal are sensitive to power fading and nonlinear intersymbol interference (ISI) induced by modulator chirp, fiber dispersion, and square-law photo-detection. We propose and experimentally demonstrate a Nyquist 4-ary pulse amplitude modulation and direct detection scheme relying on pulse-shaping with an electrical filter and optical equalization with a vestigial-sideband (VSB) filter in the transmitter. The power fading could be eliminated by using the VSB filter. Compared with conventional 4-ary pulse amplitude modulation, the Nyquist signal has a stronger resistance to nonlinear ISI.
We demonstrate a channel-reuse bidirectional 10-Gb/s/ฮป long-reach DWDM-PON and an optical beat noise-based automatic wavelength control method for a tunable laser used in a colorless optical network unit. 100-GHz channel spacing 55- and 100-km full-duplex bidirectional 320โโGb/s (32ร10โโGb/s) capacity transmissions are achieved without and with optical amplification. Transmission performance is also measured with different optical signal to Rayleigh backscattering noise ratios and different central wavelength shifts between upstream and downstream in the channel-reuse system.
The intersymbol interference caused by dispersion, chirp, and a vestigial sideband filter in intensity modulation and a direct detection single carrier system is analyzed theoretically and numerically. An iterative nonlinear intersymbol interference cancellation technique is proposed and experimentally demonstrated in a 40-Gbps 16-QAM Mach-Zehnder modulator-based vestigial sideband intensity modulation and direct detection half-cycle Nyquistโsubcarrier modulation system over a 100-km uncompensated standard single-mode fiber transmission for the first time. The experimental results show that 2.2-dB receiver sensitivity improvement is obtained at the forward error correction limit by using the iterative technique.
We experimentally demonstrate the superior performance of a 40-Gbps 16-QAM half-cycle Nyquist subcarrier modulation (SCM) transmission over a 100-km uncompensated standard single-mode fiber using dual-drive Mach-Zehnder modulator-based vestigial sideband intensity modulation and direct detection. The impact of modulator chirp on the system performance is experimentally evaluated. This Nyquist-SCM technique is compared with optical orthogonal frequency division multiplexing in both back-to-back and 100-km transmission experiments, and the results show that the Nyquist system has a better performance.
KEYWORDS: Signal to noise ratio, Orthogonal frequency division multiplexing, Singular optics, Frequency division multiplexing, Modulators, Receivers, Telecommunications, Signal generators, Transmitters, Amplitude modulation
We propose and experimentally demonstrate the superior performance of a 40-Gbps 16-quadrature amplitude modulation virtual single sideband (VSSB) direct detection optical frequency division multiplexing system with symbol predistortion to mitigate subcarriers-to-subcarriers beating interference. The VSSB signal is generated in the electronic domain by combining the baseband orthogonal frequency division multiplexing signals and sinusoidal waves without a frequency gap to maximize the electrical and optical spectral efficiencies. The results show that 5-dB optical signal to noise ratio sensitivity improvement is obtained by using symbol predistortion.
The presence of vestigial-sideband optical filter, dispersion and chirp of modulator increases subcarrier to subcarrier intermixing interference (SSII), which significantly restricts transmission performance. For the first time, the iterative interference cancellation method is introduced to calculate and eliminate SSII. Furthermore, we successfully demonstrate a 40-Gbps, 16-QAM, dual drive Mach-Zehnder modulator (MZM)-based system transmission through 100-km uncompensated standard single-mode fiber. The impact of chirp on iterative algorithm is also experimentally evaluated by setting different optical phase modulation amplitudes on the two arms of the dual drive MZM.
Hybrid WDM/TDM-PON as a key solution is a smooth evolution of the passive optical network to Next-Generation Passive Optical Networks (NG-PON). In order to combine the capacity of metro and access networks, it is desirable to propose the Long-Reach (LR) PON, and the propagation delay is proved to be the obstacle during the upstream resource allocation, so we propose an efficient DWPBA for the Long-Reach hybrid WDM/TDM-PON by separating the data messages and REPORT messages under multi-thread scheduling, which achieve high channel utilization and low packet delay when fiber length increased to 100 km.
A scheme of format conversion between OOK signal and optical quadrature phase shift keying (QPSK)/16-ary quadrature amplitude modulation (16QAM) signal based on cross phase modulation (XPM) effect in semiconductor optical amplifiers (SOA) is proposed. Theoretical analysis and simulations of the format conversion scheme are conducted to validate the feasibility of the proposal. In this proposal, the QPSK signal is generated after passed an SOA, and then the 16QAM signal is generated based on XPM in a single SOA-MZI after two QPSK signal coupled. The performance and the optimal design of the 10Gbit/s format conversion system under various key parameters of SOAs are evaluated and discussed. The receiver sensitivity of the converted QPSK signal and 16QAM signal after detection is -32dBm and -28.5dBm with BtB at BER of 10-9, respectively. Simulation results present useful to enable interconnection between backbone network and access network.
A scheme of all-optical QPSK signal regeneration is proposed which based on cross phase modulation (XPM) in semiconductor optical amplifier (SOA) with subsequent an optical filter. Simulations and theoretical analysis are conducted to validate the feasibility of the proposal. The QPSK signal is distorted by the negative chirp after fiber transmission, and then the distorted QPSK will be regenerated due to the positive chirp which is induced by XPM in the SOA. A power penalty 2.3dB is improved after QPSK regeneration with the receiver sensitivity of -30.7dBm.
The authors propose a novel architecture of passive optical network (PON), which consists of time division multiplexing (TDM) based downstream (10โโGbit/s) and quasi-synchronization (Q-S) electrical code division multiplexing access (ECDMA) based upstream (2.5โโGchip/s), and realize the prototype of this TDM-ECDMA PON. The high speed (2.5โโGchip/s) all digital en/decoding of upstream have been achieved by field-programmable gate array in this prototype. The frames error rate (FER) free transmission of Q-S ECDMA based upstream is demonstrated after 20 km fiber link. Then receiver sensitivity of optical line terminal in upstream transmission can be improved โผ 6โโdB by coding gain compared with traditional 2.5โโGbit/s TDM PON.
An 112โโGbit/s real-time coherent passive optical network downlink transmission experiment over 100 km standard single mode fiber with 1โถ128 splitting ratio is demonstrated. Adaptive dispersion compensation digital signal processing in the real-time receiver has compensated 100 km dispersion and 50 km dispersion difference with almost no power penalty and 43.5 dB power budget has been achieved.
We proposed a dynamic routing and frequency slots allocation scheme which adopted the adaptive modulation for a novel
Spectrum-sLICed Elastic optical path network (SLICE). In our dynamic routing scheme, both spectrum resource
availability (SRA) and distance (hop number) are considered at the modulation format selection phase for adaptive
modulation. We then conducted numerical simulation to compare our Spectrum Resource Adaptive and Distance
Adaptive (SRA-DA) mechanism with previous DA in both small network topology and 7ร7 mesh topology. Results
shown that SRA-DA mechanism achieved lower blocking rate and higher slots utilization compared to DA in bigger
networks.
A scheme of optical 16-QAM signal generation based on XPM in nest semiconductor optical amplifier based
Mach-Zehnder interferometer (SOA-MZI) is proposed. In this proposal, 10Gbit/s QPSK and 16-QAM signal can be
generated. Simulations and theoretical analysis have been conducted to validate the feasibility of the proposal by
VPItransmissionMaker 8.5. A power penalty below 1.75dB is obtained after the transmission over 160km along single
mode fiber with a receiver sensitivity of -28.5dBm.
A novel monitoring scheme based on the fiber Bragg grating sensor to achieve real-time, long-distance, and passive-support monitoring of the power transmission line galloping is proposed and experimentally demonstrated. Based on the relationship between galloping amplitude and horizontal tension of a transmission line, numerical simulation and experiments are carried out. In the experiment the galloping amplitude monitored by this novel scheme is 0.3418 m, while the actual galloping amplitude is 0.35 m, which shows that the galloping amplitude can be obtained accurately by using this monitoring scheme.
Photonic millimeter wave (mm-wave) signal generation employing a differential Mach-Zehnder modulator (DMZM) and a semiconductor optical amplifier (SOA) is proposed and evaluated by theoretical analysis and simulation. This paper presents the theoretical study of the generation of a co-polarized and phase-locked dual-pump for four-wave mixing and optical mm-wave signal, the propagation of the optical mm-wave signal in single mode fiber, and the coherent demodulation of the electrical mm-wave signal at the base station. Performance analysis and optimization design of the proposed scheme are conducted via simulations. The generation of mm-wave signals at 30, 40, and 60 GHz is simulated and analyzed. The influence of SOA and the input optical signal on the mm-wave generation and transmission is investigated. Simulation results present useful insight for the practicality of photonic mm-wave signal generation and distribution in the next-generation access network.
There has been growing interest in transmitting synchronization information over Optical Transport Network (OTN). A
novel scheme is proposed in the paper for this purpose. In order to support precise time synchronization information
transfer over OTN, the proposed scheme designs the new overhead, equipment function architectures and interworking
mechanism of synchronization message for OTN.
In order to resolve the P2P topology mismatch problem, a novel P2P service redirection scheme has been proposed by us
and the scheme is fully described in reference. Furthermore, we have successfully implemented this mechanism in
EPON system. Experimental results show that our scheme can effectively reduce core network traffic, and evidently
improve clients' downloading rate.
Optical receiver sensitivity for electronic code division multiple access over a passive optical network (ECDMA-PON) is
analyzed theoretically. Compared with TDM system, ECDMA-PON offers better receiver sensitivity due to coding gain.
Fundamental simulation results are provided to show its validity.
The convergence of EPON and WiMAX is one promising solution for Fiber Wireless access network, QoS is an important technical issue in this hybrid access network. We propose a novel QoS scheme of EPON and WiMAX integrated network based on unified QoS management which has been implemented and proved its effectiveness.
In the traditional EPON network, optical signal from one ONU can not reach other ONUs. So ONUs can not directly
transmit packets to other ONUs .The packets must be transferred by the OLT and it consumes both upstream bandwidth
and downstream bandwidth. The bandwidth utilization is low and becomes lower when there are more packets among
ONUs. When the EPON network carries P2P (Peer-to-Peer) applications and VPN applications, there would be a great
lot of packets among ONUs and the traditional EPON network meets the problem of low bandwidth utilization. In the
worst situation the bandwidth utilization of traditional EPON only is 50 percent. This paper proposed a novel EPON
architecture and a novel medium access control protocol to realize direct packets transmission between ONUs. In the
proposed EPON we adopt a novel circled architecture in the splitter. Due to the circled-splitter, optical signals from an
ONU can reach the other ONUs and packets could be directly transmitted between two ONUs. The traffic between two
ONUs only consumes upstream bandwidth and the bandwidth cost is reduced by 50 percent. Moreover, this kind of
directly transmission reduces the packet's latency.
Based on Simplified Finite State Machine (SFSM) as an improved model, an approach for passive testing consistency is
proposed. The improved model is introduced and the algorithm complexity is analysed. Also, this approach is
implemented with the EPON Tester, and proved to be feasible to analyze Multi-Point Control Protocol (MPCP)
consistency.
DWDM networks have been evolving to higher spectral efficiency. To make optical duobinary format,
which is considered as a suitable modulation format in MAN DWDM networks, can work in 50GHz
channel spacing 43Gb/s DWDM networks is very significant. In this paper, it is pointed out that the
delay time in delay-and-add optical duobinary system is one of key factors which affect system
performance. The suitable delay time for 43Gb/s systems compatible 50GHz with 100GHz channel
spacing is obtained by system simulation. The simulation results show that 0.8 bit delay time is more
suitable for 43Gb/s ODB DWDM system at compatible 50 with 100GHz channel spacing than 1 bit delay
time because of its higher Q value and bigger dispersion and nonlinearity tolerance.
An all-optical tunable wavelength converter using a combination of self-phase modulation (SPM) effects in highly nonlinear microstructure fibers and narrowband spectral filtering is investigated, which is reported for the first time to our knowledge. Wavelength conversion over aยฑ4nm bandwidth of a 10Gb/s date rate is obtained with good efficiency. A 25-m-long microstructure fiber with zero-dispersion wavelength at 800nm is used as the nonlinear medium. The core diameter of microstructure fiber is 2.4μm and the outer diameter is 125μm. The nonlinearity is γ=36km-1W-1, which is 20 times higher that that of a conversional dispersion-shifted fiber. The dispersion at the wavelength of 1550nm is ~+150ps/nm-km and the loss is 40dB/km.
With the increasing demands of new broad-band services, the construction of optical acess networks becomes one of key issues. Passive optical network (PON) technologies realize effective and economical optical access networks for these purposes. A novel protection switching scheme for PONs with ring plus tree topology is presented in this paper, which matches the fiber construction layout of access network and ensures high network surviability at low cost. The operating principles as well as protection swicthing methods that under certain circumstances are discussed in details. Reliable and
economical optical access networks, PONs, can be applied for broad-band applications with this protection switching scheme.
A novel technique is proposed for pulse compression by utilizing the nonlinear interaction between two neighboring pulses in optical fiber. By using the method of split-step Fourier (SSF), we numerically investigate the propagation of the pulse pair in optical fiber. Usually, two pulses attract each other and collide into one compression pulse periodically along the fiber. So with an appropriate choice of the fiber length-the collision length, such a fiber can act as compressor, so-called nonlinear action compressor. And then, the effects of parameters on the compression pulse have
also been investigated numerically with SSF and we find the quality factor Qc>1.
In future high bit-rate DWDM systems, the channel separations will be narrower and the bit-rate of single channel will be higher. The dispersion in transmission of fiber Bragg grating is a factor that cannot be neglected. We emphasize the effects of the 3rd order dispersion because the 3rd order dispersion is more detrimental for short pulses than the 2" order dispersion. Furthermore, the 3rd order dispersion is always positive whether the wavelength of the adjacent channel is longer than Bragg wavelength or not. So the accumulated effects are more notable than the 2nd order dispersion, which can be positive or negative. We calculated the effects of the dispersion of FBG on pulses with ips, 2ps and 5ps pulse widths under channel separations of 5O GHz and 100 GHz. It is shown the 3rd order dispersion will be more detrimental in high bit-rate DWDM systems. This paper will give some guide to FBG design for ADM application. The method we use is split-step Fourier method.
A new scheme is put forward for generation of the compressed pulse pair using fiber grating. This new compressor bases on the soliton-effect and makes use of high-order soliton supported by the fiber grating. In the anomalous GVD regime outside the photonic band gap ( ? < ? B), the third-order soliton may be formed when pulse pass through the fiber grating. As we know, the third-order soliton will split into two distinct pulses at z0/2(zois the soliton period), but the two pulses recover the original shape at the end of the soliton period. If we break the balance between the GVD and the nonlinearity at z0/2, the split two pulses will be self-existent permanently but not recover. We present the basic idea and introduce this new kind of compressor in this paper. Finally, we have proved this method by numerical simulation with SSF (Slip-Step Fourier) method.
ATM Passive optical network (ATM-PON) is a kind of low-cost access network for resident and small-business users while Usage Parameter Control (UPC) is an important traffic control function in such networks. The basic traffic control function in an ATM network is the combination of UPC, network parameter control (NPC) and connection access control (CAC). As the entrance of an ATM network, an ATM- PON must have the function of UPC to check it the cell streams entering the network comply with the traffic contract negotiated between the user and the network during the connection setup. In this paper the UPC parameters negotiation methods in ATM-PONs are introduced, and the control algorithms and their realization are also discussed with the necessary simulation results.
Burst mode transmission and receiving is one of key techniques in an ATM-PON system and a well-performed optical transceiver is very important in OLT. In this paper some problems in burst mode receiving, such as timing recovery and noise suppressing are discussed first. Then the low cost and low crosstalk design methods of the transceiver are studied. Such a low cost transceiver can satisfy both the class B/C specifications in ITU-T G.983.1.
A new passive component, plastic fiber Bragg grating (PFBG), is proposed based on our researches on fiber grating tunability and plastic fibers. We analyzed its characteristics. It shows that this kind of component can be tuned hundreds of nanometers. It can be used to demultiplex any channel in all-wave fiber WDM in the future. We also discussed the problems in application of the plastic fiber gratings.
The principle of dispersion compensation in transmission using uniform fiber Bragg gratings is described. Its compensation efficiency is analyzed numerically and the experimental results are reported. We broadened the pulse-width of the initial signals from 114.5 ps to 191.2 ps and 257.8 ps after 11.1 km and 22.2 km fiber transmission, respectively and then re-compressed them to 125.8 ps and 147.2 ps, respectively using one unchirped fiber grating with some tuning techniques.
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