Investigation of wavelength division multiplexing ring network topology to enhance the system capacity

In this paper, we have investigated the wavelength division multiplexed (WDM) system using ring network topology. This network is used to increase the capacity with eight optical add/drop multiplexers (OADMs) by using dispersion compensating fiber and semiconductor optical amplifier (SOA) to achieve a distance up to 1600 km. It is observed that network shows the acceptable results at 15 Gbps data rate with 100 GHz channel spacing. The OADM nodes are also varied to investigate the network performance in the term of BER and Q-factor.     

Add/drop applications in fiber ring networks based on a reconfigurable optical add/drop multiplexer in a re-circulating loop

A periodic add/drop system in a fiber ring network was investigated using a reconfigurable optical add/drop multiplexer (ROADM) in a re-circulating fiber loop. After seven cascaded add/drop nodes at every 150 km along the transmission, at bit error ratio (BER) equals to 10⁻⁹ and data rate of 10 Gbps, we observed a 2.5 dB power penalty for the passing through channels with 1050 km transmission distance, and 0.3 dB sensitivity penalty variation for the periodic add/drop channels at every 150 km, respectively.     

Investigation on interchannel crosstalk at ADM for an optical ring network

In this paper, we investigated the effect of interchannel crosstalk at ADM of a ring network at sweeping bandwidth of filters. Analysis has been done in a ring network [G.P. Agrawal, Fiber Optic Communication System, Wiley-interscience, New York, 1997; Tim Gyselings et al., Crosstalk analyses of multi-wavelength optical cross connects, J. Lightwave Technol. 17 (1999) 1273; R. Ramaswami, K.N. Sivarajan, Optical Networks: A Practical Perspective, Morgan Kaufmann, Los Altos, CA, 1998] that contains four nodes communication signal over two channels at 1552.2 nm. At the bit rate of 10 Gbps, ADMs at each node is modeled by using WDM add and WDM drop components. The distance between nodes is taken 12.5 and 25 km and an ideal amplifier is inserted just before one of the node to compensate for the total fiber loss in the ring. Dispersion and nonlinear effects of fibers are disabled to observe the crosstalk effect of ADM at sweeping bandwidth from 10 to 40 GHz of fourth-order Bessel filters.     

Investigation of wavelength division multiplexed hybrid ring-tree-star network topology to enhance the system capacity

In this paper, we have investigated wavelength division multiplexed (WDM) hybrid (ring-tree-star) topology. Eight optical add/drop multiplexers (OADMs) are used to make ring structure. The single mode fiber and dispersion compensating fiber and semiconductor optical amplifier (SOA) are employed between each OADM to achieve a maximum. To increase the number of users each OADM node of ring network is connected to star and tree network topology which can accommodate more than 2048 users. Various system parameters (for different channel spacing, different input power signal, different data rates and the fiber length) are varied to investigate the system performance in the term of BER and Q factor.     

Performance investigation of ring network topology in the presence of semiconductor optical amplifiers

The performance of 60 user ring network topology is investigated in the presence of semiconductor optical amplifiers. This ring network topology is evaluated by considering the signal quality factor, eye closure and received power for different signal input power. Further, this ring network topology is investigated with multiple numbers of spans. It is reported that, the maximum number of nodes supported by this ring network is >300 with acceptable quality and received power.     

Hybrid multiplexed OFDM-DWDM-EPON access network

For bottleneck problem of the broadband access networks, Ethernet-PON comes out as a striking and promising solution. Even though, EPON nodes necessitate a cost-effective up-gradation, WDM based topology proves to be a vigilant up-grading approach that deals with the deployment of multiple wavelengths in the upstream/downstream directions. Furthermore, only EPON nodes with privileged traffic can be WDM-upgraded. Accordingly, we propose and demonstrate a hybrid multiplexed OFDM/DWDM-EPON access network employing OSSB modulation scheme. Case A demonstrates a single channel OFDM-OSSB-EPON system and achieves a fiber link of 27 km with split ratio of 16. Afterwards, a contrast between OFDM-EPON and conventional EPON (C-EPON) after a fiber link of 20 km with split ratio of 16 is carried out. Case B targets the transmission of two channels with channel spacing of 0.1 nm to realize OFDM-DWDM-OSSB-EPON system and achieves a fiber link of 20 km with split ratio of 32.     

Simulation of DWDM signals using optimum span scheme with cascaded optimized semiconductor optical amplifiers

We numerically simulated the ten channels at 10 Gb/s dense wavelength division multiplexing (DWDM) transmission faithfully over 17,227 km using 70 km span of single mode fiber (SMF) and dispersion compensating fiber (DCF) using optimum span scheme at channel spacing 20 GHz. For this purpose, inline optimized semiconductor optical amplifiers (SOAs) and DPSK format are used. We optimized the SOA parameters for inline amplifier with minimum crosstalk and amplified spontaneous emission noise with sufficient gain at bias current 400 mA. For this bias current, constant gain 36.5 dB is obtained up to saturation power 21.35 mW. We have also optimized the optical phase modulator bandwidth for 400 mA current which is around 5.5 GHz with crosstalk −14.2 dB between two channels at spacing 20 GHz.We show the 10×10 Gb/s transmission over 70 km distance with inline amplifier has good signal power received as compared to without amplifier, even at equal quality factor. We further investigated the optimum span scheme for 5670 km transmission distance for 10×10 Gb/s with channel spacing 20 at 5.5 GHz optical phase modulator bandwidth. As we increase the transmission distance up to 17,227 km, there is increase in power penalty with reasonable quality.The impact of optical power received and Q factor at 5670 and 17,227 km transmission distance for different span schemes for all channels has been illustrated. For launched optical power less than saturation, all channels are obtained at bit error rate floor of 10⁻¹⁰.     

Single-wavelength-pump bi-directional hybrid fiber amplifier for bi-directional local area network application

This paper proposes a novel bi-directional hybrid fiber amplifier using a single-wavelength pump laser diode (LD) at 1495 nm. The hybrid amplifier is theoretically applied in a 50 km bi-directional local area network (LAN) with 26 ch × 10 Gb/s for bi-directional transmission. Thirteen C-band channels serve as downlink signals while the other 13 L-band channels are employed as uplink signals. Without loss of generality, four channels (two from each band) are experimentally analyzed. Erbium doped fiber (EDF) provides amplification for the C-band channels and Raman amplification amplifies the L-band channels. The pump efficiency is improved by employing a double-pass scheme for both the Erbium doped fiber amplifier (EDFA) and Raman fiber amplifier (RFA). The chromatic dispersion incurred by all the channels is precisely compensated for by inserting a fiber Bragg grating (FBG) array in appropriate locations along the dispersion compensating fiber (DCF) segments. Moreover, gain equalization of all the channels is achieved by adjusting the FBG reflectivity. Both the simulation results and experimental measurements confirm the proposed device feasibility and potential application in a bi-directional LAN.     

Theoretical analysis of the all-fiberized, dispersion-managed regenerator for simultaneous processing of WDM channels

The concept of the all-fiberized multi-wavelength regenerator is analyzed, and the design methodology for operation at 40 Gb/s is presented. The specific methodology has been applied in the past for the experimental proof-of-principle of the technique, but it has never been reported in detail. The regenerator is based on a strong dispersion map that is implemented using alternating dispersion compensating fibers (DCF) and single-mode fibers (SMF), and minimizes the nonlinear interaction between the wavelength-division multiplexing (WDM) channels. The optimized regenerator design with + 0.86 ps/nm/km average dispersion of the nonlinear fiber section is further investigated. The specific design is capable of simultaneously processing five WDM channels with 800 GHz channel spacing and providing Q-factor improvement higher than 1 dB for each channel. The cascadeability of the regenerator is also indicated using a 6-node metropolitan network simulation model.     

Proposal of an OADM configuration with ultra-large FSR combining ring resonators and photonic bandgap structures

Optical Add-Drop Multiplexers (OADMs) allow extracting and inserting data channels in WDM, user access and interconnection applications. A great interest is focused on building small footprint integrated OADMs, which can be achieved using compact ring resonators (RR). Free spectral range (FSR) values up to some tens of nanometers can be obtained by using RR with small radius or multi-stage configurations, but structural parameters are pushed to the limit in these configurations leading to very tight fabrication requirements. We propose and numerically study a novel configuration of RR-based OADM where the FSR is hugely increased to values higher than 140 nm by combining RRs with photonic bandgap structures, which remove the non-desired resonances inside the RR. Moreover, this structure can be hitless reconfigured, what is difficult to achieve in actual configurations.     

一种新型光分插复用器及其在WDM自愈环网中的应用

提出了一种新型的基于FBG和光环形器的双向光分插/复用器结构.它的结构简单,网络配置灵活,而且可实现单纤双向环网中功率放大.结合该OADM,首次给出了在单纤双向DNI环网实现保护的策略,指出此结构在各种WDM网络中实现单纤环网保护的可行性.     

Investigation of four wave mixing effect with different number of input channels at various channel spacing

In this paper the design, implementation and performance analysis of four wave mixing (FWM) in optical communication system for different number of input channels is presented using various values of channel spacing. Here, all the input channels have been spaced evenly at various values like 6.25 GHz, 12.5 GHz, 25 GHz, 40 GHz, 50 GHz with the different number of channels at the input i.e. with 2, 4, 6, 8, 12 input channels. The simulation results reveal that the four wave mixing is minimum when the channel spacing is maximum i.e. 50 GHz with minimum number of channels i.e. 2 input channels. It is observed that on increasing the channel spacing, the interference between the input frequencies decreases and hence the four wave mixing also decreases. Also, on increasing the number of input channels/users, the interference between the input frequencies increases and thus, the four wave mixing also increases.     

Optimal design of 32 channels spectrum slicing WDM for optical fiber access network system

In this article, the spectrum sliced dense wavelength division multiplexed passive optical network (SS-DWDM–PON) has been investigated as a power efficient and cost effective solution for optical access networks. In this work an AWG demultiplexer is used to operate as slicing system. The high speed SS-DWDM system has been realized and investigated for 32 channels with data rate up to 3 Gb/s using broadband ASE source (LED). The 3 Gb/s signals both non-return-to-zero (NRZ) and return-to-zero (RZ) were demonstrated in 40 km optical fiber link with BER < 10⁻¹². The results obtained here demonstrate that SS-DWDM is well suited for Fiber-to-the-Home (FTTH) network.     

Capacity enhancement in packet switched slotted ring wavelength division multiplexed transport networks

In this paper, all-optical WDM networks based on a slotted multichannel ring topology have been investigated. The nodes are equipped with one fixed-wavelength receiver, wavelength-tunable transmitter and provide packet-mode transport in WDM network. The topology provides one logical channel to be associated with each destination node. Each channel is shared in statistical time division by all nodes transmitting to a given destination. The capacity enhancement has been demonstrated by comparing all optical WDM network by increasing the number of nodes. It is concluded that by increasing the number of nodes in the topology, the token queue length capacity, the token arrival rate are increased and the token arrival period is decreased which results in overall increase in the performance and capacity of the logical WDM network.     

Transmission performance of 20 × 10 Gb/s WDM signals using cascaded optimized SOAs with OOK and DPSK modulation formats

We investigated 20 channels at 10 Gb/s wavelength division multiplexing (WDM) transmission over 1190 km single mode fiber and dispersion compensating fiber using cascaded inline semiconductor optical amplifier at a span of 70 km for RZ-DPSK (return zero differential phase-shift keying) modulation format by using same channel spacing, i.e. 100 GHz. We show for RZ-OOK (return zero on-off keying) format a transmission distance of up to 1050 km with Q factor more than 15 dB, without any power drops. We developed the SOA model for inline amplifier having minimum cross-talks and ASE (amplified spontaneous emission) noise power with sufficient gain. At optimal bias current of 400 mA, a high constant gain of 36.5 dB is obtained up to a saturation power of 21.36 mW. So reduction of cross-talk and distortion is possible by decreasing the bias current at appropriate amplification factor.The DPSK modulation format has less cross-talk as compared to OOK format for nonlinearities and saturation case. The impact of optical power received and Q factor at different distance for both RZ-OOK and RZ-DPSK modulation format has been illustrated. We have shown the optical spectrum and clear Eye diagram at the transmission distance of 1190 km in RZ-DPSK system and 1050 km in RZ-OOK systems.The bit error rate (BER) for all channels observed is less than 10⁻¹⁰ up to gain saturation for both DPSK and OOK systems. Finally, we investigated that the transmission distance decreases with a decrease in channel spacing of up to 20 GHz.     

Comparison of optical network topologies for wavelength division multiplexed transport networks

In this paper, the various network topologies comprising of various nodes have been investigated and compared. The signal is analyzed as it passes through each node in each of the network topology. For the ring topology, it is shown that there is no appreciable signal degradation in the ring network. It is seen that there is increase in Quality factor i.e. signal keeps on improving as it passes through the successive nodes. For the bus topology, the quality of signal goes on decreasing with increase in the number of nodes and the power penalty goes on increasing. For the star topology, it is observed that received power values of each node at a same distance from the hub are same and the performance is same. For the tree topology, it is observed that the performance of the optical tree is almost identical to the performance of ring topology, as signal quality is improved as it passes through the successive nodes of the hierarchy but the overall length of each segment is limited by the type of cabling used and if the backbone line breaks, the entire segment goes down.     

波分复用全光通信网中的放大自发辐射噪声积累效应研究

给出了一种全光通信网波长域计算机模拟方法，模拟了波分复用信号经过３个光分插复用节点后的信号及放大自发辐射积累的光谱图，并与实验结果进行了对比。计算了波分复用信号经过５０个光分插复用节点极限情况下的信噪比，结果表明放大自发辐射噪声积累造成的信噪比下降仍然可以保证接收机在１０Ｇｂ／ｓ时的误码率小于１０＾－９。这些结果可以被应用到未来国家或地区级全光通信网中。     

Optimum performance and analysis of RingO networks

In this paper, the RingO (ring optical network) comprising of various nodes has been demonstrated, and the signal is analyzed as it passes through each node in the network. It has been shown that there is no appreciable signal degradation in the ring network. It is seen that the signal keeps on improving as it passes through the successive nodes. Also when the whole ring structure is iterated with the help of spans, then improvement in the signal is observed. It is also observed that there is no appreciable signal degradation till the length of the fiber is increased up to 250 km. The effect of increasing the input power is also studied further, and it is seen that it can support more number of users by increasing the signal input power. The optical spectrum of the signal is seen at every node, to have the assessment of the add and the drop frequencies in the ring.     

OADM环网的实验研究

研究了光分插复用器(OADM)的关键技术,重点分析了相关的实现技术,完成了利用OADM构建全光环网的实验研究,给出了重要的实验数据,包括眼图、光谱图、光信噪比、保护与恢复等,并对这些实验数据进行了分析,为光传送网的设计与构建提供了重要的参考依据.     

Performance analysis of metro WDM network based on an optical cross connects and arrayed waveguide grating demultiplexer

In this paper, we have demonstrated the quality-of-service offered by the metropolitan area network which is based on optical cross connect (OXC) and arrayed waveguide grating (AWG) demultiplexer operating at 10 Gb/s with 0.1 nm channel spacing for NRZ signal transmission. The data is successfully transmitted to a distance of 40 km with a reasonably good BER of 2.388 × 10⁻³⁵. The OXC and AWG demultiplexers in the proposed architecture allow incremental expansion in terms of the number of wavelength channels to be transmitted. Dispersion and crosstalk are the main signal-degrading factors arising from the operation of the OXC and the effectiveness of each factor is individually investigated.