Volume 42, Issue 4

The objective of this work is to investigate and compare the impact of forward, backward and bidirectional pumping methods in repeater less distributed Raman fiber amplifier system and to analyze its benefits in long haul optical communication links. The effect of different pump wavelengths and pump powers are also analyzed. By adjusting the forward pump power as well as backward pump powers carefully, the transmission performance can be improved. The pump power ratio is adjusted to 20% so that the degradation of signal due to non-linear effect is reduced. The distributed gain and pump penetration depth for different pump power ratios are also examined. A comparison of different pumping methods reveals that bidirectional pumping gives the optimum performance in terms of higher gain and lower noise figure when compared to single pumps and unidirectional pumping. Low pump power ratios lead to better transmission performance than higher pump ratios due to lesser non-linear effects. The simulation results indicate that signal power evolution decreases with the increase in length of the fiber. It is also found that the pump power is more relevant during the first 50 km of the distributed fiber line and it decreases as it goes beyond 100 km. By choosing the optimum pumping methods and number of pumps, Raman Amplifiers can be used in almost all places where optical amplifiers are required.

In this work we have investigated semiconductor optical amplifier (SOA), erbium-doped fiber amplifier (EDFA) and RAMAN Amplifier separately under 64 channels WDM system at 10 Gbps data rate. A comparison is made based upon the values of Q- factor, bit error rate (BER), and power received for different values of laser (present at the transmitter) power. The eye diagram for the three optical amplifiers has also been analyzed. Also the performance factors (Q- factor, BER, and power received) are evaluated for different values of fiber length. In general it is observed that with respect to the power received for a particular laser power (at the transmitter) and up to a fiber length of about 120 km Semiconductor optical amplifier (SOA) gives the best result among all the three amplifiers. With respect to the quality (Q) – factor the RAMAN Amplifier gives slightly better result for a given laser power and for a short fiber length (up to a fiber length of 50 km). For long distance (fiber length greater than 160 km) the Q – factor for all the three optical amplifier saturates and become equal. In terms of Bit Error Rate, RAMAN amplifier is best as it gives minimum BER at a given laser power but up to the fiber length of 70 km EDFA provides minimum BER.

In the most recent years, developing web applications such as cloud computing, Big Data and latest cell phone applications have added more workload on the server centers. With the expansion on the network traffic, the consumption of power also increases. In past to reduce power consumption AWG based optical switch designs are proposed, and BER, energy consumption analysis has been carried out in isolated switch. In this paper, cascadability analysis of optical switches in fiber optic and data center networks is presented, and BER is calculated for isolated and cascaded switches. In fixing switch size concepts of graph theory and small world model are used. The packet loss performance is also simulated under different loading and buffering conditions. Finally, cross layer optimization concept is discussed in fixing various switch parameters.

Optical packet switching has gained popularity in past decade. However, due to technical challenges all- optical switching is not implemented till date, still hybrid switching where both optical and electrical switching are used simultaneously by-passing the limitations of both the technologies. In fiber delay lines (FDLs) buffering is limited due to accumulated losses and noises, and most of the times short term storage is enough in optical switching, but in case of long term storage, re-circulating type buffer can be used, but again due to accumulation of degrading terms re-circulation count is limited therefore in case of longer duration storage, electronic buffer is better choice. In this paper, we have proposed a hybrid buffer based optical switch where both optical and electronic buffers are used for storage of contending packets, and optical buffer is re-circulating in nature. The performance of the switch is measured in terms of bit error rate (BER) and packet loss probability, and BER performance is compared with recently proposed design, and it has been found that the proposed switch is comparatively much superior to earlier one.

Optical label switching is introduced for ensuring fast data transfer, quality of service (QoS) support, and better resource management. However, the important issue is how to optimize resource usage and satisfy traffic constraints for improving network performance and design. This paper proposes a dynamic approach that optimizes the resource in terms of link capacity and FDL (fiber delay line) buffering as well as a wavelength converter. The proposed approach decreases the resources usage and guarantees QoS support for various traffic demands. The optimization strategy consists of two stages: path building and traffic management. The path building assures logical topology making using the cumulative cost of available resource and traffic requirements including unicast and multicast. The traffic management solves the resource formulation problem during the traffic transfer by guaranteeing the required loss and blocking delay. Simulation work is conducted for validating the proposed approach and evaluating its performances and effectiveness. Simulation results show that our proposal minimizes effectively the use of link capacity of lightpath and light-tree. Moreover, our approach optimizes the use of buffering capacity and wavelength converter and guarantees QoS support according to traffic requirements.

For quite some time, the geometry-dependence of electric fields confined in two-dimensional systems of propagation has been known. We explore a lesser known way in which one can confine light, parabolically. One can use this method to understand the different forms modes take in such fibers and the appropriate eigenfunction for spectral analysis. In this paper, a fiber with a parabolic core and a circular cladding for the preservation of coaxiality are proposed.

A novel photonic crystal fiber (PCF) based on TOPAS, consisting only rectangular slots is presented and analyzed in this paper. The PCF promises not only an extremely low effective material loss (EML) but also a flattened dispersion over a broad frequency range. The modal characteristics of the proposed fiber have been thoroughly investigated using finite element method. The fiber confirms a low EML of 0.009 to 0.01 cm −1 in the frequency range of 0.77–1.05   THz and a flattened dispersion of 0.22 ± 0.01   ps/THz/cm. Besides, some other significant characteristics like birefringence, single mode operation and confinement loss have also been inspected. The simplicity of the fiber makes it easily realizable using the existing fabrication technologies. Thus it is anticipated that the new fiber has the potential to ensure polarization preserving transmission of terahertz signals and to serve as an efficient medium in the terahertz frequency range.

The proposed dual-core photonic crystal fibers (DC-PCFs) structure has been simulated using FIMMWAVE and its performance has been evaluated using Finite element method (FEM). The result indicates an enhanced flattened dispersion profile for the wide range of wavelength which is the utmost requirement of optical communication system and links.

Now a day all the telecommunication industries are using fibers for faster data communication and long distance communication. Fibers use light as the information and it is carried over long distances. Optical fiber has large advantages over a copper and co-axial cable because of its lower attenuation and interference. Optical time domain reflectometer (OTDR) is also one of the important devices using in telecommunication industries to characterize an optical fiber. This article deals with the study of long distance backbone single mode fiber and their features are discussed with the use of an OTDR. The results of this article focused on the losses and breaks of the fiber with the events. The Single mode OTDR is used to find the events, losses and breaks of the backbone fiber between the two locations. This work will give a way to study the nature of optical fibers and understand the practical application of optical fiber communication.

In this paper, we have proposed an improved hybrid passive optical network model using wavelength division multiplexing (WDM) and time division multiplexing (TDM) with 96 users in the bidirectional optical fiber networks. The performance is evaluated based on different distances and modulation formats with the help of Q factor, BER and Eye diagram. In the proposed model, the data is successfully transmitted up-to a distance of 96 km with a data rate of 10 Gbits/sec. Comparative analysis of proposed models with respect to other four models are hence put forth.

Direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems for a long-reach of standard single mode fiber (SSMF) require a large length of cyclic prefix (CP) to avoid the inter-symbol interference (ISI) effect caused by group velocity dispersion (GVD). Unfortunately, this method is inefficient due to the energy wasted in CP samples. In order to reduce the CP length and to mitigate the residual ISI, a novel blind adaptive channel shortening equalizer (CSE) is proposed in this paper. Based on the orthogonality between subcarriers in the fast Fourier transform (FFT) property, the proposed algorithm attempts to minimize the sum-squared correlation (SSCM) between each sample located in a well-defined window to update the CSE coefficients. Thus, the combined channel-CSE response is shortened. Therefore, it can cancel the residual ISI effect due to the GVD and the short CP length. The performance of the system is evaluated on basis of bit error rate (BER) versus optical signal to noise ratio (OSNR) for different CP lengths. The simulation results validate the new algorithm SSCM and show that it can reduce the CP length with a much better system improvement than existing algorithms.

In this paper, the performance of a novel multilevel signaling based on Manchester code namely four-level Manchester Coding (4-MC) technique is investigated for next generation high-speed optical fiber communication links. The performance of 4-MC is studied and compared with conventional Manchester modulation and four-level pulse amplitude modulation (4-PAM) formats in terms of receiver sensitivity, spectral efficiency and dispersion tolerance at the bit rate of 40 Gb/s. The bit error rate (BER) calculation model for the proposed multilevel scheme has also been developed. The calculated receiver sensitivity and the chromatic dispersion tolerance at the BER of 10 –9 of the proposed scheme are −22 dBm and 67.5 ps/nm, respectively. It is observed that, 4-MC scheme is superior in comparison to 4-PAM by 3.5 dB in terms of receiver sensitivity in back-to-back scenario. Therefore, the proposed scheme can be considered as an alternative to current 4-PAM system.

The fiber nonlinearities are one of the main performance limiting factors in any optical communication system. There are several parameters that effectively contribute in mitigation of these fiber nonlinearities such as fiber dispersion, effective area of fiber core, etc. Here, we have investigated the four wave mixing (FWM) nonlinear impairments in 16-channel WDM system. The FWM crosstalk becomes very critical to handle for long haul transmission systems at high power levels. Here, 16 channels WDM is being implemented and its performance is evaluated in terms of bit error rate (BER), Q factor, etc. for distance transmission upto 500 km.

Wavelength division multiplex (WDM) system with on/off keying (OOK) modulation and direct detection (DD) is generally simple to implement, less expensive and energy efficient. The determination of the possible design capacity limit, in terms of the bit rate – distance product in WDM – OOK –DD systems is therefore crucial, considering transmitter/receiver simplicity, as well as energy and cost efficiency. A 32-channel WDM system is designed and simulated over 1000 km fiber length using Optsim commercial simulation software. The standard channel spacing of 0.4 nm was used in the C–band range from 1.5436 to 1.556 nm. Each channel used the simple non return to zero – on/off keying (NRZ – OOK) modulation format to modulate a continuous wave (CW) laser source at 40 Gbps using an external modulator, while the receiver uses a DD scheme. It is proposed that the design will be suitable for long haul mobile backbone in a national network, since up to 1.28 Tbps data rates can be transmitted over 1000 km. A bit rate length product of 1.28 Pbps.km was obtained as the optimum capacity limit in 32 channel dispersion managed WDM – OOK – DD system.

With advancement in communication systems and ever increasing demand of bandwidth, research has been oriented towards 5G networks. For achieving high data rates, mm waves are employed using radio over fiber (RoF) technique. This work focus on employing mm waves in free space optics. Two independent channels are employed with each having 5 Gbps data rate and 60 GHz of radio signal. Output signal received is observed by analyzing using BER and eye diagrams.

Radio over Fiber technology is utilizing the high capacity of optical fiber system and wireless mobility network. In this work, we proposed two different optical propagation modes namely Laguerre-Gaussian (LG) and Hermite-Gaussian (HG) setting to (0.1), (0.2) mode types generated by a special CW laser source at varying wavelength from 800 nm to 1150 nm with 50 nm spacing channel Mode division Multiplexing (MDM) technique. These wavelengths transmitted×5Gb/s data modulated on PSK modulator having 100 GHz radio frequency subcarrier over 5 km Parabolic-Index Multimode Fiber link. Q factor value and eye diagram used to evaluate system performance which showed the maximum Q factor value found at 800 nm channel 1 equal to 12.0113 for both LG 0 1 and HG 0.1. While the maximum Q factor appears at 800 nm channel 1 equal to 8.49756 for LG 0,2 and 3.56785 at 1000 nm channel 5 for HG 0.2.

In this paper, dual polarization has been studied along with different forms of quadrature amplitude modulation schemes. Also the comparison of various QAMs (QPSK, DP-16QAM, DP-32QAM, DP-64QAM, DP-128QAM) is carried out in terms of Q-factor and distance.