Volume 43, Issue 3

Amplification through hybrid optical amplifiers (HOAs) is a propitious and proficient technology for high speed and high capacity dense wavelength-division-multiplexing (DWDM) systems. HOAs are intended to improve system reach and to accomplish wide gain bandwidth with enhanced flatness of gain. In this work, an ultradense 16 channel WDM system is demonstrated and performance of diverse hybrid amplifiers is evaluated in terms of output power, Q-factor, gain flatness and BER. Spacing among the WDM channels is 25 GHz in order to make system bandwidth efficient and scrutinized its effect on four wave mixing (FWM) in case of EDFA-EDFA, Raman-EDFA and SOA-EDFA. It is observed that SOA-EDFA is more and Raman-EDFA is less prone to FWM. Moreover, for distance 20 Km–140 Km, Raman-EDFA is optimal configuration for amplification and from 150 Km–200  Km, SOA-EDFA shows better performance. For prolonged link lengths such as beyond 200  Km, EDFA-EDFA is a right hybrid amplifier. In order to achieve maximum gain flatness in proposed architecture, EDFA-EDFA is recommended to use.

A spherical wave propagates through the strong underwater turbulence media is modeled as gamma–gamma random variable in the underwater wireless optical communication (UWOC) systems. To mitigate turbulence-induced fading, spatial diversity over UWOC links is proposed. Furthermore, the exact bit error rate (BER) expressions for both single-input single-output (SISO) and single-input multiple-output (SIMO) UWOC systems with optimal combining based on on–off keying (OOK) modulation are analytically derived. Then the system performance is simulated with various variations of the underwater turbulence, i.e. the rate of dissipation of kinetic energy per unit mass of fluid, the ratio of temperature to salinity contributions to the refractive index spectrum, and the UWOC system link length. The results show that the analytical expressions for describing the system performance are valid and spatial diversity can considerably improve the system performance.

We propose a very compact structure for all-optical XOR, XNOR, NAND and OR logic gates based on photonic crystal 3-dB coupler in binary-phase-shift-keyed (BPSK) signals. The square lattice of dielectric rods in SiO2 background has been considered for photonic crystal structure. The photonic band gap (PBG) and light propagation simulations of proposed logic structure have been accomplished by plane wave expansion and finite difference time domain methods. The proposed structure can achieve logical function when the refractive index of all rods and substrate is fabricated with relaxed error tolerance within −0.005 to 0.005 from designed parameters. The proposed logic functions may potentially be used as key components in all-optical information networks for processing the BPSK signals.

This paper has presented the simulation of single fiber Bragg grating (FBG) characteristics using Optigrating simulation software at the worst case. Various types of the same/different refractive index grating/fiber profiles are employed in order to test the transmittivity/reflectivity, bandwidth, and average group delay ripple factor level measurement of single FBG with optimum case. As well as output pulse intensity spectrum is examined for each case. It is observed that minimum side lobes strength, maximum output pulse intensity spectrum, dominant mode, narrow spectral bandwidth, maximum transmittivity/reflectivity spectral response are achieved with grating (exponential)/core (exponential)/region 1 (Gaussian cladding) FBG profile configuration, and grating (exponential)/core (parabolic)/region 1 (Gaussian cladding) profile configuration. Optigrating simulation results give an idea about the efficiency of the suggested hybrid FBG refractive index profiles to analyze FBG technical characteristics.

Data centers are very critical elements which store and distribute data over the Internet. current data centers heavily rely on electronics, and thus require vast amount of power and speed is limited. These limitations can be tackled using optical technology. In general optical devices consume lesser amount of power, and support very high data rates. In this paper, a hybrid buffer-based optical packet switch which can be used in data centers as aggregated or core switches is discussed. The physical layer analysis is presented and performance is measured in terms of bit error rate (BER) obtained at various power levels. The analysis is carried out in presence of crosstalk of various components and for acceptable BER≤10 –9 , minimum power required for all optical, all electronic and hybrid buffer is evaluated. Finally power penalty is also evaluated which is required to overcome the effect of amplified spontaneous noise (ASE) and components crosstalk.

A new approach to generate high-quality optical frequency comb (OFC) with good flatness, high bandwidth, and tunable frequency spacing is proposed. The OFC generator includes a polarization modulator and an intensity modulator (IMS), and the polarization modulator is modulated by a radio frequency multiplication circuit. The theoretical analysis model of the proposed scheme is established. The experiment stimulation results show that 35-line OFC with tunable frequency spacing and spectrum flatness of 0.3 dB and side-mode suppression ratio of 15.53 dB is gotten easily by adjusting the amplitude and frequency of the RF and the direct current bias voltage of the modulators. The stimulation results are in good agreement with the theoretical model.

In this manuscript, an attempt has been made to enhance the performance of colorless wavelength division multiplexed-passive optical network (WDM–PON) system using a combination of dual-drive Mach–Zehnder modulator and single sideband-suppressed carrier (SSB-SC) technique along with splicing. The proposed design makes use of SSB-SC technique for optical line terminal (OLT) as well as for optical network unit (ONU) that is generated by using dual-drive modulator which in turn reduces the expense for complete communication process. Suppressed RF signals with four channels at a bit rate of 10 Gbps for each channel are multiplexed before injecting into fiber span of 25   km at OLT side. Half of the downlink power is consumed for re-modulating the data signal at ONU side. The performance is further improved by using signal splicing method. Due to suppression in the carrier in this technique, there is no carrier Rayleigh scattering problem. The proposed model is compared with the existing one for error-free transmission of signal. The results revealed that the proposed model possess less value of bit error rate with the same value of received optical power as well as channel.

Visible light communications (VLC) is considered as an alternative communications technology for providing indoor wireless services. VLC systems are expected to offer high data transmission rate and seamless coverage. In order to achieve these requirements, VLC systems utilizing multi-lightbeam access points (multibeam VLC-AP) for downlink transmission have been proposed recently. In this paper, we present a lightbeam configuration method and an interference elimination resource scheduling mechanism (IERS) for indoor multibeam multi-access point VLC systems. The proposed lightbeam configuration method ensures seamless connectivity between user equipment and VLC-AP. The proposed IERS mechanism consists of a beam assignment algorithm and a resource allocation algorithm for eliminating co-channel interference as well as improving system performance. Performance results obtained by computer simulation indicate that there are significant improvements in terms of downlink signal to interference plus noise ratio, user throughput and packet delay when the proposed IERS mechanism is deployed.

We demonstrated a full duplex hybrid passive optical network and indoor optical wireless system employing coherent optical frequency division multiplexing. To accomplish reliable transmission in passive optical networks integrated visible-light communication (VLC), yellow light-emitting diode and infrared LED is used in downstream and upstream, respectively, for intra building network. In order to support high data rate, pulse-width reduction scheme based on dispersion compensation fiber is incorporated and system successfully covered the distance of 50 km. A data stream at the rate of 30 Gb/s is transmitted for each user out of eight users. VLC-supported users are catered with the bit rate of 1.87 Gb/s over 150 cm and in order to realize a low-cost system, visible and infrared LEDs are used in downlink and uplink, respectively.

In the current work, we focus on the optimization of lightpath routing in a Space Division Multiplexing based Elastic Optical Network (SDM-b-EON) for which we propose an online routing algorithm, named as Resource Efficient Online Routing Algorithm with Regeneration (REORAwR) which, in addition to ensuring the routing of translucent lightpaths through spectral super-channels over spatial modes links also accounts for the presence of the transceivers in the network. The proposed REORAwR algorithm is tunable such that it can either aim to reduce the bandwidth blocking probability or can aim to minimize the overall consumed power. In regard to regeneration, we investigate two scenarios which differ in their regeneration variability level in addition to the adjustment of modulation formats as per the transmission route characteristics. We conduct extensive simulations considering two realistic network topologies and realistic transmission reach values. The obtained results demonstrate that significant benefits can be obtained in regard to the utilization of both the major network resources (spectrum and transceivers) when regeneration is conducted with complete flexibility and modulation format conversion is also permitted at every node of the SDM-b-EON. In addition, the obtained results also show that when compared to spectrum usage, in terms of the overall consumed power, the performance profits which can be obtained in a translucent SDM-b-EON are very small.

Nowadays, bandwidth demand is enormously increasing, that causes the existing passive optical network (PON) to become the future optical access network. In this paper, next generation passive optical network 2 (NG-PON2) based, optical time division multiplexing passive optical network (OTDM-PON), wavelength division multiplexing passive optical network (WDM-PON) and time & wavelength division multiplexing passive optical network (TWDM-PON) systems with 20 Gbps (8 × 2.5 Gbps) downstream and 20 Gbps (8 × 2.5 Gbps) upstream capacity for eight optical network units has been proposed. The performance has been compared by varying the input power (−6 to 27 dBm) and transmission distance (10–130 km) in terms of Q -factor and optical received power in the presence of fiber noise and non-linearities. It has been observed that TWDM-PON outperforms OTDM-PON and WDM-PON for high input power and data rate (20/20 Gbps). Also, TWDM-PON shows its superiority for long-reach transmission up to 130 km, which is a cost-effective solution for future NG-PON2 applications.

There is now an increasing awareness about the possibility of health hazards due to excessive electromagnetic radiations around us within the indoor environment. Hence, the alternative communication technologies such as indoor mobile communication system based on LED lighting are gaining more attention in the present scenario. The dual use of LEDs i. e. for illumination as well as for setting up of an indoor communication network infrastructure simultaneously makes it an attractive preposition. The LED lighting based communication system is qualified to be part of green technology networks. This paper investigates the optimal LED placement strategy for such a system to optimize the overall communication system parameters including the transmit power optimization. It is observed that the overall optimization of LEDs improve the signal to noise ratio and also a significant reduction in root mean square delay at lower semi-angle values besides improving the mobile coverage area.

This work presents the joint use of advance modulation scheme i. e. m-QAM and optical chaos to combine the best of the two advantages i. e. higher data rates and security. A semiconductor laser diode is driven into chaotic region using direct modulation scheme and 4-QAM signal is added by Chaos message masking (CMS). The chaotically masked data stream is transmitted over an optical communication link to investigate the propagation issues and synchronization of chaos at the receiver. The transmitted chaos is synchronized at the receiver to unmask the QAM stream and binary data by using subtraction rule and conventional QAM demodulator, respectively. The deterioration of constellation diagrams and bit error rate found dependent upon transmitter/receiver synchronization and link parameters. The use of 4-QAM chaotic scheme is extendable to m-QAM and is applicable to long haul, short haul point to point and for passive optical networks.

This work is focused on transmission of duobinary and alternate mark inversion (AMI) modulation, adopting mode division multiplexing (MDM) of Laguerre Gaussian (LG) modes has been capitalized in wavelength division multiplexing (WDM) system, resulting in a 1.6 Gbps eight-channel free space optical communications (FSO) system. The simulation results show that duobinary offers better bit error rate (BER) performance compared to AMI for proposed hybrid MDM-WDM-FSO system.

Radio over fiber is a technology in which the light signals at the central station are modulated by a radio frequency signal, and by using the optical fiber it is transmitted to base stations. The data stream being sent is separated into subcarrier frequencies by the technique of orthogonal frequency division multiplexing. The orthogonality between the sub-carriers is provided by FFT modulation, which avoids the demodulators from accepting other frequencies. It is possible to transmit high-data rate signals over short and long distance by implementing orthogonal frequency division multiplexing with radio over fiber system along with the optical fiber. This enhances the system with more coverage area, and without increasing the cost of the system it provides the flexibility. The proposed work is to investigate the performance analysis of single side band orthogonal frequency division multiplexing in radio over fiber system with external and direct modulations using spectral analysers and constellation visualizers. The Mach-Zender modulator is proposed for external modulation, the vertical cavity surface emitting laser is used in direct modulation. The simulations were carried out by using Optisystem Software version 15.0 with global parameters for both intensity modulation schemes.

This paper presents a combination of the FSK (frequency shift keying) and the PPM (pulse position modulation) techniques for visible-light communication systems. We propose novel modulator architecture, which is referred as combined FSK-PPM (CFPPM), to observe the average power requirement of FSK technique. The proposed combined scheme is compared with the traditional FSK method in terms of average transmission power and BER (bit error rate) performance. The average transmission power of FSK modulation technique is independent on M that is expressed as modulation order. The results show that the requirement of average transmission power of proposed FSK can be gradually decreased dependent on M.

Sigma Delta Radio over Fiber (S-DRoF) systems are looked upon as an enabling technology due to their advantages that comes due to combination of analog and digital radio over fiber (RoF) systems. In this paper, we have proposed and experimentally demonstrated a Multi-stAge-noise-SHaping (MASH) based Sigma Delta Modulated RoF system targeting 5G C-RAN (cloud/centralized radio access network) fronthaul applications. The evaluation has been done for LTE 20 MHz signal having 256 quadrature amplitude modulation with a carrier frequency of 3.5 GHz up to 5 Km of Standard Single Mode Fiber (SSMF). Furthermore, a comprehensive analysis of the design is explained followed by the experimental setup. The performance is reported in terms of error vector magnitude (EVM) and adjacent channel leakage ratio. It is concluded that S-DRoF substantiates the desired range of the 5G C-RAN fronthaul networks.