Volume 45, Issue 3

Long band (L-Band) passive optical networks (PONs) are attracting a lot of attention these days, thanks to rising capacity demands. Because of PONs requesting more and more channels, fault detection/monitoring is critical. Fault detection in the conventional band (C-Band) employing reflecting Fiber Bragg Gratings (FBGs) and a probe signal integrating an additional amplified spontaneous noise (ASEN) source has been frequently demonstrated. However, interference occurs when ASEN and transmitter signals are in the same wavelength band, and adding additional ASEN sources to the network raises the overall cost. So, in L-Band PONs, a cost-effective, low-complexity fault detection/monitoring system is required. Therefore, in this work, a fault detection/monitoring system for L-Band PON using C-Band ASEN from inline erbium doped fiber amplifier (EDFA) and dual purpose FBG, i.e. (1) ASEN reflection for fault monitoring and (2) dispersion compensation is proposed. A 4 × 10 Gbps L-Band PON is investigated over 40 km feeder fiber (FF) and 1 km drop fibers (DFs) that serve 32 optical network units (ONUs)/different input powers, dispersion values, and laser linewidths in terms of reflective power of FBGs, eye opening factor, and bit error rate (BER), respectively.

A hybrid optical amplifier (HOA) is designed and optimized for the transmission of 40 dense wavelength division multiplexed system (DWDM) channels modulated at 10 Gbps having 25 GHz spacing at the edge of the L and U wavelength bands over more than 250 km. Multi-parameter optimization process is used to achieve the highest gain and best gain flatness. Different power combinations distributed among four lasers of a total forward pumping power (1270 mW) and total backward pumping power of either 730 mW or 850 mW are investigated for their effect on the hybrid amplifier gain and flatness. The best power distribution among the pumps provides about 31 dB overall gain with a flatness about 0.8 dB and noise figure ∼5.7 dB. It is found that the red-shifted pumps’ wavelengths should be used in the forward direction, while the blue-shifted pumps’ wavelengths should be used in the backward direction.

For realizing an all optical photonic crystal (PhC)-based Arithmetic Logic Unit (ALU), one needs an optical 4 to 1 digital multiplexer. This device is a logic circuit in which by using two control ports one can connect four input lines to the output port. In this paper we used nonlinear ring resonators combined with optical waveguides to realize an optical digital multiplexer inside two dimensional PhC structure. The final structure was simulated using finite difference time domain method. The simulation results show that the maximum time delay of the final structure is about 3 ps.

In this work, we demonstrate a tunable optical frequency comb (OFC) source based on a cascaded frequency modulator (FM) and two Mach–Zehnder modulators (MZMs). The setup includes one FM and two MZMs, and a sinusoidal RF signal source that directly drive all these modulators. A Flat OFC source with a high number of comb lines, and tunable frequency spacing and center wavelength is analytically modelled and simulated. The results reveal that 51 comb lines with a frequency spacing of 25 GHz are generated when only FM is used. Thirteen of these lines have power variations of 1 dB. Next, by cascading FM with two MZMs, 127 comb lines are obtained. In addition, 101 of these lines have power variations of 1 dB. An optical frequency comb, with tunable frequency spacing ranging from 10 to 40 GHz is successfully generated. Moreover, the center wavelength of the generated OFC can be tuned from 1310 to 1610 nm.

An all optical Gray to BCD converters will be proposed and designed based on photonic crystals. The proposed structure is composed of one XOR gate and a buffer. The final structure consists of 6 optical waveguides and two nonlinear ring resonators. The nonlinear defects are made of doped glass with the Kerr coefficient of 10 −14  m 2 /W. The rest of the structure was made of Si rods with the refractive index of 3.46. The maximum rise time for the proposed structure is 1 ps.

Plasmonics is an emerging and very advantageous technology which provides high speed and tiny size devices for fulfilling the demand of today’s high-speed world. SPPs are the information carrying elements in plasmonics, which are capable of breaking the diffraction limit. Plasmonics technology has shown its application in uncountable nanophotonic applications like switching, filtering, light modulation, sensing and in many more fields. Modulators are the key components of integrated photonic system. Various modulators which work on different effects are discussed in this study for providing a universal idea of modulators to researchers. Some useful plasmonic active materials are also discussed which are used in most of plasmonic modulators and other active devices. Previously, many researchers have worked on many kinds of modulators and switches, which operate on different kind of operating principles. For providing an overview about plasmonic modulators, their classification and their operation, we have discussed the state of art of some previously introduced modulators and switches which operates on electro-refractive effects and include electro-optic effect, Pockels effect, free charge carrier dispersion effect, phase change effect, elasto-optic effect, magneto-optic effect, and thermo-optic effect . Instead of different effects used in plasmonic switches and modulators different active materials like liquid crystals, graphene, vanadium di-oxide, chalcogenides, polymers, indium tin oxide, bismuth ferrite, barium titanate, and lithium niobate are also explained with their properties. Additionally, we also compared modulators based on different effects in terms of their design characteristics and performances.

In this paper, two-and-three channel all-optical AND logic gates based on four-wave mixing in a highly nonlinear fiber for 120 Gbps on–off keying signals were designed, simulated, and investigated. Simulation results show low bit error rate and consequently fairly high Q-factor at the receiving end in both two and three inputs AND gates, as well as the logic operation, is confirmed by the open eye diagrams with moderate power penalties for both designs.

In this paper, we propose a low-complexity fiber nonlinearity impairments compensation scheme based on nonlinear step size and modified adaptive digital back propagation. To verify the feasibility of the proposed algorithm, we construct a simulation system of single channel 12.5 GBaud polarization division multiplexing 16-ary quadrature amplitude modulation (PDM-16QAM) optical transmission system. Comprehensive numerical simulation results demonstrate that the proposed scheme can not only search for the fiber nonlinear coefficient adaptively, but also has the characteristics of high performance and low complexity.

Bimetal clad planar waveguide having polyaniline polymer as a guiding layer is proposed and studied for biosensing applications. The dispersion relation and reflectivity of the proposed sensor is obtained using transfer matrix method. The sensing performance and stability of proposed waveguide-based sensor is optimized using different volume fraction of Ag–Au bimetal. The volume fraction 1 represents pure Ag metal coating waveguide that shows maximum sensing performance in our all considered cases. In this case, maximum obtain sensitivity, detection accuracy and quality parameter is 74.140, 11.199 and 559.970°/RIU respectively, at the cover refractive index 1.410. Since, resonance angle and full width at half maxima of resonance peak decreases with increase of Ag metal percentage in Ag–Au bimetal therefore the presence of Au metal decreases the sensing performance of the sensor. Hence, a small volume fraction of Au metal is recommended for higher sensitivity with stability.

Mode division multiplexing (MDM) is very competent next generation multiplexing technique and is becoming popular among researchers these days. In this research article, an integrated passive optical network (PON) using MDM and wavelength division multiplexing (WDM) is proposed at 25 Gbps over 3 km multimode fiber (MMF) link distance. For MDM, diverse Laguerre–Gaussian (LG) such as LG12, LG15, LG18, LG111 and LG114 are incorporated and also for cost reduction, vertical cavity surface emitting laser (VCSEL) is located in optical line terminal (OLT). Performance of diverse advanced modulations such as compressed spectrum return to zero (CSRZ), duo-binary return to zero (DRZ) and modified duo-binary return to zero (MDRZ) is evaluated and compared with non-return to zero (NRZ) in terms of Bit error rate (BER) at varied MMF link lengths. Results revealed that CSRZ performance stand out and NRZ provide worst performance.

Optical packet switching has gained lot of momentum in last decade due to the advantages of optical fiber over copper cables. Optical switching is beneficial in optical networks which form connections of links and switching nodes. In these high speed networks minimum delay and high throughput are two important parameters which are considered. To minimize network delay shortest path algorithm is used for route selections. In previous studies while choosing shortest path distance among various nodes is considered. In this work we have shown that it is necessary to consider both distance and number of hops while choosing path from source to destination to minimize power per bit used for the transmission.

In the development of ethernet passive optical networks (EPONs), quality of service (QoS) support and fairness per optical network unit (ONU) are crucial issues. However, making an elaborate analysis of the existing prediction-based bandwidth allocation algorithm, light load penalty, low prediction precision are pointed out. We present an improved dynamic bandwidth pre-allocation algorithm (R-DBA), which employs recurrent neural network (RNN) to predict the high-priority service traffic in EPON. And we introduce mixed integer linear programming (MILP) for optimally building DBA algorithm. This algorithm achieves the prediction of the high-priority service traffic by RNN during the waiting time and supports bandwidth pre-allocation, thus ensuring the fairness of the bandwidth allocation.

From the advent of communication, there has been a constant demand for increasing communication capacity. In optical communications, capacity can be increased by implementing more fibers or can be increased by using the same fiber to transmit more than one signal. The process is known as the wavelength division multiplexing or WDM. Channels placed closer to each other in the wavelength scale leads to the process of DWDM or dense WDM networks. But with so many channels transmitted together over minimum distances of 10 km, the power of each channel decreases significantly within the fiber, hence a Raman amplification system has been incorporated within the network. The whole system is designed at the 1300 nm optical window which has shown the least dispersion among the other optical windows. Results from simulating a 16 channel network with 8 optical pumps, where all are configured in co and counter propagating directions. They have shown good amount of gain, relatively low noise and good SNR over the whole communication band of channels rendering the system to be a faithful communication network.

Elastic optical networks (EONs) offer tremendous benefits to deal with the exponential increase of the data center traffic. The granularity offered in spectrum allocation supports efficient management of available bandwidth and accommodates multiple traffic to be routed through common links. However, this brings the inherent challenges of routing and spectrum allocation (RSA) constraints. This becomes more complex for elastic optical data center networks (EODCNs), wherein multiple requests arrive at the same time, requiring identical or different bandwidths and each request may have the same or different destination and paths. Also, data requested by different users could be of varying importance levels. Under such a scenario, maintaining the quality of service (QoS) by minimizing the probability of traffic failure and bandwidth blocking is a major task for service providers. To address these problems, we propose an enhanced methodology using path prediction and link-state analysis for efficient allocation of frequency slots and reuse of bandwidth for data centers connected through EONs. Our proposed strategy intents to minimize the number of blocked requests due to non-availability of resources and reduce the failure probability. We introduce here the concept of connectivity degree and Kuhn-Munkres multi-objective optimization for spectrum allocation. We also evaluate the call request blocking probability varying the number of data centers and traffic load. The obtained results show that the proposed algorithm is highly effective in reducing the traffic failure and blocking probability for EODCNs.

In this article, we designed an experimental system for underwater wireless optical communications. A function generation device sent frequencies (1–500 kHz) by amplitude shift key modulation technology, and these frequencies were loaded over light-emitting diode to propagate through a glass water tank with a length of 1 m, width of 40 cm, and height of 30 cm containing clean water of 80 L. These frequencies were received by a photodiode (BPX61), and the received signal was displayed through a digital storage oscilloscope device. Four techniques, single input–single output (SISO), single input–multiple output, multiple input–single output, and multiple input–multiple output (MIMO), were applied under the same optical conditions to know the quality of receiving the optical signal and the difference between them. Finally, the parameter values of signal-to-noise ratio, peak-to-peak voltage, and voltage gain were checked for each technique, and they were the lowest values for the SISO technique and the highest values for the MIMO technique.

Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) is a familiar modern wireless broadband technology due to its resistance against multipath fading, high data transmission rate, and spectral efficiency. This technology delivers dependable communication as well as a large range of coverage. The precise recovery of Channel State Information (CSI) and synchronization among the receiver and transmitter are two major challenges for MIMO-OFDM systems. Several estimate procedures, like blind, pilot-aided, and semi-blind channel estimating, are used to recover channel state information. Yet, those systems have several flaws that cause them to perform poorly. Hence, this paper describes the basic introduction of the Channel Estimation (CE) process in the MIMO-OFDM system. The main goal of this survey is to study analyzing and categorizing the channel estimation algorithms, and simulation tools in different contributions. Further, the performance analysis with different performance metrics from diverse contributions is pointed out. Thus, this review article presents a detailed overview of the various channel estimation schemes that have been exploited in the OFDM channel to enhance the estimation of the CSI in the MIMO-OFDM systems. This work presents and discusses the relevant comparative results and computational complexity for all of these CE systems. Furthermore, there is a list of open study directions for further exploration.

Dual polarization quadrature phase shifting keying (DP-QPSK) modulation format along with coherent receiver helps in increasing the data carrying capability of existing optical networks without any major change in existing transmission infrastructure. The various linear and nonlinear fiber effects, frequency and phase errors are corrected in electrical domain at the receiver end with digital back propagation algorithms (DBP) instead of in-line compensation. In such a case the selection of optimum values of system parameters make the task easier for DBP algorithms. This paper highlights the importance of finding optimum operating point of continuous modulus algorithm (CMA) for better adaptive equalization (AE). The paper also discusses the optical pulse shaping using Gaussian optical band-pass filter to improve the spectral characteristics of DP-QPSK signal.

Optical communication systems introduced paradigm shift in the forte of data transmission at higher speeds and over longer distances where, on contrary electrical transmission systems failed due to higher amplitude degradation, interferences and lower bandwidths. However, pulse width increase (PWI) in the optical fiber limits the overall distance reach and also introduces more bit errors which needs to addressed. So far, pulse width shortening fibers (PFs) and fiber Bragg grating (FG) used individually in most of the reported studies, however pulse width shortening (PWS) took either high cost (in PFs) or lower PWS efficiency (PWSE) (in FG). Therefore, in this research manuscript, we made emphasis on the combined PWS effects of diverse techniques such as optical phase conjugation (OC), FG and PFs in ultra-dense wavelength division multiplexing (WDM) system. Total link length of 400 km has been covered in 128 channels ultra dense wavelength division multiplexing (UDWDM) system at 10 Gbps by incorporating diverse combined organized placements of FG, OC and PFs such as FG-PF, OC-PF and FG-PF-OC. Results revealed that economical and maximum PWSE arrangement for proposed system is FG-PF-OC.

For underwater blue–green light multiple-input multiple-output orthogonal frequency division multiplexing modulation system (MIMO-OFDM), the underwater MIMO channel gain matrix corresponding to the change of receiver spacing was analyzed and derived, and a proportional power allocation scheme combined with singular value decomposition (SVD) precoding was proposed, in order to eliminate inter-channel interferences of the MIMO system. The simulation results show that when the transmitter spacing is fixed, and the receivers adopt the same spacing as the transmitters, which is difficult to achieve in the complex underwater environment, the system bit error rate (BER) performance under the proposed proportional power allocation scheme is the same as that of the average power allocation. When the receiver spacing increases, the system BER under the proposed scheme can ensure better overall performance compared with that of the traditional average allocation scheme.

Free space optical communication is a potential technology that exploits the visible light frequency band for communication. In this paper, a free-space optical link (FSOL) optimization in visible light communication (VLC) is used to improve the channel performance for signal strength and analyze the effect of signal failures in a communication system. The data transmission and reception phenomenon are established using a light-emitting diode (LED) as a carrier at transmitter and photodiode as a detector at the receiver, respectively. The OptiSystem tool uses to optimize the component parameters of this proposed communication system. The bit error rate (BER) analyzer displays the signals as an eye diagram with the challenges of components uncertainty for better signal performance. The optimized components solve the problem encountered transmitting improve and enhance the signals strength. The acceptable eye diagram displayed from the BER analyzer has been resolved as a result of component optimizations by adding and removing noise to ascertain the behavior of the channel. A better signal retrieve by the display of the acceptable eye diagram from the OptiSystem software used. The FSOL components optimization improve the loss of data, weak signal, loss of power, signal failure, and signal errors which guarantee multi-mobile users with the shared signal. OptiSystem software package used to fully characterize the FSOL system.

This paper first determines the generalized optical orthogonal code (GOOC) parameters to minimize the bit error probability in fiber-optic code division multiple access systems. The systems use on-off keying as the modulator and the optical AND logic gate as the receiver. In situations where the problem of finding the lowest bit error probability has more than one answer, we introduce and examine four approaches to choose the optimal answer. Finally, by employing a complete search of code parameters, we determine GOOC parameters (if there are any) to achieve the maximum bandwidth efficiency considering the design constraints, i.e., the number of network users and the maximum acceptable probability of error.

In this paper, the performance of free space optics (FSO) technology is investigated under the effect of external electric fields perturbations; standard parameters of the proposed system adopted by performing experimental setup measurements on the laser propagation axis and computer simulation using the “OptiSystem” program. The experimental results show linear relation between the electric field and the fluctuation of the output power As a result of the interference between the transmitted signal and the noise created by an electric field. The simulation results illustrate that when the transmitter divergence angle increased the Q-factor decreased, but not high enough to cause a complete blocking to the transmitted signal. The significance of these results, they help to understand the effect of electric discharges and Corona phenomenon of the electric field produced by the transmission line conductors nearby the optical communication systems where, (1 mrad) is the most effective divergence angle that reduces these effects.

Optical wireless technologies like Free Space Optics (FSO) have proven to be a perfect choice for 5G communication systems. FSO can offer low latency, high capacity, extensive connectivity, and high reliability at a low cost. However, the major limitation of FSO is its susceptibility to atmospheric turbulences, especially rain at high frequencies. In this paper, a rain efficient 10 Gbps 5G communication system using multibeam FSO and multilevel Differential Phase Shift Keying (M-ary DPSK) encoder is proposed. To evaluate the system performance at different rain intensities, the state-of-the-art Charbonneau channel model for rain attenuation has been used. The performance efficiency of the proposed system is evaluated in terms of quality factor (Q-factor), bit error rate (BER), optical signal-to-noise ratio (OSNR), and received power. The results convey that the proposed system can perform well up to 4.25 km, 3.24 km, and 2.55 km under below average, average, and above average rain conditions, respectively, with attenuation of 6.28 dB/km, 9.65 dB/km, and 19.27 dB/km, respectively. Moreover, the comparative analyses show that the proposed system performs better than the recent conventional systems in terms of bandwidth and power efficiency.

In the present era of technology, it is quite fascinating to design a system capable of transmitting information from one end to another by using the optical spectrum. This system differs from optical fibre communication in terms of channel medium. Optical fibre technology uses the end-to-end physical connection via fibre. In contrast, Light-based wireless communication networks, also known as wireless optical communication (WOC) networks or fibreless optical communication networks, use light as a carrier and air as an unguided propagation media for transmission. Fibreless optical communication eliminates the need for Licensing and Buried Fibre Cables; also, its installation is relatively easy. This survey article describes the evolution of WOC technologies right from the old methods of communication to today’s deep-space optical satellite communication. This article briefly describes the WOC system working principle, categorization of wireless optical systems (based on the carrier frequency wavelength, distance covered, and application), different modulation techniques adopted for wireless optical communication, challenges associated with channel medium and channel modelling, performance analysis of WOC system, various application areas of WOC network, commercial developments in the field of WOC, and some other emerging trends associated with WOC.

In this paper, we study a dual hop hybrid radio frequency-visible light communication (RF-VLC) system with wireless energy harvesting technique. In the proposed model the RF channel and the VLC channel are modelled by generalized-K distribution and lambertian emission model, respectively. A decode and forward relay is used as an intermediate node where power splitting relaying (PSR) protocol is employed to harvest energy from the received RF information signal. The source transmits the information signal towards the relay via RF channel. The relay then decodes the received signal and convert it into corresponding light signal. Simultaneously the energy harvesting circuit at relay harvests the energy from the received RF signal. The relay utilizes the harvested energy to aid the transmission of the light signal towards the user situated inside the building’s room at the destination. Further, the statistics of the instantaneous SNR of the hybrid RF-VLC system at the destination are derived by employing the PSR protocol to obtain an accurate closed form analytical expression for the system’s end-to-end ergodic capacity and achievable throughput in terms of Meijer’s G function. Further, with the help of numerical simulations, we analysed the end-to-end ergodic throughput performance of the hybrid system under the influence of varying channel parameters such as signal to noise ratio, power splitting factor, shadowing parameters, distance between source & relay and source transmitted power.

The analysis of average spectral efficiency (ASE) of multi-pulse position modulation (MPPM) scheme with optimal rate adaptation (ORA) and channel inversion with fixed rate (CIFR) adaptation schemes over the gamma–gamma free space optical (FSO) channel has been carried out in this paper. The performance of the adaptation schemes has been analyzed in terms of the average channel capacity and has been further scrutinized under the aperture averaging effects in moderate and strong atmospheric turbulence. For the first time, closed form expressions for MPPM with ORA and CIFR transmitter adaptation schemes have been derived in terms of Meijer’s G functions. Using the derived expressions, the performance of the two adaptation policies have been compared for different transmitter power and varying FSO length, MPPM modulation order and aperture averaging. The analysis results revealed that generally, ORA performs better than CIFR under the considered turbulence strength, modulation order and aperture averaging. However, aperture averaging offers more gain in ASE in strong turbulence than moderate turbulence for both ORA and CIFR. Furthermore, the results revealed that aperture averaging effects offers much more gain in ASE when used with CIFR than ORA.

The research of optical network virtualization technology is gradually deepening among optical network virtualization for network cloud service is one of the main research directions of optical network in the future. The dynamic VN mapping algorithm, the most critical part of the virtual network layer, was not studied. As mentioned earlier, optical networks for cloud-oriented services face the challenge of how to respond to the dynamic changes in VN resource requests during virtualization.