Band 44, Heft 4

Carriers temperature in quantum dot (QD) optical amplifiers has been modelled theoretically taken into account hole contribution, which is not considered early. The contributions of wetting layer (WL), first excited state (ES 1 ), and second excited state (ES 2 ) have also been considered. Effect of WL−ES 2 recombination time of both electrons and holes, carrier heating (CH) time of electrons and holes, in addition to electron hole recombination time are examined. The results show that there is a gap between electron and hole heating temperature due to the difference between there recovery times. It is found that fast hole (long electron) recombination time yield a high carrier temperature.

In this regard, we directed a theoretical study with numerical simulations. This study allowed us to illustrate how a photonic crystal fiber (PCF) structure could divide an optical signal. One of the most fundamental components used to construct photonic integrated circuits (PIC) is the splitter, which is using light coupling between the cores as a control until the output ports by using pure silica to replace some air-hole zones along the PCF axis and split the single signal on two ports with almost equal intensity in each port. Optical interconnects are one of the most basic components of integrated optics, and splitters for photonic power are a key element of a connected family. With the least amount of loss, a competent photonic splitter can guide light input of a certain wavelength to several ports at various intensities.

All-optical processor capable of processing optical bits has been a long-standing goal of photonics. In this paper, we report the results obtained by numerical simulations regarding the designing of an all-optical combinational circuit of an adder and subtractor circuits based on Si 3 N 4 microring resonators. The designs of combinational circuit like adders and subtractor based on the use of all-optical basic logic gates are discussed while presenting the numerically simulated results. Extinction ratios of 5.2 dB, 3.5 dB and 2.7 dB are obtained for the half adder, full adder and half subtractor, respectively.

The study has outlined various photonic crystal fibers (PCFs) configurations for the key solution to the optimization of data rates transmission. The proposed fibers that are namely octagonal photonic crystal fiber (OPCF), hexagonal photonic crystal fiber (HPCF), and elliptical photonic crystal fiber (E-PCF) are used in the system. The dispersion parameter coefficient, pulse broadening variations, and data rates transmission are examined for proposed fibers under the same fiber lengths and number of quantization level with using pulse code modulation (PCM). The system performance is enhanced with OPCF with reducing dispersion factor, pulse broadening effects and consequently increasing data rates transmission.

The access network is developing towards large capacity, wide-coverage, and low delay, which puts forward higher requirements for network structure and data exchange performance of optical access network equipment. In this paper, we have designed a high-speed optical network device with 40/10G TDM-PON. To effectively solve the problem of network switching capability in high-speed data transmission, we propose a low delay large capacity switching algorithm, which minimizes the network switching delay. We model the network by integer linear programming and simulate the network based on OMNeT++. The simulation results show that the algorithm can effectively solve the problem of network switching delay in the high-speed network environment.

In this paper, we proposed a fast recovery strategy for a dual link failure (DLF) in elastic optical network (EON). The EON is a promising solution to meet the next generation higher bandwidth demand. The survivability of high speed network is very crucial. As the network size increases the probability of the DLF and node failure also increases. Here, we proposed a parallel cross connection backup recovery strategy for DLF in the network. The average bandwidth blocking probability (BBP), bandwidth provisioning ratio (BPR), and recovery time (RT) for our proposed Intermediate node cross-connect backup for shared path protection (INCB-SPP) for ARPANET are 0.38, 2.71, 4.68 ms, and for DPP 0.70, 6.02, 8.71 ms and for SPP 0.40, 2.87, and 16.33 ms respectively. The average BBP, BPR, and RT of INCB-SPP for COST239 are 0.01, 1.71, 3.79 ms and for DPP are 0.39, 3.50, 8.20 ms and SPP are 0.04, 1.75, and 12.47 ms respectively. Hence, the proposed strategy shows lower BBP, fast connection recovery, and BPR when compared with the existing shared path protection (SPP) and dedicated path protection (DPP) approaches. Simulation is performed on ARPANET and COST239 topology networks.

In this tutorial, we give an introduction to optical burst switching (OBS) networks and compare different methods that have been given to improve performance of these networks. OBS is an alternative to optical circuit switching and optical packet switching by separating data from control packets and sending them in a different wavelength. OBS networks suffer from an issue based on their bufferless nature, burst contentions. In these networks, when two data bursts are competing on the same wavelength, one of them is dropped and it leads to a significant reduction on the performance of the network. A lot of researches have been done to solve this problem. Some of them are addressed in this paper.

Passive optical network (PON)-supported orthogonal frequency-division multiplexing is viewed as a capable answer designed for subsequent generation optical networks in terms of traffic coloring when integrated with monarch butterfly optimization (MBO). Traffic coloring optimization (TCO) or MBO algorithmic rule solves the matter of controlling the traffic, began by end-user transceivers with multiple parameters through rescheduling transmission capacity and bandwidth allocation strategy of the optical network, which are done by means of its operator functions. The TCO method with granularity adjustment components outcome signifies an improvement in quality of service as it reduces jitter and increases throughput in PON by 350 µs and 12.5 %, respectively. It even improves the blocking probability and fairness index.

In the present optical fog/cloud computing environment, optical line terminals and optical network units are used as the most promising optical fog devices (OFDs). The inherent characteristics of fog computing provide certain granted privileges to the attacker to hack devices and make them malicious. Also, existing security solutions generate false alarms that affect the performance of the underlying network. In this paper, a secure framework is proposed that not only predicts the malicious OFDs but also reduces false alarms. Hidden Markov model and intrusion detection system are used to detect the malicious one by computing the probability of shifting (POS) and then shift it to the virtual honeypot which is kept hidden by deploying it at the optical fog layer. In addition, it also reduces the generation of false alarm and logs all malicious activities for further analysis. In the experiment section, Python is used to validate the proposed framework. Further, HMM is simulated and tested in the MATLAB to reduce the false alarm rate. Results show that the proposed framework effectively reduces the false alarms and detects the malicious one and then shifts it onto the virtual honeypot efficiently.

Network security is an important component of today’s networks to combat the security attacks. The passive optical network (PON) works at the medium access layer (MAC). A distributed denial of service (DDOS) attack may be launched from the network and transport layers of an Optical Network unit (ONU). Although there are various security techniques to mitigate its impact, however, these techniques cannot mitigate the impact on the MAC Layer of the PON and can cause an ONU to continuously drain too much bandwidth. This will result in reduced bandwidth availability to other ONUs and, thus, causing an increase in US delays and delay variance. In this work we argue that the impact of a DDOS attack can be mitigated by improving the Dynamic bandwidth assignment (DBA) scheme which is used in PON to manage the US bandwidth at the optical line terminal (OLT). The present DBA schemes do not have the capability to combat a security attack. Thus, this study, uses a machine learning approach to learn the ONU traffic demand patterns and presents a security aware DBA (SA-DBA) scheme that detects a rogue (attacker) ONU from its traffic demand pattern and limits its illegitimate bandwidth demand and only allows it the bandwidth assignment to it as per the agreed service level agreement (SLA). The simulation results show that the SA-DBA scheme results in up to 53%, 55% and 90% reduced US delays and up to 84%, 76% and 95% reduced US delay variance of T2, T3 and T4 traffic classes compared to existing insecure DBA schemes.

In this paper, we report the modeling and simulative investigation of a mode division multiplexing (MDM)-based Radio over Free space optics (RoFSO) transmission system. Two separate 10 Gbit/s–10 GHz information signals are transported successfully over 30 km link range using distinct Hermite Gaussian (HG) modes. Also, the decomposition of distinct modes at the receiver terminal has been reported in this work. Furthermore, the impact of different fog conditions and scintillation effect on the performance of the proposed link has also been discussed in this paper.

The paper investigates the impact of Rayleigh-distributed statistical behavior of peak-to-average power ratio (PAPR) associated with a pre-clipped signal on the performance metrics of a direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) system. The analytical model for the system takes into consideration a pre-clipped and dc-shifted baseband OFDM signal, driving an optical source over its linear operating range. The model employs a bias-scaling factor, which is heuristically varied over the entire range (0 to 1) to examine improvement in overall power efficiency. Further, it utilizes the cumulative distribution function (CDF) of the pre-clipped signal to get a weighted estimate of the available signal power within the clipped PAPR. The model also takes into consideration the clipping noise effects due to limited linearity of the optical source during electrical-to-optical conversion of baseband OFDM signal. Using this model, the paper aims to arrive at a realistic estimate of the system behavior in terms of bit error rate, electrical power-efficiency and spectral efficiency. Using theoretical simulation results, for a given set of operating parameters viz., signal power, PAPR, bias-scaling factor, modulation order and sub-carrier count, the paper examines the trade-offs involved in optimizing the performance metrics over appropriate dynamic range of the DCO-OFDM transmitter.

Gain flatness of erbium-doped fiber amplifier (EDFA) is an important aspect to support high speed multimedia applications for smart devices, cloud computing, big data analysis and high definition television (HDTV) as it achieves equal power for all dense wavelength division multiplexing (DWDM) channels. In this paper, we compare 32 and 64 channels 10 Gbps DWDM system using hybrid EDFA+ Ytterbium-doped silica fiber amplifier (YDFA) in C + L band for 0.4, 0.8 and 1.6 nm wavelength spacing along with FBG for gain flattening. The system performance has been analyzed in terms of optical signal to noise ratio and spectral gain fluctuation observed from the optical power spectrums. It is observed that YDFA although extends the amplification window of EDFA from 1530 to 1610 nm (C to L band), but gain fluctuates over the operating wavelength range. Gain flatness is enormously improved (5–10 dB) by adding FBG as a gain flattening filter to the hybrid (EDFA+YDFA) amplifier. It is found that as the channel spacing decreases (from 1.6 to 0.4 nm) and the number of channels increases (from 32 to 64), the gain reduces due to inter-channel crosstalk and four wave-mixing effect.

Atmospheric turbulence induced fading may severely impair free-space optical (FSO) communication systems, affecting the quality of the propagated laser beam and lead to significant performance degradation. Recent research works reveal that performance can be improved by using orthogonal FDM. In this paper, an analytical approach is presented to evaluate the bit error rate performance of an OFDM FSO link with optical intensity modulation and coherent homodyne receiver taking into consideration the effect of strong atmospheric turbulence. The turbulence effect is modeled as gamma-gamma distribution and the performance results are evaluated in terms of average CNR and BER. Power penalty suffered by the system due to the effect of turbulence at a given BER is evaluated for several system parameters viz. link distance, turbulence parameter, local oscillator power etc. It is noticed that effect of turbulence can be significantly reduced by increasing the number of OFDM subcarrier. For example, power penalty for BER of 10 –9 at a link distance of 3,600 m is 6 dB when number of subcarrier is 4 and can be reduced to 0.5 dB by increasing the number of subcarrier to 64. In addition, by utilizing coherent optical receiver and synchronous demodulation at the receiving end, we have introduced local oscillator (LO) for both Optical and RF state which have ability to track the signal’s phase changes over time relative to the LO’s phase and helps the system to remain stable.

In this paper, dispersion decreased profiled tapered fiber is designed whose dispersion characteristics and soliton propagation is investigated numerically using Darboux transformation. The result reveals that solitons pulse gets compression as it propagates along the length of the tapered region.

In this paper, new spectral optical codes based on the construction parity check matrix of LDPC codes were designed and implemented in an optical code-division multiple access communication system. Two types optical family codes can be obtained with respectively a cross correlation of λ c = 0 {\lambda _c} = 0 and λ c = 1 {\lambda _c} = 1 . In each case, the codes can either be decoded using the direct detection or the balanced detection. Performance was evaluated by referring to the Q factor, the bit error rate and the eye pattern diagrams using Optisystem 9.0.

The congestion in the radio frequency spectrum has posed a serious challenge for mobile service providers. Radio-over-free space optics (Ro-FSO) technology has been considered as a front runner to deal with the problem of spectrum congestion and to provide future generation high-capacity wireless networks. This work proposes designing and numerical analysis of differential phase shift keying (DPSK) modulation-based 20   Gbit/s–40 GHz hybrid mode division multiplexing-radio-over-free space optics (MDM-Ro-FSO) link up to 40 km transmission range under clear weather. Quality Factor (Q Factor), log of bit error rate (BER), signal to noise ratio (SNR), and received power are the key metrics used to probe the proposed system performance. The impact of increasing divergence angle and different fog weather conditions on the proposed system performance is also numerically evaluated. Further, the decomposition analysis of different spatial modes at the receiving unit is carried out in this work.