Volume 38, Issue 3 -

We demonstrate higher saturation powers for Raman and fiber optical parametric-cascaded amplifier (FOPA). Analysis of Raman-parametric amplifier cascade has been done for saturated gain regime. The second-order dispersion analysis of cascaded amplifier has been in the saturation region. Comparisons have been made with conventional parametric amplifiers in both single pump and dual pump. Results show 14 dB gain enhancement in saturation power for proposed cascade. Uniform gain for careful optimized values of dispersion has been observed in saturated region with minimum gain value enhanced by 10 dB than dual-pump parametric amplifier. This is important for exploring Raman–FOPA hybrid amplifiers for high-power, long-haul wavelength division multiplexed (WDM) systems.

This paper investigates the performance of an optical system based on optimized semiconductor optical amplifier (SOA) at 160 Gbps with 0.8 nm channel spacing. Transmission distances up to 280 km at –30 dBm input signal power and up to 247 km at –32 dBm input signal power with acceptable bit error rate (BER) and Q -factor are examined. It is also analyzed that the transmission distance up to 292 km has been covered at –28 dBm input signal power using Dispersion Shifted (DS)-Normal fiber without any power compensation methods.

A simple and low-cost scheme is proposed for reducing the distortions in the coherent optical orthogonal frequency-division multiplexing (CO-OFDM) system. The total wireless channel noise and the distortions in the receiver can be considered as an additive white Gaussian noise model and all distortions can be reduced using maximum likelihood sequence estimation (MLSE) equalizers. The performance of the CO-OFDM is analyzed for different fiber lengths and laser powers. Results show that the MLSE-equalized system can outperform with a higher Q -factor of 8 dB than conventional CO-OFDM system.

In recent years, free-space optics (FSO) communication links have gained importance due to the availability of high data transmission rates and channel bandwidth. Although FSO links have many advantages, it also suffers from many limitations, which degrade the performance of the communication link. In this paper, the performance of an FSO link has been evaluated under fog weather condition as it severely degrades the quality of the received signal. One of the most important techniques to improve the quality of received signal in an FSO link is by using an array of photodetectors at the receiver end. In this paper, the performance evaluation of an FSO link has been performed using an array of photodetectors at the receiver end using OPTISYSTEM simulation software. The performance has been analyzed by evaluating Q -factor, bit error rate (BER), and signal-to-noise ratio (SNR) of the received signal.

A semi-analytical technique, effective index-based matrix method (EIMM), has been applied to determine the coupling length of continuous wave UV-written directional coupler for different gaps between the waveguides as well as the pure bending loss and transition loss of S-curved waveguides estimated to optimize the transition length ( L ) and lateral offset ( h ). The refractive index profiles of the directional coupler were computed by solving the heat flow equation on the surface of LiNbO 3 crystal, and used as input to EIMM.

In this paper, a compact low-cost simple-to-fabricate demultiplexer is proposed for coarse wavelength division multiplexing (CWDM). The device consists of two layers of the same semiconductor material: the first layer is homogeneous medium with a given refractive index n2${n_2}$, while the second layer is an inhomogeneous medium, where its refractive index is graded according to a creation profile. The proposed design exploits the ray’s spatial shift that results from material dispersion as difference wavelengths propagate through the structure. Through analytical analysis and numerical evaluation, we investigate the effects of the various design parameters on the amount of achieved spatial shift between the adjacent wavelengths and the size of the device. The results show promising results for four- and eight-channel devices operating on the standard CWDM wavelength grid.

Waveguide dispersion can be tailored but not the material dispersion. Hence, the total dispersion can be shifted at any desired band by adjusting the waveguide dispersion. Waveguide dispersion is proportional to d2βdk2${{{d^2}\beta} \over {d{k^2}}}$ and need to be computed numerically. In this paper, we have tried to compute analytical expression for d2βdk2$ {{{d^2}\beta} \over {d{k^2}}}$ in terms of β$ \beta $ for the case of an asymmetric planar slab. To compute d2βdk2${{{d^2}\beta} \over {d{k^2}}}$ accurately with numerical technique, β$\beta $ should be accurate enough up to ≈10−5$ \approx {10^{- 5}}$ decimal point. This constraint sometimes generates the error in calculation of waveguide dispersion. To formulate the problem we will use the graphical method. Our study reveals that we can compute the waveguide dispersion enough accurately for various modes by knowing –β$\beta $ only.

This paper investigates the number of nodes supported in bus and ring network topologies based on bias current of semiconductor optical amplifier (SOA) at 10 Gb/s. It is found that in bus topology, maximum 91 nodes are supported for 400 mA bias current of SOA at –30 dBm signal input power. In ring topology, more than 100 nodes are supported for 400 mA current of SOA. It is also found that for 100 mA current, 28 nodes are supported in bus topology but in ring topology maximum supported nodes are 39. The number of supported nodes increases with increase in bias current of SOA.

For improving the survivability and energy saving of multi-rate multicast, a novel energy-saving path-shared protection based on diversity network coding (EPP-DNC) for multi-rate multicast in wavelength division multiplexing (WDM) mesh networks is proposed in the paper. In the EPP-DNC algorithm, diversity network coding on the source node for multi-rate multicast is adopted to reduce the coding energy consumption by avoiding network coding on the network’s intermediate nodes. To decrease the transmission energy, shortest path shared based on heuristic is proposed to transmit the protection information for the request. To provision request’s working paths efficiency, the working paths are routed on the preselected P-cycles with minimum required links and minimum energy consumption. Simulation results show that the proposed EPP-DNC can save energy consumption and improve bandwidth utilization.

Free Space Optics (FSO) link exploits the tremendous network capacity and is capable of offering wireless communications similar to communications through optical fibres. However, FSO link is extremely weather dependent and the major effect on FSO links is due to adverse weather conditions like fog and snow. In this paper, an FSO link is designed using an array of receivers. The disparity of the link for very high attenuation conditions due to fog and snow is analysed using aperture averaging technique. Further effect of aperture averaging technique is investigated by comparing the systems using aperture averaging technique with systems not using aperture averaging technique. The performance of proposed model of FSO link has been evaluated in terms of Q factor, bit error rate (BER) and eye diagram.

Intersymbol interference and attenuation of signal are two major parameters affecting the quality of transmission in Free Space Optical (FSO) Communication link. In this paper, the impact of these parameters on FSO communication link is analysed for delivering high-quality data transmission. The performance of the link is investigated under the influence of amplifier in the link. The performance parameters of the link like minimum bit error rate, received signal power and Quality factor are examined by employing erbium-doped fibre amplifier in the link. The effects of amplifier are visualized with the amount of received power. Further, the link is simulated for moderate weather conditions at various attenuation levels on transmitted signal. Finally, the designed link is analysed in adverse weather conditions by using high-power laser source for optimum performance.

Higher spectral efficiency and greater data rate per channel are the most cost-effective strategies to meet the exponential demand of data traffic in the optical core network. Multilevel modulation formats being spectrally efficient enhance the transmission capacity by coding information in the amplitude, phase, polarization or a combination of all. This paper presents the design architecture of a 32-channel dense wavelength division multiplexed (DWDM) system, where each channel operates with multi-level phase modulation formats at 40 Gbps. The proposed design has been simulated for 50 GHz channel spacing to numerically compute the performance of both differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) modulation formats in such high-speed DWDM system. The transmission link is analyzed with perfect dispersion compensation and also with under-compensation scheme. The link performance in terms of quality factor ( Q ) for varying input powers with different dispersion compensation schemes has been evaluated. The simulation study shows significant nonlinear mitigation for both DPSK- and DQPSK-based DWDM systems up to 1,000 km and beyond. It is concluded that at higher power levels DQPSK format having a narrower spectrum shows better tolerance to dispersion and nonlinearities than DPSK format.

In this paper, we study the performance of a next-generation cellular backhaul network that is based on a hybrid architecture using radio-over-fiber (RoF) and millimeter-wave (MMW) techniques. We develop a mathematic model and comprehensively analyze the performance of a MMW/RoF-based backhaul downlink under the impacts of various physical layer impairments originated from both optical fiber and wireless links. More specifically, the effects of nonlinear distortion, chromatic dispersion, fading, and many types of noises including shot noise, thermal noise, amplifier noise, and relative intensity noise are investigated. The numerical results show that the nonlinear distortion, fiber dispersion, and wireless fading are key factors that limit the system performance. Setting the modulation index properly helps minimize the effect of nonlinear distortion while implementing dispersion shifted optical fibers could be used to reduce the impact of dispersion and as a result, they can improve the bit-error rate. Moreover, it is also verified that, to mitigate the effect of multipath fading, remote radio heads should be located as near the remote antenna units as possible.

Crosstalk effects in wavelength multiplexed subcarrier multiplexing radio-over-fiber (RoF) transmission system due to cross phase modulation (XPM) are investigated in the present paper. The crosstalk has been evaluated including the effects of dispersion along with its higher order terms (HOD) and walk-off parameter for different modulation frequencies and transmission distances. Results show that the crosstalk level can be as high as –43 dB after transmission over a 25 km of fiber with two wavelengths and 15 dBm per wavelength of transmitted power. An increment of 7 dB is observed with increase in walk-off parameter and 5 dB with increase in dispersion parameter. The crosstalk also depends upon spacing between optical wavelengths. Simulative investigation shows that increase in separation between wavelengths degrade the overall system performance, which limits the number of optical wavelengths that can be used in transmission system.

Inter-satellite communication links are very crucial between satellites orbiting around the earth in order to transmit information between them and also for the purpose of data relaying from one satellite station to other stations and ground stations. Inter-satellite optical wireless communication (IsOWC) links involve the application of optical wireless signals as compared to radio frequency signals used in traditional satellite communication systems. One of the major problems leading to the performance degradation of IsOWC link is the signal degradation due to satellite vibrations also known as pointing errors. In this paper, the performance of an IsOWC communication link has been investigated for different system parameters such as data transmission rates, antenna aperture diameter, transmission power levels, operating wavelength and responsivity of photodiode by analyzing Q -factor, signal-to-noise ratio (SNR), and total power of received signal to mitigate the effects of signal degradation of received signal due to satellite vibrations.

The current study examines the fiber optic connectivity from Chinese boundary to Rawalpindi and proposes a novel technique for carrying large capacity triple play services across China Pakistan economic corridor (CPEC). With the help of this technique, various wavelength data services can be extended to Pakistan, which can decrease the low bandwidth, poor connectivity and low speed problems of data transfer in Pakistan. This study contributes toward the existing literature in a way that this novel technique of data transmission not only relaxes the laying of fiber optic cable but also reduces the total cost of the project. The proposed technique proposes the deployment of optical frequency comb technique for 820 km CPEC route which could support 4 Tbps data. From the perspective of time energy consumption, the assessment suggests that the laying of fiber optic cable in CPEC is feasible with the existing route at the lowest cost between the two sovereign countries.

Understanding the nonlinear characteristics of the optical link is essential to exploit it effectively. Even though various expensive experimental investigations have been conducted in the literature, this paper presents a simulation model to understand the nonlinear relationship that exists between the laser intensity, the nonlinear regime of the fiber and the error probability. Firstly, an analysis model is introduced to observe the numerical relevance between the aforesaid parameters. The analysis results are graphically portrayed to determine the relevance effectively. Secondly, an optical-neural model is adopted based on the feed-forward neural network architecture to relate the parameters mathematically, without hard technical constraints. The model is experimented for the fair estimation of the required laser intensity, which achieves the least desired error probability, when the nonlinear regime of the fiber is known.

In this paper, 1 Gb/s non-linear optical code division multiple access system have been simulated and modeled. To reduce multiple user interference multi-diagonal (MD) code which possesses the property of having zero cross-correlation have been deployed. The MD code shows better results than Walsh-Hadamard and multi-weight code under the nonlinear effect of four-wave mixing (FWM) and cross-phase modulation (XPM). The simulation results reveal that effect of FWM reduces when MD codes are employed as compared to other codes.