Volume 39, Issue 2 -

In this paper, simulative analysis and performance comparison of different EDFA (Erbium-doped fiber amplifier) configurations in a 10 Gbps inter-satellite optical wireless communication (IsOWC) link have been reported for a 5,000 km long link and 1,550 nm operating wavelength. The results show that system in which both pre-amplifier and booster amplifier stages are implemented simultaneously outperforms systems with only pre-amplifier and booster amplifier stage. From the results, it can be seen that by deploying a transmission power level of 15 dBm, a link distance of 9,600 km can be achieved with a quality factor of 6.01 dB and BER (Bit error rate) of 1.07×10−9$$1.07 \times {10^{- 9}}$$. Also, in this paper, the performance of an 8×7 Gbps WDM-IsOWC link has been reported. The results show that by using both EDFA pre-amplifier and booster amplifier stages, a link distance of 8,000 km for each channel is achievable with desired performance levels (Q≥6 and BER≤10−9$${10^{- 9}}$$). Also, the effect of channel spacing on the performance of WDM-IsOWC link is investigated. The results show that the received signal has acceptable performance levels when the channel spacing is 100 GHz but when the channel spacing is reduced to 80 GHz, the quality of the received signal degrades and link distance decreases.

In this paper, we present new tap configurations of a feedforward equalizer to mitigate mode coupling in a 60-Gbps 18-channel mode-wavelength division multiplexing system in a 2.5-km-long multimode fiber. The performance of the equalization is measured through analyses on eye diagrams, power coupling coefficients and bit-error rates.

A CO-OFDM system combines the advantages of both coherent detection and OFDM modulation for future high speed fiber transmission. In this paper, we propose an I/Q modulation technique using dual-drive MZMs for high rate 10 Gb/s CO-OFDM system. The proposed modulator provides 10.63 dBm improved optical spectra compared to a single dual-drive MZM. The simulation results in terms of BER and Q factor are quite satisfactory upto a transmission reach of 3,000 km and that to without making use of any dispersion compensation. A BER of about 8.03×10 −10 and 15.06 dB Q factor have been achieved at −10.43 dBm received optical power.

The optical switching phenomenon enhances the speed of optical communication systems. It is widely used in the wavelength division multiplexing (WDM). In this work, an optical OR gate is proposed using the Mach-Zehnder interferometer (MZI) structure. The detailed derivation of mathematical expression have been shown. The analysis is carried out by simulating the proposed device with MATLAB and Beam propagation method.

In this work, photonic method of generating the millimeter waves has been done based on Brillouin scattering effect in optical fiber. Here different approaches are proposed to get maximum frequency shift in mm-wave region using only pumps, radio signals with Mach-Zehnder modulator. Moreover for generated signal validation, signals modulated and send to both wired and wireless medium in optical domain. It is observed that maximum shift of 300 GHz is realized using 60 GHz input sine wave. Basically a frequency doubler is proposed which double shift of input frequency and provide better SNR. For the future generation network system, the generation of millimeter waves makes them well reliable for the transmission of the data.

Modal dispersion is seen as the primary impairment for multimode fiber. Mode division multiplexing (MDM) is a promising technology that has been realized as a favorable technology for considerably upsurges the capacity and distance of multimode fiber in conjunction with Wavelength Division Multiplexing (WDM) for fiber-to-the-home. This paper reveals the importance of an equalization technique in conjunction with controlling the modes spacing of mode division multiplexing-wavelength division multiplexing of Laguerre-Gaussian modes to alleviate modal dispersion for multimode fiber. The effects of channel spacing of 20 channels MDM-WDM were examined through controlling the azimuthal mode number and the radial mode number of Laguerre-Gaussian modes. A data rate of 40Gbit/s was achieved for a distance of 1,500 m for MDM-WDM.

An analytic design-oriented model of microwave optical links has been developed. The core of the model is the non-linear and noise model of a Mach-Zehnder LiNbO 3 interferometer. Both a 100 MHz–20 GHz link and a linearized microwave link, comprising an auxiliary modulator, have been designed and prototyped by using the model.

Free space optical (FSO) communication is a wireless communication technology in which data is transferred from one point to another through highly directed beam of light. The main factors that limit the FSO link availability is the local weather conditions. It guarantees the potential of high bandwidth capacity over unlicensed optical wavelengths. The transmission medium of FSO is atmosphere and is significantly affected by the various weather conditions such as rain, fog, snow, wind, etc. In this paper, the modulation techniques under consideration are RZ, NRZ and CSRZ. Analysis is carried out regarding Q-factor with respect to varying distance, bit rates and input laser power.

In this work, we analyze the outage and error performance of a one-way inter-relay assisted free space optical link. The assumption of the absence of direct link between the source and destination node is being made for the analysis, and the feasibility of such system configuration is studied. We consider the influence of path loss, atmospheric turbulence and pointing error impairments, and investigate the effect of these parameters on the system performance. The turbulence-induced fading is modeled by independent but not necessarily identically distributed gamma–gamma fading statistics. The closed-form expressions for outage probability and probability of error are derived and illustrated by numerical plots. It is concluded that the absence of line of sight path between source and destination nodes does not lead to significant performance degradation. Moreover, for the system model under consideration, interconnected relaying provides better error performance than the non-interconnected relaying and dual-hop serial relaying techniques.

Backward pumping in fiber Raman amplifiers has been investigated in this paper in terms of on-off Raman gain, noise figure and optical signal-to-noise ratio. The results exhibit that with four first-order pumps and one second-order pump scheme can be employed to achieve 8.2 dB noise figure in 64 channel fiber optic communication system. It has also been reported that 2.65 dB gain ripple, 0.87 dB noise figure tilt and 2.02 dB OSNR tilt can be attained with the second-order pumping in fiber Raman amplifiers. The main advantage of the scheme is that only 50 mW second-order pump shows appreciable improvement in the system performance. It shows that further increase in first-order and second-order pump powers increase system noise implications.

The main task of optical code division multiple access (OCDMA) system is the detection of code used by a user in presence of multiple access interference (MAI). In this paper, new method of detection known as XOR subtraction detection for spectral amplitude coding OCDMA (SAC-OCDMA) based on double weight codes has been proposed and presented. As MAI is the main source of performance deterioration in OCDMA system, therefore, SAC technique is used in this paper to eliminate the effect of MAI up to a large extent. A comparative analysis is then made between the proposed scheme and other conventional detection schemes used like complimentary subtraction detection, AND subtraction detection and NAND subtraction detection. The system performance is characterized by Q-factor, BER and received optical power (ROP) with respect to input laser power and fiber length. The theoretical and simulation investigations reveal that the proposed detection technique provides better quality factor, security and received power in comparison to other conventional techniques. The wide opening of eye in case of proposed technique also proves its robustness.

A new family of two-dimensional optical hybrid code which employs zero cross-correlation (ZCC) codes, constructed by the balanced incomplete block design BIBD, as both time-spreading and wavelength hopping patterns are used in this paper. The obtained codes have both off-peak autocorrelation and cross-correlation values respectively equal to zero and unity. The work in this paper is a computer experiment performed using Optisystem 9.0 software program as a simulator to determine the wavelength hopping/time spreading (WH/TS) OCDMA system performances limitations. Five system parameters were considered in this work: the optical fiber length (transmission distance), the bitrate, the chip spacing and the transmitted power. This paper shows for what sufficient system performance parameters (BER≤10−9, Q≥6) the system can stand for.

The impairment-aware routing and wavelength assignment algorithm with probe flow (P-IA-RWA) can make an accurate estimation for the transmission quality of the link when the connection request comes. But it also causes some problems. The probe flow data introduced in the P-IA-RWA algorithm can result in the competition for wavelength resources. In order to reduce the competition and the blocking probability of the network, a new P-IA-RWA algorithm with segmentation monitoring-control mechanism (SMC-P-IA-RWA) is proposed. The algorithm would reduce the holding time of network resources for the probe flow. It segments the candidate path suitably for the data transmitting. And the transmission quality of the probe flow sent by the source node will be monitored in the endpoint of each segment. The transmission quality of data can also be monitored, so as to make the appropriate treatment to avoid the unnecessary probe flow. The simulation results show that the proposed SMC-P-IA-RWA algorithm can effectively reduce the blocking probability. It brings a better solution to the competition for resources between the probe flow and the main data to be transferred. And it is more suitable for scheduling control in the large-scale network.

Free Space Optics (FSO) also known as Optical Wireless Communication (OWC) is a communication technology in which free space/air is used as the propagation medium and optical signals are used as the information carriers. One of the most crucial factors which degrade the performance of FSO link is the signal attenuation due to different atmospheric weather conditions such as haze, rain, storm, and fog. In this paper, an improved performance analysis of a 2.5 Gbps FSO link under rain conditions has been reported using Erbium-Doped Fiber Amplifier (EDFA) as a pre-amplifier. The results show that the maximum link distance for an FSO link under rain weather conditions with acceptable performance levels (Q ∼6$$\sim6$$ and BER ≤10−9)$$ \le {10^{- 9}})$$ in the absence of EDFA pre-amplifier is 1,250 m which increases to 1,675 m with the use of EDFA pre-amplifier.

Weak atmospheric turbulence condition in an optical wireless communication (OWC) is captured by log-normal distribution. The analytical evaluation of average bit error rate (BER) of an OWC system under weak turbulence is intractable as it involves the statistical averaging of Gaussian Q-function over log-normal distribution. In this paper, a simple closed form approximation for BER of OWC system under weak turbulence is given. Computation of BER for various modulation schemes is carried out using proposed expression. The results obtained using proposed expression compare favorably with those obtained using Gauss-Hermite quadrature approximation and Monte Carlo Simulations.