Volume 40, Issue 3 -

In this paper we have examined the performances of 180×10 Gbps super dense wavelength division multiplexing (SD-WDM) system using the RAMAN–thulium-doped tellurite fiber amplifier (TDTFA) hybrid optical amplifier (HOA) with the channel spacing of 50 GHz in S+C+L band. Accepted rating flattened gain of 39.21 dB with the noise figure less than 5 dB is archived with the dual-pumping ( power level of 500 mW at 980 nm and at 1100 nm for RAMAN optical amplifier and similar, power level of TDTF amplifier is set to 500 mW and 350 mW at 1150 nm) technique. The effect of the proposed hybrid amplifier is evaluated in terms of gain and noise figure without using any coast effective technique. The outcome from the proposed model is also compared here with the existing optical amplifier.

We employ ABCD matrix formalism in order to investigate the coupling optics involving laser diode to single-mode circular core parabolic index fiber excitation via upside-down tapered hyperbolic microlens on the fiber tip. Analytic expressions for coupling efficiencies both in absence and in presence of transverse and angular mismatches are formulated. The concerned investigations are made for two practical wavelengths namely 1.3 µm and 1.5 µm. The execution of the prescribed formulations involves little computation. It has been found that the wavelength 1.5 µm is more efficient in respect of coupling. It is also seen that the present coupling device at both the wavelengths shows more tolerance with respect to angular mismatch. As regards tolerance with respect to transverse mismatch, the result is poor at both the wavelengths used. Consequently, it is desirable that designers should not to exceed transverse mismatch beyond 1 μm.

This paper presents the impact of optical coupler parameters like length of coupling region, spacing between the coupling region and materials profile on the performance of optical directional coupler (ODC) based on Surface plasmon polaritons (SPPs). On photonic chips a directional coupler is an essential photonic device used to design the various mixers, balanced power amplifiers, modulators, measurements system, circularly polarized antennas and beam-forming networks. It is observed that the least excess loss (0.2 dB) is achieved at 1550 nm input transmission wavelength using titanium dioxide (TiO 2 ) profile material with value of coupling length (8.58 µm), spacing between the two coupling slits (1.55 µm) and input transmission power (0.1 W/m). The received optical power at both output port of ODC is varied due to the variations in spacing between the two couplings slits and length of coupling region.

We have investigated nonlinear properties and optically diode action capability in graded nonlinear one-dimensional photonic crystals-made up of graded index and thickness layers using transfer matrix method (TMM). We have considered the efficacy of index and thickness gradient parameters on the nonlinear properties in right to left and left to right optical pumping. It is found that the difference between the up-switch threshold input intensities of the left to right and right to left impinging lights and optical bistability (OBS) threshold can be tunable with thickness gradation parameter and index gradation parameter, respectively. Proposed structure can be useful in designing low threshold and high speed optical diode, switches and rectifiers.

A design of all-optical half-subtractor (AOHS) is presented based on two-dimensional (2-D) photonic crystal (PhC) waveguides without using optical amplifiers and nonlinear materials. It is an essential component of various photonic integrated circuits. The design of AOHS circuit is based on beam interference principle, using square lattice of Y-shaped and T-shaped waveguides with silicon dielectric rods in air substrate. It is validated through finite-difference time-domain and using MATLAB simulations.

With the rapid development of multi-source optical multicast application, the wavelength division multiplexing (WDM) with limited number of wavelength channels is facing with the new challenge of bandwidth shortage. Optical multicast adopting network coding can improve the bandwidth utilization, but optical network coding needs to increase optical storage and computation overhead in WDM optical network. For reducing the number of optical network-coded links, an improved adaptive genetic algorithm (IAGA) is proposed to minimize the number of network-coded links for multicast. By designing the maximization difference crossover operation, IAGA can guarantee the diversity of population and avoid individuals from falling into a local optimal. By adaptively adjusting the crossover probability, IAGA makes the population diverse at the beginning stages and makes the excellent individuals remain in a stable condition. Compared with other algorithms, the simulation result shows that the proposed algorithm has fastest convergence speed, which means that it takes the shortest time to find the minimum numbers of coded link solutions.

This article presents investigation for all optical multilogic function in the proposed single photonic network. Logic operations the AND, OR, NOR, XNOR, NOT, Buffer, AˉB$\bar AB$, ABˉ$A\bar B$ have been executed simultaneously at higher data rate for nonreturn-to-zero pattern on the different C-band wavelengths. Numerous logic functions have been accomplished by the optical multiplexer, couplers exploiting SOA nonlinearities, which are else contemplated as cons, if SOA is exercised as an amplifying device. Numerical simulation for parameters as bias voltage of the modulator, nonreturn-to-zero, return-to-zero, Mach-Zehnder type modulation formats, data rate and numerous drives as on-off-ramp, raised cosine, on-off-exp, on-off in conjunction with key design features length, width, thickness of SOA have been aptly explored in terms of the extinction factor. Investigations depicted good performance for the nonreturn-to-zero format. Accordingly, output patterns for the multilogic executions have been verified at 10 Gbps data rate with nonreturn-to-zero pattern. The proposed schematic could be one of the feasible means for the design of upcoming composite photonic computation higher data rate links, as it excludes need for most expensive optoelectronic translations.

The internet traffic is increasing exponentially with cloud services. This demands high and efficient data center networks (DCNs). Current DCNs are equipped with electronic counter parts which consumes high power to provide the cloud services. Optical interconnection network (OIN) architectures provide high scalability, low latency, high throughput and low power consumption. This paper presents a study of the OIN architectures as the future requirements of the DCNs are the need for high scalability and low latency. This paper also presents a comparative study of their average latency and scalability.

In this paper, fallacious node algorithm is formulated for performance enhancement of an optical-burst-switching (OBS) network. With the procedural and observational analysis, we have demonstrated that the blocking probability is extremely unnoticeable, during a call establishment, while collectively discarding the faulty nodes from the selected paths. There may be distinguishing values of blocking probability because of random value of congestion on each path. The blocking probability is restrained so as not to be more than 10 % on several values on traffic and congestion. The blocking probability diminishes and becomes imperceptible with the incorporation of fallacious node algorithm and subsequently the performance of optical network is highly aggrandized. Thus the fallacious node algorithm manifests incredible prospects for optical networks as the key features such as the accessibility; sustainability and reliability of the network are highly appreciated and upgraded.

A novel analytical approach is presented to evaluate the bit error rate (BER) performance of a multi-wavelength optical code division multiple access (MW-OCDMA) free space optical (FSO) system using optical domain encoder and sequence inverse keying (SIK) balanced photodetector direct detection receiver taking the effect of pointing errors into considerations. The analysis is carried out to find the expression for the signal, multi-access interference (MAI) and crosstalk at the output of the SIK receiver in presence of pointing error. The BER performance results are evaluated for different values of standard deviation of pointing error, code length, number of simultaneous user and other system parameters. It is found that, MW-OCDMA system offers improved BER performance over single wavelength OCDMA FSO system. However, the performance of an MW-OCDMA system is degraded due to the effect of pointing error between the laser transmitter and optical receiver and the system suffers significant power penalty at a given BER of 10 −9 . The penalty is found to be 11.0 dB, 24.0 dB and 30 dB for jitter standard deviation of 1.3, 1.8 and 2.5 respectively when code length is 512 and number of user is 8 for number of wavelength 8. Further, the penalty can be greatly reduced by increasing the code length for a given number of user and number of wavelength.

A full duplex WDM-PON system is designed and demonstrated based on carrier reusing scheme and by employing differential quadrature phase shift keying (DQPSK) modulation in downlink and inverse return-to-zero modulation in the uplink to transmit 40 Gbps and 20Gbps data-rate respectively. Three Mach-Zehnder modulators are used sequentially to realize the 67 % carrier suppressed return to zero (CS-RZ) DQPSK modulation in the downlink transmission. Very low bit error rate values @10 ‒9 and clear eye-diagrams are observed over a 40 km single-mode-fiber transmission in our proposed full-duplex configuration.

The paper investigates the performance of DWT (Discrete Wavelet Transform) and CWT (Continuous Wavelet Transform) techniques based on On – Off keying modulation (OOK) for reduced BER with increase in SNR in optical wireless system. In this work, the effects of Inter-symbol Interference (ISI) and light interference on Artificial Neural Network (ANN) receiver are analyzed and reported. In proposed optical wireless system the On- Off Keying (OOK) modulation is used at receiver to analyze BER and SNR. It is further concluded that error prospect in the received signal relates to the noise level, which is given in terms of obtained SNR value.

Spectral amplitude coding optical code division multiple access (SAC-OCDMA) is a promising innovation for burst and asynchronous environment. This paper endeavors to analyze the efficacy of the proposed optimum SAC-OCDMA system by utilizing enhanced double-weight (EDW) code for six users operating at a bit rate of 60 Gb/s (10×6 Gb/s). Also, an algorithm is designed for EDW code with mapping technique for any weight that can be greater than two. The EDW code is analyzed for bit error rate (BER) and Q-factor using direct detection technique. Further, the system is compared with three dispersion compensating techniques (pre, post and symmetrical). The results indicate that by using symmetrical compensation the maximum usable distance increases to more than twice as compared to without compensation for the targeted BER (10 −9 ), whereas by using p- and post-compensation the BER value increases to 10 −13 as compared to without compensation whose BER value is 10 −5 . The comparison results show acceptable performance improvement.

In this article, diverse dispersion compensating techniques are demonstrated and also examined their performance in the presence of nonlinearites at different data rates in between 2.5 and 20 Gbps. Dispersion compensation formats such as pre-compensation, post-compensation, hybrid (symmetrical) compensation, Fiber Bragg grating (FBG) and optical phase conjugation (OPC) are used in single-channel light-wave system. The performance is evaluated on the behalf of different parameters such as Q value, Bit error rate (BER) and eye patterns. It is observed that in dispersion compensation, hybrid compensation format gives better results than the other compensation formats. It is also observed that hybrid compensation format is suitable for high data rates up to 20 Gbps while pre- and post-compensation gives better results up to 15 Gbps and FBG and OPC formats covered better results up to 10 Gbps.

This work is focused on transmission of 10 Gbps data and 60 GHz millimeter signal over 60 km optical fiber for 5 G applications. 5 G networks generally use millimeter range of frequencies. Radio over fiber is revolutionary technology to transmit radio signals over optical fiber. Furthermore, the comparative analysis of non-return to zero (NRZ) and return to zero (RZ) encoding schemes is also done. The results are reported in terms of Q-factor, bit error rate and eye diagrams. The reported results show the successful transmission of high speed 10 Gbps data and 60 GHz millimeter signal over 60 km optical fiber.

Radio-over-fiber (RoF) is revolutionary technique to transmit radio signals over optical fiber. It can be also suitable to distribute wireless local area networks (WLANs) due to its low-cost implementation. WLANs generally operate on 5 GHz radio signals. Thus in this work, four high speed radio channels, each carrying 2.5   Gbps data and 5 GHz radio signal, are transmitted by incorporating alternate mark inversion (AMI) scheme and wavelength division multiplexing (WDM) scheme over optical fiber having span of 50   km. The performance of proposed AMI-WDM-RoF transmission system is reported in terms of Q-factor, bit error rate, signal-to-noise ratio, total received power and eye diagrams.

Presently, research activities are geared towards optical switching technologies that involve all-optical switching, without transformation from optical domain to electronic domain. However, blocking in these systems is a huge problem due to the absence of appropriate optical buffers. In this paper, we propose an optical buffer design based on SOA and DCFBG (dispersion compensation fiber Bragg grating) for contention resolution in all-optically switched networks, and hence improved the power performance of the existing design.

Free space optical (FSO) communication links have recently received lot of attention as high bandwidth and cost-effective access technique. However, the transmission medium, i. e. atmosphere, itself is a major spoilsport factor as atmospheric turbulence may lead to fading. The legacy of spatial diversity techniques which have already proven their worth as effective mechanism to counter channel fading in radio links has also been extended to FSO links in this paper. A mathematical model to evaluate error rate performance of FSO links over strong turbulent conditions using gamma–gamma and double-generalized gamma channel model for different modulation techniques has also been included. It was observed that higher modulation techniques such as binary phase shift keying (BPSK) and differential phase shift keying (DPSK) allow superior error performance as compared to on–off keying (OOK) links, and this performance further enhances with incorporation of spatial diversity techniques. However, across different diversity options, explained in this paper, BPSK–MISO links were the best choice for turbulent conditions.

In this paper, we study the performance improvement of free space optical (FSO) communication system with spatial diversity techniques employing hybrid pulse position modulation-binary phase shift keying-subcarrier intensity modulation (PPM-BPSK-SIM). The involvement of multiple photo-detectors in diversity based FSO systems offers an effective way to overcome scntillation. In this paper, we have simulated the bit error rate (BER) with respect to different parameters like average SNR, link distance at various weather conditions. The simulation results are verified in Matlab environment with the mathematical analysis. The simulation results show that higher order single input multiple output (SIMO) system achieves better BER performance and hybrid PPM-BPSK-SIM has significant improved performance than the common modulation schemes like PPM, BPSK-SIM.

Different modulation formats for 64×20-GB/s dense wavelength division multiplexed (DWDM) system has been compared and simulated using Optsim. Various performance parameters including Q -factor, bit error rate, jitter, eye opening & eye closure are observed and analyzed. It is reported that RZ Soliton format is a better choice among the tested formats. Also, for the proposed system, minimum channel spacing should be 50 GHz.

In this paper, we investigate the performance of a decode-and-forward relayed mixed radio frequency-free space optical (RF-FSO) dual-hop link. The transmitter to receiver link’s first-hop is a RF channel and the second-hop is a FSO channel. The RF link experiences long-term shadowing and short-term multi-path fading effects, while the FSO channel suffers atmospheric turbulence fading, path loss, and pointing error-induced misalignment fading. The performance of the system is analyzed considering the impact of these parameters. We model the RF link by generalized- K fading distribution and the atmospheric turbulence over the FSO link by the gamma–gamma fading. The expressions in closed form for the outage probability, symbol error rate for the system employing q$q$-ary PSK modulation schemes, and the channel capacity of the system are derived. The obtained numerical results are also depicted by numerical plots.