Volume 40, Issue 1 -

In this paper, dual-order bidirectional pumping schemes of distributed fiber Raman amplifier are compared with standard first-order pumping in wavelength division multiplexed optical transmission systems. The novel comparison analysis is carried out in terms of Optical signal-to-noise ratio and Q-factor, on-off gain and noise figure by varying optical input power and fiber lengths. The results indicate that dual-order schemes present 0.02 dB higher OSNR and 5 dB higher Q-factor in comparison to first-order pumping when input optical power is varied from −4 to 5 dBm. Similarly, there is 4 dB higher on-off gain with dual order comparatively to first order when fiber length varied from 10 to 100 km. However, there is degradation in noise figure and Q-factor due to DRBS noise with dual-order pumping when fiber length from 10 to 100 km. Further, the signal power evolutions along fiber length show that there is 5 dBm improvement for 100 km fiber. The novelty of the work is that comparative analysis exhibits improvement in OSNR, on-off gain and Q-factor using dual-order bidirectional pumping.

In this paper, we numerically investigate the behavior of solitons in a Mach–Zehnder interferometer made of dual-core photonic crystal fibers. The goal was to obtain logic gates with modulated information in ON-OFF keying (OOK). We considered ultra-short solitonic pulses propagating throughout the system in two distinct regimes of pump power and obtained the OR and XOR gates with fundamental solitons. In addition, the A→B and A←B Boolean expressions were obtained with high peak power. As these logical expressions were obtained with the same length of the obtained logic gates, they are important and therefore can be used to save space in the design of complex circuits.

In this paper, a 4-channel demultiplexer for WDM systems is designed by using 2-dimensional photonic crystals with square structure. Various wavelengths can be conducted in the certain paths of crystals using defects that look like ring resonator. The characteristic of this demultiplexer can be analyzed by obtaining the pass band spectrum. The property of this designation relative to previous works can be stated as size reduction, minimum crosstalk in output channels, minimum distance (about nm) for distinct wavelengths in output bands and bandwidth increasing in consequence. These improvements have been verified by simulation results.

In this paper, we propose a high-quality factor (QF) ultra-compact structure for designing all optical filter based on two dimensional (2D) photonic crystals that can operate in third communication window range (1550 nm). The simulation results calculated by using 2D finite difference time domain (FDTD) method and photonic band gap (PBG) region are calculated by plane wave expansion (PWE) method. The average transmission efficiency, average QF and optical full width at half maximum (FWHM) bandwidth more than 95 %, 4300 and 0.4 nm obtained, respectively. The value of QF for the proposed structure is a major QF for ring resonator-based filters. We studied the effect of changing the air background to liquid crystal (LC) surrounding the dielectric rods. Results showed that by increasing LC refractive index ( n ) peak of wavelengths red shifted. The footprint of proposed filter is 160μm2${{\mu}}{{\rm{m}}^{\rm{2}}}$ which make the proposed structure promising candidate for optical integrated circuits.

A modified periodic encoder for increasing the pulse height in PON monitoring system is presented and demonstrated experimentally, which can reduce the receiving sensitivity of the photoreceiver. Comparing with the pulse sequence generated by the periodic encoder, the maximum and minimum pulse height generated by the modified periodic encoder increased by rough 22 % and 19 %, respectively. This significantly reduces the receiving sensitivity of the photoreceiver at the expense of a little user cost.

Dynamic characteristics of directly modulated laser are investigated by simulating the single mode laser rate equations, emphasized on the effect of the gain compression for the two laser models: one adiabatic chirp dominated and another with a combination of adiabatic and transient chirp-dominated laser. The influence of laser adiabatic and transient chirp on system performance in normal and anomalous propagation regime is investigated by simulation. It is shown that in the anomalous propagation regime, the presence of fiber nonlinearity can be beneficial, improving the system performance by opening the eye diagram at system output. Contrarily, in the normal propagation regime, presence of high gain compression coefficient (ε > 4 × 10 –17 cm 3 ) can strongly degrade the system performance by closing the eye diagram at system output. Finally, it is shown that the laser model with a combination of adiabatic and transient chirp with anomalous dispersion coefficient shows much better result in the saturated regime. This can be used to extend the transmission distance in optical communication.

A novel network of “broadcast-star” constituted by a few of injection semiconductor laser cells and its synchronization in chaos are presented to apply in logic gates. Chaotic “broadcast-star” synchronization network is achieved in numerical simulation, where a broadcast using an injected laser drives three response systems with three injected lasers as three “stars” to achieve synchronization between the broadcast and stars while the “stars” obtain synchronization between themselves. The synchronization network model and equation are demonstrated. And logic controlling principle and equation are deduced. We create theoretically the constructions of fundamental gates based on the synchronization network in the “stars” and define their computational principle. Logic gate cell or logic computation can be implemented via controlling logic input and output to the system to synchronize or desynchronize appropriately the chaotic states of twin stars. We present and emulate a lot of all-optical XNOR, NOR, NOT, optoelectronic and combinational optoelectronic logic gates via the optical or optoelectronic modulation while we introduce these logic computational methods. Finally, we analyzed effects of resynchronization and desynchronization on logic detection in a practical implementation of the system. Results show the feasibility of the method.

In this investigation comparison of various Passive optical networks (PON) standards has been done. Bidirectional fiber to home architecture is projected which simultaneously transmits the video and audio signals. The system uses travelling wave semiconductor optical amplifier with injection current of 0.45 A for both upstream and downstream channels. This architecture is investigated for a distance of 40 km and it accommodates 96 users. Further the effect of varied distance and power on Q-factor of system is investigated.

Dynamic bandwidth assignment (DBA) schemes for long reach PONs face a suffer from higher upstream channel idle time due to long round trip time (RTT). In ITU PONs, the DBA schemes; Immediate allocation with colorless grant (IACG), Efficient bandwidth utilization (EBU) and GPON redundancy eraser algorithm (GREAL) minimize idle time by sending bandwidth grants to the optical network units (ONUs) every downstream frame (DF). EBU further improves IACG by utilizing unused bandwidth (UBW) of other traffic classes. Sending the grant results every DF requires optical line terminal (OLT) to remember all previous grants sent to ONU during RTT and subtract them from the received queue reports. Since, both IACG and EBU assign the excess bandwidth equally to ONUs. Therefore, the OLT is actually not aware of the complete grant to each traffic class and thus do not subtract these completely from receiving reports. This leads to wastage of bandwidth and higher US delays due to over granting. GREAL resolves this problem by not utilizing the excess bandwidth which also leads to increased US delays. The proposed scheme in this study eliminates this shortcoming by allocating excess bandwidth to each traffic class completely at the OLT. Moreover, the UBW assignment mechanism of EBU is also improved. Simulation results show a 50–85 % reduction in delays of type-2 (T2) and type-3 (T3) traffic classes versus GREAL and IACG and up to 40 % reduction in delays for type-4 (T4) versus EBU.

In this paper, we analyze the performance of the 4 × 2.5 Gb/s wavelength division multiplexing (WDM) transparent metro ring network comprising of one network node and eight access nodes. Here, the power requirement of 360 km ring network has been evaluated using the optical signal to noise ratio (OSNR), Q-factor, inter-symbol interference (ISI) and power penalty. The metro network utilized the cost-effective directly modulated laser (DML) and a negative dispersion fiber called MetroCor in order to give enhanced performance in terms of Q-factor. The power requirement of the network is optimized for the signals over SMF-28 and MetroCor fibers. Also, the comparison is drawn between uncompensated and compensated (with -post and -symmetrical) SMF-28 fibers in the metro environment. The excellent value of Q-factor is obtained at all the nodes. Also, the results show higher OSNR values in the metro environment. Although, smaller power penalties are detected for nodes closer to the network node, but distant nodes require higher power for better transmission.

The ever increasing heterogeneity and growing traffic volume has resulted in significant innovations and paradigm shifts within the telecom backbone networks. In order to cost-effectively respond to the diverse variety of traffic requirements having heterogeneous service demands, wavelength division multiplexed (WDM) optical networks have adopted the mixed line rate (MLR) strategy. In MLR networks, many wavelength channels with various line rates can co-exist within the same fiber which, however, raises many important design issues; one of them being the choice of the channel spacing. The quality of signal is affected by the channel spacing in terms of the bit-error rate (BER), which in turn affects the maximum optical reach of the lightpaths that depends on the line rates. In regard to the aforementioned, different methods can be adopted in order to set the width of the channel spacing, viz., (a) choice of a 50 GHz uniform fixed channel spacing specified by the ITU-T grid, (b) exploring various channel spacing values for different line rates so as to optimize the usage of the fiber spectrum, or (c) seek for an optimal value of the channel spacing which results in the minimum network cost. In the current work, we evaluate the MLR network cost for various channel spacings; hence, we find an optimal value of the channel spacing that leads to the minimum MLR network cost. The simulation results reveal that, for a MLR network, even with the assumption of uniform channel spacing, optimal values of the channel spacing for a minimum cost network can be identified.

In this paper, we investigate the impact of modulation index on the performances of SCM SAC-OCDMA system. Knowing that zero cross-correlation (ZCC) codes remove the effect of multiple access interference and of phase-induced intensity noise, SCM SAC-OCDM has been investigated using ZCC codes with two types of direct detection, one and all wavelengths of the code. In this hybrid system, the SNR depends on the modulation index for a given effective power of broadband source. In order to maximize the SNR, the optimum values of the modulation index, for different number of subcarriers, are determined analytically for two types of detection. The performance of the optimized system is evaluated based up on BER. The obtained numerical results show that, by optimizing the modulation index, the number of subcarriers (number of active users per ZCC code) is increased and the performance is significantly improved.

In Optical Time Division Multiplexing (OTDM)-based systems, several optical signals with low bit rate B share the same carrier frequency and are optically multiplexed to form a composite bit stream at the higher bit rate N*B, where N denotes the number of channels multiplexed. In this paper, the analysis and investigation of the performance of OTDM link are carried out with help of simulation. In this paper, OTDM link is designed based on four channels having data rate of each channel which is equal to 10 Gbps with the use of RZ and NRZ schemes being analyzed. The proposed optical link achieved maximum transmission distance of 348 km over single mode fiber. The system operated over a distance of 348 km with bit error rate of 1.39×10 −31 and Q-value of 11.60 with RZ, and bit rate of 1.47×10 −24 and Q-value of 10.13 with NRZ respectively. The results shows that the proposed link performance is better optimized using RZ modulation scheme in comparison to NRZ scheme. This simulation work is done in optisystem 7.0. Further in this proposed OTDM link the comparison of the link performance is also analyzed using different pulse shapes for RZ and NRZ. The results being presented in this paper are significantly taken at transmitted power of 0 dBm and 2 dBm.