Volume 38, Issue 2 -

This paper presents the comparison of various modulation formats for 64×10 Gbps dense wavelength division multiplexing system using Raman–erbium-doped fiber amplifier optical amplifier with 100 GHz interval. We evaluate the suitability of various data formats like return-to-zero (RZ) raised cosine (RC), RZ rectangular (Rect), non-return-to-zero (NRZ) RC and NRZ-Rect for an optical transmission link. The results have been carried out by evaluating the value of quality factor, bit error rate (BER) and average opening of an eye. It is found that using NRZ-Rect data format, the signal can travel up to transmission length of 234 km with acceptable BER (1.10e −09 ) and Q -factor (15.57 dB), respectively. In addition, the effect of dispersion on various data formats has also been discussed. Further, we investigate the optical RZ pulse with variable duty cycle indicating the highest quality factor and optical output power for duty cycle 0.6 observed for the case of back-to-back system.

Binary to octal and octal to binary code converter is a device that allows placing digital information from many inputs to many outputs. Any application of combinational logic circuit can be implemented by using external gates. In this paper, binary to octal and octal to binary code converter is proposed using electro-optic effect inside lithium-niobate based Mach–Zehnder interferometers (MZIs). The MZI structures have powerful capability to switching an optical input signal to a desired output port. The paper constitutes a mathematical description of the proposed device and thereafter simulation using MATLAB. The study is verified using beam propagation method (BPM).

In this paper, an optical power divider with one input and four outputs has been proposed in a two-dimensional photonic crystal with triangular lattice and simulated using dielectric holes in an air substrate. The dividing properties of the power divider have been numerically simulated and analyzed using the plane wave expansion and finite difference time domain methods. The results show that the transmittance of this divider can be as high as 94.22 % for λ =1.55 µm; thus, the proposed structure is suitable for wavelength division multiplexing communication systems. Also, due to the small footprint of the proposed structure, this optical power divider is applicable for optical-integrated circuit design.

This paper includes optical Boolean function generator unit. It can generate multiple logical operations (16 operations). The device is proposed using electro-optic effect inside lithium niobate-based Mach–Zehnder interferometers (MZIs). The MZI structures have powerful capability to switching an optical input signal to a desired output port. The paper constitutes mathematical description of the device and thereafter simulation using MATLAB. The study is verified using beam propagation method.

This paper presents a simple method of linewidth enhancement factor (LEF) measurement of a semiconductor laser through narrowband optical frequency modulation (FM) generation by direct modulation. The narrowband optical FM is generated by using small-amplitude direct-current modulation, thereby limiting the resultant optical intensity modulation index level typically within 10%. The LEF is found to decrease linearly with the increase in bias current of the laser diode above threshold.

In this work, the authors propose a modified type of multi-stage directional couplers and combine it with a wavelength-tunable laser to measure the refractive index of an undetermined biochemical liquid/solution. Tuning the wavelength of the laser incident on the modified multi-stage directional couplers, the relationship between the wavelength corresponding to the maximal output optical power and the refractive index of the unknown fluid has been obtained.

There has been increasing demand for connection setup with a higher quality of service (QoS) in WDM/DWDM networks, especially in fields like radio over fiber, where phase modulation affects the link quality. Hence to meet guaranteed QoS in a phase modulated link, the effects of phase modulation on link quality are very much needed. The link quality is termed as quality factor (Q-factor). The primary objective is to use effectively the connections available to optimize the computed number of connections and reduce the blocked connections but at the same time guaranteeing QoS as per client’s need. The analysis has been done by taking care of routing and wavelength assignment (RWA) techniques. The performance analysis is presented in terms of blocking probability.

This article explores performance study for optical combinational designs based on nonlinear characteristics with semiconductor optical amplifier (SOA). Two configurations for optical half-adder with non-return-to-zero modulation pattern altogether with Mach–Zehnder modulator, interferometer at 50-Gbps data rate have been successfully realized. Accordingly, SUM and CARRY outputs have been concurrently executed and verified for their output waveforms. Numerical simulations for variation of data rate and key design parameters have been effectively executed outcome with optimum performance. Investigations depict overall good performance of the design in terms of the extinction factor. It also inferred that all-optical realization based on SOA is competent scheme, as it circumvents costly optoelectronic translation. This could be well supportive to erect larger complex optical combinational circuits.

Free Space Optics (FSO) technique is an advanced form of the wireless communication system capable of transmitting data at higher transmission rates with higher channel bandwidth and over longer link distances. One of the major challenges faced by FSO technology is the distortion of received signal due to atmospheric effects which degrade the performance of the communication link by increasing the bit error rate (BER). By implementing Erbium Doped Fiber Amplifier (EDFA) in the FSO link, the degradation of the information signal due to atmospheric effects can be minimized. Also, by deploying spatial diversity technique in the FSO link, where multiple copies of the information signal are transmitted to increase the redundancy of the system, the system performance can be enhanced. In this paper, the performance of an FSO communication link has been analyzed under fog weather condition using a different number of Tx/Rx pairs and EDFA amplifier using OPTISYSTEM simulation software. Performance has been analyzed on the basis of Q Factor, SNR, BER, and total power of the received signal. Results show a significant improvement in the system performance by deploying multiple transceiver techniques.

A novel architecture of bidirectional gigabit signal transport system over long-haul single-mode fiber (SMF) using wavelength division multiplexed passive optical network technique is proposed and demonstrated. In order to offer multimedia services of high bandwidth, four signals of 5 Gbps data rates are externally modulated and transmitted through four channels over 100-km SMF in uplink and downlink. In our proposed scheme, an excellent bit error rate, good Q -factor and clear eye diagrams are observed for both 100-km uplink and downlink transmission. This architecture has potential to transmit 4×5 Gbps over long-haul fiber backbone and it will be useful in future broadband communications.

Dispersion and nonlinear effects will increase the effect on the system when the optical information transmits in high speed and long distance. The new optical modulation technology can reduce the attenuation caused by transmission procedure. In this paper, OptiSystem and Matlab were combined to set a model by comparing the dispersion tolerance and nonlinear effect of different code modulation formats. After that, the better performance code of IRZ (Inverse Return-to-Zero) and DQPSK (Differential Quadrature Phase Shifted Keying) will be used to study their properties in 10Gbit/s re-modulation WDM-PON access model. The DQPSK was used in downlink, IRZ modulation was used in uplink adopts the IRZ modulation was used in 10 Gbit/s re-modulation WDM passive optical network access model uplink on the basis of the above method. A simulation analysis is also made between the different duty ratios of the DQPSK and IRZ. Compared with the NRZ type, the IRZ has a better anti-dispersion property, channel crosstalk suppression ability and higher spectrum efficiency although it costs 3 dB powers. At the same time, it simplifies the structure of the ONU on the premise of not increasing the power and the cost. So, it fits the large capacity requirements between user stations and the central office in the future.

In this paper, security issues for optical orthogonal frequency division multiplexed (OFDM) systems are emphasized. The encryption has been done on the data of coded OFDM symbols using data encryption standard (DES) algorithm before transmitting through the fiber. The results obtained justify that the DES provides better security to the input data without further bandwidth requirement. The data is transmitted to a distance of 1,000 km in a single-mode fiber with 16-quadrature amplitude modulation. The peak-to-average power ratio and optical signal-to-noise ratio of secure coded OFDM signal is fairly better than the conventional OFDM signal.

Inter-satellite optical wireless communication (IsOWC) systems can be chosen over existing microwave satellite systems for deploying in space in the future due to their high bandwidth, small size, light weight, low power and low cost. However, the IsOWC system suffers from various attenuations due to weather conditions, turbulence or scintillations which limit its performance and decreases its availability. So, in order to improve the performance, IsOWC system using directly modulated laser source is proposed in this work. The system is designed and evaluated to be suitable for high data rate transmissions up to 10 Gbps. The performance of the system is investigated in order to reduce the cost and complexity of link and improving the quality of information signal. Further the proposed IsOWC system is analysed using BER analyser, power meter and oscilloscope Visualizer.

This paper presents a high-speed, power-compensated novel architecture of N × N reconfigurable multiwavelength optical cross connect (RM-OXC) based on tunable fiber Bragg grating (T-FBG) and optical circulator (OC). FBG and OC-based OXCs are network elements that play a significant role in optical networks to offer more network survivability and reconfiguration flexibility. Optical signal-to-noise ratio of 71.05, 69.05 and 67.05 dB is achieved with acceptable quality factor of 7.54, 6.95 and 6.41, respectively, with 10 Gbps having input transmission power of −8 dBm at different transmission distances (40, 50, 60 km). It is found that the signal is communicated to a maximum distance of 60 km in the presence of fiber nonlinearities without optical amplifier at 0.8-nm channel spacing.

A stimulated Raman scattering (SRS)-aware routing and wavelength assignment (RWA) scheme, called assign minimum interference and shortest algorithm, is proposed to minimize the effect of SRS in network. The design parameter, the number of interference of routes in the proposed algorithm is investigated to analyze its capabilities of influence the network performance. The various setting of the parameter is tested in 15-nodes Mesh and 14-nodes National Science Foundation networks for analysis in order to provide useful guidelines for designing effective SRS-aware RWA scheme. The ultimate objective is to define the necessary and sufficient rules that must be followed in the proposed algorithm by identifying the necessary RWA parameters in order to minimize the effect of SRS in optical networks. The result shows that the smaller the number of interference of routes, the lower the blocking probability in the mentioned topologies.

An analytical approach is developed to find the effect of cross-polarization (XPol)-induced crosstalk on the bit error rate (BER) performance of a polarization division multiplex (PDM) quadrature phase shift keying (QPSK) optical transmission system with polarization diversity receiver. Analytical expression for the XPol-induced crosstalk and signal to crosstalk plus noise ratio (SCNR) are developed at the output of polarization diversity PDM-QPSK coherent optical homodyne receiver conditioned on a given value of mean misalignment angle. Considering Maxwellian distribution for the pdf of the misalignment angle, the average SCNR and average BER are derived. Results show that there is significant deterioration in the BER performance and power penalty due to XPol-induced crosstalk. Penalties in signal power are found to be 8.85 dB, 11.28 dB and 12.59 dB correspondingly for LO laser power of −10 dBm, −5 dBm and 0 dBm at a data rate of 100 Gbps, mean misalignment angle of 7.5 degree and BER of 10 −9 compared to the signal power without crosstalk.