Volume 39, Issue 3 -

The implementation of hybrid optical amplifiers has led to the emergence of DWDM in optical communication systems. By implementation of hybrid optical amplifiers, the performance of DWDM transmission can be enhanced. In this paper, different configurations of hybrid optical amplifiers are discussed which can be implemented at low cost and efficient performance of DWDM transmission system. Optical amplifiers can be used in different hybrid configurations to enhance the performance of the optical link and minimize the limitations of existing amplifiers.

In this paper, a new design for a demultiplexer device for Wavelength Division Multiplexing (WDM) communication system is proposed. The proposed device consists of an inhomogeneous layer of a semiconductor material with refractive index that is graded according to a given profile. To minimize the size of the proposed device and achieve better spatial shift between the multiplexed wavelengths, several mirrors are placed at different locations inside the device. These mirrors will force the multiplexed light to be reflected before reaching the total internal reflection point. By controlling the different design parameters such as incident angle, the refractive index profile, etc., a small size, low cost and less complexity WDM device can be realized. In the design process, we exploits the ray’s spatial shift that results from the introduced mirrors and the material dispersion. In addition, the effect of the aforementioned design parameters on the amount of spatial shift between the adjacent wavelengths and the size of the device has been investigated. Results show that the proposed design achieves higher spatial shift as well as smaller device size in comparison with precedent WDM device designs.

Transmission efficiency and quality factor are two of the most crucial characteristics in designing optical band pass filters. In this paper, we proposed a novel structure for realizing an optical filter. For the wavelength selecting part of the filter, we employed a V-shaped resonant cavity. The obtained filter has a resonant mode at 1313 nm with transmission efficiency and quality factor as much as 97 % and 3548, respectively.

An all optical communication is fast and reliable for next generation information carrying systems. For successful operation of fast data over flexible transmission line is only possible by all optical multiplexer and can serve for network. A 60 Gbps all optical multiplexer using cheap components has been realized and also tested on different speeds of input data streams. For integral and flexible multiplexer, optical semiconductor-based MZI switch taken into consideration. MZI-SOA is used to generate two logical gates outputs such as (AND)(XOR) gate. Multiplexer working is based on SOA nonlinearity properties and optical coupler. XOR logic gate contingent on cross-phase modulation in amplifier and logic AND for four-wave mixing is obtained from cross port and bar port respectively. Simulation is performed and multiplexer is tested for different launched power in tree architecture. System performance indicates that it can work for high speed (60 Gbps) and different data entities.

Lithium niobate (LiNbO 3 ) nanostructures are synthesized on n-silicon substrate by spin coating technique with stirrer times; 8 h, 24 h and 48 h. LiNbO 3 is characterized and analyzed by Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and UV-visible and Photoluminescence (PL). The measurements show that as stirrer time increases, the structures start to crystallize to become more regular distribution, which helps to apply in optical waveguides. In addition, the calculated refractive index and optical dielectric constant are in agreement with experimental data.

In this paper, passively Q-switched fiber laser is demonstrated and the laser output energy is stabilized by using 2.4 m Erbium-doped fiber laser (EDFL) with a graphene oxide used as saturable absorber (GO-SA). According to the experimental results in the Q-switched configuration, the laser cavity emits a wavelength centered at 1,558.75 nm, and by inserting the GO-SA into EDFL cavity, hence, the laser output energy around 1.68 nJ with an FWHM pulse width of 2.3 µs at 123.5 kHz was achieved.

Aiming at the problem of energy efficient transmission for multiple paths under differential delay constraint, we propose a method of optical grooming based on dynamic splitting under differential delay constraint algorithm (OG-DSDA) for optical networks. When a multicast demand cannot be groomed due to the bandwidth fragment, the method constructs two types of logic light-tree sets according to the differential delay constraint between source node and destinations. In order to reduce the network link costs caused by too many split parts, the method gives high priority to the first type logic light-trees with the maximum available bandwidth to meet the requirement. When the bandwidth of first type logic light-tree is insufficient for all sub-requests, the rest of sub-demands is adaptively groomed into a light-tree in second set of light-trees with the lower power consumption. Simulation results show that the proposed method can effectively decrease the network blocking probability and reduce network’s energy consumption.

In real-time communication, the bandwidth required by traffic may fluctuate over time, and the network should allocate spectrum flexibly to satisfy such demands. In this paper, a novel spectrum assignment scheme is proposed. It reduces the spectrum fragmentation by minimizing the number of spectrum-free windows and establishes a virtual sub-connection in a non-contiguous spectrum block for the incremental bandwidths of time-varying traffic, to eliminate the traffic relocation and interruption caused by traffic change. Numerical results demonstrate that the scheme proposed in this paper effectively reduces the network blocking probability, decreases the traffic interrupt ratio, and improves the performance of serving traffic.

Fiber-Wireless (FiWi) access network is a promising broadband access network. Taking its heterogeneous structure into consideration, the paper introduces the Software Defined Networks (SDN) into FiWi access network. Survivability is an important issue in FiWi access network. Once there is a single fiber fails, many high-rate traffic flows may loss. A failure detection scheme is proposed for one distribution fiber fault in the new architecture. For the affected data flows recovery, we focus on the bandwidth allocation scheme for different priorities queues to meet the QoS. The simulation results show that the proposed scheme can maintain the QoS performance in terms of delay, loss rate and network throughput. The survivability is improved efficiently.

Free Space Optics (FSO) communication technique is a unique method for the communication between optical transmitter and optical receiver using a free space as a medium. The advantages of FSO over other wireless communication techniques is its low power, high security, low cost infrastructure, high data rates and unlicensed spectrum. There are many atmospheric disturbances like rain, fog, water molecules particles which degrade the performance of the FSO Link. In this paper, the FSO Link is optimized at different optical wavelengths of 1550 nm, 850 nm, 650 nm and 532 nm keeping into consideration the various atmospheric challenges and weather conditions. The performance of the proposed FSO link is evaluated in terms of BER and Quality factor. Simulation results for the proposed FSO link achieve maximum link range of 1000 m at 1550 nm. The achieved values of Bit Error Rate (BER) and Quality Factor (Q) for FSO link at 1550 nm are 10e-9 and 5.58 respectively.

The Radio over Fiber (RoF) system has emerged out a promising solution to the last mile connectivity along with higher data rates making it the preference for future communication networks. But fiber nonlinearities induce crosstalk and degrade the performance of the system. This paper presents a simulative investigation & comparison of Mach Zehender Modulator (MZM) and Optical Phase Modulator (OPM) including the effects of Self Phase Modulation. A single channel RoF system has been designed using MZM and OPM respectively. The model is analyzed for different ranges of dispersion and input channel power. It is observed that as the dispersion modulus increases the SPM induced pulse broadening also increases. The pulse broadening also increases with increase in the channel input power. Further it is revealed that MZM offers 0.3 dB more channel output power compared to OPM when dispersion is increased from 2 to 10 ps/nm/km. With the increase in channel input power from 10 to 17.5 dBm, OPM suppress SPM effects better than MZM and provides 2 dB more channel output power.

In this paper, average channel capacity of optical wireless communication system is evaluated under the combined effect of geometrical loss, attenuation due to weather conditions and weak atmospheric turbulence using a simple closed form expression. Fading induced due to atmospheric turbulence is modeled by log-normal distribution. Considering the fact that the sum of log-normal random variables can be well approximated by another log-normal random variable, the proposed expression has been utilized to compute the channel capacity for spatial diversity reception employing maximum ratio combining and equal gain combining over uncorrelated turbulence-induced fading conditions. It is shown that spatial diversity is an effective technique to mitigate the impairments caused by various atmospheric conditions such as haze, rain and fog. The quantitative improvement in channel capacity achieved by using diversity techniques is investigated and compared. Accuracy of the results is validated with exact results computed using Monte Carlo simulation.

A new method for constructing optical zero-correlation zone (OZCZ) codes based on the Hadamard matrix and the concatenation operation is proposed. The most important property of the obtained codes is that the periodic correlation function of the proposed codes is zero for the phase shifts within the zero-correlation zone. The structure of the proposed OZCZ code is simple and their construction is more flexible. The proposed code is expected to be useful for reducing co-channel interference in optical code division multiple access system.