Volume 34, Issue 4

We change the core gap radius, the distance between two concentric cores of a single mode Fiber Raman Amplifier (FRA), having a step profile. Based on well known scalar wave equation and its analysis, we study crucially the effects of this variation on the performance characteristics of FRA for the first time. For practically important frequency shift band of 20 cm −1 to 700 cm −1 , our interesting observation is that values of core gap radii in a certain higher range show better flattening of effective Raman gain in comparison to those in lower range with single pump; side by side, larger negative coefficient of dispersion is achieved in the operating range of wavelength with increase of core gap radius. These promising criteria should attract the attention of system designers engaged in fabrication of FRA.

The simulative implementation of differential phase shift keying (DPSK) modulated data transmission incorporating single-pump highly efficient dispersion compensated Raman/EDFA hybrid amplifier is demonstrated. The simulative results are discussed to compare two different types of configurations of dispersion compensated 16-channel wavelength division multiplexing (WDM) system to achieve transmission of Tbit/s data. In pre-compensation technique, dispersion compensated fiber (DCF) is used prior to fiber Raman amplifier (FRA) (Type I) and in post-compensation technique; the DCF is used after FRA (Type II) in a WDM optical communication system. The pumped dispersion shifted fiber (DSF) is in use to act as FRA amplifier. The performance characteristics such as Q factor, BER and eye closure penalty are premeditated to realize the ultra high speed WDM systems by employing DCF based FRA together with DPSK modulation. From simulated results, it is recommended to implement Type I over Type II to realize the feasibility of such high speed WDM systems.

An analysis of Near Travelling Wave-Semiconductor Optical Amplifier (NTW-SOA) is presented to investigate its inline detector performance. The detected voltage is evaluated for various lengths and positions of the electrode along the active region of the device, for input optical power levels ranging from −25;  dBm to +5  dBm. Under optimum conditions, the differential detection scheme shows an improvement of 3.7  dB, 4  dB for 40  mA, 50  mA bias currents respectively at −10  dBm input power, when compared with the best differential inline detection scheme reported in the literature. Further an improvement of 4.3  dB and 5.5  dB are obtained, when compared with the single electrode detection model under similar operating conditions.

We introduce a novel method based on mathematical equations to evaluate Photonic Band Gap (PBG) of the 2D hexagonal structures. By using regression analysis, extraction of PBG in all of 2D hexagonal structures is possible. We show that the mathematical equations that reached in this work have sufficient validity with comparing other numerical methods such as Plane Wave Expansion (PWE) and so etc. We demonstrate this validity for both 2D hexagonal air holes in dielectric medium and dielectric rods in air cases. The results show that the PBG region of both above mentioned kinds tend toward lower normalized frequencies by increasing the refractive index of dielectric material. The developed formulas in this work consist all of the physical parameters of structures such as lattice constant, refractive indices and dielectric radiuses. The resulting equations are suitable for applicable optical devices designing to tune the desired PBGs. These equations have minimum errors compared with other methods and it has been shown that results are matched very well with numerical simulations.

Light-trails have been proposed as a solution for optical networking to provide support for emerging services such as video-on-demand, pseudo-wires, data-centers, etc. Node architecture and its transmission performance are one of the most important issues for the physical layer of light trail network. In this paper, the light trail node architectures designed specially for the mesh topology WDM network are addressed. A novel node architecture is proposed, which supports both global wavelength switching and local access wavelength switching with lower costs. In order to verify the transmission performance of the proposed node architecture, a DWDM based optical communication platform is built. Extensive simulations are made for the light trails when changing the LT node number from three to six. In the mean time, the optical spectrums of signal and noise as well as the eye diagrams of OSC channel, local access wavelength channel and global wavelength channel are measured and recorded. Simulation results show that the light trail which adopted the proposed LT node architecture can travel up to five nodes. In this case, the BER of the OSC channel is 1.73e-015 and Q factor is 7.86. The BER of the local access wavelength channel is 1.84e-016 and Q factor is 8.14. The BER of global wavelength channel is 3.53e-015 and Q factor is 7.78. Hence, the proposed light trail node architecture can meet the requirement of physical layer at mesh WDM networks for most cases.

Ethernet passive optical network (EPON) is becoming one of the best schemes in the broadband access network as it combines the Ethernet and passive optical network technology. In order to avoid collision in upstream EPON, Universal Dynamic Bandwidth Allocation (UDBA) algorithm is proposed in this paper where it can support a universal priority in the entire EPON system. For proof-of-concept, the UDBA algorithm is implemented inside a proposed peripheral interface controller (PIC) based EPON testbed in order to evaluate the communication protocol involved. To the best of our knowledge, this is the first time PIC is being used in EPON testbed for this purpose. To ensure that the testbed is valid, we compare the result that we achieved via testbed with the results achieved via MATLAB simulation in terms of throughput, delay and fairness. The simulated results show a good agreement with the experimental with some minor expected differences.

We have studied Raman amplification for upgrading the existing passive optical network (PON). We focus on the upgrading of 10G-EPON (also XG-PON) system. First of all, we investigate transmission properties using distributed Raman amplification both theoretically and experimentally. Then, we investigate hybrid amplification, Er-doped fiber amplifier and a lumped Raman amplifier. Finally, Raman amplification for 10G-EPON systems is discussed.

Due to optical node light splitting constraint, the minimal cost optical multicast routing tree is an important issue solved normally by bypassing the nodes which violate splitting capability with a good few route cost or consuming more wavelength channel. The method of shortest path first to re-route the contending optical packet to destination nodes is presented for optimization the re-route cost and wavelength consumption in the paper. The minimal cost multicast tree is used first to search the tree overlaying the source node and all destination. Then, the shortest path first is designed to bypass the nodes on the tree which violate the light-splitting constraint with the minimal re-route cost increment for the optical multicast. According to the wavelength consumption cost factor, the wavelength consumption cost increment is calculated if the new wavelength channel is assigned for the tree nodes violating the light-splitting. Lastly, by comparing re-routing path multicast cost increment with the new assignment wavelength consumption cost increment, a minimal cost multicast routing is determined for the optical network with some nodes light splitting constraint. Furthermore, according to the actual network available wavelength scarcity, the wavelength consumption cost factor can be increased. Simulation results show that the proposed algorithm can achieve the optimal low-cost multicast tree and few wavelengths consumption also.

With the ever-increasing traffic demands, the infrastructure of current 10 Gbit/s optical network needs to be enhanced. The legacy infrastructure can be enhanced not only by increasing the capacity, but also by adapting advance modulation format, having increased spectral efficiency at higher data rate. In all-optical mixed line rate (MLR) network, feasibility of a lightpath is determined by physical layer impairment (PLI) accumulation. Contrary to physical layer impairment-aware routing and wavelength assignment (PLIA-RWA) algorithm applicable for a 10 Gbit/s WDM network, that selects a feasible route-keeping the signal to noise ratio value at the receiver above the threshold limit, a new Routing, Wavelength, Modulation format assignment (RWMFA) algorithm is required for a MLR optical network. This article reviews the major PLIs present in an optical fiber, emphasizing those that result in performance degradation of an MLR system. The article also surveys the advance modulation formats that are spectrally efficient and noise resistant. The article further presents a survey of different RWMFA (PLIA-RWA) algorithms for MLR networks and finally identifies several open problems for future research.

In this paper, performance investigations on PM-QPSK modulation format in a terabit capacity, long haul DWDM optical communication link resulted in high Q 2 (dB) of 20.71 and low BER of the order of 10 −28 proving the suitability of PM-QPSK. It is reported here that PM-QPSK is quite resilient against PMD effects as the variation in PMD_seed value from 0–50 at PMD_Coefficient of 0.1 and 1.0 resulted in minimum Q 2 (dB) of 18.7 and maximum BER of 10 −18 .

In this paper, we propose and demonstrate a novel survivable WDM-PON architecture using Optical Carrier Suppression (OCS) technique. It can provide protection against the feeder fiber failure. The simulation results for the scheme at 2.5 Gbit/s downstream signals and 2.5 Gbit/s upstream signals are presented to verify the feasibility of system.

This paper presents the Pseudo-Orthogonal Code generator for Optical Code Division Multiple Access (OCDMA) system which helps to reduce the need of bandwidth expansion and improve spectral efficiency. In this paper we investigate the performance of multi-user OCDMA system to achieve data rate more than 1 Tbit/s.

In this paper, different RoF (radio-over-fiber) based on various laser modulation techniques are analysed and optical preamplifiers results are compared. Then frequency bands for both the cases in hybrid amplification conditions are reported at the end.

In this paper, we have presented analysis of 2.50 Gbit/s FSO system using PPM modulation schemes and a distance of 18 km was achieved at BER 10 −6 in HAP to ground links.

Next generation wavelength division multiplexed passive optical access networks (WDM-PON), employing reflective semiconductor optical amplifiers (RSOAs), can provide a cost effective solution to jointly support both, classic PON services and transparent overlay wireless backhauling. In this approach, the wireless signals are transparently transmitted over the WDMPON, thus creating a virtual dedicated network without incurring into additional network installation and maintenance costs. In this paper, the performance of a WDM-PON transmitting an overlay orthogonal frequency-division multiplexing (OFDM) wireless signal is assessed analytically and experimentally, with relevant system impairments being identified and system design guidelines are provided.

Bit Error rate and outage rate closed form solution is derived for Gamma-Gamma free space optical wireless channel, assuming intensity modulation/direct detection with On-Off Keying. Expressions derived in this paper are developed for plane and spherical waves that are based on scintillation theory, which assumes that the irradiance of the received optical wave is modeled as the product of small-scale and large scale turbulence eddies. The results are shown for different values of received signal-to-noise ratio and different turbulence conditions, moderate to strong.

In this paper, simulative performance analysis for different modulation formats like NRZ rectangular, NRZ raised cosine, RZ soliton, RZ super gaussian, RZ raised cosine and RZ rectangular, has been demonstrated and analyzed at each node with varying bit rate. It is seen that overall NRZ modulation is performing better among all modulation driving schemes. It is also observed that by using RZ soliton format system can exist up to 90 dB of insertion loss of optical add drop multiplexers with bit rate upto 10 Gbit/s. For 10 Gbit/s of bit rate quality factor drops off below 15 dB after 85 dB of insertion loss for RZ soliton.

In this paper we demonstrated the variation of different parameterswith initial laser phase values of optical pulse generator which generates solitons, in soliton transmission and analyzed that how the difference of these two initial laser phase values effects Q-values.

Based on finite difference (FD) method, recently applied to investigate propagation characteristics of optical waveguides, we verify its applicability to predict the electric field and propagation parameter of planar waveguide for the entire range of normalized frequencies. As a test case, we crosscheck our FD result for symmetric step index planar waveguide and then predict the propagation characteristics of crucial planar waveguide structures like exponential index and Epstein layer model profile. Our findings show high degree of accuracy when compared with published results.