Volume 37, Issue 3 -

The effect of transversal design in Erbium-doped fiber amplifiers’ gain and noise figure performance is illustrated in this work. In this work, we investigate experimentally a single pass 980 nm pumped EDFA with partially doped Erbium core fiber (PDCF), which has the core partially doped with Erbium ions. Later, the enumerated results for PDCF are compared with a standard fully doped EDF, having similar Erbium ion doping concentration. The PDCF Amplifier gain and noise figure performance is studied against different pump power and signal power at different operating wavelengths. The noise figure indicates improvement due to reduced spontaneous emission from un-doped region of the core.

An all-optical modulator based on photonic crustal structures is proposed and its performance characteristics are studied. In this modulator, a carrier beam is controlled by input signal beam. A two-dimensional microring resonator is designed to employ the Kerr’s nonlinear effect and operate as modulator. We use numerical methods such as plane wave expansion and finite difference time domain for performing our simulations and studying the optical properties of the proposed structure. The insertion loss and extinction ratio are studied as a function of carrier power. Results show acceptable orders of extinction ratio about 9 dB and very low insertion loss about –10 dB. The proposed modulator is expected to show ultra-fast modulation.

In view of the characteristics of the global control and flexible monitor of software-defined networks (SDN), we proposes a new optical access network architecture dedicated to Wavelength Division Multiplexing-Passive Optical Network (WDM-PON) systems based on SDN. The network coding (NC) technology is also applied into this architecture to enhance the utilization of wavelength resource and reduce the costs of light source. Simulation results show that this scheme can optimize the throughput of the WDM-PON network, greatly reduce the system time delay and energy consumption.

A novel routing algorithm (Hierarchical Supervisor and Agent Routing Algorithm, HSARA) for LEO/MEO (low earth orbit/medium earth orbit) double-layered optical satellite network is brought forward. The so-called supervisor (MEO satellite) is designed for failure recovery and network management. LEO satellites are grouped according to the virtual managed field of MEO which is different from coverage area of MEO satellite in RF satellite network. In each LEO group, one LEO satellite which has maximal persistent link with its supervisor is called the agent. A LEO group is updated when this optical inter-orbit links between agent LEO satellite and the corresponding MEO satellite supervisor cuts off. In this way, computations of topology changes and LEO group updating can be decreased. Expense of routing is integration of delay and wavelength utilization. HSARA algorithm simulations are implemented and the results are as follows: average network delay of HSARA can reduce 21 ms and 31.2 ms compared with traditional multilayered satellite routing and single-layer LEO satellite respectively; LEO/MEO double-layered optical satellite network can cover polar region which cannot be covered by single-layered LEO satellite and throughput is 1% more than that of single-layered LEO satellite averagely. Therefore, exact global coverage can be achieved with this double-layered optical satellite network.

With the development of one point to multiple point applications, network resources become scarcer and wavelength channels become more crowded in optical networks. To improve the bandwidth utilization, the multicast routing algorithm based on network coding can greatly increase the resource utilization, but it is most difficult to maximize the network throughput owing to ignoring the differences between the multicast receiving nodes. For making full use of the destination nodes’ receives ability to maximize optical multicast’s network throughput, a new optical multicast routing algorithm based on teaching-learning-based optimization (MR-iTLBO) is proposed in the paper. In order to increase the diversity of learning, a self-driven learning method is adopted in MR-iTLBO algorithm, and the mutation operator of genetic algorithm is introduced to prevent the algorithm into a local optimum. For increasing learner’s learning efficiency, an adaptive learning factor is designed to adjust the learning process. Moreover, the reconfiguration scheme based on probability vector is devised to expand its global search capability in MR-iTLBO algorithm. The simulation results show that performance in terms of network throughput and convergence rate has been improved significantly with respect to the TLBO and the variant TLBO.

In this paper, performance enhancement of super-dense wavelength division multiplexing (SDWDM) optical add–drop multiplexer optical ring network for six nodes, 50 wavelengths having channel spacing of 0.2 nm for 300 km unidirectional nonlinear fiber is successfully demonstrated. The performance of the designed system is enhanced by comparing different modulation formats (non-return to zero (NRZ), return to zero (RZ), soliton, chirped return to zero (CRZ), carrier-suppressed RZ (CSRZ)) and hybrid amplifiers (Erbium-doped fiber amplifier (EDFA)–EDFA, semiconductor optical amplifier (SOA)–SOA, SOA, EDFA, EDFA–SOA) on the basis of eye diagram and bit error rate (BER). It has been observed that CRZ modulation format and EDFA-SOA shows the best results. It has been reported that EDFA-SOA/CRZ modulation format can achieve BER as better as e-13, which gives best performance. The effect of channel spacing on SDWDM system and performance degradation due to crosstalk is also evaluated.

A novel scheme is proposed for frequency 12-tupling millimeter-wave generation based on two cascaded dual-parallel Mach–Zehnder modulators (DP-MZM) without optical filtering. The impact of imperfect extinction ratio (EXT) of each sub-MZM on optical sideband suppression ratio (OSSR) and RF spurious suppression ratio (RSSR) is investigated. Theoretical and simulation results show that the proposed scheme is feasible and system performance is insensitive to EXT when EXT is not less than 29 dB. Optical mm-wave with 26.4 dB OSSR and 20.3 dB RSSR can be obtained when the DPMZM is consisted of two sub-MZMs with 30 dB EXT. Furthermore, the system performance improvement through sub-MZM modulation index enhancement is analyzed.

Luby Transform (LT) code is the first practical implementation of digital fountain code. The coding behavior of LT code is mainly decided by the degree distribution which determines the relationship between source data and codewords. Two degree distributions are suggested by Luby. They work well in typical situations but not optimally in case of finite encoding symbols. In this work, the degree distribution optimization algorithm is proposed to explore the potential of LT code. Firstly selection scheme of sparse degrees for LT codes is introduced. Then probability distribution is optimized according to the selected degrees. In image transmission, bit stream is sensitive to the channel noise and even a single bit error may cause the loss of synchronization between the encoder and the decoder. Therefore the proposed algorithm is designed for image transmission situation. Moreover, optimal class partition is studied for image transmission with unequal error protection. The experimental results are quite promising. Compared with LT code with robust soliton distribution, the proposed algorithm improves the final quality of recovered images obviously with the same overhead.

This paper successfully demonstrates bidirectional wavelength division multiplexing passive optical network (WDM-PON) system for 32 channels, 0.8 nm (100 GHz) channels spacing with 3.5 GHz filter bandwidth. The system delivers 160 GB/s data rate and 80 GB/s data rate in downstream and upstream, respectively. The optical source for downstream data and upstream data is mode-locked laser at central office and reflective semiconductor optical amplifier (RSOA) at optical network unit. The maximum reach of designed system is 50 km without using any dispersion compensation scheme. This paper comprises comparison of series of modulation format in downstream and upstream such as SOLITON, NRZ, RZ, MANCHESTER, CSRZ and CRZ-DPSK and optimization of the performance of designed system. It has been observed that CRZ-DPSK/NRZ gives best performance in downstream and upstream transmission for designed system. The simulation work report of minimum BER is e −13 for CRZ-DPSK in downstream and e −16 for NRZ in upstream transmission in case of 32-channel bidirectional WDM-PON.

We report formulation of simple but accurate analytical expressions at the splice for both angular and transverse mismatches in case of single mode triangular index fibers. Here, we employ the simple series expression for fundamental modal field of such fibers. The analysis takes care of large V values appropriate for single-moded guidance in such fibers as well as low V values. As regards evaluation of the said parameters by our formalism, little computation will be involved. We also show that our predictions match excellently with the available exact numerical results. Moreover, splices show high tolerance with respect to longitudinal separation and accordingly we restrict our analysis to the practical cases of transverse and angular offsets only. The present investigation should be of immense importance to the packagers and system engineers in the field of optical technology involving such kind of fibers.