Volume 36, Issue 1 -

In this paper, a new detection technique called modified single photo-diode (MSPD) detection for SAC-OCDMA system is proposed. The proposed system based on the single photo-diode (SPD) detection technique. The new detection technique is proposed to overcome the limitation of phase-induced intensity noise (PIIN) in SPD detection technique. However, the proposed detection is based on an optical hard limiter (OHL) followed by a SPD and a low-pass filter (LPF) in order to suppress the phase intensity noise (PIIN) at the receiver side. The results show that the MSPD detection based on OHL has a good performance even when the transmission distance is long, which is different from the case of SPD detection technique. Therefore, the MSPD detection technique is shown to be effective to improve the bit error rate (BER<10 −9 ) and to suppress the noise in the practical optical fiber network.

It addresses orthogonal frequency division multiplexing (OFDM) transmission over optical links with high spectral efficiency, i.e. by using high-order quadrature amplitude modulation (QAM) schemes as a mapping method prior to the OFDM multicarrier representation. Here we address especially coherent optical OFDM modem in long distance which is affected by nonlinear distortion caused by fiber nonlinearity. Fiber nonlinearity is a majo performance-limiting factor in advanced optical communication systems. We proposed a nonlinear electrical equalization scheme based on the Volterra model. To compare with other popular linear compensation technique such as the least mean square (LMS), simulation results are presented to demonstrate the capability of a Volterra model based electrical equalizer used in a coherent optical orthogonal frequency division multiplexing system. It is shown that the Volterra model based equalizer can significantly reduce nonlinear distortion.

To improve the limited number of wavelength utilization and decrease the traffic blocking probability in sparse-grooming wavelength-division multiplexing (WDM) networks, a multicast sparse-grooming algorithm based on network coding (MCSA-NC) is put forward to solve the routing problem for dynamic multicast requests in this paper. In the proposed algorithm, a traffic partition strategy, that the coarse-granularity multicast request with grooming capability on the source node is split into several fine-granularity multicast requests, is designed so as to increase the probability for traffic grooming successfully in MCSA-NC. Besides considering that multiple destinations should receive the data from source of the multicast request at the same time, the traditional transmission mechanism is improved by constructing edge-disjoint paths for each split multicast request. Moreover, in order to reduce the number of wavelengths required and further decrease the traffic blocking probability, a light-tree reconfiguration mechanism is presented in the MCSA-NC, which can select a minimal cost light tree from the established edge-disjoint paths for a new multicast request.

In this paper, we have derived closed form expressions for the outage probability and average capacity of multihop free space optical communication system, employing either decode and forward relaying or amplify and forward relaying. The atmospheric channel is characterized by an aggregate channel model, which includes atmospheric attenuation, atmospheric turbulence and pointing errors. Gamma-Gamma channel model is used to model the turbulence of the atmosphere, and pointing error effects are considered by jitter standard deviation parameter. The results obtained from the analytical expressions are verified by Monte Carlo simulation. The performance of the multihop free space optical communication system improves with hop count for both relaying techniques, for same link length. The pointing error deteriorates the performance of the system under consideration, and the performance of a decode and forward relaying is better than the amplify and forward relaying, in terms of both average capacity and outage probability.

A novel orthogonal frequency division multiplexing passive optical network (OFDM-PON) is proposed in this paper. By using polarization multiplexing (PoLMUX) technology, this network can not only support source free in optical domain but also in electric domain. This network can also realize wireless access by optical heterodyne technology. The optical carrier suppression and separation (OCSS) technology is used to improve utilization rate of the optical source. Besides, the cross-modulation technology is used to mitigate the influence of the Rayleigh backscattering. By simulation, the functions mentioned above are demonstrated. And simulation results show this network has good performance.

Coherent optical system contains the ability of high data transmission at long distance. In this respect, laser power is effective parameter that plays important role on the receiver output. We studied the effect of laser power on constellation diagram with and without noise by varying length of the fiber. We examined for the best laser power value for the coherent optical system.

We have investigated and demonstrated a novel scheme to generate 2.5 Gbit/s 64 QAM orthogonal frequency division multiplexing (OFDM) signals for Radio Over Fiber (ROF) systems. We employ Fiber Bragg Grating (FBG) because the repetitive frequency of the RF source and the bandwidth of the optical modulator are largely reduced and the architecture of the ROF system is simpler. Wavelength-Division-Multiplexed Passive Optical Network (WDM-PON) has been considered as a promising solution for future broadband access networks. Principle of WDM-PON access network compatible with OFDM-ROF systems is investigated. This novel scheme which has multiple double-frequency technique to generate mm-wave signal to carry OFDM signals is a practical scheme to be applied for future broadband access networks.

The modulation and demodulation methods of the optical Differential Quadrature Phase Shift Keying (DQPSK), Optical Differential Phase Shift Keying (DPSK) and the different modulation formats including nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CS-RZ) are introduced, studying the ability of anti-dispersion for different optical signals in the 40 Gb/s high speed transmission system. The system is simulated in optical fiber by way of dispersion compensation. And then analyzed the compensation effect of the different dispersion compensation method for different phase modulation formats. It is shown that the ability of anti-dispersion and anti-PMD is better in the CS-RZ-DQPSK modulation format, and this format has the smallest eye-opening penalty (EOP) with a wider range of power into the optical fiber.

In order to increase the capacity of the existing optical communication networks advanced modulation schemes are utilized. Keeping this in view, an radio-over-fiber subcarrier multiplexing (SCM) employing ASK modulation technique is proposed. Response of the system is analysed by varying the linewidth and the power of the CW Laser and the optimum value is concluded for the same so as to achieve reliable communication.

This paper compares the performances of 100 Gbit/s carrier-suppressed return-to-zero differential quadrature phase shift keying coded modulation signal through 3,600 km both in optical and photoelectric dispersion compensation schemes. Different dispersion compensation fiber methods are adopted in optical compensation while the photoelectric compensation is the combination of electronic dispersion compensation and optical compensation. It is shown that pre-compensation of DCFs and mixed (pre- and post-) compensation of DCFs are more excellent than the other two schemes in optical compensation, corresponding to mixed (pre- and post-) compensation of DCFs method, while pre-compensation of DCFs method is the best strategy in photoelectric compensation.

With the growth of multi-point to multi-point multicast applications, the optical network bandwidth resource consumption is increasing rapidly. It attracted more and more researchers to improve the limited wavelength bandwidth utilization for multicast applications in wavelength division multiplexing (WDM) networks. In the paper, a multi-core shared multicast tree algorithm based on network coding is proposed to minimize the fiber link stress. The proposed algorithm includes three processes: searching the core node candidate set excluding core node loop path, selecting the core nodes from the convergence matrix based on heuristic algorithm, and constructing the multi-core nodes shared trees. The convergence matrix based on the heuristic method is constructed for selecting the core nodes from candidate core node set. To improve the limited wavelength utilization, we introduce network coding into the shared tree to compress the transmitting information. The simulation results show that the proposed algorithm’s performance is better than the existing algorithms’ performance in terms of link stress and balance degree.

Stimulated Brillouin scattering (SBS) is one kind of fiber nonlinearities representing the fundamental limiting mechanisms to the amount of data that can be transmitted on a single optic fiber. SBS is the main limiting factors for getting high output fiber. To achieve high output power and high threshold power we have to suppress this SBS effect. When light ray propagates through an optical fiber, spectral broadening is occurred due to the self-phase modulation (SPM) and cross-phase modulation (XPM) effect. In this paper, we analyze the effect of spectral broadening due to the SPM and XPM and using this effect we minimize SBS effect. From the numerical simulation results, we have found that spectral broadening factors are 1.058, 1.217 and 1.443 for input power 30, 60 and 90 mW, respectively, due to SPM effect at 10 km transmission length. Using these broadening factors and input optical powers, the amounts of threshold power improvements are 2.1, 3.2 and 4.5 mW, respectively, for a source spectral width of 200 MHz. We also analyze this XPM effect considering equal channel power and unequal channel power.