Volume 33, Issue 3

Conventional detection techniques used in optical code-division multiple access (OCDMA) systems are not optimal and result in poor bit error rate performance. This paper analyzes the coded performance of optical CDMA systems with AND detectors for enhanced throughput efficiencies and improved error rate performance. The results show that the use of AND detectors significantly improve the performance of an optical channel.

In this work design, simulation and fabrication of three thin-layer optical filter based on 1D Photonic Crystals (PhCs) has been proposed. Each filter is suitable for a specific area of visible spectrum such as blue, green and red respectively. Each of three filters is placed on top of an imager sensor and is consists from seven layers of TiO 2 and SiO 2 materials. These layers are respectively deposited on a substrate matter using RF-sputtering. The substrate matter is an all-pass visible filter. The wavelengths of visible light spectrum that the human eye is more sensitive to them, can be extracted by these filters and then are focused on its own sensors. The Transfer Matrix Method (TMM) is used for computing of thickness of all layers and transmission factor of each filter. Results were proved by MATLAB simulation such that the central wavelength of the blue, green and red light filters would be 437 nm, 533 nm and 564 nm respectively.

In this paper, the bandwidth of a photonic crystal (PhC) based band pass filter is tailored to accommodate a carrier wavelength in presence of maximum shifts specified for a coarse wavelength division multiplexing (CWDM) system. For desired tailoring we introduce defects, whose distribution is crucial in determining flatness of the filter pass band. To analyze filter performance, transfer matrix method is employed, and a condition guiding distribution of defects within the structure is derived. Design parameters of proposed model are optimized through simulation using MATLAB . To validate the MATLAB simulation results for practical implementation, the filter is further simulated by CST MW Studio . Both simulation results show close agreement with each other. According to ITU-T Recommendation G.694.2 for a CWDM system, a channel wavelength may undergo a maximum shift of ±(6–7) nm. The flat top pass band of our proposed filter can support such channels. The most striking feature of the filter is that it is expected to perform satisfactorily, even if during fabrication, the dimension of individual unit cell deviates from its estimated value. The choice of silicon and silicon dioxide as PhC materials provides easy realization of integrated filter structure.

Eigenmodes of simplified square-latticed photonic crystal waveguides with several layers of periodical rods on both sides of the optical channels are obtained by plane wave expansion (PWE) method and supercell method in this paper. In case of one/two layers of rods, the propagating modes have quasi-periodical variations of intensities in the regions outside the optical paths. As the number of layers increases to equal or more than three, the optical power is well confined to the optical channel and the modal profile approaches the same limit.

A vibration sensor system based on Distributed Feedback Fiber Lasers (DFB-FL) and digital Phase Generated Carrier (PGC) demodulation is presented in this paper. The external sound signals is collected by DFB-FL, and then the signal is gathered into the computer and is processed. The sensing of the system need no power supply, so the system can deal with unexpected disasters. Moreover, the system can be used for remote warning.

We demonstrate a novel scheme to generate Return to Zero Differential Phase Shift Keying (RZ-DPSK) modulation signal that only one using single Mach Zehnder Modulation (MZM) format with hybrid Raman and Erbium Doped Fiber Amplifier (EDFA) configuration that can compensate for dispersion impairment and improve nonlinear effects to investigate transmission distance performances in the 48 × 40 Gbit/s Dense Wavelength Division Multiplexing (DWDM) system. The proposed 48 × 40 Gbit/s DWDM system scheme successfully employs single MZM RZ-DPSK modulation format to reduce modulation complex configuration with employs hybrid Raman/EDFA configuration to promote the power signal and using Single Mode Fiber (SMF) with Dispersion Compensation Fiber (DCF) in 27 spans over 3240 km ultra-long haul fiber transmission successfully.

A new scheme is proposed to realize the remote communication and monitor the sensor network, which is based on GPON. It is suited to carry data collected from optical sensor networks and to monitor environment on a public network. It is a cost-effective system architecture, which not only avoids re-laying of additional sensor fiber channel for sensor data communication, but also increases the flexibility of sensor network. In order to facilitate sensor monitoring center to receive and analyze sensor data, a novel frame format of sensor signal is designed to carry the low-rate sensor data. Here, TDMA techniques have been employed to upload data of various sensor networks to one port of ONU, which makes full use of time domain resources. The delay effect, identification method of the sensor data, and various interference factors which influence the sensor data to be correctly received are analyzed. The uplink simulation indicates that the accurate judgement can be obtained in the condition of time synchronization. The integration of the sensor network and communication network is feasible in reality. However, the time synchronization error, the laser response time delay and the received signal power difference will degrade the system performance to some extent.

As the network is converting to transparent optical networks, the impact of physical layer impairments on transmission performance can't be ignored. The impairments will decrease the quality of signals. To find a lightpath with high quality of transmission (QoT), this paper adds impairment constraints to the routing and wavelength algorithm based on wavelength rotation graph (WRG-RWA) and proposes impairment aware WRG-RWA algorithm. The constraints consider amplified spontaneous emission noises and polarization mode dispersion which are the most important liner impairments. The new algorithm estimates the impact of the impairments after the route is selected, and selects another route when the previous one fails in comparing with the constraints. By simulating, the new algorithm has preferably improvement on blocking probability and wavelength efficiency by contrast with the WRG-RWA algorithm and the impairment aware FF algorithm. The simulation results show the new algorithm can effectively decrease the blocking probability of transmission and improve the performance of optical networks.

A novel orthogonal-frequency-division-multiplexing (OFDM) passive optical network (PON) architecture with centralized light sources and colorless optical network units (ONUs) has been proposed in this paper. The proposed architecture provides bidirectional transmission and employs 2N wavelengths to support 2N ONUs for the downstream and upstream signals. We experimentally and analytically study the performance of downstream 10 Gbit/s OFDM signals and the upstream 2.5 Gbit/s NRZ signals. The study results indicate the system can alleviate the effect of Rayleigh backscattering and crosstalk.

We numerically investigate a feed-forward optical carrier recovery method for quadrature amplitude modulation (QAM) signals, which includes fast Fourier transformation (FFT) method for carrier frequency estimation (CFE) and blind phase search (BPS) algorithm for carrier phase estimation (CPE), respectively. Simulation results for 16- and 64-QAM systems verify the good performance of this carrier recovery method. For 10 Gbaud 16- and 64-QAM systems, any frequency offset between −1.25 and 1.25 GHz can be estimated using FFT method with maximum errors of several MHz. Through further CPE by BPS algorithm, the optical signal to noise ratio (OSNR) penalties at BER of 1·10 −3 for 16-QAM system with linewidth times symbol period product of 2·10 −4 and for 64-QAM system with linewidth times symbol period product of 5·10 −5 are 1.2 and 1.1 dB, respectively.

Triplexer was one of the key components in FTTH systems, which employed an analog overlay channel for video broadcasting in addition to bidirectional digital transmission. To enhance the survivability of triplexer as well as the robustness of FTTH system, a multi-ports device named triplexer monitor was designed and realized, by which failures at triplexer ports can be detected and localized. Triplexer monitor was composed of integrated circuits and its four input ports were connected with the beam splitter whose power division ratio was 95∶5. By means of detecting the sampled optical signal from the beam splitters, triplexer monitor tracked the status of the four ports in triplexer (e.g. 1310 nm, 1490 nm, 1550 nm and com ports). In this paper, the operation scenario of the triplexer monitor with external optical devices was addressed. And the integrated circuit structure of the triplexer monitor was also given. Furthermore, a failure localization algorithm was proposed, which based on the state transition diagram. In order to measure the failure detection and localization time under the circumstance of different failed ports, an experimental test-bed was built. Experiment results showed that the detection time for the failure at 1310 nm port by the triplexer monitor was less than 8.20 ms. For the failure at 1490 nm or 1550 nm port it was less than 8.20 ms and for the failure at com port it was less than 7.20 ms.

The generation, extraction, identification and regeneration of optical label is one of the key problems in optical label switching technology. This paper proposes an optical labeling technique based on the use of CSRZ-DPSK modulation for the high-rate payload data and Manchester-SCM for the label information, and then analyzes its performance. Simulation results show that the optimal SC frequency is equal to payload rate or its half and label rate will affect the receiving of payload signal.

We present a comparative study of the influence of dispersion induced phase noise for CO-OFDM systems using Tx channel multiplexing and Rx matched filter (analogue hardware based); and digital FFT multiplexing/IFFT demultiplexing techniques (software based). An RF carrier pilot tone is used to mitigate the phase noise influence. From the analysis, it appears that the phase noise influence for the two OFDM implementations is very similar. The software based system provides a method for a rigorous evaluation of the phase noise variance caused by Common Phase Error (CPE) and Inter-Carrier Interference (ICI) and this, in turns, leads to a BER specification. Numerical results focus on a CO-OFDM system with 1 GS/s QPSK channel modulation. Worst case BER results are evaluated and compared to the BER of a QPSK system with the same capacity as the OFDM implementation. Results are evaluated as a function of transmission distance, and for the QPSK system the influence of equalization enhanced phase noise (EEPN) is included. For both types of systems, the phase noise variance increases significantly with increasing transmission distance. An important and novel observation is that the two types of systems have very closely the same BER as a function of transmission distance for the same capacity. For the high capacity QPSK implementation, the increase in BER is due to EEPN, whereas for the OFDM approach it is due to the dispersion caused walk-off of the RF pilot tone relative to the OFDM signal channels. For a total capacity of 400 Gbit/s, the transmission distance to have the BER < 10 −4 is less than 277 km. For an RF pilot located in the center of the OFDM band in a CO-OFDM implementation with n-level PSK channel modulation the current results suggest that the walk-off effect is equivalent to the EEPN impact in a single channel n-level PSK system with the same capacity. This observation is important for future design of coherent long-range systems since it shows that there is a free choice between CO-OFDM and a high capacity nPSK implementation at least as long as the phase noise influence is concerned.

The focus of this paper is to report a detailed investigation of dispersion compensated optical communication system of different optical pulses such as RZ super Gaussian, NRZ and RZ pulses using pre-, post- and symmetrical-dispersion compensation techniques. The dispersion compensated optical communication system consists of standard single-mode fiber (SSMF) of 16 ps/nm/km after, whose dispersion is compensated using different DCF compensation schemes with proportionate length of dispersion compensated fiber of −80 ps/nm/km. The performance of these three compensation schemes is compared by computing Q-parameter, Eye-closer penalty and required optical power at sensitivity at varied values of Laser line width from 100 MHz to 100 KHz to underscore the best possible performance. A relationship among the attributes laser line width, different optical pulses and different DCF schemes implemented at high transmission rate.