In this paper we first provide a novel WDM-upgraded EPON architecture with single wavelength downstream at 10Gbps
and multiple wavelengths upstream at 1Gbps using hybrid WDM/TDM access method. After reviewing previous work
and deficiency on dynamic wavelength and bandwidth allocation schemes of WDM EPONs, we propose evolutionary
schemes which based on bandwidth debit and credit to solve the problem of unfair bandwidth allocation. This proposed
original method can achieve a win-win situation for both credit ONUs and debit ONUs. The credit ONUs obtain better
service after crediting bandwidth to others; while the debit ONUs can consume more bandwidth in emergency, and
return the debited bandwidth later. The simulation results show that these algorithms performed well in successful
assurance of the SLA guaranteed bandwidth of ONUs in normal utilization and efficient network utilization, rather than
penalties executed on all ONUs when there were some greedy ONUs.
Wavelength Division Multiplex Ethernet Passive Optical Network (WDM EPON), due to its simple configuration and enormous capacity advantage over present access network technology, is considered by many experts to be the promising solution to realize FTTH. In this paper, we proposed a model of WDM EPON system using OPNET, collected the statistical parameters and analyzed the network capacity through simulation. Based on the network topology and WDM technology features, we designed the network configuration to be P2MP in the downstream direction using broadcasting mechanism and P2P in the upstream direction using independent wavelength channels. We studied the MAC protocol stacks under WDM EPON hierarchy and designed the OLT and ONU node modules based on the theoretical models. ONU dynamic registration and MAC mappings of data switching in OLT are the two key technologies introduced in the model to realize the communication within the system. Simulation results approve that WDM EPON system has great bandwidth capacity and extremely little terminal-to-terminal latency, thus displaying great capability advantages and developing prospects.
Hybrid TDM/WDM PON is a promising optical access network solution which taking advantages of both TDM-PON and WDM-PON, and suitable for near future deployment in pragmatic migration from current TDM-PONs to future WDM-PONs. In this paper, we review and compare five types of the representative hybrid TDM/WDM PON architectures: TDMA based hybrid PON, WDMA based hybrid PON, TDM over WDM hybrid PON, WDM over TDM hybrid PON, and SUCCESS hybrid PON. Several key issues and enabling technologies for deploying hybrid TDM/WDM PON, including wavelength assignment, media access control and wavelength management protocols, light sources, and protection, are also discussed in the paper.
The characteristic of polarization of random laser is investigated by numerical method. We use the random laser model coupling semi-classical laser theory with Maxwell's equations. The model couples electronic number equations at different levels with field equations. The equations are solved by finite-difference time-domain method. We calculate the evolvement of transverse electric wave and transverse magnetic wave in a two-dimensional laser system, respectively. We draw conclusions as follows. Polarization influences the frequency and the position of mode in a random laser system. The threshold is affected by polarization as well.
We use the semi-classical random laser model, which is described by the Maxwell equations and the rate equations, and utilize the finite-difference time-domain method (FDTD) to investigate the differential characteristic of one-dimensional random laser. The results of the calculation indicate that emitting frequency changes continuously with the slight modification of the thickness of film. Thereby, the random laser is a stable system, not a chaotic system. Those thin films in the center of localized regime have stronger effect on the emitting frequency than those beyond the position of localized regime. The thin films in the center of localized regime form a resonant cavity actually and those thin films beyond the position of localization form reflecting mirrors of cavity. Modifying the thickness of the thin films in the center of the localized regime mean modification of the length of cavity, consequently the emitting frequency is changed. Modification of thickness of the thin films out of localized regime mean change of the reflectivity of the reflecting mirrors of cavity. So it has no effect on the emitting frequency, but it affects the emitting energy of laser. If the modification of the thickness is very great, it maybe changes the position of the localized regime and the emitting frequency of mode.