Rujian Lin

Design and FPGA implementation of OLT for EPON

This paper presents the field programmable gate array (FPGA) design and implementation of the OLT used for Ethernet passive optical network (EPON). To reduce working frequency of the FPGA, the byte-to-word conversion is proposed. Propagation delays are equalized by ranging procedure so as to avoid data collision. VLAN solution is illustrated in detail to guarantee data segregation and priority scheduling. A fast CAM scheme is introduced to finish search operation in one clock cycle. Experimental results show that the proposed system can function properly in a low cost FPGA

Flat frequency comb generation based on Mach-Zehnder modulator and phase modulator

A method to generate flat optical frequency comb is proposed and demonstrated which is based on Mach-Zehnder modulator and phase modulator cascade. Utilizing this method, we have analyzed flat optical frequency comb generation in the condition of different RF driving voltages. We also illustrate and correct the optimal operation condition for generating flat optical comb lines through the modulators.

Theoretic and experimental study on mm-wave radio over fiber system based on OFM

This paper presents an overview on millimeter wave radio over fiber systems based on millimeter wave generation by optical frequency multiplication (OFM). The disadvantage of original OFM technique is checked and a novel bi-directional mm-RoF system based on new OFM technique using dual-drive MZM as high-order optical side-modes generator is proposed in principle and experimentally verified by a bi-directional mm-RoF system which not only produces 38 GHz information bearing signal in downstream, but also provides 40GHz local reference for down-conversion of upstream signal. Finally the advantage of OFM technique in reducing fading effect of fiber dispersion is theoretically proved.

Study on methods to yield a periodically wavelength-swept lightwave signal based on 60GHz radio-over-fiber system

In order to generate a stable and pure 60GHz millimeter-wave signal, a periodically wavelength-swept lightwave signal over a limited wavelength range which center wavelength at 1310nm and frequency-swept rate up to 1GHz is an important component of the whole system. In this paper, we focus on three methods to yield the wanted periodically wavelength-swept lightwave signal, which are sinusoidal wavelength scan, triangular wavelength scan and saw-toothed wavelength scan. We analyze in theory the power characteristics and the spectrum characteristics of the 60GHz millimeter-wave signals relative to the different wavelength-swept lightwave signal generated by different wavelength-swept methods. Furthermore, we simulate the 60GHz radio-over-fiber transmission systems respectively with the three wavelength sweep methods and gain the results in agreement with the analysis in theory.

Dynamic survivable routing in WDM networks with shared risk link groups

In this paper, we study the problem of dynamic survivable routing in optical networks with Shared Risk Link Groups (SRLG). Survivability and service continuity have been well recognized as the most important issues in the design of control and management planes for the next-generation optical networks with wavelength-division multiplexing (WDM) as the core technology. To make the connections survivable after various failure scenarios such as fiber cut and duct cut, it is necessary to consider SRLG diverse routing constraints in the traffic grooming problem. To jointly consider the working and backup paths, we first formulate the diverse routing problem into an Integer Linear Programming (ILP) process, in which the working and shared backup paths corresponding to a connection request are solved in a single step. We proposed failure-dependent SRLG protection heuristics algorithms for fiber selection. We compared the performance of various routing algorithms through simulation studies based on different metrics. Another contribution of this paper is a well-designed link-state metric is proposed for allocating the backup path and two selection schemes considering path costs are developed.

Algorithms for lightpath establishment in wavelength-routed networks

We consider the problem of routing and wavelength assignment problem (RWA) in wavelength-routed networks, which consists of the Wavelength Division Multiplexers (WDM) and optical cross-connect (OXCs) devices interconnected via point-to-point WDM links. Assume that none of the OXCs has wavelength conversion capability. The paper shows that the problem of RWA can be solved simultaneously by employing an efficient graph theoretic formulation, named as multi-layered graph model. On the basis of this notion, a heuristic RWA algorithm for static case is proposed. The numerical examples confirm that the proposed approach for static lightpath establishment (SLE) can obtain better solution for the number of requested lightpaths. The paper also considers the dynamic lightpath establishment (DLE) problem. We propose another heuristic DLE algorithm based on alternate-lightpath routing, according to a global selection criterion. We make a comparison of blocking probability according to different selection criterion. The performance of the proposed DLE algorithms is also evaluated and compared with that of the conventional algorithm via simulation of an arbitrary mesh network, where lightpath requests are assumed to arrive according to a Poisson process with exponentially distributed holding times.

Analysis of OFDM signal distortion in optical fiber links

This paper is dealing with the non-linear distortion of different optical modulators including directly modulated laser diode (LD), Mach-Zehnder modulator (MZM) and reflective semi-conductor optical amplifier (RSOA), which are candidates of optical device used to make colorless ONUs. To analyze the performance of different optical modulators a unified mathematic model is developed in which the optical OFDM signal output from an optical modulator is expressed as a power series including 1-st order and higher order terms. Based on this statistical model, the performance of the modulators are computed and compared. The effect of third order distortion in modulating signal on error vector magnitude (EVM) is particularly evaluated for optimizing the fiber transmission link.

Performance analysis of flat optical comb generation based on recirculating frequency shifter

The performance of the optical frequency comb generation based on the re-circulating frequency shifter has been analyzed and demonstrated in this paper. We have theoretically analyzed the condition for flatness of the optical frequency comb and the relative intensity noise influence. And the resulting performance analysis has been confirmed by a successfully generated 16 comb lines, which are stable and flat with spacing 12.5 GHz.

R+WFQ : A novel SLA-supported packet fair queueing algorithm for OLT scheduler

To implement both fairness and priority scheduling in OLT scheduler, this paper proposes a SLA-supported packet fair queueing algorithm named R+WFQ. It employs WFQ discipline to serve high-priority sessions and Round Robin discipline to transmit low-priority sessions in free moments existed in traditional WFQ. Computer simulation results as well as theoretic analysis show that the proposed algorithm has excellent performance in terms of the implementation complexity, fairness and delay properties.

Performance of optical OFDM transmission over RoF system with Mach-Zehnder modulator

This paper is concerned with the effect of the nonlinearity of an MZM (Mach-Zehnder modulator) on optical OFDM signal distortion. The optical OFDM signal output from the MZM is expressed as a Taylor series including third-order and fifth-order nonlinear distortion terms, by which we can easily establish a mathematical model of the optical OFDM signals in different formats and rates. According to the model, we can get the EVM at the optimized point. Moreover, the proposed theoretical model is proved in good agreement with experiment results of the RoF (Radio over Fiber) system.