Hanyi Zhang

Simplified optical millimeter-wave generation configuration by frequency quadrupling using two cascaded Mach―Zehnder modulators

We propose what we believe to be a novel method to generate optical millimeter-wave signals with frequency quadrupling using two cascaded Mach-Zehnder modulators (MZMs). Both theoretical analysis and experimental demonstration are presented. By symmetrically biasing the MZMs, without any optical filters or electrical devices, a high-quality millimeter wave at 40 GHz with an optical harmonic distortion suppression ratio of more than 25 dB is obtained. Furthermore, it is also proved to be valid that the proposed scheme is insensitive to the MZM bias drift, which demonstrates a relatively higher stability.

An Efficient Distributed Control Scheme for Lightpath Establishment in Dynamic WDM Networks

An adaptive hybrid reservation protocol (AHRP) is proposed for the purpose of quickly and efficiently establishing a lightpath in dynamic wavelength routed networks. This protocol uses a special reservation-and-probe (RESV_PROB) packet and extends the signaling to integrate forward reservation and backward reservation into one monolithic process. To decrease the blocking probability that happens in cases where two end nodes associated with a specific link simultaneously reserve the same wavelength, an adaptive wavelength selection policy is specially employed in AHRP. A discrete-event simulation tool based on ns-2 is developed to investigate AHRPs performance, including its blocking probability, average lightpath setup delay, and signaling overhead. AHRP is also compared with existing protocols. Results show that during highly dynamic traffic conditions, AHRP possesses the lowest blocking probability, shorter setup delay, and less signaling overhead.

Impact of group delay ripples of chirped fiber grating on optical beamforming networks

The impact of group delay ripples of chirped fiber gratings (CFG) on the performance of optical beamforming networks (OBFN) is investigated. The paper theoretically analyzes the quantified relations among the amplitude and period of CFG, the optical angle frequency interval at the inter-element arrays and the beampointing shift. The wavelength instability of the optical source is also investigated. This instability-induced phase jitter of RF signal has been verified experimentally. The theoretical models are proposed to analyze the performance of CFG-based OBFN systems.

Performance Study of Distributed Wavelength Reservation Protocols within Both Single and Multi-Fiber WDM Networks

Distributed wavelength reservation protocols are employed to dynamically set up and tear down lightpaths in WDM networks. In this paper, discrete event-driven simulations are carried out to investigate the performance of different protocols under both single and multi-fiber circumstances. Simulation results indicate that the behavior of these protocols varies noticeably between single and multi-fiber networks. Discussions on these results are also presented. It is found that the preferred scheme in the literature, which adopts backward reservation with random wavelength selection, does well in single-fiber scenarios. But this scheme fails to be excellent in multi-fiber scenarios since it cannot take full advantage of multiple fibers. Then, we extend the reservation protocols for multi-fiber networks and propose a novel wavelength selection policy called Maximum-Availability policy. Results show that our scheme will give an outstanding performance in both single and multi-fiber networks.

X-band continuously variable true-time delay lines using air-guiding photonic bandgap fibers and a broadband light source

We propose a novel implementation of true-time delay (TTD) using air-guiding photonic bandgap fibers (PBGFs) and a broadband light source. The air-guiding PBGFs are experimentally studied and used in the TTD module for the first time, to the best of our knowledge. The proposed approach shows the advantages of simple architecture, compact size, larger dispersion, low-temperature sensitivity, and high immunity to nonlinear effects in our experiments. The PBGFs were spliced with single-mode fibers with a 2 dB loss, and the characteristics of the PBGFs were measured. The PBGF-TTD with a continuously tunable time delays from 0 to 500 ps was demonstrated using the amplified spontaneous emission light of an erbium-doped filter amplifier as a broadband light source.

The impact of phase errors on arrayed waveguide gratings

The impact of phase errors on arrayed waveguide gratings (AWGs) due to waveguide length deviation in AWGs has been analyzed theoretically. A statistical model to estimate the influence of phase errors in silica-based arrayed waveguide multiplexers was developed, using Fourier optics and scalar diffraction theory. In addition, the insertion loss and crosstalk of AWGs caused by phase errors were analyzed. To maintain the adjacent crosstalk at less than -25 dB, a maximum standard deviation /spl sigma//sub max/ of phase errors to the design of AWGs is obtained.

Achieving Resource-Efficient Survivable Provisioning in Service Differentiated WDM Mesh Networks

A resource-efficient provisioning framework (RPF) is proposed in this paper for optical networks providing dedicated path protection (DPP) and shared path protection (SPP) services. The framework reduces resource consumption by considering spare capacity reservation of DPP and SPP cooperatively while provides 100% survivability guarantee and maintains the recovery time for both protection types against the predominant single link failures. To tackle the service provisioning problem under the framework, an integer linear programming (ILP) formulation is presented to find the optimal routing solution for a given set of traffic demands. The objective is to minimize total capacities consumed by working and backup paths of all demands. Then, heuristics are developed for on-line routing under dynamic change of traffic. Numerical results show that compared with traditional provisioning framework (TPF), the RPF has the following advantages: (1) Over 10% capacity savings are achieved for static service provisioning; (2) blocking probability of both protection types is greatly reduced; (3) lower resource over build is achieved; and (4) average backup-path hop distance of shared-path-protected flows is reduced. Finally, network survivability in face of double link failures is discussed under the framework.

Multisideband Detection Radio-Over-Fiber Link With Phase Modulation and Fiber Demodulation for Vector Signal Transmission

We propose and demonstrate a multisideband detection (MSD) radio-over-fiber (RoF) link with optical phase modulation (PM) and fiber demodulation to transmit vector signals. In the scheme, the optical PM signal is demodulated by the fiber dispersion. The fading effect can be almost entirely overcome thanks to the MSD. In case of 50-Msymbols/s vector signal with frequencies of subcarrier ranging from 2 to 12 GHz over 25-, 50-, and 100-km single-mode fibers, respectively, the RoF-links error vector magnitude of better than 4.5% and spurious-free dynamic range of more than 97 dB·Hz2/3 are obtained experimentally.

Performance Analysis of Distributed Protocols for Bidirectional Wavelength Reservations in Dynamic WDM Networks

In this paper, we present an analytical model to investigate the blocking performance of distributed wavelength reservation protocols in dynamic WDM networks. This model extends the approach of [S. Arakawa et al., Proceedings of ITC-CSCC, (Sado, Japan, July 1999), pp. 828--831] in two aspects: firstly we take into account the contention between the two end nodes of bidirectional links in bidirectional wavelength reservations. Secondly, we make a distinction between the effects of different kinds of network delays, which include signaling transmission delay, signaling processing delay, and optical cross-connects (OXC) operation delay. As an application, we use our method to analyze the performance of two different signaling processing schemes, namely forward after cross-connect (FAXC) and forward before cross-connect (FBXC) [M. Goyal et al., Technical Digest of OFC2002 (Anaheim, CA, Mar. 2002) pp. 489--490]. The accuracy of our analytical model is validated by discrete-event simulations. Numerical results show that the FBXC scheme can give a lower network blocking probability than FAXC, and the efficiency of FBXC becomes more significant as the OXC operation delay increases.

Impact of concatenated AWG filters in metro transparent network with DML

This paper studies the impact of concatenated AWG routers of metro transparent network with directly modulated lasers (DML). The wide bandwidth and central frequency shift of the directly modulated laser entail a large signal penalty, thereby limiting the allowable number of AWG routers in a metro network. The degradation caused by the concatenation of passband-flattened AWG is much lower than that of the conventional round-top AWG of the same number. Therefore the passband-flattened AWG has the largest allowable number in the metro network based on DML.