Semiconductor space switches based on multimode interferencecouplers

It is shown theoretically that selective perturbation by electrorefractive effect of the even-order modes in III-V semiconductor multimode interference couplers gives rise to high-performance optical switching. The calculated performance of the proposed switch is 3.4 GHz/Vmm, compared to 0.85 GHz/Vmm for an equivalent Mach-Zehnder interferometer (MZI) switch. The effects of electroabsorption and dimension variations are analyzed to demonstrate the feasibility of the proposed device     

Three-dimensional method for simulation of multimode interferencecouplers

A three-dimensional (3-D) method for modeling multimode interference devices based on a finite element formulation is presented as an alternative to models having one-dimensional cross-sections only. The method is tested for couplers with two different strongly confined waveguides structures. The results show that full treatment of two-dimensional cross-section is of special importance for design and simulation of waveguide devices for which the effective index approximation is no longer valid. For deep rib waveguide geometries, excess loss greater than 15 dB can be obtained if the 3-D method is not used in the design of the couplers     

The bandwidth of a multimode fiber chain

We propose a new method for evaluating the baseband transmission in a multimode fiber chain. Carnevale and Paek (Bell Syst. Tech. J., vol. 62, pp. 1415-1431, 1983) stated that errors in the fiber manufacturing process will randomly distort a desired index profile, presumably of power-law type. We extend their discussion to the bandwidths of concatenated fibers, by considering Gaussian approximations to actual transfer functions. The bandwidth can thus be separated into two parts, one of which is due to the over- and undercompensation of individual, idealized power-law profiles and the other of which refers to random profile distortions as well as possible mode coupling within mode groups. The former part should normally dominate the length dependence of longer chains. The latter part may be replaced by an expectation value, typical for the actual manufacturing process. A remarkably good agreement is achieved between experimental and predicted bandwidths for various chain configurations.     

多模光纤带宽的计算与优化

文章对多模光纤的带宽进行了理论分析,并进行仿真计算和优化,找出了不同工作波长下多模光纤最优折射率指数(gopt),同时对50/125μm新一代多模光纤的带宽进行了分析.     

Launching condition dependence of graded-index multimode fiber lossand bandwidth

Theoretical and experimental studies of the launching-condition dependence of graded-index 50-μm core, 0.2-numerical aperture multimode fiber transmission loss and baseband bandwidth are discussed. A combination of a SGS mode scrambler and a mandrel wrap mode filter was used as the launching system. It was found that steady-state fiber loss measurements should be carried out at an approximate mandrel curvature of ρ=0.07 mm^-1. This curvature is much smaller than the curvature ρ=0.15 mm^-1 which produces an equilibrium-mode distribution as defined by the International Telegraph and Telephone Consultative Committee (CCITT). Measurement at ρ=0.15 mm^-1 is shown to underestimate steady-state loss. It was also found that reproducible and reasonable bandwidth measurement can be obtained by choosing ρ=0 to 0.07 mm^-1     

LED bandwidth of multimode fibers as a function of laser bandwidth and LED spectral characteristics

Equations have been developed that relate the bandwidth performance of 62.5-μm core diameter (NA = 0.29) graded-index multimode fiber when measured with LED sources to the LED's spectral characteristics and to the bandwidth measured with laser sources. Because the fiber's spectral loss characteristic filters the LED's power spectrum by shifting its center wavelength and narrowing its spectral width, these equations suggest that chromatic bandwidth scales more favorably than inverse linearly with length. The equations developed here have been used to predict hundreds of LED bandwidths measured independently both in the laboratory and in field installations. With typical agreement between these predictions and the measurements having an rms error of about 11 percent, these equations allow for system design and prediction of the bandwidth performance of LED-based multimode links.     

Comparison of measured and predicted bandwidth of graded-index multimode fibers

Measurements of pulse spreading in three graded-index fibers have been performed over an extensive range of wavelengths, including regions in which the index profiles become optimal and the bandwidths correspondingly high. The refractive index distributions and profile dispersion parameter have been measured and used in a ray-tracing algorithm in order to predict bandwidths. Comparison reveals that averaging processes on the index data are usually necessary to account for noncircularity of the fiber and small variations in the deduced profile caused by the wavelength dependence of the near-field intensity distribution. Results obtained by this means usually tend to slightly underestimate the true fiber bandwidth, while α-profile predictions always result in overestimates by about one order of magnitude. Remaining discrepancies between measured and predicted bandwidths are attributed to small variations of the index profiles along the fiber length.     

Multi-service applications on high modal bandwidth glass multimode fibre

The work reported deals with the demonstration of the use of high modal bandwidth OM4 multimode fibre as multi-purpose transmission media for short-range indoor or outdoor applications taking advantage of the wavelength division multiplexing concept. Simultaneous transmission of a digital 10 GbE signal and a radio-frequency multiband orthogonal frequency division multiplexing ultra-wide band (band group 5) signal at 480 Mbits has been successfully achieved over 1.1 km fibre length without any error and with relative constellation error (RCE) less than 5.5% rms, respectively. Concerning the radio signal, an additional 1 m-long wireless path has also been demonstrated that led to an overall RCE value of 7.2%.     

Fairly adjusted multimode dynamic guard bandwidth admission control over CDMA systems

Guard-based call admission control schemes support admission priorities based on resources sharing with differentiated resource capacity limits. To minimize deviation from call blocking/dropping targets due to nonstationary call arrival condition, dynamic guard-based schemes with predictive adaptation control adjust differentiated capacity limits according to predicted future arrival rates based on specified estimation algorithms. Existing dynamic guard admission schemes are developed under the assumption of perfect estimation, which may not be possible in a highly nonstationary environment and, thus resulting in failures to maintain targeted blocking/dropping probabilities. This paper presents the fairly adjusted multimode-dynamic guard bandwidth scheme, which is a dynamic-guard-based scheme over code-division multiple-access systems with predictive adaptation control to adapt interference-based guard loading-limits under nonstationary call arrival condition; and reactive adaptation control to counteract arrival rate estimation errors. When the predictive adaptation control policy mode is not able to maintain long-term call blocking or dropping targets due to estimation error, this will trigger reactive adaptation control policy modes that include temporary blocking (preemption) of one or more lower priority classes subject to fairness constraints to ensure lower priority classes are not preempted at all costs during estimation error recovery. Analytical and simulation results show that proposed scheme is able to provide performance guarantees in terms of dropping probabilities under nonstationary traffic arrival and imperfect arrival rate estimation.     

Explanation of launch condition choice for GRIN multimode fiberattenuation and bandwidth measurements

In order to predict the attenuation and bandwidth of a graded index (GRIN) multimode fiber system accurately, the fiber composing the system is best characterized by a restricted launch attenuation measurement and an over-filled-launch (OFL) bandwidth measurement of the fibers. The rationale for these launches is provided in terms of the power evolution in the fiber and its impact on system performance, and the basic physics of GRIN multimode fiber. Experimental results are shown that demonstrate the results     

n×m涡卷混沌吸引子的研究及硬件实现

提出了产生n×m涡卷混沌吸引子的一种新方法,用三角波函数序列和阶跃函数序列构造网格多涡卷混沌系统,找出函数中平衡点和转折点的值,并对系统的基本动力学特性进行了研究,包括理论分析和计算机模拟仿真。用模块化的方法设计了现场可编程门阵列（FPGA）硬件实验电路,给出了相关的实验结果。计算机仿真和FPGA硬件实验结果相吻合,由此证明了该系统的混沌特性。     

Launching condition dependence of bandwidth in graded-index multimode fibers fabricated by MCVD or VAD method

Baseband frequency response of a single or concatenated MCVD and VAD fibers measured by two representative launching conditions-equilibrium mode distribution (EMD) and overfill mode distribution (OMD)-is studied. From computations based on the WKB approximation method and from experiments, it is found that the OMD exciter on the average results in a greater 6-dB bandwidth than the EMD exciter for a single MCVD fiber, but is does a smaller bandwidth for a single VAD fiber. On the other hand, in concatenated fibers, the EMD exciter results in a greater bandwidth of about 10 percent in comparison with the OMD exciter. The concatenation factors for MCVD fiber and VAD fiber are different for EMD excitation, while they are nearly identical with each other for OMD excitation.     

Pulse broadening in multimode optical fibres with large ?n/n: numerical results

The r.m.s. impulse response width of germania doped fibres having power-law profiles at the carrier wavelength is evaluated with the help of a numerical method and measured values of dn/d?. For ?n/n?0.02, our result exceeds by more than one order of magnitude that obtained from an analytical formula based on the assumption that n dn/d? varies linearly with n2. The optimum profiles are found to differ very significantly from power-law profiles. Our numerical technique is based on scalar-ray optics. It is applicable to any fibre having a large V-number and a smooth profile.     

Signal transmission with optical carriers in multimode range of single-mode fibres

Low-cost optical transmission systems consisting of GaAlAs transmitter devices, Si-APD receivers and single-mode fibres with 1.2 ?m cutoff have been investigated. Theoretical and experimental results are presented which demonstrate the potential as well as the limitations of such systems for local network applications.     

Signal bandwidth consideration of mutual coupling effects on adaptive array performance

The effect of mutual coupling on the performance of a least mean square (LMS) adaptive array using dipole elements is analyzed in consideration of the signal bandwidth. The purpose here is to illustrate quantitatively the significance of the effect of mutual coupling. The results show that the effect in the broad-band signal cases is much greater than that in the narrow-band cases, particularly when few antenna elements are used.     

Measurement of variation of multimode fibre bandwidth withwavelength in 850 nm region using mode-locked Styryl-9 dye laser

A tuneable mode-locked dye laser has been used to measure the frequency response of a multimode fibre as a function of wavelength in the 850 nm region. The narrow spectral width of the dye laser gives an improved accuracy for large length-bandwidth product fibres. The results are compared with those obtained using both pulsed and CW semiconductor lasers     

PON上行带宽通用管理模型研究与实现

目前,PON接入方式正成为各电信运营商发展宽带业务的主要技术方式。主要针对PON的上行链路带宽的管理进行研究,探讨GPON与EPON在这方面的异同,进而提出一种通用管理模型,并研究其实现。     

An experimental and theoretical study of the offset launchtechnique for the enhancement of the bandwidth of multimode fiber links

This paper reports an experimental and theoretical study of bandwidth enhancement in multimode fiber links achieved by using offset launch techniques. It is found, both from theory and experiment, that an up to four-fold bandwidth enhancement can be obtained compared to standard overfilled launch techniques despite exciting over 50% of the fiber modes, thus allowing good stability. The enhancement technique is found to be achieved for a range of fibers with different core diameters and core refractive index profiles. The level of bandwidth enhancement depends upon the inherent bandwidth of the fiber, being particularly effective in improving the performance of low bandwidth “worst case” fibers. The launch is found to be stable with respect to environmental variations, showing bandwidth enhancement for injection positions or connector offsets of up to 5 μm from optimum. In addition, unlike many restricted launch techniques, it is found to be tolerant to angular fiber misalignment for angles up to 6° from normal     

Effective bandwidth of general Markovian traffic sources andadmission control of high speed networks

A prime instrument for controlling congestion in a high-speed network is admission control, which limits calls and guarantees a grade of service determined by delay and loss probability in the multiplexer. It is shown that for general Markovian traffic sources it is possible to assign a notional effective bandwidth to each source that is an explicitly identified, simply computed quantity with provably correct properties in the natural asymptotic regime of small loss probabilities. It is the maximal real eigenvalue of a matrix that is directly obtained from the source characteristics and the admission criterion, and for several sources it is simply additive. Both fluid and point process models are considered. Numerical results show that the acceptance set for heterogeneous classes of sources is closely approximated and conservatively bounded by the set obtained from the effective bandwidth approximation. The bandwidth-reducing properties of the leaky bucket regulator are exhibited numerically