Modal Bandwidth Research Articles

Statistical Study of Graded-Index Perfluorinated Plastic Optical Fiber

Plastic fiber-based optical links have been proposed for a wide variety of high-speed short reach applications. Graded-index (GI) multimode plastic optical fiber (POF) that supports 10 Gb/s over 50 m is commercially available and 40 Gb/s over 100 m has been demonstrated. However, unlike single-mode fiber and like silica multimode fiber (MMF), GI POF exhibits a range of performance that depends on launch condition and the accuracy of the index profile. Here, we report on the first statistical study of a large set of GI POF. We examine >; 40 samples of 62.5 μm core POF with four different cabling types that represent current-generation commercially available POF. We assess performance in terms of the 10 GbE requirements and quantify loss, chromatic dispersion, differential modal delay, effective modal bandwidth (EMB), and eye closure penalty. We find that nearly all of the measured 100 m fibers support the strict 10 GbE vertical-cavity surface emitting laser source EMB requirement, and that many fibers can support >; 40 Gb/s over 100 m. We thus demonstrate that GI POF can reliably support 10 Gb/s and larger bit rates to distances of 100 m.

Potential of the high modal bandwidth OM4 glass multimode fiber for the multi-services concept

In this paper, we report new results dealing with the wavelength multiplexing transmission scheme over the OM4 high modal bandwidth multimode fiber. Fiber bandwidth measurements both at 850 nm and 1300 nm clearly show the huge bandwidth/length product of this fiber. The simultaneous transmission of a high data rate baseband signal (10 GbE) at 850 nm and a radiofrequency MultiBand Orthogonal Frequency Division Multiplexing Ultra-Wide Band (band group 5–10 GHz) MB-OFDM UWB signal (480 Mbps) at 1300 nm is presented. The measurements – Bit Error Rate (BER) for the 10 GbE signal and Error Vector Magnitude (EVM) for the MB-OFDM UWB signal – that are hereby reported show safe results under the requirements of the corresponding communication standards; they give this architecture an affordable approach for home/office networking at high data rate in a joint fixed and wireless environment.

Indoor coverage improvement of MB-OFDM UWB signals with radio over POF system

Abstract A radio over fiber system using the fluorinated based polymer multimode fibers (PMMF) is presented in this paper for the enhancement of the indoor coverage of the multiband orthogonal frequency division multiplexing ultra-wideband standard (MB-OFDM UWB) inside a building. A preliminary part related the cost analysis owing to glass and polymer multimode fiber deployment inside a fiber network is reported. The study of the physical properties of the polymer optical fibers (core diameter, numerical aperture, differential mode delays, modal bandwidth…) is firstly performed in order to effectively exhibit the potentialities and the robustness of such fibers to be used in a low cost radio over fiber system. The DMD measurements of four fluorinated based polymer optical fiber are reported. The designed system operates at 850 nm with commercial off the shelf (COTS) devices combined to the intensity modulation/direct detection technique. The opportunity of using polymer fibers and COTS components to improve the indoor coverage of the MB-OFDM UWB standard is so reported by the measurement of the Error Vector Magnitude or the Relative Constellation Error variation as a function of the system parameters (RF power, optical attenuation, fiber length…) as well as the compliance of the eye diagram with the mask testing. By the way, the transmission performance of both 200 and 480 Mbps signals is demonstrated over up to 200 m link length of polymer multimode fibers: transmission penalties are quantified by relative constellation error with values under the standard requirements. A comparative study with classical OM2 50 μm based glass multimode fiber having the same bandwidth/length product than the PMMF is done.

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%.

Twin Symmetric E-plane Slab Loaded Waveguide Structure for Point Beam Acceleration

Renewed interest regarding the exploitation of dielectric loaded waveguides in high gradient accelerator structures requires a closed form field formulation as cut-off frequencies and optimisation are problematic for numerical methods. In this paper we will present efficient closed form solution for generic slab loaded waveguide boundary value problems. This solution offers flexibility in a sense that it can be further exploited to derive a Green’s function linking transverse field expressions for planar structures. The developed solution is demonstrated for a twin slab E-plane slab loaded structure coupled to a Point source emitter assembly. The emission characteristics of the point source emitter assembly are optimized to generate a high intensity and focused beam to be fed to this E-plane slab loaded waveguide structure for beam acceleration. The field analysis, mode nomenclature, modal hierarchy, modal bandwidth, cut-off plane, impedance plane and dispersion relations for this accelerating structure is included for sake the of completeness.

Differential Mode Delay Measurements of Fluorinated Graded Index Polymer Optical Fiber

We have performed a detailed study of four different perfluorinated graded index polymer optical fibers issued from two manufacturers. After the description of the test bench that has been set up in order to measure the differential mode delays, we report on the corresponding measurements in time domain and the deduced ones in the frequency domain allowing us to get the optical modal bandwidth.

A Complete 8-GHz QPSK-MODEM Featuring Novel Subcarrier and Data Synchronization for Optical Communications

We describe the application of subcarrier multiplexing (SCM) to enable broadband transmission beyond the modal bandwidth of multimode fiber (MMF) optical links. The application of a quadrature phase-shift keying modem featuring novel carrier and symbol-timing recovery circuits, demonstrates significant enhancement in channel capacity. By using a 2.7-GHz pilot-tone-injected phase-locked loop (PLL) and referencing subscriber data to a prescaled version of the subcarrier, zero-latency carrier and data synchronization has been achieved exhibiting 675 Mb/s bit-oriented clock extraction in network terminal equipments. The novel scheme is scalable to higher aggregate rates and upgrades to existing installed-base 50 mum MMF infrastructure to provide low-cost, high-capacity interconnects for storage area and campus network applications

Overcoming Modal Bandwidth Limitation in Radio-over-Multimode Fiber Links

Employing the optical frequency multiplication method, the theoretical modal bandwidth limitation of multimode fiber (MMF) can be overcome in radio-over-fiber links. The principle is analyzed theoretically and supported experimentally by generation and transmission of microwave carriers up to 40 GHz and 16- and 64-level quadrature-amplitude-modulated (QAM) radio signals in the 24- to 30-GHz band over 4.4-km MMF link

Dispersion penalty analysis for VSR —1 optical links

This paper presents and approach to calculate dispersion penalty for VSR-1 optical links. Based on parameters of a specific VSR-1 link, dispersion penalties are computed for various modal dispersion bandwidths respectively. The worst-case eye closure is expressed numerically by using the signal waveform at time 0, and the signal waveform is obtained in frequency domain through FFT algorithm. By this approach, the dispersion penalty is determined by the shape of transfer functions of the various components in the links. To simplify the derivation of multimode fiber link transfer function, a Gaussian form of normalized impulse response is used. This calculation approach can be used to estimate the worst-case dispersion penalty of VSR-1 links in the link budget analysis.

Modal bandwidth enhancement in a plastic optical fiber by W-refractive index profile

A plastic optical fiber (POF) having a W-shaped refractive index profile (W-shaped POF) was prepared for the first time that had a possibility to realize a higher bit rate transmission than those of the conventional silica-based multimode fiber and graded index (GI) POF links. Since the W-shaped POF has a valley of the refractive index at the boundary of the core and cladding of the conventional graded-index (GI) POF, the group delay of higher order modes is strongly influenced, and the modal dispersion in the GI POF is compensated. By comparing the propagating mode properties of the W-shaped POF with those of the GI POF, we clarified theoretically and experimentally that the index valley has a remarkable modal dispersion compensation effect.

Simulation of internal waves using GM model and comparison against measurements during ARMEX-I

A linear internal wave model based on the Garrett-Munk (hereafter GM) modal spectrum has been developed. The model simulates sound speed structure due to internal waves in the ocean. CTD yoyo (go up and down continuously) data collected during the ARMEX-I experiment has been utilized to validate the model. Internal waves amplitudes at the experimental site are found to be >1m. EOF and modal decomposition analyses reveal that the modal bandwidth parameter j* = 3 and modal energy damping parameter P = 1 or 2 and follows the GM suggested values. Comparison of the measured sound speed profiles against the simulated reveals that the GM model is capable of reproducing most of the variability due to IW in the deep-waters. The agreement between the observed and simulated perturbations is quite good.

Evolution of the beam diameter in a multimode fiber link through offset connectors

We find that using an overfilled launch, transmission of an 8-Gb/s nonreturn-to-zero (NRZ) signal can suffer a significant power penalty due to modal noise or fiber bandwidth fluctuations if an offset connector is located before the 300-m-long multimode fiber link. This is an important problem as multimode fiber links in the premises typically contain several (potentially offset) connectors. A possible solution in state-of-the-art multimode fibers having a small refractive index center defect is to employ a single-mode center launch. To evaluate the robustness of this technique in the presence of several offset connectors in the link, a thorough study of the evolution of the beam diameter is performed. It suggests that at least five standard connectors may be employed without incurring significant power penalties.

The importance of modal bandwidth in Gigabit Ethernet systems

AbstractThis article deals with the evaluation of bandwidth measurements in Gigabit Ethernet Systems using an empirical data model. It concentrates on the use of multimode fibers due to the advent of Vertical Surface Emitting Laser (VCSEL) technology that improves the performance of multimode fiber optics. Copyright © 2001 John Wiley & Sons, Ltd.

Influence of core diameter on the 3-dB bandwidth of graded-index optical fibers

The frequency response and bandwidth of multimode silica glass fibers are investigated in this paper. The theoretical model incorporates both wavelength and modal effects including power coupling from random microbends. The 3-dB bandwidth is examined through the study of the fiber transfer function which introduces the wavelength and modal effects as two separate filter functions. The formal derivation of the chromatic transfer function is analytical. On the other hand, the modal bandwidth is obtained by numerically solving the power flow equation in the frequency domain using the Crank-Nicholson method. As an application, the transfer function is illustrated and subsequently discussed with special focus spent on analyzing the influence of the fiber size in combination with the launching conditions. We show in particular that the larger the core, the greater the bandwidth potential of the fiber when operated under selective mode excitation. Some measurements are also carried out and excellent agreement between this model and data is achieved.

Bistatic reverberation in range-independent waveguides

The basis for predictions of the temporal evolution of bistatic reverberation in range-independent waveguides is obtained under a modal framework using the narrow-band approximation. Approximate expressions for the field incident on the bottom at any given time are obtained as a function of modal group speed, dispersion, bandwidth, and azimuthal Fourier order. These functions, combined with the range-dependent spatial correlation functions of Gaussian distributed scatterers, which are also approximated as a function of Fourier order, provide the basis for the prediction of reverberation intensity and three-dimensional spatial coherence as a function of time after shot in multipath environments. The predicted characteristics of the reverberation are shown for several scenarios, emphasizing the differences caused by frequency, bandwidth, waveguide parameters, and receiver aperture characteristics.

Overcoming the modal bandwidth limitation of multimode fiber by using passband modulation

It is demonstrated that the bandwidth limitation of multimode fiber links arising from modal dispersion can be overcome by using passband modulation in the frequency range beyond the 3 dB bandwidth. Transmission of 1.25 Gb/s over 500 m of near-worst case 62.5 /spl mu/m multimode fiber is achieved using two subcarrier multiplexed channels at the 850-nm wavelength.

Bandwidth reduction in gigabit ethernet transmission over multimode fiber and recovery through laser transmitter mode conditioning

The experimental work carried out by members of the Gigabit Ethernet Standard's Modal Bandwidth Investigation group are reviewed to provide an understanding and to propose a solution to the bandwidth reduction observed in high-speed fiber optic test links based on laser transmitters and multimode fiber. The reduced bandwidth values, as compared to the manufacturers specified values, were caused by differ- ential mode delay (DMD) in the optical signal. The cause of the DMD is linked to a combination of the launch conditions established between the laser source and multimode fiber. The criteria for developing a solution with the goal of modifying the launch conditions to eliminate DMD in laser transmission over 99% of multimode fibers are established. © 1998 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(98)00912-X)

High bandwidth data transmission in multimode fibre links using subcarrier multiplexing with VCSELs

Subcarrier multiplexing techniques are shown to allow data transmission over multimode fibre links at carrier frequencies of more than 20 times the 3 dB modal bandwidth of the fibre.

Optimizing the performance of closed-loop adaptive-optics control systems on the basis of experimentally measured performance data

An experimental method is presented to optimize the control algorithm for a closed-loop adaptive-optics system employed with an astronomical telescope. The technique uses wave-front sensor measurements from an independent scoring sensor to calculate adjustments to the wave-front reconstruction algorithm and the bandwidth of the adaptive-optics control loop that will minimize the residual mean-square phase distortion as measured by this sensor. Specifying the range of possible adjustments defines the class of control algorithms over which system performance will be optimized. In particular, the technique can be used to compute an optimized wave-front reconstruction matrix for use with a prespecified adaptive-optics control-loop bandwidth, optimize the control-loop bandwidth for a given reconstruction matrix, optimize the individual modal control bandwidths for a fixed modal reconstructor, or simultaneously optimize both the wave-front modes and their associated control bandwidths for a fully optimized modal control algorithm. The method applies to closed-loop adaptive-optics systems that incorporate one or more natural or laser guide stars and one or more deformable mirrors that are optically conjugate to distinct ranges along the propagation path. Initial experimental results are reported for the case of a hybrid adaptive-optics system incorporating one natural guide star, one laser guide star, and one deformable mirror. These results represent what is to the authors’ knowledge the first stable closed-loop operation of an adaptive-optics system using multiple guide stars.

Transient response of coupled modes in complex structures

The transient response of coupled modes is considered. Numerical and experimental results are presented for resonators, beams, and plates subjected to impulsive and random excitations. Using a random vibration analysis the time constant of response for a resonator is found to be inversely proportional to the damping bandwidth. Using a transient SEA formulation the time constant for a modal response is found to be inversely proportional to the modal bandwidth which includes the effects of both the damping and coupling loss factors.