Multimode fibers (MMF) provide a reasonable and efficient solution for radio over fiber systems. However, in MMF systems the modal dispersion and chromatic dispersion can be very high. In this article, an efficient compensator is purposed and investigated. The impact of the compensator is tested with different radio modulations by simulations and experiments, and the compensated transfer function is analyzed as well. The application of the compensator provides significant improvement in the error vector magnitude. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:204–207, 2015

Dispersion compensation in millimeter wave radio over multimode fiber systems

Large-core silica multimode fibers, whose core diameters are generally 50 μm or 62.5 μm, form the bulk of short and medium haul optical fiber links in existence today, owing to their low cost and ease of deployment. However, modal dispersion significantly limits the maximum data rates that they support. Recently, the ability to multiplex several streams of data through optical fibers has spawned the development of few-mode multimode fibers. These fibers possess the low-dispersion characteristics of single-mode fibers and the ability to multiplex several data streams using multiple-input multiple-output (MIMO) techniques and mode-specific filtering to increase data rates. While fibers with larger core diameters possess a larger number of spatial modes, they do not support data rates as high as few-mode fibers. In this paper, we describe a simulation based approach to characterize the tradeoffs between fiber diameter, achievable data rates and alignment tolerances of coherent links that employ graded-index multimode fibers (MMFs) of various dimensions, using the information theoretic outage capacity as the metric. The simulations used fibers' intermodal coupling characteristics to measure its multiplexing abilities and dispersion limitations with mode-specific filters and launch and detection spatial filter arrays. The simulations indicate that the bandwidth-length product achievable over few-mode fibers with MIMO techniques can exceed 250 Gb/s-km, while heavy mode spreading and limited mode selectivity limits the bandwidth-length product to under 25 Gb/s-km in fibers core diameters larger than 50 μm.

Impact of fiber core diameter on dispersion and multiplexing in multimode-fiber links.

Analysis of second order harmonic distortion due to transmitter non-linearity and chromatic and modal dispersion of optical OFDM SSB modulated signals in SMF-MMF fiber links

The power-flow equation is employed to calculate bandwidth of step-index plastic optical fibers (POFs) for different launch conditions. The outcome specifies bandwidth as a function of the mean input angle and width of the launch-beam distribution. For small distribution widths, bandwidth is shown to decrease with increasing mean input angle of the launch-beam distribution. For large distribution widths, bandwidth becomes independent of the launch angle. Launch-beam distribution, mode-dependent attenuation, and mode dispersion and coupling in POFs strongly influence the bandwidth of data transmission systems.

Influence of launch-beam distribution on bandwidth in step-index plastic optical fibers.

In this paper, we focus on the study of large bandwidth wireless signal transmission following a 60 GHz standard over a multimode fiber link used to cover optical distribution for the last mile. To reduce the multimode effects within the fiber, a single mode fiber is first added to play a role of mode filter, and then replaced by a Mandrel as a filter. Error vector magnitude (EVM) is used as a metrics to analyze the signal degradation. Simulation results are confirmed by measurements. The EVM of the RoF links on single mode fiber, multimode fiber with and without filtering are compared.

Improvements on broadband signals in radio over fiber systems by mode filtering

The multimode (MM) optical fiber maximum operational range is defined by the fiber bandwidth (related to the intermodal dispersion) rather than by the fiber attenuation. The relationship between the modal bandwidth of the fiber, the launching condition and mode coupling is fairly complicated. There is presented a theoretical study on the modal bandwidth of the multimode fiber. The theory is based on a numerical solution of the coupled mode diffusion equation that allows the bandwidth of the MM optical fiber to be calculated. It is shown that appropriate modal filtering at the receiver side of the fiber link increases the link bandwidth.

J. Siuzdak

Papers

Influence of modal filtering on the bandwidth of multimode optical fibers