The promise of the infinite-dimensionality of orbital angular momentum (OAM) and its application to free-space and fiber communications has attracted immense attention in recent years. In order to ...facilitate OAM-guidance, novel fibers have been proposed and developed, including a class of so-called ring-fibers. In these fibers, the wave-guiding region is a high-index annulus instead of a conventional circular core, which for reasons related to polarization-dependent differential phase shifts for light at waveguide boundaries, leads to enhanced stability for OAM modes. We review the theory and implementation of this nascent class of waveguides, and discuss the opportunities and limitations they present for OAM scalability.
This paper describes an advanced multimode-fiber-link model that was used to aid the development of Telecommunication Industry Association standard specifications for a next-generation 50-/spl ...mu/m-core laser-optimized multimode fiber. The multimode-link model takes into account the interactions of the laser, the transmitter optical subassembly, and the fiber, as well as effects of connections and the receiver preamplifier. We present models for each of these components. Based on these models, we also develop an efficient and simple formalism for the calculation of the fiber transfer function and the signal at the link output in any link configuration. We demonstrate how the model may be used to develop specifications on transmitters and fibers that guarantee any desired level of performance.
The performance of plastic optical fiber is greatly influenced by the related but distinct effects of mode coupling and differential modal attenuation (DMA). We establish a method for estimating the ...matrix that governs both of these effects and allows us to distinguish the two. We obtain partial quantitative estimates of this matrix for a particular graded-index plastic optical fiber (GI-POF). The sample we studied exhibited strong but incomplete mode coupling over 100-m lengths, while DMA was largely limited to a centerline defect. We show that much of the loss of the fiber can be attributed to mode coupling between mode groups with similar effective indexes.
This paper presents the scientific arguments used in the specification development process by the Telecommunications Industry Association (TIA) Working Group FO-2.2.1 to develop the new multimode ...fiber and vertical-cavity surface-emitting laser specifications for high-speed application in data communications. Numerous engineering and commercial tradeoffs are described. The specification minimizes the link failure rate and overall link cost through utilization of communication-theory-based modeling and experimental verification. This was balanced against the reality of manufacturing costs attempting to maximize the yield of individual link components. The specific application used as an example has 50- mu m graded-index multimode fiber operating at 10 Gb/s (e.g., 10 Gb/s Ethernet and fiber channel). The link performance is determined by the interaction of the fiber intermodal dispersion measured by the differential modal delay, and the transceiver launch distribution into the multimode fiber measured by encircled flux. A theoretically based model and the simulation approach that were used to simulate 40 000 links are described. The information from these simulations was used to determine the specification limits. In addition, sensitivity to the specification limits was evaluated. The experimental results of a round robin conducted by the TIA are presented, which confirm that the modeled performance would yield the expected results in actual practice.
We propose a pair of related new techniques for measuring the modal power distribution (MPD) of light launched into a multimode fiber (MMF). For modern applications involving laser launches, our ...method has several potential advantages over ray optics-based methods such as and recent extensions of them . Instead of relying on a time-averaged measurement of near-field intensity with a CCD camera to spatially resolve the launched power, our method uses a specially designed probe fiber to temporally resolve the launched power. If the source can be modulated fast enough (as is necessary for 10 Gbps serial transmission, for instance), the measurement is straightforward and the calculation of the MPD is trivial. For slower sources, a more involved measurement and inversion algorithm are required.
A pedagogically oriented review is given of progress made over the past year in our understanding of physics related to the charm quark. Included are discussions of the
R
c
deficit, the ψ′ anomaly, ...charm spectroscopy,
D nonleptonic decays, searches for flavor-changing neutral currents, new limits on
D
0 −
D
0
mixing and prospects for future experimental studies of the charm sector.
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