Showing papers on "Mode scrambler published in 1981"
TL;DR: In this paper, the cutoff characteristics of the first higher-order mode and phase coefficient, group velocity and power distribution characteristics of dominant modes are presented over a wide range of parameters and a two-layer step index elliptical fiber waveguide is presented as a special case.
Abstract: Single mode propagation in three-layer step index elliptical fiber waveguides is investigated theoretically. Previous analysis of the elliptical dielectric tube waveguide is extended to include cladded, W-type and tube-type fibers. Numerical results on cutoff characteristics of the first higher-order mode and phase coefficient, group velocity and power distribution characteristics of the dominant modes are presented over a wide range of parameters. A two-layer step index elliptical fiber waveguide is presented as a special case. High eccentricity single mode fibers have small modal beat lengths but have small core size and greater power distribution in the claddings. W-type fiber in the middle range of eccentricities is suggested for single mode single polarization applications.
17 citations
TL;DR: In this paper, an experimental investigation about the reliability of an attractive method recently proposed for modal power distribution measurements in multimode fibres is performed, and the method is shown to work also in some common cases when the hypotheses of validity are not rigorously fulfilled.
Abstract: An experimental investigation about the reliability of an attractive method recently proposed for modal power distribution measurements in multimode fibres is performed. The method is shown to work also in some common cases when the hypotheses of validity are not rigorously fulfilled. Finally, an illustrative application to the testing of mode scramblers is presented.
9 citations
TL;DR: It is shown that the signal-to-noise ratio caused in this way is of the same order of magnitude as in suitable multimode-fiber systems.
Abstract: So-called single-mode fibers are generally bimodal in that they can propagate two modes with orthogonal polarizations. If both transverse offset and angular misalignment are present in a single-mode fiber connector, the loss will be mode dependent. Physical distortions of the fiber before a connector cause modal noise. It is shown that the signal-to-noise ratio caused in this way is of the same order of magnitude as in suitable multimode-fiber systems.
6 citations
TL;DR: A new technique is presented for observing the modal structure of a multimode fiber as a function of time, and the times of arrival of the modes are recorded with a temporal resolution of 0.03 psec.
Abstract: A new technique is presented for observing the modal structure of a multimode fiber as a function of time. The times of arrival of the modes are recorded with a temporal resolution of 0.03 psec, together with the mode patterns. The experiments were made on a fiber carrying less than 10 modes, and the length of the fiber under test was 1.5m.
5 citations
TL;DR: It is confirmed that frequency domain measurements make it simple to obtain mode conversion coefficients and mode dependent losses and that the dynamic equilibrium is attained after propagation over a few kilometers even in available step-index fibers.
Abstract: A simplified method for the measurement of mode conversion coefficients and mode dependent losses is proposed. The method utilizes sinusoidally modulated light instead of optical pulses and is applied to step-index multimode fibers. The results obtained by frequency domain measurement agree satisfactorily with those obtained by time domain measurement. It is confirmed that frequency domain measurements make it simple to obtain mode conversion coefficients and mode dependent losses. Experiments also show that mode dependent losses in the fibers are roughly independent of the mode order, and that the dynamic equilibrium is attained after propagation over a few kilometers even in available step-index fibers.
3 citations
25 Feb 1981
TL;DR: In this article, a method for producing microlenses on the ends of single-modeoptical fibers was devised for coupling light between single mode fibers and single mode planar waveguides, where a lens is formed by dipping the fiber end into negative photoresist while the fiber core carries Z 0.1 mW of HeNe laser light.
Abstract: Philip D. BearMcDonnell Douglas Astronautics Company -St. Louis, St. Louis, Missouri 63166AbstractA new method has been devised for producing microlenses on the ends of single -modeoptical fibers. A lens is formed by dipping the fiber end into negative photoresistwhile the fiber core carries Z0.1 mW of HeNe laser light. The photoresist lenses re-quire no developing or rinsing. The lenses are shown to transform the near -Gaussianbeam emitted by the fiber into another near -Gaussian beam with a reduced waist diameter.The size of the new waist can be selected by varying the number of times the fiber isdipped into the photoresist. The waist reduction is shown to increase coupling intosingle -mode optical waveguides.IntroductionWhen coupling light between single mode fibers and single mode planar waveguides, oneshould be cognizant of the variables upon which the process depends. The degree to whichthe phase and amplitude distributions are matched determines the efficiency of coupling.First, let us address the matching of the phase distributions of the light. A single modefiber emits a beam which begins diverging upon exiting the fiber so that the waist of thebeam, which exhibits a planar phase, is located at the fiber end. The phase of the lightin a single mode planar waveguide is also planar. Therefore, to achieve maximum couplingwith respect to phase matching, the fiber end should be butt -coupled to the edge of theplanar waveguide.In order to match the amplitude distributions there are two conditions to be considered.The first is that the coupling is affected by the relative displacement of the two modes.When the regions of maximum mode intensity for each mode lie on a common optic axis thecoupling is maximized with respect to this parameter. The second condition concerns therelative sizes of the two modes. The closer the mode in the fiber is to matching the modesize in the waveguide the better the coupling efficiency which is achievable.Fabrication of microlensesIt may be difficult, in general, to vary parameters such as the indices of refractionor wavelength in order to match the mode sizes. For example, the single -mode fiber used inthis laboratory has a waist diameter of 2 Wo
1 citations
28 Jul 1981
TL;DR: In this article, the tradeoffs between the choice of multimode and single mode optical fiber transmission are discussed and the practical limit for transmission between 0.8-1.6 μm.
Abstract: Both multimode and single mode optical fiber transmission systems can provide long distance transmission at moderate to high data rates. Multimode graded index optical fibers are clearly adequate up to about 20 Mb/s at any wavelength between 0.8-1.6 μm. On the other hand, the lower dispersion of single mode fibers is advantageous at data rates above 100 Mb/s. Between 20 Mb/s and a few hundred megabits per second, there are tradeoffs between the choice of multimode and single mode optical fiber transmission. This paper addresses these tradeoffs and the practical limit for transmission between 0.8-1.6 μm. Both attenuation and dispersion limits to transmission distance are reviewed. The limitations due to the small diameter of the single mode fiber are also highlighted.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.