Matsuhiro Miyamoto

Length dependence of bandwidth for fibers with random-axial profile fluctuations

Length dependence of bandwidth for graded-index optical fibers with random-axial profile fluctuations is investigated theoretically in connection with optical equalization in long spliced fibers. Based on the statistical approach, a simple analytical formula is derived on the assumption that the profile fluctuation does not cause mode coupling. At a short distance, the bandwidth has been found to be inversely proportional to square root of distance due to the profile fluctuation. The length dependence presents a remarkable contrast to that of the mode-coupling case showing the same dependence at a long distance.

Design and performance of Gaussian-profile dispersion-shifted fibers manufactured by VAD process

Design and manufacturing of dispersion-shifted fibers with a Gaussian profile, which is compatible to the VAD process, are studied. From the viewpoint of stable cabling, the parametric analysis is made with emphasis on the bending loss. To make the bending sensitivity of the Gaussian core fibers comparable with the conventional 1.3- μm zero-dispersion fibers, an 0.8 percent or higher index difference is required. In the experiment, the achieved loss at the 1.55-μm dispersionless wavelength is 0.21 dB/km. The effects of a ring profile around the Gaussian core on the fiber transmission characteristics also are examined. While the cutoff wavelengths are greatly lengthened by the ring, the bending sensitivity is not so affected. It is found that the index difference of the main core still dominates the bending loss of the fiber.

Bending loss evaluation of single-mode fibres with arbitrary core index profile by far-field pattern

An evaluation of the bending loss of single-mode fibers based on the measured mode field is described. The field decay constant and the normalized field intensity in the cladding are determined. Experimental results verified the validity of this method. Its accuracy is determined by the accuracy of field measurement. The mode field is calculated from the far-field distribution measured with finite dynamic range of more than 50 dB. Far-field measurement with finite dynamic range limits the accuracy of field evaluation. Dispersion shifted fibers are easier for evaluation because of the wider far-field distribution. Bending loss and mode field diameter can be measured simultaneously, and the method is applicable to any single-mode fibers with a matched clad structure. A microbending loss formula is also determined by the decay constant and the normalized field intensity in the cladding as well as uniform bending loss. >

Vapor axial deposition single-mode fibers with ultimate low-core eccentricity

Introduction of single-mode fibers into subscriber loops is being studied from the viewpoint of technical feasibility.1 The technique of low-loss mass splicing is a major problem, and core eccentricity seems to limit the reduction of splice loss. We describe newly developed VAD single-mode fibers with ultimate tow-core eccentricity. Using the VAD process a core and a whole cladding have been synthesized with a high deposition rate.