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In this paper, we present a detailed experimental and theoretical study, showing that a novel nonzero dispersion-shifted fiber with negative dispersion enhances the capabilities of metropolitan area optical systems, while at the same time, reducing the system cost by eliminating the need of dispersion compensation. The performance of this dispersion-optimized fiber was studied using different types of optical transmitters for both 1310-and 1550-nm wavelength windows and for both 2.5and 10-Gb/s bit rates. It is shown that this new fiber extends the nonregenerated distance up to 300 km when directly modulated distributed feedback (DFB) laser transmitters at 2.5 Gb/s are used. The negative dispersion characteristics of the fiber also enhance the transmission performance in metropolitan area networks with transmitters that use electroabsorption (EA) modulator integrated distributed feedback (DFB) lasers, which are biased for positive chirp. In the case of 10 Gb/s, externally modulated signals (using either EA-DFBs or external modulated lasers using Mach-Zehnder modulators), we predict that the maximum reach that can be accomplished without dispersion compensation is more than 200 km for both 100-and 200-GHz channel spacing. To our knowledge, this is the first demonstration of the capabilities of a nonzero dispersion-shifted fiber with negative dispersion for metropolitan applications.

A theoretical and experimental study of a new, efficient technique to couple a broad-area laser, emitting a highly elliptical beam, to a single-mode fiber without the use of bulk optical components is presented. The technique involves butt coupling the laser to a wedge-shaped fiber endface. Such a n endface approximates a cylindrical lens which corrects for the phase front mismatch between the curved laser beam wavefront and the planar fiber beam. The fabrication process uses a wedge-shaped polishing tool and a simple polishing procedure. A theoretical formula for the coupling efficiency in the absence of both angular and transverse misalignments is derived. Based on the estimated mode field radii of the two-dimensional laser beam and assumed mode field radius of the fiber beam, a maximum coupling efficiency of 46% is predicted by the theory compared to the measured value of 47% (15.2-mW power coupled to the single-mode fiber) obtained by using a well-designed wedge-shaped fiber endface. For the square endface, the measured coupling efficiency was 20%. The technique was further refined by incorporating an uptapered, wedge-shaped endface to decrease the transverse misalignment sensitivity. The transverse misalignment tolerance for 3-dB reduction in maximum coupled power increases from 0.4 pm for the straight fiber wedge shape to 0.7 pm for the uptapered wedge shape. Using this technique, a single 980-nm, 30-pm stripe width, broad-area laser provided enough power to pump an erbium-doped fiber amplifier to obtain 24-dB gain. Richard S. Vodhanel (M'89) received the B.S. degree from the University of California, Irvine, in 1974, and the M.S. and Ph.D. degrees from the University of Illinois, Urbana, in 1976 and 1981, respectively, all in physics. His doctoral dissertation was on nuclear gamma ray spectroscopy.In 1980 he joined Bell Laboratories as a member of the Technical Staff, where he conducted research on the topic of single-mode fiber transmission systems. In 1984 he joined Bellcore, Red Bank, NJ, where he is presently engaged in research on coherent-optical fiber transmission systems. He has over 70 publications in physics and optical fiber communications.Dr.

We report, for the first time (to our knowledge), generation of Brillouin dynamic gratings (BDGs) in few-mode optical fibers. A moving acoustic grating is generated by stimulated Brillouin scattering using a writing beam in one fiber mode, which is used to reflect a reading beam at a different wavelength in another fiber mode. With single-end pumping, a BDG with a tunable reflectance of up to 0.1% is demonstrated in a 15 km specially designed two-mode optical fiber.

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