Abstract: Embodiments of the invention include an optical fiber laser system with a cascaded Raman resonator (CRR) or other suitable Raman frequency shifting device having a length of optical fiber with at least one input pump reflector, a series of Raman-Stokes order reflectors and an output reflector therein. The reflectors are written to provide sufficient conversion efficiency despite the use of the cascaded Raman resonator with differing pump laser wavelengths. The reflectors are written not necessarily in correspondence with the gain maxima of the intermediate Stokes orders, but instead are written to reflect with less than maximum gain conversion intensity, yet in a manner that allows different pump laser wavelengths to be converted thereby. When operating the cascaded Raman resonators at sufficiently high pump powers, input pump reflectors are not necessary. Cascaded Raman resonators designed in accordance with embodiments of the invention are useful with different pump laser wavelengths.

Abstract: A multi-mode optical fiber having an improved refractive index profile is disclosed. The refractive index profile is modified from a conventional by at least one of (i) a step formed in the index profile at the boundary of the core and cladding regions, in combination with a linear correction; (ii) a ripple near the core-cladding boundary, in combination with a linear correction, with or without an index step; and (iii) an annular ridge formed in the index profile of an &agr;-profile with a center dip defect. The invention further relates to a communications system comprising the inventive fiber.

Abstract: Our method of making high bandwidth silica-based multimode optical fiber comprises provision of a non-circular preform, and drawing fiber of chiral structure from the preform. The non-circular preform can be made by maintaining the inside of the tubular preform under reduced pressure during at least part of the collapse, resulting in a non-circular core and cladding. It can also be made by removal (e.g., by grinding or plasma etching) of appropriate portions of the preform, resulting in a circular core and non-circular cladding. In the latter case, fiber is drawn at a relatively high temperature such that, due to surface tension, the cladding assumes substantially circular shape and the core assumes a non-circular shape. The chiral structure is imposed on the fiber in any appropriate way, e.g., by twisting during fiber drawing the fiber alternately in clockwise and couterclockwise sense relative to the preform.

Abstract: The performance of optical fiber Raman devices can be increased by substitution of a broadband reflector (typically a multilayer dielectric mirror) for some of the narrowband reflectors (typically fiber Bragg gratings) that are conventionally used to define the optical cavities of the device. The device exemplarily is a Raman laser or amplifier, and in preferred embodiments a broadband reflector reflects all the Stokes-shifted wavelengths, such that the cavities are defined by the single broadband reflector and by a multiplicity of appropriately selected narrowband reflectors. Optionally the broadband reflector also serves to reflect the pump radiation.

Abstract: Simultaneous dense WDM operation in both the 1310 nm and 1550 nm transparency windows of silica-based optical fiber, is enabled by a fiber design providing for nulled dispersion within a critically positioned wavelength range. Design provides for values of dispersion in both windows sufficiently low for desired per-channel bit rate, and, at the same time, sufficiently high to maintain effects of non-linear dispersion within tolerable limits for WDM operation. Fiber fabrication and system design are described.

Abstract: In accordance with the invention, a Ge-doped optical fiber having reduced Brillouin scattering loss is made by modulating the tension applied to the fiber during draw. The draw tension is modulated between a low range 10-50 g and a high in the range 150-250 g. The result is SBS suppression with no significant change to end-to-end fiber loss or dispersion factors.

Abstract: The conversion efficiency of a cascaded Raman laser (CRL) can be significantly improved if it comprises one or more of the below recited design features. The CRL comprises an intracavity section between an input section and an output section. The CRL is adapted for receiving pump radiation of wavelength .lambda..sub.p, and for emitting output radiation of wavelength .lambda..sub.n >.lambda..sub.p, and each of the input section and output section comprises fiber Bragg gratings of center wavelengths .lambda..sub.1, .lambda..sub.2 . . . .lambda..sub.n, where n.gtoreq.2 and .lambda..sub.1 <.lambda..sub.2 < . . . .lambda..sub.n-1. Among the efficiency-increasing features is ordering of the fiber Bragg gratings such that in the input section and the output section the gratings of center wavelengths .lambda..sub.1 . . . .lambda..sub.n and .lambda..sub.1 . . . .lambda..sub.

Abstract: Disclosed is an improved WDM optical fiber communication system that comprises, in addition to dispersion compensating fiber, dispersion slope compensating fiber (DSCF) selected to provide substantially all channels of the WDM system with nominally zero total chromatic dispersion. Exemplary refractive index profiles for DSCF are disclosed. Such fibers exemplarily can be produced by MCVD.

Abstract: An optical fiber communication system according to the invention comprises an optical fiber filter that can be manufactured at low cost and that can be conveniently incorporated into the system, substantially like a conventional fiber jumper. The filter comprises a length L of axially uniform optical fiber selected to have substantially no loss (e.g., <1 dB) at a wavelength .lambda..sub.1, and to have relatively high loss (e.g., >20 dB) at a wavelength .lambda..sub.2. The length L will typically be less than 100 m. In one embodiment the optical fiber is a single mode optical fiber at .lambda..sub.1 (e.g., 1.3 .mu.m) that does not have a guided mode at .lambda..sub.2 (e.g., 1.55 .mu.m). In another embodiment the fiber contains a dopant that does substantially not absorb radiation of wavelength .lambda..sub.1, but substantially absorbs at .lambda..sub.2. In the second embodiment, .lambda..sub.1 can be greater than .lambda..sub.2.