Abstract: The disclosed fiber Raman device comprises means for coupling pump radiation of a first wavelength &lgr;1 and a second wavelength &lgr;2 into a length of silica-based fiber, with &lgr;1 being different from &lgr;2, and with both of &lgr;1 and &lgr;2 being less than an output radiation &lgr;0 of the fiber Raman device. The Raman device further comprises at least a first and a second wavelength-selective element disposed to provide one or more optical cavities for Raman shifting of light in the fiber. At least one of the optical cavities is selected such that at least one of &lgr;1 and &lgr;2 is off resonance. Exemplarily, the Raman device is a topologically linear or circular Raman laser or amplifier, and the wavelength selective element is a fiber Bragg grating or a WDM. The Raman device is advantageously used in an optical fiber communication system.

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: Optical fiber bundles having high optical throughput can be produced with relatively high yield if gaps between fibers are eliminated by application of a particle-containing glass precursor material, exemplarily fumed silica in an aqueous medium. Manufacture of optical fiber bundles that comprise two or more fibers that each comprise a substantially planar surface (with the planar surfaces facing each other) is improved by application of a particle-free glass precursor material, e.g., partially hydrolysed tetramethyl orthosilicate, to the fiber bundle. After drying of the applied glass precursor material the fiber bundle is heated to fuse the fibers together.

Abstract: In accordance with the invention, a pumped waveguide device comprising a pump waveguide and an active waveguide is provided with a pump power monitor by disposing between the pump source and the active waveguide, an indicator waveguide having a core doped with a material sensitive to the pump light. For example the material can fluoresce in response to pump light or absorb pump light and generate heat. Pump power is then accurately measured by the fluorescence or heat from the indicator waveguide. Since the fluorescence or heat is generated in the doped core, the measurement is sensitive to the pump power that will enter the active waveguide and is relatively insensitive to changes in mode distribution. Exemplary embodiments include monitored cladding pumped fiber lasers, amplifiers and light sources.

Abstract: Dual concentric core fiber is used for optical communication. Inbound messages lying in a first wavelength channel are received from a terminal portion of the fiber, and outbound messages lying in a second such channel are injected into the terminal portion. The optical fiber has at least one annular portion surrounding a central core portion. The inbound messages are received from the annular portion, and the outbound messages are injected into the central core portion. Alternatively, the inbound messages are received from the central core portion, and the outbound messages are injected into the annular portion.

Abstract: In accordance with the invention, an optical fiber communication system comprises one or more Nd doped fiber amplifiers for amplified transmission in the 1400 nm window. The amplifier is designed with a combination of waveguide effects and selective absorption to reduce amplified spontaneous emission to acceptable levels.

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: A cladding-pumped fiber structure, suitable for use as a laser, provides for efficient clad-to-core energy transfer. The outside interface of the pump-clad is constructed from a rod-shaped preform by local melt-displacement using an open flame.

Abstract: A cladding-pumped fiber structure is disclosed in which mode mixing of pump light injected into the fiber is induced by index modulation. In one embodiment, the index modulation is created by a stress-inducing region disposed in the cladding which simultaneously maintains the polarization within the core to produce a polarization-maintaining fiber useful for multi-mode and laser applications.

Abstract: The specification describes fiber laser devices with cores containing aluminum in which the composition of the core is modified to minimize the core .DELTA., thereby allowing a larger core diameter, and a reduction in the fiber laser length by a factor equal to the square of the diameter difference. This result is achieved by compensation doping the core with phosphorus to offset the index-modifying contribution of aluminum.

Abstract: An optical fiber amplifier is pumped by a fiber pump laser which has a pair of separate active media within a common resonator. The fiber gain section of the amplifier is also located within the resonator.

Abstract: Optical fiber according to the invention comprises a core, with an inner cladding surrounding the core, and an outer cladding surrounding the inner one. The fiber comprises preform-derived glass. The outer cladding comprises a first outer cladding region between the inner cladding region and a second outer cladding region. The first outer cladding region is selected to have an effective refractive index less than 1.35, and such that the optical characteristics of the optical fiber are essentially independent of the second outer cladding, and/or such that the fiber is re-coat insensitive. The first outer cladding typically comprises elongate features extending in the fiber axial direction, with a web material joining the inner cladding to the second outer cladding. The elongate features are filled with a low-index material, exemplarily air, but could of course be evacuated. Fibers according to the invention have many uses, e.g., cladding-pumped optical fiber or fiber with a long period grating.

Abstract: A cladding-pumped fiber structure, suitable for use as a laser, provides for efficient clad-to-core energy transfer. The outside interface of the pump-clad is constructed from a rod-shaped preform by local melt-displacement using an open flame.

Abstract: The specification describes a process and apparatus for monitoring and controlling the ellipticity of preform tubes during Modified Chemical Vapor Deposition. In response to computer generated signals from the monitoring device, the tube collapse rate is adjusted dynamically by locally changing the temperature of the glass tube, or by changing the physical force acting to collapse the tube.

Abstract: In accordance with the invention, light is coupled from a plurality of semiconductor emitters to a cladding-pumped fiber via tapered fiber bundles fusion spliced to the cladding-pumped fiber. Individual semiconductor broad stripe emitters can be coupled to individual multimode fibers. The individual fibers can be bundled together in a close-packed formation, heated to melting temperature, drawn into a taper and then fusion spliced to the cladding-pumped fiber. Advantageously, the taper is then overcoated with cladding material such as low index polymer. In addition, a fiber containing a single-mode core can be included in the fiber bundle. This single-mode core can be used to couple light into or out of the single-mode core of the cladding-pumped fiber.

Abstract: Disclosed are non-periodic microstructured optical fibers that guide radiation by index guiding. By appropriate choice of core region and cladding region, the effective refractive index difference .DELTA. between core region and cladding can be made large, typically greater than 5% or even 10 or 20%. Such high .DELTA. results in small mode field diameter of the fundamental guided mode (typically<2.5 .mu.m), and consequently in high radiation intensity in the core region. Exemplarily, a fiber according to the invention has a solid silica core region that is surrounded by an inner cladding region and an outer cladding region. The cladding regions have capillary voids extending in the axial fiber direction, with the voids in the outer cladding region having a larger diameter than those in the inner cladding region, such that the effective refractive index of the outer cladding region is greater than that of the inner cladding region. Non-periodic microstructured fiber potentially has many uses, e.g.

Abstract: Multistage Er-doped fiber amplifiers (EDFAs) are disclosed. They comprise a first stage that comprises Er and Al, and further comprise a second stage that comprises Er and a further rare earth element, exemplary Yb. Such multistage EDFAs can have advantageous characteristics e.g., a relatively wide flat gain region (e.g. 1544-1562 nm), and relatively high output power, without significant degradation of the noise figure. Exemplary, the amplifiers are used in WDM systems and in analog CATV systems.

Abstract: A cladding pumped optical fiber laser comprises a length of optical fiber having a rare earth-doped region of diameter d.sub.RE >d.sub.01 where d.sub.01 is the mode diameter of the LP.sub.01 mode of the fiber at the laser radiation at wavelength .lambda.. In one embodiment the fiber has a core diameter d.sub.c selected such that the LP.sub.01 mode is the only guided spatial mode of the fiber, and d.sub.RE is greater than d.sub.c. In another embodiment the fiber supports at least one higher order guided spatial mode, typically LP.sub.11 or LP.sub.02, and d.sub.RE is approximately equal to or larger than d.sub.c. Currently preferred embodiments comprise a grating-defined laser cavity that comprises a mode-coupling refractive index grating. Cladding pumped lasers according to the invention will typically have efficient conversion of pump radiation to laser radiation, and consequently can typically be shorter than analogous prior art cladding pumped lasers.

Abstract: Applicants have determined that the temperature sensitivity of long-period grating devices is due to differential variation with temperature of the refractive indices of the core and cladding. They have further determined that the cladding profile and fiber composition can be redesigned to substantially reduce this differential variation, thereby reducing the temperature sensitivity of long-period gratings of less than 4 nm per 100.degree. C. and preferably less than 2 nm per 100.degree. C. This design permits the use of long-period grating devices without temperature control or compensation.

Abstract: In an optical fiber light source a section of multimode fiber is interposed between an energizing laser (e.g,, a diode laser) and a single mode fiber active medium. In a preferred embodiment the single mode fiber active medium is surrounded by a multimode cladding coupled to the multimode fiber. The source may serve as a pump laser for a fiber amplifier or as an amplified spontaneous emission source. Arrangements for coupling several energizing lasers to the active medium are also described.