Abstract: This invention is predicated on applicants' discovery that one can design long-period gratings having a center wavelength versus A characteristic which changes polarity of slope near a wavelength of interest. Such a grating can be chirped to exhibit a wider bandwidth than chirped conventional gratings, e.g. 100 nm as compared to 20 nm. The new wide bandwidth gratings are highly useful in optical communications systems for dispersion compensation and for compensation of spectrally dependent optical amplifiers.

Abstract: Embodiments of the invention include an optical fiber system and method for separating the different wavelengths of transmitted light transmitted therethrough and for monitoring the respective optical power in the separated spectral components. More specifically, embodiments of the invention scan or modify the physical parameters of in-fiber gratings that couple light between spatially different modes of light within a wavelength-division-multiplexed (WDM) optical fiber system, separate the spatial modes using a mode-discriminating device (MDD) and monitor or detect the separated spectral components using a conventional or other suitable detector. By scanning the in-fiber gratings, the peak wavelength of coupling between two dissimilar modes is modified, thus allowing control of the coupling within the fiber optic system. Scanning the grating is performed, e.g., by changing the temperature or modifying the physical dimensions of the grating.

Abstract: Applicants have discovered that exposing optical fiber to an electrical arc produces a perturbation in its refractive index and that gratings can be made by exposing fiber to arcs at a series of locations along its length. In a first variation of the process, the fiber is exposed under tension to a high current arc (>15 mA) for a prolonged period of time (>2 s). Using this method, long period gratings can be successfully fabricated from fiber without the use of special dopants. In a second variation, the fiber is doped and the tension is reduced. The resulting grating is optically weaker but mechanically stronger. A third variation uses hydrogen-sensitized fibers and reduced currents and times. The resulting grating is optically and mechanically strong.

Abstract: Applicants have determined that the temperature sensitivity of long period grating devices is substantially affected by the provision of a polymeric coating over the conventional glass cladding and, in particular, that by providing a polymer overcoating with an appropriately selected index of refraction, one can minimize temperature sensitivity. In a preferred embodiment, the temperature sensitivity of a long period grating written in conventional dispersion-shifted fiber is reduced to 0.40 nm/100.degree. C.

Abstract: A device and method for dynamically tuning a long-period grating of an optical fiber is disclosed. The grating is made tunable by using a controlled strain imposed on the fiber adjacent the grating, wherein the strain comprises an electromechanical force, magnetostrictive force, magnetic force, or a thermally-induced force. An improved optical communication system comprising a dynamically gain-equalized amplifier device, a wavelength feedback device, and the tunable long-period grating device is also disclosed. In the communications system, the grating device is reconfigured to have a desired broadband filtering frequency, thus equalizing the amplifier gain, in response to feedback from the wavelength detector.

Abstract: Embodiments of the invention include a method for fabricating Bragg reflector gratings using an amplitude mask and an amplitude mask apparatus for fabricating Bragg reflectors. The inventive Bragg reflector gratings have periodicities greater than conventional short period gratings but much less than conventional long period gratings. Short period, Bragg reflector gratings according to embodiments of the invention have periodicities, e.g., within the range from 1 .mu.m to 10 .mu.m. The fabrication method includes positioning an amplitude mask having appropriate slits formed therein over the photosensitive waveguide of interest and then illuminating the waveguide through the slits thereby photoinducing a periodic pattern of refractive index perturbations characteristic of a Bragg reflector. The short period, Bragg grating produced by the inventive amplitude mask is a reflective grating whose reflection characteristics approach approximately 99.99%.

Abstract: In accordance with the invention, an optical switch employs a long-period grating for switching light between alternative optical paths. In essence, the device comprises a variable intensity light source, a length of optical waveguide dimensioned for co-propagating light in two distinguishable modes, and a long-period grating in the waveguide for coupling between the two modes. The waveguide is nonlinear so that the effective refractive index is a function of intensity. As a consequence the coupling produced by the grating is a function of intensity. Thus different levels of light intensity can switch between the separate modes. Advantageously a mode separator is provided for directing light in the two modes onto respectively different optical output paths. A variety of two-mode switches and optical limiters are described, as well as an optical system using the switch.

Abstract: A self-tuning optical waveguide filter for attenuating a lower power light signal at .lambda..sub.1 more than a higher power signal at .lambda..sub.2 comprises a length of single core waveguide and a light injector for applying .lambda..sub.1, .lambda..sub.2 into the waveguide in two propagating modes subject to mode beating. The mode beating produces high intensity regions of .lambda..sub.1 physically displaced from high intensity regions of .lambda..sub.2. A portion of the waveguide is doped with a saturable absorber for disproportionately attenuating wavelengths at lower power levels. Advantageously the waveguide is a single-core fiber having its central core doped with rare-earth saturable absorber. In a preferred embodiment, the fiber is dimensioned to propagate .lambda..sub.1, .lambda..sub.2 in the LP.sub.01 and LP.sub.02 modes, and the saturable absorber is Erbium.

Abstract: Known dispersion-compensating (DC) optical fibers typically are sensitive to small changes in fiber parameter (e.g., fiber diameter and/or core refractive index), and thus are difficult to manufacture. The disclosed DC fibers are relatively insensitive to small departures from the nominal fiber parameters, and are therefore more manufacturable. Exemplarily, the nominal refractive index profile of a DC fiber is selected such that the fiber supports LP.sub.01 and LP.sub.02 (and typically one or more further higher order modes), and the dispersion is substantially all in LP.sub.02. The total dispersion is more negative than -200 ps/nm.km over a relatively wide wavelength range. The nominal refractive index profile typically comprises a refractive index "ring" that is spaced from the fiber core.

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: 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: The present invention provides an optical signal shaping device, such as a long period grating, for use with an optical fiber having a core of a first prescribed refractive index n.sub.1 and a cladding of a second prescribed refractive index n.sub.2 and configured to transmit an optical signal therethrough. The optical signal shaping device comprises a long period grating of predetermined length formed within the optical fiber. The long period grating has a nonuniform refractive index profile extending over at least a portion of the predetermined length and is configured to alter the optical signal to produce an asymmetrical optical signal.

Abstract: The present applicants have discovered that one can fabricate a long-period grating wherein the grating peak wavelength .lambda..sub.p will be shifted in different directions when the grating is subject to temperature and tensile strain, respectively. Accordingly, a long-period grating can be designed and packaged such that a temperature-induced shift in .lambda..sub.p is compensated by a corresponding strain-induced shift arising from a single packaging material. Thus, by proper design of the grating and choice of the packaging material expansion coefficient, a temperature stable grating having temperature sensitivity of less than 4 nm per 100.degree. C. can comprise a grating fiber encased in or attached to a package comprising a single material such as glass, polymer or metal. Such designs permit the use of long-period grating devices without temperature control.

Abstract: In accordance with the invention a multiwavelength optical fiber cross connect is provided with an active all-fiber optical router for multiplexing/demultiplexing. The router is comprised of one electronic component--a phase controller--and four fiber components: 1) a fiber directional coupler, 2) a fiber reflective grating filter, 3) a fiber tap, and 4) a fiber phase modulator. The application describes how to make optical routers from these components ranging in complexity from a single wavelength drop router to an N-port, N-wavelength router for add/drop multiplexing. The application also describes how optical wavelength routers can be combined to create optical fiber Cross connect (OXCs), ranging in complexity from 2.times.2 single wavelength OXCs to NXN, M-wavelength OXCs.

Abstract: The optical waveguide system comprises a mode discriminating coupler and reflective mode coupling means. These components can be combined in a variety of ways to perform a variety of functions. Among them are drop multiplex devices, add multiplex devices, add/drop multiplex devices, and power combiners. The device combinations can have low loss as well as high reliability, the latter due to the robust structure of the devices.

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 accordance with the invention a high power, broad bandwidth light source comprises at least one rare earth doped fiber coupled to a long period grating. When the rare earth doped fiber is pumped to operate as an amplified spontaneous emission source, the grating flattens and broadens the output spectrum. Using an Nd doped fiber, applicants have achieved an output power of 25 mW at a center wavelength of 1.08 .mu.m, a spectral width of 40 nm and a coherence length of 10 .mu.m. The source has a flat output spectrum with a maximum slope of 0.1 dB/nm across the full spectral width, and it can be conveniently dropped into any fiber system requiring high power and a broad spectrum. Using an Er-doped fiber, applicants have achieved an output power of 7.3 mW at a center wavelength of 1.55 .mu.m and a spectral width of 38 nm. The source has a flat output spectrum with a maximum ripple of 1.7 dB across the full width. This source is compatible with the needs for a spectrum sliced source.

Abstract: The present invention provides an optical switching system for use with an optical fiber that has a core of a prescribed refractive index and a cladding and that is configured to carry an optical signal of a prescribed bandwidth. Preferably, the optical fiber's core includes a photosensitive dopant. In a preferred embodiment, the optical switching system comprises an optical switch coupled to the optical fiber and includes a grating within the core. The optical switch has selectable non-diverting and forward-diverting modes of operation wherein the optical switch alters the prescribed refractive index: to render the grating substantially transparent to the optical signal as the optical switch operates in the non-diverting mode or, alternatively, to allow the grating to divert at least a portion of the optical signal forward and into the cladding as the optical switch operates in the forward-diverting mode.