Abstract: An optical waveguide includes a core region extending substantially along a lengthwise centerline of the optical waveguide, a first cladding region formed along a first side of the core region, and a second cladding region formed along a second side of the core region. The optical waveguide includes a first diode segment and a second diode segment that each include respective portions of the core region, the first cladding region, and the second cladding region. The second diode segment is contiguous with the first diode segment. The first diode segment forms a first diode across the optical waveguide such that a first intrinsic electric field extends across the first diode segment in a first direction, and the second diode segment forms a second diode across the optical waveguide such that a second intrinsic electric field extends across the second diode segment in a second direction opposite the first direction.

Abstract: An optical waveguide includes a core region extending substantially along a lengthwise centerline of the optical waveguide, a first cladding region formed along a first side of the core region, and a second cladding region formed along a second side of the core region. The optical waveguide includes a first diode segment and a second diode segment that each include respective portions of the core region, the first cladding region, and the second cladding region. The second diode segment is contiguous with the first diode segment. The first diode segment forms a first diode across the optical waveguide such that a first intrinsic electric field extends across the first diode segment in a first direction, and the second diode segment forms a second diode across the optical waveguide such that a second intrinsic electric field extends across the second diode segment in a second direction opposite the first direction.

Abstract: A photodetector includes a photodiode that has a germanium junction formed between an n-doped region and a p-doped region. The germanium junction is formed to have an input interface at a light input end of the germanium junction. The input interface has a substantially flat shape or a convex-faceted shape. The photodetector also includes an input waveguide connected to the input interface of the germanium junction. The input waveguide has a substantially linear shape along a lengthwise centerline of the input waveguide. The input waveguide is oriented so that the lengthwise centerline of the input waveguide is positioned at a non-zero angle relative to input interface of the germanium junction.

Abstract: An optical coupling device includes an optical waveguide disposed on a substrate. An index of refraction of the optical waveguide is greater than an index of refraction of the substrate. The optical coupling device includes a cladding material disposed alongside and above the optical waveguide. An index of refraction of the cladding material is less than the index of refraction of the optical waveguide. The optical coupling device includes an optical buffering layer disposed within the cladding material above the optical waveguide. The optical buffering layer has an index of refraction greater than the index of refraction of the cladding material. The optical buffering layer is positioned a distance away from a top surface of the optical waveguide so as to guide an input optical mode at controlled vertical level relative to the optical waveguide, with the input optical mode overlapping the optical waveguide.

Abstract: An optical waveguide includes a core region extending substantially along a lengthwise centerline of the optical waveguide, a first cladding region formed along a first side of the core region, and a second cladding region formed along a second side of the core region. The optical waveguide includes a first diode segment and a second diode segment that each include respective portions of the core region, the first cladding region, and the second cladding region. The second diode segment is contiguous with the first diode segment. The first diode segment forms a first diode across the optical waveguide such that a first intrinsic electric field extends across the first diode segment in a first direction, and the second diode segment forms a second diode across the optical waveguide such that a second intrinsic electric field extends across the second diode segment in a second direction opposite the first direction.

Abstract: A hollow core fiber has a cladding comprising a matrix of cells, wherein each cell comprises a hole and a wall surrounding the hole. The fiber further has a hollow core region comprising a core gap in the matrix of cells, wherein the core gap spans a plurality of cells and has a boundary defined by the interface of the core gap. The matrix of cells comprises a plurality of lattice cells, and a plurality of defect cells characterised by at least one difference in at least one property from that of the lattice cells. The cells at the core region boundary include lattice cells and defect cells that are arranged in a pattern so as to produce birefringence in a light propagating through the hollow core fiber. Further described is a technique for making the fiber.

Abstract: In an optical fiber, a plurality of individual cores extend through a common cladding. Each individual core supports at least one local transverse spatial mode. The individual cores and surrounding cladding are structured to support propagation of plurality of desired signal-carrying modes, while suppressing undesired modes, thereby supporting the propagation of one or more spatially multiplexed signals. The core-to-core spacing of the fiber is configured to maintain an acceptably low level of mode-coupling between cores.

Abstract: A hollow core fiber has a cladding comprising a matrix of cells, wherein each cell comprises a hole and a wall surrounding the hole. The fiber further has a hollow core region comprising a core gap in the matrix of cells, wherein the core gap spans a plurality of cells and has a boundary defined by the interface of the core gap. The matrix of cells comprises a plurality of lattice cells, and a plurality of defect cells characterised by at least one difference in at least one property from that of the lattice cells. The cells at the core region boundary include lattice cells and defect cells that are arranged in a pattern so as to produce birefringence in a light propagating through the hollow core fiber. Further described is a technique for making the fiber.

Abstract: A hollow core fiber has a cladding comprising a matrix of cells, wherein each cell comprises a hole and a wall surrounding the hole. The fiber further has a hollow core region comprising a core gap in the matrix of cells, wherein the core gap spans a plurality of cells and has a boundary defined by the interface of the core gap. The matrix of cells comprises a plurality of lattice cells, and a plurality of defect cells characterized by at least one difference in at least one property from that of the lattice cells. The cells at the core region boundary include lattice cells and defect cells that are arranged in a pattern that define two orthogonal axes of reflection symmetry, so as to produce birefringence in a light propagating through the hollow core fiber.

Abstract: Described is a general strategy of bend-compensated, single-mode LMA fibers extended into a regime with higher total index contrast and where a larger gradient is used to cancel the perturbation of a tighter anticipated bend.

Abstract: Optical fiber profiles are shown in which the optical fiber has a large mode area, but is nevertheless sufficiently bend-insensitivity to comply with technical specifications for telecommunication optical fibers. The optical fibers meet two bend-loss conditions. First, they meet tight bend conditions, which reflects macro-bending due to coiling or bending of the optical fiber. Second, these optical fibers meet cable bend conditions, which reflect macro-bending conditions that are introduced as a result of cabling. By satisfying the tight bend-loss condition and then adjusting for the cable bend-loss condition, the optical fiber permits larger effective areas than normally achievable with only bend-compensation designs.

Abstract: A hollow core fiber exhibiting selective birefringence is provided. The selective birefringence is induced by harnessing properties of surface modes that cause transmission loss and are otherwise considered as detrimental. Birefringence and signal loss in a preferred polarization state are engineered by fabricating an asymmetrical web structure surrounding the core. In one implementation the asymmetry in the web structure is induced by a thicker core web preferably at the core inner cladding interface, by selectively introducing defect cells at the hollow core inner cladding interface. The hollow core fiber further includes shunt cores to facilitate near single-mode transmission by additionally using intermittent bend-induced index matching to resonantly couple unwanted core modes including one or more, higher order modes to shunt modes.

Abstract: An optical fiber includes a core region having a longitudinal axis. At least a portion of the core region has a substantially helical shape about a helical axis. The longitudinal axis may be substantially tangential to a helical bend in the optical fiber. A cladding region surrounds the core region. The core region and cladding region may be configured to support and guide the propagation of signal light in a fundamental transverse mode in the core region in the direction of the longitudinal axis. The fiber has a bend-induced gradient in its equivalent index of refraction over the portion of the core region. The fiber has a bend-induced equivalent index of refraction. At least a portion of cladding region has a graded refractive index opposite that of the bend-induced gradient. The cladding region may be configured to have a substantially flat equivalent index in response to a helical bend of the optical fiber.

Abstract: A technique is described for providing compensation for the thermo-optic effect in a large-mode-area optical fiber, filter fiber, or the like. An optical fiber is provided having a refractive index profile with ambient temperature loss characteristics including a low loss for a first type of light and a high loss for a second type of light. A hot region of the fiber connected into an optical system is identified, in which a thermal index gradient is induced in the fiber. The thermal index gradient, in the absence of a compensating index gradient, would result in degradation of the fiber's ambient temperature loss characteristics. The fiber is arranged according to a layout having a position-varying bending diameter. Throughout the identified hot region, the fiber has a compensating bending diameter that induces a compensating index gradient in the fiber.

Abstract: Techniques for analyzing output modal content of optical fibers that support more than one spatial mode are disclosed. These techniques are based on spatially resolving interference between co-propagating modes and constructing a spatial beat pattern between the co-propagating modes. By doing so, these techniques provide information about the modes that propagate along the optical fiber.

Abstract: A few-moded fiber device has several discrete sections of few-moded fibers that are separated by mode converters, with each mode converter accomplishing mode conversion between one or more pairs of modes. The mode conversions can be accomplished using a sequence, such as a periodic or cyclic sequence that would cause (1) a signal wave launched with any mode to assume every other mode for one or more times; (2) the number of times the signal remains in any modal state is substantially the same; and (3) the net signal gain or loss or group delay of the input signal is substantially the same regardless of the state of input mode. A laser few-mode amplifier is provided. An optical transmission system is also provided.

Abstract: Optical fiber profiles are shown in which the optical fiber has a large mode area, but is nevertheless sufficiently bend-insensitivity to comply with technical specifications for telecommunication optical fibers. The optical fibers meet two bend-loss conditions. First, they meet tight bend conditions, which reflects macro-bending due to coiling or bending of the optical fiber. Second, these optical fibers meet cable bend conditions, which reflect macro-bending conditions that are introduced as a result of cabling. By satisfying the tight bend-loss condition and then adjusting for the cable bend-loss condition, the optical fiber permits larger effective areas than normally achievable with only bend-compensation designs.

Abstract: A LMA, single-mode optical fiber comprises a core region, an inner cladding region surrounding the core region, and an outer cladding region surrounding the inner cladding region. The inner cladding region is configured to provide bend compensation. In one embodiment the index profile of the inner cladding region is graded with a slope of ?ncore/Rb, where ncore is the refractive index of the core region, Rb is the bend radius, and ?=0.6-1.2. In addition, the inner cladding is annular and the ratio of its outer radius to its inner radius is greater than 2. In a preferred embodiment this ratio is greater than 3. The overall index profile may be symmetric or asymmetric.

Abstract: An optical fiber has two or more core regions disposed within a common cladding region. Each of the core regions is configured to guide a respective light transmission comprising at least one optical mode along the length of the fiber. The cores are arranged within the common cladding region according to a core configuration that substantially prevents crosstalk between modes of neighboring cores in the fiber, in a deployment of the fiber in which cross-coupling between neighboring cores is affected by perturbations arising in the deployed fiber.

Abstract: An optical fiber includes a core region having a longitudinal axis. At least a portion of the core region has a substantially helical shape about a helical axis. The longitudinal axis may be substantially tangential to a helical bend in the optical fiber. A cladding region surrounds the core region. The core region and cladding region may be configured to support and guide the propagation of signal light in a fundamental transverse mode in the core region in the direction of the longitudinal axis. The fiber has a bend-induced gradient in its equivalent index of refraction over the portion of the core region. The fiber has a bend-induced equivalent index of refraction. At least a portion of cladding region has a graded refractive index opposite that of the bend-induced gradient. The cladding region may be configured to have a substantially flat equivalent index in response to a helical bend of the optical fiber.