Abstract: An optical waveguide sensor arrangement for sensing at least one physical parameter is provided. This arrangement comprises an optical waveguide having guided modes, lossy non-guided modes, and a long period grating coupling the guided modes to the lossy non-guided modes wherein the long period grating produces a wavelength transmission spectrum functionally dependent on the physical parameter sensed. A source means provides light to the optical waveguide sensor and an optoelectronic detector, which is positioned in an operable relationship to the optical waveguide sensor, detects light transmitted through the optical waveguide sensor. Lastly, a processing means is attached to the optoelectronic detector for correlating the wavelength transmission spectrum with a numerical value for the physical parameter sensed. The physical parameters sensed by the optical waveguide sensor include: temperature, strain, shape, refractive index and corrosion.

Abstract: A method of controlling the polarization properties of a photo-induced device in an optical waveguide and a method of investigating the structure of a light guiding body such as an optical waveguide are disclosed. A device, such as gratings, is written by exposing one side of the optical waveguide to light. The unexposed side is then exposed to an amount of light sufficient to impart the desired birefringence to the written device. The birefringence can be minimized in the written device by exposing the opposite side to light in an amount sufficient to minimize the amount of birefringence. The light guiding body is investigated by cleaving the elongated light guiding body, such as an optical waveguide, to expose its cross-section. The cleaved section is then treated to expose difference between the core and cladding. Treatment may include etching in an acid or base.

Abstract: In accordance with the invention, an optical filter comprises a plurality of optical fibers having a coupling region where the axially extending cores are closely spaced within a common cladding. The coupling region includes a long period grating for selectively shifting light of selected wavelengths from guided modes into non-guided modes. These non-guided modes are picked up by an adjacent core and light of the selected wavelengths is thus shifted from one core to another. The result is an optical filter particularly useful as a demultiplexer or a tapping device. In one embodiment the grating is formed in one of the cores. In an alternative embodiment, it is formed in the common cladding.

Abstract: A method of controlling the polarization properties of a photo-induced device in an optical waveguide and a method of investigating the structure of a light guiding body such as an optical waveguide are disclosed. A device, such as gratings, is written by exposing one side of the optical waveguide to light. The unexposed side is then exposed to an amount of light sufficient to impart the desired birefringence to the written devices. The birefringence can be minimized in the written device by exposing the opposite side to light in an amount sufficient to minimize the amount of birefringence. The light guiding body is investigated by cleaving the elongated light guiding body, such as an optical waveguide, to expose its cross-section. The cleaved section is then treated to expose difference between the core and cladding. Treatment may include etching in an acid or base.

Abstract: A method of controlling the polarization properties of a photo-induced device in an optical waveguide and a method of investigating the structure of a light guiding body such as an optical waveguide are disclosed. A device, such as gratings, is written by exposing one side of the optical waveguide to light. The unexposed side is then exposed to an amount of light sufficient to impart the desired birefringence to the written device. The birefringence can be minimized in the written device by exposing the opposite side to light in an amount sufficient to minimize the amount of birefringence. The light guiding body is investigated by cleaving the elongated light guiding body, such as an optical waveguide, to expose its cross-section. The cleaved section is then treated to expose difference between the core and cladding. Treatment may include etching in an acid or base.

Abstract: A method of controlling the polarization properties of a photo-induced device in an optical waveguide and a method of investigating the structure of a light guiding body such as an optical waveguide are disclosed. A device, such as gratings, is written by exposing one side of the optical waveguide to light. The unexposed side is then exposed to an amount of light sufficient to impart the desired birefringence to the written device. The birefringence can be minimized in the written device by exposing the opposite side to light in an amount sufficient to minimize the amount of birefringence. The light guiding body is investigated by cleaving the elongated light guiding body, such as an optical waveguide, to expose its cross-section. The cleaved section is then treated to expose difference between the core and cladding. Treatment may include etching in an acid or base.

Abstract: In accordance with the invention, the index of refraction of a region of a glass body is selectively increased by treating the material with hydrogen and then simultaneously applying heat and actinic radiation to the region. Preferably the body is heated to a temperature in excess of 150.degree. C. and the heat and radiation are simultaneously applied. The result is a substantial and long-lived increase in excess of 5.times.10.sup.-5 in the refractive index of the irradiated region. This process can be used to make and adjust a variety of optical waveguide devices such as photoinduced Bragg gratings.

Abstract: In accordance with the invention, an optical fiber system is provided with a tapered fiber device for filtering, wavelength shift detecting, or switching. Specifically, applicant has discovered that a multiclad single mode optical fiber with a fundamental mode cutoff can be tapered to form a compact component useful in optical fiber systems, e.g. a filter in telecommunications systems, a wavelength shift detector in sensing systems, or a switch in any optical system.

Abstract: Disclosed is optical fiber that can advantageously be used to compensate chromatic dispersion in an optical fiber communication system, typically a system that is upgraded from 1.3 .mu.m to 1.55 .mu.m operating wavelength (.lambda..sub.op). The fiber typically has a power law core refractive index profile, a refractive index "trench" surrounding the core, and a refractive index "ridge" surrounding the trench. The refractive index profile of the fiber preferably is designed such that the fiber supports the fundamental mode (LP.sub.01), does not support the LP.sub.11 mode but does support the LP.sub.02 mode, all at .lambda..sub.op. At .lambda..sub.op, LP.sub.01 has dispersion more negative than -150 ps/nm.multidot.km and, in a preferred embodiment, LP.sub.01 also has negative dispersion slope at .lambda..sub.op. In a further embodiment of the invention the refractive index profile is designed such that the cut-off wavelength of the LP.sub.11 mode is less than that of the higher order mode, typically LP.sub.

Abstract: In accordance with the present invention, optical fiber communications systems are provided with one or more long period spectral shaping devices to shift light of unwanted wavelength from guided modes into non-guided modes. Such devices can be used for removing unused laser pump energy, for removing amplified spontaneous emission, and for flattening the spectral response of an erbium amplifier. Such devices can also provide optical fiber sensing systems with inexpensive shift detectors.

Abstract: In accordance with the invention, a mode-field transforming waveguide region comprise an elongated glass core surrounded by glass cladding wherein the normalized index differential between the cladding and the core (termed .DELTA.) varies along the length. Preferably the waveguide comprises an optical fiber having a hydrogen-loaded germanosilicate core. The variation of .DELTA. as a function of longitudinal distance can be effected by exposing the fiber to ultraviolet light and varying the dosage of exposure as a function of longitudinal distance.

Abstract: An extrinsic Fizeau fiber optic sensor comprises a single-mode fiber, used as an input/output fiber, and a multimode fiber, used purely as a reflector, to form an air gap within a silica tube that acts as a Fizeau cavity. The Fresnel reflection from the glass/air interface at the front of the air gap (reference reflection) and the reflection from the air/glass interface at the far end of the air gap (sensing reflection) interfere in the input/output fiber. The two fibers are allowed to move in the silica tube, and changes in the air gap length cause changes in the phase difference between the reference reflection and the sensing reflection. This phase difference is observed as changes in intensity of the light monitored at the output arm of a fused biconical tapered coupler. The extrinsic Fizeau fiber optic sensor behaves identically whether it is surface mounted or embedded, which is unique to the extrinsic sensor in contrast to intrinsic Fabry-Perot sensors.

Abstract: Optical waveguide amplifiers and lasers having a novel fluorescent dopant distribution are disclosed. Exemplarily, in a Si-based optical fiber the fluorescent dopant (e.g., Er) has an annular distribution, with the concentration maximum not at the center of the core but typically between the center and the core/cladding interface. The novel waveguides can be relatively insensitive to variations in cut-off wavelength and/or modal distribution of pump power.

Abstract: Tapered two-mode optic fibers are used as sensors with sensitivity varying as a function of length. The optical fiber sensors act as vibrational-mode filters thereby performing initial signal processing of the sensor signal. The sensors are based on the differential propagation constant in a two-mode fiber that is directly dependent on the normalized frequency or V-number. Tapering the fiber changes the V-number and hence can change the sensitivity of the sensor along its length. By choosing an appropriate weighting function in the manufacture of the sensor, it is possible to implement vibrational-mode analysis, vibrational-mode filtering and other functions that are critical in control system applications.