Abstract: A Bragg grating sensor for measuring distributed strain and temperature at the same time comprises an optical fiber having a single mode operating wavelength region and below a cutoff wavelength of the fiber having a multimode operating wavelength region. A saturated, higher order Bragg grating having first and second order Bragg conditions is fabricated in the optical fiber. The first order of Bragg resonance wavelength of the Bragg grating is within the single mode operating wavelength region of the optical fiber and the second order of Bragg resonance wavelength is below the cutoff wavelength of the fiber within the multimode operating wavelength region. The reflectivities of the saturated Bragg grating at the first and second order Bragg conditions are less than two orders of magnitude of one another.

Abstract: A fiber optic measurement system capable of greatly improving the cost, complexity, and efficiency with which flexible body shape estimates are made. The fiber optic shape measurement system uses Bragg grating sensor technology and time, spatial, and wavelength division multiplexing, to produce a plurality of strain measurements along one fiber path. Using a plurality of fibers, shape determination of the body and the tow cable can be made with minimal ambiguity. Also disclosed is a method to resolve the body shape based on strain-to-shape structural analysis. Possible applications include, but are not limited to, sensing the shape and position of flexible bodies, aid in improving the efficiency of existing acoustic surveying processing techniques, and related applications in geophysical prospecting.

Abstract: Cascaded waveguide sensors with different sensitivities to temperature and strain produce independent temperature and strain measurements. In one embodiment a first sensor is formed of a first optical material having a corresponding first sensible thermomechanical response and a second sensor is formed of a second optical material having a corresponding second sensible thermomechanical response. The first and second thermomechanical responses are sufficiently different so as to produce independent temperature and strain measurements. Particular embodiments employ intrinsic or extrinsic Fabry-Perot interferometers (IFP, EFP),sensors, in-line fiber etalon (ILFE) sensor and a fiber-optic Bragg grating.

Abstract: An optical fiber device for measuring strain has a first portion which generates a first signal, and a second portion which generates a second signal and is located proximate the first portion. The first and second portions are made of different component types of optical fibers. A fiber carries a superposed signal to readout interferometers which recover individual strain signals from the superposed signal. The individual strain signals are processed to obtain strain measurements in two or more orthogonal directions in the host material. The optical fiber device may also include a third portion which generates a third signal and is located proximate the second portion opposite the first portion.

Abstract: A fiber optic sensor employs tapered fiber optics in a tapered gun barrel. The fiber optic sensor employs a single-mode optical fiber, a light source supplying light to the single-mode fiber and at least one tapered dual-mode optical fiber secured to the barrel in a longitudinal direction. The single-mode fiber is spliced to with an end of a proximal one of the dual-mode fibers for carrying the light signal. A partial reflector is inserted between the dual-mode fibers to partially reflect and partially transmit light. A reflector is coupled to a distal end the dual-mode fiber, at the open end of the muzzle of the gun, to reflect the transmitted light. A coupler couples the single-mode fiber to the proximal dual-mode fiber. A coherent multiplexer is connected to the coupler for receiving and multiplexing the reflected light. A processor is responsive to the multiplexer for processing the multiplexed sensing information.

Abstract: The invention herein provides a method and apparatus for fabricating optical fiber vibration modal filtering sensors. Such filtering sensors are used in vibration control of engineered structures, especially flexible structures. In particular, the optical fiber sensor is made by a functionally weighted exposure of an optical fiber to ultra-violet (UV) laser source thereby modifying the refractive index of the optical fiber core resulting in a vibrational modal filtering sensor using a single mode interferometric detection scheme. The apparatus for making the same uses a multiple reel stepper motor mechanism, a process controller and a UV laser source.

Abstract: This invention pertains to an integral Fabry-Perot stress corrosion, strain and material corrosion sensor and associated system that allows for in-situ monitoring of stress-corrosion, strain and corrosion at a given location of a specimen in real-time. The sensor uses an intrinsic Fabry-Perot cavity with one mirror integrally mounted on the specimen that provides a means for: i) transducing information of stress-corrosion of the specimen; ii) measuring strain of the specimen; and iii) measuring the corrosive environment.

Abstract: Optical fiber sensor coated with linear work hardening elastic-plastic materials is provided that are used for a non-destructive optical damage detection sensor. The detection coating's intrinsic and extrinsic properties are critical on the sensor's continuous performance while being subjected to adverse environmental conditions. The damage detection sensor can also be used as an alternative to the conventional fiber fracture sensor for sensing impact damage. Other uses include maintaining a permanent record of the load/damage history of a loaded structure. A simple damage detection system is described that detects the sensor's permanent output phase-shift.