D.A. Jackson

Simple multiplexing scheme for a fiber-optic grating sensor network

A new approach for the interrogation of a large number of fiber-optic grating sensors is proposed and demonstrated for a small number of sensors in which signal recovery is achieved by matching a receiving grating to its corresponding sensor. This technique is demonstrated for both quasi-static and periodic measurands, and the resolution achieved for a single sensor–receiving grating pair for quasi-static strain is 4.12 μ∊.

Monomode optical fibre interferometers for precision measurement

The evolution of optical interferometers into extreme resolution large dynamic range sensors implemented in a guided wave form is discussed. The design and performance of fibre optic interferometric sensors optimised for specific periodic and quasi-steady-state measurands such as rotation, magnetic field, temperature, etc., are described.

Synthesized source for white-light sensing systems

We report a novel technique in which by combining the output from two multimode laser diodes a synthesized source with an extremely short coherence length is produced for use in white-light interferometric sensing systems. Experimentally and theoretically it is demonstrated that, by summing the autocorrelation function of two multimode laser diodes with a wavelength difference of 108 nm, a synthesized source with an equivalent coherence length of ~4 microm is generated, greatly reducing the signal-to-noise ratio required to identify the central fringe position.

Coherence multiplexing of remote fibre optic fabry-perot sensing system

Abstract A monomode fibre optic coherence multiplexing sensor system incorporating passive miniature fibre optic probes is demonstrated using a coherence tuned local interferometer to sequentially interrogate the individual sensors. An example of its use as a high resolution relative point temperature measurement system is described with a range to resolution in excess of 10 4 .

Miniature Faraday current sensor based on multiple critical angle reflections in a bulk-optic ring

A novel optical element for a bulk glass current sensor that utilizes the Faraday effect is presented with a demonstrated sensitivity of 1 amp-turn and a flat frequency response in the range of 10-10(4) Hz. The new sensing element overcomes the problems associated with birefringence in optical fiber current sensors and the requirement to make bulk-optic current sensors in complex three-dimensional topologies.

Non-contact surface vibration analysis using a monomode fibre optic interferometer incorporating an open air path

A very high sensitivity non-contacting vibration analysis system based upon a monomode fibre optic Mach Zehnder interferometer incorporating an open air path is described. The system was operated in both a closed loop limited tracking range (>105) homodyne mode and an effective infinite tracking range novel pseudo-heterodyne mode. For periodic signals, amplitude detection sensitivities of approximately 2*10-10 m at 10 Hz to 5*10-11 m at 10 kHz have been demonstrated for both modes of operation.

Simultaneous spatial, time and wavelength division multiplexed in-fibre grating sensing network

Abstract A simultaneous spatial, time and wavelength division multiplexing topology, with combination of a tunable wavelength filter and an interferometric wavelength scanner, is proposed to interrogate a range of in-fibre Bragg grating (FBG) sensors. An eleven-element FBG sensor network based upon this topology is demonstrated for quasi-static strain sensing. Preliminary experimental results show that a strain resolution of ∼7 μϵ with a ∼30 Hz bandwidth (∼1.3 μϵ⧸ Hz for quasi-static strain measurement has been obtained.

Coaxial optical-fiber frequency shifter.

A fiber-optic frequency shifter utilizing a traveling torsional acoustic wave to couple the polarization eigen-modes of a highly linearly birefringent optical fiber is demonstrated. The frequency-shifter configuration is such that the acoustic-wave generator and optical fiber are coaxial. The device is thus more rugged than previous free-fiber frequency shifters, which have incorporated a T junction between the acoustic generator and optical fiber. The optical frequency shift was 3.204 MHz, and an optical coupling efficiency of 12% was obtained with 4 W of electrical drive power applied to the acoustic transducer.

Monomode fiber-optic strain gauge with simultaneous phase- and polarization-state detection

A fiber-optic sensor for the measurement of strain is described, in which the measurand-induced changes in both phase and polarization state are simultaneously recovered. A simple optical arrangement based on the fiber Fabry-erot interferometer is used to realize a high-resolution instrument with enhanced measurement range.

Faraday effect optical current clamp using a bulk-glass sensing element

A new topology for an openable Faraday current sensor is presented with a demonstrated resolution of 7.2 mA/ radicalHz over a measurement range from 1 to 1500 A. The sensitivity of the system is 2.21 x 10(-5) rad/A. Since this sensor is fabricated in an openable form, emulating a conventional current clamp, it can be used either in permanent installations or for short-term diagnostic studies.