8,002 research outputs found

    Fiber-optic push-pull sensor systems

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    Fiber-optic push-pull sensors are those which exploit the intrinsically differential nature of an interferometer with concommitant benefits in common-mode rejection of undesired effects. Several fiber-optic accelerometer and hydrophone designs are described. Additionally, the recent development at the Naval Postgraduate School of a passive low-cost interferometric signal demodulator permits the development of economical fiber-optic sensor systems

    Polarization properties of interferometrically interrogated fiber Bragg grating and tandem-interferometer strain sensors

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    Lead sensitivity in low-coherence interferometric fiber-optic sensors is a well-known problem. It can lead to a severe degradation in the sensor resolution and accuracy through its effect on the fringe visibility and interferometric phase. These sensitivities have been attributed to birefringence in the various components. In the current work, an analysis of the polarization properties of fiber Bragg grating and tandem-interferometer strain sensors, using Stokes calculus and the Poincare sphere, is presented. The responses of these sensors as a function of the birefringence properties of the various components under different illuminating conditions are derived. The predicted responses demonstrate very good agreement with experimentally measured responses. These models provide a clear insight into the evolution of the polarization states through the sensor networks. Methods to overcome the lead sensitivity are discussed and demonstrated, which yield a differential strain measurement accuracy of 18 n epsilon - rms for a fiber Bragg grating sensor

    Efficient large-scale multiplexing of fiber Bragg grating and fiber Fabry-Perot sensors for structural health monitoring applications

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    Fiber Bragg gratings have been demonstrated as a versatile sensor for structural health monitoring. We present an efficient and cost effective multiplexing method for fiber Bragg grating and fiber Fabry-Perot sensors based on a broadband mode-locked fiber laser source and interferometric interrogation. The broadband, pulsed laser source permits time and wavelength division multiplexing to be employed to achieve very high sensor counts. Interferometric interrogation also permits high strain resolutions over large frequency ranges to be achieved. The proposed system has the capability to interrogate several hundred fiber Bragg gratings or fiber Fabry-Perot sensors on a single fiber, whilst achieving sub-microstrain resolution over bandwidths greater than 100 kHz. Strain resolutions of 30n epsilon/Hz(1/2) and 2 n epsilon/Hz(1/2) are demonstrated with the fiber Bragg grating and fiber Fabry-Perot sensor respectively. The fiber Fabry-Perot sensor provides an increase in the strain resolution over the fiber Bragg grating sensor of greater than a factor of 10. The fiber Bragg gratings are low reflectivity and could be fabricated during the fiber draw process providing a cost effective method for array fabrication. This system would find applications in several health monitoring applications where large sensor counts are necessary, in particular acoustic emission

    Experimental feasibility of measuring the gravitational redshift of light using dispersion in optical fibers

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    This paper describes a new class of experiments that use dispersion in optical fibers to convert the gravitational frequency shift of light into a measurable phase shift or time delay. Two conceptual models are explored. In the first model, long counter-propagating pulses are used in a vertical fiber optic Sagnac interferometer. The second model uses optical solitons in vertically separated fiber optic storage rings. We discuss the feasibility of using such an instrument to make a high precision measurement of the gravitational frequency shift of light.Comment: 11 pages, 12 figure

    The goldstone real-time connected element interferometer

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    Connected element interferometry (CEI) is a technique of observing a celestial radio source at two spatially separated antennas and then interfering the received signals to extract the relative phase of the signal at the two antennas. The high precision of the resulting phase delay data type can provide an accurate determination of the angular position of the radio source relative to the baseline vector between the two stations. This article describes a recently developed connected element interferometer on a 21-km baseline between two antennas at the Deep Space Network's Goldstone, California, tracking complex. Fiber-optic links are used to transmit the data to a common site for processing. The system incorporates a real-time correlator to process these data in real time. The architecture of the system is described, and observational data are presented to characterize the potential performance of such a system. The real-time processing capability offers potential advantages in terms of increased reliability and improved delivery of navigational data for time-critical operations. Angular accuracies of 50-100 nrad are achievable on this baseline

    Efficient fiber Bragg grating and fiber Fabry-Pe'rot sensor multiplexing scheme using a broadband pulsed mode-locked laser

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    A pulsed broadband mode-locked laser (MLL) combined with interferometric interrogation is shown to yield an efficient means of multiplexing a large number of fiber Bragg grating (FBG) or fiber Fabry-Perot (FFP) strain sensors with high performance. System configurations utilizing time division multiplexing (TDM) permit high resolution, accuracy, and bandwidth strain measurements along with high sensor densities. Strain resolutions of 23-60 n epsilon/Hz(1/2) at frequencies up to 800 Hz (expandable to 139 kHz) and a differential strain-measurement accuracy of +/- 1 mu epsilon are demonstrated. Interrogation of a low-finesse FFP sensor is also demonstrated, from which a strain resolution of 2 n epsilon/Hz(1/2) and strain-measurement accuracy of +/- 31 n epsilon are achieved. The system has the capability of interrogating well in excess of 50 sensors per fiber depending on crosstalk requirements. A discussion on sensor spacing, bandwidth, dynamic range, and measurement accuracy is also given

    Polarization mode dispersion in radio-frequency interferometric embedded fiber-optic sensors

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    The effect of fiber birefringence on the propagation delay in an embedded fiber-optic strain sensor is studied. The polarization characteristics of the sensor are described in terms of polarization mode dispersion through the principal states of polarization and their differential group delay. Using these descriptors, an analytical expression for the response of the sensor for an arbitrary input state of polarization is given and experimentally verified. It is found that the differential group delay, as well as the input and output principal states of polarization, vary when the embedded fiber is strained, leading to fluctuations in the sensor output. The use of high birefringence fibers and different embedding geometries is examined as a means for reducing the polarization dependency of the sensor

    Instantaneous quadrature low-coherence interferometry with 3x3 fiber-optic couplers

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    We describe fiber-based quadrature low-coherence interferometers that exploit the inherent phase shifts of 3 x 3 and higher-order fiber-optic couplers. We present a framework based on conservation of energy to account for the interferometric shifts in 3 x 3 interferometers, and we demonstrate that the resulting interferometers provide the entire complex interferometric signal instantaneously in homodyne and heterodyne systems. In heterodyne detection we demonstrate the capability for extraction of the magnitude and sign of Doppler shifts from the complex data. In homodyne detection we show the detection of subwavelength sample motion. N x N (N> 2) low-coherence interferometer topologies will be useful in Doppler optical coherence tomography (OCT), optical coherence microscopy, Fourier-domain OCT, optical frequency domain reflectometry, and phase-referenced interferometry

    Ultra-high-sensitivity two-dimensional bend sensor

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    A multicore fibre Fabry-Perot-based strain sensor interrogated with tandem interferometry for bend measurement is described. Curvature in two dimensions is obtained by measuring the difference in strain between three co-located low finesse Fabry-Perot interferometers formed in each core of the fibre by pairs of Bragg gratings. This sensor provides a responsivity enhancement of up to 30 times that of a previously reported fibre Bragg grating based sensor. Strain resolutions of 0.6 n epsilon/Hz(1/2) above 1 Hz are demonstrated, which corresponds to a curvature resolution of similar to 0.012 km(-1)/Hz(1/2)
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