129 research outputs found
Brillouin spectral deconvolution method for centimeter spatial resolution and high-accuracy strain measurement in Brillouin sensors
This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=ol-30-7-705. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Shahraam Afshar V., Xiaoyi Bao, Lufan Zou, and Liang Che
Enhancement of stimulated Brillouin scattering of higher-order acoustic modes in single-mode optical fiber
This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=ol-30-20-2685. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Solving the elastic wave equation exactly for a GeO2-doped silica fiber with a steplike distribution of the longitudinal and shear velocities and density, we have obtained the dispersion, attenuation, and fields of the leaky acoustic modes supported by the fiber. We have developed a model for stimulated Brillouin scattering of these modes in a pump-probe configuration and provided their Brillouin gains and frequencies for an extended range of core sizes and GeO2 doping. Parameter ranges close to cutoff of the acoustic modes and pump depletion enhance the ratio of higher-order peaks to the main peak in the Brillouin spectrum and are suitable for simultaneous strain-temperature sensing.Shahraam Afshar V., V. P. Kalosha, Xiaoyi Bao, Liang Che
Acousto-Optic Comb Interrogation System for Random Fiber Grating Sensors with Sub-nm Resolution
The broad-frequency response and nanometer-range displacements of ultrasound detection are essential for the characterization of small cracks, structural health monitoring and non-destructive evaluation. Those perturbations are generated at sub-nano-strain to nano-strain levels. This corresponds to the sub-nm level and, therefore, to about 0.1% of wavelength change at 1550 nm, making it difficult to detect them by conventional interferometric techniques. In this paper, we propose a demodulation system to read the random fiber grating spectrum using a self-heterodyne acousto-optic frequency comb. The system uses a self-heterodyne approach to extract phase and amplitude modulated signals to detect surface acoustic waves with sub-nanometer amplitudes in the frequency domain. The method can detect acoustic frequencies of 1 MHz and the associated displacement. The system is calibrated via phase detection with a heterodyne interferometer, which has a limited frequency response of up to 200 kHz. The goal is to achieve sub-nanometer strain detection at MHz frequency with random fiber gratings.Funding: Ministerio de Educación, Cultura y Deporte (Spain) para la Formación de Profesorado
Universitario FPU2016: FPU16/03695; Ministerio De Ciencia, Innovación y Universidades (Spain),
ayudas de movilidad EST18/00617. This work has been supported by the Madrid Government (Comunidad de Madrid-Spain) under the Multiannual Agreement with UC3M in the line of Excellence
of University Professors (EPUC3M26), and in the context of the V PRICIT (Regional Programme of
Research and Technological Innovation)
Time-delay signature suppression in a chaotic semiconductor laser by fiber random grating induced distributed feedback
We demonstrate that a semiconductor laser perturbed by the distributed
feedback from a fiber random grating can emit light chaotically without the
time delay signature. A theoretical model is developed based on the
Lang-Kobayashi model in order to numerically explore the chaotic dynamics of
the laser diode subjected to the random distributed feedback. It is predicted
that the random distributed feedback is superior to the single reflection
feedback in suppressing the time-delay signature. In experiments, a massive
number of feedbacks with randomly varied time delays induced by a fiber random
grating introduce large numbers of external cavity modes into the semiconductor
laser, leading to the high dimension of chaotic dynamics and thus the
concealment of the time delay signature. The obtained time delay signature with
the maximum suppression is 0.0088, which is the smallest to date
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