Abstract
The application of the sensor optical fibers in the areas of scientific instrumentation and industrial instrumentation is very attractive due to its numerous advantages. In the industry of civil engineering for example, quasi-distributed sensors made with optical fiber are used for reliable strain and temperature measurements. Here, a quasi-distributed sensor in the frequency domain is discussed. The sensor consists of a series of low-finesse Fabry-Perot interferometers where each Fabry-Perot interferometer acts as a local sensor. Fabry-Perot interferometers are formed by pairs of identical low reflective Bragg gratings imprinted in a single mode fiber. All interferometer sensors have different cavity length, provoking frequency-domain multiplexing. The optical signal represents the superposition of all interference patterns which can be decomposed using the Fourier transform. The frequency spectrum was analyzed and sensor’s properties were defined. Following that, a quasi-distributed sensor was numerically simulated. Our sensor simulation considers sensor properties, signal processing, noise system, and instrumentation. The numerical results show the behavior of resolution vs. signal-to-noise ratio. From our results, the Fabry-Perot sensor has high resolution and low resolution. Both resolutions are conceivable because the Fourier Domain Phase Analysis (FDPA) algorithm elaborates two evaluations of Bragg wavelength shift.
Highlights
Bragg grating has a very particular peak in its reflection spectrum; the peak is centered at the Bragg wavelength λ BG = 2nΛ [1], where Λ is the grating pitch and n is the effective fiber refraction index
To test and compare our theoretical analysis, we performed a numerical simulation of a quasi-distributed sensor based on low-finesse Fabry-Perot interferometers
The quasi-distributed optical fiber sensor based on the low-finesse Fabry-Perot interferometer was studied theoretically and simulated numerically
Summary
The monitoring system needs to detect the wavelength shift with very high resolution, permitting its correct evaluation This shift is evaluated from optical measurements, for example, a dual-OFC FBG Bragg gratings play an important role in fiber-optic sensor technology Such sensors are very attractive for quasi-distributed sensing, employing only one optical fiber with many gratings printed along a fiber length. The conventional Bragg grating sensors use a broadband light source and a direct spectrometric detection technique Their principal problem concerns the detection of relatively small shifts in the resonant wavelength of grating arrays exposed to strain or slow temperature changes. An additional application of Bragg gratings in sensor technology is to build interferometers within a single path fiber In this case, Bragg gratings act as selective mirrors. Frequency-division multiplexing, wavelength-division multiplexing, and time-division multiplexing can be implemented [5,6,7,8,9,10,11,12]
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