A Theoretical Study and Numerical Simulation of a Quasi-Distributed Sensor Based on the Low-Finesse Fabry-Perot Interferometer: Frequency-Division Multiplexing

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.

Twin-Grating Fiber Optic Sensors Applied on Wavelength- Division Multiplexing and Its Numerical Resolution

“…(1) and (4), the cavity length defines the frequency of all interference patterns. Its size can be found in the interval of [3]…”

“…The frequency-division multiplexing scheme [3] is illustrated in Figure 1b for a quasidistributed sensor based on the twin-grating fiber optic sensor. Each twin-grating sensor [4,5] consists of two identical Bragg gratings and acts as a local sensor.…”

“…In particular, the quasi-distributed sensor Figure 1. A scheme of a quasi-distributed fiber optic sensor: (a) Bragg gratings and (b) twin-grating interferometers [3]. consists of a serial array of twin-grating sensors.…”

“…consists of a serial array of twin-grating sensors. Each twin-grating sensor acts as a low-finesse Fabry-Perot interferometer [3,10]. All interferometers have the same cavity length L FP but each twin-grating sensor has its own Bragg wavelength.…”

Interference Pattern Representation on the Complex s-Plane

“…Physical implementation and signal demodulation are very important for the good measurement. Many implementations are based on the Bragg gratings, fiber optics, vacuum, mirrors, crystals, polarizer, and their combinations [11][12][13][14][15]; whereas in the signal demodulation, has been applied commonly the Fourier transform [16][17][18][19][20]. This transform permits us to know all frequency components of any interference pattern, doing possible the signal demodulation for the interferometer systems.…”