Signal-processing algorithm for white-light optical fiber extrinsic Fabry–Perot interferometric sensors

Abstract

We present a novel signal-processing algorithm for single-mode optical fiber extrinsic Fabry-Perot interferometric sensors that can achieve both high-resolution, absolute measurement of the cavity length and a large dynamic measurement range simultaneously. The algorithm is based on an accurate model of the characteristics of a fiber-optic sensor that takes into account the phase shift that is due to the coupling of light reflected at the second surface to the lead-in fiber end.

Spiro-oxazine photochromic fiber optical switch

“…Using this principle, FP resonators have recently been used in fiber for sensing applications. [15][16][17] A drawback to using SPO is that the photochromic reaction is slow in polymer blends and is prohibited in crystal form 18 as the conformation change is impeded by the solid phase. Therefore, we combine the SPO liquid solution with optical fibers.…”

Optical Fiber Extrinsic Micro-Cavity Scanning Microscopy

“…In the following, we will describe the model used for describing the reflected signal from the cavity and its dependence on the geometrical and dielectric variations. In presence of a low reflectivity surface, the electromagnetic analysis of the optical fiber extrinsic Fabry-Perot cavity can be done approximately by using a two-beam approximation, in which only two interfering beams are considered: i.e., the reflected signal at the fiber interface and back-reflected signal from the external surface [1,7,8], while higher order interferences are neglected. Although this approach gives a simple and compact analytical expression for the interference signal that couple-back to the fiber, it does not characterize rigorously the electromagnetic behavior of the cavity, in which a multi-beam interference takes place.…”

“…Fabry-Perot cavities have always received a great deal of interest in the realization of interferometric sensors due to their high sensitivity, simple structure and immunity to electromagnetic interference [1][2][3][4][5][6][7]. In recent works, Fabry-Perot micro-cavities were applied to measure the refractive index of optical glasses [8], or to realize wide-range displacement sensors with sub-nanometer resolution for Confocal Laser Microscopy [9].…”

Multiplexed Optical Fiber Sensors for Coal Fired Advanced Fossil Energy Systems

“…Non-constant phase-induced OPD demodulation jumps To interrogate a low-finesse FP sensor, the phase of the periodic fringe pattern is measured at either a fraction or all of the sampling points in the spectrogram [20,21,22,23]. This interference spectrum is represented by S(k)  cos[Φ(k)], where k=2π/λ is the optical wavenumber, λ is the wavelength, Φ(k) is the total interferogram phase which is expressed as Φ(k) = k  OPD + φ 0 , where φ 0 is an additional phase term caused by beam reflection and propagation [19,24]. In traditional OPD-based demodulation, the additional phase term φ 0 is usually assumed to be constant during measurement process and needs to be pre-calibrated [21,22].…”

“…In traditional OPD-based demodulation, the additional phase term φ 0 is usually assumed to be constant during measurement process and needs to be pre-calibrated [21,22]. However, physical changes in IFPI sensors can cause this term to vary during measurement (as discussed in Section 3.3.1, and in Ref [19,24] The SMS-IFPI sensors were typically interrogated using a swept-laser interrogation system (Micron Optics Si-720) over a spectral range of 1520-1570nm with spectral resolution of 2.5pm, dynamic range of 70dB, and a scanning rate of 0.5Hz. Each collected spectrum was subsequently processed using a peak tracking method, in which local curve fitting is used to identify the exact locations of every fringe peak in the interferogram, and their corresponding fringe orders are determined to measure OPD [20, 21,23].…”