A Dual-Polymer Fiber Fizeau Interferometer for Simultaneous Measurement of Relative Humidity and Temperature

Abstract

This paper presents a novel design method in which a dual-polymer fiber Fizeau interferometer (DPFFI) is proposed for simultaneously measuring relative humidity (RH) and temperature (T). Since the polymer is intrinsically highly sensitive to both RH and T, the polymer fiber Fizeau interferometer (PFFI) exhibits cross-sensitivity of RH and T. In general, it is difficult to demodulate the optical responses from both variations of RH and T using a single PFFI. If two PFFIs with different structures are combined, they will individually exhibit distinct sensitivity responses with respect to RH and T, respectively. The technical problem of analyzing multiple interferences of the optical spectra of the DPFFI and the individual sensitivity of RH and T to each PFFI is obtained using the fast Fourier transform (FFT). A mathematical method is applied to solve the simultaneous equations of the DPFFI, so that the two variables RH and T can be determined at the same time. Experimental results, indicating good sensitivity and accuracy, with small measurement errors (average errors of ~1.46 °C and ~1.48%, respectively), are shown, determining the feasibility, and verifying the effectiveness, of the proposed DPFFI sensor.

A Novel State of Charge Estimating Scheme Based on an Air-Gap Fiber Interferometer Sensor for the Vanadium Redox Flow Battery

“…The proposed fiber sensor for sensing electrolyte's RI consists of two single-mode fibers (SMFs, Corning SMF-28) with well-cleaved end faces and a designed air gap with a length of d = 43 μm, as shown in Figure 3a, aligned precisely on a V-groove holder (Figure 3b). An AGFFPI is formed using this configuration, where reflections can only occur at the two low-reflectivity fiber/air interfaces [28]. To derive the interference characteristics of the designed AGFFPI, the two-beam optical interference theorem is adopted in this study [24].…”

Optical Fiber FP Sensor for Simultaneous Measurement of Refractive Index and Temperature Based on the Empirical Mode Decomposition Algorithm

“…In contrast, when the FPI's cavity is open, the amplitude, the position of fringes, and the FSR of the fringes will vary depending on the refractive index of the exit medium. Other FPIs designs are based on a set of films deposited at the tip of the optical fiber [9][10][11]. Here, the complexity of the overall spectrum of the reflected intensity distribution of the interferometer increases with the number of films, since it is formed by the superposition of several spectra which are due to multiple reflections occurring between the interfaces of the layers.…”

“…For dual sensing applications the complexity to model and to determine the values of each variable from a single spectrum can be increased if this is formed by the superposition of different spectra, which change their characteristics due to the temperature, the relative humidity [10] or the refractive index of the exit medium. For these cases, it is quite important to systematically relate the changes observed in the reflected spectrum with the physical variables to be measured.…”

“…To perform the measurements, some authors have proposed to establish linear relationships between the physical variables and either the dip position of some fringes [12] or the intensity or the shift of a resonant dip wavelength [5]. Other authors have proposed to use the Fourier transform to determine the harmonic components of a FPI's reflection spectrum and relate them with a physical variable [10]. This type of approximation has proved to be simple and that the refractive index and the temperature can be estimated with high sensitivity, but usually with a very limited dynamic measurement range.…”

Low-Finesse Fabry–Pérot Interferometers Applied in the Study of the Relation between the Optical Path Difference and Poles Location

“…Diverse transformations were applied to study the OPD parameter, for example: Fourier transform and Hilbert transform [11][12][13][14]. Their studies permitted the signal demodulation for the interferometry systems, and, consequently, new sensing systems were developed [15,16].…”