Russell G. May's research while affiliated with Virginia Tech (Virginia Polytechnic Institute and State University) and other places

... Light at a certain wavelength can couple to a backward propagating fundamental mode or a forward propagating cladding mode depending on the grating type. As shown in Figure 10a in the case of an FBG, there is coupling between a forward and backward propagating mode over a narrow band of selected wavelengths only, which creates a peak in the reflection spectrum, giving rise to a specific Bragg-reflective wavelength λ B , given as [75]: ...

... Fabry-Perot (EFPI) sensors have shown their ability to be immune to lightwave polarization and only sensitive to axial strain components. By examining the interferometric output spectrum of an EFPI sensor, we can determine the absolute air gap cavity length without initialization [15,16]. It is possible to design the interferometer to only sense one or two parameters which eliminate response to interfering parameters. ...

... Tere are several FOS solutions for corrosion detection which utilize diferent sensing approaches [13][14][15][16]. One principle of operation employs fber Bragg grating (FBG) corrosion sensors based on tensile stress relaxation and volume expansion [17][18][19][20][21][22][23]. In the frst case, i.e., tensile stress relaxation detection, the fber is pretensioned; thus, when the corrosion occurs, the relaxation of the fber grating instigates a wavelength shift. ...

... It can accurately measure physical parameters such as pressure [1], strain [2], temperature [3,4], displacement [5,6], amongst others. Fiber interferometry is widely used to monitor the health of large steel structures [7], underwater acoustic detection [8], biomedical imaging [9,10], etc. There are polarization and phase fading problems in most fiber interferometers, and many methods have been proposed to solve these problems. ...

... If the light shows no preference to a particnlar polarization state, it is unpolarized. An example is natural or t should be noted that in many experimental situations, depolarization can readily occur md care must be taken to either account for it or minimize it (Kim & Ryu, 1996) (Li et ,1998). The most co=on source of depolarization in optical measurement is multiple cattering by such systems as dense suspensions or liquid crystals. ...

... When the fibre-optic sensor is to be installed in harsh settings, it is common to use polyimide-coated optical fibres, for their durability at high temperatures and in other challenging environments. Polyimide coatings provide excellent long-term protection to fibres up to 300˚C in air for long period of time in harsh environment applications (shorter term to 350˚C) [1][2][3]. Yet, there are many use-cases where long-term, higher temperature monitoring of processes and assets using distributed fibre-optic sensing techniques would be beneficial [4][5][6][7]. In these specific cases, fibres with metal coatings such as aluminum or gold, which can withstand higher temperatures, are sometimes used. ...

... Using hetero-dyne decoding [19] and using dynamic hologram reception [20] are some applications of this modulation mechanism. Speckle field from a multi-mode fiber was published in [21], and the study of the spatial coherence properties of the fiber speckle field has been subsequently analysed in [22]. ...

... The deformation of diaphragm will cause the changes of Fabry-Perot (F-P) cavity length and the reflected intensity. So the pressure and frequency of acoustic signal can be demodulated from the changes of the reflected intensity that detected by the interferometric/intensity demodulation mechanism [12]. For an interferometric/intensity based fiber acoustic sensor, the reflected intensity of the sensor Fig. 2. Schematic of fiber acoustic sensor detection unit. ...

... A wide range of fiber-optic sensor systems have been used for monitoring the cross-linking process and these can be classified into qualitative and quantitative techniques [1]. The qualitative techniques include intensity-based sensor designs234 . Quantitative analysis of the cross-linking kinetics is obtained using sensor designs that enable UV–visible [5], infrared [6] and evanescent wave [7] spectra to be obtained. ...

... Intensity demodulation is relatively simple and economical. However, it is considerably affected by the stability of the light source, and the measurement results commonly contain relatively large errors [13]. Spectral interrogation is most commonly used for phase demodulation. ...