Frequency-Shifted Interferometry — A Versatile Fiber-Optic Sensing Technique

Abstract

Fiber-optic sensing is a field that is developing at a fast pace. Novel fiber-optic sensor designs and sensing principles constantly open doors for new opportunities. In this paper, we review a fiber-optic sensing technique developed in our research group called frequency-shifted interferometry (FSI). This technique uses a continuous-wave light source, an optical frequency shifter, and a slow detector. We discuss the operation principles of several FSI implementations and show their applications in fiber length and dispersion measurement, locating weak reflections along a fiber link, fiber-optic sensor multiplexing, and high-sensitivity cavity ring-down measurement. Detailed analysis of FSI system parameters is also presented.

Method of hybrid multiplexing for fiber-optic Fabry–Perot sensors utilizing frequency-shifted interferometry

“…On the other hand, it can also be seen that the amplitudes of all the reflection spectra are more or less changed, especially for F-P 12 . This may be the reason that the polarization state of reflected light by sensors drifted during the FSI measurement [16]. According to these spectra measured by FSI, we can further demodulate the cavity length and cavity-length shift of each sensor, which normally carry the information of the parameters measured.…”

“…For a single reflection site, the differential intensity at the balanced detector (BD) is a cosine function of f [15,16]; therefore, for the mth (m 1; 2; …; or M) channel sensor link, including N reflection sites, the intensity is a summation of N cosine functions, which can be given as [15]…”

“…As a novel fiber-optic sensor sensing technique, frequency-shifted interferometry (FSI) was proposed and quickly developed by the research group of Qian [13][14][15][16][17], and has many outstanding advantages. FSI needs only one CW light source, one low-speed data acquisition element, and one slow detector, compared with TDM, and the detector is a shared one, unlike SDM.…”

Single-Arm Frequency-Shifted Interferometry Using a Bidirectional Electro-Optic Modulator

“…O PTICAL sensing using fiber Bragg grating (FBG) arrays is one of the most commonly employed method to achieve multi-point sensing, such as in structural health monitoring [1]- [3] and temperature sensing [4]. Frequency shifted interferometry (FSI) [5] has emerged in recent years as a practical technique to interrogate fiber-optic sensor arrays [6], [7]. Utilizing asymmetric frequency shifts in a common-path interferometer, FSI can perform location-resolved sensing using a low cost broadband source and a slow detector [5].…”

“…Frequency shifted interferometry (FSI) [5] has emerged in recent years as a practical technique to interrogate fiber-optic sensor arrays [6], [7]. Utilizing asymmetric frequency shifts in a common-path interferometer, FSI can perform location-resolved sensing using a low cost broadband source and a slow detector [5]. Compared to the wavelength-division multiplexing (WDM) technique [8] for sensor multiplexing, FSI can work with FBGs reflecting in the same (or different) wavelength regions, significantly increasing the dynamic range of the FBG sensors, as well as reducing the fabrication cost of the FBG arrays.…”