Abstract
A self-referencing, intensity-based fiber optic sensor (FOS) is proposed and demonstrated. The theoretical analysis for the proposed design is given, and the validity of the theoretical analysis is confirmed via experiments. We define the measurement parameter, X, and the calibration factor, β, to find the transfer function, Hm,n, of the intensity-based FOS head. The self-referencing and multipoint sensing characteristics of the proposed system are validated by showing the measured and relative error versus the optical power attenuation of the sensor head for four cases: optical source fluctuation, various remote sensing point distances, fiber Bragg gratings (FBGs) with different characteristics, and multiple sensor heads with cascade and/or parallel forms. The power-budget analysis and limitations of the measurement rates are discussed, and the measurement results of fiber-reinforced plastic (FRP) coupon strain using the proposed FOS are given as an actual measurement. The proposed FOS has several benefits, including a self-referencing characteristic, the flexibility to determine FBGs, and a simple structure in terms of the number of devices and measuring procedure.
Highlights
Over the past 20 years the field of fiber optic sensors (FOS) has been a major user of technology associated with the optoelectronic and fiber optic communications industries [1]
The proposed intensity-based FOS shown in Figure 1 is implemented with a broadband light source (BLS) of −16.6 dBm optical power per 0.1 nm bandwidth at 1550 nm, a 1 × 2 50:50 split ratio optical coupler, eight fiber Bragg gratings (FBGs), six sensor heads, a tunable F-P filter with a wavelength range of 1525–1567 nm, a scan frequency of 3 kHz, and a full width at half maximum (FWHM) of 0.12 nm, and a switchable gain photodiode module
The power budget analysis and limitations of the measurement rates are discussed, and the fiber-reinforced plastic (FRP) coupon strain with the proposed FOS are given as an actual measurement
Summary
Over the past 20 years the field of fiber optic sensors (FOS) has been a major user of technology associated with the optoelectronic and fiber optic communications industries [1]. Among fiber-optic-based sensors, intensity-based FOSs are important for their simplicity and potential low cost, as well as from a historical perspective as they were the first developed. Today they continue to be an attractive choice in many sensing applications due to their ability to measure a wide variety of parameters, their use of inexpensive light sources and simple detection schemes while still benefiting from the intrinsic advantages of photonic sensors: low weight, small size, and electromagnetic immunity. The interrogation of fiber optic intensity sensors using a combination of the frequency-modulated continuous wave concept with the spectral selective reflectivity of FBGs is demonstrated [16].
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