Abstract
Based on a dual-loop optoelectronic oscillator (OEO) with Vernier effect, a scheme of fiber Bragg grating (FBG) interrogation system with an improved scale factor has been proposed and experimentally demonstrated. Functioning as the optical carrier of the OEO, the reflection signal of two cascaded FBGs is divided into two optical beams by using a wavelength division multiplexer (WDM). The two optical beams at different wavelengths travel along single mode fibers with different lengths. After combined together by another WDM, the two optical beams go through a section of dispersion compensation fiber (DCF). The oscillating frequency shift of the OEO is determined by the overall time delay, which is affected by the wavelength change of the sensing FBG. Thus, the wavelength change of the sensing FBG can be converted into the oscillating frequency shift of the OEO. Furthermore, due to the length difference between the two optical beams, an obvious Vernier effect has been generated in the frequency response of the OEO. By detecting the frequency shift of the envelope peak of the frequency response curve, the sensitivity of the sensing interrogation can be enhanced greatly. A proof-of-concept OEO-based FBG sensor for axial strain sensing experiment is performed. The experimental results show that the sensitivity is about 0.31 KHz/μϵ for a single-loop OEO. By employing Vernier effect, the sensitivity can be improved to -11 KHz/μϵ, which is 35 times higher than that of the single-loop OEO.
Highlights
During the last few decades, fiber Bragg grating (FBG) sensors have been considered a promising sensing technology and have been investigated extensively due to their intrinsic advantages, including immunity to electromagnetic interference, compact size, low weight and unique wavelength multiplexing capability [1]
The most common approaches to interrogate the FBG sensor tend to rely on the use of optical spectrum analyzer (OSA), optical filter, a tunable laser or an optical interferometer, which is implemented in the optical domain
The frequency shift on microwave photonics bandpass filter (MPF) inserted in optoelectronic oscillator (OEO) can be affected by FBG sensors, which is sensitive to detecting physical parameters
Summary
During the last few decades, fiber Bragg grating (FBG) sensors have been considered a promising sensing technology and have been investigated extensively due to their intrinsic advantages, including immunity to electromagnetic interference, compact size, low weight and unique wavelength multiplexing capability [1]. The frequency shift on MPF inserted in OEO can be affected by FBG sensors, which is sensitive to detecting physical parameters Based on this principle, several interrogation systems have been proposed to detect refractive index [10, 11], pressure [12], axial strain and temperature [13, 14]. The oscillating frequency of the OEO is determined by the overall time delay of the loop, which will be affected by the wavelength change of the sensing FBG According to this concept, another approach to implement an OEO-based FBG sensor has been proposed for position location [15], axial strain detection [16] and magnetic field measure [17]. With the advantages of Vernier effect, the shift of envelope is more distinct, making the sensor’s sensitivity enhance greatly and measurement error reduce enormously
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