Coherence-length-gated distributed optical fiber sensing based on microwave-photonic interferometry

Abstract

This paper presents a new optical fiber distributed sensing concept based on coherent microwave-photonics interferometry (CMPI), which uses a microwave modulated coherent light source to interrogate cascaded interferometers for distributed measurement. By scanning the microwave frequencies, the complex microwave spectrum is obtained and converted to time domain signals at known locations by complex Fourier transform. The amplitudes of these time domain pulses are a function of the optical path differences (OPDs) of the distributed interferometers. Cascaded fiber Fabry-Perot interferometers (FPIs) fabricated by femtosecond laser micromachining were used to demonstrate the concept. The experimental results indicated that the strain measurement resolution can be better than 0.6 µε using a FPI with a cavity length of 1.5 cm. Further improvement of the strain resolution to the nε level is achievable by increasing the cavity length of the FPI to over 1m. The tradeoff between the sensitivity and dynamic range was also analyzed in detail. To minimize the optical power instability (either from the light source or the fiber loss) induced errors, a single reflector was added in front of an individual FPI as an optical power reference for the purpose of compensation.

Distributed Acoustic Sensing Based on Coherent Microwave Photonics Interferometry

“…(4), and the amplitude is also be corrected by using the calculated interference phase. Several ways to build a sensing network using the CMPI system have been demonstrated [24,37], and we used two of these methods to validate the proposed concept. The first set of experiments used a single pair of in-fiber reflectors to illustrate the signal processing.…”

“…Frequency modulation in the GHz bandwidth enables spatial resolution in the cm range [27]. Distributed systems based on this approach have been developed for interrogating Rayleigh scattering [28], fiber Bragg grating (FBG) arrays [29][30][31], and interferometers [24,27]. Recently, coherence-length-gated microwave-photonics interferometry (CMPI) was developed to improve strain sensitivity using cascaded interferometers [24,32].…”

“…Distributed systems based on this approach have been developed for interrogating Rayleigh scattering [28], fiber Bragg grating (FBG) arrays [29][30][31], and interferometers [24,27]. Recently, coherence-length-gated microwave-photonics interferometry (CMPI) was developed to improve strain sensitivity using cascaded interferometers [24,32]. The coherence length of the light probe is well controlled to enable localized high-contrast optical interference while avoiding crosstalk among interferometers.…”

Information integrated glass module fabricated by integrated additive and subtractive manufacturing

“…Fiber-optic sensors have been widely demonstrated and applied for harsh environment applications. Compared with electronic sensors, fiber-optic sensors have the unique advantages of light weight, chemical resistance, high temperature resistance and distributed sensing capability [1][2][3][4][5]. Additionally, because of their immunity to electromagnetic interference (EMI), fiber optic sensors can be applied in strong EMI harsh environments [2][3][4][5][6][7][8][9].…”

“…Compared with electronic sensors, fiber-optic sensors have the unique advantages of light weight, chemical resistance, high temperature resistance and distributed sensing capability [1][2][3][4][5]. Additionally, because of their immunity to electromagnetic interference (EMI), fiber optic sensors can be applied in strong EMI harsh environments [2][3][4][5][6][7][8][9]. Over the past years various optical fiber sensors have been proposed and demonstrated for temperature sensing, such as fiber interferometers, long period fiber gratings, fiber Bragg gratings and optical fiber directional couplers [6,[8][9][10][11].…”