• Advanced Photonics Nexus
  • Vol. 3, Issue 4, 046011 (2024)
Xun Cai1,2, Yi Zhuang1,2, Tongtong Xie1,2, Shichen Zheng1,2, and Hongyan Fu1,2,*
Author Affiliations
  • 1Xiamen University, Department of Electronic Engineering, Xiamen, China
  • 2Xiamen University, Fujian Key Laboratory of Ultrafast Laser Technology and Applications, Xiamen, China
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    DOI: 10.1117/1.APN.3.4.046011 Cite this Article Set citation alerts
    Xun Cai, Yi Zhuang, Tongtong Xie, Shichen Zheng, Hongyan Fu, "Temperature-insensitive fiber-optic refractive index sensor based on cascaded in-line interferometer and microwave photonics interrogation system," Adv. Photon. Nexus 3, 046011 (2024) Copy Citation Text show less

    Abstract

    A compact and high-resolution fiber-optic refractive index (RI) sensor based on a microwave photonic filter (MPF) is proposed and experimentally validated. The sensing head utilizes a cascaded in-line interferometer fabricated by an input single-mode fiber (SMF) tapered fusion with no-core fiber-thin-core fiber (TCF)-SMF. The surrounding RI (SRI) can be demodulated by tracing the passband’s central frequency of the MPF, which is constructed by the cascaded in-line interferometer, electro-optic modulator, and a section of dispersion compensation fiber. The sensitivity of the sensor is tailorable through the use of different lengths of TCF. Experimental results reveal that with a 30 mm length of TCF, the sensor achieves a maximum theoretical sensitivity and resolution of -1.403 GHz / refractive index unit (RIU ) and 1.425 × 10 - 7 RIU, respectively, which is at least 6.3 times higher than what has been reported previously. Furthermore, the sensor exhibits temperature-insensitive characteristics within the range of 25 ° C - 75 ° C, with a temperature-induced frequency change of only ±1.5 MHz. This value is significantly lower than the frequency change induced by changes in the SRI. The proposed MPF-based cascaded in-line interferometer RI sensor possesses benefits such as easy manufacture, low cost, high resolution, and temperature insensitivity.
    T=TMMI×TMZI=12(1+A1cosθ1)×12(1+A2cosθ2)=14[1+A1cosθ1+A2cosθ2+12A1A2cos(θ1+θ2)+12A1A2cos(θ1θ2)],

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    θi=2π(ncoreeffnclad,ieff)Liλ,

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    λdip=2(ncoreeffnclad,ieff)Li2k+1.

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    FSRλ2ΔniLi=λ2(ncoreeffnclad,ieff)Li.

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    f=1DLDCF×FSR=(ncoreeffnclad,ieff)LiDLDCFλ2,

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    dfdSRI=dnclad,ieffdSRI×LiDLDCFλ2.

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    Xun Cai, Yi Zhuang, Tongtong Xie, Shichen Zheng, Hongyan Fu, "Temperature-insensitive fiber-optic refractive index sensor based on cascaded in-line interferometer and microwave photonics interrogation system," Adv. Photon. Nexus 3, 046011 (2024)
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