Abstract
The temperature sensitivity of the free spectral range (FSR) for a polymer-overlaid microfiber Mach-Zehnder interferometer (MZI) is investigated both theoretically and experimentally. The waist diameter of the optical microfiber can be controlled to alter the thermal expansion and optic properties of the polymer-coated MZI. Inserting an optical microfiber with a strong evanescent field into the MZI, a low index polymer with high thermal characteristics is deposited on the surface of the microfibers to realize a polymer-overlaid microfiber MZI. It was found that the thermal expansion factor in the proposed MZI plays an important role in the temperature sensitivity of the FSR. The temperature sensitivity of the polymer-overlaid microfiber MZI is improved, which is measured to be −8.29 nm/°C at 25 °C. The optical transmission spectrum of the polymer-overlaid microfiber MZI is converted to the spatial frequency spectrum via fast Fourier transform. The temperature sensitivity of the spatial frequency in the proposed polymer-overlaid MZI is estimated to be 18.31 pm−1 °C−1, which is 17 times higher than that of the microfiber MZI without polymer coating (1.04 pm−1 °C−1).
Highlights
Fiber-optic interferometric sensors have been widely investigated for their various applications to mechanical, chemical, and biological measurement [1]
By using the finite element method (FEM), we analyzed the effect of the thermal expansion and the thermo-optic factors on the free spectral range (FSR) variation in the proposed polymer-overlaid microfiber Mach-Zehnder interferometer (MZI) as the external temperature increased
It is notable that the contribution of the thermal expansion factor to the temperature sensitivity of the FSR in the polymer-overlaid microfiber MZI is ~16 times higher than that of the thermo-optic term
Summary
Fiber-optic interferometric sensors have been widely investigated for their various applications to mechanical, chemical, and biological measurement [1]. A polymer-overlaid microfiber MZI is fabricated by coating the microfiber with low index polymer. By considering the waist diameter of the microfiber, the thermal expansion, and the thermo-optic factors in the polymer-overlaid MZI, the temperature sensitivity of the proposed microfiber MZI is investigated. The temperature sensitivity of the free spectral range (FSR) in the polymer-overlaid microfiber. Compared with the−temperature range (FSR) frequency in the polymer-overlaid is improved, and is measured to be. The transmission spectra of the proposed polymer-overlaid microfiber MZI is transformed to the temperature sensitivity of fast the Fourier spatialtransform frequency is Compared effectivelywith increased via the proposed spatial frequency spectra using the temperature sensitivity of. C ), the temperature sensitivity to of the spatial frequency is effectively increased via the proposed polymer-overlaid microfiber MZI, Sensors. 2017, 17, sensitivity temperature of the proposed microfiber MZI, it and is measured to be 18.31 pm−1 ◦ C −1 in the temperature range of 25 to 80 ◦ C
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