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Bi-tapered Fiber Sensor Using a Supercontinuum Light Source for a Broad Spectral Range

Garcia Mina, Diego Felipe
http://orcid.org/0000-0001-9001-0795
http://rave.ohiolink.edu/etdc/view?acc_num=dayton1492001857501804

Abstract Details

2017, Doctor of Philosophy (Ph.D.), University of Dayton, Electro-Optics.
We describe the fabrication bi-tapered optical fiber sensors designed for shorter wavelength operation and we study their optical properties. The new sensing system designed and built for the project is a specialty optical fiber that is single-mode in the visible/near infrared wavelength region of interest. In fabricating the tapered fiber we control the taper parameters, such as the down-taper and up-taper rate, shape and length, and the fiber waist diameter and length. The sensing is mode is via the electromagnetic field, which is evanescent outside the optical fiber and is confined close to the fiber’s surface (within a couple hundred nanometers). The fiber sensor system has multiple advantages as a compact, simple device with an ability to detected tiny changes in the refractive index. We developed a supercontinuum light source to provide a wide spectral wavelength range from visible to near IR. The source design was based on coupling light from a femtosecond laser in a photonic crystal fiber designed for high nonlinearity. The output light was efficiently coupled into the bi-tapered fiber sensor and good signal to noise was achieved across the wavelength region. The bi-tapered fiber starts and ends with a single mode fiber in the waist region there are many modes with different propagation constants that couple to the environment outside the fiber. The signals have a strong periodic component as the wavelength is scanned; we exploit the periodicity in the signal using a discrete Fourier transform analysis to correlate signal phase changes with the refractive index changes in the local environment. For small index changes we also measure a strong correlation with the dominant Fourier amplitude component. Our experiments show that our phase-based signal processing technique works well at shorter wavelengths and we extract a new feature, the Fourier amplitude, to measure the refractive index difference. We conducted experiments using aqueous medium with controlled refractive index, such as water-glycerol mixtures. We find sensitivity to changes in the refractive index close to 0.00002 in so-called Refractive Index Units (RIUs). That is smaller than reported in recent literature, but by no means a limiting value. The technique is not limited to aqueous solutions surrounding the fiber, but it can also be adapted to study volatile organic compounds. Future improvements in the fiber sensing system are discussed, including adding thin films to the surface for label-free detection and to draw the electromagnetic field to the fiber’s surface.
Joseph W Haus, Ph.D. (Advisor)
Andrew Sarangan, Ph.D. (Committee Member)
Imad Agha, Ph.D. (Committee Member)
Karolyn Hansen, Ph.D. (Committee Member)
106 p.
Optics
Tapered optical fiber; Fiber sensor; Supercontinuum; Fourier signal analysis; Refractive index

Recommended Citations

Citations

  • Garcia Mina, D. F. (2017). Bi-tapered Fiber Sensor Using a Supercontinuum Light Source for a Broad Spectral Range [Doctoral dissertation, University of Dayton]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1492001857501804

    APA Style (7th edition)

  • Garcia Mina, Diego. Bi-tapered Fiber Sensor Using a Supercontinuum Light Source for a Broad Spectral Range. 2017. University of Dayton, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=dayton1492001857501804.

    MLA Style (8th edition)

  • Garcia Mina, Diego. "Bi-tapered Fiber Sensor Using a Supercontinuum Light Source for a Broad Spectral Range." Doctoral dissertation, University of Dayton, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1492001857501804

    Chicago Manual of Style (17th edition)

dayton1492001857501804
490
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This open access ETD is published by University of Dayton and OhioLINK.