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Proceedings Paper

Waveguide sensors for liquid using gapped optical fibers
Author(s): Kazutaka Baba; Keita Chiba
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Paper Abstract

A waveguide sensor using a gapped optical fiber for measurements of refractive index and absorptance of liquid has been theoretically investigated. The gap formed in the single mode optical fiber is filled with the liquid whose optical characteristics are to be measured. An optical loss of the gapped optical fiber depends on the refractive index and absorptance of the liquid in the gap. The optical loss becomes smaller with the refractive index of the liquid as the light beam greatly expands in the media with smaller refractive index because of diffraction. On the other hand, the optical loss becomes larger with the absorptance of the liquid. Therefore, the refractive index and absorptance can be measured by using two waveguide sensors with different gap width. In the previous work, we investigated the theoretical characteristics of the sensors by using the two-dimensional slab waveguide for simplification. In this work, we have derived an equation for evaluation of the optical losses by approximating the fundamental mode in the optical fiber by a Gaussian function for practical use. And we clearly show the relationship between the optical loss and the refractive index of liquid filled into the gap for various gapped optical waveguides. The optical loss more greatly changes in the gaped optical fiber in comparison with the gaped slab waveguide. We have designed a saccharimeter for the liquid with Brix scale 0–20% by using the gapped waveguide. For example, the optimum gap widths are evaluated as 1.8 mm for the spot sizes of 0.01 mm. We have also designed waveguide sensor for measurements of not only refractive index but also absorptance of liquid.

Paper Details

Date Published: 8 March 2014
PDF: 7 pages
Proc. SPIE 8988, Integrated Optics: Devices, Materials, and Technologies XVIII, 89881K (8 March 2014); doi: 10.1117/12.2037166
Show Author Affiliations
Kazutaka Baba, Sendai National College of Technology (Japan)
Keita Chiba, Sendai National College of Technology (Japan)

Published in SPIE Proceedings Vol. 8988:
Integrated Optics: Devices, Materials, and Technologies XVIII
Jean Emmanuel Broquin; Gualtiero Nunzi Conti, Editor(s)

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