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Appl Opt. 1991 Apr 20;30(12):1474-9. doi: 10.1364/AO.30.001474.

Simple interferometer for evanescent field refractive index sensing as a feasibility study for an immunosensor.


We describe a fiber optic interferometric refractive index sensor to illustrate that, by using the evanescent field of an optical waveguide, a potentially very sensitive determination of changes in the refractive index on the waveguide surface can be obtained. These changes can, e.g., be the result of immunoreactions. We used a Mach-Zehnder interferometer configuration with a flow-through cuvette in one arm with a decladded multimode glass fiber of 0.6-mm diameter and 2-cm interaction length. The obtained resolution in measuring refractive index changes is 1 x 10-(3). We also developed the theory describing the sensitivity of this sensor using the modal and the geometrical ray description.

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