Launching the excitation light to a taper externally: Comprehensive performance improvement of fiber-optic evanescent-wave sensor

A taper at one end of the fiber serving as the sensing element is widely used to enhance the performance of evanescent-wave (EW) fiber-optic sensors. However, almost all sensors of this type launch the excitation light into the core at the opposite end and the entire taper has to be immersed into the bulky sample volume. This paper introduces a new way of injecting excitation light: from the outside of the taper perpendicularly. As a result, several desirable features are achieved simultaneously, including a dramatic increase of collectable EW signal, elimination of stray excitation light, easy system construction and reduction of the sample volume to mere microliters.