Exploring the use of a virtual reference spectrum in the Vernier effect

The optical Vernier effect (OVE) has been widely exploited as a method to enhance the sensitivity of interferometric optical fiber sensors. This is usually achieved by cascading or paralleling two interferometers, one as sensing element, and other as reference. Here it is explored the use of a single interferometer, which detects the changed signal, and a virtual reference spectrum to be superimposed with the sensing optical signal, realizing the OVE. Open Fabry-Perot interferometer (FPI) cavities with different lengths (Lsens from 118 to 539 m) are characterized to refractive index (RI) variations, using glucose solutions with varying concentrations. One of the sensors with the highest sensitivity (<i>L_sens</i>= 292 &mu;m) is chosen for further exploration of the OVE. Using the optical spectrum obtained when this sensor was immersed in water, virtual reference optical spectra corresponding to FPIs with different lengths (<i>L_ref</i> from 320 to 390 &mu;m) are simulated, using, in this case, the OriginPro software. Once the most suitable conditions are chosen, the behavior of the spectral overlap is evaluated, and the sensing magnification resulting from the OVE application is determined. A sensitivity of (20562 &plusmn; 1461) nm/RIU is achieved, which corresponds to a magnification factor, <i>M</i> = 14.1. The use of a virtual reference signal in the OVE is a simpler and more economical approach, with the possibility to adjust the magnified sensitivity.