Critical-angle-based sensor with improved figure of merit using dip detection

It is demonstrated theoretically and experimentally that a one-dimensional photonic crystal (1D-PC) made of quarter waves stacked on top of a prism exhibits both TE and TM resonances that coincide with the critical angle θ(c) when the 1D-PC is semi-infinite and with very little deviation from θ(c) for a finite 1D-PC. As a refractive index (RI) sensor, it behaves as a total internal reflection sensor at θ(c) with the advantage of detecting a narrow dip rather than an edge and enhanced figure of merit by increasing the number of periods in the 1D-PC. Using the diverging beam approach on an optical bench, a two channel sensor is demonstrated with a sensitivity of 120.9 deg/RIU and a detection limit of 1.9×10(-5) RIU.