The application of leaky anti-resonant reflecting optical waveguides as optical sensors (L-ARROW)

Abstract

A multimode leaky ARROW sensor was investigated for sensing applications. The refractive index and wavelength sensitivities of the TM 0 (first leaky mode) and TM 1 (second leaky mode) were examined. Of the two modes the TM 1 mode was found to be the most suitable for sensing applications, exhibiting good signal stability, higher refractive index sensitivity and greater resistance to wavelength fluctuations. In the first experiment refractive index sensitivity of a multimode configuration was examined. The angular sensitivity was highest for the TM 4 leaky mode at 220.02°/RIU (refractive index units) and lowest for the TM 0 mode at 113.01°/RIU. In the second part of the investigation a PDMS waveguiding layer was fabricated supporting six leaky modes. The asymmetric core was used to detect to toluene vapor the highest order mode was seven times more sensitive to the gas than a planar evanescent waveguide. Finally the peak intensity of the TM 0 mode was used to measure pH. The change in the modal intensity of the ARROW sensor was used to characterize the expansion and contraction of a waveguide as function of pH with a resolution of 1.0 × 10 −3 pH units and an average response time of 6 min.