Determination of hexavalent chromium with a high-performance optical microring resonator

An optical microring resonator model that allows for the measurement of low concentrations of hexavalent chromium was numerically investigated with the finite element method. The optical microring resonator based on whispering gallery modes was optimized in terms of microring radius, microring width, and gap distance. Thus, the optimization of these geometric parameters has been illustrated. A free spectral range of 3.2 nm, full width at half maximum of 0.10 nm, quality factor of 5,485, and finesse of 31.66 make the high-performance device suitable for the measurement of hexavalent chromium. The reduction in optical intensity at the resonance wavelength of 542 nm strongly depends on the imaginary part of the refractive index. The excellent performance of the sensor clearly showed a linear trend of optical intensity with increasing concentration of hexavalent chromium.