This work presents a design method for an Optical Microring Resonator (OMR) dedicated to specific heavy metal species sensing. A Top-Down design approach is used to create an OMR specifically designed for hexavalent chromium sensing, and suitable to a final Lab on Chip integration. Its operating principle is based on optical absorption measurement. This spectral absorption is induced by the colorimetric metallic complexation of hexavalent chromium with 1,5 diphenylcarbazide (DPC). The light enhancement at resonance wavelengths in an OMR allows highly sensitive measurements of the fluid optical absorbance by enhancing the effective path length. Chromate ions react with DPC at visible range. Singular red–violet complex is formed and induce a significant change of light intensity in the transmission spectrum. The intrinsic maximum absorption of metallic complex around 545 nm makes the polymer ring resonator parameters changing namely its effective index and attenuation value at resonance. The design considerations of the OMR have been analyzed to optimize critical parameters regarding the polymer ring resonator geometry. Simulations results have been investigated which lead to the geometry of a prototype device.