Analysis of Wavelength and Intensity Interrogation Methods in Cascaded Double-Ring Sensors

Optical waveguide sensors based on cascaded double-ring resonators are analyzed theoretically and experimentally, for both wavelength interrogation and intensity interrogation methods. It is shown that for the wavelength interrogation, the sensitivity can be increased by over three orders of magnitude by combining the intensity ratio detection of two central peaks, compared with the simple digital operation mode of the central peak wavelength shift detection of the transmission spectrum. While the detection limit of the wavelength interrogation method is several times smaller than that of intensity interrogation method, the latter has advantages of simplicity and low cost which can outweigh the sensitivity reduction for many practical applications. Experimental results showed good agreements with the theoretical analysis.