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Highly sensitive optical sensor based on two cascaded micro-ring resonators with an LED light source

A highly-sensitive and low-cost optical sensor that requires only power measurement is proposed and investigated. It consists of two cascaded micro-ring resonators with slightly different optical path lengths, used in conjunction with an LED light source. The transmission spectrum of the sensor has a series of peaks with a sinusoidal-like envelope function. The variation of the refractive index of the analyte sample results in an amplified shift in the transmission envelope function, and consequently a change in the transmitted LED power. It is shown that a refractive index variation in the order of 7.0×10-7 can be detected without any spectral measurement. Preliminary experimental results using a broadband light source are presented.