High sensitivity photonic crystal sensor based on transition between photonic bands

Abstract In this work, we performed a study of an interferometric high sensitivity photonic crystal (PhC) sensor applied to measure glucose concentration in human urine samples. The architecture of the photonic sensor numerically simulated is based on a Mach–Zehnder interferometer formed by a coupled waveguide-cavity system. The sensor operates using photonic mode transitions detected from the photonic band diagram analysis, driven by changes in the glucose concentration in the urine samples that affect the refractive index of the optical sampling cavity. The photonic mode transition causes a phase shift between the wave traveling in the reference arm of the interferometer and the propagating electromagnetic wave in the sensing cavity containing the probing sample. As a consequence, the transmittance at the output of the interferometer can be modulated, making it extremely sensitive to changes in the refractive index of the sensing cavity. Since the PhC sensor studied works under variations in transmittance, we proposed a sensitivity coefficient as a function of the change in transmittance per unit change in the refractive index. The sensitivity achieved by the photonic sensor presents a value of 7000%/RIU, which indicates a variation in transmittance of 70% for changes in the refractive index of 0.01. These results demonstrate the feasibility of using photonic transitions between modes as a sensing tool in integrated photonic devices.