In this paper, we propose a defective photonic crystal microring resonator (DPhCMRR) by introducing a point defect into a conventional photonic crystal microring resonator (PhCMRR). The defective resonant wavelength within the photonic mode gap and the location of the defect mode distribution can be readily controlled. Unlike conventional PhCMRR, where the free spectral range (FSR) is limited by the dispersive band structure, our DPhCMRR can take advantage of the tunability of the defect mode within the photonic mode gap, leading to a significant increase of the measurement range. Moreover, the bulk refractive index sensitivity can reach 200 nm/RIU (refractive index unit) and the local refractive index sensitivity is about 5 to 10 times larger than that of the conventional PhCMRR. For sensing applications, our DPhCMRR can possess high sensitivity and wide measurement range simultaneously. As proof of principle, it is demonstrated that our proposed DPhCMRR can perform as a sensitive virus biosensor, which can detect a single virus and a concentration of viruses quantitatively. Therefore, our DPhCMRRs can provide a new platform for achieving high sensitivity and wide measurement range biosensing.
A two-parameter sensor that can detect the variation of temperature and refractive index is realized in a multilayer dielectric structure obeying parity-time (PT) symmetry. The sensor can operate near exceptional points (EPs), which have been shown to provide dramatic variations of their eigenvalues in response to small parameter changes. The optical sensing behavior is theoretically investigated based on the transfer matrix method. The results show that the sensor can work within the surrounding temperature (tp) ranging from 0 to 30℃, and the refractive index (ng) of incident medium ranging from 1.0 to 1.4. The detectable variation △ng of the sensor can reach 0.02. The sensitivity of ng and tp can reach 372496.53 RIU-1 and 249.18℃-1, respectively. Our structures show great promise in temperature monitoring in cold environment and identification of chemical gases or liquids.
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