A comprehensive electromagnetic mathematical model of an ultra-high Q-factor 1D-PhC ring resonator (1D-PhCRR) is proposed. The 1D-PhCRR results by the integration of a 1D-PhC in a ring cavity and its operation is based on the slow-light effect, allowing an improvement of the Q-factor of at least three orders of magnitude in comparison with the values obtained for a ring resonator without the grating. Accurate modelling and simulation of such ultra-high-Q ring resonator require very long simulation time and huge computing resource by using the conventional numerical methods, as the finite element method and finite difference time domain, because of the structure complexity. Therefore, to overcome these bottlenecks, an accurate mathematical model has been developed, able to take into account the waveguide curvature and dispersion, and the effect of the grating in the coupling region, reducing also the computation time. An ultra-high Q-factor (>10 9 ) 1D-PhCRR in Si 3 N 4 technology with a footprint of 16 mm 2 has been simulated in relatively short computer time, using the model described in the paper. This performance makes the 1D-PhCRR suitable for several applications, such as filters, ultra-sensitive biosensors and integrated photonic-gyroscopes, for which ultra-high Q-factor sensitive element ensures a high resolution.
In this work, a silicon metasurface designed to support electromagnetically induced transparency (EIT) based on quasi-bound states in the continuum (qBIC) is proposed and theoretically demonstrated in the near-infrared spectrum. The metasurface consists of a periodic array of square slot rings etched in a silicon layer. The interruption of the slot rings by a silicon bridge breaks the symmetry of the structure producing qBIC stemming from symmetry-protected states, as rigorously demonstrated by a group theory analysis. One of the qBIC is found to behave as a resonance-trapped mode in the perturbed metasurface, which obtains very high quality factor values at certain dimensions of the silicon bridge. Thanks to the interaction of the sharp qBIC resonances with a broadband bright background mode, sharp high-transmittance peaks are observed within a low-transmittance spectral window, thus producing a photonic analogue of EIT. Moreover, the resonator possesses a simple bulk geometry with channels that facilitate the use in biosensing. The sensitivity of the resonant qBIC on the refractive index of the surrounding material is calculated in the context of refractometric sensing. The sharp EIT-effect of the proposed metasurface, along with the associated strong energy confinement may find direct use in emerging applications based on strong light-matter interactions, such as non-linear devices, lasing, biological sensors, optical trapping, and optical communications.
TM-pass polarizers are pivotal components of photonic integrated circuits (PICs), especially those intended for biosensing applications. In the literature, several silicon TM-pass polarizers have been proposed, designed and experimentally demonstrated, but their insertion loss is not compatible with the current trend of silicon photonics aimed at exponentially increasing the component density within PICs. Herein, we propose and design a TM-pass polarizer whose insertion loss is carefully minimized to 0.05 dB at wavelength 1.55 µm by utilizing a combination of an asymmetric directional coupler and a mode evolution section. The adoption of appropriate technical solutions makes this record insertion loss value compatible with a high extinction ratio equal to 38 dB. With a device footprint of only 2.5 × 20 µm 2 , the design exhibits an insertion loss less than 1.7 dB and extinction ratio better than 30 dB over a large bandwidth of 200 nm. The design assumes the constraints of a typical silicon photonics open-access technological process and a standard 220 nm silicon-on-insulator (SOI) wafer. A very low sensitivity of the achieved performance to reasonable fabrication inaccuracies is demonstrated, with a worst-case insertion loss of only 0.32 dB at wavelength 1.55 µm.
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