We present a novel design for a high quality (Q)-factor, nonlinear planar photonic crystal (PhC) nanocavity incorporating a silicon/polymer material that is well suited to ultrafast all-optical switching. The hybrid nanocavity is created in the centre of a triangular lattice planar PhC made from silicon using the three-missing-holes point defect (L3). It is formed by infiltrating the air hole array of the PhC with polymer and by depositing a polymer layer on top of a PhC membrane. To determine the hybrid nonlinear cavity performance, we analyze the dependence of the refractive index (RI) of the top cladding on the Q-factor and resonant wavelength. The results show that, when the top cladding RI is increased from 1.5 to 1.6, corresponding to that of polymer materials, the Q-factor decreases markedly (Q < 10 3 ). Optimization of the hybrid nonlinear silicon/polymer cavity design by modulating the structure parameters yields a high Qfactor of 54 000 with a small modal volume across the telecommunications band. In addition, the field distribution of the resonant mode indicates that the radiation loss is sufficiently small. Due to the overwhelmingly large Kerr nonlinearity of polymer over silicon, this structure configuration design shows considerable promise as regards the realization of ultrafast response speed in small-sized all-optical switching integrated devices.
The optical properties of point-defect nanocavities implemented on elliptical-hole planar photonic crystal (EPhC) have been investigated for mid-infrared liquid sensing application. The EPhC nanocavities are composed of silicon planar photonic crystals with a triangular lattice of elliptical air holes, which do not require sophisticated design and high fabrication resolution. The numerical results show that the quality factor and the mode volume of the EPhC nanocavities increase exponentially with an increase in the ellipticity of the air holes. The Q factor is increased by a factor as large as 38 and 26 for H1 and L3 EPhC nanocavities, respectively, with a small mode volume by finely optimizing the EPhC nanocavities. Furthermore, the transmission spectrum of the optimized EPhC nanocavities shows that the variation in the refractive index that is used in the coating of the EPhC nanocavities induces a shift in the resonant wavelength of the nanocavity modes, thus allowing the precision measurement of liquid. In addition, a point-defect EPhC nanocavity with a sensitivity of 285 nm/refractive index unit (RIU) and a detection limit of 10−4 RIU are demonstrated. Therefore, these results suggest that the designed EPhC nanocavities are considered as a promising platform for mid-infrared liquid sensor devices with small detection volumes.
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