Broad FSR and high sensitivity refractive index sensor using photonic crystal nanobeam cavity with composite lattice cells

We propose a broad FSR and high sensitivity refractive index (RI) sensor by using a composite lattice cells based photonic crystal nanobeam cavity (CLC-PCNC). Due to the special structure of the proposed CLC, cavities with free spectra ranges (FSRs) more than 90nm meanwhile with quality factor (Q) values above 5×104 are obtained. Besides, the optical overlap integrals of nearly 30% are achieved for both of the fundamental and the first order dielectric mode of the cavity, quantitatively demonstrating strong interaction between optical and matter, resulting in high sensitivities for RI sensing. Simulation results show that sensitivities of 390.9 nm/RIU and 413.6 nm/RIU, and detection limits of 7.6×10-6 RIU and 7.2×10-6 RIU, are achieved for the fundamental and the first order dielectric mode, respectively. Furthermore, ultra-compact size of only about 220 nm × 550 nm × 10 μm (height × width × length) of the cavity is realized. Therefore, due to the remarkable performances, the proposed sensor shows great potential in realizing applications such as high integration large-scale on-chip sensing and multi-function detection in the future.