Higher Q factor and higher extinction ratio with lower detection limit photonic crystal-parallel-integrated sensor array for on-chip optical multiplexing sensing.

We introduce an alternative method to establish a nanoscale sensor array based on a photonic crystal (PhC) slab, which is referred to as a 1×4 monolithic PhC parallel-integrated sensor array (PhC-PISA). To realize this function, four lattice-shifted resonant cavities are butt-coupled to four output waveguide branches, respectively. By shifting the first to the two closest neighboring holes around the defect, a high Q factor over 1.5×10 has been obtained. Owing to the slightly different cavity spacing, each PhC resonator shows an independent resonant peak shift as the refractive index changes surrounding the resonant cavity. The specific single peak with a well-defined extinction ratio exceeds 25 dB. By applying the finite-difference time-domain (FDTD) method, we demonstrate that the sensitivities of each sensor in PhC-PISA S=60.500  nm/RIU, S=59.623  nm/RIU, S=62.500  nm/RIU, and S=51.142  nm/RIU (refractive index unit) are achieved, respectively. In addition, the negligible crosstalk and detection limit as small as 1×10 have been observed. The proposed sensor array as a desirable platform has great potential to realize optical multiplexing sensing and high-density monolithic integration.