Ultracompact On-Chip Multiplexed Sensor Array Based on Dense Integration of Flexible 1-D Photonic Crystal Nanobeam Cavity With Large Free Spectral Range and High Q-Factor

A method for the dense integration of one-dimensional (1-D) photonic crystal nanobeam cavity (PCNC) based integrated sensor array (1-D-PCNC-ISA) is proposed. The 1-D-PCNC-ISA consists of multiple parallel-connected sensing channels with airgap separations. On each channel, only a single flexible 1-D-PCNC sensor with large free spectral range (FSR) and high Q-factor is contained. With proper engineering of the FSR, multiple ultracompact high-sensitivity 1-D-PCNC sensors can be integrated into microarrays without resonance overlap, and be interrogated simultaneously between a single input/output ports. Using 3-D finite-difference-time-domain (3-D-FDTD) method, the performance of the device is investigated theoretically in the whole paper. With optimization design, a large FSR as wide as 197 nm and high Q-factor similar to 2 x 105 can be achieved. Moreover, the refractive index sensitivities of a 5-channel 1-D-PCNC-ISA as high as 170.6, 152.7, 138.5, 128.1, and 120.5 nm/RIU are obtained. Particularly, the footprint of a 5-channel 1-D-PCNC-ISA is similar to 7 mu m x 65 mu m (width by length), which is decreased by three orders of magnitude compared to the sensor arrays based on 2-D-PC cavity platforms. To the best of our knowledge, this is for the first time that a 1-D-PCNC based multichannel parallel-connected sensor array has been displayed with channel spacing as small as 0.195 mu m, extinction ratio > 20 dB and Q-factor > 105, respectively, without using particular materials or complexities in fabrication. Both the specific result and the general idea are promising in future ultracompact lab-on-a-chip applications and nanophotonic integrations.