Ln Slot Photonic Crystal Microcavity for Refractive Index Gas Sensing

We propose and experimentally demonstrate a series of L-n slot photonic crystal (PhC) microcavities, which operate as refractive index (RI) gas sensors. The cavities are simply composed of a silicon slab triangular photonic crystal with n holes replaced by a slot, which do not require sophisticated design or high fabrication resolution. With the increase in n, the quality factor of the cavity exponentially increases, which is explained by the envelope of electric field approaching a Gaussian profile. An L-9 slot PhC microcavity with a quality factor exceeding 30 000, sensitivity of 421 nm per RI unit (RIU), and detection limit down to 1 x 10(-5) RIU was experimentally demonstrated. The performance of the device is comparable with other fine-tuned PhC microcavity structures. Due to its simple structure and high fabrication tolerance, it could have wide applications in optical sensors.