Study On Silicon-based Photonic Crystal Nanobeam Cavity And Its Sensing Applications

Phtonic crystal(PhC)nanobeam cavity is a quasi-periodic structure formed by introducing defects into one-dimensional PhCs.Its ultrahigh quality factor(Q),extremely low mode volume(V),high-light-matter interaction and convenience in realization give it outstanding advantages in optical sensing applications.In recent years,silicon has become one of the most promising materials for low-cost miniaturization and high-density integrated photonics due to its excellent material properties and compatibility with complementary metal oxide semiconductor(CMOS)processing technologies.In our work,we mainly studied the applications of silicon based PhC nanobeam cavity in near infrared band optical refractive index sensing and optical force manipulation.Firstly,we present the design,fabrication,and characterization of a suspended slotted photonic crystal(SSPhC)cavity sensor based on the silicon-on-insulator platform.The sensitivity can be dramatically enhanced by the optimized SSPhC cavity as most of the light energy can be distributed in the low index region(?57%).By measuring the spectrum response of the cavity sensor immersed in NaCl solutions with different mass concentrations,an ultra-high sensitivity around 656 nm/RIU has been experimentally demonstrated.Furthermore,the total size of the sensing region is only 15.6 ?m×0.64 ?m,making the high-sensitivity sensor attractive for the realization of large-scale multi-channel on-chip sensors.Furthermore,a novel double-row subwavelength grating(S WG)waveguide sensor is designed,which can confine most of the light field in the low refractive index region due to the slot effect.The calculated sensitivity is around 560 nm/RIU,which is about 100 nm/RIU higher than the conventional S WG waveguide sensors.In addition,we show optical trapping of nanoscale single nanoparticles by using an ultrahigh Q/V bow-tie shaped PhC nanobeam cavity based on the Maxwell stress tensor model of the optical force and the 3D finite element analysis.For the trapping of a single polystyrene(PS)nanoparticle with the radius as small as 3 nm,a maximum trapping force of 1.2×105 pN/mW is theoretically obtained,which is at least one order of magnitude higher than the previous results.Furthermore,the calculated sensitivity for the cavity is around 350 nm/RIU,which provides a valid solution for monitoring the trapping process of the nanoparticles with ultra-small size.Such structure with characteristics of extreme light confinement and high trapping efficiency will be conducive to the development of multifunctional on-chip trapping devices.