A novel silicon-on-insulator microring biosensor based on Young＇s twoslit interference has been demonstrated. The transducer signal from electric field intensity distribution on the interference screen is given by using the transfer matrix method（TMM） and two-slit interference principle.The result shows that the structure we propose is advantageous for sensing as the interference pattern is very sensitive to the ambient refractive index around the microring.A small perturbation in refractive index around the microring△n_c will result in a notable shift of destructive interference points（DIPs） on the interference screen.By detecting the shift of the DIPs,the ambient refractive index change can be obtained.
We have designed an air-bridged PhC microcavity with high sensitivity and a high quality factor.The structure parameters of the microcavity are optimized by three-dimensional finite-difference time-domain method. We compare the performance of a silicon-on-insulator PhC microcavity and an air-bridged PhC microcavity,and analyze the effect of the thickness of the slab and the radius of the defect hole on the performance of the air-bridged PhC microcavity.For a thinner slab and a larger defect hole,the sensitivity is higher while the quality factor is lower.For the air-bridged photonic crystal slab,the sensitivity can reach 320-nm/RIU（refractive index unit） while the quality factor keeps a relatively high value of 120 by selecting the proper slab thickness and the defect hole radius,respectively,when the refractive index is 1.33.This is meaningful for low-detection-limit biosensing.
The effect of shape, height, and interparticle spacing of Au nanoparticles （NPs） on the sensing performance of Au NP array is systematically investigated. Lengthening the major axis of elliptical NPs with the minor axis kept constant will cause the redshift of the local surface plasmon （LSP） resonance mode, enhance the sensitivity, and widen the resonance peaks. Larger height corresponds to smaller LSP resonance wavelength and narrower resonance peak. With each NP size unchanged, larger interparticle spacing corresponds to larger resonance wavelength and smaller full-width at half-maximum （FWHM）. Moreover, duty cycle is important for sensitivity, which is largest when the duty cycle is 0.4.
Ultraviolet photo-lithography is employed to introduce two-dimensional （2D） photonic crystal （PC） structure on the top surface of GaN-based light emitting diode （LED）. PC patterns are transferred to 460-rimthick transparent indium tin oxide （ITO） electrode by inductively coupled plasma （ICP） etching. Light intensity of PC-LED can be enhanced by 38% comparing with the one without PC structure. Rigorous coupled wave analysis method is performed to calculate the light transmission spectrum of PC slab. Simulation results indicate that total internal reflect angle which modulated by PC structure has been increased by 7°, which means that the light extraction efficiency is enhanced outstandingly.
