基于集成光波导沟槽耦合器的超紧凑折射率传感器

Ultracompact Refractive Index Sensor Based on Integrated Optical Waveguide Trench Coupler

提出一种基于集成光波导沟槽耦合器的超紧凑折射率(RI)传感器。该结构包括入射波导、反射波导及透射波导,亚微米宽的沟槽位于三条波导的交汇处。入射波导中的导波光在沟槽侧壁发生受抑全内反射,使得一部分光经消逝场耦合进入透射波导,另一部分光被反射进入反射波导。因为消逝场耦合效率依赖于沟槽填充物的折射率,因此透射光强度和反射光强度都会随着沟槽填充物折射率的变化而改变,这意味着这种集成光波导沟槽耦合结构可作为微纳传感器用于实时探测液体折射率或溶液浓度。以氮化铝脊型波导为例,采用时域有限差分(FDTD)法对这种新型折射率传感器性能进行理论分析,经过结构优化,其折射率灵敏度可达207.05%/RIU。

This paper presents an ultra-compact refractive index(RI) sensor based on an integrated optical waveguide trench coupler fabricated on a chip. The coupler consists of an input waveguide, a reflective waveguide, and a transmission waveguide as well as a submicron-wide trench that is located at the intersection of the three waveguides. Light guided in the input waveguide undergoes frustrated total internal reflection on the sidewall of the trench, resulting in the evanescent coupling of light into the transmission waveguide and thus attenuation of light in the reflective waveguide. Because the evanescent field coupling efficiency is dependent on RI of the medium filling in the trench, both the transmitted and reflected light intensities are very sensitive to changes in RI of the liquid in the trench. This means that the integrated optical trench coupler mentioned above can be used as a micro-nano sensor for real-time detection of liquid RI or solution concentration. Performance of this novel optical sensor was theoretically analyzed based on the finite difference time domain(FDTD) method with use of the aluminum nitride ridge waveguide as the simulation model. After optimization of the sensor’s geometry, its refractive index sensitivity can reach 207.05 %/RIU.