Low-Cost and Highly Sensitive Liquid Refractive Index Sensor Based on Polymer Horizontal Slot Waveguide

Xiaoxia Ma,Jieyun Wu,Lingfang Wang,Kaixin Chen

doi:10.1007/s13320-019-0560-y

Abstract

We analyze and explore the potential of using a polymer horizontal slot waveguide as light-analyte interactive region to implement a low-cost and highly sensitive liquid refractive index sensor. Numerical analysis shows that the optimized polymer horizontal slot waveguide is able to realize high waveguide sensitivity. With the optimized horizontal slot waveguide, polymer liquid refractive index sensors based on Mach-Zehnder interferometer (MZI) and microring resonator (MRR) are then investigated numerically, and the results show that the MZI-based sensor can achieve high sensitivity of 17024nm/RIU and low limit of detection (LOD) of 1.76×10−6 RIU while the MRR-based sensor can achieve the sensitivity of 177nm/RIU and the LOD of 1.69×10−4 RIU with a very small footprint. Compared with the sensors employing conventional silicon or silicon nitride vertical slot waveguide, the sensors employing polymer horizontal slot waveguide exhibit comparable performances but simpler and lower fabrication costs.

Highlights

A novel structure called slot waveguide has attracted great interest due to its remarkable characteristics to guide and confine light in a nanometric low index material region
In view of the advantages above, optical sensing employing the horizontal slot waveguide as light-analyte interactive region has been explored in [13,14,15,16]. For these reported sensors based on the horizontal slot waveguides, all of them are explored with high refractive index materials such as silicon nitride [14] or silicon on insulator (SOI) [13, 15, 16] by using the costly method of chemical vapor deposition
With such a waveguide configuration, there is a discontinuity of the electric field along the y direction on the top and bottom interfaces of the slot, which results in the transvers magnetic (TM) mode that has much higher amplitude in the slot than that in the cores

Summary

Introduction

A novel structure called slot waveguide has attracted great interest due to its remarkable characteristics to guide and confine light in a nanometric low index material region. In view of the advantages above, optical sensing employing the horizontal slot waveguide as light-analyte interactive region has been explored in [13,14,15,16] For these reported sensors based on the horizontal slot waveguides, all of them are explored with high refractive index materials such as silicon nitride [14] or SOI [13, 15, 16] by using the costly method of chemical vapor deposition. Our designed MZI- and MRR-based liquid refractive index sensors with the optimized polymer horizontal slot waveguide exhibit comparable performances by virtue of their sensitivity of 17024 nm/RIU and 177 nm/RIU and the LOD of 1.76×10−6 RIU and 1.69×10−4 RIU, respectively, but simpler and lower fabrication costs in comparison with the sensors employing conventional silicon or silicon nitride vertical slot waveguide

Schematic of the polymer horizontal slot waveguide

Waveguide investigation

Sensor devices and theoretical results

MZI sensor

Microring resonant sensor

Conclusions