Unique surface sensing property and enhanced sensitivity in microring resonator biosensors based on subwavelength grating waveguides.

Hai Yan,Huiping Tian,Lijun Huang,Ray T Chen,Xiaochuan Xu,Naimei Tang,Swapnajit Chakravarty

doi:10.1364/oe.24.029724

Abstract

In this paper, unique surface sensing property and enhanced sensitivity in microring resonator biosensors based on subwavelength grating (SWG) waveguides are studied and demonstrated. The SWG structure consists of periodic silicon pillars in the propagation direction with a subwavelength period. Effective sensing region in the SWG microring resonator includes not only the top and side of the waveguide, but also the space between the silicon pillars on the light propagation path. It leads to greatly increased sensitivity and a unique surface sensing property in contrast to common evanescent wave sensors: the surface sensitivity remains constantly high as the surface layer thickness grows. Microring resonator biosensors based on both SWG waveguides and conventional strip waveguides were compared side by side in surface sensing experiment and the enhanced surface sensing capability in SWG based microring resonator biosensors was demonstrated.

Highlights

Micro- and nano-scale photonic biosensors have become a fast growing research topic driven by the need of portable bio-detection systems with high sensitivity, high throughput, real-time and label-free detection [1,2,3]
Scanning electron microscope (SEM) images of the fabricated subwavelength grating (SWG) microring resonator are shown in Fig. 5(a) with the coupling region enlarged to show the trapezoidal pillars in the microring and the rectangular pillars in the bus waveguide
A transmission spectrum of the SWG microring is shown in Fig. 5(b), from which the free spectral range is measured to be

Summary

Introduction

Micro- and nano-scale photonic biosensors have become a fast growing research topic driven by the need of portable bio-detection systems with high sensitivity, high throughput, real-time and label-free detection [1,2,3]. This type of evanescent wave sensing mechanism faces limitation in surface sensing: the sensitivity drops inevitably with increasing thickness of the surface layer accumulated on the sensor surface In real applications, this layer includes necessary oxide and chemical layers generated by surface treatment, probe proteins, target proteins and any other reagents that are used to enhance the signal. This layer includes necessary oxide and chemical layers generated by surface treatment, probe proteins, target proteins and any other reagents that are used to enhance the signal These can amount to a total layer thickness ranging from several nanometers to a few tens of nanometers, within which the sensitivity of the evanescent wave could drop considerably before it reaches the final target to be detected [21,22,23,24,25]

Methods

Results

Conclusion