Asymmetric Concentric Microring Resonator Label-Free Biosensors

Pedro Chamorro-Posada

doi:10.3390/photonics9010027

Abstract

A study of label-free silicon nitride asymmetric double-microring resonators is presented. The use of highly accurate 3D vector modal techniques permits an extensive exploration of the parameter space defining the architecture of the proposed device in the search for optimal geometries and reaching configurations not addressed in previous studies that had been limited to symmetrical configurations. Asymmetry, on the other hand, permits to access resonances that exploit the radiation-quenching properties of the structure in an optimal way. The analysis presented also includes the effect of absorption in the sensor aqueous cladding that is generally omitted. The results of the numerical survey indicate that the optimized geometries bring about a substantive performance improvement at small microring radii that are impractical for more conventional single-ring geometries due to the high radiation losses. Therefore, lower footprint devices, and a larger scale of integration, can be attained with the proposed structure.

Highlights

We present a thorough analysis of the properties of optical biosensors built using asymmetric concentric double-ring structures
These results suggest that the combination of a less extreme aspect ratio of the rectangular waveguides combined with an asymmetric concentric microring geometry may result in the TM mode fields being a usable alternative for the implementation of biosensors with improved sensitivity
A comprehensive numerical study of silicon nitride optical biosensors based on asymmetric double-ring microresonators was presented

Summary

Introduction

Whereas the coupled-resonator model is necessary for describing the operation of nonconcentric rings [16,17], the modal method used in [8,9,10,11] provides a more direct approach in concentric arrangements This technique provides a very large degree of accuracy, necessary in the design of devices to be incorporated in fabricated photonic chips [9,11], at a low computational cost. Biosensors based on pulley-type resonators have been studied in [18] These structures permit the reduction of radiation losses by wrapping the ring with the access waveguide.

Fundamentals

Single-Ring Si3 N4 Resonators with an Aqueous Cover

Asymmetric Concentric Ring Resonators

TE-Polarized Field

TM-Polarized Field

Conclusions