In-situ Microplastic Detection Sensor based on Cascaded Microring Resonators

Microplastics in the oceans is a growing concern in the recent years as it directly affects the marine life and indirectly affects the health of humans as well. Identifying these microplastics is a laborious process and often involves the bulky equipment for analysis. In this work, we proposed an in-situ microplastics detection sensor by employing the Ge on Si rib waveguide microring resonators as a core sensing element which are arranged in cascaded manner to achieve the Vernier effect thus useful for high sensitivity analysis in near and mid IR regions where the absorption spectra of most of the plastics falls under. As a Mid IR source, Optical Network Analyzer (ONA) has been used which generates source light (in Mid IR) and simulated in Lumerical Interconnect software. Finally, mode profiles, effective indices of waveguides and transmission spectrum, Free Spectral range (FSR) of PIC circuit has been calculated and presented. The simulations have been performed in Lumerical Mode for modal analysis, Lumerical FDTD for compact model generation and S-parameters extraction and Lumerical Interconnect for circuit level simulation.

I. Introduction

Microplastics (MPs), defined as plastic particles ranging from 1 mm to 5 mm in size, are now ubiquitously present in aquatic and terrestrial environments [1]. These types of Microplastics are usually created intentionally for use or result from the breakdown of larger plastics. Microplastics size and shape distribution may be influenced by activities such as weathering, photo-bleaching, chemical, and mechanical processes. Due to the different shapes, size distribution and other properties such as transparency, translucency, and surface roughness, the detection of these smaller plastics becomes challenging in practical field conditions [2].Towards this end, chemistry provides a set of identification tools capable of tackling the MP issue in its many facets [3] such as vibrational spectroscopy, densitometry, differential scanning calorimetry (DSC), gas chromatography-mass spectrometry (GC-MS) based methods and the recently proposed technique hyper-spectral imaging [4]. This work focuses on vibrational spectroscopy which is rapidly gaining ground in the analysis of small MPs. This is akin to a fingerprint of chemical structure allowing identification of the components present in the sample [5]. Ring resonators play an important role in the success of silicon photonics, because silicon enables ring resonators of an unprecedented small size [6].