High index contrast photonic platforms for on-chip Raman spectroscopy.

Ali Raza,Nicolas Le Thomas,James S Wilkinson,Jin Suntivich,Roel Baets,Chengyu Liu,Amy S K Tong,Stéphane Clemmen,Andre G Skirtach,Michiel De Goede,Pieter Wuytens,Sonia M Garcia-Blanco,Daniel J Blumenthal

doi:10.1364/oe.27.023067

Abstract

Nanophotonic waveguide enhanced Raman spectroscopy (NWERS) is a sensing technique that uses a highly confined waveguide mode to excite and collect the Raman scattered signal from molecules in close vicinity of the waveguide. The most important parameters defining the figure of merit of an NWERS sensor include its ability to collect the Raman signal from an analyte, i.e. "the Raman conversion efficiency" and the amount of "Raman background" generated from the guiding material. Here, we compare different photonic integrated circuit (PIC) platforms capable of on-chip Raman sensing in terms of the aforementioned parameters. Among the four photonic platforms under study, tantalum oxide and silicon nitride waveguides exhibit high signal collection efficiency and low Raman background. In contrast, the performance of titania and alumina waveguides suffers from a strong Raman background and a weak signal collection efficiency, respectively.

Highlights

High index contrast (HIC) waveguide structures allow a guided pump beam to interact efficiently with an analyte present in its vicinity
We present here the performance of four different photonic integration platforms (Al2O3, Si3N4, Ta2O5 and TiO2) as an on-chip Raman spectroscopy platform
The performance is compared in terms of the signal collection efficiency and the Raman background of the waveguide material

Summary

Introduction

High index contrast (HIC) waveguide structures allow a guided pump beam to interact efficiently with an analyte present in its vicinity. The analyte is excited using the waveguide mode and the scattered signal couples back to the same waveguide This waveguide based excitation and collection technique can be used for different sensing phenomena, e.g. on-chip fluorescence [1], spontaneous Raman [2], stimulated Raman [3] and surface enhanced Raman spectroscopy [4], whereby unlike confocal approaches, the signal scales with the waveguide length. An integrated photonic waveguide can, constitute the sensing part of a Raman spectroscopic system and may provide enough signal enhancement to relax the usually stringent requirement on the optical source and detectors of a Raman system. HIC is very important in this context since the overall efficiency of the conversion of the guided pump to the guided Stokes beam depends critically on this contrast [2]

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Conclusion