Power budget analysis for waveguide-enhanced Raman spectroscopy

Abstract

Waveguide-enhanced Raman spectroscopy (WERS) is emerging as an attractive alternative to plasmonic SERS approaches asit can provide more reproducible quantitative spectra on a robustchip without the need for nanostructured plasmonic materials. Realising portable WERS Raman systems with high sensitivity using low-cost laser diodes and compact spectrometers requires a detailed analysis of the power budget from laser to spectrometer chip. In this paper we describe theoretical optimisation of planar waveguidesfor maximum Raman excitation efficiency, demonstrate WERS for toluene on a silicon process compatible high index contrast tantalum pentoxidewaveguide, measure the absolute conversion efficiency from pump power to received power in an individual Raman line, and compare this with a power budget analysis of the complete system including collection with an optical fibre and interfacing to a compact spectrometer.Optimised 110nm thick Ta2O5waveguides on silica substrates excited at a wavelength of 637nm are shown experimentally to yield overallsystem power conversion efficiency of ~0.5×10-12from the pump power in the waveguide to the collected Raman power in the 1002 cm-1Raman line of toluene, in comparison with a calculated efficiency of 3.9×10-12.Collection efficiency is dictated by the numerical and physical apertures of the spectral detection system but may be improved by further engineering the spatial and angular Raman scattering distributions.

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Identifiers

ORCID for Michael Zervas: orcid.org/0000-0002-0651-4059

ORCID for Philip Bartlett: orcid.org/0000-0002-7300-6900

ORCID for James Wilkinson: orcid.org/0000-0003-4712-1697

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