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. 2023 Aug 10;18(8):e0284058.
doi: 10.1371/journal.pone.0284058. eCollection 2023.

Grating-incoupled waveguide-enhanced Raman sensor

Mohamed A Ettabib  1 , Bethany M Bowden  2 , Zhen Liu  1 , Almudena Marti  2 , Glenn M Churchill  1 , James C Gates  1 , Michalis N Zervas  1 , Philip N Bartlett  2 , James S Wilkinson  1
Affiliations

Grating-incoupled waveguide-enhanced Raman sensor

Mohamed A Ettabib et al. PLoS One. .

Abstract

We report a waveguide-enhanced Raman spectroscopy (WERS) platform with alignment-tolerant under-chip grating input coupling. The demonstration is based on a 100-nm thick planar (slab) tantalum pentoxide (Ta2O5) waveguide and the use of benzyl alcohol (BnOH) and its deuterated form (d7- BnOH) as reference analytes. The use of grating couplers simplifies the WERS system by providing improved translational alignment tolerance, important for disposable chips, as well as contributing to improved Raman conversion efficiency. The use of non-volatile, non-toxic BnOH and d7-BnOH as chemical analytes results in easily observable shifts in the Raman vibration lines between the two forms, making them good candidates for calibrating Raman systems. The design and fabrication of the waveguide and grating couplers are described, and a discussion of further potential improvements in performance is presented.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. (a) A schematic diagram illustrating the use of a grating coupler to launch light into a slab waveguide (b) A cross-sectional schematic diagram of the simulation layout used to model the grating coupler’s performance.
p denotes the period (or pitch) of the grating, e the etch depth, and h the initial film thickness.
Fig 2
Fig 2. |E|2, grating coupling efficiency and FOM as a function of the film thickness for the fundamental TE ((a) and (b)) and TM mode ((c) and (d)).
Fig 3
Fig 3. The grating coupler’s normalized coupling efficiency as a function of translational misalignment.
The squares represent the experimentally measured data, while the solid line is a polynomial fit.
Fig 4
Fig 4. (a) Scanning electron microscopy (SEM) image of the top of the Ta2O5 waveguide with the grating coupler, (b) SEM cross-section of the etched grating.
Fig 5
Fig 5. Raman spectra of toluene, benzyl alcohol and d7-benzyl alcohol.
Spectra shifted up for clarity.
Fig 6
Fig 6. The experimental apparatus used for the WERS demonstration.
Inset: illustrative photo of a 633 nm pump beam being reflected by the mirror towards the bottom of the chip and the subsequent coupling of light into the film (as indicated by the strong streak of light) by the grating coupler.
Fig 7
Fig 7
(a) The processed spectra of BnOH and d7- BnOH after background subtraction, denoising and deconvolution. Inset: Zoomed-in spectra between 900 cm-1 & 1100 cm-1. (b) Comparison of the WERS spectra with those measured using a commercial Raman microscope for (b) BnOH and (c) d7- BnOH. The Raman microscope spectra were scaled and shifted up for clarity.
See this image and copyright information in PMC

References

    1. Ettabib M. A., Marti A., Liu Z., Bowden B. M., Zervas M. N., Bartlett P. N., et al.. “Waveguide-enhanced Raman spectroscopy for biosensing: a review,” ACS Sens. 6, 2025–2045 (2021). doi: 10.1021/acssensors.1c00366 - DOI - PubMed
    1. Dhakal A., Peyskens F., Clemmen S., Raza A., Wuytens P., Zhao H., et al.. “Single mode waveguide platform for spontaneous and surface-enhanced on-chip Raman spectroscopy,” Interface Focus 6(4), 20160015 (2016). doi: 10.1098/rsfs.2016.0015 - DOI - PMC - PubMed
    1. Evans C. C., Liu C., and Suntivich J., “TiO2 nanophotonic sensors for efficient integrated evanescent Raman spectroscopy,” ACS Photon. 3, 1662–1669 (2016).
    1. Michon J., Kita D., and Hu J., “Sensitivity comparison of free-space and waveguide Raman for bulk sensing,” J. Opt. Soc. Am. B 37, 2012–2020 (2020).
    1. Laing S., Gracie K., and Faulds Karen, “Multiplex in vitro detection using SERS,” Chem. Soc. Rev. 45, 1901–1918 (2016). doi: 10.1039/c5cs00644a - DOI - PubMed

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