Table 1.
A comparison of the main coupling techniques, in terms of efficiency, bandwidth, alignment tolerance, cost and complexity, that are used for WERS devices.
Quoted coupling efficiency values correspond to those reported in the literature for WERS.
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.
|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.
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.
(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.
Raman spectra of toluene, benzyl alcohol and d7-benzyl alcohol.
Spectra shifted up for clarity.
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.
(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.