In the quest for a more compact and cheaper Raman sensor, photonic integration
and plasmonic enhancement are central. Nanoplasmonic slot waveguides exhibit the benefits
of SERS substrates while being compatible with photonic integration and mass-scale (CMOS)
fabrication. A difficulty in pursuing further integration of the Raman sensor with lasers, spectral
filters, spectrometers and interconnecting waveguides lies in the presence of a photon background
generated by the excitation laser field in any dielectric waveguide constituting those elements.
Here, we show this problem can be mitigated by using a multi-mode interferometer and a
nanoplasmonic slot waveguide operated in back-reflection to greatly suppress the excitation field
behind the sensor while inducing very little photon background.
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