  Surface Enhanced Raman Spectroscopy (SERS) is a well-established technique
for enhancing Raman signals. Recently photonic integrated circuits have been
used, as an alternative to microscopy based excitation and collection, to probe
SERS signals from external metallic nanoparticles. However, in order to develop
quantitative on-chip SERS sensors, integration of dedicated nanoplasmonic
antennas and waveguides is desirable. Here we bridge this gap by demonstrating
for the first time the generation of SERS signals from integrated bowtie
nanoantennas, excited and collected by a single mode waveguide, and rigorously
quantify the enhancement process. The guided Raman power generated by a
4-Nitrothiophenol coated bowtie antenna shows an 8 x 10^6 enhancement compared
to the free-space Raman scattering. An excellent correspondence is obtained
between the theoretically predicted and observed absolute Raman power. This
work paves the way towards fully integrated lab-on-a-chip systems where the
single mode SERS-probe can be combined with other photonic, fluidic or
biological functionalities.
