Waveguide-enhanced Raman spectroscopy (WERS) efficiently collects Stokes-shifted scattering from target molecules in the evanescent field surrounding nanophotonic waveguides. By using a sorbent material as a top cladding, vapor phase analytes can be detected and identified at ambient densities as low as a few parts-per-billion. Previous demonstrations of vapor-phase WERS have used free-space optical components, such as microscope objectives and bulk Raman filters, to couple and filter light to and from the sorbent-clad waveguide. In this work we demonstrate a complete photonic integrated circuit (PIC) assembly that is packaged and fiber-coupled enabling us to measure WERS from trace vapor concentrations. The PIC comprises low-loss edge couplers from polarization maintaining single-mode optical fibers, sensing trenches with a sorbent top-cladding, and lattice filters for separation of the Stokes signal from the laser. The PICs are fabricated at AIM Photonics using the Silicon Nitride Passive PIC process with the TLX-VIS component library. Then, they are packaged into assemblies with permanent fiber-attach using fiber arrays. The sorbent is deposited in a thin, uniform layer in the sensing trench using one of two deposition techniques: nano-plotting and drip-coating. A laser wavelength of 785 nm enables the use of a compact spectrometer with a thermoelectrically-cooled silicon detector. Spectra are obtained with exposure times of a few seconds and show parts-per-billion detection limits for select vapors. This work successfully demonstrates the use of a compact Raman spectrometer integrated with a fully assembled PIC via optical fibers for the detection of low-density vapor-phase analytes.
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