Investigation of nanophotonic lithium niobate waveguides for on-chip evanescent wave sensing

Kavli Affiliate: Scott K. Cushing

| First 5 Authors: Nathan A. Harper, Emily Y. Hwang, Philip A. Kocheril, Scott K. Cushing,

| Summary:

Thin-film lithium niobate is a promising photonic platform that could allow
for light generation, manipulation, and sample interaction all within the same
compact device. Integrated sample interaction geometries for on-chip sensors
have not yet been well explored in lithium niobate. We use a model thin-film
lithium niobate rib waveguide excited with a 406 nm laser diode to spatially
resolve the scattering and fluorescence distributions from a 60 nm dye-doped
polymer film. We determine that both the quasi-transverse-electric (TE) and
quasi-transverse-magnetic (TM) modes have propagation losses dominated by
scatter, and that the absorption due to the sample only accounts for
approximately 3% of the experiment for both modes. Although the TM mode has
better overlap with the sample, the even stronger propagation loss due to
scattering in the TM mode (32.5 $pm$ 0.3 dB/cm) compared to the TE mode (23.0
$pm$ 0.2 dB/cm) reduces how many molecules are excited with a given input
power, thus the TE mode could be more appropriate for sensing. Our findings
have important implications in compatibility with other integrated components
within a practical lithium niobate device and serve to guide future studies
into sample integration towards completely on-chip lithium niobate-based

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