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, Tze King Lam, Scott K. Cushing

| Summary:

Thin-film lithium niobate is a promising photonic platform for on-chip
optical sensing because both nonlinear and linear components can be fabricated
within one integrated device. To date, waveguided sample interactions for
thin-film lithium niobate are not well explored. Compared to other integrated
platforms, lithium niobate’s high refractive index, birefringence, and angled
sidewalls present unique design challenges for evanescent wave sensing. Here,
we compare the performance of the quasi-transverse-electric (TE) and the
quasi-transverse-magnetic (TM) mode for sensing on a thin-film lithium niobate
rib waveguide with a 5 mM dye-doped polymer cladding pumped at 406 nm. We
determine that both modes have propagation losses dominated by scatter, and
that the absorption due to the sample only accounts for 3% of the measured
losses for both modes. The TM mode has better overlap with the sample than the
TE mode, but the TM mode also has a stronger propagation loss due to sidewall
and sample induced scattering (32.5 $pm$ 0.3 dB/cm) compared to the TE mode
(23.0 $pm$ 0.2 dB/cm). The TE mode is, therefore, more appropriate for
sensing. Our findings have important implications for on-chip lithium
niobate-based sensor designs.

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