Integrated Width-Modulated SiN Long Period Grating Designed for Refractometric Applications
Résumé
A novel integrated photonic structure based on Long
Period Waveguide Gratings (LPWGs) relying on channel-width
modulation is proposed and tested for refractometric applica-
tions. These LPWGs have been fabricated through a Silicon
Nitride process and experimentally characterized in terms of both
surface and bulk sensitivities. Surface sensing configuration is
first achieved by propagating one of the coupling optical modes
into an epoxy-based negative photoresist SU8 cladding region
that is in contact with the analyte via its outer surface. We
subsequently show that the proposed LPWGs cladding layer
can be advantageously replaced by a gas-porous polymeric bulk
layer such as Styrene-co-AcryloNitrile (SAN) as the cladding
region to be directly sensed to anticipate future gas sensing
applications. Here, bulk sensing is optimized by increasing the
analyte’s influence on the modal propagation constants as it is
demonstrated to be currently the most promising solution to
effectively enhance the figure of merit of long period gratings
of given lengths. Using varying water-glycerol mixtures, the
surface sensitivity of these LPWGs has been measured at up to
240 nm per RI unit (RIU) that is in agreement with simulation.
In addition, the bulk sensitivity has been indirectly estimated
to be ∼1900 nm/RIU via temperature measurements, which
corroborates simulation results, thereby paving the way towards
gas sensing applications.
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