Abstract
We present a systematic analytic and numerical study of the detection limit of a refractive
index sensor employing a directional coupler architecture within a photonic crystal fiber (PCF).
The device is based on the coupling between the core mode and a copropagating mode of a satellite
waveguide formed by a single hole of the PCF infiltrated by a high-index analyte. Using coupled
mode theory as well as full simulations, we investigate the influence of changes in the
geometrical parameters of the PCF and the analyte's refractive index on sensor performance,
including sensitivity, resonance width, and detection limit. We show that regardless of the
details of the sensor's implementation, the smallest detectable refractive index change is
inversely proportional to the coupling length and the overlap integral of the satellite mode with
the analyte, so that best performance comes at the cost of long analyte infiltration lengths. This
is experimentally confirmed in our dip sensor configuration, where the lowest detection limit
achievable for realistic implementation is estimated to 7 × 10
$^{-8}$
refractive index units (RIU) based on realistic signal to noise ratios in a
commercially available PCF.
© 2013 IEEE
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