When comparing the sensor performances between different
configurations, it is not sufficient to compare only sensitivities (i.e.
wavelength shifts), without considering the wavelength measurement
accuracy. It is more convenient to refer to the figure of
merit (FoM) of the device. The FoM corresponds to the ratio between
the sensitivity and the linewidth of the resonance, taking
into account that it is easier to measure the exact location of a
narrow resonance than a broad one [7]. Hence, in terms of experimentally
demonstrated FoM, TFBGs outclass all other configurations
by more than one order of magnitude [2]. This results
from their sensitivity close to 500 nm/RIU and the narrowness of
their resonances.