  A means to calculate the multimodal spectral response of Bragg gratings in
general non-circular multimode waveguides is proposed. To illustrate the power
of the technique, the spectra of two Bragg temperature sensors are numerically
calculated in which coupling between 100 modes considered. It is shown how the
Bragg wavelength in multimode Bragg grating waveguides is affected by the
number of modes and energy distribution among them. Good matching of the
simulated spectrum of a multimode Bragg grating on a planar inverted rib
waveguide to the measured spectrum is seen.
