A light transmitting device comprising or incorporating a broadband Bragg grating that is formed in the direction of light propagation with grating regions of alternatingly high and low refractive index. The grating regions are formed with periodicity P and are structured as to amplitude, periodicity and/or phase in a manner which varies periodically with a modulation period L>P. Also, either one or the other or both of the grating period P and the modulation period L is or are chirped over substantially the full extent of the grating. The grating exhibits a spectral response in which broad rcflection peaks appear at each side of a reflection peak centred on the Bragg wavelength and fall under an envelope determined by the Fourier transform of the periodic modulation function.