Short-wavelength, transmission-loss suppression in Fibre Bragg Gratings

Abstract

Fibre Bragg Gratings (FBG’s) are known to suffer from short-wavelength, transmission losses due to resonant coupling into backward-propagating cladding modes [1,2]. Figure 1 shows a typical transmission spectrum of a 10cm standard FBG. The cladding mode losses increase with grating reflectivity and could eventually impose severe limitations in the use of FBG’s. The problem can be quite acute in the case that FBG wavelength-multiplexing is required. So far, several attempts have been made to eliminate the short-wavelength, transmission losses and improve grating performance [2-5]. In all cases, the resonant coupling of the forward-propagating core mode to the backward-propagating cladding modes is minimised by reducing the coupling strength.