Analysis and optimisation of the apodisation sharpness for linearly chirped dispersion compensating gratings

The impact of the apodisation sharpness on the spectral response of linearly chirped dispersion compensating gratings is evaluated. It will be demonstrated that the behaviour of the mean dispersion, group delay ripple, reflection bandwidth and insertion losses shows stronger dependence on the apodisation sharpness than on the type of apodisation profile. A detailed analysis is carried out with the view to compare the spectral characteristics of linearly chirped gratings applying different apodisation profiles with increasing sharpness to compensate the dispersion of 100 km of standard single-mode fibre. It will be shown that an apodisation factor of ~0.8 results in minimum group delay ripple impact, minimum deviation from the required dispersion value and maximum reflection bandwidth ensuring, at the same time, minor increase of grating length and insertion losses compared with the non-apodised case. This value can be considered as the optimum apodisation sharpness for the profiles under study, allowing faster modelling and more effective fabrication steps for reflective dispersion compensating gratings.