Tunable microwave fiber-optic bandpass filters

A new photonic filter which can realize both high-resolution bandpass microwave response and which is also widely tunable is presented. This is based on the use of long chirped Bragg gratings and a section of active fiber, and tuning is obtained by changing the carrier wavelength. A fractional tuning range of 20% is demonstrated experimentally, and this can readily be extended. A model is presented to describe the frequency limitations of the filter, and design guidelines are given to overcome the grating dispersion limits. The new structure enables the realization of wide-band continuously tunable filters with fast tuning and high-Q.