Design and realization of multiple quarter-wave phase-shifts UV-written bandpass filters in optical fibers

Ultraviolet (UV)-written optical fiber bandpass filters based on multiple quarter-wave phase-shifts, up to eight, are presented and modeled. It is demonstrated that the shape of the bandpass peak can be tailored by optimization of the phase-shifts locations. We show that flat top bandpass peak with negligible ripples (<0.01 dB) at the top can be designed and that a tradeoff between nearly rectangular shape and stopband width occurs when gratings containing more than two phase-shifts are to be used. We also present experimental spectral responses of gratings with up to three phase-shifts and comparisons with theoretical results.