PHASE-SHIFTED BRAGG GRATING FILTERS WITH SYMMETRICAL STRUCTURES

A comprehensive theoretical analysis of the compound phase-shifted uni form fiber Bragg grating (FBG) filter is presented. The transmission c haracteristics are examined by a transfer matrix formulation. It is sh own that the transmission spectrum of such a filter is significantly c ontrolled by the ratio of the grating lengths. By suitably choosing th e ratio, a quasi-flat-top spectrum may be obtained. The general condit ion for the optimum case is derived. This characteristic makes the com pound phase-shifted uniform FBG filter particularly advantageous for a pplications in wavelength-multiplexed optic-fiber communication system s.